| Summary: | 2018 Ocean Sciences Meeting, 11-16 February, in Portland, Oregon Transparent exopolymer particles (TEP; composed mainly of polysaccharides) and Coomassie stainable particles (CSP; composed mainly of proteins) are two subclasses of organic particles that largely affect element cycling, sea-air interactions and food-web structure in the ocean. However, the little availability of in situ data hampers our understanding of the mechanisms through which these particles are cycled in the ocean. We quantified for the first time TEP and CSP concentrations in parallel in surface waters of contrasting oceanic regions (across the Atlantic, the Southern Ocean, and the coastal NW Mediterranean Sea), and explored the potential drivers of their distribution. TEP concentrations overall ranged from below detection limit to 80.9, and averaged 19.0 (±5.4), 31.4 (±14.4) and 34.1 (±20.1) µg XG eq L-1 in the Atlantic, Antarctic - Subantarctic, and NW Mediterranean waters, respectively. CSP concentrations overall ranged from below detection limit to 64.3, and averaged 5.9 (±5.9), 15.0 (±10.0) and 9.9 (±6.5) µg BSA eq L-1, respectively, in the same regions. Over a time series study in the NW Mediterranean, TEP concentrations presented their maxima in early summer, probably related to nutrient deficiency, whilst CSP showed their highest concentrations in early winter, associated with higher chlorophyll levels. The horizontal distributions of both particle types were uncoupled across the Atlantic Ocean, but correlated significantly in the Antarctic – Subantarctic (r=0.46, n=42, p-value=0.0027), suggesting that they have different drivers in oligotrophic areas but both are associated with phytoplankton in productive areas. Token samples were examined for vertical profiles and size distributions. The comparison of TEP and CSP stocks with a broad suite of environmental and biological variables will allow better understanding of particulate organic matter cycling in the upper ocean and its consequences for the biological carbon pump Peer ...
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