Ikaite crystal distribution in winter sea ice and implications for CO2 system dynamics

Søren Rysgaard, Dorthe H. Søgaard, M. Cooper, M. Pucko, Kunuk Lennert, T. N. Papakyriakou, F. Wang, N. X. Geilfus, Ronnie N. Glud, J. Ehn, Daniel F. McGinnis, Karl Attard, J. Sievers, J. W. Deming, D. Barber

Publikation: Bidrag til tidsskriftTidsskriftartikelForskningpeer review

Abstrakt

The precipitation of ikaite (CaCO3·6H2O) in polar sea ice is critical to the efficiency of the sea ice-driven carbon pump and potentially important to the global carbon cycle, yet the spatial and temporal occurrence of ikaite within the
ice is poorly known. We report unique observations of ikaite in unmelted ice and vertical profiles of ikaite abundance and concentration in sea ice for the crucial season of winter. Ice was examined from two locations: a 1m thick land-fast ice
site and a 0.3m thick polynya site, both in the Young Sound area (74 N, 20 W) of NE Greenland. Ikaite crystals, ranging in size from a fewμm to 700 μm, were observed to concentrate in the interstices between the ice platelets in both
granular and columnar sea ice. In vertical sea ice profiles from both locations, ikaite concentration determined from image analysis, decreased with depth from surface-ice values of 700–900 μmol kg−1 ice (25×106 crystals kg−1) to values
of 100–200 μmol kg−1 ice (1–7×106 crystals kg−1) near the sea ice–water interface, all of which are much higher (4–10 times) than those reported in the few previous studies. Direct measurements of total alkalinity (TA) in surface layers
fell within the same range as ikaite concentration, whereas TA concentrations in the lower half of the sea ice were twice as high. This depth-related discrepancy suggests interior ice processes where ikaite crystals form in surface sea ice layers
and partly dissolve in layers below. Melting of sea ice and dissolution of observed concentrations of ikaite would result in meltwater with a pCO2 of <15 μatm. This value is far below atmospheric values of 390 μatm and surface water concentrations of 315 μatm. Hence, the meltwater increases the potential for seawater uptake of CO2.
OriginalsprogEngelsk
TidsskriftCryosphere
Vol/bind7
Sider (fra-til)707-718
ISSN1994-0416
DOI
StatusUdgivet - 2013

Citationsformater

Rysgaard, S., Søgaard, D. H., Cooper, M., Pucko, M., Lennert, K., Papakyriakou, T. N., Wang, F., Geilfus, N. X., Glud, R. N., Ehn, J., McGinnis, D. F., Attard, K., Sievers, J., Deming, J. W., & Barber, D. (2013). Ikaite crystal distribution in winter sea ice and implications for CO2 system dynamics. Cryosphere, 7, 707-718. https://doi.org/10.5194/tc-7-707-2013