Sack Lunch Seminar (SLS)

Traditionally, export of organic carbon from the surface layer of the ocean has been measured and modeled in terms of the sinking flux of particulate organic carbon (POC). But, a large fraction of the organic carbon pool consists of small particles (and dissolved matter) that do not rapidly sink. Analysis of backscatter, fluorescence, temperature and salinity in glider profiles obtained from the 2008 North Atlantic Bloom (NAB08) study reveals that small, neutrally buoyant phytoplankton cells are transported downward along sloping isopycnal surfaces in intrusions that show distinctly different water mass characteristics from the surrounding water. Such features are also seen in a high-resolution, three-dimensional model. It is hypothesized that an alternate mechanism is contributing to the downward flux of small POC from the surface ocean to interior. Unlike the sinking of large particles or large-scale subduction on seasonal time scales, the contribution in this case, is due to downwelling or subduction associated with eddies and fronts on scales of 1-10 km, that are unresolved in global carbon cycle models. Various approaches for quantifying this eddy-driven subduction will be explored, and compared with concurrent observations of the sinking POC flux during an observational campaign in the North Atlantic in spring 2008. The overall impact of this mechanism on the surface pCO2 will be discussed.