Late Cenozoic radiometric dates, Seward and Baldwin Peninsulas, and adjacent continental shelf, Alaska

Kaufman, Darrell S.; Hopkins, David M.

doi:10.3133/ofr85374

Cited by 14 publications

(16 citation statements)

References 17 publications

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“…Throughout the Holocene, thermokarst processes have continued to operate, gradually lowering the original land surface. Thermokarst lake formation during that time falls within the range of other published thermokarst lake basal dates for the Seward Peninsula (Spiker et al, 1978;Kaufman and Hopkins, 1985) and the circum-arctic (Walter et al, 2007;Reyes and Cooke, 2011). The age of the lowermost dated sample in unit D of 8370 AE 50 yr BP falls in the period of a pronounced early Holocene climate warming in NW North America (McCulloch and Hopkins, 1966;Detterman, 1970;Ritchie et al, 1983;, a time when thermokarst lake formation peaked in Alaska and other high latitude regions (Walter et al, 2007) and intense peatland formation occurred in Alaska (Jones and Yu, 2010).…”

Section: Tablementioning

confidence: 57%

Late Quaternary environmental and landscape dynamics revealed by a pingo sequence on the northern Seward Peninsula, Alaska

Wetterich

Grosse

Schirrmeister

et al. 2012

Quaternary Science Reviews

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a b s t r a c tA terrestrial sediment sequence exposed in an eroding pingo provides insights into the late-Quaternary environmental history of the northern Seward Peninsula, Alaska. We have obtained the first radiocarbondated evidence for a mid-Wisconsin thermokarst lake, demonstrating that complex landscape dynamics involving cyclic permafrost aggradation and thermokarst lake formation occurred over stadiale interstadial as well as glacialeinterglacial time periods. High values of Picea pollen and the presence of Larix pollen in sediments dated to 50e40 ka BP strongly suggest the presence of forest or woodland early in MIS 3; the trees grew within a vegetation matrix dominated by grass and sedge, and there is indirect evidence of grazing animals. Thus the interstadial ecosystem was different in structure and composition from the Holocene or from the preceding Last Interglacial period. An early Holocene warm period is indicated by renewed thermokarst lake formation and a range of fossil taxa. Multiple extralimital plant taxa suggest mean July temperatures above modern values. The local presence of spruce during the early Holocene warm interval is evident from a radiocarbon-dated spruce macrofossil remain and indicates significant range extension far beyond the modern tree line. The first direct evidence of spruce in Northwest Alaska during the early Holocene has implications for the presence of forest refugia in Central Beringia and previously assumed routes and timing of post-glacial forest expansion in Alaska.

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Section: Tablementioning

confidence: 57%

Late Quaternary environmental and landscape dynamics revealed by a pingo sequence on the northern Seward Peninsula, Alaska

Wetterich

Grosse

Schirrmeister

et al. 2012

Quaternary Science Reviews

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“…; Ager ), occurrence of fossil beaver dams and beaver‐gnawed wood beyond the modern presence of beavers (McCulloch & Hopkins ; Hopkins et al . ; Kaufman & Hopkins ) and buried ice‐wedge casts on the Seward Peninsula (McCulloch & Hopkins ), as well as increased shrub cover, paludification of the landscape in northern Alaska (Detterman ; Oswald et al . ; Mann et al .…”

Section: Discussionmentioning

confidence: 99%

Evidence of multiple thermokarst lake generations from an 11 800‐year‐old permafrost core on the northern Seward Peninsula, Alaska

Lenz

Wetterich

Jones

et al. 2016

Boreas

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Permafrost degradation influences the morphology, biogeochemical cycling and hydrology of Arctic landscapes over a range of time scales. To reconstruct temporal patterns of early to late Holocene permafrost and thermokarst dynamics, site-specific palaeo-records are needed. Here we present a multi-proxy study of a 350-cm-long permafrost core from a drained lake basin on the northern Seward Peninsula, Alaska, revealing Lateglacial to Holocene thermokarst lake dynamics in a central location of Beringia. Use of radiocarbon dating, micropalaeontology (ostracods and testaceans), sedimentology (grain-size analyses, magnetic susceptibility, tephra analyses), geochemistry (total nitrogen and carbon, total organic carbon, d13 C org ) and stable water isotopes (d 18 O, dD, d excess) of ground ice allowed the reconstruction of several distinct thermokarst lake phases. These include a pre-lacustrine environment at the base of the core characterized by the Devil Mountain Maar tephra (22 800AE280 cal. a BP, Unit A), which has vertically subsided in places due to subsequent development of a deep thermokarst lake that initiated around 11 800 cal. a BP (Unit B). At about 9000 cal. a BP this lake transitioned from a stable depositional environment to a very dynamic lake system (Unit C) characterized by fluctuating lake levels, potentially intermediate wetland development, and expansion and erosion of shore deposits. Complete drainage of this lake occurred at 1060 cal. a BP, including post-drainage sediment freezing from the top down to 154 cm and gradual accumulation of terrestrial peat (Unit D), as well as uniform upward talik refreezing. This core-based reconstruction of multiple thermokarst lake generations since 11 800 cal. a BP improves our understanding of the temporal scales of thermokarst lake development from initiation to drainage, demonstrates complex landscape evolution in the ice-rich permafrost regions of Central Beringia during the Lateglacial and Holocene, and enhances our understanding of biogeochemical cycles in thermokarst-affected regions of the Arctic.

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“…The high frequency of lake drainage events coincides with the medieval climate anomaly (MCA), which occurred 1050–550 cal yr BP in northwest Alaska [ Mann et al , 2002] and 1050–250 cal yr BP in southwest Alaska [ Chipman et al , 2009], suggesting that a warmer climate resulted in greater permafrost degradation that led to increased lake drainage. Peat initiation in the oldest of our dated drained thermokarst lake basins (Kit‐75, 9140 ± 129 cal yr BP) corresponds to end of the Holocene thermal maximum (HTM) on the Seward Peninsula [ Kaufman et al , 2004], as evidenced by the presence of Populus and beaver‐gnawed wood found outside of their modern ranges [ Hopkins et al , 1981; Kaufman and Hopkins , 1985]. In this study we did not record lake drainage during the cooler neoglacial interval (7500–5000 cal yr BP), but additional dating of basal peat, particularly of buried peats, would be necessary to determine if this relation holds.…”

Section: Discussionmentioning

confidence: 99%

Peat accumulation in drained thermokarst lake basins in continuous, ice‐rich permafrost, northern Seward Peninsula, Alaska

Jones¹,

Grosse²,

Jones³

et al. 2012

J. Geophys. Res.

112

153

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[1] Thermokarst lakes and peat-accumulating drained lake basins cover a substantial portion of Arctic lowland landscapes, yet the role of thermokarst lake drainage and ensuing peat formation in landscape-scale carbon (C) budgets remains understudied. Here we use measurements of terrestrial peat thickness, bulk density, organic matter content, and basal radiocarbon age from permafrost cores, soil pits, and exposures in vegetated, drained lake basins to characterize regional lake drainage chronology, C accumulation rates, and the role of thermokarst-lake cycling in carbon dynamics throughout the Holocene on the northern Seward Peninsula, Alaska. Most detectable lake drainage events occurred within the last 4,000 years with the highest drainage frequency during the medieval climate anomaly. Peat accumulation rates were highest in young (50-500 years) drained lake basins (35.2 g C m À2 yr À1 ) and decreased exponentially with time since drainage to 9 g C m À2 yr À1 in the oldest basins. Spatial analyses of terrestrial peat depth, basal peat radiocarbon ages, basin geomorphology, and satellite-derived land surface properties (Normalized Difference Vegetation Index (NDVI); Minimum Noise Fraction (MNF)) from Landsat satellite data revealed significant relationships between peat thickness and mean basin NDVI or MNF. By upscaling observed relationships, we infer that drained thermokarst lake basins, covering 391 km 2 (76%) of the 515 km 2 study region, store 6.4-6.6 Tg organic C in drained lake basin terrestrial peat. Peat accumulation in drained lake basins likely serves to offset greenhouse gas release from thermokarst-impacted landscapes and should be incorporated in landscape-scale C budgets.

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Late Cenozoic radiometric dates, Seward and Baldwin Peninsulas, and adjacent continental shelf, Alaska

Cited by 14 publications

References 17 publications

Late Quaternary environmental and landscape dynamics revealed by a pingo sequence on the northern Seward Peninsula, Alaska

Late Quaternary environmental and landscape dynamics revealed by a pingo sequence on the northern Seward Peninsula, Alaska

Evidence of multiple thermokarst lake generations from an 11 800‐year‐old permafrost core on the northern Seward Peninsula, Alaska

Peat accumulation in drained thermokarst lake basins in continuous, ice‐rich permafrost, northern Seward Peninsula, Alaska

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