A study shows that researchers can tweak a natural process to increase the amount of carbon that reaches the ocean floor and the speed at which it does so — merely by coating the water's surface with clay dust.
Dartmouth College scientists and collaborators made the discovery by testing algae bloom water from the Gulf of Maine, EurekAlert! reported. If the clay is added to the water at the end of a bloom, it bonds to carbon particulates and keeps them from entering the atmosphere.
That's because microscopic zooplankton eat these flocs — a combination of the carbon and clay, which is turned into balls by a bacteria-produced glue — and then deposit them deep in the ocean via their excrement, speeding up the process by days.
As part of the biological pump, "the ocean's natural cycle for removing carbon from the atmosphere," per the outlet, zooplankton rise hundreds or thousands of feet every night to eat nutrients at the surface. The site compared it to townspeople walking hundreds of miles a night to eat at a restaurant. At sunrise, the zooplankton — bellies full of flocs — retreat and defecate.
The clay dust increased the carbon concentration of the organic particles tenfold, and it captured up to 50% of carbon before it could reach the atmosphere. There were also fewer bacteria that facilitated the release of carbon into the air in this seawater.
The research — one of many studies involving zooplankton, including how the creatures react to the rising temperature in Lake Erie — was backed by a 2020 Guggenheim Fellowship award.
"This particulate material is what these little guys are designed to eat. Our experiments showed they cannot tell if it's clay and phytoplankton or only phytoplankton — they just eat it," said Mukul Sharma, a corresponding author of the study and professor of earth sciences. "And when they poop it out, they are hundreds of meters below the surface and the carbon is, too."
The method will likely be tested off the Southern California coast with a crop duster, according to the information relayed by EurekAlert! Sensors in the ocean will measure how zooplankton species differ in their consumption of the flocs, which will allow Sharma and Co. to figure out where and when clay dust should be sprayed and, perhaps most importantly, how much carbon the method sequesters in the depths.
"It is very important to find the right oceanographic setting to do this work. You cannot go around willy-nilly dumping clay everywhere," he said. "We need to understand the efficiency first at different depths so we can understand the best places to initiate this process before we put it to work. We are not there yet — we are at the beginning."
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