Dynamics of pCO₂and related air‐ice CO₂ fluxes in the Arctic coastal zone (Amundsen Gulf, Beaufort Sea)

Abstract

.[1] We present an Arctic seasonal survey of carbon dioxide partial pressure (pCO 2 ) dynamics within sea ice brine and related air-ice CO 2 fluxes. The survey was carried out from early spring to the beginning of summer in the Arctic coastal waters of the Amundsen Gulf. High concentrations of pCO 2 (up to 1834 matm) were observed in the sea ice in early April as a consequence of concentration of solutes in brines, CaCO 3 precipitation and microbial respiration. CaCO 3 precipitation was detected through anomalies in total alkalinity (TA) and dissolved inorganic carbon (DIC). This precipitation seems to have occurred in highly saline brine in the upper part of the ice cover and in bulk ice. As summer draws near, the ice temperature increases and brine pCO 2 shifts from a large supersaturation (1834 matm) to a marked undersaturation (down to almost 0 matm). This decrease was ascribed to brine dilution by ice meltwater, dissolution of CaCO 3 and photosynthesis during the sympagic algal bloom. The magnitude of the CO 2 fluxes was controlled by ice temperature (through its control on brine volume and brine channels connectivity) and the concentration gradient between brine and the atmosphere. However, the state of the ice-interface clearly affects air-ice CO 2 fluxes.

Winter observations of CO<sub>2</sub> exchange between sea ice and the atmosphere in a coastal fjord environment

“…The formation of CaCO 3 and CO 2(aq) and the decreasing CO 2 solubility of the increasingly saline brine (Tison et al, 2002), drives the brine to higher CO 2 partial pressure (pCO 2 ) (Geilfus et al, 2012). Hence, the temperature sensitivity of carbon speciation in sea-ice brines supports the premise that thermochemical processes within brine exposed to the atmosphere facilitates an air-ice pCO 2 gradient, thereby linking CO 2 exchange to site energetics via brine carbon chemistry (Loose et al, 2011a, b).…”

“…the notion that given sufficiently permeable sea ice (Golden et al, 1998;Loose et al, 2011a, b), brine concentration/dilution alters the pCO 2 gradient across the sea-ice surface and thus the potential for CO 2 exchanges (Geilfus et al, 2012;Killawee et al, 1998;Tison et al, 2002;Nomura et al, 2006;Papadimitriou et al, 2004);…”

“…the formation/dissolution of calcium carbonate (CaCO 3 · 6 H 2 O) within brine (Dieckmann et al, 2008;Fischer et al, 2013;Marion, 2001;Papadimitriou et al, 2004;Rysgaard et al, 2013), which leads to an increase/decrease in brine pCO 2 , thus changing the potential for CO 2 exchanges at the ice surface (Geilfus et al, 2012;Miller et al, 2011b;Sogaard et al, 2013); 3. CaCO 3 · 6 H 2 O being observed in brine-soaked snow at the snow-ice interface Nomura et al, 2013).…”

“…CO 2 fluxes within the range −78 ± 180 mmol m −2 day −1 were reported on first-year ice in the Canadian Arctic during May through June 2002 (Papakyriakou and. Using chamber instrumentation, CO 2 fluxes within the range 1.5 ± 1.5 mmol m −2 day −1 were observed at ice stations of various characteristics in the Canadian Arctic during April through June 2008 (Geilfus et al, 2012). The disparity in strength and direction of observed CO 2 fluxes at sites of different characteristics and at different times of the year confirm that sea ice is a very dynamic system and that further studies are necessary to understand the full potential of sea ice in offsetting both regional-and global-scale carbon cycles.…”

“…Consequently, most carbon-cycle research has treated ice cover as areas of zero (or very low) exchange (Tison et al, 2002). This view has been challenged by reports of significant fluxes of CO 2 over first and multiyear sea ice during both spring/summer (Delille et al, 2007;Geilfus et al, 2012;Semiletov et al, 2004Semiletov et al, , 2007Zemmelink et al, 2006) and autumn/winter (Else et al, 2011;Geilfus et al, 2013;Miller et al, 2011a, b) and challenged by suggestions of a coupling between the carbonate system in sea ice, the underlying sea water and the atmosphere (Anderson et al, Figure 1. (a) Regional and (b) local overview of field sites in Young Sound, northeast Greenland.…”