The relative contributions of biological and abiotic processes to carbon dynamics in subarctic sea ice

Søgaard, Dorte Haubjerg; Thomas, David N.; Rysgaard, Søren; Glud, Ronnie N.; Norman, Louiza; Kaartokallio, Hermanni; Juul-Pedersen, Thomas; Geilfus, Nicolas-Xavier

doi:10.1007/s00300-013-1396-3

Cited by 40 publications

(58 citation statements)

References 93 publications

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“…There are several reports of ikaite precipitation in Arctic sea ice Rysgaard et al, 2012aRysgaard et al, , 2013Geilfus et al, 2013a, b;Søgaard et al, 2013). In this study, however, only a few crystals were observed and they dissolved within minutes after melting the sea ice.…”

Section: Discussioncontrasting

confidence: 66%

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

et al. 2015

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Abstract. 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 mmol m −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 mmol m −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 C yr −1 . This represents an additional uptake of CO 2 associated with Arctic sea ice that needs to be further explored and considered in the estimation of the Arctic Ocean's overall CO 2 budget.

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Section: Discussioncontrasting

confidence: 66%

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

et al. 2015

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“…As a result, the concentration of dissolved salts, including inorganic carbon, increases within the brine and promotes the precipitation of calcium carbonate crystals such as ikaite (CaCO 3 q 6H 2 O) (Marion, 2001). These crystals have been reported in both natural (Dieckmann et al, 2008;Nomura et al, 2013;Søgaard et al, 2013) and experimental sea ice (Geilfus et al, 2013b;Rysgaard et al, 2014) and have been suggested to be a key component of the carbonate system Fransson et al, 2013;.…”

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confidence: 80%

Estimates of ikaite export from sea ice to the underlying seawater in a sea ice–seawater mesocosm

et al. 2016

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Abstract. The precipitation of ikaite and its fate within sea ice is still poorly understood. We quantify temporal inorganic carbon dynamics in sea ice from initial formation to its melt in a sea ice-seawater mesocosm pool from 11 to 29 January 2013. Based on measurements of total alkalinity (TA) and total dissolved inorganic carbon (TCO 2 ), the main processes affecting inorganic carbon dynamics within sea ice were ikaite precipitation and CO 2 exchange with the atmosphere. In the underlying seawater, the dissolution of ikaite was the main process affecting inorganic carbon dynamics. Sea ice acted as an active layer, releasing CO 2 to the atmosphere during the growth phase, taking up CO 2 as it melted and exporting both ikaite and TCO 2 into the underlying seawater during the whole experiment. Ikaite precipitation of up to 167 µmol kg −1 within sea ice was estimated, while its export and dissolution into the underlying seawater was responsible for a TA increase of 64-66 µmol kg −1 in the water column. The export of TCO 2 from sea ice to the water column increased the underlying seawater TCO 2 by 43.5 µmol kg −1 , suggesting that almost all of the TCO 2 that left the sea ice was exported to the underlying seawater. The export of ikaite from the ice to the underlying seawater was associated with brine rejection during sea ice growth, increased vertical connectivity in sea ice due to the upward percolation of seawater and meltwater flushing during sea ice melt. Based on the change in TA in the water column around the onset of sea ice melt, more than half of the total ikaite precipitated in the ice during sea ice growth was still contained in the ice when the sea ice began to melt. Ikaite crystal dissolution in the water column kept the seawater pCO 2 undersaturated with respect to the atmosphere in spite of increased salinity, TA and TCO 2 associated with sea ice growth. Results indicate that ikaite export from sea ice and its dissolution in the underlying seawater can potentially hamper the effect of oceanic acidification on the aragonite saturation state ( aragonite ) in fall and in winter in ice-covered areas, at the time when aragonite is smallest.

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“…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).…”

Section: Thermochemical Carbon Processes In the Icementioning

confidence: 99%

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

et al. 2015

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Abstract. Eddy covariance observations of CO 2 fluxes were conducted during March-April 2012 in a temporally sequential order for 8, 4 and 30 days, respectively, at three locations on fast sea ice and on newly formed polynya ice in a coastal fjord environment in northeast Greenland. CO 2 fluxes at the sites characterized by fast sea ice (ICEI and DNB) were found to increasingly reflect periods of strong outgassing in accordance with the progression of springtime warming and the occurrence of strong wind events: F ICE1 CO 2 = 1.73 ± 5 mmol m −2 day −1 and F DNB CO 2 = 8.64 ± 39.64 mmol m −2 day −1 , while CO 2 fluxes at the polynya site (POLYI) were found to generally reflect uptake F POLY1 CO 2 = −9.97 ± 19.8 mmol m −2 day −1 . Values given are the mean and standard deviation, and negative/positive values indicate uptake/outgassing, respectively. A diurnal correlation analysis supports a significant connection between site energetics and CO 2 fluxes linked to a number of possible thermally driven processes, which are thought to change the pCO 2 gradient at the snow-ice interface. The relative influence of these processes on atmospheric exchanges likely depends on the thickness of the ice. Specifically, the study indicates a predominant influence of brine volume expansion/contraction, brine dissolution/concentration and calcium carbonate formation/dissolution at sites characterized by a thick sea-ice cover, such that surface warming leads to an uptake of CO 2 and vice versa, while convective overturning within the sea-ice brines dominate at sites characterized by comparatively thin sea-ice cover, such that nighttime surface cooling leads to an uptake of CO 2 to the extent permitted by simultaneous formation of superimposed ice in the lower snow column.

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The relative contributions of biological and abiotic processes to carbon dynamics in subarctic sea ice

Cited by 40 publications

References 93 publications

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

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

Estimates of ikaite export from sea ice to the underlying seawater in a sea ice–seawater mesocosm

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

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The relative contributions of biological and abiotic processes to carbon dynamics in subarctic sea ice

Cited by 40 publications

References 93 publications

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

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

Estimates of ikaite export from sea ice to the underlying seawater in a sea ice–seawater mesocosm

Winter observations of CO&lt;sub&gt;2&lt;/sub&gt; exchange between sea ice and the atmosphere in a coastal fjord environment

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