| Summary: | The Arctic Ocean is particularly susceptible to ocean acidification (OA) compared to other oceans, as the cold surface water with relatively low salinity promotes high carbon dioxide (CO2) solubility. Sea-ice microorganisms are a vital part of polar ecosystems, and experience more extreme concentrations of CO2 than their planktonic counterparts, as “impurities”, such as salts and gases, are concentrated in brine channels as seawater freezes. We participated in the Research Vessel/Ice Breaker (RVIB) Oden cruise to the North Pole in late summer, 2018, with the objective to sample High Arctic sea ice biota and the carbonate chemistry of sea ice. RVIB Oden was moored to a large ice floe and established a temporary ice camp to collect ice and atmospheric information. Our sampling included samples from that floe, but also from other areas that were reached using a helicopter. Ice cores were sampled following established best practices (Miller et al., 2015) using a 0.9 m Kovacs ice corer driven by a small electric drill. Cores were removed from the corer, and temperatures were taken using a Amadigit thermistor. All cores were then cut using a stainless-steel saw into 10 centimeter (cm) sections. Ice samples were thawed together with filtered seawater in the dark from 4-10⁰ Celsius (C) for approximately 24 hours before analysis. Subsamples for bacterial counts were fixed with 2% formaldehyde and stored at −20 C until microscopy analysis by DAPI-staining. Samples for pEPS were filtered through 25 millimeter (mm) 0.4 µm nucleopore filters and returned to UW for analysis using the phenol–sulfuric acid assay (DuBois et al. 1956). Filtrate (< 0.2 μm) from Experiments 1 and 3 was collected for analysis of DOC, frozen at −20 C, and analyzed using a Shimadzu TOC-Vcsh DOC analyzer. Samples for inorganic nutrients were frozen at −20 C and analyzed using a QuAAtro autoanalyzer. Additional cores were collected for experimental analysis in a ships cold room, where the carbonate chemistry was altered by immersing core sections in seawater with enhanced DIC levels. All experiments were conducted using Tedlar bags to eliminate atmospheric exchanges of gases. Samples were processed at the end of 10 days as above. Results have been reported in Torstensson et al. (2021).
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