The Arctic Ocean is characterized by an extreme range of surface irradiance, which forces a distinctive response in phytoplankton, hence affecting energy transfer to higher trophic levels, and carbon sequestration in deep waters. The productive period is tightly linked to the seasonal dynamic of sea ice (coverage and thickness), with early summer phytoplankton blooms generally driven by increased diatom abundance at the edge of retreating sea ice, fostered by salinity stratification. REFINE will explore the Baffin Bay (ABB).

Temperate and sub-polar areas are characterized by distinctive seasonal signals in phytoplankton dynamics, highly dependent on the seasonal cycle of the mixed layer. Following the winter “resetting” of nutrient concentrations in the upper layer, a spring bloom will develop, generally dominated by diatoms. Next will come a summer period characterized by low to moderate production conditions. This phenological sequence is accompanied by marked regional nutrient-driven differences. The Labrador Sea (LS) and the Iceland Sea (IS) in the North Atlantic subpolar gyre are the places where the global ocean’s largest spring/summer blooms are recorded. West of the Kerguelen Plateau (EKP) in the Southern Ocean are found typical waters of the Southern Ocean which are iron-limited and consequently associated with low phytoplankton biomass and a low-intensity spring bloom. By contrast, East of the Kerguelen Plateau (EKP), waters are iron-enriched, which stimulates phytoplankton growth and potentially export.

Low-latitude areas are generally characterized by permanently stratified conditions matched with fairly weak seasonality and the presence of deep chlorophyll maxima (DCM) largely associated with small phytoplankton. While equatorial and sub-equatorial waters are characterized by productive DCMs, this is much less the case of tropical and subtropical waters. REFINE will thus explore a gradient of trophic conditions in such environments from the most desertic waters of the planet in the South Pacific subtropical Gyre (SPG) and the North Pacific subtropical Gyre (NPG) to the productive waters of the Guinea Dome (GD), a quasi-permanent cyclonic structure in eastern subequatorial Atlantic. Similar gradient will be explored from the less productive and essentially unknow waters of the Tropical Indian Ocean (TIO) to the Arabian Sea (ARS) waters, whose productivity is largely driven by monsoon cycle and where anoxic conditions in the twilight zone strongly impact on the resulting export.