Microscopic marine organisms can create parachute-like mucus structures that stall CO₂ absorption from atmosphere
Marine snow sedimentation with flow
field. Artistics rending of real imaging data collected across Gulf of Main
using a rotating microscope. Credit: PrakashLab, Stanford
New
Stanford-led research unveils a hidden factor that could change our
understanding of how oceans mitigate climate change. The study, published Oct. 11 in Science,
reveals never-before seen mucus "parachutes" produced by microscopic
marine organisms that significantly slow their sinking, putting the brakes on a
process crucial for removing carbon dioxide from the atmosphere.
The surprising discovery implies that
previous estimates of the ocean's carbon sequestration potential may have been
overestimated, but also paves the way toward improving climate models and informing policymakers in their efforts to
slow climate change.
"We haven't been looking the right
way," said study senior author Manu Prakash, an associate professor of
bioengineering and of oceans in the Stanford School of Engineering and Stanford
Doerr School of Sustainability.
"What we found underscores the importance of fundamental scientific observation and the need to study natural processes in their true environments. It's critical to our ability to mitigate climate change."
Video of marine snow sinking in an infinite water
column generated by gravity machine. The sinking marine snow interacts with a
wide variety of plankton as it travels through the vertical column. Credit:
PrakashLab, Stanford
The biological pump
Marine snow—a mixture of dead
phytoplankton, bacteria, fecal pellets, and other organic particles—absorbs about a third of human-made carbon dioxide
from the atmosphere and shuttles it down to the ocean floor where it is locked
away for millennia.
Scientists have known about this
phenomenon—known as the biological pump—for some time. However, the exact
manner in which these delicate particles fall (the ocean's average depth is 4
kilometers, or 2.5 miles) has remained a mystery until now.
The researchers unlocked the
mystery using an unusual invention—a rotating
microscope developed in Prakash's lab that flips the problem on its head. The
device moves as organisms move within it, simulating vertical travel over
infinite distances and adjusting aspects such as temperature, light, and
pressure to emulate specific ocean conditions.
Over the past five years, Prakash
and his lab members have brought their custom-built microscopes on research
vessels to all the world's major oceans—from the Arctic to Antarctica.
On a recent expedition to the Gulf
of Maine, they collected marine snow by hanging traps in the water, then rapidly
analyzed the particles' sinking process in their rotating microscope.
Since marine snow is a living
ecosystem, it is important to make these measurements at sea. The rotating
microscope allowed the team to observe marine snow in its natural environment
in exquisite detail—instead of a distant lab—for the first time.
The results stunned the
researchers. They revealed that marine snow sometimes creates parachute-like
mucus structures that effectively double the time the organisms linger in the
upper 100 meters of the ocean.
This prolonged suspension increases the likelihood of other microbes breaking down the organic carbon within the marine snow particles and converting it back into readily available organic carbon for other plankton—stalling carbon dioxide absorption from the atmosphere.
Schematic of gravity machine - a
rotating microscope that enables virtual reality arena for plankton and marine
snow. The tool enables an infinite field of view microscope in the Z-axis,
enabling observation of a sedimenting particle over long periods of time.
Credit: Rebecca Konte, PrakashLab, Stanford
Beauty and complexity in the smallest details
The researchers point to their work
as an example of observation-driven research, essential to understanding how
even the smallest biological and physical processes work within natural
systems.
"Theory tells you how a flow
around a small particle looks like, but what we saw on the boat was
dramatically different," said study lead author Rahul Chajwa, a
postdoctoral scholar in the Prakash Lab. "We are at the beginning of
understanding these complex dynamics."
This work lays out an important
fact. For the last 200 years, scientists have studied life, including plankton,
in a two-dimensional plane, trapped in small cover slips under a microscope.
On the other hand, doing microscopy
at high resolution is very hard on the high seas. Chajwa and Prakash emphasize
the importance of leaving the lab and conducting scientific measurements as
close as possible to the environment in which they occur.
Supporting research that
prioritizes observation in natural environments should be a priority for public
and private organizations that fund science, the researchers argue.
"We cannot even ask the
fundamental question of what life does without emulating the environment that
it evolved with," Prakash said. "In biology, stripping it away from
its environment has stripped away any of our capacity to ask the right
questions."
Beyond its importance in directly
measuring marine carbon sequestration, the study also reveals the beauty in
everyday phenomena. Much like sugar dissolving in coffee, marine snow's descent
into the depth of the ocean is a complex process influenced by factors we don't
always see or appreciate.
"We take for granted certain
phenomena, but the simplest set of ideas can have profound effects,"
Prakash said. "Observing these details—like the mucus tails of marine
snow—opens new doors to understanding the fundamental principles of our
world."
The researchers are working to
refine their models, integrate the datasets into Earth-scale models, and
release an open dataset from the six global expeditions they have conducted so
far. This will be the world's largest dataset of direct marine snow sedimentation
measurements. They also aim to explore factors that influence mucus production,
such as environmental stressors or the presence of certain species of bacteria.
Although the researchers' discovery
is a significant jolt to how scientists have thought about tipping points in
ocean-based sequestration, Prakash and his colleagues remain hopeful. On a
recent expedition off the coast of Northern California, they discovered
processes that can potentially speed up carbon sequestration.
"Every time I observe the world of plankton via our tools, I learn something new," Prakash said.
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