Impacts of the Physical Ocean Environment on Sea Ice Biogeochemistry

Sea ice is thought to play a substantial role in greenhouse gas cycles (e.g. CO₂), although the exact nature of this process is poorly constrained. The main reason for a lack of quantitative knowledge is the high variability of physical and chemical sea ice properties such as thickness, concentrations of salts, gases and dissolved gases. As sea ice forms, it excludes salts from its crystalline form, creating highly saline brine. Most of this brine is rejected during sea ice formation, but some becomes trapped in pockets and slowly drains by gravity. Most of the dissolved inorganic carbon (DIC) in sea ice resides in this brine. This study links the physical ocean environment, particularly current velocity in surface waters under the ice, to brine volume and therefore DIC, total alkalinity and salinity of bulk sea ice.

High resolution bulk sea ice samples were taken at two sites with different physical characteristics near Cambridge Bay, Nunavut. Site A showed a low average current velocity with little tidal influence, shallow snow and comparatively thick ice. Site B showed high current velocity, strong tidal patterns, deep snow, and comparatively thin ice.

The results show a significant (F>14) difference between average DIC concentrations at the two locations. These differences are well explained by established physical theories regarding sea ice formation and growth, particularly those regarding the speed of ice growth. Additionally other factors, such as snow depth, which influence physical, chemical and even biological variation in sea ice can be at least partially explained by current velocity through surface roughness. Based on the coupling of physical theory found in the literature and the laboratory results in this study, with more data we may be able to predict much more accurate end members for sea ice carbonate chemistry based on known physical environments.