Mid-Wisconsin to Holocene permafrost and landscape dynamics based on a drained lake basin core from the northern Seward Peninsula, Northwest Alaska

Permafrost-related processes drive regional landscape dynamics in the Arctic terrestrial system. A better understanding of past periods indicative of permafrost degradation and aggradation is important for predicting the future response of Arctic landscapes to climate change. Here, we used a multi-proxy approach to analyze a ~4 m long sediment core from a drained thermokarst lake basin on the northern Seward Peninsula in western Arctic Alaska (USA). Sedimentological, biogeochemistical, geochronological, micropaleontological (ostracoda, testate amoeba) and tephra analyses were used to determine the long-term environmental Early-Wisconsin to Holocene history preserved in our core for Central Beringia. Yedoma accumulation dominated throughout the Early to Late-Wisconsin but was interrupted by wetland formation from 44.5 to 41.5 ka BP. The latter was terminated by deposition of 1 m of volcanic tephra, most likely originating from the South Killeak Maar eruption at about 42 ka BP. Yedoma deposition continued until 22.5 ka BP and was followed by a depositional hiatus in the sediment core between 22.5 and 0.23 ka BP. We interpret this hiatus as due to intense thermokarst activity in the areas surrounding the site, which served as a sediment source during the Late-Wisconsin to Holocene climate transition. The lake forming the modern basin on the upland initiated around 0.23 ka BP, which drained catastrophically in spring 2005. The present study emphasizes that Arctic lake systems and periglacial landscapes are highly dynamic and permafrost formation as well as degradation in Central Beringia was controlled by regional to global climate patterns and as well as by local disturbances.

Sedimentology of cores from the continental rise west of the Antarctic Peninsula

The continental rise west of the Antarctic Peninsula includes a number of large sediment mounds interpreted as contourite drifts. Cores from six sediment drifts spanning some 650 km of the margin and 48 of latitude have been dated using chemical and isotopic tracers of palaeoproductivity and diatom biostratigraphy. Interglacial sedimentation rates range from 1.1 to 4.3 cm/ka. Glacial sedimentation rates range from 1.8 to 13.5 cm/ka, and decrease from proximal to distal sites on each drift. Late Quaternary sedimentation was cyclic, with brown, biogenic, burrowed mud containing ice-rafted debris (IRD) in interglacials and grey, barren, laminated mud in glacials. Foraminiferal intervals occur in interglacial stages 5 and 7 but not in the Holocene. Processes of terrigenous sediment supply during glacial stages differed; meltwater plumes were more important in stages 2-4, turbidity currents and ice-rafting in stage 6. The terrigenous component shows compositional changes along the margin, more marked in glacials. The major oxides Al2O3 and K2O are higher in the southwest, and CaO and TiO2 higher in the northeast. There is more smectite among the clay minerals in the northeast. Magnetic susceptibility varies along and between drifts. These changes reflect source variations along the margin. Interglacial sediments show less clear trends, and their IRD was derived from a wider area. Downslope processes were dominant in glacials, but alongslope processes may have attained equal importance in interglacials. The area contrasts with the East Antarctic continental slope in the SE Weddell Sea, where ice-rafting is the dominant process and where interglacial sedimentation rates are much higher than glacial. The differences in glacial setting and margin physiography can account for these contrasts.

(Table 1) Age determination of Cape Shpindler, Yugorski Peninsula, northwest Russia

Depositional environments, stratigraphic relations, and 35 new AMS 14C dates at Cape Shpindler, Yugorski Peninsula, help constrain the late Pleistocene glacial and environmental history of the southern Kara Sea region. Fifteen- to fifty-meter-high coastal exposures reveal a complex package of shallow marine, fluvial, glacial, and postglacial deposits, and are documented here in a 19-km-long cross-section and eight vertical sections. The shallow marine (Unit A), estuarine or prodeltaic (Unit B), and fluvio-deltaic (Unit C) deposits contain an interglacial molluscan fauna, yield radiocarbon dates greater than 40 ka, and may correspond with a regional sea-level highstand during the Eemian. These units are overlain by a diamicton (Unit D), and are pervasively deformed by folds and low- to high-angle faults into a stacked glaciotectonic accretionary complex. The diamicton (Unit D) is a subglacial till, and associated massive ground ice with deformed debris bands (Unit E) appears to be relict glacier ice. Glaciotectonic structures document both southward- and northward-directed glacier movement. Above the till and associated glaciotectonic horizons lies 0- to 11-m-thick postglacial deposits of peatland, eolian, fluvial, and primarily lacustrine origin (Unit F). The postglacial deposits yield radiocarbon ages of 12.8 to 0.8 ka. Thus, at least one regional glaciation is prominently represented in the stratigraphy, and occurred probably after the Eemian but before 12.8 ka. We infer that the bulk of the glacial record corresponds with southward advance by an early Weichselian Kara Sea Ice Sheet, in agreement with other recently documented, regional records from Yamal Peninsula and the Pechora Basin. The timing and source of northward-directed glacier ice are less well constrained. Across the broad expanse of the Eurasian Arctic, Quaternary stratigraphy is still sparsely documented. The new data from Cape Shpindler fill a spatial gap in paleoenvironmental research.