To address the response of E. huxleyi to ocean warming and changing water masses, I have prepared and validated a long-term satellite dataset of E. huxleyi blooms in the Barents Sea, an Arctic shelf sea, which connects the Atlantic with the Arctic Ocean. I found striking and fast-paced changes in the distribution pattern of blooms of Emiliania huxleyi, a marine calcifying phytoplankton species typically associated with temperate waters. Over the last three decades, blooms of this species have shifted poleward at rates up to 56 km per year and thereby testify to one of the most rapid poleward expansions of marine organisms reported so far. The observed biogeographic shift is attributed to climate change-induced increases in the inflow and warming of Atlantic waters into the Arctic Ocean. I further showed that E. huxleyi calcite concentration was modulated by strong seasonal cycles of temperature, light and mixed layer depth.
To examine if the enormous amounts of calcite produced by E. huxleyi blooms ballast organic carbon I used optical measurements of particle backscatter, chlorophyll-a fluorescence and beam attenuation on Biogeochemical-Argo profiling floats. My results show the feasibility of identifying E. huxleyi blooms and quantifying associated calcite concentration from optical measurements on floats, consistent with results from an optical model for E. huxleyi that I set up. Results obtained from a Biogeochemical-Argo float that sampled sinking carbon particles associated with three distinct phytoplankton blooms of calcifying and non-calcifying phytoplankton suggests that E. huxleyi blooms promote deeper carbon fluxes compared to carbon fluxes associated with blooms from non-calcifying phytoplankton. These observations are thus the first high-resolution observations of the calcite ballast effect in the ocean.
