Minimum distribution of subsea ice‐bearing permafrost on the U.S. Beaufort Sea continental shelf

Brothers, Laura L.; Hart, Patrick E.; Ruppel, Carolyn D.

doi:10.1029/2012gl052222

Cited by 51 publications

(87 citation statements)

References 33 publications

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“…The analyses of Brothers et al . [] indicate poorer IBPF preservation on this part of the margin than elsewhere, consistent with sustained exposure to the open ocean. Barrier island wells in this sector are confined to the westernmost and easternmost ends of the Maguire Islands (Challenge Island and Alaska State F1 on North Star Island, respectively) and to the western end of Flaxman Island (Alaska State D1).…”

Section: Results and Interpretationsmentioning

confidence: 97%

“…The data compiled here provide the first comprehensive overview of direct borehole constraints on the occurrence of subsea permafrost along a ∼500 km long part of the U.S. Beaufort Sea margin stretching from Pogik Bay to nearly the U.S.‐Canada border. The results also yield insights into along‐margin and shore‐perpendicular variations in the current state of subsea permafrost and can be compared with subsea permafrost distributions inferred from regional‐scale seismic analyses [ Brothers et al ., ]. The analysis also has implications for permafrost distribution beneath the present‐day continental shelf at the end of the Last Glacial Maximum, which in turn may provide hints about the fate of subsea permafrost under a regime of continued future global warming.…”

Section: Discussionmentioning

confidence: 99%

“…This paper presents the first compilation of direct borehole constraints on subsea IBPF distribution on the U.S. Beaufort Sea margin based on a comprehensive analysis of well logging data. The results in this paper complement the recent seismic‐based analyses [ Brothers et al ., ] and provide a data set comparable to the borehole interpretations developed for the Canadian part of this margin [e.g., Hu et al ., ]. The analysis also extends to the offshore area the mostly onshore interpretations by Collett et al .…”

Section: Introductionmentioning

confidence: 99%

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Subsea ice‐bearing permafrost on the U.S. Beaufort Margin: 2. Borehole constraints

Ruppel

Herman²,

Hart

2016

Geochem Geophys Geosyst

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Borehole logging data from legacy wells directly constrain the contemporary distribution of subsea permafrost in the sedimentary section at discrete locations on the U.S. Beaufort Margin and complement recent regional analyses of exploration seismic data to delineate the permafrost's offshore extent. Most usable borehole data were acquired on a $500 km stretch of the margin and within 30 km of the contemporary coastline from north of Lake Teshekpuk to nearly the U.S.-Canada border. Relying primarily on deep resistivity logs that should be largely unaffected by drilling fluids and hole conditions, the analysis reveals the persistence of several hundred vertical meters of ice-bonded permafrost in nearshore wells near Prudhoe Bay and Foggy Island Bay, with less permafrost detected to the east and west. Permafrost is inferred beneath many barrier islands and in some nearshore and lagoonal (back-barrier) wells. The analysis of borehole logs confirms the offshore pattern of ice-bearing subsea permafrost distribution determined based on regional seismic analyses and reveals that ice content generally diminishes with distance from the coastline. Lacking better well distribution, it is not possible to determine the absolute seaward extent of ice-bearing permafrost, nor the distribution of permafrost beneath the present-day continental shelf at the end of the Pleistocene. However, the recovery of gas hydrate from an outer shelf well (Belcher) and previous delineation of a log signature possibly indicating gas hydrate in an inner shelf well (Hammerhead 2) imply that permafrost may once have extended across much of the shelf offshore Camden Bay.

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Section: Results and Interpretationsmentioning

confidence: 97%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Subsea ice‐bearing permafrost on the U.S. Beaufort Margin: 2. Borehole constraints

Ruppel

Herman²,

Hart

2016

Geochem Geophys Geosyst

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“…This led to the formation of permafrost and possibly permafrost‐associated gas hydrate in the sediments that now comprise the shelf. During subsequent sea level rise of 100 m or more, the permafrost and gas hydrate has probably mostly thawed, and recent seismic analyses indicate that permafrost probably does not remain beyond ~30 km (~20 m isobath) from the present‐day coastline [ Brothers et al ., ]. Permafrost‐associated gas hydrates, which are not known to form BSRs and whose existence on the U.S. Beaufort Sea shelf is probably not widespread, are not considered in this study.…”

Section: Settingmentioning

confidence: 99%

Widespread gas hydrate instability on the upper U.S. Beaufort margin

et al. 2014

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The most climate-sensitive methane hydrate deposits occur on upper continental slopes at depths close to the minimum pressure and maximum temperature for gas hydrate stability. At these water depths, small perturbations in intermediate ocean water temperatures can lead to gas hydrate dissociation. The Arctic Ocean has experienced more dramatic warming than lower latitudes, but observational data have not been used to study the interplay between upper slope gas hydrates and warming ocean waters. Here we use (a) legacy seismic data that constrain upper slope gas hydrate distributions on the U.S. Beaufort Sea margin, (b) Alaskan North Slope borehole data and offshore thermal gradients determined from gas hydrate stability zone thickness to infer regional heat flow, and (c) 1088 direct measurements to characterize multidecadal intermediate ocean warming in the U.S. Beaufort Sea. Combining these data with a three-dimensional thermal model shows that the observed gas hydrate stability zone is too deep by 100 to 250 m. The disparity can be partially attributed to several processes, but the most important is the reequilibration (thinning) of gas hydrates in response to significant (~0.5°C at 2σ certainty) warming of intermediate ocean temperatures over 39 years in a depth range that brackets the upper slope extent of the gas hydrate stability zone. Even in the absence of additional ocean warming, 0.44 to 2.2 Gt of methane could be released from reequilibrating gas hydrates into the sediments underlying an area of~5-7.5 × 10 3 km 2 on the U.S. Beaufort Sea upper slope during the next century.

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“…Although these studies documented a thick and extensive permafrost interval underlying much of the shelf, its maximum seaward extent is poorly defined. Analyses of industry seismic data inferred that the outer limit of permafrost was near the 90 m isobath and the shelf/slope boundary [ Pullan et al ., ], in contrast to ~20 m isobath lying 30 km offshore on the U.S. Beaufort Shelf [ Brothers et al ., ]. No wells have been drilled across this boundary, but as industry prepares for exploratory drilling in the outer Beaufort Sea, there is renewed interest in understanding physical properties of offshore permafrost and its maximum seaward extent.…”

Section: Introductionmentioning

confidence: 99%

Numerical model of the geothermal regime on the Beaufort Shelf, arctic Canada since the Last Interglacial

Taylor

Dallimore

Hill

et al. 2013

J. Geophys. Res. Earth Surf.

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[1] A finite element geothermal model is developed for the outer Mackenzie Delta-Beaufort Sea shelf to predict permafrost evolution since the Last Interglacial~130-116 kaBP(cal). The purpose is to reconcile sparse observations of the depth and extent of ice-bonded permafrost with sediment properties and the paleoenvironment. Sea level curves determine, as a function of time, areas of the shelf that were subaerially exposed, promoting permafrost aggradation, and areas that were submerged, promoting permafrost degradation. Assuming as a model starting point that a paleoclimate similar to today persisted through the Last Interglacial, permafrost subsequently aggrades in depth and advances seaward from the present shoreline to the shelf/slope bathymetric break by the Last Glacial Maximum (LGM)~26 kaBP(cal). Modeled permafrost exhibits reduced growth in depth and seaward progression that correlate with early and middle Wisconsin stillstands in sea level. Following the LGM and rise in sea level, offshore permafrost degrades and permafrost base rises~100 m to its present depth of 600 m. The offshore limit of modeled ice-bonded permafrost lies at the~95 m isobath, within 1 km of the bathymetric shelf/slope break. The model replicates features of offshore permafrost body observed seismically and demonstrates that warm outflow from the Mackenzie River depresses the upper surface of offshore permafrost by tens of meters to the 20 m isobath. Although Pleistocene permafrost predated the Wisconsinan, the model demonstrates that the paleoenvironment of the last 125,000 years is sufficient to develop the depth, seaward extent, and principal features of the permafrost body.

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Minimum distribution of subsea ice‐bearing permafrost on the U.S. Beaufort Sea continental shelf

Cited by 51 publications

References 33 publications

Subsea ice‐bearing permafrost on the U.S. Beaufort Margin: 2. Borehole constraints

Subsea ice‐bearing permafrost on the U.S. Beaufort Margin: 2. Borehole constraints

Widespread gas hydrate instability on the upper U.S. Beaufort margin

Numerical model of the geothermal regime on the Beaufort Shelf, arctic Canada since the Last Interglacial

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