GEL-LIKE PARTICLES DOMINATE PARTICULATE ORGANIC CARBON IN THE OCEAN’S INTERIOR — EVIDENCE FROM SUBTROPICAL AND EQUATORIAL REGIONS OF THE CENTRAL PACIFIC

Marine gel phase concept has challenged the conventional dichotomy between dissolved organic carbon (DOC) and particulate organic carbon (POC) in marine environments, proposing a unified theory for the DOC-POC continuum involving colloidal particles that are intimately regulated by complex actions of microbes in seawater. However, we still know little about the role of gel-like particles in biogeochemical cycles in the ocean’s interior partly because of the paucity of data on gel-like particle abundance in meso- and bathypelagic layers. Here we examined full depth distributions of transparent extracellular polymeric particle (TEP) concentration in subtropical and equatorial regions of the central Pacific and compared these data with POC concentration and other biogeochemical parameters. TEP concentration was on average 27.3±7.4 µg Xeq. L^-1 and distributed relatively uniformly throughout the water column below the bottom of the euphotic zone (200–5000 m), except for the depth-dependent increase in TEP concentration in the bathypelagic layer at equatorial station. Using a TEP to carbon conversion factor reported in the literature, TEP-carbon was estimated to be 1.7 to 17 times higher than POC in deep waters. High TEP-carbon relative to POC might be in part explained by the presence of colloidal TEP that passed through GFF filters used for the determination of POC, although we note that our estimates of TEP-carbon have inherent errors associated with the TEP to carbon conversion factor. Despite uncertainty, our results support the notion that gel-like particles, either delivered from upper layers, produced by microbes residing in deep waters, or both, dominate the POC pool and can affect largely material fluxes in the ocean’s interior.