Multi-satellite approach to phytoplankton mesoscale biogeography in the Kerguelen region

One of the purposes of biogeography is to identify areas within which a characteristic ecosystem is expected to occur. In the case of phytoplanktonic communities this knowledge is key to separate regions characterised by different biogeochemical processes, design efficient sampling strategies and recognize ecological hotspots. Meso and submesoscale (1-100 km, few days to months) high variability interacts with typical bloom spatial and temporal scales and makes investigating phytoplankton biogeography challenging especially in remote regions like the Southern Ocean, where in-situ observations are extremely sparse. In this study we combine multi-satellite observations (color of the ocean, its re-analysis PHYSAT and altimetry) to describe and interpret the mesoscale biogeography of dominant phytoplanktonic type (DPT) in the iron-enriched Kerguelen bloom. We use GlobColour and PHYSAT to describe the seasonal variability of different types during the phytoplanktonic bloom and altimetry-derived velocity fields to define a “threshold” model relating DPT with Lagrangian properties of water parcels. We find out that, in spite of the simplicity of the threshold model approach, we obtain spatial patterns that statistically relate to PHYSAT observations. Finally we compare PHYSAT and different versions of the threshold model to a dataset of in-situ pigment observations from the KEOPS2 research voyage. A pigment-defined diagnostic for diatom-dominance shows a positive significant correlation with the threshold model but not with the respective PHYSAT climatology, suggesting sensitivity to the high temporal variability of the region.