Oral Session 9 | Thursday, October 6, 09:00–09:20 | Abstract 492

Influence of coccolithophore blooms on ocean carbon sequestration using ocean colour remote sensing and BioGeoChemical-Argo floats

The gravitational sinking of biogenic carbon particles from the surface to the deep ocean is a major pathway for biological sequestration of atmospheric CO2. Biogenic carbon particles are generated by phytoplankton in the sunlit surface ocean and comprise Particulate Organic and Inorganic Carbon (POC and PIC). Here we compare and contrast the downward transfer of particles associated with blooms of calcifying and non-calcifying phytoplankton, corresponding to high PIC and high POC concentrations, respectively. We merged time series of ocean colour satellite observations of POC and PIC in the near-surface ocean with observations of particle backscattering and chlorophyll-a fluorescence in the water column obtained from BioGeoChemical-Argo floats (BGC-Argo). We present observations from floats operating in four distinct biogeochemical provinces: the Nordic Seas, the Icelandic Basin, the Patagonian shelf, and the Southern Ocean frontal zone. In all four provinces we detected clearly distinct pulses of sinking particles associated with distinct phytoplankton blooms of different composition. Our results show that blooms of calcifying phytoplankton lead to a much deeper transfer of particles into the mesopelagic, whereas the pulses of sinking particles associated with blooms of non-calcifying phytoplankton were quickly attenuated. On the Patagonian shelf, where the float operated at high temporal resolution, calculations of the sinking speed of particles show that particles associated with calcifying phytoplankton blooms sank twice as fast. These results provide first in situ evidence of the impact of high-density calcite material on carbon transfer through the mesopelagic ocean.  

Griet Neukermans, Ghent University, 0000-0002-8258-3590

Nathan Briggs, National Oceanography Centre

Terrats Louis, Sorbonne Université

Hervé Claustre, Sorbonne Université

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