Boreas最新文献

We, the editors, are grateful to all reviewers for their help in processing volume 53 of Boreas.

Jan A. Piotrowski

Nicolaj Krog Larsen

Two major glaciations have been identified on land in England during the Middle Pleistocene. The earliest occurred during the Anglian Stage (= Elsterian, c. Marine Isotope Stage, MIS 12), evidence for which is best developed in lowland Britain, as well as offshore in the southern North Sea and Irish Sea basins. The second took place during the late Middle Pleistocene, with the most compelling evidence found in the West Midlands, intermediate between the Hoxnian (= Holsteinian; broadly MIS 11) and Ipswichian (= Eemian; broadly MIS 5e) interglacial stages during the Late Wolstonian Substage. Until recently this younger glacial episode was less clearly represented in the Pleistocene record and, as a result, had been little studied and weakly defined. Interpreted as the Moreton Stadial glaciation during the Late Wolstonian Substage (= Late Saalian Substage/Drenthe Stadial, c. MIS 6), it was originally recognized in the English Midlands, subsequently being identified in Yorkshire, Lincolnshire and northern East Anglia, and potentially further SW as far as the Bristol Channel. Mapping, in particular by members of the British Geological Survey, however, resulted in the Wolstonian Stage glacial deposits being thought to pre-date the stage. This was particularly so in East Anglia where there was considerable controversy concerning the number and relationships of glacial sequences, during the 1970–1980s. Yet to the west of East Anglia there remained unequivocal evidence for glaciation during the stage, particularly in Fenland and the eastern English Midlands. Recent radiometric dating across lowland Britain on glacial sediments long thought to belong to a glaciation event in the Wolstonian Stage have now placed a geochronological control on the established regional stratigraphy and confirmed that glaciation occurred in two phases between 199 and 147 ka during the Late Wolstonian Substage. The glacial events of the British Middle Pleistocene can clearly be correlated with the European continent.

The Middle Pleistocene Reinsdorf sequence at the Lower Palaeolithic sites of Schöningen offers the opportunity to reconstruct a rarely well-preserved post-Holsteinian environmental transition from an interglacial into a glacial phase along with its highly dynamic interjacent climatic oscillations. Combining biological proxies, element composition and stable isotope ratios of two lakeshore sequences at excavation site 13 II, we demonstrate repeated variations in climate, hydrology and catchment vegetation cover. New ostracod-based quantitative mean summer and winter air temperature reconstructions with the Mutual Ostracod Temperature Range (MOTR) method provide the first detailed information about the temperature evolution. The interglacial temperature maximum, probably corresponding to Marine Isotope Stage 9e, is followed by a first dry phase and, during the younger part of the Reinsdorf sequence, by a second dry period. Both were marked by lower precipitation/evaporation ratios, reduced vegetation cover in the catchment and increased surface inflows from springs. Temperature reconstructions of these two steppe (open woodland) phases yield very narrow ranges for mean January (−4–0 °C) and July (+17–19 or +17–21 °C) air temperatures, demonstrating that, while summers were similar to those of today, winters were at least 1 °C colder, hinting at a more pronounced continental climate. Precise temperature estimates for the interjacent woodland and steppe (woodland) phase are hindered by generally wider ranges produced by the MOTR method (January mean −4–3 °C, July mean +15–21 °C). The development of a more extensive vegetation cover, reducing surface runoff and erosion in favour of increased river and groundwater discharge, as indicated by a shift in microfossil and stable isotope records, suggests generally more humid climates with higher precipitation/evaporation ratios as well as reduced seasonal temperature variations.

Lake Paravani, located on the volcanic Javakheti Plateau in the central part of the Lesser Caucasus at 2073 m a.s.l., forms a unique geo-bio-archive for palaeoenvironmental reconstructions in this remote region. Based on sediment cores from the southwestern part of the lake we expand the existing palynological and sedimentological records beyond the Last Glacial Maximum (LGM). For the first time, it is possible to reconstruct the palaeoenvironment in this part of the Lesser Caucasus back to c. 28 cal. ka BP. Our study shows that until 16 cal. ka BP glacial conditions dominated (Phase I) in the region; there is, however, proof that the lake already existed during the LGM. In the following transitional Phase II from 16 until 6 cal. ka BP, cold and arid conditions with sparse steppe vegetation and a lowered lake level prevailed. Around 10 cal. ka BP, tree pollen started to expand while herbaceous pollen, especially Chenopodiaceae, declined. In Phase III, since 6 cal. ka BP, mixed forest probably represented the Holocene climatic optimum. Fluctuating lake levels indicate shifting climatic conditions. The minor changes of arboreal pollen hin the uppermost part of Phase II may be an indication of human activity. The more humid, vegetation-rich environment and mild climate around 4.5–2 cal. ka BP correlate with the expansion of the Late Bronze Age settlements in this area (from ~3.5 cal. ka BP/~1.5 ka BC). The proliferation of sites on the plateau, along with even higher-altitude sites possibly dating to the same period, may indicate that this climate amelioration played an important role in enabling more sustained human occupation. The results extend the record on Lake Paravani by several millennia beyond the LGM and complement the palaeo-lake reconstructions of the wider region, e.g. at Lake Van (Türkiye) or Lake Sevan (Armenia).

Here we present the first Lateglacial and Holocene glacial history from Rotsunddalen, northern Troms and western Finnmark county, northern Norway, based on both relative and numerical moraine dating using Schmidt hammer, soil chronosequencing and terrestrial cosmogenic nuclide dating. We combine these chronological data with a regional map of the glacial geomorphology to hypothesize key events in the glacial history from around 14 ka to present. Our reconstruction shows that, following deglaciation of the main ice sheet across central Troms and Finnmark, mountain glaciers were terminating on land, close to the coast, between around 12.1 and 10.6 ka. Continued recession of the main Fennoscandian Ice Sheet margin towards the SE led to the isolation of several large plateau icefields and outlet glaciers that generated moraines at around 10.2–9.2 ka, which we ascribe to the Erdalen Event, and 8.4–8.2 ka, which is broadly contemporaneous with the 8.2 ka cold event. Although the latter corresponds with the Scandinavian Finse Event, very few moraines have been dated to this time and we therefore view it as a tentative hypothesis for future work to test. During the Holocene Thermal Maximum (~6.6 to 6.3 ka) most (if not all) glaciers in the region disappeared, but then regrew during the Neoglaciation and produced large moraines dated to around 4.7 ka that lie a few hundred metres distal to the prominent Little Ice Age moraines (previously dated to AD 1810s–1870s). Given the limitations of our dating approach, the preservation of moraines dated to this period in northern Norway also warrants further investigation. We also highlight that terrestrial cosmogenic nuclide dating of the moraines is not consistent with other dating approaches and the widely established deglaciation history of the region, probably owing to cosmogenic inheritance and insufficient glacial erosion.

Glacial deposits are important sources of palaeoclimatic information but not all deposits are formed by processes that reflect the overall climatic conditions of a region; surge-type glaciers undergo periodic episodes of rapid ice movement, often unrelated to ambient climatic conditions. This study examines the glacier forefields of Öldufellsjökull and western Sléttjökull, two outlet glaciers of the Mýrdalsjökull Ice Cap in southern Iceland, to identify landform characteristics indicative of past episodes of fast flow. Previous studies suggest episodes of fast flow at these glaciers in the past century. Remotely sensed data and field investigations were combined to complete a landsystem analysis of the forefields of these glaciers and an uncrewed aerial vehicle was used to collect high-resolution imagery of areas of particular interest. Two assemblages of landsystems are identified on each forefield, which pass from streamlined landforms containing abundant flutes close to the glacier to spatially restricted bands of arcuate moraines with associated glaciofluvial and glaciolacustrine deposits more distally. This distribution of landsystem tracts has limited similarity to the current surge-type glacier landsystem model, suggesting that other processes are controlling the development of landform–sediment assemblages. Using a high-resolution digital elevation model of an area within the 1984 ice margin, two distinct landform types were identified that were not apparent on the coarse resolution imagery: hummocky moraine and a circular feature hypothesized to have formed as a result of water escape caused by changing hydrological regimes. The forefields of Öldufellsjökull and western Sléttjökull lack many of the characteristics typical of surge-type landsystems and instead are more similar to the active temperate landsystem common in Iceland.

Neck cysts can be classified as congenital, infectious-inflammatory, and neoplastic. Hydatid disease is a parasitic infection caused by Echinococcus, is usually seen in the liver and lung and, is rare in the head and neck region even in endemic areas. If not treated, a life-threatening condition may be encountered. In this study, a case of hydatid cyst operated due to a cystic lesion with a diameter of approximately 8 cm in the neck was presented by reviewing the literature.

This contribution summarizes the most informative loess–palaeosol sequences (LPS) and fluvial terrace records from the late Middle Pleistocene (LMP) of northern France demonstrating the reliability of the cyclostratigraphic approach for the interpretation of pedosedimentary sequences controlled by major glacial–interglacial climatic cycles. In this area, continental mollusc assemblages from interglacial fluvial silts and calcareous tufas are particularly rich and diverse and marker species define the malacological signatures of each interglacial optimum for Marine Isotope Stages (MIS) 11, 9 and 5e. This approach shows that the forest was less developed during MIS 7, suggesting that climatic conditions were either drier and/or cooler than during other Pleistocene interglacials. In the Somme basin, the terrace system shows that two alluvial formations were deposited between early MIS 8 and late MIS 7. In some LPS, the occurrence of two pedosedimentary sub-cycles (IIa and IIb), separated by a relatively long (~12 ka) and cold period, corresponding to an ‘aborted glacial’ (MIS 7d), underlines the complex pattern of this unusual ‘interglacial’. Overall, during the LMP, each soil complex corresponding to interglacial and early-glacial periods from MIS 11 to MIS 5 is broadly made up of the same soil facies but exhibits a specific succession pattern or signature. Throughout the area, LPS show a huge change in both the deposition rates and the geographical extent of typical calcareous loess at the beginning of MIS 6. This so-called ‘Loess Revolution’ probably reflects a change in the palaeogeography of the southern North Sea and eastern Channel source areas at times marked by the coalescence of the British and Scandinavian ice sheets. MIS 6 is also characterized by the oldest evidence of permafrost development in the area. In addition, this work allows the age of the Lower/Middle Palaeolithic boundary to be confirmed, with the oldest occurrence of Levallois technology being around 300 ka.

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.