Air-Sea CO2 Fluxes in Hudson Bay during the Spring Sea Ice Melt Season

Mohamed Ahmed, University of Calgary, Calgary, AB, Canada, Brent Else, University of Calgary, Department of Geography, Calgary, AB, Canada, Brian Butterworth, University of Wisconsin Madison, Department of Atmospheric and Oceanic Sciences, Madison, WI, United States, David W Capelle, University of Manitoba, Centre for Earth Observation Science, Winnipeg, MB, Canada, Lisa Ann Miller, Institute of Ocean Sciences, Fisheries and Oceans Canada, Sidney, BC, Canada and Tim N Papakyriakou, Univ Manitoba, Winnipeg, MB, Canada
Hudson Bay is the largest inland continental shelf sea in the world. It receives nearly one-third of Canada’s river discharge and transitions from complete ice cover in winter to open water in summer. Since Hudson Bay receives such a substantial amount of seasonal freshwater from river runoff and sea-ice melt, the timing and magnitude of freshwater inputs must have a significant role in carbon biogeochemistry and air-sea CO2 fluxes. However, there is high uncertainty and limited understanding of the carbon system in this region (especially during the spring and early-summer seasons) due to lack of observations and rapid climate change. Therefore, the aim of our study is to fill this knowledge gap by reporting the first bay-wide air-sea CO2 fluxes made during the spring sea ice melt season. Underway measurements of surface salinity, temperature, wind speed, and surface water CO2 partial pressure (pCO2sw) were collected during the 2018 BaySys cruise carried out onboard the CCGS Amundsen icebreaker. Observed pCO2sw varied regionally, with the eastern and southern portions of the bay mainly undersaturated in pCO2sw (with respect to the atmosphere). We observed a significant correlation between salinity and pCO2sw at various locations across Hudson Bay, suggesting strong impacts of sea-ice melt and riverine input on pCO2sw spatial variability. Our results show that Hudson Bay acts as a strong sink of atmospheric CO2 during the spring season. This result is in contrast to previous estimates of CO2 fluxes in Hudson Bay that found this region acts as a weak sink or even as a source of CO2 during the summer and fall seasons. Given the lack of existing measurements in Hudson Bay, these observations will lead to better estimates of this important shelf region’s role in global carbon cycles.