Coccolithophores Productivity in the Iberian Margin During Marine Isotope Stage (MIS) 11 and 12: Results from IODP Sites U1385 and U1391

Abstract:

Coccolithophores are a main phytoplankton group and among the most important pelagic calcifying organisms playing a key role in the ocean biogeochemistry and ecosystem, as primary producers and calcifiers. Reconstruction of coccolithophores productivity is critical for understanding past climate change and defining past levels of atmospheric CO2. Upwelling systems, such as the one along the Iberian margin, are important carbon sinks. Using the coccolith Sr/Ca ratio, a recent geochemistry-based proxy, we reconstructed coccolithophores productivity changes during MIS 12 to 11 at IODP Sites U1385 and U1391, the latter closer to shore and under stronger upwelling influence. The MIS 12 is considered the most extreme glacial of the last 1 Myr and MIS 11 one of the longer lasting interglacial periods. Studying these two climatic extremes will allow a better constraining of the influence of upwelling on the coccolithophores community and understand their role in phytoplankton ecology and the carbon cycle. For a clear assessment the coccolith Sr/Ca data needs to be corrected for temperature and species composition changes and the extraction of these secondary influences were made using UK37 - SST and the coccolith community.

Results for the Iberian margin showed higher coccolithophores productivity during the glacial period, and lower during the interglacial with an increasing trend during the glaciation and a steep decline during the deglaciation. Higher productivity during colder conditions might be associated to stronger winds that increased upwelling and/or the mixing of the upper water column and thus nutrient replenishment at the surface. These results will be placed into context of other proxy data from the Sites or region, e.g. TOC, total alkenones, diatom and coccolith abundances.