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The late Quaternary climatic and environmental history of the Severnaya Zemlya Archipelago in the Russian High Arctic has been the focus of many palaeoenvironmental studies since the 1970s. However, the existing data are highly fragmentary and sometimes contradictory. New information concerning the archipelago's environmental history was derived from a 2.46‐m‐long sediment core from Lake Tvyordoe, located in the northwestern part of Bolshevik Island. The core was investigated by a multi‐proxy approach that comprises radiocarbon dating as well as lithological, granulometrical, palynological and geochemical analyses. The results provide new insights into the vegetation history as well as changes in lake level, lake‐ice cover, and water and sediment input since the Last Glacial Maximum (LGM). Fine‐grained, laminated sediments at the core base, which were dated to c. 24.2 cal. ka BP, suggest lacustrine sedimentation under a permanent ice cover with low meltwater supply. This, along with a lack of glacial and glacial‐lacustrine deposits, supports earlier assumptions that Bolshevik Island was not covered by the Barents‐Kara Ice Sheet during the LGM. Furthermore, even the Mushketov Ice Cap, the closest ice mass to Lake Tvyordoe, did not expand from the denudation plateau to the lake. During the terminal Pleistocene, starting c. 14.5 cal. ka BP, warmer and wetter climate conditions resulted in higher sediment loads. The most favourable environmental conditions prevailed on Bolshevik Island throughout the Early and Middle Holocene (c. 11.7–6.5 cal. ka BP), when low shrub tundra associations with dwarf birch, willow and alder dominated the vegetation. After c. 10.0 cal. ka BP, a shift to climate drying occurred, which, after 6.5 cal. ka BP, was accompanied by a climate cooling. The Late Holocene climate, according to pollen data (suggesting sparse lichen–moss–grass cover) and relatively low total organic carbon (TOC) contents, was rather similar to that during the Lateglacial. [ABSTRACT FROM AUTHOR]

The Arctic atmospheric boundary layer (AABL) in the central Arctic was characterized by dropsonde, lidar, ice thickness and airborne in situ measurements during the international Polar Airborne Measurements and Arctic Regional Climate Model Simulation Project (PAMARCMiP) in April 2009. We discuss AABL observations in the lowermost 500 m above (A) open water, (B) sea ice with many open/refrozen leads (C) sea ice with few leads, and (D) closed sea ice with a front modifying the AABL. Above water, the AABL had near-neutral stratification and contained a high water vapor concentration. Above sea ice, a low AABL top, low near-surface temperatures, strong surface-based temperature inversions and an increase of moisture with altitude were observed. AABL properties and particle concentrations were modified by a frontal system, allowing vertical mixing with the free atmosphere. Above areas with many leads, the potential temperature decreased with height in the lowest 50 m and was nearly constant above, up to an altitude of 100-200 m, indicating vertical mixing. The increase of the backscatter coefficient towards the surface was high. Above sea ice with few refrozen leads, the stably stratified boundary layer extended up to 200-300 m altitude. It was characterized by low specific humidity and a smaller increase of the backscatter coefficient towards the surface. [ABSTRACT FROM AUTHOR]