Gennady G Matishov

Postglacial emergence and distribution of late Weichselian ice-sheet loads in the northern Barents and Kara seas, Russia

Reconstructions of late Weichselian glacier coverage on the continental shelves of the Russian Arctic range from a large ice sheet terminating in northern Siberia to isolated ice caps restricted to Arctic archipelagos. This disparity in glacier reconstructions reflects the lack of chronological control on glacial and deglacial landforms. We present new Holocene relative sea-level data from Franz Josef Land and northern Novaya Zemlya, Russia, that place the thickest glacier loads in the northern Barents Sea and not over Novaya Zemlya. Radiocarbon ages from shelf and terrestrial areas at the former ice-sheet margin support deglaciation of the northern Barents Sea between 13.0 and 10.3 ka, considerably later than inferred from isotopic records for the Arctic Ocean. This analysis indicates that the Barents Sea ice sheet was a dominant sea-level reservoir in northern Eurasia, and that glacier loading of Novaya Zemlya was comparatively limited during the last glaciation.

Postglacial emergence of western Franz Josef Land, Russian, and retreat of the barents sea ice sheet

Uncertainty remains on the timing and extent of Late Weichselian glaciers over the QSR Barents and Kara sea shelves. Franz Josef Land, Russia, is a critical area for deciphering the record of glacier fluctuations and postglacial relative sea-level change. Coastal forelands on the archipelago are covered by a well-preserved raised-beach sequence containing abundant and pristine driftwood, whalebone, and shell. ~4C dating of these materials provides site-specific emergence records for the archipelago, and some of the oldest ages on deglaciation of 10,400 BP. Three apparent still-stands in emergence are inferred from morphology of the raised-beach sequence and ~4C dating between 9900 and 6200 BP, and at ca. 5500 BP and 3500 BP. The earliest sea-level arrest, after formation of the marine limit, reflects a balance between glacio-isostasy and eustasy, concomitant with the final phase of global sea-level rise. The latter two sea level arrests during the middle- to late-Holocene are less pronounced and may indicate increased height of the ocean surface with greater storminess and extended open-water conditions. Raised beaches at 1-2 m a.s.l, and J4C dated at 1000 to 2000 BP give contemporary emergence rates of 1 to 2 mm/year. The low current rates of emergence on Franz Josef Land are similar to areas in Fennoscandinavia that sustained modest Late-Weichselian glacier loads (<1500 m), within a few 100s of km of the inferred ice sheet margin. The pattern of postglacial emergence and strandline tilts indicates that past glacier loads were greater over the adjacent Barents Sea, than Franz Josef Land. Marine and terrestrial records from Franz Josef Land place retreat of glaciers from coastal areas by 10,400 BP, whereas the adjacent Franz Victoria Trough was deglaciated by 13,000 BP. Retreat of the Barents Sea Ice Sheet was probably underway by 13,500 BP, coincident with rising global sea-level and elevated summer insolation. We infer that iceberg calving through the deep troughs bordering the Barents Sea, particularly with rapidly rising sea level ca. 12,000 BP was an important process controlling the demise of the Barents Sea Ice Sheet. Copyright

Holocene relative sea-level history of Franz Josef Land, Russia

One of the largest uncertainties in ice-volume changes during the late Quaternary Period is the extent of ice sheets over the Barents and Kara seas. Field research on central and eastern Franz Josef Land, Russia, provide new observations on postglacial emergence and deglaciation that further constrain the magnitude and timing of late Weichselian glaciations. Radiocarbon dating of driftage from raised-marine sequences place deglacial unloading prior to 9.4 ka. At a number of localities within 1 to 2 km of the present glacier margin, in situ shells from raised-marine sediments yield 14C ages between 9.7 and 8.4 yr B.P., evidence that outlet glaciers were at or behind present margins by the early Holocene Period.nnThe altitude of the marine limit on Franz Josef Land ranges from 49 to 20 m above sea level (asl) and is low compared to eastern Svalbard (110 to 60 m asl). The age of the marine limit ranges from ≥10.4 ka to ca. 6.0 ka and exhibits greater diachrony where emergence is <35 m. A low initial rate of emergence reflects glacio-isostatic compensation offset by a eustatic rise in sea level, and perhaps an additional component from renewed water loading of the Barents Sea after deglaciation. The presence of raised beaches at 1 to 4 m asl that are 1 to 2 ka indicates that uplift is incomplete. An exponential extrapolation of uplift data for Franz Josef Land and eastern Svalbard yields current maximum uplift estimates of 0.7 to 1.6 mm/yr, an inferred <5.5 m of uplift remaining. These values are at least 50% to 80% lower than the inferred uplift residual for a modeled ice sheet in the Barents and Kara seas. The discrepancy indicates that further refinement is needed for this ice-sheet model.nnThe compilation of emergence data from Franz Josef Land, Svalbard, and Novaya Zemlya confine maximum glacio-isostatic compensation to the Barents Sea; comparatively minor ice sheet loads were over Novaya Zemlya and the southeastern Barents Sea. Emergence isobases since 5 and 9 ka descend northward across Franz Josef Land, indicating a diminishing glacio-isostatic response into the Arctic Ocean.