Inorganic carbon dynamics of melt pond-covered first year sea ice in the Canadian Arctic

• Main Authors: Geilfus, Nicolas Xavier, Galley, R. J., Crabeck, O., Papakyriakou, Tim, Landy, J., Tison, Jean-Louis, Rysgaard, Søren
• Format: Article in Journal/Newspaper
• Language: French
• Published: 2015
• Subjects: Sciences de la terre et du cosmos; Arctic; Nunavut; Resolute Passage; Sea ice
• Online Access: http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/206528; https://dipot.ulb.ac.be/dspace/bitstream/2013/206528/3/doi_190155.pdf

Melt pond formation is a common feature of spring and summer Arctic sea ice, but the role and impact of sea ice melt and pond formation on both the direction and size of CO 2 fluxes between air and sea is still unknown. Here we report on the CO 2 -carbonate chemistry of melting sea ice, melt ponds and the underlying seawater as well as CO 2 fluxes at the surface of first-year landfast sea ice in the Resolute Passage, Nunavut, in June 2012. Early in the melt season, the increase in ice temperature and the subsequent decrease in bulk ice salinity promote a strong decrease of the total alkalinity (TA), total dissolved inorganic carbon (T CO 2 ) and partial pressure of CO 2 (pCO 2 ) within the bulk sea ice and the brine. As sea ice melt progresses, melt ponds form, mainly from melted snow, leading to a low in situ melt pond pCO 2 (36 μatm). The percolation of this low salinity and low pCO 2 meltwater into the sea ice matrix decreased the brine salinity, TA and T CO 2 , and lowered the in situ brine pCO 2 (to 20 μatm). This initial low in situ pCO 2 observed in brine and melt ponds results in air-ice CO 2 fluxes ranging between -0.04 and -5.4 mmolm -2 day -1 (negative sign for fluxes from the atmosphere into the ocean). As melt ponds strive to reach pCO 2 equilibrium with the atmosphere, their in situ pCO 2 increases (up to 380 μatm) with time and the percolation of this relatively high concentration pCO 2 meltwater increases the in situ brine pCO 2 within the sea ice matrix as the melt season progresses. As the melt pond pCO 2 increases, the uptake of atmospheric CO 2 becomes less significant. However, since melt ponds are continuously supplied by meltwater, their in situ pCO 2 remains undersaturated with respect to the atmosphere, promoting a continuous but moderate uptake of CO 2 (∼-1 mmolm -2 day -1 ) into the ocean. Considering the Arctic seasonal sea ice extent during the melt period (90 days), we estimate an uptake of atmospheric CO 2 of -10.4 Tg of Cyr -1 . This represents an additional uptake of CO 2 ...