Program

Photosynthesis by phytoplankton, represented as primary production (PP), provides the basic food block to support the marine food web, which is also the fundamental step of the biological pump that sends a portion of CO2 to the deep oceans in an organic form. Because of the enormous size of the oceans, it is imperative to employ measurements taken by ocean-color satellites in order to achieve reasonable estimation of the primary production and then the export to deep oceans in basin scales. In the past decades various algorithms have been developed for the estimation of PP and then its export. Generally, following traditional practices, these involve: 1) estimate the concentration of chlorophyll-a (Chla) in the upper water column based on measurements of water color; 2) calculate water-column-integrated PP (PP_int) based on Chla, light intensity, and photosynthetic efficiency parameters; and 3) estimate exported organic carbon with an empirically determined export ratio (or export efficiency) based on the calculated PP_int. With the availability of global ocean color measurements, both PP_int and exported organic carbon are now available, but with large uncertainties. However, some of the uncertainties are inherently embedded in the chain of steps for this estimation. We would like to discuss and highlight the issues associated with this traditional system in estimating basin-scale biological pump, and to point out key components that are critical for a reliable estimation of biological pump from ocean color remote sensing.