PAOC Colloquium – Amala Mahadevan (WHOI)

Eddy-driven subduction of carbon and oxygen from the upper ocean

How organic carbon and oxygen produced through photosynthesis in the upper ocean make their way in to the stratified interior is of relevance for the biological pump. Sinking of particulate organic matter contributes to exporting carbon and nitrogen. But, oxygen necessarily relies on an advective flux that feeds the bacterial demand for decomposing organic matter at depth. Glider profiles of oxygen, backscatter and chlorophyll are analyzed following the spring phytoplankton bloom in the subpolar North Atlantic and show signatures of subducting water features intertwined within the eddy field. A numerical model reveals how eddies subduct surface waters rich in carbon and oxygen during the phase of mixed layer stratification that follows the onset of the spring bloom. The downward flux can be quantified in terms of the horizontal and vertical gradients of buoyancy and tracer. Evaluation of the scaling estimate over the global oceans shows that eddy-driven subduction following the spring bloom makes a sizable contribution to the export of carbon and oxygen from the high-latitude oceans.