Ocean acidification research alongside extended continental shelf exploration in the western Arctic Ocean

Research investments funded to fulfill the requirements of the UN Convention on the Law of the Sea in the western Arctic have allowed simultaneous acquisition of marine chemistry data, including baseline monitoring of changes in ocean acidification. Our participation in the Extended Continental Shelf cruises on the USCGC Healy in the western Arctic have allowed us to collect data focused on understanding processes driving rapid changes in seawater chemistry that result from increased oceanic uptake of CO₂ (ocean acidification), increased freshwater runoff, changes in sea ice growth and decay processes and changes in biogeochemical processes. Carbonate mineral saturation data collected during HLY1002, HLY1102, and HLY1202 (summers 2010-2012) document undersaturation with respect to aragonite (Ω_aragonite) in ~20% of the surface waters of the Canada and Makarov Basins, in direct association with areas of recently accelerated sea ice loss. Conservative tracer studies using salinity, stable oxygen isotopic composition, dissolved silica and barium augment this work by elucidating contributions from distinct water sources. These data show that while surface water in this entire area retains abundant freshwater from meteoric sources, it is freshwater additions from melting of multiyear sea ice which is most closely linked to the areas of aragonite undersaturation. Depth profiles from 20 oceanographic stations taken during the cruises show a ~100 m thick lens of Ω_aragonite undersaturated water at ~150 m depth in the western Arctic, but not further north than 85°N. The surface waters in the Canada and Makarov Basins have pCO₂ values much lower than the atmospheric pCO₂ (~390 uatm), ranging between 350 μatm and 100 μatm, and are a strong sink for atmospheric CO₂. The strong sink areas are found in the Chukchi Sea and western Beaufort shelf areas. These studies represent the frontiers of ocean acidification research in the western Arctic, in which baseline data have been greatly expanded with the support of the ECS surveys.