Multidecadal Increase in North Atlantic Coccolithophores and Potential Role of Increasing CO2

Sara Rivero-Calle, Johns Hopkins University, Anand Gnanadesikan, Johns Hopkins University, Department of Earth and Planetary Sciences, Baltimore, MD, United States, Carlos E del Castillo, NASA GSFC, Greenbelt, MD, United States, William M Balch, Bigelow Lab for Ocean Sciences, East Boothbay, ME, United States and Seth Guikema, University of Michigan Ann Arbor, Ann Arbor, MI, United States
Abstract:
As anthropogenic CO2 emissions acidify the oceans, calcifiers are expected to be negatively impacted. Using data from the Continuous Plankton Recorder, we show that coccolithophore occurrence in the North Atlantic has increased from ~2 to over 20% from 1965 through 2010. We used Random Forest models to examine more than 20 possible environmental drivers of this change. CO2 and the Atlantic Multidecadal Oscillation were the best predictors. Since coccolithophore photosynthesis is strongly carbon-limited, we hypothesize that higher CO2 levels might be encouraging growth. A compilation of 41 independent laboratory studies supports our hypothesis. Our study shows a long-term basin-scale increase in coccolithophores and suggests that increasing pCO2 and temperature accelerated the growth rate of a key phytoplankton group for carbon cycling. 
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