ALBERT

Description: Ex situ total oxygen uptake (DOU) at the sediment water interface was assessed on the Northeast Greenland shelf with R/V Polarstern during PS109 between September and October 2017 using a camera-equipped multiple corer (TV-MUC; core area 0.007 m2). Upon arrival on deck, part of the overlying water of three MUC cores was collected and stored separately at in situ temperature. The remaining overlying water was adjusted to 10m above the sediment by gently pushing the sediment upwards by avoiding a disturbance of the surface sediment. The cores were then placed in a temperature-controlled water bath in the ship-board laboratory which had been adjusted to the in-situ temperature at the seafloor (information was retrieved from ship-board sensors). A magnetic stirrer was deployed in order to homogenise the overlying water, and a small air pump gently aerated the water. After the assessment of diffusive oxygen uptake (DOU) by microprofiling, total oxygen uptake (TOU) was measured. The air pump was removed to ensure no air bubbles in the overlying water, and the cores were closed air tight. The oxygen concentration was measured continuously in the overlying water every 60 seconds for approximately 48hours (at least 36h). Total sediment oxygen flux was determined as the decrease in oxygen concentration in the water phase, which was read from the continuous oxygen sensor data. The oxygen sensors had been two-point calibrated using oxygen-saturated water and anoxic solution of sodium dithionite. The incubation was terminated at ≤ 80% initial [O2]. TOU fluxes were calculated from the initial linear decrease in O2 concentration versus time (first 30 h) in the enclosed overlying water body (Glud et al., 1994, doi:10.1016/0967-0637(94)90072-8).