November 29, 2024
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“Marine snow” research shows how the ocean eats up carbon
The ocean’s digestive system is dictated by fastidious microbes and the precise dynamics of drifting debris.
Carbon falls as “marine snow” across the ocean layers.
From the sunny 200 meter surface of the sea, plankton bodies, excrement and silt particles are constantly drifting towards the depths. As this so-called sea snow sinks, pieces can stick together or break up, gain speed or sink more slowly, or be eaten by bacteria. They descend from darker, colder, denser waters, taking carbon with them and settling on the bottom as biomass.
The oceans absorb billions of tons of carbon each year, a process that is key to accounting for in climate models. But researchers have long wondered how much carbon gets to the seafloor, and stays there. To find out, oceanographers are studying how carbon is eaten, excreted, and affected as it drifts through what some scientists call the ocean’s “digestive system.”
Measuring the rate of carbon storage involves looking at the composition of the sink, how particles stick together and therefore sink faster or slower, deceleration effects. slime-producing phytoplankton—and also for a new published study in the year sciencedietary preferences of specific microbes.
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“Currently we don’t have a very good way of relating processes at the surface to what reaches the seafloor,” says Monterey Bay Aquarium Research Institute oceanographer Colleen Durkin. “We know that they are connected, but it has been very difficult to observe the mechanisms that encourage this connection.”
Recent advances in sensor development, imaging and DNA sequencing are giving researchers a closer look at the exact organisms and processes at work. By isolating and testing bacterial populations in sea snow, study co-author Benjamin Van Mooy of the Woods Hole Oceanographic Institution and his colleagues found that specific microbial populations prefer to eat phytoplankton that contain specific types of fatty acid biomolecules called lipids.
Lipids make up 30 percent of the ocean’s surface particulate organic matter, so the dietary preferences of bacteria in a given region can significantly alter how much carbon-containing biomass reaches the seafloor. “If we start to understand what (microbes) can do, then we can imagine a future where we can potentially start to predict the fate of carbon based on the organisms that are there,” says Van Mooy, who received an award. MacArthur Fellowship in 2024 for his work.
Scientists are also working to document what falls from specific locations over different periods of time. Sediment traps provide a snapshot of the sea snow in certain areas, and Durkin and others are deploying sensors with autonomous cameras to observe particles as they sink over longer periods of time. Looking at the complexity of sea snow distribution, says Rutgers University microbial oceanographer Kay Bidle, “it shows how we can’t necessarily model and understand carbon flow through the very simple constructs and equations and laws that we had before.”
