CO2 and CH4 in sea ice from a subarctic fjord (original) (raw)
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Sources and sinks of methane in sea ice
Elementa, 2021
We report on methane (CH 4) stable isotope (d 13 C and d 2 H) measurements from landfast sea ice collected near Barrow (Utqiagvik, Alaska) and Cape Evans (Antarctica) over the winter-to-spring transition. These measurements provide novel insights into pathways of CH 4 production and consumption in sea ice. We found substantial differences between the two sites. Sea ice overlying the shallow shelf of Barrow was supersaturated in CH 4 with a clear microbial origin, most likely from methanogenesis in the sediments. We estimated that in situ CH 4 oxidation consumed a substantial fraction of the CH 4 being supplied to the sea ice, partly explaining the large range of isotopic values observed (d 13 C between-68.5 and-48.5 ‰ and d 2 H between-246 and-104 ‰). Sea ice at Cape Evans was also supersaturated in CH 4 but with surprisingly high d 13 C values (between-46.9 and-13.0 ‰), whereas d 2 H values (between-313 and-113 ‰) were in the range of those observed at Barrow.These are the first measurements of CH 4 isotopic composition in Antarctic sea ice. Our data set suggests a potential combination of a hydrothermal source, in the vicinity of the Mount Erebus, with aerobic CH 4 formation in sea ice, although the metabolic pathway for the latter still needs to be elucidated. Our observations show that sea ice needs to be considered as an active biogeochemical interface, contributing to CH 4 production and consumption, which disputes the standing paradigm that sea ice is an inert barrier passively accumulating CH 4 at the ocean-atmosphere boundary.
Physical controls on the storage of methane in landfast sea ice
2014
We report on methane (CH 4) dynamics in landfast sea ice, brine and under-ice seawater at Barrow in 2009. The CH 4 concentrations in under-ice water ranged from 25.9 to 116.4 nmol L −1 sw , indicating a supersaturation of 700 to 3100 % relative to the atmosphere. In comparison, the CH 4 concentrations in sea ice ranged from 3.4 to 17.2 nmol L −1 ice and the deduced CH 4 concentrations in brine from 13.2 to 677.7 nmol L −1 brine. We investigated the processes underlying the difference in CH 4 concentrations between sea ice, brine and under-ice water and suggest that biological controls on the storage of CH 4 in ice were minor in comparison to the physical controls. Two physical processes regulated the storage of CH 4 in our landfast ice samples: bubble formation within the ice and sea ice permeability. Gas bubble formation due to brine concentration and solubility decrease favoured the accumulation of CH 4 in the ice at the beginning of ice growth. CH 4 retention in sea ice was then twice as efficient as that of salt; this also explains the overall higher CH 4 concentrations in brine than in the under-ice water. As sea ice thickened, gas bubble formation became less efficient, CH 4 was then mainly trapped in the dissolved state. The increase of sea ice permeability during ice melt marked the end of CH 4 storage.
Sea ice contribution to the air–sea CO<sub>2</sub> exchange in the Arctic and Southern Oceans
Tellus B, 2011
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.
Annals of Glaciology, 2015
In March and April 2010, we investigated the development of young landfast sea ice in Kongsfjorden, Spitsbergen, Svalbard. We sampled the vertical column, including sea ice, brine, frost flowers and sea water, to determine the CO 2 system, nutrients, salinity and bacterial and ice algae production during a 13 day interval of ice growth. Apart from the changes due to salinity and brine rejection, the sea-ice concentrations of total inorganic carbon (C T), total alkalinity (A T), CO 2 and carbonate ions (CO 3 2-) in melted ice were influenced by dissolution of calcium carbonate (CaCO 3) precipitates (25-55 µmol kg-1) and played the largest role in the changes to the CO 2 system. The C T values were also influenced by CO 2 gas flux, bacterial carbon production and primary production, which had a small impact on the C T. The only exception was the uppermost ice layer. In the top 0.05 m of the ice, there was a CO 2 loss of �20 µmol kg-1 melted ice (1 mmol m-2) from the ice to the atmosphere. Frost flowers on newly formed sea ice were important in promoting ice-air CO 2 gas flux, causing a CO 2 loss to the atmosphere of 140-800 µmol kg-1 d-1 melted frost flowers (7-40 mmol m-2 d-1).
Sea ice contribution to the air-sea CO2 exchange in the Arctic and Southern Oceans
Tellus B, 2011
A B S T R A C T 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.
Air-ice carbon pathways inferred from a sea ice tank experiment
Elementa: Science of the Anthropocene, 2016
Given rapid sea ice changes in the Arctic Ocean in the context of climate warming, better constraints on the role of sea ice in CO2 cycling are needed to assess the capacity of polar oceans to buffer the rise of atmospheric CO2 concentration. Air-ice CO2 fluxes were measured continuously using automated chambers from the initial freezing of a sea ice cover until its decay during the INTERICE V experiment at the Hamburg Ship Model Basin. Cooling seawater prior to sea ice formation acted as a sink for atmospheric CO2, but as soon as the first ice crystals started to form, sea ice turned to a source of CO2, which lasted throughout the whole ice growth phase. Once ice decay was initiated by warming the atmosphere, the sea ice shifted back again to a sink of CO2. Direct measurements of outward ice-atmosphere CO2 fluxes were consistent with the depletion of dissolved inorganic carbon in the upper half of sea ice. Combining measured air-ice CO2 fluxes with the partial pressure of CO2 in se...
Methane release from open leads and new ice following an Arctic winter storm event
Polar Science, 2022
We examine an Arctic winter storm event, which led to ice break-up, the formation of open leads, and the subsequent freezing of these leads. The methane (CH4) concentration in under-ice surface water before and during the storm event was 8-12 nmol L-1 , which resulted in a potential sea-toair CH4 flux ranging from +0.2 to +2.1 mg CH4 m-2 d-1 in open leads. CH4 ventilation between seawater and atmosphere occurred when both open water fraction and wind speed increased. Over the nine days after the storm, sea ice grew 27 cm thick. Initially, CH4 concentrations in the sea ice brine were above the equilibrium with the atmosphere. As the ice grew thicker, most of the CH4 was lost from upper layers of sea ice into the atmosphere, implying continued CH4 evasion after the leads were ice-covered. This suggests that wintertime CH4 emissions need to be better constrained. 1. Introduction CH4 emissions in a warming Arctic climate are suggested to increase gradually (Shuur et al., 2015). Arctic Ocean (AO) waters, which are largely covered by sea ice, receive CH4 gas from numerous geological sources, such as dissociating gas hydrates (Paull et al., 2007; Westbrook et al., 2009), gas reservoirs (e.g., sub-sea and land-based hydrocarbon seeps) (
Air–sea flux of CO<sub>2</sub> in arctic coastal waters influenced by glacial melt water and sea ice
Tellus B, 2011
Annual air-sea exchange of CO 2 in Young Sound, NE Greenland was estimated using pCO 2 surface-water measurements during summer (2006-2009) and during an ice-covered winter 2008. All surface pCO 2 values were below atmospheric levels indicating an uptake of atmospheric CO 2. During sea ice formation, dissolved inorganic carbon (DIC) content is reduced causing sea ice to be under saturated in CO 2. Approximately 1% of the DIC forced out of growing sea ice was released into the atmosphere while the remaining 99% was exported to the underlying water column. Sea ice covered the fjord 9 months a year and thereby efficiently blocked air-sea CO 2 exchange. During sea ice melt, dissolution of CaCO 3 combined with primary production and strong stratification of the water column acted to lower surface-water pCO 2 levels in the fjord. Also, a large input of glacial melt water containing geochemically reactive carbonate minerals may contribute to the low surface-water pCO 2 levels. The average annual uptake of atmospheric CO 2 was estimated at 2.7 mol CO 2 m −2 yr −1 or 32 g C m −2 yr −1 for the study area, which is lower than estimates from the Greenland Sea. Variability in duration of sea ice cover caused significant year-to-year variation in annual gas exchange.
Annals of Glaciology, 2015
In March and April 2010, we investigated the development of young landfast sea ice in Kongsfjorden, Spitsbergen, Svalbard. We sampled the vertical column, including sea ice, brine, frost flowers and sea water, to determine the CO2 system, nutrients, salinity and bacterial and ice algae production during a 13 day interval of ice growth. Apart from the changes due to salinity and brine rejection, the sea-ice concentrations of total inorganic carbon (C T), total alkalinity (A T), CO2 and carbonate ions (CO3 2–) in melted ice were influenced by dissolution of calcium carbonate (CaCO3) precipitates (25–55 μmol kg-1) and played the largest role in the changes to the CO2 system. The C T values were also influenced by CO2 gas flux, bacterial carbon production and primary production, which had a small impact on the C T. The only exception was the uppermost ice layer. In the top 0.05 m of the ice, there was a CO2 loss of ∼20 μmol kg-1 melted ice (1 mmol m-2) from the ice to the atmosphere. Fr...
Journal of Geophysical Research: Oceans, 2015
Sea ice is a defining feature of the polar marine environment. It is a critical domain for marine biota and it regulates ocean-atmosphere exchange, including the exchange of greenhouse gases such as CO 2 and CH 4. In this study, we determined the rates and pathways that govern gas transport through a mixed sea ice cover. N 2 O, SF 6 , 3 He, 4 He, and Ne were used as gas tracers of the exchange processes that take place at the ice-water and air-water interfaces in a laboratory sea ice experiment. Observation of the changes in gas concentrations during freezing revealed that He is indeed more soluble in ice than in water; Ne is less soluble in ice, and the larger gases (N 2 O and SF 6) are mostly excluded during the freezing process. Model estimates of gas diffusion through ice were calibrated using measurements of bulk gas content in ice cores, yielding gas transfer velocity through ice (k ice) of $5 3 10 24 m d 21. In comparison, the effective airsea gas transfer velocities (k eff) ranged up to 0.33 m d 21 providing further evidence that very little mixed-layer ventilation takes place via gas diffusion through columnar sea ice. However, this ventilation is distinct from air-ice gas fluxes driven by sea ice biogeochemistry. The magnitude of k eff showed a clear increasing trend with wind speed and current velocity beneath the ice, as well as the combination of the two. This result indicates that gas transfer cannot be uniquely predicted by wind speed alone in the presence of sea ice.