Glacial and environmental changes over the last 60000years in the Polar Ural Mountains, Arctic Russia, inferred from a high-resolution lake record and other observations from adjacent areas

Our knowledge about the glaciation history in the Russian Arctic has to a large extent been based on geomorphological mapping supplemented by studies of short stratigraphical sequences found in exposed sections. Here we present new geochronological data from the Polar Ural Mountains along with a high-resolution sediment record from Bolshoye Shchuchye, the largest and deepest lake in the mountain range. Seismic profiles show that the lake contains a 160-m-thick sequence of unconsolidated lacustrine sediments. A well-dated 24-m-long core from the southern end of the lake spans the last 24cal. ka. From downward extrapolation of sedimentation rates we estimate that sedimentation started about 50-60 ka ago, most likely just after a large glacier had eroded older sediments from the basin. Terrestrial cosmogenic nuclide (TCN) exposure dating (Be-10) of boulders and Optically Stimulated Luminescence (OSL) dating of sediments indicate that this part of the Ural Mountains was last covered by a coherent ice-field complex during Marine Isotope Stage (MIS) 4. A regrowth of the glaciers took place during a late stage of MIS 3, but the central valleys remained ice free until the present. The presence of small- and medium-sized glaciers during MIS 2 is reflected by a sequence of glacial varves and a high sedimentation rate in the lake basin and likewise from Be-10 dating of glacial boulders. The maximum extent of the mountain glaciers during MIS 2 was attained prior to 24cal. ka BP. Some small present-day glaciers, which are now disappearing completely due to climate warming, were only slightly larger during the Last Glacial Maximum (LGM) as compared to AD 1953. A marked decrease in sedimentation rate around 18-17cal. ka BP indicates that the glaciers then became smaller and probably disappeared altogether around 15-14cal. ka BP.