The eddy subduction pump.
The eddy subduction pump is a physical mechanism promoting the local growth of surface phytoplankton and subsequently injecting biogenic material produced this way deeper in the water column.
This production-injection mechanism is mainly due to water mass movements at the periphery of rotating eddies, a consequence of eventual gradients between dense and less-dense waters. In these spots ranging over spatial scales of several kilometers, strong variations in water movement over the vertical dimension are observable.
Movements with positive velocities (known as obduction) bring dense waters and their nutrient content into the illuminated surface layer. There, conditions encourage phytoplankton growth and local development of biomass hotspots. These phytoplankton-rich dense waters will later flow under less dense waters via water movements with negative velocities (known as subduction). Thanks to eddy rotation and its associated vertical movement of waters, locally produced biogenic material is physically transported to depths, sometimes as deep as 500 m.