Marine CO2 system at the Hola cold water coral reef, Vesterålen, Norwegian Sea in 2022 and 2023

Marine CO2 system data (total alkalinity, and total dissolved inorganic carbon), and salinity and temperature were collected during three research cruises with RV Kronprins Haakon (KH 2022707 from 8th- 15th June 2022, R/V Kristine Bonnevie 2022617 (3rd July 2022), and KH 2023007005 from 7th- 16th April 2023) focusing on the bottom water at the Hola cold water coral reef. The Hola reef is located on the continental shelf of Vesterålen, near the Lofoten Vesterålen (LoVe) Ocean Observatory and samples were taken from Node 7 and 1.
The seawater samples were collected in 250 ml borosilicate bottles from a CTD-Rosette (24-Niskin bottle) following standard procedures. In addition, bottom water samples were also taken using Niskin bottles attached to the ROV (Aurora) in April 2023. The samples were preserved with 50 µL of saturated mercuric chloride (HgCl2) solution immediately after sampling and stored cool and dark until analysis within 6 months at Institute of Marine Research, Tromsø, Norway. 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). 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 ±2 and ±2 µmol kg-1 for DIC and AT, respectively. The remaining carbonate system parameters, including pH on the total scale (pHT) at in situ temperature and pressure, partial pressure of CO2 (pCO2), and the saturation states of calcium carbonate (CaCO3) minerals aragonite (ΩAr) and calcite (ΩCa), were calculated from DIC and TA using the CO2SYS software (Pierrot et al., 2011). The calculations used the thermodynamic constants from Mehrbach et al. (1973) as refitted by Dickson & Millero (1987), and the KHSO4 value from Dickson (1990). The solubility constants for CaCO3 were estimated according to (Mucci, 1983).

This study is funded by the Research Council of Norway EMAN7 (Environmental impact of Methane seepage and sub-seabed characterization at LoVe-Node 7) project number 320100. With additional support from Institute of Marine Research, Norway and the Fram Centre CLEAN program and Ecopulse project.