Boreas最新文献

Svalbard spans large climate gradients, associated with atmospheric circulation patterns and variations in ocean heat content and sea ice cover. Future precipitation increases are projected to peak in the northeast and to mainly occur in winter, but uncertainties underscore the need for reconstructions of long-term spatial and temporal variations in precipitation amounts and seasonality. We use lipid biomarkers from four sedimentary lake records along a climatic gradient from western to northeastern Svalbard to reconstruct Holocene water cycle changes. We measured the leaf wax hydrogen isotopic composition of long-chain (terrestrial) and mid-chain (aquatic) n-alkanoic acids, reflecting δ²H of precipitation (δ²H_precip) and lake water (δ²H_lake), respectively. δ²H_precip values mainly reflect summer precipitation δ²H and evapotranspiration, whereas δ²H_lake values can reflect various precipitation seasonality due to varying lake hydrology. For one lake, we used the difference between δ²H_precip and δ²H_lake (ε_precip-lake) to infer summer evapotranspiration changes. Relatively ²H-enriched δ²H_precip values and higher ε_precip-lake in the Early and Middle Holocene suggest warm summers with higher evapotranspiration, and/or more proximal summer moisture. After c. 6 cal. ka BP, ²H-depleted δ²H_precip values and lower ε_precip-lake indicate summer cooling, less evapotranspiration, or more distally derived moisture. Early to Middle Holocene decrease in δ²H_lake values in two northern Spitsbergen lakes reflects an increase in the proportion of winter relative to summer precipitation, associated with regional warming and increased moisture supply, which may be due to increased distal moisture supply and/or reduced sea ice cover. Our northern Svalbard δ²H_lake records suggest great Late Holocene climate variability with periodic winter precipitation increases or decreases in summer precipitation inflow to the lakes. We find that Holocene summer precipitation δ²H values mainly follow changes in summer insolation and temperature, whereas the seasonal distribution of precipitation is sensitive to catchment hydrology, regional ocean surface conditions, and moisture source changes.

The postglacial recolonization of Fennoscandian flora and fauna was initiated when the land became accessible as the last ice sheet retreated. In northern Sweden, plants are represented in pollen and macrofossil records, but there is no genetic evidence from the first plants, animals or humans in the region, mainly owing to an absence of osteological finds. The questions of who the first postglacial peoples, or pioneers, were and where they came from therefore remain unanswered. Previous palaeogenomic analyses from remains from adjacent regions have suggested that two main routes into Sweden could have been taken by the pioneers, one from the SW through modern-day Denmark and Norway, and one from the east via Finland. However, no direct genetic evidence from the pioneers of northern Sweden exists. Modern technology has provided the ancient DNA field with an updated toolbox that could allow for novel approaches for revealing the origin and genetic profiles of the first Scandinavians, of which sedimentary ancient DNA (sedaDNA) is well placed. Lake sediments are now a routine source of sedaDNA that have been used to record environmental changes and detect species that lived in the surrounding lake catchment. This review will provide context and background, a summary of the ground-breaking studies within the field of lacustrine sedaDNA, and relevant methodology to address the scientific questions at hand. We conclude that the field is mature enough to provide insight into the origins and arrival times of the first postglacial humans that migrated into northern Sweden.

The Koksu River valley is located in the Pamir-Alay mountain range and contains 25 glaciers larger than 1 km² and numerous smaller glaciers. The largest glacier in the catchment is Abramov Glacier with a current surface area of 22.55 km² (in 2022), which was extensively monitored between 1965 and 1999, and resumed in 2011. The long and detailed mass balance time series provide, among other information, benchmark climate variables for the Pamir-Alay range. We report 10 new cosmogenic ¹⁰Be exposure dates of glacial moraines directly deposited by Abramov Glacier to extend the glacial history of the valley. Six boulders indicate that the Local Last Glacial Maximum occurred at 17.1±1.0 ka. Four boulders suggest a Little Ice Age (LIA) glacial advance around AD 1750. Secular glacier mass balance reconstructions suggest a progressively negative mass balance since the LIA advance. The decrease in mass balance accelerated in the last quarter of the 20th century. Results from repeated ground penetrating radar (GPR) measurements suggest that Abramov Glacier lost about 403 million m³ of ice volume between 1986 and 2018. Based on the reconstruction of the glacier surface, the corresponding equilibrium line altitude, which is closely correlated with the mass balance, increased by about 70 to 80 m during this period. Our results also suggest that Abramov Glacier has become increasingly out of equilibrium with the climate over the last two decades. This is supported by repeated GPR measurements of the tongue area, which indicate a dramatic decrease in glacier area and ice volume over the period 1986–2018.

The calcareous tufa sequence and associated Palaeolithic site of Caours were discovered in 2002 during a test-pit campaign aimed at identifying last interglacial (MIS 5e) archives in the fluvial terrace system of the Somme basin, northern France. The presence of an outstanding stratigraphical succession with four in situ Palaeolithic layers within the tufa sequence has motivated archaeological excavations of the site since 2005. The first malacological studies and U-series ages quickly showed that the sequence was mainly deposited during the Eemian interglacial (MIS 5e). After 20 years of investigations, we propose here a summary of this multidisciplinary research project including stratigraphy, sedimentology, geochronology, geochemistry, malacology, mammals, palaeovegetation and archaeology. By combining 25 dates obtained by U-series, ESR/U-series, TL and OSL methods, the Caours calcareous tufa sequence is securely dated to the Eemian (123.1±2.8 ka). Based on the summary of the whole information, we propose a robust and detailed reconstruction of the modification of the valley environments between the Late Saalian and the Early Weichselian. At the scale of northwestern Europe, Caours provides a reference terrestrial molluscs record for the Eemian interglacial, including the climatic optimum, that is also described in the same layers by δ¹⁸O and δ¹³C analyses on calcite and by mammal remains. Moreover, the 300-m-long transect crossing the fluvial terrace covered by the tufa sequence and the bottom valley formation, combined with the chronology established from U-series and OSL ages, shows that the incision of the present-day valley, leading to the setting of the Very Low Terrace, was achieved during the first stages of the Early Weichselian (MIS 5d–5c). From an archaeological point of view, the configuration of the Caours site is unique at the scale of western Europe and demonstrates the adaptation of Neandertals to a forested environment and to fully temperate conditions during the Eemian.

The interglacial known as MIS 11c (c. 426 000–396 000 years ago) receives intensive international interest because of its perceived role as an analogue for the current interglacial and its importance for understanding future climate change. Here we review the current understanding of the stratigraphy of this interglacial in Europe. This study considers (i) the evidence for the environmental history of this interglacial as reconstructed from the varved lake records from northern Europe, (ii) the climate history of MIS 11c as preserved in the long pollen records of southern Europe and (iii) a comparison of both of these with marine records from the North Atlantic. The result of this review is a discussion of the evidence for millennial and centennial scale climate change found in European records of MIS 11c, the patterns of warming that are seen across this interglacial and the discrepancy in aspects of the duration of this interglacial that seems to exist between the marine and terrestrial records of this warm period. A review of the recent advances in the study of MIS 11c in Europe confirms its importance for understanding both the past evolution of the Holocene and the future patterns of long-term climate change.

Environmental changes on the northern Taymyr Peninsula were reconstructed based on a new pollen record from a 46-m-long sediment core recovered from Lake Levinson-Lessing (latitude 74°27′54″N, longitude 98°39′58″E). The record is continuous and has a relatively good age control and high temporal resolution. Reaching a basal age of 62 cal. ka BP, it provides a unique environmental archive for the central Russian Arctic. The results reveal that open landscapes dominated 62.0–50.8 cal. ka BP, but presence of shrubs reflects a relatively warm summer climate. Numerous Pediastrum colonies in the sediments point to a rather low lake stand. A decrease in algae remains in the pollen spectra reflects a higher lake level after c. 50.8 cal. ka BP. From c. 47.8 to 25.5 cal. ka BP, lower contents of Betula and higher percentages of herb pollen point to colder and drier conditions. Besides, larger amounts of Pre-Quaternary palynomorphs and Pediastrum colonies point to increased erosion processes and a lower lake stand. After c. 25.5 cal. ka BP, herb communities further increased. Poaceae and Artemisia show the highest contents between c. 20.3 and 19.2 cal. ka BP, suggesting the coldest and driest climatic conditions during the studied time interval coincident with the Last Glacial Maximum (LGM). Pollen spectra dated c. 19.20–16.05 cal. ka BP reflect a slightly warmer and wetter climate in comparison to the LGM. Increased amounts of coprophilous fungi spores indirectly indicate that grazing animals were abundant around the lake. After с. 16.05 cal. ka BP, increases in shrubs and sedges reflect somewhat warmer and/or wetter conditions. The pollen data also well document the Allerød warming and Younger Dryas cooling events, reflecting an Atlantic influence on the regional climate development during these times. The transition from the Lateglacial to the Holocene at c. 11.63 cal. ka BP is characterized by drastic increases in pollen of shrubs, which document a significant warming. The Early Holocene (c. 11.63–8.30 cal. ka BP) pollen spectra reflect the Holocene Thermal Maximum in the study region. After c. 8.3 cal. ka BP, gradual cooling prevailed and led to climate conditions similar to modern ones at c. 2 cal. ka BP.

We present the first climatic and environmental reconstruction based on subfossil chironomid head capsules from the Middle Pleistocene Reinsdorf sequence, Schöningen, northern Germany, corresponding to Marine Isotope Stage 9e-a. The sequence is characterized by interglacial forest successions followed by alternating woodland and steppe phases. Higher levels of runoff formed lacustrine habitats during post-interglacial, cool steppe (woodland) phases. These were characterized by diverse chironomid assemblages with up to 27 chironomid morphotypes occurring simultaneously. Warmer forest phases were mostly void of chironomids when the site Schöningen 13 II fell dry owing to higher vegetational coverage and therefore lower runoff. Transitional periods between woodland and steppe phases show higher abundances of profundal, bottom-dwelling chironomid taxa, suggesting oligo-mesotrophic aquatic conditions, while steppe phases are dominated by shallow-lake taxa with higher tolerance to increasing productivity. We applied temperature inference models to the chironomid assemblages based on a Swiss–Norwegian and a Swiss–Norwegian–Polish chironomid–temperature calibration data set to reconstruct mean July air temperatures for the Reinsdorf sequence. The Swiss–Norwegian–Polish training set (TS) seems better suited owing to a longer temperature gradient and the presence of the dominant taxon, Propsilocerus lacustris-type, which is missing from the Swiss–Norwegian TS. In sections of the record with low taxon richness (Shannon index <2) and a dominance of P. lacustris-type, indicating increased nutrient impact, summer temperatures may have been overestimated by the Swiss–Norwegian–Polish TS. In the other sections, the chironomid-based reconstructions based on the Swiss–Norwegian–Polish TS were in line with ostracod and plant remains-based temperature reconstructions, suggesting summer temperatures of the post-interglacial Reinsdorf oscillations between 16.5 and 22 °C. Our results show that summer air temperatures were lower during warmer, wetter transitional zones (−0.5–0.2 °C colder/warmer than today) and increasing during cooler, dry steppe phases (1 °C warmer than today), most likely caused by higher continentality.

Here we present a new eastern Baltic Chironomidae training set (TS) containing 35 sites that was collected and merged with neighbouring published Finnish (82 lakes) and northern part of the Polish (nine lakes) TSs. Chironomidae, non-biting midges, are known to be strongly responsive to the July air temperature and are widely used to infer palaeotemperature. Several modern analogue-based TSs necessary for calibrating the relationships between mean July air temperature (MJAT) and chironomids are available for Europe. However, none of these is representative of the transitional climate typical for eastern Baltic (Estonia, Latvia, Lithuania). The Finno–Baltic–Polish TS contains 121 sites and covers a geographically continuous 70–50°N latitudinal and 7 °C (12.1–19.2 °C) MJAT gradient. Canonical correspondence analysis revealed that, among the tested environmental variables (pH, water depth, dissolved oxygen, MJAT), the MJAT explains the highest amount of variation, both for the eastern Baltic separately and the Finno–Baltic–Polish TSs. The weighted averaging–partial least squares-based cross-validation test reveals that the Finno–Baltic–Polish TS has a low root mean square error of prediction (0.7 °C) confirming the high reliability of the TS. The temperature optima of the taxa included in the new Finno–Baltic–Polish TS and widely used Swiss–Norwegian TS were examined. The observed dissimilarities can be attributed to the differences in the temperature ranges represented by the TS, the taxonomic identification level, the general cosmopolitan taxa distribution patterns and the influence of TS-specific geographic position, climatic or environmental conditions. The new Finno–Baltic–Polish TS adds to the knowledge on the modern distribution of Chironomidae taxa and widens the geographical area of reliable Chironomid-based MJAT reconstructions into the eastern European lowland.

The dynamics of the last Fennoscandian Ice Sheet (FIS) are relatively well constrained in the Nordic countries. Ice-sheet dynamics in NW Russia, however, are comparatively less well understood owing to the scale and resolution of existing studies. New large-scale glacial geomorphological datasets from NW Russia based on high-resolution remotely sensed imagery allow for an independent reassessment of the extent and dynamics of the FIS during the Younger Dryas and Early Holocene (c. 12.9–10 ka) in NW Russia. The reconstruction provides a more detailed link between geomorphological expressions of palaeoglaciation than previous proposals. Rather than a continuous Younger Dryas ice marginal zone (IMZ) stretching from Finland to northern Norway, the geomorphological signature of NW Russia reveals 14 IMZs that document discrete stationary ice-margin positions (possibly standstill and/or readvance events) during the overall retreat. The relative age sequence of the IMZs, supported by an updated numerical age database, suggests that they formed time-transgressively during the Younger Dryas and Early Holocene rather than contemporaneously. Moreover, specific landform assemblages reveal contrasting glacial landsystems in NW Russia: (i) a northern subpolar glacial landsystem; and (ii) a southern temperate glacial landsystem. The model presented herein provides robust empirical constraints for testing and validating numerical ice-sheet models and understanding ice-sheet responses to rapid climate change.

The results of geomorphological mapping and survey of Lateglacial and Holocene displaced shorelines in the Clyde estuary and around Loch Lomond, western central Scotland are described. On the basis of morphology, sedimentology, altitude and radiocarbon dating, four discrete shorelines are identified and are correlated with previously identified Scottish displaced shorelines. The shoreline formerly referred to as the Main Postglacial Shoreline is renamed the Menteith Shoreline. This body of data, combined with data on displaced shorelines for Scotland as a whole has been analysed using Gaussian quadratic trend surface analysis in order to determine the centre of glacio-isostatic displacement for each shoreline. These Gaussian models of palaeo-relative sea-level suggest that the zone of greatest displacement lay NNW of Loch Lomond in the Lateglacial then moved SSE to the region of Loch Lomond during the Holocene and the Clyde in the Late Holocene. The factors responsible for the movement of the zone of greatest uplift are discussed, including temporal variations in the ice-sheet thickness, variations in water load in the adjacent sea-lochs and neotectonic processes. Comparison is made with glacial isostatic adjustment (GIA) models. A sensitivity analysis has been carried out on the use of Gaussian trend surface analysis glacio-isostatic modelling and this is included in the research evaluation, and reported in full in the Supporting Information files, along with the raw data used throughout this study.