Microbial ecosystem responses to alkalinity enhancement in the North Atlantic Subtropical Gyre

In addition to reducing carbon dioxide (CO 2 ) emissions, actively removing CO from the atmosphere is widely considered necessary keep global warming well below 2°C. Ocean Alkalinity Enhancement (OAE) describes a suite of such removal processes that all involve enhancing buffering capacity seawater. theory, OAE both stores and offsets ocean acidification. practice, response marine biogeochemical system must be demonstrably negligible, or at least manageable, before it can deployed scale. We tested two natural seawater mixed layer microbial communities in North Atlantic Subtropical Gyre, one Western gyre boundary, middle gyre. conducted 4-day microcosm incubation experiments sea, spiked with three increasing amounts alkaline sodium salts 13 C-bicarbonate tracer constant pCO . then measured dissolved particulate parameters constrain chemical biological these additions. Microbial demonstrated occasionally measurable, but mostly responses alkalinity enhancement. Neither site showed significant increase biologically produced CaCO 3 , even extreme loadings +2,000 μmol kg −1 At enhancement did not significantly impact net primary production rates. contrast, central decreased by ~30% The incubations shift toward smaller particle size classes, suggesting may community composition and/or aggregation/disaggregation processes. terms effects, we identify equilibration inorganic precipitation, immediate effects during mixing solutions seawater, as important considerations for developing experimental methodologies, practical deployment. These initial results underscore importance performing more studies diverse environments, need investigate coupling between OAE, processes, composition.