Sinking particles called marine snow help remove greenhouse gas from the atmosphere
Scientists have discovered that parts of the ocean with no oxygen are more efficient at absorbing and storing carbon dioxide from the atmosphere, a key part of the Earth’s carbon cycle. Researchers at University of Maryland Center for Environmental Science found that carbon is being delivered and stored in the deep ocean through marine snow, microscopic particles that form in the surface of the ocean and sink into the deep ocean. These sinking particles help remove carbon dioxide, the greenhouse gas mainly responsible for climate change, from the atmosphere.
“We didn’t know why a lot of carbon makes it to the bottom of oxygen deficient zones, and this discovery allows us to understand this part of the carbon cycle,” said Jacob Cram, lead researcher of the study.
Oxygen deficient zones are growing in response to climate change and play a large role in the carbon cycle on Earth. To know how the carbon cycle will change in response to climate change, it is important to better understand the connection of oxygen deficient zones and the carbon cycle.
In oxygen deficient zones, more particles sink to greater depths, for reasons that were not well-understood. While oxygen deficient zones are known in the Gulf of Mexico and other regions as harmful environments, in this region, they are natural and important parts of the marine ecosystem.
In the ocean carbon cycle, the ocean takes up carbon dioxide from the atmosphere when tiny plant-like organisms called phytoplankton use sunlight and carbon dioxide to grow. Most of the time, when these organisms die and get eaten by bacteria, their carbon goes back into the atmosphere. However, if the bodies of these dead phytoplankton become part of marine snow and sink into the deep ocean, it can take a lot longer for that carbon to return to the atmosphere.
“Our measurements suggest that one reason that particles sink to deeper depths in oxygen-poor or lacking environments is because microbes consuming the particles are slower when there is no oxygen.” said Cram
Scientists used underwater cameras to observe marine snow particles in the world’s largest naturally occurring oxygen deficient zone located west of Mexico. To find the amount and size of particles in the oxygen deficient zone, they used traps to find how many particles were sinking and used acoustic pulses to measure where in the water column animals were at different times of day.
Cram and colleagues compared the observations to predictions from several computer simulations representing possible mechanisms that were thought to explain why particles are consumed less in water without oxygen.
The paper "Slow Particle Remineralization, Rather Than Suppressed Disaggregation, Drives Efficient Flux Transfer Through the Eastern Tropical North Pacific Oxygen Deficient Zone" is a combined effort by Clara Fuchsman, Klaus Huebert, and Jacob Cram from the University of Maryland Center for Environmental Science, as well as researchers from University of Washington, University of Alaska, and University of Southern California. It was published by the journal Global Biogeochemical Cycles.
