Where is carbon exported in the ocean?

Accurate estimates of the magnitude of organic carbon export from satellite measurements of ocean color would lead to a better understanding of the global sink for atmospheric CO2. However, we have yet to fully understand how the distribution of phytoplankton in the surface ocean translates into organic carbon export.

There is evidence that certain groups of phytoplankton contribute disproportionately to export, and may thrive in the low-light high-nutrient environment of the deep euphotic zone. In a recent paper in GRL, my colleagues and I used an estimate of vertical mixing rate to partition export and primary production between the mixed layer and the deep euphotic zone of the South Pacific Gyre. This approach led us to determine that most export was produced beneath the mixed layer in this region, despite the fact that most primary production occurred within the mixed layer.

This finding suggests that perhaps organisms in the deep euphotic zone, a region difficult to image via satellite, contribute significantly to export in oligotrophic regions. If this proves to be true for large regions of the ocean, then quantifying the vertical export gradient may be key in developing accurate estimates of export via satellite.