Latest / Night Science Stories / What Found In the Deepest Place on Earth - Mariana Trench. Documentary for Sleep

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What Found In the Deepest Place on Earth - Mariana Trench. Documentary for Sleep · Night Science Stories

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  Speaker 1: Hi, and welcome to Night Science Stories. Pressure more than 1,000
• 0:06
  Speaker 1: times higher than at the surface, water temperature close to
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  Speaker 1: the freezing point, and darkness complete from horizon to horizon.
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  Speaker 1: These are the baseline conditions at the deepest place on Earth.
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  Speaker 1: Equipment fails here if a single gasket is chosen poorly.
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  Speaker 1: Metals creak. Even light must be carried. Yet life is present.
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  Speaker 1: It is not just surviving. It is using these conditions
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  Speaker 1: as its normal state. The surprising finds in the trench
• 0:39
  Speaker 1: do not begin with large creatures. They begin with microorganisms
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  Speaker 1: that treat crushing pressure as ordinary weather. The trench hosts
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  Speaker 1: communities of bacteria and of archaea that metabolize without sunlight.
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  Speaker 1: Instead of photosynthesis, they rely on chemistry. Some oxidize ammonia
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  Speaker 1: into nitrate through a pathway that works best at low temperature.
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  Speaker 1: Some reduce sulfate to sulfide using organic carbon that falls
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  Speaker 1: from far above. Others use hydrogen or methane when those
• 1:17
  Speaker 1: molecules seep from the crust. They are piecophiles, a precise
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  Speaker 1: term that means pressure-loving. If you remove the pressure, many
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  Speaker 1: of them die. Adaptations appear at every level of their biology.
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  Speaker 1: Cell membranes in these microbes are unusually flexible because they
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  Speaker 1: contain more unsaturated fatty acids. That fluidity counters the tendency
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  Speaker 1: of pressure to stiffen the membrane. Proteins inside the cells
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  Speaker 1: are supported by small molecules called osmolites that stabilize shape.
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  Speaker 1: Trimethylamine oxide, spoken slowly as trimethylamine oxide so that the
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  Speaker 1: words are clear for audio, is one such molecule. It
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  Speaker 1: prevents proteins from collapsing under pressure and also improves function
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  Speaker 1: at low temperature. Enzymes from these cells frequently show subtle
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  Speaker 1: changes in the amino acids at their cores. adjustments that
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  Speaker 1: keep the active sites working when pressure increases the density
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  Speaker 1: of water around them. In sediment cores taken from the bottom,
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  Speaker 1: scientists have recorded rates of respiration that are higher than
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  Speaker 1: predicted for such a cold and dark place. The explanation
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  Speaker 1: lies in the constant rain of organic matter down the
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  Speaker 1: water column and in the special structure of trench topography.
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  Speaker 1: The V-shaped profile of a trench collects particulate material that
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  Speaker 1: drifts sideways as currents bend around the slopes. It is
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  Speaker 1: a natural funnel. Microbes use this steady input like a
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  Speaker 1: slow conveyor belt of resources. In culture, Strains of moritella
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  Speaker 1: and of colwellia isolated from near the trench have shown
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  Speaker 1: optimal growth at pressures that would crush an unprotected instrument.
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  Speaker 1: Their names appear in the literature as signals of a
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  Speaker 1: lifestyle that does not translate to the surface. Viruses are
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  Speaker 1: part of this invisible web. Bacteriophages, the viruses that infect bacteria,
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  Speaker 1: occur in the trench just as they do in other
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  Speaker 1: parts of the ocean. Their presence is not a footnote.
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  Speaker 1: Viral lysis releases nutrients back to the dissolved pool and
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  Speaker 1: changes the flow of carbon. The turnover is one reason
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  Speaker 1: the trench does not become an inert storage locker of
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  Speaker 1: organic debris. Processes run slowly, but they run without pause.
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  Speaker 1: Among the most arresting organisms in video frames from the
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  Speaker 1: bottom are giant single cells called xenopheophores. Each one is
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  Speaker 1: a foraminiferin that builds a delicate test or shell by
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  Speaker 1: gluing together fine particles from the sediment. Some individuals span
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  Speaker 1: several centimetres across and hold thin internal chambers that look
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  Speaker 1: like lace under a microscope. They are not colonies. They
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  Speaker 1: are single cells that reach sizes normally associated with small animals.
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  Speaker 1: Where calcium carbonate dissolves under pressure and in water rich
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  Speaker 1: in carbon dioxide, these foraminifera replace mineral tests with organic ones.
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  Speaker 1: That is a direct response to the chemistry of deep water.
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  Speaker 1: The xenophiophores form carpets that trap other particles, increasing the
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  Speaker 1: surface area available for bacteria and small animals. In effect,
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  Speaker 1: a single cell engineers a small habitat that benefits a
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  Speaker 1: miniature ecosystem. Another set of single-celled actors are Allogromyid foraminifera.
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  Speaker 1: They build flexible organic tests and occupy pore spaces in
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  Speaker 1: the sediment where oxygen has been lowered by microbial activity.
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  Speaker 1: Many of these foraminifera house symbiotic bacteria that help process nitrogen.
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  Speaker 1: The combination of foraminifera and symbiont acts like a slow
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  Speaker 1: filtration unit for the surface layer of the seafloor. chemical
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  Speaker 1: surprises sit beside biological ones. Sediments from the deepest sites
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  Speaker 1: have yielded traces of industrial chemicals that were banned at
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  Speaker 1: the surface decades ago. Polychlorinated biphenyls and related compounds are
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  Speaker 1: present in amphipods that feed on detritus. These molecules did
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  Speaker 1: not dissolve away harmlessly. They rode particle after particle down
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  Speaker 1: to a place that many assumed would be free of
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  Speaker 1: our materials. The concentrations provide a quiet index of how
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  Speaker 1: persistent human pollution can be in the global ocean. Microbial
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  Speaker 1: genomes recovered from trench sediments tell an additional story. Genes
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  Speaker 1: for breaking down long-chain hydrocarbons appear across many taxa. Genes
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  Speaker 1: for tolerating heavy metals are present and expressed. Many sequences
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  Speaker 1: encode for chaperone proteins that refold enzymes after stress. Even ribosomes,
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  Speaker 1: the molecular machines that build proteins, show subtle modifications that
• 7:01
  Speaker 1: appear to help translation under high pressure. If one asks
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  Speaker 1: what life has learned at 11,000 meters, one answer is
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  Speaker 1: that stress management is an everyday task. The microbial communities
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  Speaker 1: also govern rates of nitrogen fixation and of denitrification. Some
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  Speaker 1: convert nitrogen gas to bioavailable forms. Others send reactive nitrogen
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  Speaker 1: back to an inert state. In many cores, oxygen is
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  Speaker 1: consumed quickly, within the top few centimetres, and then manganese
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  Speaker 1: and iron oxides take over as electron acceptors. That cascade
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  Speaker 1: defines which microbes can live where. When conditions favour sulphate reduction,
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  Speaker 1: hydrogen sulphide accumulates and feeds another group of organisms that
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  Speaker 1: can use it. Even without sunlight, The energy budget can
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  Speaker 1: support complex interactions and a high diversity of metabolisms. Large
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  Speaker 1: filamentous bacteria build mats near localised seeps where hydrogen-rich fluids percolate.
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  Speaker 1: These mats resemble the biofilms of shallow hot springs but
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  Speaker 1: grow at a temperature only a few degrees above freezing.
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  Speaker 1: Each filament is a chain of cells embedded in a
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  Speaker 1: sheath that helps channel nutrients and, perhaps, shares mechanical strength
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  Speaker 1: against the gentle but constant motion of the water column.
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  Speaker 1: Under a microscope, you can see sulphur granules shining inside
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  Speaker 1: the cells like tiny beads. The presence of such bacteria
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  Speaker 1: confirms that chemical energy from the crust occasionally reaches the
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  Speaker 1: trench floor and that microbes are ready to harvest it.
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  Speaker 1: Viruses again participate, this time with an effect on evolution.
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  Speaker 1: Some viruses carry genes that help their hosts use sulfur
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  Speaker 1: or nitrogen more efficiently. When such genes are expressed during infection,
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  Speaker 1: host metabolism accelerates. The virus benefits by creating more building
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  Speaker 1: blocks for its own replication. The host population benefits indirectly
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  Speaker 1: by acquiring new functions. Over long periods, this transfer of
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  Speaker 1: useful genes blurs the line between hosts and their parasites
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  Speaker 1: and speeds the innovation of metabolic pathways. There are also
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  Speaker 1: archaea that oxidize ammonia at very low concentrations. These organisms
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  Speaker 1: are so efficient that they maintain activity where an instrument
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  Speaker 1: barely reads a signal. The product of their work, nitrite,
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  Speaker 1: accumulates sufficiently to feed a second group that converts nitrite
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  Speaker 1: to nitrate. Together, they complete the first step in the
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  Speaker 1: nitrogen cycle under conditions that would stall many surface microbes.
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  Speaker 1: Laboratory cultures kept at pressures that mimic The trench reveal
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  Speaker 1: that the enzymes of these archaea bind ammonia more tightly
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  Speaker 1: and release energy more gently, an adaptation to conserve resources.
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  Speaker 1: Not everything in the microbial story points to endurance. Some
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  Speaker 1: microbes discovered in the trench are surprisingly fragile outside of
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  Speaker 1: their high-pressure environment. When researchers recover them using pressure-retaining samplers,
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  Speaker 1: and then relieve the pressure too quickly, the cells rupture
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  Speaker 1: or their membranes leak. It is an immediate demonstration that
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  Speaker 1: we are the extreme ones, not they. The pressure that
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  Speaker 1: seems impossible to us is the comfort zone for them.
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  Speaker 1: The microorganisms provide the context for larger animals. What looks
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  Speaker 1: like an empty plain of mud is not empty at all.
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  Speaker 1: It is a slow farm managed by bacteria and grazed
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  Speaker 1: by small crustaceans. Near the middle of the food web
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  Speaker 1: are amphipods. The species Hirondelia gigas is one of the
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  Speaker 1: most studied. It swims in a jerky pattern close to
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  Speaker 1: the bottom and rushes to baited cameras in large numbers.
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  Speaker 1: Chemical analysis of its stomach suggests that it can digest
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  Speaker 1: cellulose from wood that filters down, a rare trait in
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  Speaker 1: the deep sea. The trick seems to involve enzymes that
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  Speaker 1: work under pressure and molecules that strip aluminum from sediment
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  Speaker 1: and bind it as a gel on the amphipod shell.
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  Speaker 1: The thin coating may protect the exoskeleton, which otherwise would
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  Speaker 1: be prone to dissolution because calcium carbonate is unstable in
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  Speaker 1: the high carbon dioxide deep water. Amphipods bring us to
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  Speaker 1: fish because they are the prey that supports the deepest
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  Speaker 1: vertebrates known. The record holders are snailfish. The species described
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  Speaker 1: from the trench is named for a naturalist who sailed
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  Speaker 1: during an early exploration of the Pacific. These fish live
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  Speaker 1: at depths greater than 8,000 meters, beyond the reach of
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  Speaker 1: most other vertebrates. They are not large. Their bodies are
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  Speaker 1: soft with minimal mineralisation of bone and no heavy scales.
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  Speaker 1: The skull is partially cartilage. The muscles are pale and
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  Speaker 1: contain high levels of trimethylamine oxide, the same molecule used
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  Speaker 1: by microorganisms for protein stability. The concentration increases with depth.
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  Speaker 1: There seems to be an upper limit where the body
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  Speaker 1: would become so filled with these osmolites that cells could
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  Speaker 1: not function. That limit may set a maximum depth for
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  Speaker 1: fish that is only a little deeper than where the
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  Speaker 1: Mariana snailfish actually lives. The sensory system of snailfish is
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  Speaker 1: tuned to a world without light. Eyes are small. Many
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  Speaker 1: individuals have reduced visual pigments. In compensation, the lateral line
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  Speaker 1: system that detects water movement is well developed. It allows
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  Speaker 1: them to hunt amphipods that swarm around patches of organic matter.
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  Speaker 1: Mouths are wide and teeth are small, reflecting a strategy
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  Speaker 1: of gulping rather than tearing. Stomachs have been found packed
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  Speaker 1: with amphipods, evidence that energy is collected in bursts when
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  Speaker 1: prey density permits, and stored until the next burst. Reproduction
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  Speaker 1: in these fish appears to follow a schedule that respects
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  Speaker 1: slow growth in the cold. Eggs are large compared to
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  Speaker 1: body size, with thick shells that resist pressure. In the laboratory,
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  Speaker 1: related snailfish from shallower trenches show parental care. Whether the
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  Speaker 1: deepest species guard eggs is not yet confirmed. But the
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  Speaker 1: sizes of oocytes suggest a low number of high investment offspring.
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  Speaker 1: This is a common pattern in extreme environments where mortality
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  Speaker 1: from factors other than predation is high. Why do other
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  Speaker 1: fish not follow them deeper? The osmotic pressure imposed by
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  Speaker 1: stabilizing molecules seems to be the decisive limit. Theory and
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  Speaker 1: experiment agree that to keep proteins functional under higher pressure,
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  Speaker 1: a fish would need such a high concentration of stabilizers
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  Speaker 1: that water movement across membranes would become energetically prohibitive. In short,
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  Speaker 1: The chemistry that protects structure would break water balance. Rather
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  Speaker 1: than evolve impossible workarounds, fish stop at depths where the
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  Speaker 1: trade-off makes sense. That boundary is a natural experiment in
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  Speaker 1: physiology and evolution. Other unusual fishes visit the slopes of
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  Speaker 1: the trench. Grenadiers, also called rat-tails because of their shape,
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  Speaker 1: patrol the abyssal plains and the upper Hadal zones. They
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  Speaker 1: are not trench specialists, but their presence is a constant.
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  Speaker 1: in baited camera footage. Some eel pouts and cusk eels
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  Speaker 1: approach the edges of the trench. These groups use pressure-tolerant
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  Speaker 1: forms of haemoglobin and maintain buoyancy with lipids rather than
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  Speaker 1: with gas bladders that would collapse. None challenge the snailfish
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  Speaker 1: for depth records, but they help demonstrate that there is
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  Speaker 1: not a single recipe for life under pressure. Returning to
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  Speaker 1: the microbial foundation, an equal lesson emerges about the carbon cycle.
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  Speaker 1: Measurements show that microbial communities at the trench floor remineralize
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  Speaker 1: a significant fraction of the organic carbon that reaches them.
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  Speaker 1: The rest is buried. Over geologic time, that burial contributes
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  Speaker 1: to long-term carbon storage. Trenches act as temporary reservoirs because
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  Speaker 1: they collect particles faster than surrounding planes. Earthquakes occasionally disturb
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  Speaker 1: the deposits and drive turbidity currents that sweep material downslope
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  Speaker 1: into deeper basins. These events mix old and new layers
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  Speaker 1: and create lenses of unusually fine sediment where microbes respond
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  Speaker 1: with brief increases in activity. Observational technology shapes what we know.
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  Speaker 1: The crude bathyskaf Trieste reached the deepest point in the
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  Speaker 1: year 1960. It returned a short report that included a
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  Speaker 1: flatfish sighting that later observers have questioned. A half century later,
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  Speaker 1: a purpose-built submersible piloted by a filmmaker reached the same
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  Speaker 1: zone and stayed longer. It recorded amphipods, sea cucumbers, and
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  Speaker 1: jelly-like organisms. In the years since, free-falling landers equipped with
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  Speaker 1: cameras and chemical sensors have repeatedly visited the trench, confirming
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  Speaker 1: the presence of active communities. Pressure retaining samplers now allow
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  Speaker 1: researchers to bring mud up while keeping pressure near in
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  Speaker 1: situ values. That step alone transformed our understanding of trench microbes.
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  Speaker 1: because many species simply did not survive earlier methods. An
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  Speaker 1: aspect that tends to be overlooked in popular summaries is
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  Speaker 1: the precise mineralogy of the sediments. With depth, calcium carbonate disappears,
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  Speaker 1: the clay fraction dominates, volcanic ash from eruptions in the
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  Speaker 1: island arc contributes glass shards and altered minerals. These materials
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  Speaker 1: deliver trace elements that microbes can use as cofactors in enzymes.
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  Speaker 1: Manganese nodules, which are common on abyssal plains, are scarce here,
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  Speaker 1: probably because the steep slopes do not permit quiet growth
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  Speaker 1: over long times. In their place, concretions of barite and
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  Speaker 1: phosphate sometimes occur where microenvironments allow precipitation. Trace gas measurements
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  Speaker 1: reveal low but detectable levels of methane in some layers.
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  Speaker 1: Stable carbon isotope signatures suggest that the methane is a
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  Speaker 1: mix of thermogenic origin from deeper sediments and biological origin
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  Speaker 1: from acetoclastic pathways in the upper layers. Archaea that carry
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  Speaker 1: the genes for methane production are rare in counts, but
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  Speaker 1: disproportionately active according to transcript data. Their role may be
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  Speaker 1: localized around pockets of organic, rich material. A surprising discovery
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  Speaker 1: in the past decade has been the presence of microplastics
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  Speaker 1: in trench sediments and in the tissues of amphipods. Particles
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  Speaker 1: in the size range of tens to hundreds of micrometers
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  Speaker 1: are common. Polymer types include polyethylene, polypropylene and polyester. When
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  Speaker 1: researchers analyze the chemical signatures, they can match some particles
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  Speaker 1: to common textile fibers. The route to the bottom is
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  Speaker 1: simple and sobering. Fibers pass from wastewater into the sea,
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  Speaker 1: attach to organic matter, and sink. Amphipods ingest them along
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  Speaker 1: with detritus. The presence of microplastics in the deepest amphipods
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  Speaker 1: suggests that there is no level of the ocean uninfluenced.
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  Speaker 1: by surface activity. Heavy metal concentrations reveal similar patterns. The
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  Speaker 1: metal element lead and the element mercury are present in
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  Speaker 1: small amounts in sediments, along with cadmium and others, likely
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  Speaker 1: carried by particles. In animal tissues, these metals are usually
• 21:10
  Speaker 1: found at low levels because the local food web is
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  Speaker 1: short and there is little biomagnification compared with surface ecosystems.
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  Speaker 1: Even so, the record shows that the trench is a
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  Speaker 1: collector not just of particles, but of global history. From
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  Speaker 1: a physical point of view, the water column above the
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  Speaker 1: trench is a stratified archive. Nutrient-rich deep water flows slowly
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  Speaker 1: through the region as part of the global conveyor circulation.
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  Speaker 1: At shallow levels, the oxygen minimum zone can be pronounced,
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  Speaker 1: shaping the vertical distribution of bacteria and protists and altering
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  Speaker 1: the composition of organic matter that reaches the trench. Sinking
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  Speaker 1: particles change character as they fall. Lipids become oxidized. Proteins
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  Speaker 1: are broken into amino acids and then further into ammonia.
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  Speaker 1: Sugars are consumed quickly. By the time the material reaches
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  Speaker 1: the bottom, it is a selected diet to which the
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  Speaker 1: resident microbes are adapted. Research teams have also found filamentous
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  Speaker 1: fungi in sediment samples. These fungi tolerate pressure and likely
• 22:32
  Speaker 1: colonize particulate organic matter rather than live free in the mud.
• 22:37
  Speaker 1: Some produce enzymes that break down lignin. the tough polymer
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  Speaker 1: from plant cell walls that survives long transit from land.
• 22:47
  Speaker 1: Their presence broadens the list of eukaryotes that participate in
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  Speaker 1: deep carbon processing and opens questions about spores and dispersal
• 22:57
  Speaker 1: in the water column. Protists are diverse. Flagellates graze on
• 23:02
  Speaker 1: bacteria and are in turn eaten by small animals. Ciliates
• 23:08
  Speaker 1: with complex mouthparts navigate among grains. Tests constructed by agglutinating
• 23:14
  Speaker 1: particles come in many forms and sizes. Some are delicate
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  Speaker 1: and collapse when retrieved without pressure control, which means they
• 23:25
  Speaker 1: were undercounted in early surveys. With newer techniques, the diversity
• 23:31
  Speaker 1: is higher than expected, approaching the values measured in shallower,
• 23:36
  Speaker 1: abyssal zones. The trench slope communities include small holothurians, commonly
• 23:44
  Speaker 1: called sea cucumbers, that use tentacles to collect sediment for feeding.
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  Speaker 1: Some species are transparent and show internal organs in high-definition footage.
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  Speaker 1: Their slow motion resembles time-stretching because there is no reference
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  Speaker 1: for scale in the absence of plants or other landmarks.
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  Speaker 1: For the animals, the feeding strategy is simple and effective.
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  Speaker 1: Ingest sediment, extract organic molecules and microbes, and pass the rest.
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  Speaker 1: Tracks on the bottom preserve their trails until currents erase them.
• 24:23
  Speaker 1: Returning to fishes, there is evidence that the distribution of
• 24:27
  Speaker 1: snailfish near the bottom of the trench is structured by
• 24:31
  Speaker 1: temperature gradients and by prey abundance. In areas where amphipods concentrate,
• 24:38
  Speaker 1: baited cameras record more fish and in shorter intervals. In
• 24:44
  Speaker 1: warmer pockets where water from shallower layers intrudes, growth rates
• 24:49
  Speaker 1: may be marginally faster. The differences are subtle. The unifying
• 24:54
  Speaker 1: theme remains scarcity, punctuated by episodic abundance. Hearing in the
• 25:00
  Speaker 1: deep is often overlooked. Sound travels far in water. Even
• 25:05
  Speaker 1: in the trench, background noise from the surface storms propagates downward,
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  Speaker 1: although at reduced intensity. Some fishes use the lateral line primarily,
• 25:17
  Speaker 1: but bones of the inner ear can also detect. low-frequency
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  Speaker 1: pressure changes. That capacity may help them find prey swarms
• 25:27
  Speaker 1: as amphipods respond to the fall of a large food item.
• 25:32
  Speaker 1: One final layer of the microbial story involves spores and dormancy.
• 25:38
  Speaker 1: Some species form resistance stages that endure long periods with
• 25:42
  Speaker 1: little energy input. When a pulse of fresh organic matter arrives,
• 25:47
  Speaker 1: enzymes activate and metabolism resumes this ability to wait fits
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  Speaker 1: the patchy delivery of food to the trench it also
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  Speaker 1: means that when sediments are disturbed by earthquakes as they
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  Speaker 1: occasionally are the community can reassemble quickly Putting these elements together,
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  Speaker 1: the deepest place on Earth is not defined by absence.
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  Speaker 1: It is defined by a particular balance of chemistry, physics
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  Speaker 1: and biology. Micro-organisms exploit chemical gradients and adapt their molecular
• 26:25
  Speaker 1: machinery to pressure and cold. Single-celled giants build structures that
• 26:32
  Speaker 1: act as micro-habitats. Amphipods process detritus and move energy up
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  Speaker 1: to vertebrates that live at physiological limits. Fishes exhibit a
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  Speaker 1: suite of anatomical adjustments that keep them within narrow bands
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  Speaker 1: where life remains possible for their lineage. Alongside this natural system,
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  Speaker 1: Markers of human activity are present as chemicals and as microplastics,
• 27:00
  Speaker 1: reminding us that the deep ocean is connected to our
• 27:04
  Speaker 1: actions through pathways we do not always see. As research continues,
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  Speaker 1: new tools arrive. Autonomous landers now carry incubations that measure
• 27:16
  Speaker 1: microbial activity in situ without ever raising the sample. Optical
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  Speaker 1: systems record changes in the micro layer above the sediment
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  Speaker 1: where chemical gradients are steepest. Genetic surveys recover entire communities
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  Speaker 1: from a spoonful of mud and link sequence data with microscopy.
• 27:37
  Speaker 1: Pressure-tolerant cameras ride along in fleets to capture time series
• 27:42
  Speaker 1: rather than snapshots. Each addition refines the picture. The story
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  Speaker 1: of what scientists have found in the trench can therefore
• 27:53
  Speaker 1: be summarised in a calm list that remains open at
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  Speaker 1: the end. They have found specialised microbes that turn chemistry
• 28:02
  Speaker 1: into slow energy without sunlight. They have found giant single
• 28:08
  Speaker 1: cells that act as architects of micro-landscapes. They have found
• 28:13
  Speaker 1: amphipods that digest wood, coat their shells with aluminum bound
• 28:18
  Speaker 1: by chemistry, and carry pollutants that began as industrial products
• 28:24
  Speaker 1: at the surface. They have found fishes at the predicted
• 28:28
  Speaker 1: boundary of vertebrate endurance, with bodies tuned to cold and pressure.
• 28:35
  Speaker 1: They have recorded viruses that shape ecology and evolution in silence.
• 28:41
  Speaker 1: They have measured carbon burial and carbon processing rates that
• 28:45
  Speaker 1: connect the trench to the climate story. They have documented
• 28:49
  Speaker 1: the presence of plastics and metals, evidence that no depth
• 28:54
  Speaker 1: is untouched by human activity. All of this knowledge serves
• 28:59
  Speaker 1: the practical goals of ocean science. It guides the design
• 29:04
  Speaker 1: of equipment that can operate reliably in the huddle zone.
• 29:08
  Speaker 1: It informs our understanding of global biogeochemical cycles. It helps
• 29:15
  Speaker 1: decide where protected areas would be most meaningful. It contributes
• 29:20
  Speaker 1: to the long practice of exploration that does not romanticize
• 29:24
  Speaker 1: the world, but treats it with patient attention. The deepest
• 29:30
  Speaker 1: place does not change quickly. What changes is our ability
• 29:35
  Speaker 1: to visit without disturbing and to listen without projecting our
• 29:40
  Speaker 1: our assumptions. In the trench life is ordinary by its
• 29:44
  Speaker 1: own standards. Microbes glide through reactions as if pressure were
• 29:49
  Speaker 1: as unremarkable as weather. Fish swim where chemistry allows, not
• 29:55
  Speaker 1: because they want to be extraordinary but because that is
• 29:59
  Speaker 1: where their lineage led. That quiet normalcy is the final finding.
• 30:05
  Speaker 1: The extreme feels extreme only because we are not adapted
• 30:09
  Speaker 1: to it. The inhabitants are not outliers in their own frame.
• 30:14
  Speaker 1: They are the baseline of a world that happens to
• 30:16
  Speaker 1: lie below 11,000 metres of water. Giant amphipods dominate many
• 30:23
  Speaker 1: frames recorded at the bottom. They arrive within minutes after
• 30:27
  Speaker 1: a baited lander touches the sediment. Numbers build quickly and
• 30:32
  Speaker 1: then stabilize as the scent disperses. The behavior is consistent
• 30:38
  Speaker 1: across deployments. Individuals patrol close to the seafloor, antennae forward,
• 30:44
  Speaker 1: using chemical and mechanical cues to guide short bursts of
• 30:49
  Speaker 1: swimming and walking. The body plan is standard for amphipods,
• 30:53
  Speaker 1: but proportions differ at depth. The head and thorax are robust,
• 30:59
  Speaker 1: the abdomen narrower, and the antennae long. The largest hadal
• 31:04
  Speaker 1: forms reach lengths measured in tens of centimetres. Supergiant species
• 31:10
  Speaker 1: from other trenches exceed 30 centimetres. At the deepest stations
• 31:16
  Speaker 1: of the Mariana region, the typical size is smaller but
• 31:20
  Speaker 1: still large compared with shallow relatives. Mass is carried as
• 31:25
  Speaker 1: muscle and as lipid. The exoskeleton is relatively thin in
• 31:30
  Speaker 1: carbonate because calcium carbonate becomes unstable in cold water that
• 31:37
  Speaker 1: holds more dissolved carbon dioxide. chitin and proteins take a
• 31:42
  Speaker 1: larger role in structure. Trace elements from sediment contribute to
• 31:47
  Speaker 1: surface chemistry in unusual ways. One species in particular, Hirondellia gigas,
• 31:54
  Speaker 1: shows a surface coating rich in the metal element aluminum.
• 31:59
  Speaker 1: The aluminum does not originate inside the animal. It is
• 32:03
  Speaker 1: leached from clay minerals during digestion by organic acids produced
• 32:08
  Speaker 1: in the gut. Once in contact with alkaline seawater, the
• 32:13
  Speaker 1: aluminum forms a gel of aluminum hydroxide that settles on
• 32:18
  Speaker 1: the exoskeleton. The layer is thin but consistent in specimens
• 32:23
  Speaker 1: that live below the carbonate compensation depth. The practical result
• 32:29
  Speaker 1: is protection. The gel slows chemical attack on the exoskeleton
• 32:34
  Speaker 1: where carbonate is scarce. It also appears to reduce abrasion.
• 32:39
  Speaker 1: This is an example of environmental chemistry repurposed as armour.
• 32:45
  Speaker 1: Feeding biology explains the constant presence of amphipods around camera landers.
• 32:52
  Speaker 1: They are opportunistic scavengers and effective processors of particulate organic matter.
• 32:59
  Speaker 1: Laboratory assays show activity of enzymes that break down cellulose
• 33:05
  Speaker 1: and hemicellulose. Wood that sinks from the surface becomes usable food.
• 33:11
  Speaker 1: Lipid-rich material from dead animals is also consumed quickly. When
• 33:16
  Speaker 1: a large food fall reaches the trench floor, amphipods detect
• 33:21
  Speaker 1: dissolved chemical cues and converge from many directions. Rapid aggregation
• 33:28
  Speaker 1: is a key trait in a habitat where large meals
• 33:32
  Speaker 1: are rare and widely spaced. Energy from a single event
• 33:36
  Speaker 1: is stored as wax esters and neutral lipids and used
• 33:40
  Speaker 1: over long intervals. The sensory system is tuned for low
• 33:45
  Speaker 1: light and for heavy reliance on chemical gradients. Amphipods at
• 33:50
  Speaker 1: the trench floor carry numerous sensilla on antennae and mouthparts.
• 33:55
  Speaker 1: These hair-like structures are plugged into dense arrays of neurons.
• 34:02
  Speaker 1: The lateral body plates show pores that likely house pressure-sensitive receptors.
• 34:08
  Speaker 1: The result is efficient detection of flow and of concentration changes.
• 34:15
  Speaker 1: Orientation behavior has been measured in lander experiments that release
• 34:20
  Speaker 1: tracer compounds at controlled rates. Individuals show directed movement up
• 34:26
  Speaker 1: the concentration gradient and remain near the source until satiated
• 34:31
  Speaker 1: or displaced by larger animals. Growth and reproduction follow a
• 34:37
  Speaker 1: schedule shaped by temperature and pressure. Amphipods grow through molts.
• 34:43
  Speaker 1: The timing is irregular because it depends on food pulses
• 34:47
  Speaker 1: and on the condition of the exoskeleton. Females carry eggs
• 34:52
  Speaker 1: and juveniles in a brood pouch under the thorax. Broods
• 34:56
  Speaker 1: are small and the eggs are large. Embryos develop slowly.
• 35:02
  Speaker 1: Juveniles emerge ready to feed and to avoid predators. The
• 35:06
  Speaker 1: pattern is conservative. It favours high survival of a small
• 35:11
  Speaker 1: number of offspring instead of large broods with high mortality.
• 35:15
  Speaker 1: Longevity is not well constrained, but isotope turnover in tissues
• 35:21
  Speaker 1: and mark and recapture style analyses suggest lives measured in
• 35:26
  Speaker 1: several years. Physiology reflects pressure management. Trimethylamine oxide, spoken as
• 35:34
  Speaker 1: trimethylamine oxide to avoid confusion in audio, is present at
• 35:39
  Speaker 1: concentrations that increase with depth. The molecule stabilizes proteins and
• 35:46
  Speaker 1: offsets the destabilizing effect of urea and of pressure on
• 35:50
  Speaker 1: protein folding. Cell membranes are enriched in unsaturated fatty acids
• 35:56
  Speaker 1: that keep the bilayer flexible. Ion channels in nerve and
• 36:01
  Speaker 1: muscle are subtly altered in amino acid sequence to preserve
• 36:06
  Speaker 1: opening and closing kinetics when pressure compresses water and changes viscosity. Hemocyanin,
• 36:13
  Speaker 1: the blue copper-based oxygen carrier in many crustaceans, shows variants
• 36:19
  Speaker 1: that maintain oxygen affinity at low temperature and high pressure.
• 36:26
  Speaker 1: These features are consistent with a design goal of ordinary
• 36:31
  Speaker 1: function in an environment that would arrest the physiology of
• 36:35
  Speaker 1: shallow species. Chemical contamination is recorded directly in amphipod tissues.
• 36:42
  Speaker 1: Polychlorinated biphenyls and related persistent pollutants occur in lipid stores
• 36:49
  Speaker 1: at concentrations that map to global production and deposition histories.
• 36:56
  Speaker 1: Microplastics are present in the gut contents of many trench amphipods.
• 37:02
  Speaker 1: Fibres from synthetic textiles dominate the counts. Fragments of polyethylene
• 37:08
  Speaker 1: and polypropylene and polyester are common. The route from coast
• 37:13
  Speaker 1: to trench is well established. Fibres and particles enter rivers
• 37:19
  Speaker 1: and coastal waters, attached to organic matter and sink. Amphipods
• 37:25
  Speaker 1: ingest them with detritus. Most pass through, but some remain
• 37:30
  Speaker 1: for days within the gut. The measurements do not show
• 37:34
  Speaker 1: immediate toxicity at the levels observed, yet they demonstrate that
• 37:40
  Speaker 1: no part of the ocean floor is free of human material.
• 37:45
  Speaker 1: Stable isotope data clarify where amphipods sit in the food web.
• 37:51
  Speaker 1: Ratios of carbon-13 to carbon-12 and of nitrogen-15 to nitrogen-14
• 37:57
  Speaker 1: indicate that most Hadal amphipods feed one to two steps
• 38:02
  Speaker 1: above sinking phytodetritis. The signal shifts when large carrion is available,
• 38:09
  Speaker 1: reflecting the higher trophic position of the food fall. Lipid
• 38:14
  Speaker 1: biomarkers agree with the isotope story. The presence of certain
• 38:19
  Speaker 1: long-chain fatty acids points to inputs from diatoms and from
• 38:24
  Speaker 1: bacterial reworking of organic matter during descent. The combination of
• 38:30
  Speaker 1: markers allows researchers to reconstruct diet over weeks rather than
• 38:36
  Speaker 1: over hours. Locomotion at pressure requires efficient muscle. Electron microscopy
• 38:43
  Speaker 1: of muscle fibers shows dense arrays of mitochondria and long
• 38:47
  Speaker 1: sarcomeres that favor slow sustained contractions over rapid bursts. This
• 38:53
  Speaker 1: matches behavior seen in video. Most movement is deliberate. Quick
• 38:59
  Speaker 1: escape swimming is rare and brief. The emphasis is on
• 39:03
  Speaker 1: endurance and on posture control around bait and in currents
• 39:08
  Speaker 1: near the sea floor. The body shape reduces drag when
• 39:12
  Speaker 1: the animal hugs the ground. When swimming is necessary, pleopods
• 39:18
  Speaker 1: beat in coordinated series to produce steady thrust. Population structure
• 39:24
  Speaker 1: changes with depth and with location along the trench axis.
• 39:29
  Speaker 1: Surveys show that different species replace one another over a
• 39:33
  Speaker 1: span of a few hundred meters in depth. This zonation
• 39:38
  Speaker 1: likely reflects physiological limits and and food availability. Temperature gradients
• 39:44
  Speaker 1: of one or two degrees Celsius between deep basins and
• 39:49
  Speaker 1: adjacent slopes also play a role. Genetic data reveal limited
• 39:54
  Speaker 1: gene flow between basins that are separated by sills and
• 39:58
  Speaker 1: by long distances. The trench is not a continuous habitat
• 40:04
  Speaker 1: in a biological sense. It is a chain of basins
• 40:08
  Speaker 1: and slopes with distinct conditions. Mechanical interaction with baited landers
• 40:15
  Speaker 1: has supplied measurements that would be difficult to collect otherwise.
• 40:20
  Speaker 1: The force with which an amphipod can grasp and manipulate
• 40:25
  Speaker 1: bait has been estimated by the displacement of tethered weights
• 40:30
  Speaker 1: and by strain sensors on bait arms. Values scale with
• 40:35
  Speaker 1: body and match the need to tear soft tissue and
• 40:39
  Speaker 1: to carry fragments away from competition. The loads are modest
• 40:44
  Speaker 1: in absolute terms, but they are high relative to body mass.
• 40:50
  Speaker 1: This is consistent with the muscular investment seen in anatomy.
• 40:56
  Speaker 1: Some Hadal amphipods show gut microbes that assist digestion of
• 41:01
  Speaker 1: refractory materials. Metagenomic surveys of gut contents identify genes that
• 41:06
  Speaker 1: code for enzymes such as endobeta, gluconases, and xylanases. These
• 41:13
  Speaker 1: enzymes act on plant cell walls. The presence of these
• 41:17
  Speaker 1: genes supports the observation that wood and plant debris are
• 41:22
  Speaker 1: significant occasional foods. It also extends the role of amphipods
• 41:27
  Speaker 1: from scavengers of animal tissue to general processors of carbon
• 41:32
  Speaker 1: that falls to death. Mortality events are rare in observation
• 41:38
  Speaker 1: because the habitat is large and landers sample small areas
• 41:43
  Speaker 1: for short times. Indirect evidence comes from the dynamics of
• 41:47
  Speaker 1: population size structure. When a series of deployments over a
• 41:52
  Speaker 1: season shows a surge in juveniles, a previous reproductive event
• 41:58
  Speaker 1: is inferred. When size classes shift without recruitment, predation or
• 42:03
  Speaker 1: export by currents may be responsible. Larger predators at hadal
• 42:08
  Speaker 1: depths are few. Fish are the main consumers of amphipods,
• 42:15
  Speaker 1: along with other amphipods. Cannibalism is common during crowding at bait.
• 42:23
  Speaker 1: The amphipod chapter leads into the wider community of invertebrates.
• 42:29
  Speaker 1: Sea cucumbers are among the most frequent large animals on
• 42:33
  Speaker 1: abyssal plains. In the trench, they persist in smaller forms
• 42:38
  Speaker 1: and with different body plans that handle steep slopes and
• 42:43
  Speaker 1: soft mud. These animals, members of the echinoderm group, move
• 42:49
  Speaker 1: slowly across the sediment using tube feet that are powered
• 42:53
  Speaker 1: by a water vascular system. The body wall is supported
• 42:57
  Speaker 1: by microscopic ossicles rather than by heavy plates. This choice
• 43:02
  Speaker 1: of materials fits the chemistry of deep water, where carbonate
• 43:07
  Speaker 1: tends to dissolve. The feeding strategy is simple. A ring
• 43:12
  Speaker 1: of tentacles collects surface sediment and transfers it to the mouth.
• 43:18
  Speaker 1: The gut extracts bacteria and organic molecules. The remainder is
• 43:25
  Speaker 1: egested as clean pellets that alter the microtopography. Species diversity
• 43:32
  Speaker 1: is not high compared with the shallower abyssal plains, but
• 43:37
  Speaker 1: functional diversity is sufficient to process available detritus. Some Hadal
• 43:43
  Speaker 1: holothurians are nearly transparent. High-resolution footage reveals the intestine and
• 43:50
  Speaker 1: the gonads through the body wall. Others are dark and
• 43:54
  Speaker 1: covered with short papillae that increase surface area for chemical sensing.
• 44:00
  Speaker 1: Individuals leave tracks that persist for hours in low current conditions.
• 44:07
  Speaker 1: Track density gives a minimum count of animals that passed
• 44:11
  Speaker 1: within a time window. Combined with video, These traces supply
• 44:18
  Speaker 1: estimates of activity budgets. Sea cucumbers manage pressure without the
• 44:23
  Speaker 1: copper-based blood pigments seen in crustaceans. Oxygen transport relies on
• 44:29
  Speaker 1: diffusion across moist surfaces and on respiratory proteins dissolved in
• 44:35
  Speaker 1: body fluids. Metabolic rates are low. The animals spend most
• 44:40
  Speaker 1: of their time in a slow forward crawl punctuated by pauses.
• 44:45
  Speaker 1: When a pulse of fresh organic material arrives, measured as
• 44:50
  Speaker 1: a change in fluorescence in the top millimetre of sediment,
• 44:54
  Speaker 1: feeding rates increase. This flexible response is essential in a
• 45:00
  Speaker 1: system where supply is variable. Reproduction among Hadal holothurians takes
• 45:08
  Speaker 1: two forms. Some broadcast spawn, releasing eggs and sperm into
• 45:13
  Speaker 1: the water column. Others brood young. Brooding is common where
• 45:18
  Speaker 1: currents are strong and where the probability that sperm and
• 45:23
  Speaker 1: eggs meet is low. In brooding species, the adult carries
• 45:28
  Speaker 1: embryos in a pouch or attached to the body surface
• 45:31
  Speaker 1: until they are competent to feed on their own. Oocytes'
• 45:35
  Speaker 1: size tends to be large. Fecundity is low. The pattern
• 45:41
  Speaker 1: mirrors the amphipod strategy of investing in survival of fewer young.
• 45:48
  Speaker 1: Other invertebrates share the sediment. Polychaete worms live in burrows
• 45:54
  Speaker 1: and tubes. Their jaws are reduced when diet is dominated
• 45:59
  Speaker 1: by bacteria and detritus. Where more active predation is possible,
• 46:04
  Speaker 1: jaw structures are more complex. Tube builders use mucus and
• 46:10
  Speaker 1: small particles to construct shelters that withstand the weight of
• 46:14
  Speaker 1: overlying mud. When a turbidity current passes, many tubes are
• 46:19
  Speaker 1: destroyed and the community resets. Recovery is measurable over months,
• 46:26
  Speaker 1: as new tubes appear and as tracks and burrow openings
• 46:31
  Speaker 1: repopulate the surface. Isopods occupy a similar niche to amphipods,
• 46:37
  Speaker 1: but move more slowly and often burrow. Hadal isopods are
• 46:42
  Speaker 1: less conspicuous in videos because they do not swarm to bait.
• 46:47
  Speaker 1: They contribute to sediment mixing and to the slow turnover
• 46:51
  Speaker 1: of organic matter. Some species show extreme sexual dimorphism with
• 46:58
  Speaker 1: males much smaller than females and specialized for locating mates
• 47:04
  Speaker 1: through chemical signals. Bivalve mollusks occur near seep locations where
• 47:10
  Speaker 1: reduced chemicals like hydrogen sulfide and methane reach the sediment surface.
• 47:16
  Speaker 1: The bivalves host bacterial symbionts in their gills. The bacteria
• 47:21
  Speaker 1: oxidize the reduced compounds and feed the host. These communities
• 47:27
  Speaker 1: are patchy and small in the trench compared with continental
• 47:32
  Speaker 1: margin seeps. but they demonstrate that chemosynthesis operates to some
• 47:37
  Speaker 1: extent even in the deepest basins. Canadarians are present as
• 47:42
  Speaker 1: small anemones attached to hard fragments and to shells. Tentacles
• 47:48
  Speaker 1: extend to collect suspended particles. The animals withstand burial by
• 47:53
  Speaker 1: extending through thin layers of new sediment. Their distribution correlates
• 47:59
  Speaker 1: with the presence of coarser grains where attachment is possible.
• 48:04
  Speaker 1: On soft mud with no fragments, anemones are rare. Echinoderms
• 48:10
  Speaker 1: other than sea cucumbers are less common but not absent.
• 48:14
  Speaker 1: Small brittle stars occur on slopes where currents keep the
• 48:18
  Speaker 1: surface free of fluff. They lift arms into the flow
• 48:22
  Speaker 1: to capture particles. Sea stars adapted to soft sediment hunting
• 48:27
  Speaker 1: are recorded less often. The scarcity of hard prey and
• 48:32
  Speaker 1: the dominance of fine organic matter make deposit feeding a
• 48:36
  Speaker 1: better strategy in most areas of the trench. A diverse
• 48:41
  Speaker 1: suite of maia fauna lives between grains. Nematodes dominate counts
• 48:47
  Speaker 1: in many samples. Harpacticoid cope pods and small foraminifera share
• 48:53
  Speaker 1: the habitat. These animals are the first consumers of bacteria
• 48:57
  Speaker 1: and help transfer energy upward. They also stabilize the sediment
• 49:03
  Speaker 1: surface and affect how water and solutes move across the boundary.
• 49:09
  Speaker 1: Counts vary with the amount of organic carbon in the
• 49:12
  Speaker 1: top centimetre. Where a recent fall of material has occurred,
• 49:18
  Speaker 1: densities rise over weeks and then decline as the pulse
• 49:23
  Speaker 1: is processed. Jelly-like animals are recorded in the water column
• 49:28
  Speaker 1: close to the bottom. Small Medusae and Ctenophores drift past
• 49:33
  Speaker 1: cameras and do not interact with the sediment. Their presence
• 49:38
  Speaker 1: indicates that not all energy at depth arrives from above
• 49:44
  Speaker 1: as particles. Some arrives as living plankton that has descended.
• 49:49
  Speaker 1: These forms are fragile and rarely captured, so optical methods
• 49:54
  Speaker 1: provide most observations. Crustaceans beyond amphipods include tannades and cumations
• 50:02
  Speaker 1: that move in short runs and use claws to dig.
• 50:06
  Speaker 1: Their life cycles are short compared with amphipods. They breed
• 50:10
  Speaker 1: within a season when food is ample and retreat to
• 50:14
  Speaker 1: low activity when it is scarce. These groups are under-sampled
• 50:20
  Speaker 1: because they avoid bait and are small enough to slip
• 50:23
  Speaker 1: through coarse sieves used in early work. With fine mesh
• 50:28
  Speaker 1: and with suction samplers on landers, their true abundance has
• 50:33
  Speaker 1: become clear. Sponges are rare at hadal depths due to
• 50:37
  Speaker 1: the lack of stable hard substrate and to low silica availability,
• 50:42
  Speaker 1: but anchored forms do occur on occasional rock outcrops. Microbial
• 50:48
  Speaker 1: symbionts in sponge tissues perform nitrification and other steps in
• 50:54
  Speaker 1: the nitrogen cycle. The contribution is local but measurable in
• 50:59
  Speaker 1: incubations that enclose a patch of seafloor. The role of
• 51:05
  Speaker 1: invertebrates in bioturbation is central. Tracks, burrows and feeding pits
• 51:11
  Speaker 1: pump oxygenated water into the upper millimetres of sediment and
• 51:16
  Speaker 1: bring reduced compounds to the surface where microbes can oxidise them.
• 51:22
  Speaker 1: This vertical mixing increases the effective thickness of the active
• 51:27
  Speaker 1: layer where carbon processing occurs. Rates measured with tracer techniques
• 51:34
  Speaker 1: show that without animal activity, the oxygen penetration depth would
• 51:39
  Speaker 1: be smaller and the efficiency of organic matter degradation would decline.
• 51:45
  Speaker 1: In a low-energy environment, small increments matter less. Predation among
• 51:51
  Speaker 1: invertebrates is modest but present. Polychaetes with eversible jaws prey
• 51:57
  Speaker 1: on smaller worms and on maia fauna. Large amphipods eat
• 52:01
  Speaker 1: smaller ones. Sea cucumbers host parasitic copepods and are occasionally
• 52:07
  Speaker 1: attacked by nematodes that enter through the anus and feed
• 52:11
  Speaker 1: on internal tissues. The balance of these interactions changes with
• 52:16
  Speaker 1: food input. After a large food fall, competition at bait
• 52:20
  Speaker 1: increases and cannibalism rates rise. During lean periods, interference declines
• 52:28
  Speaker 1: and animals spread out. Adaptations to steep slopes include body
• 52:34
  Speaker 1: shapes that resist sliding and behaviors that anchor the animal.
• 52:39
  Speaker 1: Sea cucumbers use tube feet to hold position. Polychaetes extend
• 52:44
  Speaker 1: parapodia laterally to increase friction. Amphipods tuck under small ridges
• 52:51
  Speaker 1: and face into the current. Landers that record for days
• 52:56
  Speaker 1: show that animals maintain position during slow mass movements of
• 53:00
  Speaker 1: fluff sediment triggered by small earthquakes. When failure occurs on
• 53:06
  Speaker 1: a larger scale, the community is reset in that sector
• 53:11
  Speaker 1: and recolonisation begins from adjacent areas. Sampling at these depths
• 53:18
  Speaker 1: requires hardware modifications. Nets that close at the bottom to
• 53:23
  Speaker 1: prevent loss of small animals during ascent, pressure chambers that
• 53:28
  Speaker 1: keep captured organisms at in situ pressure, and lights that
• 53:32
  Speaker 1: work at low intensity to avoid attraction or avoidance responses
• 53:37
  Speaker 1: are now standard. These tools have reduced the bias that
• 53:42
  Speaker 1: once favoured large scavengers in datasets. The result is a
• 53:47
  Speaker 1: more balanced view of the invertebrate assemblage. Interactions between macrofauna
• 53:55
  Speaker 1: and microbes are two-way. Sea cucumbers and polychaetes irrigate sediment
• 54:01
  Speaker 1: and supply oxygen that bacteria use. Bacteria produce extracellular polymers
• 54:08
  Speaker 1: that stabilize fecal pellets and make them easier for deposit
• 54:12
  Speaker 1: feeders to handle. Amphipods carry microbial communities on their exoskeletons
• 54:19
  Speaker 1: that process dissolved organic matter in the boundary layer as
• 54:24
  Speaker 1: the animals move. This feedback improves capture of resources that
• 54:29
  Speaker 1: would otherwise be lost. Energy budgets derived from respirometry and
• 54:35
  Speaker 1: from activity monitoring show narrow margins. For many invertebrates at
• 54:40
  Speaker 1: the trench floor, annual energy intake barely covers basal metabolism
• 54:46
  Speaker 1: and reproduction. Growth occurs in brief intervals after food pulses.
• 54:52
  Speaker 1: The system is steady not because the input is constant,
• 54:57
  Speaker 1: but because the community has evolved to match variable input
• 55:02
  Speaker 1: with flexible demand. The giant amphipods and the sea cucumbers
• 55:07
  Speaker 1: are therefore not curiosities. They are the principal workers that
• 55:12
  Speaker 1: keep carbon moving at the deepest point. Amphipods locate, shred
• 55:18
  Speaker 1: and redistribute food. Sea cucumbers and other deposit feeders process
• 55:24
  Speaker 1: the sediment blanket that accumulates when pulses end. Worms and
• 55:29
  Speaker 1: small crustaceans mix the surface layer and maintain exchange with
• 55:34
  Speaker 1: the water above. The structure is simple and efficient. It
• 55:39
  Speaker 1: functions year after year under pressure and cold that are
• 55:44
  Speaker 1: outside the design limits of most organisms on Earth. The
• 55:49
  Speaker 1: transition from amphipods to holothurians and then to the rest
• 55:54
  Speaker 1: of the invertebrate guilds shows a consistent theme. The trench
• 55:59
  Speaker 1: is not empty. It is organized around a limited energy
• 56:03
  Speaker 1: supply and around physical rules that make some materials and
• 56:08
  Speaker 1: strategies more viable than others. Carbonate is discouraged, so skeletons
• 56:14
  Speaker 1: are light or replaced by other chemistries. Rapid growth is discouraged,
• 56:20
  Speaker 1: so life cycles stretch and reproduction invests in fewer young.
• 56:26
  Speaker 1: Active pursuit is discouraged, so feeding is based on detritus
• 56:30
  Speaker 1: and on scavenging. Within those constraints, the variety of forms
• 56:36
  Speaker 1: and behaviours is sufficient to occupy the space and to
• 56:40
  Speaker 1: keep the system stable. With these two chapters in place,
• 56:45
  Speaker 1: the picture of the deepest ecosystem gains resolution. The small
• 56:50
  Speaker 1: and the large are linked by chemistry and by the
• 56:54
  Speaker 1: physics of sinking particles. The camera frames show more than silhouettes.
• 57:00
  Speaker 1: They show a working seafloor where each taxon holds a
• 57:04
  Speaker 1: narrow function that supports the rest. The data behind the
• 57:09
  Speaker 1: images confirm that this function is durable across seasons and
• 57:14
  Speaker 1: across years. The message is consistent. The deepest site on
• 57:20
  Speaker 1: the planet is not a limit that excludes. It is
• 57:24
  Speaker 1: a filter that selects for designs that match pressure, cold
• 57:28
  Speaker 1: and low energy. Pollution is recorded here with the same
• 57:33
  Speaker 1: precision that biology is recorded. The deepest sediments and the
• 57:38
  Speaker 1: animals that live within them hold chemicals that were made
• 57:42
  Speaker 1: for factories and for household use many decades ago. Polychlorinated biphenyls,
• 57:50
  Speaker 1: the group of compounds once used as coolants and in
• 57:53
  Speaker 1: electrical equipment, appear in extracts from amphipod tissues and from
• 57:58
  Speaker 1: mud cores. They are joined by other persistent organic pollutants
• 58:04
  Speaker 1: that were designed not to break down easily. These molecules
• 58:08
  Speaker 1: are hydrophobic. They attach to tiny particles and to organic
• 58:13
  Speaker 1: flakes as they sink. The trench is a collector of
• 58:17
  Speaker 1: such particles because its V-shaped walls and focused currents act
• 58:22
  Speaker 1: as a funnel. Over years and over decades, the slow
• 58:27
  Speaker 1: rain of matter carries a history of the surface into
• 58:31
  Speaker 1: the Hadal zone. Microplastics provide the most visible evidence. Fibres
• 58:38
  Speaker 1: and fragments that began as synthetic clothing or as packaging
• 58:43
  Speaker 1: drift down after binding to organic material. In the laboratory,
• 58:47
  Speaker 1: filtration of sediment slurries, followed by Raman spectroscopy, identifies polymer
• 58:54
  Speaker 1: types such as polyethylene, polypropylene, and polyester. Counts of fibers
• 59:00
  Speaker 1: per gram of dry sediment are not zero at any
• 59:04
  Speaker 1: depth tested. Amphipods and other deposit feeders ingest these particles
• 59:10
  Speaker 1: along with detritus. Most fragments pass through the gut within
• 59:15
  Speaker 1: hours or days. Some remain longer and can be found
• 59:19
  Speaker 1: embedded in mucus within the intestines. The quantities measured do
• 59:25
  Speaker 1: not show a single dramatic number. They show a steady
• 59:30
  Speaker 1: presence that mirrors the ubiquity of plastic at the surface.
• 59:36
  Speaker 1: A separate signal comes from radiocarbon, the isotope carbon-14. During
• 59:42
  Speaker 1: the 1950s and the 1960s, atmospheric nuclear tests increased the
• 59:49
  Speaker 1: ratio of carbon-14 in surface waters. That tracer, sometimes called
• 59:55
  Speaker 1: bomb carbon, has worked its way through the ocean. In
• 59:59
  Speaker 1: trench amphipods, the radiocarbon content of some tissues is slightly
• 1:00:05
  Speaker 1: elevated compared with what would be expected if the animals
• 1:00:09
  Speaker 1: fed only on very old carbon. The conclusion is that
• 1:00:14
  Speaker 1: at least part of their diet is recent, with a
• 1:00:18
  Speaker 1: surface origin. That is consistent with video records that show
• 1:00:23
  Speaker 1: these animals swarming to pieces of fresh carrion and to wood.
• 1:00:27
  Speaker 1: Heavy metals add to the picture. The metal element mercury
• 1:00:32
  Speaker 1: and the metal element lead occur in small concentrations in
• 1:00:37
  Speaker 1: trench sediments. The metal element cadmium and the element arsenic
• 1:00:42
  Speaker 1: are also present at low levels. These metals arrive attached
• 1:00:47
  Speaker 1: to particles and remain locked in minerals or in organic complexes.
• 1:00:53
  Speaker 1: In animals, the levels are generally low because the food
• 1:00:57
  Speaker 1: web is short and dilution through growth is large. Even so,
• 1:01:02
  Speaker 1: the presence of these elements confirms that no current moves
• 1:01:06
  Speaker 1: without carrying some trace of the continents and of human industry.
• 1:01:13
  Speaker 1: Antibiotic residues are a subtle case. Direct measurements are few
• 1:01:18
  Speaker 1: because concentrations fall below the detection limits of many methods.
• 1:01:23
  Speaker 1: Indirect measurements look for genes that encode enzymes capable of
• 1:01:29
  Speaker 1: degrading antibiotic molecules. These genes appear in metagenomes from trench sediments.
• 1:01:37
  Speaker 1: This does not prove contamination by modern pharmaceuticals Resistance genes
• 1:01:42
  Speaker 1: are ancient and occur naturally. The sober interpretation is that
• 1:01:48
  Speaker 1: microbial communities in the trench carry a diverse toolkit, and
• 1:01:54
  Speaker 1: that some of those tools happen to target chemicals that
• 1:01:58
  Speaker 1: humans also target. Wider chemistry in the sediment shows how
• 1:02:03
  Speaker 1: the system processes what arrives, Lipid biomarkers track the origin
• 1:02:08
  Speaker 1: of organic matter. Long chain alkanones indicate inputs from haptophyte algae.
• 1:02:15
  Speaker 1: Specific sterols point to diatoms. Pigments are degraded, but their
• 1:02:19
  Speaker 1: breakdown products still speak of surface blooms. As the material descends,
• 1:02:25
  Speaker 1: it is reworked by microbes. Proteins are cleaved to amino
• 1:02:29
  Speaker 1: acids and then to ammonia. Carbohydrates are hydrolyzed to simple
• 1:02:35
  Speaker 1: sugars and then oxidized. What reaches the trench floor is
• 1:02:40
  Speaker 1: not pristine. It is a selected mixture that still holds
• 1:02:44
  Speaker 1: enough energy to support a community. Alongside these natural compounds
• 1:02:50
  Speaker 1: ride the synthetic molecules that tell us the deep sea
• 1:02:55
  Speaker 1: is connected to every river mouth and every coastal city.
• 1:03:01
  Speaker 1: The record of pollution has one more element that is
• 1:03:05
  Speaker 1: not chemical. In the late 2010s, video from a deep
• 1:03:10
  Speaker 1: lander showed a piece of plastic film on the trench floor.
• 1:03:14
  Speaker 1: The object did not affect any measured process. It lay
• 1:03:19
  Speaker 1: on the mud as any other piece of debris would lie.
• 1:03:23
  Speaker 1: Its importance was symbolic. It made plain in a single
• 1:03:27
  Speaker 1: frame what datasets had been implying for years. If a
• 1:03:31
  Speaker 1: bag can reach this place, so can fibres, microbeads and
• 1:03:37
  Speaker 1: unwanted additives. The conclusion is not an appeal. It is
• 1:03:43
  Speaker 1: a fact that sets the context for the biology described here.
• 1:03:49
  Speaker 1: The discovery of new species in this environment proceeds slowly
• 1:03:54
  Speaker 1: and without publicity. Names are assigned only after careful anatomical
• 1:04:00
  Speaker 1: and genetic work. Among the crustaceans, the amphipod genera that
• 1:04:06
  Speaker 1: dominate baited lander videos include species that were unknown two
• 1:04:11
  Speaker 1: decades ago. One now well-known example is the amphipod Eurythenes plasticus.
• 1:04:18
  Speaker 1: pronounced u-ree, then ees-plas-tee-cus described from another trench. Its name
• 1:04:24
  Speaker 1: acknowledges the presence of plastic in its gut, but the
• 1:04:29
  Speaker 1: species is defined by anatomy and by gene sequences. In
• 1:04:34
  Speaker 1: the Mariana region, surveys continue to reveal members of the
• 1:04:39
  Speaker 1: same genus that differ in size, in the shape of
• 1:04:43
  Speaker 1: the nathopods, and in the morphology of mouthparts. Each difference
• 1:04:49
  Speaker 1: maps to a gene tree that shows separation across basins
• 1:04:54
  Speaker 1: and across depth ranges. Beyond amphipods, tanidaceans and cumaceans present
• 1:05:01
  Speaker 1: a steady stream of new records. These small crustaceans burrow
• 1:05:06
  Speaker 1: and avoid cameras. They enter samples when coras recover intact
• 1:05:11
  Speaker 1: surface layers or when suction samplers sweep the top few
• 1:05:15
  Speaker 1: centimetres of mud into a chamber. Species descriptions note the
• 1:05:20
  Speaker 1: shape of the carapace, the number and arrangement of satay
• 1:05:24
  Speaker 1: on appendages, and the form of uropods. Many are endemic
• 1:05:29
  Speaker 1: to single trenches, or even to segments of a trench.
• 1:05:34
  Speaker 1: Their life cycles appear short and flexible, suited to exploiting
• 1:05:39
  Speaker 1: brief pulses of food. Isopods at Hadal depths include lineages
• 1:05:45
  Speaker 1: with extreme sexual dimorphism. Males are tiny compared with females
• 1:05:51
  Speaker 1: and lack functional mouthparts in some species. Their lives are
• 1:05:55
  Speaker 1: focused on locating a female and fertilizing eggs. Females feed
• 1:06:01
  Speaker 1: on detritus and on microbial mats on the surface of
• 1:06:05
  Speaker 1: the sediment. Such strategies reduce competition between sexes and guarantee
• 1:06:10
  Speaker 1: that sparse populations can still reproduce. Descriptions of these isopods
• 1:06:17
  Speaker 1: rely on delicate features that are easily damaged during ascent.
• 1:06:23
  Speaker 1: Pressure-retaining containers and gentle sieving have improved the quality of
• 1:06:28
  Speaker 1: specimens and the clarity of the taxonomy. Among worms, the
• 1:06:33
  Speaker 1: Polychaetes provide the richest set of new species. Deposit-feeding families
• 1:06:39
  Speaker 1: such as Capitellids occur widely. Tube-building Amphiretids and Pterabelids construct
• 1:06:46
  Speaker 1: small dwellings from mucus and silt and extend palps across
• 1:06:52
  Speaker 1: the sediment to gather particles. Predator families such as Psyllids
• 1:06:57
  Speaker 1: and Dorvillids have reversible jaws that grip small prey. The
• 1:07:02
  Speaker 1: deep environment selects for reduced calcification. Cete and jaws are
• 1:07:07
  Speaker 1: robust where needed, but the rest of the body is light.
• 1:07:11
  Speaker 1: Many trench polychaetes show enlarged parapodia that help them stay
• 1:07:17
  Speaker 1: in place on slopes. Their burrows and tubes increase the
• 1:07:21
  Speaker 1: exchange of water within the top layer of sediment, and that,
• 1:07:25
  Speaker 1: in turn, increases the activity of bacteria. A peculiar group
• 1:07:31
  Speaker 1: of worms called Pogonophorans, also known as beard worms, occur
• 1:07:36
  Speaker 1: near seeps in the trench region. They lack a digestive
• 1:07:40
  Speaker 1: tract as adults and rely on endosymbiotic bacteria for nutrition.
• 1:07:47
  Speaker 1: The bacteria oxidise reduced chemicals such as sulphide or methane
• 1:07:53
  Speaker 1: when those molecules are present in the pore waters. The
• 1:07:56
  Speaker 1: worms supply oxygen and other substrates through a vascular system. Together,
• 1:08:03
  Speaker 1: they form a living reaction network that converts geochemical energy
• 1:08:08
  Speaker 1: into biomass with high efficiency. New species of these worms
• 1:08:14
  Speaker 1: continue to be described from slope sites adjacent to the
• 1:08:18
  Speaker 1: main trench axis. Nematodes dominate the maiofauna. Their diversity is high,
• 1:08:25
  Speaker 1: and many lineages are known only from molecular barcodes at present.
• 1:08:30
  Speaker 1: In some cores, the number of nematode species rivals counts
• 1:08:35
  Speaker 1: from shallower depths, although the abundances per square centimetre are lower.
• 1:08:41
  Speaker 1: The small body size allows nematodes to exploit microenvironments created
• 1:08:46
  Speaker 1: by grains and by biological structures, Their feeding modes range
• 1:08:52
  Speaker 1: from bacterial grazing to predation on other nematodes. Each new
• 1:08:58
  Speaker 1: sequence added to genetic databases becomes an anchor for future
• 1:09:03
  Speaker 1: studies that will connect names to functions. Analids beyond polychaetes
• 1:09:10
  Speaker 1: include rare oligachaetes that resemble earthworms in basic design, but
• 1:09:16
  Speaker 1: are adapted to saline water. They move through sediment slowly
• 1:09:21
  Speaker 1: and process organic matter. Quinoa Hinch sometimes called mud dragons
• 1:09:27
  Speaker 1: because of their spiny plates and their segmented appearance also
• 1:09:31
  Speaker 1: occur in small numbers. They grasp grains with well-developed mouthparts
• 1:09:37
  Speaker 1: and pull themselves forward with a telescoping motion. For many
• 1:09:42
  Speaker 1: of these small taxa, the trench represents the limit of
• 1:09:46
  Speaker 1: their distribution, not because of pressure alone, but because the
• 1:09:50
  Speaker 1: energy available per square metre is low. New species survive
• 1:09:55
  Speaker 1: here by minimising demand and by maximising flexibility in diet.
• 1:10:02
  Speaker 1: To connect these biological discoveries with the geology of the region,
• 1:10:08
  Speaker 1: one must address fluids that percolate upward through the crust.
• 1:10:12
  Speaker 1: Hydrothermal vents, in the strict sense of very hot springs
• 1:10:16
  Speaker 1: that precipitate metal sulphides and form chimneys, are most common
• 1:10:22
  Speaker 1: along mid-ocean ridges and in back-arc basins. The axis of
• 1:10:27
  Speaker 1: the Mariana Trench is not such a place. However, the
• 1:10:31
  Speaker 1: broader subduction zone includes mud volcanoes and seeps on the fore-arc,
• 1:10:37
  Speaker 1: where fluids altered by reactions in the subducting slab rise
• 1:10:42
  Speaker 1: to the seafloor. These fluids are alkaline and cool to
• 1:10:46
  Speaker 1: warm rather than hot. They carry dissolved hydrogen, methane and
• 1:10:51
  Speaker 1: small amounts of sulphide. They create localised chemistry that differs
• 1:10:56
  Speaker 1: sharply from ordinary deep water. At some seamounts near the trench,
• 1:11:02
  Speaker 1: thick flows of serpentinized mud ooze from vents and shape
• 1:11:07
  Speaker 1: low domes. The temperatures measured in the fluids are only
• 1:11:11
  Speaker 1: a few degrees above ambient sea water. The alkalinity is high.
• 1:11:17
  Speaker 1: The pH, which we will call the alkalinity level to
• 1:11:20
  Speaker 1: avoid abbreviations, reaches values near 12 in some samples. In
• 1:11:26
  Speaker 1: these places, carbonate minerals precipitate as unique forms. Brussite and
• 1:11:32
  Speaker 1: aragonite form chimneys that are fragile and pale. Within these structures,
• 1:11:38
  Speaker 1: microbial communities thrive on hydrogen and on methane. They use
• 1:11:43
  Speaker 1: enzymes that split hydrogen to capture energy and enzymes that
• 1:11:48
  Speaker 1: oxidize methane. Bivalves and gastropods host symbiotic bacteria that process
• 1:11:55
  Speaker 1: these reduced chemicals. The animals live as thin communities scattered
• 1:12:01
  Speaker 1: across vents where flow is steady. On slopes within the trench,
• 1:12:06
  Speaker 1: low-level seeps exhale fluids that are less alkaline but still
• 1:12:12
  Speaker 1: enriched in reduced compounds. Here, mats of filamentous bacteria grow,
• 1:12:17
  Speaker 1: producing sulfur granules inside their cells. Small polychaetes graze on
• 1:12:23
  Speaker 1: the mats. Bivalves with symbionts colonize patches where sulfide flux
• 1:12:30
  Speaker 1: is persistent. These seep communities are small compared with famous
• 1:12:35
  Speaker 1: ridge vents, but they demonstrate that the subduction environment feeds
• 1:12:40
  Speaker 1: chemosynthesis in more than one way. The result is that
• 1:12:46
  Speaker 1: carbon entering the trench from surface production is not the
• 1:12:50
  Speaker 1: only source of energy. Crustal chemistry contributes a second path.
• 1:12:57
  Speaker 1: Mineral evidence of past hydrothermal activity appears in sediment records
• 1:13:03
  Speaker 1: as layers enriched in barium and in silica. These signals
• 1:13:08
  Speaker 1: likely mark periods when plume fallout from back arc spreading
• 1:13:12
  Speaker 1: centres reached the trench region. Volcanic ash layers also occur.
• 1:13:18
  Speaker 1: Each layer is a time marker. Dating them with radiometric
• 1:13:23
  Speaker 1: methods allows correlation with known eruptions and with known episodes
• 1:13:29
  Speaker 1: of increased hydrothermal output. Biological markers sometimes coincide, as when
• 1:13:36
  Speaker 1: the diversity of siliceous sponges or radiolarians changes in bands
• 1:13:42
  Speaker 1: that match the chemistry. Hydrothermal and seep fluids alter the
• 1:13:48
  Speaker 1: mechanical properties of sediment. Poor waters with high alkalinity levels
• 1:13:54
  Speaker 1: can cement grains and make crusts that resist erosion. When
• 1:13:58
  Speaker 1: such crusts form on steep slopes, they can stabilize patches
• 1:14:03
  Speaker 1: of habitat and allow colonization by animals that need a
• 1:14:07
  Speaker 1: firm base. In other places, gas bubbles accumulate and weaken layers.
• 1:14:14
  Speaker 1: Small failures occur and leave scars visible in side-scan sonar.
• 1:14:19
  Speaker 1: These events reshape the microtopography that in turn influences where
• 1:14:24
  Speaker 1: invertebrates settle and feed. The microbiology of vent and seep
• 1:14:30
  Speaker 1: sites near the trench shows metabolic versatility. Hydrogen-oxidizing bacteria use
• 1:14:36
  Speaker 1: a group of enzymes called hydrogenases to capture electrons from
• 1:14:42
  Speaker 1: hydrogen and to feed them into energy pathways. Methane-oxidizing bacteria
• 1:14:48
  Speaker 1: use particulate methane, monooxygenase, and soluble methane, monooxygenase enzymes, to
• 1:14:55
  Speaker 1: convert methane into methanol and then into carbon dioxide while
• 1:15:00
  Speaker 1: harvesting energy. Sulfur-oxidizing bacteria run pathways that convert sulfide to sulfate.
• 1:15:09
  Speaker 1: In combination, these processes support a food web that is
• 1:15:13
  Speaker 1: independent of sunlight. Many strains show pressure-adapted versions of their enzymes,
• 1:15:19
  Speaker 1: with amino acid substitutions that stabilize active sites in compressed water.
• 1:15:26
  Speaker 1: Membrane lipids are more unsaturated to maintain fluidity. These are
• 1:15:32
  Speaker 1: the same themes seen in non-chemosynthetic communities, tuned to a
• 1:15:38
  Speaker 1: different energy source. The physics of seepage sets a slow rhythm,
• 1:15:44
  Speaker 1: subducting plates dewater as they descend. The released fluids percolate
• 1:15:50
  Speaker 1: through faults and through permeable layers. Flow rates at the
• 1:15:54
  Speaker 1: seafloor are low by human standards, measured in centimetres per
• 1:15:59
  Speaker 1: day to metres per day. Even so, the gradients created
• 1:16:04
  Speaker 1: are enough to sustain communities for decades. When flow shifts,
• 1:16:09
  Speaker 1: communities decline and a new patch comes to life elsewhere.
• 1:16:14
  Speaker 1: This mosaic is one reason why surveys over many years
• 1:16:19
  Speaker 1: are required to build a map of chemosynthetic habitats in
• 1:16:24
  Speaker 1: the trench region. Chemical signatures of these fluids appear in
• 1:16:28
  Speaker 1: the stable isotope composition of carbon in animal tissues. Values
• 1:16:34
  Speaker 1: shifted toward very light carbon indicate a diet based on methane.
• 1:16:40
  Speaker 1: Values closer to the marine plankton average indicate reliance on
• 1:16:46
  Speaker 1: photosynthetically derived material. Animals can switch between sources. Bivalves with
• 1:16:53
  Speaker 1: symbionts may show a strong methane signal, while their neighbours
• 1:16:58
  Speaker 1: show a mixed diet. The plasticity supports survival in a
• 1:17:02
  Speaker 1: patchy environment. The geology also affects oxygen levels in poor waters.
• 1:17:09
  Speaker 1: Where reduced fluids rise, oxygen is consumed quickly. Redox boundaries sharpen.
• 1:17:15
  Speaker 1: Microbial diversity is high at these boundaries because many processes
• 1:17:20
  Speaker 1: can proceed side by side. Iron reducers and manganese reducers
• 1:17:27
  Speaker 1: occupy thin bands adjacent to oxidizers. Denitrifiers work where nitrate
• 1:17:34
  Speaker 1: diffuses downward from the water column. The resulting layered chemistry
• 1:17:39
  Speaker 1: creates habitats that support maio fauna with specific preferences. Nematodes
• 1:17:46
  Speaker 1: select particular depths. Foraminifera choose depths where their symbionts can
• 1:17:52
  Speaker 1: find the right balance of oxidants and reductants. A word
• 1:17:58
  Speaker 1: about temperature helps keep expectations realistic. The Hadal environment close
• 1:18:04
  Speaker 1: to the trench axis is cold. With the exception of
• 1:18:08
  Speaker 1: local seeps and mud volcanoes, there are no hot spots.
• 1:18:13
  Speaker 1: Black smoker chimneys do not rise from the trench floor.
• 1:18:18
  Speaker 1: The existence of chemosynthetic communities here relies on the chemistry
• 1:18:23
  Speaker 1: of loss rather than on the chemistry of heat. Serpentinization
• 1:18:28
  Speaker 1: of ultramathic rocks produces hydrogen. Decomposition of subducted organic matter
• 1:18:35
  Speaker 1: produces methane. The sums are small compared with ridge vents,
• 1:18:41
  Speaker 1: but they are sufficient to sustain life that specializes in
• 1:18:46
  Speaker 1: low flux, as with other parts of the trench story.
• 1:18:50
  Speaker 1: technology determines resolution. Chemical sensors capable of detecting nanomolar changes
• 1:18:57
  Speaker 1: in sulfide and in methane guide cameras to patches of activity.
• 1:19:02
  Speaker 1: Mass spectrometers operate in situ and report compositions in real time.
• 1:19:08
  Speaker 1: Flow meters record slow exhalations and inhalations of the sea floor.
• 1:19:14
  Speaker 1: Pressure retaining samplers recover fluids without degassing and permit laboratory
• 1:19:20
  Speaker 1: analysis of dissolved gases and of microbial cells. Each instrument
• 1:19:27
  Speaker 1: adds clarity to a picture that had been guessed at
• 1:19:31
  Speaker 1: for years. The three themes of this chapter form a
• 1:19:36
  Speaker 1: single system. Pollution gives a record of connection to the surface.
• 1:19:42
  Speaker 1: New species of crustaceans and worms show how life adapts
• 1:19:48
  Speaker 1: to the most constrained budgets and to the most stable
• 1:19:52
  Speaker 1: of environments. Hydrothermal and seepage processes provide a second stream
• 1:19:58
  Speaker 1: of energy that intersects with the first. Together they explain
• 1:20:03
  Speaker 1: why the deepest place on earth is not barren. It
• 1:20:07
  Speaker 1: is structured, busy at a slow pace, and sensitive to
• 1:20:11
  Speaker 1: inputs from both above and below. Mineral formations at the
• 1:20:16
  Speaker 1: trench floor record chemistry with the discipline of a logbook.
• 1:20:20
  Speaker 1: The first rule is the scarcity of calcium carbonate. In
• 1:20:25
  Speaker 1: the Pacific, the level at which calcium carbonate dissolves sits
• 1:20:29
  Speaker 1: far above the trench axis. Below that level shells of
• 1:20:34
  Speaker 1: calcite and of aragonite tend to disappear. What arrives from
• 1:20:39
  Speaker 1: the surface is dissolved and redistributed before it can build
• 1:20:44
  Speaker 1: a lasting layer. As a result, the sediment is dominated
• 1:20:48
  Speaker 1: by clay by volcanic ash altered to new minerals, and
• 1:20:53
  Speaker 1: by particles that form directly within the mud through slow reactions.
• 1:20:58
  Speaker 1: Where carbonates do occur, they are usually born in place
• 1:21:03
  Speaker 1: as products of unusual local chemistry rather than as rain
• 1:21:07
  Speaker 1: from above. One such local chemistry appears near alkaline seeps
• 1:21:13
  Speaker 1: on the fore-arc Fluids rich in dissolved carbonate species precipitate
• 1:21:18
  Speaker 1: fragile forms of aragonite and brucite as they meet ordinary seawater.
• 1:21:24
  Speaker 1: The result is a foam of white chimneys and crusts
• 1:21:28
  Speaker 1: that are light enough to crumble at a touch. Samples
• 1:21:32
  Speaker 1: show delicate needles and rosettes when examined under a microscope.
• 1:21:37
  Speaker 1: The crystals grow grain by grain as flow continues. When
• 1:21:42
  Speaker 1: the flow stops, the structures become fossils of chemistry rather
• 1:21:47
  Speaker 1: than living conduits. Away from those seep patches, the trench
• 1:21:52
  Speaker 1: sediments show other orthogenic minerals. Barite, a mineral of barium sulfate,
• 1:21:59
  Speaker 1: forms tiny rosettes where sulfate reduction and reoxidation create micro-environments
• 1:22:07
  Speaker 1: that favour its precipitation. The rosettes persist as beads in
• 1:22:12
  Speaker 1: the clay. Phosphate minerals occur where organic matter has been
• 1:22:17
  Speaker 1: buried and degraded. In thin layers, they cement grains into
• 1:22:22
  Speaker 1: subtle hard grounds that resist erosion and change how animals
• 1:22:27
  Speaker 1: can feed. Pyrite appears as framboids, the classic clusters of
• 1:22:33
  Speaker 1: tiny crystals that resemble raspberries. These framboids mark zones where
• 1:22:39
  Speaker 1: microbes have used sulfate as an electron acceptor and created
• 1:22:43
  Speaker 1: sulfide that then reacted with dissolved iron. Silica records add
• 1:22:50
  Speaker 1: another line to the mineral chapter. Skeletons of radiolarians and
• 1:22:55
  Speaker 1: of diatoms fall from above and deliver opaline silica. Most
• 1:23:00
  Speaker 1: dissolve during descent or within the upper sediment, but some
• 1:23:05
  Speaker 1: persist and become part of a mixed matrix that later
• 1:23:10
  Speaker 1: flows downslope. as turbidites. In places where volcanic ash layers
• 1:23:15
  Speaker 1: were delivered by eruptions from arc volcanoes, that ash alters
• 1:23:20
  Speaker 1: slowly to zeolites such as philipsite and clinoptilolite. These alteration
• 1:23:27
  Speaker 1: minerals trap cations and water within frameworks that tell geologists
• 1:23:32
  Speaker 1: about the time the ash spent within the seawater column
• 1:23:36
  Speaker 1: and within pore waters. In cores, the presence of zeolites
• 1:23:41
  Speaker 1: marks intervals of ash input and helps identify sources when
• 1:23:47
  Speaker 1: chemistry is compared to known volcanoes. Hard rock is scarce
• 1:23:54
  Speaker 1: on the trench floor because sedimentation is active and slopes
• 1:23:58
  Speaker 1: are steep, but where outcrops exist, they carry their own
• 1:24:03
  Speaker 1: mineral record. Iron and manganese crusts coat the rock with
• 1:24:08
  Speaker 1: a thin, dark film. These ferromanganese crusts grow at rates
• 1:24:14
  Speaker 1: of millimetres per million years. They are hydrogenous in origin,
• 1:24:19
  Speaker 1: accumulating directly from metal ions dissolved in seawater. Their chemical
• 1:24:24
  Speaker 1: layers hold traces of rare metals and of isotope ratios
• 1:24:30
  Speaker 1: that reflect changes in the ocean over long spans. A
• 1:24:34
  Speaker 1: chipped fragment of such a crust can therefore act as
• 1:24:38
  Speaker 1: a small history book of marine chemistry. Grains within the
• 1:24:43
  Speaker 1: trench sediment sometimes bear a varnish of manganese oxides that
• 1:24:49
  Speaker 1: also accumulates from seawater. The varnish darkens the grains and
• 1:24:54
  Speaker 1: increases their density. Under a scanning instrument, tiny platelets of
• 1:24:59
  Speaker 1: bernicite and other manganese oxides appear Layered with iron oxyhydroxides,
• 1:25:07
  Speaker 1: the balance of iron and manganese can shift with microenvironmental
• 1:25:12
  Speaker 1: redox changes, which means the varnish is both a product
• 1:25:16
  Speaker 1: and a record of the chemistry of the thin film
• 1:25:20
  Speaker 1: of water that moves through the sediment bed. Volcanic contributions
• 1:25:26
  Speaker 1: are frequent because the trench parallels a chain of islands
• 1:25:30
  Speaker 1: with active and dormant cones. Ash falls enter the ocean
• 1:25:36
  Speaker 1: and settle through the water column. In cores taken near
• 1:25:40
  Speaker 1: the trench axis, distinct ash layers alternate with clay. The
• 1:25:44
  Speaker 1: glass shards that make up the ash alter to pelagonite
• 1:25:49
  Speaker 1: and then to zeolites through slow reactions with seawater. Trace
• 1:25:54
  Speaker 1: element signatures, such as ratios of strontium to neodymium and
• 1:25:59
  Speaker 1: of rare earth elements, allow correlation with eruptions on land.
• 1:26:05
  Speaker 1: In this way, a quiet mud core contains time-stamped pages
• 1:26:09
  Speaker 1: written by distant volcanoes. Not all mineral features grow quietly.
• 1:26:15
  Speaker 1: Some are created by rapid deposition during slope failures. When
• 1:26:20
  Speaker 1: currents rush downslope after an earthquake, they carry a mixture
• 1:26:25
  Speaker 1: of silt, sand and fragments that settles as a graded bed,
• 1:26:30
  Speaker 1: coarser at the base and finer at the top. Within
• 1:26:34
  Speaker 1: these beds, oriented mica flakes and imbricated clasts record flow direction.
• 1:26:41
  Speaker 1: The base of a large event bed can cut down
• 1:26:44
  Speaker 1: into older layers, leaving an erosional surface that appears in
• 1:26:49
  Speaker 1: seismic profiles as a reflector. Cementation within these deposits can
• 1:26:56
  Speaker 1: create lenses that later stand out as firmer patches compared
• 1:27:01
  Speaker 1: with surrounding mud. Ancient processes leave macroscopic and microscopic signatures
• 1:27:08
  Speaker 1: that let geologists reconstruct events step by step. Turbidites appear
• 1:27:14
  Speaker 1: as repeated sequences of coarse to fine layers, the boomer
• 1:27:19
  Speaker 1: sequence familiar to sedimentologists. Between these event beds lie intervals
• 1:27:25
  Speaker 1: of slow pelagic rain, the red clay that builds grain
• 1:27:29
  Speaker 1: by grain over thousands of years. Tefra layers from eruptions
• 1:27:35
  Speaker 1: are thin and widespread. They are dated by radiometric methods
• 1:27:40
  Speaker 1: and by paleomagnetism. The reversal of the magnetic field known
• 1:27:45
  Speaker 1: as the Matuyama to Brunhess boundary, which occurred roughly three-quarters
• 1:27:51
  Speaker 1: of a million years ago, appears as a flip in
• 1:27:54
  Speaker 1: the orientation of magnetic grains within cores. That flip anchors
• 1:28:01
  Speaker 1: the age model for many sections. At rarer intervals, microtectites
• 1:28:09
  Speaker 1: appear in deep ocean cores. These glassy spherules were formed
• 1:28:14
  Speaker 1: when meteorites struck continents or shallow seas and melted target
• 1:28:19
  Speaker 1: rocks that were then launched and cooled in the air.
• 1:28:23
  Speaker 1: While not abundant within the trench axis where deposition is complex,
• 1:28:29
  Speaker 1: They occur in nearby deep basins and provide correlation points
• 1:28:34
  Speaker 1: for impacts, including the event that marked the boundary between
• 1:28:38
  Speaker 1: the Cretaceous period and the Paleogene. Their presence in Pacific
• 1:28:45
  Speaker 1: records shows how far such debris can travel, and how
• 1:28:50
  Speaker 1: faithfully the ocean keeps the pieces. Mass-wasting leaves scars on
• 1:28:57
  Speaker 1: the seafloor that modern mapping can see in detail. High-resolution
• 1:29:02
  Speaker 1: multibeam surveys show step-like features called scarps, hummocky terrain below
• 1:29:08
  Speaker 1: slide sources and long run-out deposits where flows pond within basins.
• 1:29:14
  Speaker 1: Some scars align with faults created as the oceanic plate
• 1:29:19
  Speaker 1: bends into the trench. Those bending faults cut the crust
• 1:29:23
  Speaker 1: and provide pathways for fluids. Where water percolates along them,
• 1:29:29
  Speaker 1: alteration of olivine and pyroxene to serpentine occurs, a reaction
• 1:29:35
  Speaker 1: that produces hydrogen and changes rock density. The topographic record
• 1:29:41
  Speaker 1: of such processes is subtle but detectable as ridges and
• 1:29:45
  Speaker 1: troughs that parallel the trench. Terraces along the inner wall
• 1:29:50
  Speaker 1: of the trench tell of repeated slumping and of slow
• 1:29:55
  Speaker 1: backstop movement, as material is scraped off the subducting plate
• 1:30:00
  Speaker 1: and added to the upper plate as an accretionary prism.
• 1:30:04
  Speaker 1: Each terrace holds a stack of deformed layers, folded and faulted.
• 1:30:10
  Speaker 1: Seismic lines show packages of reflectors that dip landward, the
• 1:30:16
  Speaker 1: fingerprint of accretion. Between terraces, canyons carry sediment down to
• 1:30:21
  Speaker 1: the axis. Their heads are often linked to rivers on
• 1:30:25
  Speaker 1: the islands through a chain of gullies and shelf breaks,
• 1:30:30
  Speaker 1: demonstrating a full pathway from volcanic flank to trench floor.
• 1:30:35
  Speaker 1: Some cores contain layers enriched in the element iridium and
• 1:30:41
  Speaker 1: in chrome-rich spinals, signatures associated with meteorite material. These layers
• 1:30:47
  Speaker 1: are thin and require careful chemical separation to detect. Where found,
• 1:30:54
  Speaker 1: they point to local fallout from distant impacts or from
• 1:30:58
  Speaker 1: reworking of older impact layers by currents. While not headline features,
• 1:31:04
  Speaker 1: Such layers add to the quiet evidence that global events
• 1:31:08
  Speaker 1: leave marks even in the most remote basins. Gas hydrates
• 1:31:13
  Speaker 1: are a potential mineral phase where pressure is high and
• 1:31:17
  Speaker 1: temperature is low. These ice-like lattices that trap methane and
• 1:31:23
  Speaker 1: other gases are common on some continental margins at depths
• 1:31:28
  Speaker 1: much shallower than the trenches. Within the trench axis, direct
• 1:31:33
  Speaker 1: sampling of hydrate is scarce, likely because organic matter delivery
• 1:31:38
  Speaker 1: is limited and because the geology does not favour the
• 1:31:42
  Speaker 1: formation of thick hydrate layers. On adjacent slopes and in
• 1:31:48
  Speaker 1: the fore-arc, hydrate indicators appear more often. Seismic blanking and
• 1:31:54
  Speaker 1: pockmarks suggest past episodes of gas escape. The implication is practical.
• 1:32:01
  Speaker 1: The trench is not a reservoir for hydrates, but the
• 1:32:04
  Speaker 1: broader subduction environment cycles, gas, that can from time to
• 1:32:10
  Speaker 1: time form hydrate in favourable pockets. A separate set of
• 1:32:15
  Speaker 1: markers of ancient processes resides in the clay mineral assemblage.
• 1:32:21
  Speaker 1: The relative abundance of elite Kaolinite, smectite and chlorite reflects
• 1:32:27
  Speaker 1: the balance between volcanic inputs, continental weathering products carried by wind,
• 1:32:33
  Speaker 1: and in situ alteration. Shifts in those proportions track climate
• 1:32:39
  Speaker 1: change on land and ocean circulation changes. For example, increased
• 1:32:45
  Speaker 1: smectite can indicate more volcanic ash or more alteration of
• 1:32:50
  Speaker 1: basaltic glass. While increased elite may signal stronger input from
• 1:32:56
  Speaker 1: continental dust, these proxies operate slowly and provide context to
• 1:33:02
  Speaker 1: the faster stories told by turbidites and Tifra. Taken together,
• 1:33:07
  Speaker 1: the mineral and stratigraphic record under the trench floor is
• 1:33:12
  Speaker 1: not blank. It is a layered archive of steady rain,
• 1:33:16
  Speaker 1: punctuated delivery from slopes and pulses from volcanoes and from
• 1:33:21
  Speaker 1: rarer global events. Each component is independent in origin but
• 1:33:28
  Speaker 1: stored together. When analysed, the combined record describes a dynamic
• 1:33:34
  Speaker 1: system that concentrates, sorts and preserves. Against this background of
• 1:33:41
  Speaker 1: minerals and structures, animals that look spectral to a human
• 1:33:46
  Speaker 1: eye stand out. The phrase ghost crab has been used
• 1:33:50
  Speaker 1: in popular accounts to describe pale decapods at great depth.
• 1:33:56
  Speaker 1: Strictly speaking, true shore ghost crabs live in shallow sands
• 1:34:00
  Speaker 1: and do not occur in trenches. In the Hadal zone
• 1:34:04
  Speaker 1: of the Mariana region, Most decapod crustaceans are scarce for
• 1:34:09
  Speaker 1: physiological reasons. The magnesium content of seawater interferes with their
• 1:34:15
  Speaker 1: nerve function under very high pressure, a condition sometimes called
• 1:34:21
  Speaker 1: magnesium narcosis in the literature. This limitation sets a practical
• 1:34:27
  Speaker 1: depth boundary for many crabs and for many shrimps. There
• 1:34:31
  Speaker 1: are exceptions and workarounds. In the broader Mariana system, at
• 1:34:37
  Speaker 1: vents and at seeps in the back arc and on
• 1:34:40
  Speaker 1: the forearc, decapods occur that are pale, with reduced eyes
• 1:34:46
  Speaker 1: and thickened sati. Some are squat lobsters of the genus Munidopsis,
• 1:34:52
  Speaker 1: which is an anamurin group rather than a true crab.
• 1:34:56
  Speaker 1: They carry long claws and a compact body and often
• 1:35:00
  Speaker 1: look ghostly white in camera light. Others are vent crabs
• 1:35:04
  Speaker 1: in families that specialize in chemosynthetic settings. They detect chemical
• 1:35:10
  Speaker 1: cues with enhanced antennal sensilla and graze microbial mats or
• 1:35:16
  Speaker 1: scavenge around vents. While these animals are not typical residents
• 1:35:21
  Speaker 1: of the trench axis, their presence in the regional province
• 1:35:25
  Speaker 1: contributes to the impression of a pale, spectral crustacean fauna.
• 1:35:32
  Speaker 1: Wood falls and carcass falls provide another occasion for unusual crustaceans.
• 1:35:39
  Speaker 1: On rare deployments, a piece of wood lowered by a
• 1:35:42
  Speaker 1: lander has been colonised rapidly by white squat lobsters and
• 1:35:47
  Speaker 1: by isopods with reduced pigmentation. They rasp the wood with
• 1:35:52
  Speaker 1: mouthparts adapted for scraping and rely on gut symbionts to
• 1:35:56
  Speaker 1: digest cellulose. The pale colour is not an adaptation to
• 1:36:01
  Speaker 1: avoid predators because there is almost no light to detect it.
• 1:36:06
  Speaker 1: It is simply a consequence of living where pigment is
• 1:36:11
  Speaker 1: not required. Other animals deserve the label strange because they
• 1:36:17
  Speaker 1: alter body plans in ways that are uncommon elsewhere. Holothurians
• 1:36:23
  Speaker 1: with fins can swim briefly above the bottom to relocate.
• 1:36:27
  Speaker 1: When seen in profile, they resemble the body of a
• 1:36:31
  Speaker 1: headless bird. Transparent sea cucumbers show internal anatomy in clarity
• 1:36:38
  Speaker 1: that would normally require dissection. They inflate and deflate to
• 1:36:43
  Speaker 1: adjust buoyancy within a narrow range. The slow undulation of
• 1:36:48
  Speaker 1: their fringe structures looks dramatic in time-lapse, yet is measured
• 1:36:52
  Speaker 1: and small in absolute speed. Single-celled giants called Xenophyphores are
• 1:36:59
  Speaker 1: part of this ghostly category in a different sense. They
• 1:37:02
  Speaker 1: build tests by gluing together particles, including sponge spicules and
• 1:37:08
  Speaker 1: volcanic shards, and they reach sizes that the word single-cell
• 1:37:13
  Speaker 1: does not prepare a listener to expect. Under soft lighting,
• 1:37:17
  Speaker 1: they resemble pale roses pressed into the mud. Their surfaces
• 1:37:22
  Speaker 1: host other organisms, from tiny worms to bacteria. In essence,
• 1:37:27
  Speaker 1: they act as islands of complexity that break the uniformity
• 1:37:33
  Speaker 1: of the sediment plane. Anemones anchored to small stones or
• 1:37:38
  Speaker 1: shell fragments lift translucent tentacles into currents barely perceptible to cameras.
• 1:37:45
  Speaker 1: They close whenever new sediment settles and reopen minutes later.
• 1:37:50
  Speaker 1: Catenophores drift by like small lanterns, though the water above
• 1:37:55
  Speaker 1: the bottom and are visible only in the beam of
• 1:37:59
  Speaker 1: the camera. Polychaetes with reversible jaws leave brief sketches in
• 1:38:04
  Speaker 1: the mud when they erupt from burrows to seize prey.
• 1:38:08
  Speaker 1: Most of the time, the only sign of their presence
• 1:38:11
  Speaker 1: is a pair of small holes and a halo of
• 1:38:15
  Speaker 1: disturbed grains. Among fish, the snailfish continues to be the
• 1:38:20
  Speaker 1: emblem of a world near the edge of vertebrate possibility.
• 1:38:25
  Speaker 1: Individuals filmed near the trench floor look almost gelatinous. Their
• 1:38:30
  Speaker 1: bones are lightly mineralized, their bodies rich in osmolites that
• 1:38:35
  Speaker 1: stabilize proteins, and their heads bear little in the way
• 1:38:40
  Speaker 1: of scales. They move with short undulations of the body
• 1:38:45
  Speaker 1: conserving energy. When they open their mouths over bait, the
• 1:38:50
  Speaker 1: action is calm and assured. There is no wasteful strike.
• 1:38:55
  Speaker 1: Video analysis of their movements shows efficient use of the
• 1:39:00
  Speaker 1: tail finite element by finite element. The effect is spare
• 1:39:05
  Speaker 1: rather than spectacular. Bioluminescence is present but subdued near the bottom.
• 1:39:12
  Speaker 1: Many pelagic animals in the water column above the trench
• 1:39:16
  Speaker 1: use light for communication or for camouflage. On the floor,
• 1:39:21
  Speaker 1: flashes recorded by cameras are infrequent and generally weak. Some
• 1:39:26
  Speaker 1: come from small ostracods that release light to distract predators.
• 1:39:32
  Speaker 1: Some may come from bacteria that colonize organic particles. There
• 1:39:36
  Speaker 1: is no display. There is only the occasional spark. The
• 1:39:40
  Speaker 1: category strange life forms also includes animals that adjust strategies
• 1:39:46
  Speaker 1: in non-intuitive ways. Some small crustaceans increase lipid storage to
• 1:39:52
  Speaker 1: a degree that makes them nearly neutrally buoyant in cold water,
• 1:39:57
  Speaker 1: allowing them to hover above the sediment and drift down
• 1:40:01
  Speaker 1: onto food with minimal effort. Certain worms grow elaborate sensory
• 1:40:07
  Speaker 1: head structures that let them map chemical gradients with precision
• 1:40:12
  Speaker 1: finer than a millimeter. Anemones align their columns parallel to
• 1:40:18
  Speaker 1: the weak near-bottom flows to reduce drag. Each of these
• 1:40:23
  Speaker 1: features is a solution to the same problem, the economy
• 1:40:27
  Speaker 1: of energy in a place where energy arrives in pulses
• 1:40:31
  Speaker 1: and is scarce between them. Claims of large unknown predators
• 1:40:36
  Speaker 1: or of exotic creatures unfamiliar to science have not stood
• 1:40:40
  Speaker 1: when tested against good images and specimens. Most shapes resolve
• 1:40:46
  Speaker 1: into known groups once observed clearly and catalogued with their parts.
• 1:40:51
  Speaker 1: What remains to be described is not monsters but details,
• 1:40:57
  Speaker 1: the number of segments on a mouthpart. the sequence of
• 1:41:01
  Speaker 1: atoms in an enzyme, the exact composition of a mineral
• 1:41:07
  Speaker 1: crust on a grain. These details are the coins in
• 1:41:12
  Speaker 1: which knowledge here is bought. In summary, mineral formations in
• 1:41:18
  Speaker 1: the trench combine orthogenic products like barite, pyrite and zeolites
• 1:41:24
  Speaker 1: with hydrogenous coatings of iron and manganese and with occasional
• 1:41:29
  Speaker 1: carbonates born of unusual alkalinity. Stratigraphy records ancient processes through turbidites, tifra,
• 1:41:38
  Speaker 1: magnetic reversals and subtle chemical layers. The so-called ghost crabs
• 1:41:43
  Speaker 1: of the deep are mostly pale anamurans and vent decapods
• 1:41:47
  Speaker 1: that dwell away from the axis, while at the axis
• 1:41:51
  Speaker 1: itself the spectral cast is supplied by pale amphipods, transparent holothurians, xenophyophores,
• 1:42:00
  Speaker 1: and finely adapted worms. The system is consistent across these scales.
• 1:42:06
  Speaker 1: It writes its history slowly, holds the products of chemistry carefully,
• 1:42:11
  Speaker 1: and supports life that is spare and efficient.