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Biogeosciences An interactive open-access journal of the European Geosciences Union
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Volume 14, issue 24 | Copyright
Biogeosciences, 14, 5727-5739, 2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 20 Dec 2017

Research article | 20 Dec 2017

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

Naohiro Kosugi1, Daisuke Sasano2, Masao Ishii1, Shigeto Nishino3, Hiroshi Uchida3, and Hisayuki Yoshikawa-Inoue4 Naohiro Kosugi et al.
  • 1Meteorological Research Institute, Tsukuba, 305-0052, Japan
  • 2Japan Meteorological Agency, Tokyo, 100-8122, Japan
  • 3Japan Agency for Marine-Earth Science and Technology, Yokosuka, 237-0061, Japan
  • 4Graduate School of Environmental Science, Faculty of Environmental Earth Science, Hokkaido University, Sapporo, 060-0810, Japan

Abstract. In September 2013, we observed an expanse of surface water with low CO2 partial pressure (pCO2sea) (<200µatm) 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 (∼ 360µatm). 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 (<250µatm) in the depth of 30–50m 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 (>20µmolkg−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.

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Recent variation in air–sea CO2 flux in the Arctic Ocean is focused. In order to understand the relation between sea ice retreat and CO2 chemistry, we conducted hydrographic observations in the Arctic Ocean in 2013. There were relatively high pCO2 surface layer and low pCO2 subsurface layer in the Canada Basin. The former was due to near-equilibration with the atmosphere and the latter primary production. Both were unlikely mixed by disturbance as large sea-ice melt formed strong stratification.
Recent variation in air–sea CO2 flux in the Arctic Ocean is focused. In order to understand the...