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Calculations show that 2–44% of carbon retention in surface waters could be attributed to mobilization by enzymes associated with sinking aggregates, and up to 57% if enzymes associated with suspended particles are included. No difference in bulk EEA was observed between size fractions, but POC- and cell-specific EEA was significantly elevated on sinking aggregates. Significant positive correlations observed between EEA and both chlorophyll a and δ 13C POC suggest that EEA is elevated in waters dominated by marine-derived POC. Samples were collected by in situ filtration at depths of 25-100 m at ten stations (156-1,142 m deep) in the Amundsen Gulf and Beaufort Sea in June–July, 2008, during the Circumpolar Flaw Lead project. To evaluate this role, we used fluorogenic substrate analogs to measure extracellular enzyme activity (EEA) associated with particle size fractions considered suspended (1-70 μm) and sinking (>70 μm).
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The role of microbial hydrolytic activity in attenuating POC flux is generally understudied, and particularly complex on Arctic continental shelves influenced by other sources of POC. Export of autochthonously produced particulate organic carbon (POC) is a globally important mechanism for sequestering carbon in the deep sea.