Discovery and characterization of submarine groundwater discharge in the Siberian Arctic seas: a case study in the Buor-Khaya Gulf, Laptev Sea

Charkin, Alexander; Loeff, Michiel Rutgers v. d.; Shakhova, Nataljya Evgenjevna; Gustafsson, Örjan; Dudarev, Oleg; Cherepnev, Maksim Sviatoslavovich; Salyuk, A.; Koshurnikov, Andrey; Spivak, Eduard; Gunar, A. Yu.; Ruban, Alexey; Semiletov, I. P.

doi:10.5194/tc-11-2305-2017

Cited by 38 publications

(30 citation statements)

References 86 publications

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“…SGD is in many ocean areas a major pathway for inputs of 228 Ra to the ocean (Moore et al, ). Due to the wide extent of permafrost it has been doubted whether SGD plays a role in the Arctic Ocean, but 228 Ra inputs from this source have been identified by a recent study in the Laptev Sea (Charkin et al, ). However, because of the ubiquitous presence of 238 U and 232 Th in soils, SGD supplies 226 Ra along with 228 Ra.…”

Section: Discussionmentioning

confidence: 99%

Radium Isotopes Across the Arctic Ocean Show Time Scales of Water Mass Ventilation and Increasing Shelf Inputs

et al. 2018

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The first full transarctic section of 228 Ra in surface waters measured during GEOTRACES cruises PS94 and HLY1502 (2015) shows a consistent distribution with maximum activities in the transpolar drift. Activities in the central Arctic have increased from 2007 through 2011 to 2015. The increased 228 Ra input is attributed to stronger wave action on shelves resulting from a longer ice-free season. A concomitant decrease in the 228 Th/ 228 Ra ratio likely results from more rapid transit of surface waters depleted in 228 Th by scavenging over the shelf. The 228 Ra activities observed in intermediate waters (<1,500 m) in the Amundsen Basin are explained by ventilation with shelf water on a time scale of about 15-18 years, in good agreement with estimates based on SF 6 and 129 I/ 236 U. The 228 Th excess below the mixed layer up to 1,500 m depth can complement 234 Th and 210 Po as tracers of export production, after correction for the inherent excess resulting from the similarity of 228 Ra and 228 Th decay times. We show with a Th/Ra profile model that the 228 Th/ 228 Ra ratio below 1,500 m is inappropriate for this purpose because it is a delicate balance between horizontal supply of 228 Ra and vertical flux of particulate 228 Th. The accumulation of 226 Ra in the deep Makarov Basin is not associated with an accumulation of Ba and can therefore be attributed to supply from decay of 230 Th in the bottom sediment. We estimate a ventilation time of 480 years for the deep Makarov-Canada Basin, in good agreement with previous estimates using other tracers. RUTGERS VAN DER LOEFF ET AL. 4853

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Section: Discussionmentioning

confidence: 99%

Radium Isotopes Across the Arctic Ocean Show Time Scales of Water Mass Ventilation and Increasing Shelf Inputs

et al. 2018

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“…Submarine groundwater discharge may be taking place near the river mouth, as is observed in the vicinity of the Lena River Delta in the Laptev Sea (Charkin et al, 2017), but not farther offshore where cores were collected. A plausible explanation for this difference may be related to the seaward extent of permafrost.…”

Section: 1029/2018gc007623mentioning

confidence: 96%

Freshwater Seepage Into Sediments of the Shelf, Shelf Edge, and Continental Slope of the Canadian Beaufort Sea

Gwiazda

Paull

Dallimore

et al. 2018

Geochem Geophys Geosyst

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Long‐term warming of the continental shelf of the Canadian Beaufort Sea caused by the transgression associated with the last deglaciation may be causing decomposition of relict offshore subsea permafrost and gas hydrates. To evaluate this possibility, pore waters from 118 sediment cores up to 7.3‐m long were taken on the shelf and slope and analyzed for chloride concentrations and δ180 and δD composition. We observed downcore decreases in pore waters Cl− concentration in sediments from all sites from the inner shelf (<20‐m water depth), from the shelf edge, from the outer slope (down to 1,000‐m water depths), and from localized shelf features such as midshelf pingo‐like features and inner shelf pockmarks. In contrast, pore water freshening is absent from all investigated cores of the Mackenzie Trough. Downcore pore waters Cl− concentration decreases indicate regional widespread freshwater seepage. Extrapolations to zero Cl− of pore water Cl− versus δ180 regression lines indicate that freshwaters in these environments carry different isotope signatures and thus are sourced from different reservoirs. These isotopic signatures indicate that freshening of shelf sediments pore waters is a result of downward infiltration of Mackenzie River water, freshening of shelf edge sediments is due to relict submarine permafrost degradation or gas hydrate decomposition under the shelf, and freshening of slope sediments is consistent with regional groundwater flow and submarine groundwater discharge as far as 150 km from shore. These results confirm ongoing decomposition of offshore permafrost and suggest extensive current groundwater discharge far from the coast.

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“…The Biogeochemical Reaction Network Simulator (BRNS) (Regnier et al, 2002;Aguilera et al, 2005;Centler et al, 2010) -an adaptive simulation environment suitable for simulating large, mixed kinetic-equilibrium reaction networks in porous media (e.g. Jourabchi et al, 2005;Thullner et al, 2005;Dale et al, 2009) -is used to quantitatively explore the fluxes and transformations of methane in a sediment column representative for ESAS conditions.…”

Section: Brns: Reaction-transport Modelmentioning

confidence: 99%

Assessing the potential for non-turbulent methane escape from the East Siberian Arctic Shelf

et al. 2020

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Abstract. The East Siberian Arctic Shelf (ESAS) hosts large yet poorly quantified reservoirs of subsea permafrost and associated gas hydrates. It has been suggested that the global-warming induced thawing and dissociation of these reservoirs is currently releasing methane (CH4) to the shallow coastal ocean and ultimately the atmosphere. However, a major unknown in assessing the contribution of this CH4 flux to the global CH4 cycle and its climate feedbacks is the fate of CH4 as it migrates towards the sediment–water interface. In marine sediments, (an)aerobic oxidation reactions generally act as a very efficient methane sink. However, a number of environmental conditions can reduce the efficiency of this biofilter. Here, we used a reaction-transport model to assess the efficiency of the benthic methane filter and, thus, the potential for benthic methane escape across a wide range of environmental conditions that could be encountered on the East Siberian Arctic Shelf. Results show that, under steady-state conditions, anaerobic oxidation of methane (AOM) acts as an efficient biofilter. However, high CH4 escape is simulated for rapidly accumulating and/or active sediments and can be further enhanced by the presence of organic matter with intermediate reactivity and/or intense local transport processes, such as bioirrigation. In addition, in active settings, the sudden onset of CH4 flux triggered by, for instance, permafrost thaw or hydrate destabilization can also drive a high non-turbulent methane escape of up to 19 µmol CH4 cm−2 yr−1 during a transient, multi-decadal period. This “window of opportunity” arises due to delayed response of the resident microbial community to suddenly changing CH4 fluxes. A first-order estimate of non-turbulent, benthic methane efflux from the Laptev Sea is derived as well. We find that, under present-day conditions, non-turbulent methane efflux from Laptev Sea sediments does not exceed 1 Gg CH4 yr−1. As a consequence, we conclude that previously published estimates of ocean–atmosphere CH4 fluxes from the ESAS cannot be supported by non-turbulent, benthic methane escape.

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Discovery and characterization of submarine groundwater discharge in the Siberian Arctic seas: a case study in the Buor-Khaya Gulf, Laptev Sea

Cited by 38 publications

References 86 publications

Radium Isotopes Across the Arctic Ocean Show Time Scales of Water Mass Ventilation and Increasing Shelf Inputs

Radium Isotopes Across the Arctic Ocean Show Time Scales of Water Mass Ventilation and Increasing Shelf Inputs

Freshwater Seepage Into Sediments of the Shelf, Shelf Edge, and Continental Slope of the Canadian Beaufort Sea

Assessing the potential for non-turbulent methane escape from the East Siberian Arctic Shelf

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