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A 24,000-year record of plant community dynamics, based on pollen and ancient DNA from the sediments (sedaDNA) of Lake Bolshoye Shchuchye in the Polar Ural Mountains, provides detailed information on the flora of the Last Glacial Maximum (LGM) and also changes in plant community composition and dominance. It greatly improves on incomplete records from short and fragmented stratigraphic sequences found in exposed sedimentary sections in the western Russian Arctic. In total, 162 plant taxa were detected by sedaDNA and 115 by pollen analysis. Several shifts in dominance between and within plant functional groups occurred over the studied period, but most taxa appear to have survived in situ. A diverse arctic-alpine herb flora characterised the interval ca. 24,000–17,000 cal years BP and persisted into the Holocene. Around 17,000 cal years BP, sedges (e.g. Carex) and bryophytes (e.g. Bryum, Aulacomnium) increased. The establishment of shrub-tundra communities of Dryas and Vaccinium sp., with potentially some Betula pubescens trees (influx ∼290 grains cm2 year−1), followed at ca. 15,000 cal years BP. Forest taxa such as Picea and ferns (e.g. Dryopteris fragrans, Gymnocarpium dryopteris) established near the lake from ca. 10,000 cal years BP, followed by the establishment of Larix trees from ca. 9000 cal years BP. Picea began to decline from ca. 7000 cal years BP. A complete withdrawal of forest tree taxa occurred by ca. 4000 cal years BP, presumably due to decreasing growing-season temperatures, allowing the expansion of dwarf-shrub tundra and a diverse herb community similar to the present-day vegetation mosaic. Contrary to some earlier comparative studies, sedaDNA and pollen from Lake Bolshoye Shchuchye showed high similarity in the timing of compositional changes and the occurrence of key plant taxa. The sedaDNA record revealed several features that the pollen stratigraphy and earlier palaeorecords in the region failed to detect; a sustained, long-term increase in floristic richness since the LGM until the early Holocene, turnover in grass and forb genera over the Pleistocene-Holocene transition, persistence of a diverse arctic-alpine flora over the late Quaternary, and a variable bryophyte flora through time. As pollen records are often limited by taxonomic resolution, differential productivity and dispersal, sedaDNA can provide improved estimates of floristic richness and is better able to distinguish between different plant assemblages. However, pollen remains superior at providing quantitative estimates of plant abundance changes and detecting several diverse groups (e.g. Poaceae, Cyperaceae, Asteraceae) which may be underreported in the sedaDNA. Joint use of the two proxies provided unprecedented floristic detail of past plant communities and helped to distinguish between long-distance transport of pollen and local presence, particularly for woody plant taxa.

Marine-terminating glaciers and ice streams are important controls of ice sheet mass balance. However, understanding of their long-term response to external forcing is limited by relatively short observational records of present-day glaciers and sparse geologic evidence for paleo-glaciers. Here we use a high-resolution ice sheet model with an accurate representation of grounding line dynamics to study the deglaciation of the marine-based south-western Norwegian sector of the Scandinavian Ice Sheet and its sensitivity to ocean and atmosphere forcing. We find that the regional response to a uniform climate change is highly dependent on the local bedrock topography, consistent with ice sheet reconstructions. Our simulations suggest that ocean warming is able to trigger initial retreat in several fjords, but is not sufficient to explain retreat everywhere. Widespread retreat requires additional ice thinning driven by surface melt. Once retreat is triggered, the underlying bedrock topography and fjord width control the rate and extent of retreat, while multi-millennial changes over the course of deglaciation are modulated by surface melt. We suggest that fjord geometry, ice-ocean interactions and grounding line dynamics are vital controls of decadal-to centennial scale ice sheet mass loss. However, we postulate that atmospheric changes are the most important drivers of widespread ice sheet demise, and will likely trump oceanic influence on future ice sheet mass loss and resulting sea level rise over centennial and longer time scales. publishedVersion

In recent decades, knowledge of the glacial history of the last Pleistocene glaciation in Eurasia has changed tremendously. According to recent investigations, a major ice advance first entered the Russian mainland as early as 80–100 ka, blocking all drainage and damming huge lakes in West Siberia and European Russia. Drainage was diverted southward to the Caspian Sea and Black Sea. While in the east this Early Weichselian glaciation was the most extensive, so far few traces of this ice sheet have been found in the western regions. About 60 ka BP, a mid-Weichselian glaciation covered large parts of northern Russia and Siberia. Only the last, Late Weichselian glaciation was restricted to the shelf areas of the Barents and Kara Sea and did not extend into the Russian mainland. In the west, this was the most extensive Weichselian glaciation. In the Alps and in Britain, little evidence has been found so far of the extent of the Early Weichselian ice sheets.

In the middle Pleistocene, Eurasia was affected by three major glaciations. The extent of the largest glaciation, the Don glaciation, is still incompletely known. For the Elsterian glaciation as well, the eastern limits are only roughly estimated. The ice sheet probably covered the West Siberian Plain and may have been the most extensive glaciation in Central Siberia. In the Saalian, the Older Saalian glaciation was the largest. The most extensive ice sheet in West Siberia is traditionally ascribed to this stage. Middle and Younger Saalian glaciations were less extensive. Correlation of the Nordic glaciations with the glacial sequence of the Alps is still difficult, and it seems clear that more glaciations occurred than Penck and Bruckner had originally envisioned.

In recent decades, knowledge of the glacial history of the Last Pleistocene Glaciation in Eurasia has changed tremendously. According to recent investigations, a first major ice advance entered the Russian mainland as early as 80–100 ka ago, blocking all drainage and damming huge lakes in West Siberia and in European Russia. Drainage was diverted southward to the Caspian Sea and Black Sea. Whilst in the east this early Weichselian glaciation was the most extensive, so far no traces of this ice sheet have been found in the western regions. About 70 ka BP, a mid-Weichselian glaciation covered large parts of northern Russia and Siberia. Only the last, late Weichselian glaciation was restricted to the shelf areas of the Barents and Kara Sea and did not extend on to the Russian mainland. In the west, this was the most extensive Weichselian glaciation. In the Alps and in Britain, so far little evidence is found about the extent of the early Weichselian ice sheets.

In the Middle Pleistocene, Eurasia was affected by three major glaciations. The extent of the oldest glaciation, the Don glaciation, is still incompletely known. Also, for the Elsterian glaciation, the eastern limits are only roughly estimated. The ice sheet may have covered the west Siberian lowlands. However, it may have been the most extensive glaciation in eastern central Siberia. In the Saalian, the Older Saalian glaciation was the largest. It may have been the most extensive ice sheet in western Siberia, but the limits are still unclear, and west of the Urals the Saalian limit is not very well-defined. Middle and Younger Saalian glaciations were much less extensive. Correlation of the Nordic glaciations with the glacial sequence of the Alps is still difficult, and it seems clear that more glaciations occurred than Penck and Bruckner had originally envisioned.

Whilst glaciation of Antarctica goes back to the Oligocene, glaciation of South America and Greenland started some 14 Mya. Massive glaciation of the Northern Hemisphere started only some 1 Mya in the late Matuyama Chron. So far, evidence of this early glaciation is largely restricted to North America. Scandinavia may have been glaciated, but most of Asia probably was still ice-free.

This chapter discusses the present knowledge of the Quaternary ice sheet history in the Barents and Kara Sea region. A reconstruction of the ice sheet extent during the Last Glacial Maximum (LGM) is presented in the chapter. The reconstructions are based on a review of published geological and geophysical data from the shelf and adjacent islands and have also taken into account unpublished results. The ice sheet extent during the LGM has been much debated over the past decades, and was considered to represent one of the largest uncertainties in the global distribution of glaciers. According to one extreme view, much of northern Eurasia was covered by an enormous shelf-centered ice sheet at the LGM whereas others visualize more localized ice caps over the Arctic islands. Based on comprehensive investigations, it has now been demonstrated that a major ice sheet did exist in the Barents Sea region at this time. However, this ice sheet did not expand onto the Russian Lowland and there was no major ice dispersal centres over the Kara Sea shelf during the LGM.

This paper summarizes the results of studies of the Late Weichselian periglacial environments carried out in key areas of northern Eurasia by several QUEEN teams (European Science Foundation (ESF) programme: “Quaternary Environment of the Eurasian North”). The palaeoglaciological boundary conditions are defined by geological data on timing and extent of the last glaciation obtained in the course of the EU funded project “Eurasian Ice Sheets”. These data prove beyond any doubt, that with the exception of the northwestern fringe of the Taymyr Peninsula, the rest of the Eurasian mainland and Severnaya Zemlya were not affected by the Barents–Kara Sea Ice Sheet during the Last Glacial Maximum (LGM). Inversed modelling based on these results shows that a progressive cooling which started around 30 ka BP, caused ice growth in Scandinavia and the northwestern areas of the Barents–Kara Sea shelf, due to a maritime climate with relatively high precipitation along the western flank of the developing ice sheets. In the rest of the Eurasian Arctic extremely low precipitation rates (less than 50 mm yr−1), did not allow ice sheet growth in spite of the very cold temperatures. Palaeoclimatic and palaeoenvironmental conditions for the time prior to, during, and after the LGM have been reconstructed for the non-glaciated areas around the LGM ice sheet with the use of faunal and vegetation records, permafrost, eolian sediments, alluvial deposits and other evidences. The changing environment, from interstadial conditions around 30 ka BP to a much colder and drier environment at the culmination of the LGM at 20–15 ka BP, and the beginning of warming around 15 ka BP have been elaborated from the field data, which fits well with the modelling results.

The maximum limits of the Eurasian ice sheets during four glaciations have been reconstructed: (1) the Late Saalian (>140 ka), (2) the Early Weichselian (100–80 ka), (3) the Middle Weichselian (60–50 ka) and (4) the Late Weichselian (25–15 ka). The reconstructed ice limits are based on satellite data and aerial photographs combined with geological field investigations in Russia and Siberia, and with marine seismic- and sediment core data. The Barents-Kara Ice Sheet got progressively smaller during each glaciation, whereas the dimensions of the Scandinavian Ice Sheet increased. During the last Ice Age the Barents-Kara Ice Sheet attained its maximum size as early as 90–80,000 years ago when the ice front reached far onto the continent. A regrowth of the ice sheets occurred during the early Middle Weichselian, culminating about 60–50,000 years ago. During the Late Weichselian the Barents-Kara Ice Sheet did not reach the mainland east of the Kanin Peninsula, with the exception of the NW fringe of Taimyr. A numerical ice-sheet model, forced by global sea level and solar changes, was run through the full Weichselian glacial cycle. The modeling results are roughly compatible with the geological record of ice growth, but the model underpredicts the glaciations in the Eurasian Arctic during the Early and Middle Weichselian. One reason for this is that the climate in the Eurasian Arctic was not as dry then as during the Late Weichselian glacial maximum.

Lake and peat deposits from the Timan Ridge, Arctic Russia, were pollen analysed, reconstructing the vegetation history and paleoenvironment since the Last Glacial Maximum (LGM) 20–18,000 years ago. The sites studied are located inside the margins of a large paleolake of about 20 km 2 , by us named Lake Timan. This lake developed in the Late Weichselian, more than 30,000 years after the deglaciation of this region, and was formed due to increased precipitation and warmer summers that accelerated the melting of stagnant ice within its catchment. The lake was drained during the early Holocene when the outlet rivers eroded the spillways. A new generation of much smaller lakes formed during the Holocene when the last remnants of buried glacier ice melted away causing the exposed floor of Lake Timan to subside. Since deglaciation, the following regional vegetation development has been recorded: (1) During the initial stage of Lake Timan, the dominant vegetation was discontinuous steppe/tundra, with patches of snow bed vegetation. (2) A dwarf-shrub tundra established during the Late Weichselian interstadial (Allerod), probably reflecting warmer and moister conditions. (3) The Younger Dryas cooling is recognised by a reversal to steppe/tundra and snowbeds on unstable mineral-soils, and higher palynological richness. (4) Soon after the transition into the Holocene, a birch-forest established on the Timan Ridge. (5) A cooling starting around 8200 cal. years BP initiated the deforestation of the exposed hills. In the most protected sites, birch trees persisted until later than 4000 years ago, reflecting a gradual development into the present treeless dwarf-shrub tundra.

The history of the Late Weichselian northwestern Barents Shelf, including western Svalbard, has been investigated by provenance/sedimentologist studies of five cores from the continental shelf and slope west of Svalbard. The chronostratigraphy of the cores is based on AMS 14C dates and oxygen isotope analyses. Interpretations of the cores suggest that the ice sheets of western Svalbard and northwestern Barents Sea experienced advances and retreats in two steps. The first significant ice advance beyond the present coastline occurred ca. 22,000 14C yr B.P. and was followed by an ice advance to the shelf edge ca. 18,000 14C yr B.P. Ice recession from the outer shelf and the southwestern Barents Sea began 14,800 14C yr B.P. and was followed by a second ice recession between 13,000 and 12,000 14 C yr B.P. during which ice withdrew from the inner shelf. A minor readvance of the ice sheet on the shelf west of Svalbard occurred close to 12,400 14C yr B.P. The first deglaciation event was associated with release of icebergs containing ice-rafted detritus, while the later episode also included significant amounts of meltwater and fine-grained sediment.