Limited contribution of ancient methane to surface waters of the U.S. Beaufort Sea shelf

Sparrow, Katy J.; Kessler, J. D.; Southon, John; Garcia‐Tigreros, Fenix; Schreiner, K. M.; Ruppel, Carolyn D.; Miller, J. B.; Lehman, Scott J.; Xu, Xiaomei

doi:10.1126/sciadv.aao4842

Cited by 54 publications

(73 citation statements)

References 41 publications

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“…However, CH 4 released at the seafloor or in thawing subsea permafrost does not necessarily reach the atmosphere (9). In particular, it may dissolve in and be oxidized in the water column (5,(9)(10)(11), become trapped below the pycnocline (12), and be lost in the sulfate reduction zone just below the sediment-seawater interface (13) or even deep in the sediment itself (14). For this reason, reliable methods of determining the sea to atmosphere emissions are needed, especially in regions with highly spatially heterogeneous fluxes, such as above seafloor gas seeps.…”

Section: Introductionmentioning

confidence: 99%

Shipborne eddy covariance observations of methane fluxes constrain Arctic sea emissions

et al. 2020

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We demonstrate direct eddy covariance (EC) observations of methane (CH4) fluxes between the sea and atmosphere from an icebreaker in the eastern Arctic Ocean. EC-derived CH4 emissions averaged 4.58, 1.74, and 0.14 mg m−2 day−1 in the Laptev, East Siberian, and Chukchi seas, respectively, corresponding to annual sea-wide fluxes of 0.83, 0.62, and 0.03 Tg year−1. These EC results answer concerns that previous diffusive emission estimates, which excluded bubbling, may underestimate total emissions. We assert that bubbling dominates sea-air CH4 fluxes in only small constrained areas: A ~100-m2 area of the East Siberian Sea showed sea-air CH4 fluxes exceeding 600 mg m−2 day−1; in a similarly sized area of the Laptev Sea, peak CH4 fluxes were ~170 mg m−2 day−1. Calculating additional emissions below the noise level of our EC system suggests total ESAS CH4 emissions of 3.02 Tg year−1, closely matching an earlier diffusive emission estimate of 2.9 Tg year−1.

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Section: Introductionmentioning

confidence: 99%

Shipborne eddy covariance observations of methane fluxes constrain Arctic sea emissions

et al. 2020

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“…A wealth of data on subsea permafrost in the Arctic shelf collected through Russian and international research projects [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] has revealed large-scale methane emission from bottom sediments into water and on into the atmosphere. The gases in the Arctic shelf are often attributed to increasing microbial methane generation, migration of gas through taliks and faults, as well as to decomposition of intrapermafrost and subpermafrost gas hydrates during progressive degradation of subsea permafrost [11,[16][17][18][19][20][21].…”

Section: Introductionmentioning

confidence: 99%

Role of Warming in Destabilization of Intrapermafrost Gas Hydrates in the Arctic Shelf: Experimental Modeling

et al. 2019

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Destabilization of intrapermafrost gas hydrates is one of the possible mechanisms responsible for methane emission in the Arctic shelf. Intrapermafrost gas hydrates may be coeval to permafrost: they originated during regression and subsequent cooling and freezing of sediments, which created favorable conditions for hydrate stability. Local pressure increase in freezing gas-saturated sediments maintained gas hydrate stability from depths of 200–250 meters or shallower. The gas hydrates that formed within shallow permafrost have survived till present in the metastable (relict) state. The metastable gas hydrates located above the present stability zone may dissociate in the case of permafrost degradation as it becomes warmer and more saline. The effect of temperature increase on frozen sand and silt containing metastable pore methane hydrate is studied experimentally to reconstruct the conditions for intrapermafrost gas hydrate dissociation. The experiments show that the dissociation process in hydrate-bearing frozen sediments exposed to warming begins and ends before the onset of pore ice melting. The critical temperature sufficient for gas hydrate dissociation varies from −3.0 to −0.3 °C and depends on lithology (particle size) and salinity of the host frozen sediments. Taking into account an almost gradientless temperature distribution during degradation of subsea permafrost, even minor temperature increases can be expected to trigger large-scale dissociation of intrapermafrost hydrates. The ensuing active methane emission from the Arctic shelf sediments poses risks of geohazard and negative environmental impacts.

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“…For example, more extensive measurements of CH4 concentration and isotopic composition across the land-ocean continuum would assist in determining CH4 and CO2 sources and sinks. Radiocarbon measurements would demonstrate whether ancient CH4 sources such as thawing permafrost are significant (Sparrow et al, 2018). Such studies will provide critical information to characterize current and future Arctic greenhouse gas cycling, improving quantitative estimates of changes in CH4 and CO2 emissions.…”

Section: Discussionmentioning

confidence: 99%

River inflow dominates methane emissions in an Arctic coastal system

Manning¹,

Preston²,

Jones³

et al. 2019

Preprint

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Measurements of greenhouse gases in Arctic waters are strongly biased toward low-ice summer conditions, with few observations during periods of seasonal ice retreat. We present a year-round time series of dissolved methane (CH4) and nitrous oxide (N2O), along with targeted observations during ice melt of CH4 and carbon dioxide (CO2) in a river and estuary adjacent to Cambridge Bay, Nunavut, Canada. CH4 displayed dramatic seasonality, in contrast to limited seasonal changes in N2O. During the river freshet, CH4 concentrations in the river and ice-covered estuary were up to 240,000% saturation and 19,000% saturation, respectively, but quickly dropped by >100-fold following ice melt. Observations with a robotic kayak revealed that river-derived CH4 and CO2 were transported to the estuary and rapidly ventilated to the atmosphere once ice cover retreated. We estimate that river discharge accounts for >95% of annual CH4 sea-to-air emissions from the estuary.

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Limited contribution of ancient methane to surface waters of the U.S. Beaufort Sea shelf

Abstract: Ancient methane emitted to Arctic Ocean shelf waters is largely prevented from reaching the atmosphere.

Cited by 54 publications

References 41 publications

Shipborne eddy covariance observations of methane fluxes constrain Arctic sea emissions

Shipborne eddy covariance observations of methane fluxes constrain Arctic sea emissions

Role of Warming in Destabilization of Intrapermafrost Gas Hydrates in the Arctic Shelf: Experimental Modeling

River inflow dominates methane emissions in an Arctic coastal system

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