Spatial variability of the marine CO2 system and inorganic nutrients in the water column along the Vardø-North section in the Barents Sea to the Nansen Basin, Arctic Ocean in September 2012

Marine CO2 system data (total alkalinity (AT), and total dissolved inorganic carbon, CT) and nutrients such as nitrate+nitrite (NO3), phosphate (PO4) and silicic acid (Si(OH)4) were collected from the water column as part of the IMR repeat Vardø-N section (Barents Sea) and the A-TWAIN research program for the adjacent Nansen Basin, Arctic Ocean. Sampling were performed on two cruises in September 2012 on board the RV Johan Hjort (cruise #2012209) and RV Lance. The seawater samples were collected from a CTD-Rosette (12-Niskin bottle) following standard procedures and analyzed at Institute of Marine Research, Tromsø, Norway after the cruises following the method described in Dickson et al. (2007). 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). 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 and precision of the measurements, which was better than ±2 and ±2 µmol kg-1 for DIC and AT, respectively. Description of the data set analytical methods and interpretation can be found in the annual report by Chierici et al., 2013 and Gerland et al., in review. Sea water samples for the macronutrients nitrate+nitrite [NO3–+NO2-, referred as NO3- since NO2- is low in these samples], phosphate [PO43–], and silicic acid [Si(OH)4] were drawn from the Niskin bottles into 20 mL vials. Samples from the Vardø-N section were preserved with chloroform and stored at 4 °C. Analysis were carried out using a Flow Solution IV analyzer from O.I. Analytical, United States, following Grasshof et al. (2009) at the Institute of Marine Research, Bergen, Norway. The uncertainty based on QUASIMEME ring-test were 0.4 µmol kg-1 for [NO3-+NO2–], 0.06 µmol kg-1 for [PO43–] and 0.7 µmol kg-1 for Si(OH)4, respectively. Samples collected on the A-TWAIN were stored dark and frozen at -20 C and analysed at the Arctic University of Norway-University in Tromsø. The analyzer was calibrated using reference seawater from Ocean Scientific International Ltd. UK. Three parallels were analyzed for each sample. Data from Barents Sea is a contribution to the project “Monitoring ocean acidification in Norwegian waters/Havforsuringsovervåking i norske farvann” funded by the Norwegian Environment Agency (Miljødirektoratet) project# 17078007, and the data collected within the A-TWAIN program is funded by the Flagship program “Ocean acidification and effects in northern waters” within the FRAM-High North Research Centre for Climate and Environment. Data is also published in “Vannmiljø” as well as contributes to SDG 14.3.1 Indicator: Average marine acidity (pH)