Sea surface pCO2 and ice concentration in the Canada Basin of the Arctic Ocean

Michael D DeGrandpre, University of Montana, Missoula, United States, Wiley Evans, Hakai Institute, Heriot Bay, BC, Canada, Mary-Louise Timmermans, Yale University, Department of Geology and Geophysics, New Haven, United States, Richard A Krishfield, Woods Hole Oceanographic Institution, Woods Hole, MA, United States and Michael Steele, Univ Washington, Seattle, United States
The Arctic Ocean has a well-documented loss of perennial sea ice. The minimum ice extent, which typically occurs around mid-September, is less than half of the levels recorded 40 years ago. Among many possible consequences, loss of ice cover has increased exchange of CO2 with the atmosphere potentially altering the inorganic carbon cycle. Because the partial pressure of CO2 (pCO2) is generally lower than atmospheric CO2 in the Arctic Ocean, the loss of ice could lead to increased sea surface CO2 levels, changing air-sea CO2 fluxes and accelerating the rate of ocean acidification. Previous studies have found evidence that pCO2 is increasing in the western Arctic Ocean. It has, however, been challenging to determine if there is a relationships between pCO2 and ice cover because research cruises have been infrequent and spatially disparate. In this study, we evaluate pCO2 data collected from 2012-2017 along a fixed cruise track in the Canada Basin. This study is part of the Beaufort Gyre Observing System and Joint Ocean Ice Study that takes place annually on the Canadian icebreaker CCGS Louis S. St-Laurent. We have found that mean sea surface pCO2 is higher during low ice years with pCO2 increasing by 60-80 µatm (>360 µatm) relative to under ice values. A simple model that computes changes in sea surface pCO2 since the day of ice retreat (i.e. when ice concentration is < 15%), indicates that the increase is primarily driven by surface heating and uptake of atmospheric CO2 but with large inter-annual variability in these processes. These findings indicate that, with increased heating during ice-free periods, the Arctic Ocean could convert from a net sink of atmospheric CO2 to a net source.