Seasonal variability of the marine CO2 system and nutrients in the Atlantic water inflow to the Arctic Ocean in 2014

Marine CO2 system data (total alkalinity, total dissolved inorganic carbon and pH on the total scale) were collected from 8 to 12 discrete depths in January, May, August 2014 on repeat stations in the eastern Fram Strait along 79N, and north of Svalbard. The seawater samples were collected from a CTD-Rosette (12-Niskin bottle) following standard procedures and analyzed at Institute of Marine Research, Tromsø, Norway. The DIC and AT were analyzed after the cruises at the Institute of Marine Research (IMR Tromsø, Norway) 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). 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. pH was determined onboard in January 2014 using a diode-array spectrophotometer and the unpurified indicator dye m-cresol purple (mCP) following the method of Clayton and Byrne (1993). The perturbation of the sample pH due to the addition of the indicator dye was corrected for according to Chierici et al. (1999). The precision was generally around ± 0.001. Description of the analytical methods can be found as a summary in the data file. Water samples for analysis of nutrients [NO2, NO-, Si(OH)4, PO4] were frozen until post-cruise analysis by standard methods (Grasshoff et al., 2009) using a Flow Solution IV analyzer from O.I. Analytical, United States. The analyzer was calibrated using reference seawater from Ocean Scientific International Ltd., United Kingdom. Three replicates were analyzed for each sample. Note that we refer to the NO3- concentration throughout the study, but it is actually the sum of NO2 and NO3, since NO2 levels are considered to be low in this area (Codispoti et al., 2005). This study is a contribution to the Carbon Bridge (RCN-226415) project funded by the Norwegian Research Council and the Flagship Research Program “Ocean acidification and effects in Northern waters” within the FRAM-High North Research Centre for Climate and Environment.