Benguela Upwelling Filaments Are a Significant Pathway of New Nutrients to the South Atlantic Subtropical Gyre

Abstract

In the transition zones between eastern boundary upwelling regions and subtropical gyres, upwelling and offshore moving filaments generated by frontal instabilities play an important role in the gyre‐ward transport of new nutrients and phytoplankton biomass. However, quantification of such transport using field data remains sparse. Here we used a combination of remote sensing, in situ biogeochemical data and surface ocean velocity measurements to describe the distribution and transport of nutrients and chlorophyll‐a in two filaments in the Benguela upwelling system of the Southeast Atlantic Ocean. Nitrate and chlorophyll‐a concentrations were enhanced up to 100 and 10‐fold, respectively, in filaments compared to surrounding waters. Our estimations reveal that a single upwelling filament can export of up to 18 μmol m ⁻²  d ⁻¹ of nitrate and 38 tonnes of chlorophyll‐a biomass daily from the upwelling system to the subtropical gyre. This represents up to 2%–5% of the daily nitrogen supply required to sustain new primary production in the gyre.