Dilution limits dissolved organic carbon utilization in the deep ocean

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Science  19 Mar 2015:
DOI: 10.1126/science.1258955

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Oceanic dissolved organic carbon (DOC) is the second largest reservoir of organic carbon on Earth. About 72% of the global DOC inventory is stored in deep oceanic layers for years to centuries, supporting the current view that it consists of materials resistant to microbial degradation. An alternative hypothesis is that deep-water DOC consists of many different, intrinsically labile compounds at concentrations too low to compensate for the metabolic costs associated to their utilization. Here we present experimental evidence showing that low concentrations rather than recalcitrance preclude consumption of a significant fraction of DOC leading to slow microbial growth in the deep ocean. These findings demonstrate an alternative mechanism for the long-term storage of labile DOC in the deep ocean, which has been hitherto largely ignored.

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