Vertical profiles of nitrous oxide, methane and nutrients in the Passage Drake during RV METEOR cruise M179

The Drake Passage is the narrowest constriction of the Antarctic Circumpolar Current (ACC), which connects the Atlantic, Pacific, and Southern Oceans. This region significantly influences global ocean circulation, climate patterns, and the distribution of marine species. Additionally, the strong currents and turbulent waters of the Drake Passage provide valuable insights into ocean mixing processes and their role in heat and greenhouse gas exchanges with the atmosphere. Dissolved nitrous oxide (N2O), and methane (CH4) were sampled during the M179/2 FjordFlux cruise, conducted aboard the German research vessel METEOR, between January 14th and February 14th, 2022. The southern Patagonian Cold Estuarine System (PCES; 54°S), including the Drake Passage (DP; 60°S), was covered. From a total of 41 stations, we present data from 8 stations covering the DP. These stations include vertical profiles of gases such as CH4, N2O and nutrients (NO3-, NO2-, PO43-). Vertical profiles of temperature and salinity were obtained with a CTD profiler SBE3 and SBE4 respectively, only at 0m, T and S were obtained with a Salinometer YSI 30. Water samples at different depths were collected using Niskin bottles attached to a rosette for gas determination (CH4 and N2O); 20 mL of water were taken in triplicate in a glass vials, and 50 μL of saturated HgCl2 were added to preserve them. The vials were carefully sealed with rub and aluminum caps to avoid contamination with the atmosphere, then stored in darkness until analysis in the laboratory. N2O and CH4 were analyzed manually using the phase equilibrium method (McAuliffe, 1963) by creating a 5 mL headspace of ultrapure helium and equilibrating for 1h at 30°C. Mesurements were carried out through gas chromatography using an Electron Capture Detector (Shimadzu 17A) and Flame Ionization Detector (Agilent technologies 6850), respectively. A Restek Rt-QS- Bond column (30 m length, 0.53 mm inner diameter, 20 μm film thickness) was employed, maintained at a temperature of 30 °C with a flow of 2.6 mL min−1 using He as an ultra- pure gas carrier. For both gasses, a 5-point calibration curve was developed: He (as ~0 value) and four standard gas mixtures (Scott Mini-Mix, from Air Liquide) concentrations of 0.25, 0.35, 0.55 and 1 ppm for N2O and 1, 2.5, 5, and 10 ppm concentrations for CH4. The uncertainty of the measurements was calculated from the standard deviation of the triplicate measurements by depth. Samples with a variation coefficient above 10% were not considered. The solubility equations based on the in situ T and S of Wiesenburg and Guinasso (1979) and Weiss and Price (1980), were used to calculate N2O and CH4 concentrations. Once the gases were analyzed, the sample (15mL) was analyzed for nutrients trough a SealAA3 segmented flow auto-analyzer, using standard colorimetric techniques (Grasshoff et al., 1983). This analyser had 4 different channels, equipped with specific modules for each nutrient (including silicates) and delivers the final concentration. The detection limit for every nutrient were NO3- (0.015 – 67.5 μM), NO2- (0.015 – 7.5 μM), PO43- (0.010 – 4.5 μM).