Latest / The Climate Translation / Snowing in the Deep

Transcript

Snowing in the Deep · The Climate Translation

0:00
Imagine you took a submarine to the deepest parts of our oceans.
0:12
If you looked out at a porthole and had an external light source, you might notice something strange.
0:19
It might look like it's snowing.
0:22
What you're seeing is a mixture of tiny pieces of organic material slowly falling from
0:27
the sunlit ocean above.
0:30
Scientists call it marine snow.
0:33
And while it may not look important, this constant underwater snowfall is one of the
0:39
ways the ocean moves carbon away from the atmosphere and stores it in the deep sea.
0:46
Today we're going to talk about this phenomenon, the microscopic organisms that feed on it,
0:51
and why the texture of a tiny particle can matter for the climate of an entire planet.
0:58
Welcome back to the podcast, I'm Dr. Mac, and this is the Climate Translation.
1:09
So where does marine snow actually come from?
1:13
Well most of it begins near the ocean surface, the upper part of the ocean that receives sunlight,
1:20
which makes it home to an enormous number of microscopic organisms called phytoplankton.
1:27
You can think of phytoplankton as the ocean's version of plants.
1:31
They use sunlight to carry out photosynthesis, and just like plants on land, they take
1:37
in carbon dioxide and use that carbon to build their bodies.
1:43
That's where our story is going to begin.
1:46
Carbon dioxide from the atmosphere dissolves into the surface ocean, and phytoplankton
1:51
use some of that carbon, then tiny animals call zooplankton eat the phytoplankton.
1:58
Fish eat the zooplankton, larger animals eat the fish, and carbon begins moving through
2:05
the marine food web.
2:07
But of course organisms don't live forever.
2:11
Cells die, animals produce waste, predators eat messily and leave tiny pieces behind.
2:18
Plankton shed material, and many marine organisms produce mucus.
2:23
All of these little scraps begin floating through the water.
2:27
And at first, many of them are incredibly small, but the ocean is full of sticky biological
2:33
material.
2:35
Particles bump into one another and begin clumping together.
2:38
A dead plankton cell sticks to some mucus, a piece of waste sticks to that.
2:44
Tiny mineral grains become attached.
2:47
Eventually these tiny particles grow into larger flakes, which we call marine snow.
2:53
Some of the flakes are barely visible, others can grow really large, and gravity begins
2:58
pulling them downward.
3:00
It creates a nearly constant rain of material from the productive waters near the surface
3:06
to the deep dark ocean below.
3:09
But marine snow is not just ocean garbage, it's carrying carbon.
3:15
The carbon that phytoplankton originally took from carbon dioxide at the surface is now
3:21
physically moving into deeper water.
3:25
Scientists call this process part of the biological carbon pump.
3:30
Think of the process like an elevator.
3:33
Life near the surface loads carbon into the elevator, and the marine snow carries it
3:39
downward.
3:40
And the farther down the carbon travels, the longer it may remain separated from the atmosphere.
3:47
But there's a problem.
3:49
Most marine snow doesn't make it that far.
3:53
The ocean is filled with bacteria and other organisms looking for food.
3:58
To them, this falling snow is lunch.
4:02
As the particles sink, bacteria begin breaking down the organic material.
4:08
Animals eat pieces of it, and some of the carbon is converted back into carbon dioxide
4:14
and released into the surrounding water.
4:17
So the marine snow gradually disappears.
4:21
Scientists estimate that more than 10 billion metric tons of carbon begin sinking away from
4:28
the surface ocean every year.
4:31
But only a fraction of that makes it deep enough to remain stored for centuries or longer.
4:38
That means the biological carbon pump really depends on a race.
4:43
Gravity is pulling the particles down.
4:47
Microbes are breaking them apart.
4:49
But if a particle sinks quickly enough, more carbon can reach the deep ocean.
4:54
If bacteria destroy it first, much of the carbon remains closer to the surface, where
5:00
it can eventually return to the atmosphere.
5:03
So scientists have been spending decades trying to understand what determines who wins
5:09
that race.
5:10
And it turns out, part of the answer may depend on something surprisingly simple.
5:16
Just how gooey the snow is.
5:20
So why would the gooiness or stickiness of marine snow matter?
5:25
To answer that, we have to talk about viscosity.
5:29
Viscosity is simply a measure of how strongly a fluid resists flowing.
5:35
Imagine two pails, ones filled with water and the others filled with honey.
5:40
Now you place ping pong balls in each.
5:43
If you slide your hand through the water one, both your hand and the balls move easily.
5:49
Water has a relatively low viscosity.
5:53
Now try the same thing with honey.
5:56
Everything moves more slowly.
5:57
You have to push harder because the honey itself resists being moved and flowing around
6:04
your hand and the balls.
6:06
That resistance is viscosity, honey has a higher viscosity than water.
6:12
Marine snow is not all built the same.
6:15
Some particles are relatively loose and watery, others are thicker and stickier.
6:21
Until recently, scientists had a difficult time seeing what the difference meant at the
6:26
scale of bacteria.
6:29
That changed, however, in a study published in October of 2026 in the journal Science.
6:35
The research was led by Bryce Inman, who was working with Farooq Azam at the Scripps
6:40
Institute of Oceanography and Steward Humphries at the University of Lincoln in the United
6:46
Kingdom.
6:47
Their team developed a way to map the physical structure inside individual pieces of marine
6:53
snow.
6:54
They used specialized fluorescent or glowing molecules and special 3D instruments to see
7:01
differences in viscosity within the particle itself, and what they found was pretty surprising.
7:08
Marine snow is not just one uniform blob, it almost has a landscape.
7:14
Some regions are soft and relatively easy for bacteria to enter, other regions are thicker
7:20
and harder to penetrate.
7:22
Think about cutting into an apple.
7:24
The soft flesh is relatively easy to cut through and eat.
7:28
The tougher core, it takes more work.
7:31
Bacteria face something similar when they land on a piece of marine snow.
7:35
They can colonize the less viscous portions relatively easily, and once there they release
7:42
enzymes that begin breaking down the organic material.
7:46
But if they reach a thicker, more viscous region, the process slows down.
7:51
The bacteria cannot move through it easily.
7:53
They have to gradually break down the material before they can get farther inside.
7:59
And that delay is important.
8:01
As we mentioned, gravity is constantly pulling particles downward while the bacteria are
8:07
trying to eat it.
8:08
If the marine snow is easy to break apart, the bacteria can recycle the carbon while it
8:14
still relatively close to the surface.
8:18
But if the particle is gooier, degradation takes longer, and every minute, every hour
8:24
the particle survives, it gives gravity more time to carry it into the deep ocean.
8:31
The researchers tested this in laboratory experiments, and then used computer simulations
8:37
to ask what that difference might mean for carbon transport.
8:41
Their simulations suggested that highly viscous marine snow could carry up to six times
8:48
more carbon into the deep ocean, as compared to less viscous particles.
8:54
Now, it doesn't mean that every sticky particle has the ability to store six times more carbon.
9:01
Instead, it's describing a model estimate that shows how strong viscosity can influence
9:08
the journey.
9:09
And it reveals something scientists hadn't fully appreciated before.
9:13
The ocean's carbon pump is controlled not only by how much marine snow forms, or how fast
9:20
it sinks.
9:22
It depends on the microscopic texture of the particle itself.
9:27
Something happening at this scale smaller than a grain of sand can influence whether carbon
9:32
remains near the surface, or gets carried hundreds or even thousands of meters into the
9:38
deep ocean.
9:40
So what makes one piece of marine snow gooier than the other?
9:45
Scientists are still working out the complete answer.
9:48
Marine snow is not manufactured according to a recipe.
9:52
Every particle is a messy combination of whatever happened to come together in that part
9:57
of the ocean, dead plankton and waste, tiny mineral grains, bacteria, fragments of organisms,
10:05
but something extremely important: slime.
10:08
Many microscopic organisms in the ocean released sticky substances made largely from complex
10:14
sugars.
10:16
Scientists call them extracellular polymeric substances.
10:20
That's a mouthful.
10:22
Just think of it as biological glue.
10:25
Phytoplankton released some of this material directly into the water, and bacteria produce
10:29
it too.
10:30
Some organisms use that mucus for feeding and protection, and when cells become stressed
10:36
or damaged or begin dying, even more organic material can enter the surrounding water.
10:43
At first, much of this material can be so small, you can't even see it under an ordinary
10:48
microscope.
10:50
But those molecules begin sticking together, and they form tiny gels.
10:54
The gels collide with other gels, and they can form larger, transparent, sticky particles.
11:01
Scientists call one important group of them, transparent extrapolymer particles, or TEP.
11:08
You can picture them almost like invisible pieces of glue floating through the ocean.
11:14
A dead phytoplankton cell bumps into one in sticks.
11:18
A tiny piece of animal waste collides with it, and sticks as well.
11:22
Then a mineral grain joins the pile.
11:25
More mucus gets wrapped around everything, and slowly, a marine snowflake begins to grow.
11:31
That's why two pieces of marine snow can look completely different.
11:36
One may contain mostly soft organic material.
11:39
Another may include shells or mineral particles.
11:42
Some may contain large amounts of that sticky biological gel.
11:47
Others may contain less.
11:49
And even within a single particle, new research is showing that the viscosity can vary from
11:54
one location to another.
11:56
One part may be relatively watery and easy for bacteria to enter.
12:01
And then a few micrometers away, another region may be thick enough to slow them down.
12:07
So, marine snow is less like a perfectly mixed spoonful of pudding, and more like tiny
12:13
floating ecosystems with different neighborhoods inside it.
12:17
And that diversity makes predicting the biological carbon pump difficult.
12:23
Scientists can't simply count how many particles are sinking, and they need to know what the
12:27
particles are made of, and how large they are, how dense they are, how fast they sink,
12:32
how easily bacteria are consuming them.
12:35
And now, apparently, how viscous they are.
12:39
There is still a lot we do not know about exactly what determines that viscosity.
12:45
Different plankton species produce different materials.
12:48
The food web activity changes what becomes incorporated into the marine snow.
12:53
Microbes modify the particles while they're sinking, and physical collisions can combine
12:58
particles that began with completely different compositions.
13:03
So the new discovery does not give scientists a simple rule that says one type of phytoplankton
13:09
always produces better carbon-carrying snow.
13:13
But it's giving them another piece of the puzzle.
13:16
The ocean's carbon pump depends not only on biology and chemistry, the physical texture
13:22
of these microscopic particles matters too.
13:26
So what happens to the biological carbon pump as the ocean itself changes?
13:31
That's a harder question to answer.
13:34
Climate change is warming the ocean, and in many places, it's also increasing something
13:39
called stratification.
13:41
That simply means the ocean's becoming more layered.
13:45
Warm water is lighter than cold water, so as the surface warms, it can become harder
13:50
for deeper water to mix upward.
13:53
That's important because deeper water contains nutrients that phytoplankton need to grow.
13:59
So if fewer nutrients are reaching the surface, phytoplankton growth can decline in regions.
14:05
Less phytoplankton could mean less organic material available to make marine snow.
14:11
But it's only one piece of the puzzle.
14:14
Different species of phytoplankton respond differently to warming, nutrients, and changing
14:18
ocean chemistry.
14:20
Some decline, others become more common, and because different organisms produce different
14:26
types of mucus, and waste, and shells, and organic particles, a changing plankton community
14:32
can also change the type of marine snow that's produced.
14:37
Then there are the microbes.
14:39
Bacteria generally become more active as temperatures rise, at least within the range they can tolerate.
14:46
That means warmer water can sometimes allow microbes to break down that sinking organic
14:51
material faster.
14:53
So if more marine snow is recycled before it reaches the deep ocean, less carbon is
14:58
going to be locked away down there for long periods.
15:02
But once again, this is not a simple global rule.
15:05
The response varies from one ocean to another.
15:08
Changes in sea ice can alter productivity in the Arctic.
15:12
Changes in nutrients can shift the food web.
15:15
Zooplankton can change how much carbon is packaged into those fast sinking fecal pellets.
15:22
Even tiny ocean currents and eddies can physically carry carbon downward.
15:27
In fact a 2026 study in Nature Communications found that some of the smaller scale processes
15:34
may account for a meaningful share of the deep ocean carbon storage, yet many current
15:40
Earth system models don't represent this very well.
15:45
That's why all of this research matters.
15:48
Scientists already knew that the amount of carbon reaching the deep ocean depended on things
15:53
like particle size and sinking speed and how quickly bacteria consumed it.
15:59
Now we have to add viscosity to the list.
16:02
And it doesn't mean scientists can plug one new number into a climate model and suddenly
16:07
know how much carbon the ocean is going to store in the next 100 years.
16:12
But it gives them another piece of the machinery to understand.
16:15
And that machinery is extremely important because the ocean is one of the largest carbon
16:21
reservoirs on Earth.
16:23
If the biological carbon pump becomes more efficient, more carbon can remain separated from
16:29
the atmosphere for longer.
16:31
If it becomes less efficient, more carbon remains near the surface and in our atmosphere
16:37
for longer periods of time.
16:40
Right now scientists are still working out how all of these changes will balance against
16:45
each other.
16:46
But one thing is becoming increasingly clear.
16:50
To understand the future of Earth's climate, we can't just look at forests and smoke stacks
16:55
and melting ice.
16:57
We have to really understand what happens in the tiny sticky pieces of marine snow as
17:03
they sink through the dark.
17:14
Marine snow is easy to overlook, it's tiny, slow and almost completely hidden from view.
17:20
But every day those sinking particles carry carbon away from the surface ocean and into
17:25
the deep.
17:26
And now we know something as simple as how sticky those particles are can help determine
17:32
how much carbon actually makes the journey.
17:35
Sometimes understanding the climate comes down to understanding the smallest details, even
17:40
the texture of a snowflake falling through the ocean.
17:45
I'm Dr. Mac and this has been the Climate Translation.
17:48
If you have a question about the climate you would too afraid to ask or if you have a
17:52
different opinion, I want to hear from you.
17:55
I can use your viewpoints in future episodes.
17:58
You can reach me at the climate translation at gmail.com.
18:02
I'll see you next time.