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The sensitivity of mountain glaciers to small-scale climate fluctuations makes records of their past extent among the best proxies for identifying spatio-temporal climate variability. Here we build on the few existing Holocene records of local glacier change in Greenland by using three independent geochronological methods—proglacial lake sediment analysis, cosmogenic 10Be surface-exposure dating, and in situ 14C burial modeling—to reconstruct continuous records of Holocene glacier variability on Nuussuaq, West Greenland. 10Be ages of perched boulders indicate eastern Nuussuaq was deglaciated between ∼11.0 and 10.5 ka. Radiocarbon-dated sediments from two lakes on Nuussuaq contain mineral-rich layers between ∼9.6 and 9.0 and ∼8.7–8.0 cal ka BP that may be correlative with nearby ice sheet moraines deposited in the early Holocene. Multiple proxies for glacier size indicate frequent, high-amplitude glacier fluctuations superimposed on net glacier growth during the late Holocene, with significant ice expansion phases at ∼3.7 ka, 2.8 ka, and throughout the past ∼2 ka. Mean 10Be ages from five nested moraine crests confirm that local glacier extents on Nuussuaq culminated during both the Little Ice Age [∼1470 C.E. (n = 3) and 1750 C.E. (n = 3)] and the preceding centuries (∼520–1320 C.E.; n = 11). Results reveal that local glaciers on Nuussuaq episodically advanced and retreated at centennial timescales throughout the Holocene, most likely in response to regional climate changes in West Greenland superimposed on the progressive insolation-driven cooling trend in the Northern Hemisphere. Our new 10Be moraine chronologies coupled with other glacier-size proxies corroborate an emerging pattern of significant summer cooling and glacier expansion in the centuries prior to the Little Ice Age in the Arctic.

Mountain glaciers and ice caps (GIC) independent of the Greenland Ice Sheet respond rapidly to climate variations and records of their past extent provide information on the natural envelope of climate variability. Here, we use a multi-proxy approach that combines proglacial lake sediment analysis, cosmogenic nuclide surface-exposure dating (in situ 10Be and 14C), and radiocarbon dating of recently ice-entombed moss to generate a centennial-scale record of Holocene GIC fluctuations in southwestern Greenland. Following local deglaciation ∼10-9 ka, sediments from proglacial Crash Lake record a glacier advance at ∼9 ka that is indistinguishable from nearby ice sheet moraines, implying a synchronous response of GIC and the Greenland Ice Sheet to a centennial-scale climate event. Following this local glacier advance, GIC experienced net recession until ∼4.6 ka. Radiocarbon ages of in situ moss (n = 29) and Crash Lake sediments reveal intervals of glacier expansion at ∼1.8, 1.2 and 0.7 ka that are superimposed on an overall trend of net glacier expansion throughout the late Holocene. In situ 14C concentrations from bedrock adjacent to radiocarbon-dated moss samples further constrain the duration of ice cover through the Holocene in this region. We find that our glacier-size proxy records during the past ∼4 ka are broadly consistent with relatively lower temperatures recorded in GISP2 and occur during, or following, intervals of volcanic perturbations. Thus, we speculate that volcanic activity, although less frequent and intense than in the early Holocene and during the Little Ice Age, may have led to centennial-scale variability imprinted on net glacier expansion due to decreasing summer insolation through the late Holocene.

Although humans have impacted their environment over millennia, details of these impacts, especially on aquatic systems, is still surprisingly scarce despite potential disturbance by early land use. This study examined a high-resolution radiocarbon-dated Holocene record from the Danish Lake Vaeng, using geochemical and biological proxies, and related the observed impacts to other lake records with catchment disturbance. The results indicate a lengthy and varying history of aquatic eutrophication linked to human activity. Modest impacts on the lake coincided with the first signs of landscape disturbance during the Neolithic (c. 4500 cal. yrs BP). Observed impacts intensified in the Late Bronze and Pre-Roman Iron Age. Viking Age/Medieval deforestation and erosional inputs to the lake associated with new ploughing technology (1200 cal. yrs BP), however, led to a major reorganisation of the aquatic ecosystem. Filamentous bloom-forming cyanobacteria, common today in heavily culturally impacted lakes, reached a historical maxima. The lake ecosystem subsequently recovered somewhat but remains eutrophic to date. The erosion record from Lake Vaeng shows a striking similarity with other Danish lake records, especially the notable increase in Medieval Period catchment inputs, which are observed in other European lacustrine records. Numerous European lowland lakes may have shifted into a degraded ecological state millennia ago, but degradation intensified during the onset of the Medieval Period. Hence, assuming pre-industrial conditions as relatively pristine reference baselines for more recent cultural eutrophication could be flawed in landscapes intensively used by humans for millennia.

Pockmarks or crater-like depressions formed due to fluid venting, is a well-known geological phenomenon. On a global scale, pockmarks expel a significant amount of fluids and greenhouse gasses to the marine environment and the atmosphere. Despite pockmarks being well-studied, the longevity and history of activity are rarely addressed. In this study, we analyse more than twenty nearshore seafloor depressions of varying morphology and size in the shallow waters of the western Limfjord in northern Denmark. By using high-resolution seismo-acoustic and sediment core data, we characterize the morphology and sediments of the pockmarks. We further use 14C-dating and pore water analyses to address the timing and activity of the depressions. Our results show that the depressions coincide with submarine groundwater discharge areas and hence represent freshwater pockmarks. The pockmarks most likely formed initially due to two eruptive events of thermogenic light oil/gas ca. 2000 and 900 yrs. BP, both triggered by relative sea-level fall. Freshwater seepage continues to sustain and develop the pockmark morphology and we show that pockmarks grow by collapse of pockmark walls and amalgamation of discrete erosive seepage sites at the bottom. The episodic expulsions of thermogenic fluids and the continuous seepage of freshwater probably prolonged the longevity of the studied pockmarks and further demonstrates the complex nature of pockmark formation and activity. While thermogenic and biogenic gas escape to the surface, on the global scale, is relevant for the greenhouse gas budget, the outflow of groundwater which may or may not be polluted is relevant with respect to the geochemistry, biota and productivity of the receiving marine environment especially in shallow water settings.

The Beagle Channel crosses the southernmost tip of South America (Tierra del Fuego), connecting the South Atlantic with the Southeastern Pacific. Raised beaches occur up to 10 m above mean sea level (m a.m.s.l.), especially along the northern (Argentinian) shore, and have been dated using marine shells. The southern (Chilean) shore is well-known for its abundance of shell middens at different levels above the present shore, particularly along the island of Isla Navarino, but the relative sea level history in this glacially impacted landscape has not previously been investigated. In this study we present postglacial relative sea level changes on Isla Navarino, based on sediment cores from six lagoons, bogs or lakes, and stratigraphic investigations of three open sections, of which one is of MIS 5e age. In addition, one core from a lagoon in the south-western Beagle Channel has been analysed and a system of terraces was mapped in the north-western Beagle Channel. The analyses of the core sites have resulted in two tentative relative sea level curves, displaying a rapid sea level rise at 8500−6500 cal yr BP, amounting to ∼10 and 14 m in eastern and western Isla Navarino, respectively, and reaching levels of ∼8 and > 10 m, respectively, followed by a slow relative sea level fall. Our sea level observations have been compared with a range of modelling results of glacial-isostatic adjustments (GIA) for estimating timing of deglaciation and ice sheet thicknesses. Based mainly on the GIA modelling of the altitude of the MIS 5e beach sediments, situated at 13 m, we can conclude that no other uplift than GIA is needed to explain their altitude. Regarding the modelling of postglacial sea levels we can conclude that no model has been found that satisfies all of the observational evidence, but that deglaciation most likely preceded Northern Hemisphere main deglaciation by at least 3 kyr, which agrees with the deglaciation age of Isla Navarino (>16 000 cal yr BP). In addition, our model runs imply that the Patagonian and Tierra del Fuego ice sheet thicknesses were in the order of ∼1500 m.

Limited information on the East Antarctic Ice Sheet (EAIS) geometry during Marine Isotope Stage 3 (MIS 3; 60-25 ka) restricts our understanding of its behaviour during periods of climate and sea level change. Ice sheet models forced by global parameters suggest an expanded EAIS compared to the Holocene during MIS 3, but field evidence from East Antarctic coastal areas contradicts such modelling, and suggests that the ice sheet margins were no more advanced than at present. Here we present a new lake sediment record, and cosmogenic exposure results from bedrock, which confirm that Rauer Group (eastern Prydz Bay) was ice-free for much of MIS 3. We also refine the likely duration of the Last Glacial Maximum (LGM) glaciation in the region. Lacustrine and marine sediments from Rauer Group indicate the penultimate period of ice retreat predates 50 ka. The lacustrine record indicates a change from warmer/wetter conditions to cooler/drier conditions after ca. 35 ka. Substantive ice sheet re-advance, however, may not have occurred until much closer to 20 ka. Contemporary coastal areas were still connected to the sea during MIS 3, restricting the possible extent of grounded ice in Prydz Bay on the continental shelf. In contrast, relative sea levels (RSL) deduced from field evidence indicate an extra ice load averaging several hundred metres thicker ice across the Bay between 45 and 32 ka. Thus, ice must either have been thicker immediately inland (with a steeper ice profile), or there were additional ice domes on the shallow banks of the outer continental shelf. Further work is required to reconcile the differences between empirical evidence of past ice sheet histories, and the history predicted by ice sheet models from far-field temperature and sea level records.

•A synthesis of existing literature on Holocene climate change in Arctic Canada and Greenland.•Warmest-to-coldest millennium temperature change in the Holocene in Arctic Canada and Greenland is 3.0 ± 1.0 °C.•Thermal maximum conditions occurred earlier in high latitudes and at sites less influenced by North Atlantic circulation.

The global climate transition from the Lateglacial to the Early Holocene is dominated by a rapid warming trend driven by an increase in orbital summer insolation over high northern latitudes and related feedbacks. The warming trend was interrupted by several abrupt shifts between colder (stadial) and warmer (interstadial) climate states following instabilities of the Atlantic Meridional Overturning Circulation (AMOC) in response to rapidly melting ice sheets. The sequence of abrupt shifts between extreme climate states had profound impacts on ecosystems which make it challenging to reliably quantify state variables like July temperatures within a non-analogue climate envelope. For Europe, there is increasing albeit inconclusive evidence for higher stadial summer temperatures than initially thought. Here we present a comprehensive floral compilation of plant macrofossils from lake sediment cores of 15 sites from S-Scandinavia covering the period similar to 15 to 11 ka BP. We find evidence for a continued presence of plant species indicating high July temperatures throughout the last deglaciation. The presence of hemiboreal plants in close vicinity to the southern margin of the Fennoscandian Ice Sheet implies a strong thermal summer forcing for the rapid ice sheet melt. Consistent with some recent studies, we do not find evidence for a general stadial summer cooling, which indicates that other reasons than summer temperatures caused drastic setbacks in proxy signals possibly driven by extreme winter cooling and/or shorter warm seasons. (C) 2020 The Authors. Published by Elsevier Ltd.

Records from two connected proglacial threshold lakes at Paakitsoq, west Greenland have been analyzed in order to investigate the response of a land-based ice sheet margin to Holocene climate change. The results are used to test whether or not the land terminating margin at Paakitsoq behaved synchronously with the nearby marine terminating Jakobshavn Isbrae during the Holocene. The radiocarbon dated lake sediment cores indicate that the ice margin retreated to its present position ∼6.5 ka ago and thereafter maintained a relatively stable configuration similar to the present for >1000 years, despite summer temperatures >2 °C higher than today. The lakes became non-glacial after 5.4 cal. ka BP, when the ice margin retreated behind a drainage divide situated ∼1.5 km inland of the present margin. By this time, Jakobshavn Isbrae had already reached its minimum configuration. The Paakitsoq ice margin remained >1.5 km inland of its present margin until after 240 ± 20 cal. yr BP; after this time, both Paakitsoq ice margin and Jakobshavn Isbrae reached their Holocene maxima during the later stage of the Little Ice Age. Our results suggest that the present ice margin position at Paakitsoq is relatively stable in a warming climate but after a total retreat of ∼1.5 km behind the present margin position it may become marine based and more unstable due to marine melting and calving processes.

In situ cosmogenic nuclide exposure age distributions on Ice Age nunataks act as past ice thickness indicators and provide valuable targets for ice sheet model simulations of the Last Glacial Maximum. Several locations along West Greenland have been identified as being potential nunataks due to their weathered nature and their high cosmogenic nuclide inventories with little evidence for ice sheet burial. We present new in situ cosmogenic 14C measurements from four high elevation surfaces in the central Uummannaq Fjord system that were identified as potential nunataks in prior work. Building on previous work, we model cosmogenic radionuclide production and decay, and consider a range of ice sheet history scenarios. Since our results require more burial or shielding under ice than what independent methods suggest for Holocene ice cap cover, we propose that these locations were not nunataks during the Last Glacial Maximum, but rather were buried during the peak of the Last Glacial Maximum. However, we cannot confirm whether these sites were buried by the Greenland Ice Sheet or local glaciers.

In this paper we present new relative sea-level data from southern Greenland, a key area for understanding the Greenland Ice Sheet (GIS) response to climate change. Within fourteen lakes and marine lagoons from the inner part of Bredefjord (Nordre Sermilik) in southern Greenland, isolations revealed by stratigraphic and palaeoecological analyses are dated and relative sea levels reconstructed. Due to coastal emergence caused by the GIS retreat within the area, the relative sea-level fell rapidly in the early Holocene between at least c. 9600 and c. 7300 cal. yrs BP attaining a rate of 2 cm per year between 9600 and 8000 cal. yrs BP. Spatial variability in relative sea-level changes is show for southern Greenland from a comparison with the Nanortalik and the Qagortoq areas. The regression occurred about 2000 years later in the inner Bredefjord area, compared to the Nanortalik area, and about 1000 years later compared to the Qaqortoq area. This is a consequence of earlier deglaciation in areas located at the outer coast. Between c. 8000 cal. yrs BP and the present day, relative sea level was lower than today. The lowest relative sea level in the Inner Bredefjord area of between -5.4 and -15 m a.h.a.t. (above highest astronomical tide) was reached between 7000 and 1000 cal. yrs BP. The neoglacial readvance together with the collapse of the Laurentide peripheral bulge is probably responsible for the transgression in the Inner Bredefjord area, as has been indicated from the nearby sites Qagortoq and Nanortalik. Our relative sea-level reconstructions showing spatial variability within southern Greenland have implications for Glacial Isostatic Adjustment (GIA) modelling and the understanding of the GIS ice sheet dynamics. The early Holocene regression is consistent with the recession of the southern sector of the GIS from the shelf edge at c. 22 000 cal. yrs BP, reaching inland of the present day outer coast by c. 12 000 cal. yrs BP, and its present margin by c. 10 500 cal. yrs BP. (c) 2013 Elsevier Ltd. All rights reserved.

The Greenland Ice Sheet is undergoing dynamic changes that will have global implications if they continue into the future. In this regard, an understanding of how the ice sheet responded to past climate changes affords a baseline for anticipating future behavior. Small, independent ice caps adjacent to the Greenland Ice Sheet (hereinafter called “local ice caps”) are sensitive indicators of the response of Greenland ice-marginal zones to climate change. Therefore, we reconstructed late Holocene ice-marginal fluctuations of the local Istorvet ice cap in east Greenland, using radiocarbon dates of subfossil plants, 10 Be dates of surface boulders, and analyses of sediment cores from both threshold and control lakes. During the last termination, the Istorvet ice cap had retreated close to its maximum Holocene position by ∼11,730 cal yr BP. Radiocarbon dates of subfossil plants exposed by recent recession of the ice margin indicate that the Istorvet cap was smaller than at present from AD 200 to AD 1025. Sediments from a threshold lake show no glacial input until the ice cap advanced to within 365 m of its Holocene maximum position by ∼AD 1150. Thereafter the ice cap remained at or close to this position until at least AD 1660. The timing of this, the most extensive of the Holocene, expansion is similar to that recorded at some glaciers in the Alps and in southern Alaska. However, in contrast to these other regions, the expansion in east Greenland at AD 1150 appears to have been very close to, if not at, a maximum Holocene value. Comparison of the Istorvet ice-cap fluctuations with Holocene glacier extents in Southern Hemisphere middle-to-high latitude locations on the Antarctic Peninsula and in the Andes and the Southern Alps suggests an out-of-phase relationship. If correct, this pattern supports the hypothesis that a bipolar see-saw of oceanic and/or atmospheric circulation during the Holocene produced asynchronous glacier response at some localities in the two polar hemispheres.

Sediment cores from Kriegers Flak in the southwestern Baltic Sea provide a unique possibility to study the Middle Weichselian history of the Baltic Basin. Three Weichselian interstadial units have been identified and are attributed to Marine Isotope Stage 3 (MIS 3, 60–25 ka). The oldest unit A is characterized by a deglaciation sequence, gradually turning into brackish-water clay. The low-diversity benthic foraminiferal fauna, stable oxygen isotope values and Mg/Ca ratios indicate low temperature and salinity for unit A. A hiatus separates unit A from the overlying unit B, which was deposited in wetlands and shallow lakes between 42 and 36 cal. ka BP. Macrofossil and pollen analyses indicate deposition of unit B in an area dominated by a tree-less open tundra environment, possibly with some birch and pine in sheltered positions. The uppermost unit C is characterized by clay deposition, including redeposition of material from older sediments (unit B). Optically stimulated luminescence (OSL) ages indicate deposition of unit C between 26 and 28.5 ka. Radiocarbon ages of 39 and 40 cal. ka BP for unit C are considered to be too old. The following depositional model is suggested: (I) Isostatic depression of the region after an advance of the Scandinavian Ice Sheet (SIS), most likely the Ristinge ice advance, previously dated to c. 55–50 ka, enabled an inflow of marine waters into the Baltic Basin during the deposition of unit A. (II) Isostatic rebound caused a regression at Kriegers Flak, and a hiatus between units A and B. (III) Wetlands and smaller lakes formed in the uplifted area between 42 and 36 cal. ka BP (unit B). (IV) Deposition of glaciolacustrine clays at Kriegers Flak demonstrates that a growing SIS dammed Kattegat and the Baltic Basin c. 28.5 to 26 ka. The new evidence from Kriegers Flak provides a solid framework for future MIS 3 palaeoenvironmental reconstructions in the circum-Baltic area.

The outer coast of Finnmark in northern Norway is where the former Fennoscandian and Barents Sea ice sheets coalesced. This key area for isostatic modelling and deglaciation history of the ice sheets has abundant raised shorelines, but only a few existing radiocarbon dates constrain their chronology. Here we present three Holocene sea level curves based on radiocarbon dated deposits from isolation basins at the outermost coast of Finnmark; located at the islands Soroya and Rolvsoya and at the Nordkinn peninsula. We analysed animal and plant remains in the basin deposits to identify the transitions between marine and lacustrine sediments. Terrestrial plant fragments from these transitions were then radiocarbon dated. Radiocarbon dated mollusk shells and marine macroalgae from the lowermost deposits in several basins suggest that the first land at the outer coast became ice free around 14,600 cal yr BP. We find that the gradients of the shorelines are much lower than elsewhere along the Norwegian coast because of substantial uplift of the Barents Sea. Also, the anomalously high elevation of the marine limit in the region can be attributed to uplift of the adjacent seafloor. After the Younger Dryas the coast emerged 1.6–1.0 cm per year until about 9500–9000 cal yr BP. Between 9000 and 7000 cal yr BP relative sea level rose 2–4 m and several of the studied lakes became submerged. At the outermost locality Rolvsoya, relative sea level was stable at the transgression highstand for more than 3000 years, between ca 8000 and 5000 cal yr BP. Deposits in five of the studied lakes were disturbed by the Storegga tsunami ca 8200–8100 cal yr BP.

The last millennium is a key period for understanding environmental change in eastern Africa, as there is clear evidence of marked fluctuations in climate (effective moisture) that place modern concern with future climate change in a proper context, both in terms of environmental and societal impacts and responses. Here, we compare sediment records from two small, nearby, closed crater lakes in western Uganda (Lake Kasenda and Lake Wandakara), spanning the last 700 (Wandakara) and 1200 years (Kasenda) respectively. Multiproxy analyses of chemical sedimentary parameters (including C/N ratios, δ13C of bulk organic matter and δ13C and δ18O of authigenic carbonates) and biotic remains (diatoms, aquatic macrofossils, chironomids) suggest that Kasenda has been sensitive to climate over much of this period, and has shown substantial fluctuations in conductivity, while Wandakara has a more muted response, likely due to the increasing dominance of human activity as a driver of change within the lake and catchment over the length of our record. Evidence from both records, however, supports the idea that lake levels were low from ∼AD 700–1000 AD, with increasing aridity from AD 1100–1600, and brief wet phases around AD 1000 and 1400. Wetter conditions are recorded in the 1700s, but drought returned by the end of the century and into the early 1800s, becoming wetter again from the mid-1800s. Comparison with other records across eastern Africa suggests that while some events are widespread (e.g. aridity beginning ∼ AD 1100), at other times there is a more complex spatial signature (e.g. in the 1200s to 1300s, and from the 1400s to 1600s). This study highlights the important role of catchment-specific factors (e.g. lakemorphometry, catchment size, and human impact) in modulating the sensitivity of proxies, and lake records, as indicators of environmental change, and potential hazards when regional inference is based on a single site or proxy.

Detailed acoustic mapping have been carried out in the Arhus Bay in order to establish the general Late Weichselian and Holocene stratigraphy, and to map the gas related acoustic blanking. The mapping results show that the oldest seismic unit is glacial till, probably related to the latest glacial advance in the region. The glacial till is covered by late-glacial ice-lake clay and silt reaching a thickness of up to 10 m. In the deeper part of the bay, early Holocene organic material and peat has been recorded in a few cores. A thin seismic unit is observed, which probably represents an early Holocene lowstand period, when most of the Arhus Bay was dry land. The three upper seismic units are related to the Holocene transgression of the region representing different hydrographical conditions. The lowermost unit (Marine unit 1) partly drapes the basin area with clay sediments and partly shows prograding sandy coastal deposits around glacial ridges. Marine shells from this unit date back to 8700 cal. years BP which are the oldest marine shells found south of the threshold in the northern Great Belt. The next unit (Marine unit 2) consists in general of mud to sandy mud, which cover most of the western central part of the Arhus Bay and in some places reach the present seabed in areas of erosion or non-deposition. The distribution of the youngest seismic unit (mud, Marine unit 3) is confined to the sub-recent to recent sedimentation basins in the eastern central part of the area. Acoustical blanking shows that the methane production takes place in the Holocene marine sediments. A map of the distribution and depth to free methane in the muddy sediments has been produced. Combined information from the different seismic equipment used allowed a mapping of the distribution and depth to free gas in the intervals 0.5–2, 2–4 and >4 m. The map shows that acoustic blanking is found in the central part of Arhus Bay about 4 m below the seabed. In areas with high sedimentation rate, the acoustic blanking is found closer to the sediment surface and in selected key stations, pore-water chemistry have documented that depth to acoustical blanking is comparable to the methane saturation depth. Barotropic induced inflow dominates the present current system in the semi-enclosed Arhus Bay. The inflow events create turbulence in the outer eastern parts of the bay, followed by high sedimentation rates. The recent situation is reflected in the seabed sediments in the eastern part of the bay, which are characterised as soft sandy mud deposits, with gas bubbles close to the seabed. Seismic investigations have not previously been used to identify recent sedimentation areas and the most vulnerable areas in respect to possible escape of methane and toxic hydrogen-sulphide. The results of the present survey show that future monitoring must be focused in shallow gas areas in the eastern-most part of Arhus Bay.

In this review, we compile the evidence of lake and isolation basin sediments for the chronology of the last deglaciation along the coastal parts of eastern Greenland between 70°N and 83°N. Radiocarbon dates of remains of freshwater plants and bulk organic carbon extracted from lacustrine sediments suggest that the present day ice-free parts of eastern Greenland were not deglaciated prior to the early Holocene. Older dates do exist but must be used with caution due to possible contamination with old carbon. However, many inland locations in eastern North and central East Greenland became ice-free distinctly later between 10,000 and 7500 cal yr BP, depending on their relative position to the ice margin. This compilation confirms former suggestions that hitherto no secure Late glacial lacustrine sediments have been found in the ice-free parts of eastern Greenland. Late glacial sediments are only known from lakes in southern Greenland and from few marine locations off eastern Greenland. The here summarized lake sediment evidence for the last deglaciation supports the results of an earlier compilation of dates from marine shells. © 2007 Elsevier Ltd. All rights reserved.

Multi-proxy palaeoenvironmental studies of nine sediment sequences from four areas in north-western Russia reveal significant changes in climate, lake productivity and vegetation during the Lateglacial and early Holocene that show some degree of correlation with changes reconstructed from sites throughout the North Atlantic region. At Lake Nero in the Rostov-Jaroslavl’ area, which is outside the maximum limit of the Scandinavian Ice Sheet, sedimentation recommenced shortly after 15 cal ka BP in response to increases in temperature and humidity during Greenland Interstadial 1 (GI-1; Bolling-Allerod). However, climatic amelioration during GI-1 was slow to increase lake organic productivity or trigger large-scale changes in much of northwestern Russia. In general, this region was characterised by long-lasting lake-ice cover, low lake productivity, soil erosion, and dwarf shrub and herb tundra until the end of Greenland Stadial 1 (GS-1; Younger Dryas). At some sites, distinct increases in lake organic productivity, mean summer temperatures and humidity and the expansion of forest trees coincide with rapid warming at the beginning of the Holocene and the increasing influence of warm air masses from the North Atlantic. At other sites, particularly on the Karelian Isthmus, but also in Russian Karelia, the delayed response of limnic and terrestrial environments to early Holocene warming is likely related to the cold surface waters of the Baltic Ice Lake, the proximity of the Scandinavian Ice Sheet and associated strengthened easterlies, and/or extensive permafrost and stagnant ice. These multi-proxy studies underscore the importance of local conditions in modifying the response of individual lakes and their catchments. While Lateglacial vegetation was dominated by Betula nana and Salix shrubs and various herbs, pollen and plant macrofossils suggest that Betula pubescens trees became established as early as 14–13 cal ka BP in the Rostov-Jaroslavl’ area. In general, our data sets suggest that trees migrated from the southeast to the west and then spread later to the northeast and northwest, paralleling the direction of ice retreat, with Betula pubescens immigrating first, followed by Pinus sylvestris and Picea abies. However, palaeoecological records from Lake Terebenskoye in the Valdai Highlands suggest that the arrival of Picea abies preceded other trees in that area and that it colonised tundra communities as early as 12 cal ka BP. Since Lateglacial vegetation change in north-western Russia was time-transgressive, independent measures of palaeoclimate (e.g., chironomid-based palaeotemperature estimates) are needed for this region. r 2007 Elsevier Ltd. All rights reserved.

The warmest millennia of at least the past 250,000 years occurred during the Last Interglaciation, when global ice volumes were similar to or smaller than today and systematic variations in Earth's orbital parameters aligned to produce a strong positive summer insolation anomaly throughout the Northern Hemisphere. The average insolation during the key summer months (M, J, J) was ca 11% above present across the Northern Hemisphere between 130,000 and 127,000 years ago, with a slightly greater anomaly, 13%, over the Arctic. Greater summer insolation, early penultimate deglaciation, and intensification of the North Atlantic Drift, combined to reduce Arctic Ocean sea ice, allow expansion of boreal forest to the Arctic Ocean shore across vast regions, reduce permafrost, and melt almost all glaciers in the Northern Hemisphere. Insolation, amplified by key boundary condition feedbacks, collectively produced Last Interglacial summer temperature anomalies 4–5 °C above present over most Arctic lands, significantly above the average Northern Hemisphere anomaly. The Last Interglaciation demonstrates the strength of positive feedbacks on Arctic warming and provides a potentially conservative analogue for anticipated future greenhouse warming.

The late glacial and the early Holocene sediments of the classic site Bolling So in Denmark are being reinvestigated by multi-proxy analyses. We present here the record of Pediastrum species and discuss the climate-mediated changes in the aquatic ecosystem, as reflected by aquatic proxies (e.g. aquatic plants and mosses, cladocerans, ostracods, bryozoan statoblasts), as well as a number of other proxies (organic content, biogenic silica, carbonates, terrestrial plant macrofossils). Climate had warmed to such an extent at c. 12,500 14 C yrs BP that aquatic life could begin. Productivity was low and only very scarce indication of a warmer interval predating the Allerod chronozone was found. At the beginning of the Allerod chronozone climate ameliorated and productivity clearly increased. The cool climate of the Younger Dryas chronozone (YD) was more clearly reflected in the terrestrial ecosystem than in the aquatic ecosystem, where productivity appeared to remain rather high. The lake was very shallow and non-stratified during the YD, indicating low effective moisture. Probably it warmed throughout early in the open-water season and in that way enabled higher productivity, even if summer temperatures were rather low. It is also possible that the difference in July temperatures between the late part of the Allerod chronozone and the YD was not large in central Jutland. The amelioration of climate at the beginning of the Holocene is clearly reflected in all proxies. There is also evidence that the lake level rose. The lake probably remained alkaline during all of its history but some evidence suggests that pH was somewhat lowered during the YD chronozone. Pediastrum species appear to be relatively good indicators of environmental conditions; similarly, the concentrations may reflect productivity variations during changing climatic conditions.

A Holocene lacustrine record in the central North Atlantic: proxies for volcanic activity, short-term NAO mode variability, and long-term precipitation changes

Biostratigraphical and palaeoecological analyses of cores along a transect from Femer Belt to the Arkona Basin reveal that North Sea waters began to enter the western Baltic Sea between 8600 and 8400 calibrated years BP. Studies of diatoms indicate that Mecklenburg Bay was characterised by slightly brackish-water conditions between 8400 and 8000 cal. years BP. At around 8000 cal. years BP increasing salinity is indicated by a strong dominance of the diatoms Paralia sulcata and Dimeregramma minor. Some centuries later another diatom assemblage appeared and became dominant in Mecklenburg Bay. This assemblage includes Hyalinella lateripunctata and Pravifusus hyalinus species typical of shallow water areas along the Atlantic coast today. At this time the first marine molluscs made their appearance. The oldest shell of a marine mollusc found in our material is dated to 7600 cal. years BP. The associated assemblage that includes adult specimens of the gastropod Aporrhais pespelicani indicates higher salinities than today. During the Littorina Sea stage a marine diatom flora with P. sulcata, Catenula adhaerens and D. minor crossed the Darss Sill and became widely distributed in the Arkona Basin, Pomeranian Bay and the Baltic Sea proper. In contrast, taxa indicative of the Hyalinella lateripunctata/P. hyalinus assemblage are only found west of the Darss Sill in Femer Belt and Mecklenburg Bay. Apparently, the Darss Sill threshold has been acting as an important salinity border from around 7800 cal. years BP until today.

A multi-technique approach has been used to study a Pliocene shallow water marine deposit, designated the Ile de France Formation, in North-East Greenland. The sequence is correlated on the basis of 87Sr–86Sr ratios in shells and palaeomagnetic studies with the Gauss normal polarity chron, which is dated to between 2.60 and 3.58 Ma years BP. This dating is in accordance with amino acid epimerisation and evidence from dinoflagellates, foraminifers and molluscs. Sediments, marine molluscs and foraminifers show that the sequence was deposited on the inner shelf, below storm wave base. Seawater temperatures were much higher than today, as demonstrated by the occurrence of a number of southern extra-limital species. The same applies to air temperature, and the few remains of land plants may indicate a forested upland with Picea and Thuja. A number of extinct taxa are present, including Nucula jensenii that is erected as a new species.

The subsurface geology relevant to the submarine freshwater seepage in Eckernforde Bay has been investigated using shallow seismic instruments and vibrocoring. Detailed surveying revealed that the pockmarks are aligned like pearls on a string or densely clustered in furrow-like structures depending on the glacial and postglacial setting of the underlying strata. Two possible aquifers have been verified: The older Miocene sand aquifer is partly sealed by a till unit forming the central part of the Mittelgrund. The younger aquifer consists of a mixture of glacial till and meltwater sediments partly sealed by till and partly by lateglacial galciolacustrine silt and clay sediments. The investigations imply that connections exist between the aquifers and that groundwater leakage takes place in the marginal zones of the bay due to thinning and coarsening of the sediment composition of the lateglacial seal. Within the seepage areas, the pockmarks are restricted to areas covered by unconsolidated Holocene mud of low thickness’ that are easy to penetrate by artesian groundwater. Macrofossil studies and AMS 14 C dating of the lateglacial and Holocene units reveal that the Mittelgrund shoal of glacial origin has been modified by coastal processes and formation of cuspate foreland deposits during the subsequent palaeo-lake phases of 15–20 m below the present sea level (b.s.l.). The lake phases correlate in time with the regional Baltic Ice Lake highstand about 10,000 14 C years BP and the Ancylus Lake highstand about 9200 14 C years BP. This means that local contemporary lakes existed or the western margin of the regional lakes can be moved considerably further west than expected hitherto. In the earliest phase of the Littorina Sea transgression, the Mittelgrund shoal was exposed to coastal erosion once more before the final drowning and the initiation of mud sedimentation in the surrounding basins took place.

Marine–lacustrine isolation contacts from seven basins in the Nanortalik area, South Greenland have been analysed and dated. The basins were isolated from the sea as a consequence of isostatic rebound following deglaciation. The isolation contacts were identified with litho- and biostratigraphical analyses, especially sedimentary changes, grey scale analyses and analyses of macroscopical remains of plants and animals. Dating was performed by analytical mass spectroscopy radiocarbon dating of macrofossils and bulk sediment samples. A slow initial relative sea level fall that begins at 13.8 cal ka BP changes to a rapid relative sea level fall before the sea level fell below the present-day sea level just prior to 10 cal ka BP. The emergence curve goes further back in time than any previous emergence curve constructed from Greenland, which reflects the early deglaciation of the studied region. The glacio-isostatic crustal rebound following deglaciation was around 110 m. The sea level history indicates that the margin of the Greenland ice sheet probably extended out to the shelf margin during the Last Glacial Maximum, and that the ice thickness must have been at least 1500 m over the outer coast. Thus the highest coastal mountains would have been ice-covered, which is surprising given their alpine character. In addition, the major part of the recession of the ice must have occurred relatively late and quickly, maybe from 14 to 12 cal ka BP. The late Holocene transgression may, at least in part, be due to increased isostatic loading as a consequence of advancing glaciers during the Neoglaciation.

Since the final Weichselian deglaciation the water exchange between Kattegat and the Baltic Sea and hence the palaeogeographical development of the (western) Baltic has been controlled by a number of sills. Major thresholds are found at the southern entrance of the Great Belt and in the Darss Sill area. The easternmost of these structures is formed by Late Weichselian sands at a level of 24 m below present sea level (bsl) at the Falster–Rugen sand plain. A second threshold consisting of till was found within the Kadet Channel at a level of 23–24 m bsl. Thus, we exclude water exchange between Mecklenburg Bay and the Arkona Basin at levels below 24 m since the end of the Pleistocene. A high resolution sediment echosounder survey at the triple junction area of Langeland Channel, Vejsnaes Channel and Winds Grave Channel showed outcropping glacial deposits. Narrow channels incised at a level below 25 m bsl are filled partly with fine grained organic rich late- and postglacial sediments. Assuming no substantial crustal movements in this area in the Holocene no Ancylus Lake drainage at a level deeper than 25 m bsl is likely to have occurred here.

Colonisation by plants and animals and subsequent biotic development in west Greenland was studied by analyses of macrofossils in four Holocene lake sequences. One of the lake basins, located near the outer coast, was deglaciated shortly after the transition from the last glacial stage to the Holocene, and a basal date of 12,100–11,300 cal. years BP was obtained. Two of the lake basins located near the margin of the Greenland ice sheet were deglaciated several millennia later. The oldest sediments contain low-diversity floras and faunas. Some of the first immigrants were Chironomidae and Daphnia pulex, soon followed by other insects, crustaceans and other invertebrates. Water mosses, Ranunculus confervoides, Hippuris vulgaris and Potamogeton filiformis were among the first plants that colonised the lakes. The earliest Holocene terrestrial flora in west Greenland was probably entirely herbaceous, with Salix herbacea and Empetrum nigrum being some of the first woody plants to arrive. A number of invertebrates are new to the fossil fauna of Greenland, and the ostracod Ilyocypris bradyi that was found in one sequence, from 7000 to 6500 cal. years BP, has not been recorded from Greenland before.

Early Holocene finds of the freshwater plant Stratiotes aloides L. (water soldier) are reported from southern Sweden and the southwestern Baltic Sea for the first time. However, the species has previously been reported from Late Glacial deposits from Poland and The Netherlands, and from early Holocene deposits from Finland. Thus the species was an early immigrant to northwestern Europe after the last glacial maximum.

Thirteen of 18 piston cores recovered from ‘Robinson Lake’ in the mid-Arctic vegetation zone of Baffin Island, Arctic Canada, penetrated stratified lacustrine sediment beneath a thin over-consolidated diamict (till) and postglacial lacustrine sediment. The sub-till lacustrine units are up to 120 cm thick, of which the upper several decimeters frequently contain thick, layered mats of aquatic moss; pollen and diatoms are common throughout both lacustrine units. A series of 23 AMS 14C dates defines the chronology of the postglacial sequence, which records a succession from a pioneer grass- and Oxyria-dominated tundra between 10.4 and 8 ka BP, to a sedge-dominated tundra after 8 ka BP. Limiting 14C dates place the sub-till lacustrine sediments more than 40 ka BP; 10 luminescence dates centered on 85 ka indicate they were deposited late in oxygen isotope stage (OIS) 5. The dominance of shrub and tree pollen, especially shrub birch and alder, in sub-till lacustrine samples, indicates low-arctic tundra farther north than at any time during the Holocene. Pollen concentrations are comparable to or higher than in the Holocene units. Cooling late in the interglacial is indicated by declining birch and alder pollen percentages in the upper part of the section. Diatom floras in both the sub-till and postglacial lacustrine sequences indicate similar development of lake-water chemistry, but input of silica and weathering products was greater in the older lake cycle, suggesting more vigorous catchment processes. Macrofossils in the sub-till units are characteristic of lakes ice-free in summer. Based on pollen assemblages indicating local and regional vegetation diagnostic of summer temperatures higher than the Holocene, we interpret the sub-till lacustrine units to be of interglacial character. By analogy with Holocene plant succession in central and eastern Canada, all of Keewatin and Labrador/Ungava must have been ice free throughout this interval, suggesting essentially complete deglaciation of the Laurentide Ice Sheet at the time.

Remains of fishes, birds and mammals are rarely reported from Quaternary deposits in Greenland. The oldest remains come from Late Pliocene and Early Pleistocene deposits and comprise Atlantic cod, hare, rabbit and ringed seal. Interglacial and interstadial deposits have yielded remains of cod, little auk, collared lemming, ringed seal, reindeer and bowhead whale. Early and Mid-Holocene finds include capelin, polar cod, red fish, sculpin, three-spined stickleback, Lapland longspur, Arctic hare, collared lemming, wolf, walrus, ringed seal, reindeer and bowhead whale. It is considered unlikely that vertebrates could survive in Greenland during the peak of the last glaciation, but many species had probably already immigrated in the Early Holocene.