Sea ice contribution to the air–sea CO₂ exchange in the Arctic and Southern Oceans

Abstract

Although salt rejection from sea ice is a key process in deep-water formation in ice-covered seas, the concurrent rejection of CO 2 and the subsequent effect on air-sea CO 2 exchange have received little attention. We review the mechanisms by which sea ice directly and indirectly controls the air-sea CO 2 exchange and use recent measurements of inorganic carbon compounds in bulk sea ice to estimate that oceanic CO 2 uptake during the seasonal cycle of sea-ice growth and decay in ice-covered oceanic regions equals almost half of the net atmospheric CO 2 uptake in ice-free polar seas. This sea-ice driven CO 2 uptake has not been considered so far in estimates of global oceanic CO 2 uptake. Net CO 2 uptake in sea-ice-covered oceans can be driven by; (1) rejection during sea-ice formation and sinking of CO 2-rich brine into intermediate and abyssal oceanic water masses, (2) blocking of air-sea CO 2 exchange during winter, and (3) release of CO 2-depleted melt water with excess total alkalinity during sea-ice decay and (4) biological CO 2 drawdown during primary production in sea ice and surface oceanic waters.

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

“…2004; Nomura et al, 2006;Papadimitriou et al, 2004;Rysgaard et al, 2007Rysgaard et al, , 2011Rysgaard et al, , 2012Rysgaard et al, , 2013.…”

Quantification of calcium carbonate (ikaite) in first– and multi–year sea ice

“…4.2) and ikaite concentrations increase with increasing bulk salinity and TA and DIC concentrations. If ikaite crystals remain trapped in the sea ice but the CO 2 produced by ikaite precipitation is removed from the sea ice, either by gravity drainage (e.g., Rysgaard et al, 2007) or by being released to the atmosphere (e.g., Geilfus et al, 2013a), then the dissolution of ikaite during sea ice melt will result in the release of excess TA that is stored in ikaite, increasing the buffering capacity of sea ice and surface meltwater and 365 enhancing CO 2 uptake by the ocean (i.e., the sea ice driven carbon pump; Rysgaard et al, 2007;2009;2011). In the mid-1980s, multi-year sea ice accounted for 70% of Arctic winter sea ice extent but this dropped to less than 20% by 2012 (Stroeve et al, 2014).…”

“…and Arctic sea ice (Dieckmann et al, 2008;2010) and may play a significant role in the sea ice carbon pump (Rysgaard et al, 2011;Parmentier et al, 2013), but the spatial and temporal dynamics of ikaite in sea ice are poorly understood (Rysgaard et al, 2014). Ikaite that remains trapped in the sea ice matrix during the ice growth season will store TA in the sea ice, which increases the buffering capacity of sea ice and meltwater and becoming a source of excess TA to seawater when ikaite dissolves during sea ice melt, enhancing CO 2 uptake by the ocean (RysgaardSuite version 4.0.0 software.…”

CO<sub>2</sub> and CH<sub>4</sub> in sea ice from a subarctic fjord under influence of riverine input

“…Other processes affect the pCO 2 concentrations within sea ice such as the precipitation and dissolution of calcium carbonate Geilfus et al, 2012bGeilfus et al, , 2013aPapadimitriou et al 2007Papadimitriou et al , 2012Rysgaard et al, 2007Rysgaard et al, , 2011Rysgaard et al, , 2013. During the sea-ice melt, the carbonate dissolution promotes lower pCO 2 conditions (Rysgaard et al, 2011).…”