Low pCO2 under sea-ice melt in the Canada Basin of the western Arctic Ocean

• Published in: Biogeosciences
• Main Authors: Kosugi, Naohiro, Sasano, Daisuke, Ishii, Masao, Nishino, Shigeto, Uchida, Hiroshi, Yoshikawa-Inoue, Hisayuki
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2017
• Subjects: article; Verlagsveröffentlichung; Arctic; Arctic Ocean; Canada; Chukchi Sea; Pacific; canada basin; Chukchi; Point Barrow; Sea ice
• Online Access: https://doi.org/10.5194/bg-14-5727-2017; https://noa.gwlb.de/receive/cop_mods_00007715; https://noa.gwlb.de/servlets/MCRFileNodeServlet/cop_derivate_00007672/bg-14-5727-2017.pdf; https://bg.copernicus.org/articles/14/5727/2017/bg-14-5727-2017.pdf

In September 2013, we observed an expanse of surface water with low CO2 partial pressure (pCO2sea) (< 200 µatm) in the Chukchi Sea of the western Arctic Ocean. The large undersaturation of CO2 in this region was the result of massive primary production after the sea-ice retreat in June and July. In the surface of the Canada Basin, salinity was low (< 27) and pCO2sea was closer to the air–sea CO2 equilibrium (∼ 360 µatm). From the relationships between salinity and total alkalinity, we confirmed that the low salinity in the Canada Basin was due to the larger fraction of meltwater input (∼ 0.16) rather than the riverine discharge (∼ 0.1). Such an increase in pCO2sea was not so clear in the coastal region near Point Barrow, where the fraction of riverine discharge was larger than that of sea-ice melt. We also identified low pCO2sea (< 250 µatm) in the depth of 30–50 m under the halocline of the Canada Basin. This subsurface low pCO2sea was attributed to the advection of Pacific-origin water, in which dissolved inorganic carbon is relatively low, through the Chukchi Sea where net primary production is high. Oxygen supersaturation (> 20 µmol kg−1) in the subsurface low pCO2sea layer in the Canada Basin indicated significant net primary production undersea and/or in preformed condition. If these low pCO2sea layers surface by wind mixing, they will act as additional CO2 sinks; however, this is unlikely because intensification of stratification by sea-ice melt inhibits mixing across the halocline.