Potential controls on interannual partitioning of organic carbon during the winter/spring phytoplankton bloom at the Bermuda Atlantic time-series study (BATS) site

Seasonal dissolved organic carbon (DOC) accumulation and potential subsequent export, in addition to particulate organic carbon (POC) gravitational export, can be an important pathway of carbon removal from the surface ocean (>100 m) at the Bermuda Atlantic Time-series Study (BATS). We have compiled available data on seasonal DOC accumulation and POC flux during the course of the winter/spring bloom and examined some potential controls on the interannual variability of organic carbon partitioning between these two fates. When expressed as a fraction of the cumulative primary production, there was a significant negative relationship between seasonal DOC accumulation and POC flux. Over the course of the BATS data record two groups of phytoplankton, Haptophytes and Prochlorophytes, account for ∼60% of the integrated (0–140 m) chlorophyll biomass. Variability in the relative abundance of Haptophytes and Prochlorophytes was significantly correlated to the export of carbon, with increased relative abundance of Haptophytes correlated with higher seasonal accumulation of DOC and lower POC fluxes. Variability in the abundance of Haptophytes during the winter/spring period was found to correlate negatively with the winter North Atlantic Oscillation (NAO) index. This relationship suggests that Haptophytes are a more important component of the phytoplankton community when a negative NAO phase enhances winter/spring mixing in the Sargasso Sea. These findings support a recent hypothesis that the increased stratification in the North Atlantic due to global warming could favor the blooming of diatoms over Haptophytes.