Late Pleistocene and Holocene vegetation and climate on the northern Taymyr Peninsula, Arctic Russia

Pollen data from a Levinson-Lessing Lake sediment core (74°28'N, 98°38'E) and Cape Sabler, Taymyr Lake permafrost sequences (74°33'N, 100°32'E) reveal substantial environmental changes on the northern Taymyr Peninsula during the last c. 32 000 [Formula: See Text]C years. The continuous records confirm that a scarce steppe-like vegetation with Poaceae, Artemisia and Cyperaceae dominated c. 32 000-10 300 [Formula: See Text]C yr BP, while tundra-like vegetation with Oxyria, Ranunculaceae and Caryophyllaceae grew in wetter areas. The coldest interval occurred c. 18 000 yr BP. Lateglacial pollen data show several warming events followed by a climate deterioration c. 10 500 [Formula: See Text]C yr BP, which may correspond with the Younger Dryas. The Late Pleistocene/Holocene transition, c. 10 300-10 000 [Formula: See Text]C yr BP, is characterized by a change from the herb-dominated vegetation to shrubby tundra with Betula sect. Nanae and Salix. Alnus fruticosa arrived locally c. 9000-8500 [Formula: See Text]C yr BP and disappeared c. 4000-3500 [Formula: See Text]C yr BP. Communities of Betula sect. Nanae, broadly distributed at c. 10 000-3500 [Formula: See Text]C yr BP, almost disappeared when vegetation became similar to the modern herb tundra after 3500-3000 [Formula: See Text]C yr BP. Quantitative climate reconstructions show Last Glacial Maximum summer temperature about 4°C below the present and Preboreal (c. 10 000 [Formula: See Text]C yr BP) temperature 2-4°C above the present. Maximum summer temperature occurred between 10 000 and 5500 [Formula: See Text]C yr BP; later summers were similar to present or slightly warmer.     

Late Weichselian glaciation history of the northern North Sea

Based on new data from the Fladen, Sleipner and Troll areas, combined with earlier published results, a glaciation curve for the Late Weichselian in the northern North Sea is constructed. The youngest date on marine sedimentation prior to the late Weichselian maximum ice extent is 29.4 ka BP. At this time the North Sea and probably large parts of southern Norway were deglaciated (corresponding to the Alesund interstadial in western Norway). In a period between 29.4 and c. 22 ka BP, the northern North Sea experienced its maximum Weichselian glaciation with a coalescing British and Scandinavian ice sheet. The first recorded marine inundation is found in the Fladen area where marine sedimentation started close to 22 ka BP. After this the ice fronts receded both to the east and west. The North Sea Plateau, and possibly parts of the Norwegian Trench, were ice-free close to 19.0 ka, and after this a short readvance occurred in this area. This event is correlated with the advance recorded at Dimlington, Yorkshire, and the corresponding climatostratigraphic unit is denoted the Dimlington Stadial (18.5 ka to 15.1 ka). The Norwegian Trench was deglaciated at 15.1 ka in the Troll area. The data from the North Sea, together with the results from Andwa, northern Norway (Vorren et al . 1988; Møller et al . 1992), suggest that the maximum extent of the last glaciation along the NW-European seaboard from the British Isles to northern Norway was prior to c . 22 ka BP.     

Weichselian and Holocene palaeoenvironmental history of the Bol'shoy Lyakhovsky Island, New Siberian Archipelago, Arctic Siberia

Cryolithological, ground ice and fossil bioindicator (pollen, diatoms, plant macrofossils, rhizopods, insects, mammal bones) records from Bol'shoy Lyakhovsky Island permafrost sequences (73°20′N, 141°30′E) document the environmental history in the region for the past c. 115 kyr. Vegetation similar to modern subarctic tundra communities prevailed during the Eemian/Early Weichselian transition with a climate warmer than the present. Sparse tundra‐like vegetation and harsher climate conditions were predominant during the Early Weichselian. The Middle Weichselian deposits contain peat and peaty soil horizons with bioindicators documenting climate amelioration. Although dwarf willows grew in more protected places, tundra and steppe vegetation prevailed. Climate conditions became colder and drier c. 30 kyr BP. No sediments dated between c. 28.5 and 12.05 ¹⁴C kyr BP were found, which may reflect active erosion during that time. Herb and shrubby vegetation were predominant 11.6–11.3 ¹⁴C kyr BP. Summer temperatures were c. 4 °C higher than today. Typical arctic environments prevailed around 10.5 ¹⁴C kyr BP. Shrub alder and dwarf birch tundra were predominant between c. 9 and 7.6 kyr BP. Reconstructed summer temperatures were at least 4 °C higher than present. However, insect remains reflect that steppe‐like habitats existed until c. 8 kyr BP. After 7.6 kyr BP, shrubs gradually disappeared and the vegetation cover became similar to that of modern tundra. Pollen and beetles indicate a severe arctic environment c. 3.7 kyr BP. However, Betula nana, absent on the island today, was still present. Together with our previous study on Bol'shoy Lyakhovsky Island covering the period between about 200 and 115 kyr, a comprehensive terrestrial palaeoenvironmental data set from this area in western Beringia is now available for the past two glacial–interglacial cycles.     

Late Pleistocene and Holocene vegetation history of the Bale Mountains,Ethiopia

A sediment core recovered from Garba Guracha, a glacial lake at 3950 m altitude in the Bale Mountains of Ethiopia, at the boundary of the Ericaceous and Afroalpine vegetation belts, provides a 16,700-year pollen record of vegetation response to climatic change. The earliest vegetation recorded was sparse and composed mainly of grasses, Amaranthaceae–Chenopodiaceae and Artemisia, indicating an arid climate. At 13,400 cal BP, Amaranthaceae–Chenopodiaceae pollen declined sharply and Cyperaceae increased, suggesting a change to moister conditions. The Younger Dryas interval is represented by a small increase in Artemisia and reduced Cyperaceae, indicating aridity. Just after the start of the Holocene (11,200 cal BP), the upper altitudinal limit of the Ericaceous belt rose, and woody Ericaceous vegetation extended across the Sanetti plateau, in response to increased moisture and temperature. The marked change from clastic to organic lake sedimentation at this time reflects the increase in woody vegetation cover in the lake catchment, accompanied by soil stabilisation, and increased leaf litter and soil humus content. From about 6000 cal BP, and especially after 4500 cal BP, mid-altitude dry Afromontane Juniper–Podocarpus forests developed on the northern slopes of the mountains in response to reduced rainfall in a shortened wet season. Erica shrub and forest decreased in area and altitude, and the Afroalpine ecosystem expanded on the plateau. Podocarpus declined from about 2000 cal BP, as Juniperus increased to its present dominance at 2500–3300 m altitude. Human impact on the high-altitude Afroalpine and Ericaceous vegetation has been relatively minor, confirming that the endemic biodiversity of the Ethiopian mountains is a legacy of natural Holocene vegetation change, following repeated expansion and contraction of the upland ecosystems during the Quaternary.     

Late Weichselian and Holocene seismostratigraphy and depositional history of the Gulf of Riga,NE Baltic Sea

The Lateglacial and postglacial sequence in the northern Gulf of Riga is sedimentologically subdivided into nine distinctive layers. In the seismo‐acoustic sequence these layers are correlated with seven seismic/acoustic units, which largely reflect different stages in the development of the Baltic Sea. A uniform layer of the Late Weichselian till, a layer of waterlain glacial diamicton (WGD), a varved succession of the Baltic Ice Lake, a brackish‐water/freshwater sandy/silty clay of Yoldia Sea, a FeS‐rich layer of Ancylus Lake and discordantly bedded sand of the Litorina Sea and present‐day gyttja are revealed both in sediment cores and in acoustic recordings. In general, the lateral extent of the distinguished sediment layers is gradually shrinking upwards in the Quaternary sequence towards the deepest, central depression of the gulf. Two distinguished regional discontinuities divide the Lateglacial and postglacial sediment sequence into three allounits: glacial diamicton deposits in the lower part; ice‐proximal WGD, glaciolacustrine and postglacial lake/marine deposits in the middle; and brackish‐water marine deposits in the uppermost part of the sequence. The presented detailed seismostratigraphic subdivision of the Quaternary sediment sequence of the Gulf of Riga permits a correlation/comparison with similar sequences across the Baltic Sea and in other former glaciated basins.     

Late Weichselian Glaciation of the Russian High Arctic

A numerical ice-sheet model was used to reconstruct the Late Weichselian glaciation of the Eurasian High Arctic, between Franz Josef Land and Severnaya Zemlya. An ice sheet was developed over the entire Eurasian High Arctic so that ice flow from the central Barents and Kara seas toward the northern Russian Arctic could be accounted for. An inverse approach to modeling was utilized, where ice-sheet results were forced to be compatible with geological information indicating ice-free conditions over the Taymyr Peninsula during the Late Weichselian. The model indicates complete glaciation of the Barents and Kara seas and predicts a “maximum-sized” ice sheet for the Late Weichselian Russian High Arctic. In this scenario, full-glacial conditions are characterized by a 1500-m-thick ice mass over the Barents Sea, from which ice flowed to the north and west within several bathymetric troughs as large ice streams. In contrast to this reconstruction, a “minimum” model of glaciation involves restricted glaciation in the Kara Sea, where the ice thickness is only 300 m in the south and which is free of ice in the north across Severnaya Zemlya. Our maximum reconstruction is compatible with geological information that indicates complete glaciation of the Barents Sea. However, geological data from Severnaya Zemlya suggest our minimum model is more relevant further east. This, in turn, implies a strong paleoclimatic gradient to colder and drier conditions eastward across the Eurasian Arctic during the Late Weichselian.     

Postglacial emergence and Late Quaternary glaciation on northern Novaya Zemlya, Arctic Russia

Recent observations on postglacial emergence and past glacier extent for one of the least accessible areas in the Arctic, northern Novaya Zemlya are here united. The postglacial marine limit formed 5 to 6 ka is registered on the east and west coasts of the north island at 10 ± 1 and 18 ± 2 m aht, respectively. This modest and late isostatic response along with deglacial ages of >9.2 ka on adjacent marine cores from the northern Barents Sea indicate either early (>13 ka) deglaciation or modest ice sheet loading (<1500 m thick ice sheet) of Novaya Zemlya. Older and higher (up to 50 m aht) raised beaches were identified beneath a discontinuous glacial drift. Shells from the drift and underlying sublittoral sediments yield minimum limiting ¹⁴C ages of 26 to 30 ka on an earlier deglacial event(s). The only moraines identified are within 4 km of present glacier margins and reflect at least three neoglacial advances in the past 2.4 ka.     

Late Holocene beetle assemblages and environmental change in Gammelhemmet,northern Sweden

Analysis of insect fossil remains retrieved from a bog close to the abandoned farm at Gammelhemmet, near Lycksele in Swedish Lapland, enabled the reconstruction of environmental changes at the site over the last 2500 years. These results represent the first late Holocene palaeoentomological succession studied for insect remains in the Västerbotten interior, and they provide new evidence for landscape change in the area. Around 2000 years ago, at the end of the early Iron Age, disappearance of the tree and leaf litter fauna and an increase in aquatic species indicate the expansion of wetlands in the area. Patches of a multi‐aged mixed woodland with a diverse assemblage of forest‐dwelling beetles succeeded the wetland ～1500 years ago, at the beginning of the late Iron Age. A marked change to open and drier conditions, and the presence of species often found in grassland and cultivated ground took place during the post‐Medieval period. Our evidence indicates drainage of the area prior to the 18th century, placing the initiation of agricultural activities in Gammelhemmet earlier than the documentary record. Our research shows the potential of the use of fossil insects for understanding environmental change and also human impact on the landscape, even of limited scale, from natural contexts.     

贵州西部晚全新世植被演替、气候变化与火灾历史

贵州西部位于北亚热带云贵高原山地湿润-半湿润气候区,西南季风是该区域水汽来源的主要气候系统。贵州六盘水娘娘山有连片分布的垫状泥炭沼泽沉积,较完整记录了过去的植被和气候历史,是研究气候-植被-火灾-人类活动变化的理想场所。本研究以六盘水娘娘山1999 m海拔的一处泥炭湿地钻孔上部52 cm岩芯为研究材料,通过AMS ¹⁴C测年获得年代框架,采用孢粉和炭屑分析,重建了该地区晚全新世气候变化和人类活动叠加影响下的植被演替及火灾活动历史。结果表明：3500~3100 cal.a B.P. 期间,当地亚热带常绿阔叶林繁盛,火灾活动为气候控制为主的森林火灾,但火灾活动并未改变阔叶林的总体面貌;3100~600 cal.a B.P. 期间,气候呈变干趋势,阔叶类木本植物显著减少,当地植被从亚热带常绿阔叶林转变为疏林草地和针叶类疏林,极可能是趋于冷干的气候环境的结果;大约600 cal.a B.P. 之后,当地植被演变为开阔林,同时,出现大颗粒炭屑(>125 μm)以及伴人花粉的明显增加,表明人类农业活动高强度的刀耕火种已经扩张到较高海拔山区。区域对比显示,西南地区在3500 cal.a B.P. 以来,主要以区域性火灾为主,而3100 cal.a B.P. 以后的火灾活动受到气候变干和人类活动的双重影响,特别是600 cal.a B.P. 以来,人类活动(刀耕火种)成为局地火灾和植被更替的主要因素。

     

Holocene environmental history on the eastern slope of the Polar Ural Mountains, Russia

The Holocene environmental history of the eastern slope of the Polar Ural Mountains has been reconstructed using pollen, spores, algae and other microfossils from the Chernaya Gorka palsa section (67°05'N, 65°21'E, 170 m a.s.l.). An initial oligotrophic lake was formed at the study site c. 9800-9500 ¹⁴C yr BP. Although tundra communities dominated the vegetation in the area, birch and larch trees might have grown at lower elevations. Dry and disturbed soil habitats also occurred around the lake. Algae (mostly Pediastrum and Botryococcus) started to expand in the lake as climate gradually improved after c. 9500 ¹⁴C yr BP. However, the role of mosses (mostly Calliergon and Drepanocladus) was most important for the infilling of the lake basin. Increased temperatures and subsequent improvement of hydrological conditions resulted in vegetation changes: stands of willows developed rapidly and the role of tree birch in the local vegetation increased. The lake was completely filled at c. 8600 ¹⁴C yr BP. Peat accumulation started with Bryales mosses and, later, Sphagnum became dominant. Stands of Larix, Picea and Betula became well developed during the Boreal climate optimum. Tree birch began to spread into the tundra. Different Bryales mosses formed peat c. 8000-6500 ¹⁴C yr BP. Cyperaceae later became the main peat-forming element. Dense spruce canopies with Larix sibirica and Betula pubescens surrounded the study site during the Atlantic period, pointing to the warmest climate during the Holocene. Summer temperatures might have been up to 3-4°C higher than today. However, a decline of spruce and an increase of birch around 6700-6300 ¹⁴C yr BP may reflect some climate deterioration. There are no dated deposits younger than 6000 ¹⁴C yr BP. It is assumed that Subboreal climate deterioration resulted in the development of permafrost and formation of the palsa at the site. The deposits, now protruding above the surrounding terrain, were eroded by wind, water and cryogenic processes.     

Late Weichselian and Holocene shoreline displacement in the Trondheimsfjord area, central Norway

Shoreline displacement data from the Trondheimsfjord area have been collected and a synthesis of the Late Weichselian and Holocene relative uplift is presented. The isobase direction is N 30–35°E during the whole period. The gradients of the shorelines are 1.7? m/km at 11,800 years B.P., 1.3 m/km at 10,000 years B.P., gradually decreasing towards the present with a value of 0.2 m/km at 5,000 years B.P. Some irregularities in the shoreline gradient curve in the Late Weichselian and Preboreal chronozones may be ascribed to crustal readjustments by faults. An interpolation of the 9,500 years B.P. shoreline to the Ångermanland and Baltic area shows a relative uplift at 11,800 years B.P. of 400–450 m in the central area of glaciation. The island of Hitra was probably deglaciated at about 12,000 years B.P. and Ørlandet/Bjugn somewhat later. The Younger Dryas ice marginal deposits at Tautra have been deposited early in this chronozone, and deposits proximal to this at Hoklingen and Levanger were probably deposited in the late part of the same chronozone.     

Holocene vegetation history of the Okanogan Valley,Washington

Haploxylon pine(s) and Artemisia dominated the initial vegetation in front of the receding Okanogan Lobe until ca. 10,000 yr B.P., as revealed by two pollen records in north-central Washington. After 10,000 yr B.P. the macroclimate became warmer throughout the Okanogan drainage as diploxylon pines and Artemisia increased. The Mount Mazama eruption at ca. 6700 yr B.P. is recorded as two stratigraphically separate and petrographically distinct tephra units at Bonaparte Meadows. While there are apparent short-term changes in the vegetation coincident with the ashfall(s), Artemisia continues to dominate the Okanogan Valley until ca. 5000 yr B.P. By 4700 yr B.P. the modern vegetation, dominated by Pseudotsuga menziesii, had become established around Bonaparte Meadows.     

Holocene history of fire,vegetation and land use from the central Pyrenees (France)

Located on a mountain pass in the west-central Pyrenees, the Col d'Ech peat bog provides a Holocene fire and vegetation record based upon nine ¹⁴C (AMS) dates. We aim to compare climate-driven versus human-driven fire regimes in terms of frequency, fire episodes distribution, and impact on vegetation. Our results show the mid-Holocene (8500–5500 cal yr BP) to be characterized by high fire frequency linked with drier and warmer conditions. However, fire occurrences appear to have been rather stochastic as underlined by a scattered chronological distribution. Wetter and colder conditions at the mid-to-late Holocene transition (4000–3000 cal yr BP) led to a decrease in fire frequency, probably driven by both climate and a subsequent reduction in human land use. On the contrary, from 3000 cal yr BP, fire frequency seems to be driven by agro-pastoral activities with a very regular distribution of events. During this period fire was used as a prominent agent of landscape management.     

Extending the known distribution of the Vedde Ash into Siberia: occurrence in lake sediments from the Timan Ridge and the Ural Mountains,northern Russia

Tephra shards from the Vedde Ash eruption have been identified in two lakes from northwestern Russia and the Polar Ural Mountains. This is the most distal and easternmost occurrence of this regional tephra marker horizon found so far and it extends the area of the Vedde Ash tephra more than 1700 km further east than previously documented. This means that particles the size of fine sand have travelled more than 4000 km from the Katla volcano source, south Iceland. These findings offer a new possibility to correlate archives over a very long distance in the time period around the Younger Dryas.     

Late Holocene vegetational history,human impact and pollen representativity variations in northern Cumbria,England

The comparison of pollen diagrams and their inferred vegetational histories are an important component of palaeoecological research. Radiocarbon-dated pollen profiles from three cores taken from two adjacent mires located in northern Cumbria, Bolton Fell Moss and Walton Moss, have been used to reconstruct the Late Holocene vegetation history between the Bronze Age and the present day. The profiles have been interpreted in the light of available archaeological and historical records and, although the pollen records are broadly similar, there are some notable differences between them, particularly during Iron Age and medieval times. Dissimilarities between the diagrams are explored numerically, and the statistical and palynological results are discussed in relation to pollen representativity. The results suggest that it may be advantageous to construct more than one pollen diagram from a mire, or even adjacent mires, as extra-local pollen may be a more important part of the pollen rain than previously envisaged. © 1998 John Wiley & Sons, Ltd.     

Middle and Late Weichselian (Devensian) glaciation history of south-western Norway,North Sea and eastern UK

Data from eastern England, Scotland, the northern North Sea and western Norway have been compiled in order to outline our current knowledge of the Middle and Late Weichselian glacial history of this region. Radiometric dates and their geological context from key sites in the region are presented and discussed. Based on the available information the following conclusions can be made: (i) Prior to 39 cal ka and most likely after ca 50 cal ka Scotland and southern Norway were extensively glaciated. Most likely the central North Sea was not glaciated at this time and grounded ice did not reach the shelf edge. (ii) During the time interval between 29 and 39 ka periods with ameliorated climate (including the Ålesund, Sandnes and Tolsta Interstadials) alternated with periods of restricted glaciation in Scotland and western Norway. (iii) Between 29 and 25 ka maximum Weichselian glaciation of the region occurred, with the Fennoscandian and British ice sheets coalescing in the central North Sea. (iv) Decoupling of the ice sheets had occurred at 25 ka, with development of a marine embayment in the northern North Sea (v) Between 22 and 19 ka glacial ice expanded westwards from Scandinavia onto the North Sea Plateau in the Tampen readvance. (vi) The last major expansion of glacial ice in the offshore areas was between 17.5 and 15.5 ka. At this time ice expanded in the north-western part of the region onto the Måløy Plateau from Norway and across Caithness and Orkney and to east of Shetland from the Moray Firth. The Norwegian Channel Ice Stream (NCIS), which drained major parts of the south-western Fennoscandian Ice Sheet, was active at several occasions between 29 and 18 ka.     

Sediments in the Gakkel Ridge rift zone (Arctic Ocean): structure and history

The available seismic and magnetic data show the Gakkel Ridge rift zone consisting of the Atlantic and Siberian segments divided by a tectonic suture at 70° E. The two segments have had different histories recorded in their sedimentary cover. Apart from the difference in its morphology, the Siberian segment differs from the Atlantic one in the existence of a series of deposition centers, which might represent a vast Paleogenic basin that formed prior to the Gakkel Ridge. The simple model of North Atlantic spreading fails to explain the long and complex history of the Gakkel Ridge rift and the existence of the depocenters. The particular structure of this zone might have resulted from the growth of rift mountains by accretion of magmatic material during the Paleogene, without significant sea floor spreading.