Particulate Organic Carbon (POC)

Particulate organic carbon (POC) is the carbon held in organic particles suspended in seawater, from living phytoplankton and bacteria to detritus, fecal pellets, and marine snow aggregates, operationally the fraction retained on a filter. POC is the currency of the ocean’s biological carbon pump: a fraction of surface primary production, typically under 20%, sinks as POC out of the sunlit layer, exporting carbon and nutrients to depth and helping regulate atmospheric CO2. Sinking flux is measured with sediment traps and in-situ pumps, and attenuates with depth as zooplankton and microbes remineralize it. POC also indexes organic enrichment near outfalls and beneath aquaculture.