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The Southern Ocean (SO), an area highly sensitive to climate change, is currently experiencing rapid warming and freshening. Such drastic physical changes might significantly alter the SO's biological pump. For more accurate predictions of the possible evolution of this pump, a better understanding of the environmental factors controlling SO phytoplankton dynamics is needed. Here we present a satellite-based study deciphering the complex environmental control of phytoplankton biomass (PB) and phenology (PH; timing and magnitude of phytoplankton blooms) in the SO. We reveal that PH and PB are mostly organized in the SO at two scales: a large latitudinal scale and a regional scale. Latitudinally, a clear gradient in the timing of bloom occurrence appears tightly linked to the seasonal cycle in irradiance, with some exceptions in specific light-limited regimes (i.e., well-mixed areas). Superimposed on this latitudinal scale, zonal asymmetries, up to 3 orders of magnitude, in regional-scale PB are mainly driven by local advective and iron supply processes. These findings provide a global understanding of PB and PH in the SO, which is of fundamental interest for identifying and explaining ongoing changes as well as predicting future changes in the SO biological pump.

[1] The impact of the dust sea-surface forcing (DSSF) on the oceanic Primary Production (PP) is investigated here by using 1D modelling approach coupling an atmospheric radiative transfer model and a simple PP model. Simulations reveal that dust are able to induce a significant decrease of PP due to the attenuation of light by about 15–25% for dust optical depth (DOD) larger than 0.6–0.7 (at 550 nm). For DOD lower than ∼0.2–0.3, the influence of dust on PP is weak (∼5%). In addition to DOD, the important role played by dust single scattering albedo (DSSA) is also shown. Realistic applications over the Senegal coast are studied using SeaWiFS and AERONET observations. The analysis showed that PP could be reduced by about 15–20% during the spring period. This study highlights that dust/light interactions need to be parameterized in coupled ocean-atmosphere models used to estimate PP at regional scales.