Implications of a Changing Arctic on Summertime Surface Seawater pCO2 Variations in the Eastern Canadian Arctic

Abstract:

Arctic marine carbonate chemistry and rates of air-sea CO₂ exchange are anticipated to be affected by current changes in sea-ice structure and extent, freshwater inputs, ocean circulation patterns, and the seasonality of phytoplankton blooms. This study examines how such changes will impact rates of air-sea CO₂ exchange in northern Baffin Bay, Nares Strait, and the eastern Canadian Arctic Archipelago. This complex oceanographic region includes the North Water polynya; one of the most biologically productive areas in the Arctic Ocean, and the convergence site of the warm West Greenland Current with cold exported Arctic waters. Continuous measurements of atmospheric and surface seawater CO₂ (pCO₂) were collected onboard the Canadian Coast Guard Ship Amundsen during its 2013 and 2014 summer cruises. Surface seawater pCO₂ displayed considerable variability (145 – 389 ppm), but never exceeded atmospheric concentrations. Calculated CO₂ fluxes ranged from 0 to -45 mmol m^-2 day^-1 (oceanic uptake), and were estimated using the Sweeney et al. (2007) parameterization with in-situ wind speed measurements. Ancillary measurements of chlorophyll a reveal low productivity in surface waters during mid-summer with isolated sub-surface blooms. This is likely the result of nutrient limitation within the highly stratified polar mixed layer (PML). Measurements of stable oxygen isotope ratios (δ¹⁸O) and total alkalinity were used to estimate freshwater inputs (sea-ice melt vs. meteoric water) to the PML. These and in-situ observations of sea ice cover were used to interpret seawater pCO₂ variations. Surface waters influenced by sea-ice melt exhibit lower pCO₂ than those influenced by meteoric water. The results of this investigation shed light on the future role of this region as a summertime sink of atmospheric CO₂.