Chapter 16 - The Polar Ural Mountains: deglaciation history

Abstract

We here outline the deglaciation history in the Polar Ural Mountains from the Last Glacial Maximum (LGM) until the mountain range was completely ice-free during the early Holocene. Our reconstruction of the course of deglaciation is based on cosmogenic exposure dating (10Be) of erratic boulders combined with stratigraphic results from sediment cores retrieved from two neighbouring lakes, Bolshoye Shchuchye and Maloya Shchuchye, located in the interior of the mountain chain. During the LGM there were many glaciers in the mountains, but most of them were small and some were only slightly larger than those that existed during the Little Ice Age. Exposure dating and core data suggest that some glaciers attained their maximum extent a little before LGM at around 25–24ka BP. A high influx of silt and clay into the investigated basins during the LGM with the formation of annual lamination (varves) in the lake floor sediments are believed to reflect the presence of active glaciers within both catchment areas. A decrease in sedimentation rate starting around 18.7–18.4calka BP indicates that the glaciers then began to melt back. The glaciers that supplied sediments to Bolshoye Shchuchye appear to have melted away in response to the climate warming soon after the transition to the Bølling interstadial about 14.6calka BP. A similar development can be traced from the stratigraphy in Maloya Shchuchye, but here some small glaciers seem to have existed until the beginning of the Younger Dryas when the glacial imprint disappears also from this record. It seems clear that all glaciers in the Polar Urals must have melted away soon after the onset of the Holocene when the climate suddenly became significantly warmer than today, suggesting that it was impossible for glaciers to exist even in shady high-elevation locations.