Abstract: Marine CO2 system data (total alkalinity, and total dissolved inorganic carbon were collected from full water column in the Barents Sea crater area at 74.9° N, 27.7° E. Sampling was performed onboard RV Helmer Hanssen in April (CAGE 16-2, 15 April to 22 April), and June (CAGE 16-5, 16 June 2016 to 4 July) 2016 across a 9 km transect (74.91° N, 27.5° E–27.9° E) located above several craters and mounds. The seawater samples were collected from a CTD-Rosette (12-Niskin bottle) following standard procedures and analyzed at the Institute of Marine Research, Tromsø, Norway after the cruises following the method described in Dickson et al. (2007). Total dissolved inorganic carbon ,DIC, was determined using gas extraction of acidified samples followed by coulometric titration and photometric detection using a Versatile Instrument for the Determination of Titration carbonate (VINDTA 3D, Marianda, Germany) and total alkalinity, AT, was determined by potentiometric titration with 0.1 N hydrochloric acid using a Versatile Instrument for the Determination of Titration Alkalinity (VINDTA 3S, Marianda, Germany). Routine analyses of Certified Reference Materials (CRM, provided by A. G. Dickson, Scripps Institution of Oceanography, United States) ensured the accuracy of the measurements, which was better than ±1 and ±2 mmol kg-1 for DIC and AT, respectively.
The remaining parameters of the CO2 system of pH, fugacity of CO2 (fCO2) and aragonite (ΩAr) and calcite saturation (ΩCa) were calculated using a CO2- chemical speciation model (CO2SYS program, version 01.05) (Lewis & Wallace, 1998; Pierrot & Wallace, 2006) and the DIC and AT measurements, in combination with temperature, salinity and depth (pressure). The dissociation constants K1, K2 from Mehrbach et al. (1973) refitted by Dickson and Millero (1987), and pH was estimated on the total hydrogen-ion scale (pHT ). We used the HSO_4^- dissociation constant of Dickson (1990), and the boric acid dissociation constant of Uppström (1974).
This work was supported by the Ocean Acidification Flagship research program within the FRAM- High North Research Centre for Climate and the Environment, Norway and the Centre for Arctic Gas Hydrate, Environment and Climate (CAGE), the Research Council of Norway through its Centres of Excellence scheme (grant number 223259).