TPSAS-NF1676L-28148-DND

Abstract

Currently, ocean carbon biomass is estimated from ocean color measurements primarily through particulate backscatter coefficients (bbp). Small non-algal particles contribute significantly to bbp due to the fact that small particles scatter more isotropically while bigger particles scatter mostly in the forward direction. CALIPSO’s ocean subsurface cross polarization measurements (Figure 1) are not sensitive to small particles far less than 2 microns in size since these particles rarely cause depolarization. Thus, cross polarization backscatter is contributed mostly by larger, depolarizing phytoplankton particles. This is why CALIPSO’s cross polarization has much larger contrasts comparing with MODIS reflectance (CALIPSO cross polarization is very weak in Gyres and much stronger in high latitudes, See Figure 1). CALIPSO cross-polarization measurements in the Southern Oceans also suggest that water cloud droplet number concentration covaries with phytoplankton carbon biomass (Figure 2), but it has less correlation with particulate organic carbon (POC) (Figure 2) and chlorophyll concentration. The study also agrees with water cloud droplet size retrieved from Parasol’s polarization measurements.