Satellite Signature of Phytoplankton in Ocean Fronts

The contribution of sub-mesoscale fronts (10-100km) to phytoplankton growth and biodiversity is still poorly understood. It is expected that these fronts generate vertical ageostrophic secondary circulations, and thus act locally on stratification and vertical nutrient supply.
The response of phytoplankton to this input has been observed in-situ and in numerical models, but to a lesser extent by satellite imagery, which presents the opportunity to quantify results at larger spatiotemporal scales.
We improve an existing method to define sub-mesoscale frontal areas from satellite SST data in the North Atlantic. The study area is divided geographically into three zones: North of the Gulf-Stream jet, South of—and including—the jet, and further South part of the olligotrophic gyre.
For each zone the distribution of Chlorophyll-a values are estimated by satellite inside and outside these fronts. For all zones the Chlorophyll-a is found more concentrated in fronts, with differences between zones in magnitudes and seasonal cycles. The overall impact of fronts on the total Chlorophyll-a amount is quantified. We also quantify the temporal advance of the spring bloom onset in fronts. Finally, interannual trends over the last two decades are studied.