Do continental shelves export organic matter?

Abstract

It has been suggested that biological production and consumption of organic matter is not balanced in coastal marine ecosystems1,2. If, as suggested, 90% of the phytoplankton produced during the spring bloom period were exported, excess organic carbon would be sequestered on the continental slope below the permanent thermocline. Here we summarize the shelf-edge exchange processes (SEEP) experiment, designed to test the export hypothesis. The absence of a positive imbalance in the organic carbon budget, reinforced by modest sediment deposition and biomass on the continental slope, led us to reject the concept. Only a small fraction of continental shelf phytodetritus is exported; that not consumed in the spring is for the most part used on the continental shelf during the ensuing stratified season. The original hypothesis failed to recognize the contribution of pelagic microbial consumption and the lag in coupling between seasonal production and consumption processes.