Using a library of more than 10,000 deep-sea corals collected by Caltech's Jess Adkins, an international team of scientists has shown that periods of colder climates are associated with higher phytoplankton efficiency and a reduction in nutrients in the surface of the Southern Ocean (the ocean surrounding the Antarctic), which is related to an increase in carbon sequestration in the deep ocean. There is 60 times more carbon in the ocean than in the atmosphere -- partly because the ocean is so big. As such, the ocean is the greatest regulator of carbon in the atmosphere, acting as both a sink and a source for atmospheric CO2. As the sea creatures who consume those sugars -- and the carbon they contain -- die, they sink to the deep ocean, where the carbon is locked away from the atmosphere for a long time. In most parts of the modern ocean, phytoplankton deplete all of the available nutrients in the surface ocean, and the biological pump operates at maximum efficiency. However, in the modern Southern Ocean, there is a limited amount of iron -- which means that there are not enough phytoplankton to fully consume the nitrogen and phosphorus in the surface waters. Because the Southern Ocean flows around Antarctica, all of its waters funnel through that gap -- making the samples Adkins collected a robust record of the water throughout the Southern Ocean. As a result, there is a correlation between the ratio of nitrogen isotopes in sinking organic matter (which the corals then eat as it falls to the seafloor) and how much nitrogen is being consumed in the surface ocean -- and, by extension, the efficiency of the biological pump. As such, the evidence suggests that colder climates allow more biomass to grow in the surface Southern Ocean -- likely because colder climates experience stronger winds, which can blow more iron into the Southern Ocean from the continents.
We know a lot about how carbon dioxide (CO2) levels can drive climate change, but how about the way that climate change can cause fluctuations in CO2 levels? New research from an international team of scientists reveals one of the mechanisms by which a colder climate was accompanied by depleted atmospheric CO2 during past ice ages. Efficient nutrient consumption by plankton in the Southern Ocean drove carbon sequestration in the deep ocean during the ice ages, a new study suggests. https://www.sciencedaily.com/releases/2017/03/170314150916.htm
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