High interannual surface pCO2 variability in the Southern Canadian Arctic Archipelago's Kitikmeot Sea.

Warming of the Arctic due to climate change means the Arctic Ocean is now ice-free for longer as sea ice melts earlier and refreezes later. It remains unclear how the extended ice-free period will impact carbon dioxide (CO₂) fluxes due to scarcity of surface ocean CO₂ measurements. Baseline measurements are urgently needed to understand how air-sea CO₂ fluxes will spatially and temporally vary in a changing Arctic Ocean. It is uncertain whether the previous basin-wide surveys are representative of the many smaller bays and inlets that make up the Canadian Arctic Archipelago. By using a research vessel that is based in the remote Inuit community of Cambridge Bay (Ikaluqtuutiak, Nunavut), we have been able to reliably survey pCO₂ shortly after ice melt and access previously unsampled bays and inlets in the nearby region. We present four years of consecutive summertime pCO₂ measurements collected in the Kitikmeot Sea in the southern Canadian Arctic Archipelago. Overall, we found that this region is a sink for atmospheric CO₂ in August (average of all calculated fluxes over the four cruises was -8.3 mmol m^-2 d^-1) but the magnitude of this sink varies substantially between years and locations (average calculated fluxes of 0.41, -7.70, -21.26 and -2.08 mmol m^-2 d^-1 during the 2016.2017,2018 and 2019 cruises respectively). Surface ocean pCO₂ varied by up to 142 μatm between years; this highlights the importance of repeat observations in the Arctic as this high interannual variability would not have been captured by sparse and infrequent measurements. We find that the pCO₂ value of the surface ocean at the time of ice melt is extremely important in constraining the magnitude of the air-sea flux throughout the ice-free season. Further constraining the flux in the Kitikmeot Sea will require a better understanding of how pCO₂ changes outside of the summer season. Surface ocean pCO₂ measurements made in the bays and inlets in the Kitikmeot Sea were ~20-40 μatm lower than in the main channels, and pCO₂ measurements made close to ice breakup (i.e. within 2 weeks) were 50-100 μatm lower than measurements made >4 weeks after breakup. As basin-wide surveys of the CAA have focused on the deeper shipping channels and rarely measure close to the ice break-up date, we hypothesize that there may be an observational bias in previous studies, leading to an underestimate of the CO₂ sink in the Canadian Arctic Archipelago. These high-resolution measurements constitute an important new baseline for gaining a better understanding of the role this region plays in the uptake of atmospheric CO₂. [ABSTRACT FROM AUTHOR]