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A multi-tracer study of the role of sea ice in the Arctic Ocean carbon cycle Brown, Kristina Anne

Abstract

Recent Arctic warming and reduced summer sea ice extent have stimulated increased research into the role of sea ice in the high latitude carbon cycle. Using data collected on a number of field expeditions throughout the Arctic Ocean, I apply a multi-tracer approach to investigate the influence of the sea-ice life cycle on the biological and abiotic export of CO₂ into the sub-surface. The results of this study illuminate the role of sea ice in polar carbon cycling across the perennial sea ice region of the central Canada Basin and in the seasonal ice zone of the Canadian Arctic Archipelago. In the perennial sea ice region, lateral exchanges of shelf derived carbon were found to exert the most important control on carbon distribution in the central Canada Basin, both in the surface mixed layer and in the sub-surface halocline. Stable carbon isotope data suggest that surface water particulate organic carbon is derived, to a large extent, from external inputs from Eurasian rivers. Further, results from a suite of geochemical tracers show that sub-surface accumulation of dissolved inorganic carbon in the halocline reflects an organic matter remineralization signature derived from the shelves and transported into the halocline by dense Pacific winter waters. Within the seasonal ice zone, observations over the winter-spring transition illustrated a highly dynamic carbon cycle, and results from this study provide new insight into the biological, physical and chemical factors which contribute to C cycling in different depth horizons of the ice over this period. Physical constraints on inorganic carbon cycling dominated CO₂ distributions in the majority of the ice column early in the season. As the melt period advanced, sea ice melt dilution led to decreasing CO₂ partial pressures in brine, contributing to pCO₂ under-saturation and CO₂ uptake from the atmosphere as the melt period advanced. In contrast, the carbonate system in bottom ice layers was much more closely tied to the flourishing algal community. Our inorganic carbon system measurements within natural sea ice brine samples further reveal the limitations of current thermodynamic constants used to compute carbonate system equilibrium in sea ice systems.

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Attribution-NonCommercial-NoDerivs 2.5 Canada

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