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

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.