Effects of Ocean Acidification on the Ballast of Surface Aggregates Sinking through the Twilight Zone: organic and inorganic carbon content

Incubation Setup The aggregates were placed inside the settling microcosm. The microcosm was filled with GF/F filtered, artificial seawater (32 psu) with a carbonate chemistry adjusted to the present or future conditions. This reduced the biological activity to the community originally present in the aggregates. The microcosm was continuously pressurized at a rate of 30 MPa/day, until it reached 10 MPa, the equivalent to a depth of 1000 m. The full incubation lasted 80 h. The experiment was triplicated at a pCO2 of 380 µatm and 1100 µatm. Additional incubations of similar duration were done at atmospheric pressure, with triplicates at a pCO2 of 380 µatm and 1100 µatm. These aimed at isolating the effect of the increase in hydrostatic pressure. Determination of Organic and Inorganic Carbon Content Aggregate samples were concentrated onto precombusted Whatman GF/F glass filters and analyzed for organic carbon. The filters were dried at 60°C overnight. After weighting, a section of each filter was placed into a silver cup and decarbonated with 1 M HCl to determine the organic carbon content. The samples were dried at 60°C and the process repeated until bubbling stopped. The cups were closed and compacted into spheres. These samples were analyzed with a Euro-EA Elemental analyzer (Hekatech) standardized with acetanilide. The inorganic carbon content was determined from the difference between the total carbon content and the organic carbon content.