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1.
We present a Lateglacial and early Holocene chironomid‐based July air temperature reconstruction from Foppe (1470 m a.s.l.) in the Swiss Southern Alps. Our analysis suggests that chironomid assemblages have responded to major and minor climatic fluctuations during the past 17 000 years, such as the Oldest Dryas, the Younger Dryas and the Bølling/Allerød events in the Lateglacial and the Preboreal Oscillation at the beginning of the Holocene. Quantitative July air temperature estimates were produced by applying a combined Norwegian and Swiss temperature inference model consisting of 274 lakes to the fossil chironomid assemblages. The Foppe record infers average July air temperatures of ca. 9.9 °C during the Oldest Dryas, 12.2 °C during most of the Bølling/Allerød and 11.1 °C for the Younger Dryas. Mean July air temperatures during the Preboreal were 14 °C. Major temperature changes were observed at the Oldest Dryas/Bølling (+2.7 °C), the Allerød/Younger Dryas (?2 °C) and the Younger Dryas/Holocene transitions (+3.9 °C). The temperature reconstruction also shows centennial‐scale coolings of ca. 0.8–1.4 °C, which may be synchronous with the Aegelsee (Greenland Interstadial 1d) and the Preboreal Oscillations. A comparison of our results with other palaeoclimate records suggests noticeable temperature gradients across the Alps during the Lateglacial and early Holocene. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

2.
Mangerud, J., Gulliksen, S. & Larsen, E. 2009: 14C‐dated fluctuations of the western flank of the Scandinavian Ice Sheet 45–25 kyr BP compared with Bølling–Younger Dryas fluctuations and Dansgaard–Oeschger events in Greenland. Boreas, 10.1111/j.1502‐3885.2009.00127.x. ISSN 0300‐9483. We present 32 accelerator mass spectrometry (AMS) 14C dates obtained on well‐preserved bones from caves in western Norway. The resulting ages of 34–28 14C kyr BP demonstrate that the coast was ice‐free during the so‐called Ålesund Interstadial. New AMS 14C dates on shells aged 41–38 14C kyr BP are evidence of an earlier (Austnes) ice‐free period. The Ålesund Interstadial correlates with Greenland interstadials 8–7 and the Austnes Interstadial with Greenland interstadials 12–11. Between and after the two interstadials, the ice margin reached onto the continental shelf west of Norway. These events can be closely correlated with the Greenland ice core stratigraphy, partly based on identification of the Laschamp and Mono Lake palaeomagnetic excursions. We found that the pattern of the NGRIP δ18O curves for the two periods Greenland Interstadial (GI) 8 to Greenland Stadial (GS) 8 and GI 1–GS 1 (Bølling–Younger Dryas) were strikingly similar, which leads us to suggest that the underlying causes of these climate shifts could have been the same. We therefore discuss some aspects of glacial fluctuations during the Bølling–Younger Dryas in order to elucidate processes during Dansgaard–Oeschger events.  相似文献   

3.
This paper presents an event stratigraphy based on data documenting the history of vegetation cover, lake‐level changes and fire frequency, as well as volcanic eruptions, over the Last Glacial–early Holocene transition from a terrestrial sediment sequence recovered at Lake Accesa in Tuscany (north‐central Italy). On the basis of an age–depth model inferred from 13 radiocarbon dates and six tephra horizons, the Oldest Dryas–Bølling warming event was dated to ca. 14 560 cal. yr BP and the Younger Dryas event to ca. 12 700–11 650 cal. yr BP. Four sub‐millennial scale cooling phases were recognised from pollen data at ca. 14 300–14 200, 13 900–13 700, 13 400–13 100 and 11 350–11 150 cal. yr BP. The last three may be Mediterranean equivalents to the Older Dryas (GI‐1d), Intra‐Allerød (GI‐1b) and Preboreal Oscillation (PBO) cooling events defined from the GRIP ice‐core and indicate strong climatic linkages between the North Atlantic and Mediterranean areas during the last Termination. The first may correspond to Intra‐Bølling cold oscillations registered by various palaeoclimatic records in the North Atlantic region. The lake‐level record shows that the sub‐millennial scale climatic oscillations which punctuated the last deglaciation were associated in central Italy with different successive patterns of hydrological changes from the Bølling warming to the 8.2 ka cold reversal. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

4.
A chironomid–July air temperature inference model based on chironomid assemblages in the surface sediments of 81 Swiss lakes was used to reconstruct Late Glacial July air temperatures at Lac Lautrey (Jura, Eastern France). The transfer‐function was based on weighted averaging–partial least squares (WA‐PLS) regression and featured a leave‐one‐out cross‐validated coefficient of determination (r2) of 0.80, a root mean square error of prediction (RMSEP) of 1.53 ° C, and was applied to a chironomid record consisting of 154 samples covering the Late Glacial period back to the Oldest Dryas. The model reconstructed July air temperatures of 11–12 ° C during the Oldest Dryas, increasing temperatures between 14 and 16.5 ° C during the Bølling, temperatures around 16.5–17.0 ° C for most of the Allerød, temperatures of 14–15 ° C during the Younger Dryas and temperatures of ca. 16.5 ° C during the Preboreal. The Lac Lautrey record features a two‐step July air temperature increase after the Oldest Dryas, with an abrupt temperature increase of ca. 3–3.5 ° C at the Oldest Dryas/Bølling transition followed by a more gradual warming between ca. 14 200 and 13 700 BP. The transfer‐function reconstructs a less rapid cooling at the Allerød/Younger Dryas transition than other published records, possibly an artefact caused by the poor analogue situation during the earliest Younger Dryas, and an abrupt warming at the Younger Dryas/Holocene transition. During the Allerød, two centennial‐scale 1.5–2.0 ° C coolings are apparent in the record. Although chronologically not well constrained, the first of these cold events may be synchronous with the beginning of the Gerzensee Oscillation. The second is inferred just before deposition of the Laachersee tephra at Lac Lautrey and is therefore coeval with the end of the Gerzensee Oscillation. In contrast to the Greenland oxygen isotope records, the Lac Lautrey palaeotemperature reconstruction lacks a clearly defined Greenland Interstadial (GI) event 1d and the decreasing temperature trend during the Bølling/Allerød Interstadial. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

5.
The Upper Garonne Basin included the largest glacial system in the Pyrenees during the last glacial cycle. Within the long-term glacial retreat during Termination-1 (T-1), glacier fluctuations left geomorphic evidence in the area. However, the chronology of T-1 glacial oscillations on the northern slopes of the Central Pyrenees is still poorly constrained. Here, we introduce new geomorphological observations and a 12-sample dataset of 10Be cosmic-ray exposure ages from the Ruda Valley. This U-shaped valley, surrounded by peaks exceeding 2800 m a.s.l., includes a sequence of moraines and polished surfaces that enabled a reconstruction of the chronology of the last deglaciation. Following the maximum ice extent, warmer conditions prevailing at ~15–14 ka, during the Bølling–Allerød (B–A) Interstadial, favoured glacial retreat in the Ruda Valley. Within the B–A, glaciers experienced two phases of advance/stillstand with moraine formation at 13.5 and 13.0 ka. During the early Younger Dryas (YD), glacial retreat exposed the highest surfaces of the Saboredo Cirque (~2300–2350 m) at 12.7 ka. Small glaciers persisted only inside the highest cirques (~2470 m), such as in Sendrosa Cirque, with moraines stabilising at 12.6 ka. The results of this work present the most complete chronology for Pyrenean glacial oscillations from the B–A to the YD.  相似文献   

6.
A Lateglacial and early Holocene sequence of coleopteran assemblages is described from La Taphanel in the Massif Central, France. The site is a sediment-filled small lake at an altitude of almost 1000 m. The insect fauna provides evidence for a detailed palaeoecological reconstruction, and in particular enables a reconstruction of climatic changes at the close of the last glaciation. A sudden climatic warming occurs at about 13000 yr BP followed by a temperate episode equivalent in time to the Bølling period. There is clear evidence of a short cold period between the Bølling and Allerød that is approximately equivalent to the Older Dryas period. The Allerød phase is decidedly cooler than the Bølling, as is shown by the Coleoptera from several sites in northwest Europe. A clear Younger Dryas signal is provided by the Coleoptera, with climates similar in severity to those of the glacial period. The climatic improvement at the start of the Holocene is also sudden, so that by Preboreal times temperatures were equivalent to those of the present day.  相似文献   

7.
Blomvåg, on the western coast of Norway north of Bergen, is a classical site in Norwegian Quaternary science. Foreshore marine sediments, named the Blomvåg Beds and now dated to the Bølling‐Allerød from 14.8 to 13.3 cal. ka BP, contain the richest Lateglacial bone fauna in Norway, numerous mollusc shells, driftwood, and flint that some archaeologists consider as the oldest traces of humans in Norway. The main theme of this paper is that the Blomvåg Beds are overlain by a compact diamicton, named the Ulvøy Diamicton, which was interpreted previously as a basal till deposited during a glacial re‐advance into the ocean during the Older Dryas (c. 14 cal. ka BP). Sediment sections of the Blomvåg Beds and the Ulvøy Diamicton were exposed in ditches in a cemetery that was constructed in 1941–42 and have subsequently not been accessible. A number of radiocarbon and cosmogenic 10Be exposure ages demonstrate that the diamicton is not likely to be a till because minimum deglaciation ages (14.8–14.5 cal. ka BP) from the vicinity pre‐date the Ulvøy Diamicton. We now consider that sea ice and icebergs formed the Ulvøy Diamicton during the Younger Dryas. The Scandinavian Ice Sheet margin was located on the outermost coastal islands between at least c. 18.5 and 14.8 cal. ka BP; however, no ice‐marginal deposits have been found offshore from this long period. The Older Dryas ice margin in this area was located slightly inside the Younger Dryas margin, whereas farther south it was located slightly beyond the Younger Dryas margin.  相似文献   

8.
The primary objective of this study is to further substantiate multistep climatic forcing of late‐glacial vegetation in southern South America. A secondary objective is to establish the age of deglaciation in Estrecho de Magallanes–Bahía Inútil. Pollen assemblages at 2‐cm intervals in a core of the mire at Puerto del Hambre (53°36′21″S, 70°55′53″W) provide the basis for reconstructing the vegetation and a detailed account of palaeoclimate in subantarctic Patagonia. Chronology over the 262‐cm length of core is regulated by 20 AMS radiocarbon dates between 14 455 and 10 089 14C yr BP. Of 13 pollen assemblage zones, the earliest representing the Oldest Dryas chronozone (14 455–13 000 14C yr BP) records impoverished steppe with decreasing frequencies and loss of southern beech (Nothofagus). Successive 100‐yr‐long episodes of grass/herbs and of heath (Empetrum/Ericaceae) before 14 000 14C yr BP infer deglacial successional communities under a climate of increased continentality prior to the establishment of grass‐dominated steppe. The Bølling–Allerød (13 000–11 000 14C yr BP) is characterised by mesic grassland under moderating climate that with abrupt change to heath dominance after 12 000 14C yr BP was warmer and not as humid. At the time of the Younger Dryas (11 000–10 000 14C yr BP), grass steppe expanded with a return of colder, more humid climate. Later, with gradual warming, communities were invaded by southern beech. The Puerto del Hambre record parallels multistep, deglacial palaeoclimatic sequences reported elsewhere in the Southern Andes and at Taylor Dome in Antarctica. Deglaciation of Estrecho de Magallanes–Bahía Inútil is dated close to 14 455 14C yr BP, invalidating earlier dates of between 15 800 and 16 590 14C yr BP. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

9.
This paper presents the first unambiguous terrestrial palaeoecological record for the late glacial “Bølling warming” in Denmark. Pollen and macrofossil stratigraphies from pre-Bølling to 10,800 cal yr BP are presented from a small kettle hole in Southwest Denmark, during which the lake basin developed from an immature stage after the deglaciation to complete infilling in the early Holocene. Results show that the recently deglaciated landscape bore a discontinuous vegetation of pioneer plants. After the Bølling warming, an open Dryas octopetala-Betula nana community developed with Helianthemum oelandicum. Subarctic species were dominant and local successions were probably delayed by relatively unstable and infertile soils. There is no indication of a climate cooling during the period corresponding to the Older Dryas, but the occurrence of several drought tolerant and steppe species indicates that the period was relatively dry. In the Allerød period the Dryas-B. nana vegetation was initially replaced by an open Salix and grass dominated vegetation and some 400 years later, the first tree birches were documented presumably occupying moist and sheltered soils while drier land remained open. In the Younger Dryas period trees disappeared and the vegetation became open again and dominated by subarctic species. Following climate warming at the Younger Dryas–Holocene transition a shrub community of Empetrum and Juniperus developed. After approximately 200 years it was replaced by birch forest. Overall, the late-glacial vegetation cover had a more open and patchy character than inferred from previous pollen studies as assessment of the vegetation succession based on macrofossil evidence is essential. The inferred general vegetation development corresponds well with results of other studies in the region. Canonical ordinations (RDA) indicate that vegetation changes at the landscape scale during the Lateglacial period were driven by changes in climate, soils and competition for light.  相似文献   

10.
The deglaciation history of the Malangen‐Målselv fjord and valley area proximally to the Tromsø‐Lyngen (Younger Dryas) moraine at Bakkejord, Malangen, northern Norway, is reconstructed based on morphostratigraphic, lithostratigraphic and geophysical evidence, and 25 radiocarbon dates from marine shells and foraminifera. The results show that following the Skarpnes event c. 12 200 14Cyr BP, and prior to the Younger Dryas readvance, the area was deglaciated at least as far as Sandmo situated 22 km proximally to the Tromsø‐Lyngen moraine. Two moraine ridges crossing the fjord at Sandmo and buried beneath thick glaciomarine sediments are correlated with this period. The area was subsequently deglaciated between 10 300 and 9200 14Cyr BP, following the Tromsø‐Lyngen (Younger Dryas) readvance. Five ice‐front accumulations post‐dating the Tromsø‐Lyngen moraine and situated 19, 27, 42, 55 and 77 km behind it are identified and dated based on radiocarbon dates and correlation of marine limits: Målsnes (c. 10 050 14Cyr BP), Kjerresnes (c. 10 000 14Cyr BP), Solli (c. 9750 14Cyr BP), Bardufoss‐Brentmoen‐Storskogmoen (c. 9600–9700 14Cyr BP) and Alapmoen (c. 9200 Cyr BP). The largest of these, at Bardufoss‐Storskogmoen, possibly accumulated as a response to an ice advance. Fourteen dates of apparent late Allerød/Younger Dryas age (11 100–10 000 14Cyr BP), obtained from fossils in glaciomarine sediments in the Målselv valley up to 77 km proximally to the Tromsø‐Lyngen moraine, are interpreted as postdating rather than predating this moraine. Several of these are considered to be too old because of uncertain reservoir age, carbon‐dating plateaus and/or contamination. This highlights uncertainties associated with radiocarbon‐dating and the profound effect such uncertainties may have on interpreting geological events.  相似文献   

11.
A peat bed found under solifluction deposits on Godøya island, western Norway, accumulated during a few decades around 11 000 yr BP, at the end of the Allerød period of the Late Weichselian. Palaeoecological investigations showed a local vegetation succession on wet sand culminating in a mire community dominated by Carex nigra. Periodic flooding brought in sand and silt, which decreased as drainage was impeded sufficiently for standing water to develop. The surrounding terrestrial vegetation was dominated by Salix scrub, with some open heath and alpine habitats nearby. Apart from two aquatic species, the 29 insect taxa recorded are characteristic of alpine heaths, plant litter (under Salix scrub) and stream-sides. Their remains, together with the terrestrial plant macrofossils, were washed into the mire from nearby. Because the fossils are locally derived, the environmental reconstructions are of the actual conditions at Godøy at ca. 11 000 yr BP. Palaeotemperature estimates from beetles and plants are in agreement. The coleopteran estimates (Mutual Climatic Range Method) suggest mean July temperatures of 10–13°C, slightly cooler than today (13.5°), and January temperatures between +1 and ?10°C, similar to or much colder than today. Summer temperature estimates from individual plant taxa indicate that temperatures during the Allerød period were similar to today's, but estimates from the reconstructed vegetation and timber-line positions give estimates up to 3.5° cooler. Temperatures fell 2.5–7.5°C at the Younger Dryas. This abrupt and severe cooling initiated the solifluction processes on Godøya that buried the peat. The Godøy peat bed and its contained fossils provide a rare glimpse of Allerød biota and environments at the local (site) scale.  相似文献   

12.
The upwelling region off northwest Africa is one of the most productive regions in the world ocean. This study details the response of surface‐ and deep‐water environments off Mauritania, northwest Africa, to the rapid climate events of the last deglaciation, especially the Bølling–Allerød (15.5–13.5 ka BP) and Younger Dryas (13.5–11.5 ka BP). A high accumulation rate gravity core GeoB7926‐2, recovered at ～20° N, 18° W, was analysed for the grain size distribution of the terrigenous sediment fraction, the organic carbon content, diatom and benthic foraminifera communities. Humid conditions were observed during the Bølling–Allerød with a high contribution of fluvial sediment input. During the Younger Dryas intensified trade winds caused a larger sediment input of aeolian dust from the Sahara and more intense upwelling with higher primary productivity, as indicated by high diatom concentrations. The abrupt and large increase of organic matter caused low oxygen conditions at the sea floor, reflected by the poor benthic foraminiferal fauna and the dominance of the low‐oxygen‐tolerant foraminiferal species Bulimina exilis. This is surprising since low‐oxygen conditions have not been recorded during modern times at the sea floor in this region, despite present‐day intensive upwelling and high primary productivity. After the Younger Dryas, more humid conditions returned, diatom abundance decreased and B. exilis was replaced by typical deep‐sea species as found in the region today, indicating the return of more oxygenated conditions at the sea floor. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

13.
A detailed shoreline displacement curve documents the Younger Dryas transgression in western Norway. The relative sea‐level rise was more than 9 m in an area which subsequently experienced an emergence of almost 60 m. The sea‐level curve is based on the stratigraphy of six isolation basins with bedrock thresholds. Effort has been made to establish an accurate chronology using a calendar year time‐scale by 14C wiggle matching and the use of time synchronic markers (the Vedde Ash Bed and the post‐glacial rise in Betula (birch) pollen). The sea‐level curve demonstrates that the Younger Dryas transgression started close to the Allerød–Younger Dryas transition and that the high stand was reached only 200 yr before the Younger Dryas–Holocene boundary. The sea level remained at the high stand for about 300 yr and 100 yr into Holocene it started to fall rapidly. The peak of the Younger Dryas transgression occurred simultaneously with the maximum extent of the ice‐sheet readvance in the area. Our results support earlier geophysical modelling concluding a causal relationship between the Younger Dryas glacier advance and Younger Dryas transgression in western Norway. We argue that the sea‐level curve indicates that the Younger Dryas glacial advance started in the late Allerød or close to the Allerød–Younger Dryas transition. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

14.
Palaeoenvironmental change following deglaciation of the last British–Irish Ice Sheet on the continental shelf west of Ireland was investigated using multiproxy analyses of sediment and foraminifera data from nine sediment cores. Lithofacies associations record various depositional regimes across the shelf, which evolve from subglacial to postglacial conditions. Census data provide the first characterisation of benthic foraminifera populations across the continental shelf and multivariate analyses reveal three distinct biotopes. Biomineralization within these biotopes is restricted to ≤21 200 cal a bp by four radiocarbon ages. The transition from glacial to postglacial benthic foraminifera populations near the shelf break marks the establishment of productive, nutrient-rich, ice-distal conditions at ~20 900 cal a bp ; these conditions may also mark the start of favourable conditions for postglacial cold-water coral growth. Postglacial conditions on the inner shelf were not established until <14 500 cal a bp , suggesting glacial conditions west of Ireland may have persisted into the Bølling–Allerød Interstadial.  相似文献   

15.
Palynological and sedimentological analyses of a sedimentary sequence sampled at Hauterive/Rouges‐Terres, Lake Neuchâtel (Switzerland) provide documentation of changes in vegetation and lake‐level during the Bølling, Younger Dryas and Preboreal pollen zones, and have allowed a comparison with sequences covering the same period from other sites located in the western part of the Swiss Plateau. The Juniperus–Hippophaë zone (regional pollen assemblage zone (RPAZ) CHb‐2, first part of the Bølling, ca. 14 650–14 450 cal. yr BP) was characterised by a generally low lake‐level. A weak rise occurred during this zone. The Juniperus–Hippophaë to Betula zone transition coincided with a lake‐level lowering, interrupted by a short‐lived but marked phase of higher lake‐level recorded at the neighbouring site of Hauterive‐Champréveyres, but not present at Hauterive/Rouges‐Terres owing to an erosion surface. Shortly after the beginning of the Betula zone (RPAZ CHb‐3, second part of the Bølling, ca 14 450–14 000 cal. yr BP), a marked rise in lake‐level occurred. It was composed of two successive periods of higher level, coinciding with high values of Betula, separated by a short episode of relatively lower lake‐level associated with raised values in Artemisia and other non‐arboreal pollen. The last part of RPAZ CHb‐3 saw a fall in lake‐level. The lower lake‐levels during RPAZ CHb‐2 to early RPAZ CHb‐3 can be correlated with the abrupt warming at the beginning of the Greenland Interstadial (GI) 1e thermal maximum. The successive episodes of higher lake‐level punctuating the GI 1e might be linked to the so‐called Intra‐Bølling Cold Oscillations identified from several palaeoclimatic records in the North Atlantic area, and also documented in oxygen‐isotope data sets from Swiss Plateau lakes. The Hauterive/Rouges‐Terres lake‐level record provides evidence for marked climatic drying through the second part of the Younger Dryas event (GS1), during the GS1–Preboreal (RPAZ CHb‐4b–4c) transition (except for a rise at ca. 11 450–11 400 cal. yr BP), and at the RPAZ CHb‐4c–5 (Preboreal–Boreal) transition, following the Preboreal Oscillation (after 11 150 cal. yr BP). The Preboreal Oscillation coincided with higher lake‐levels, its end being followed by a rapid expansion of Corylus, Quercus, Ulmus and Tilia. The Hauterive/Rouges‐Terres lake‐level record suggests that radiocarbon plateau at 12 600, 10 000 and 9500 14C yr BP corresponded to periods of generally lower lake‐level. This suggests that an increase in solar activity may have contributed to both climatic dryness and a decrease in atmospheric radiocarbon content. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

16.
Coccoliths were studied from the ODP Hole 1002C and core PL07‐39PC in the Cariaco Basin. Increases in Emiliania huxleyi are synchronous with decreases of Gephyrocapsa oceanica and vice versa. A new index (GEX) based on the relative abundances of these two taxa is proposed, and correlates with various other proxies. It is shown that GEX can serve as upwelling proxy. This confirms that the Intertropical Convergence Zone shifted north during the Bølling/Allerød, south during the Younger Dryas and back north during the Preboreal. The upwelling proxy shows few discrepancies with the terrigenous record. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

17.
A core, recovered from a water depth of 53 m in Loch Assynt, North-West Scotland, has yielded a 9 m sequence comprising two distinct units, an upper, organic-rich unit (Unit I, ca. 6 m) overlying a sequence of laminated clays, silts and sands (Unit II, ca. 3 m). The upper unit is essentially Holocene in age based upon three bulk AMS radiocarbon dates while a fourth radiocarbon date from Unit II confirms a late-glacial age for that interval and supports a broadly linear age–depth relationship. Distinct variations in the magnetic susceptibility record of the lower unit can be visually correlated to major changes in the Greenland ice core (GISP2), this together with pollen evidence supports the radiocarbon dating suggesting an age of approximately 11,000 to around 17,000 cal. BP for Unit II, with evidence for the Younger Dryas (Loch Lomond) stadial and the Bolling–Allerød climatic phases. Variations in the magnetic susceptibility record of the late-glacial sediments are thought to relate to climatically driven changes in soil cover and erosion rates. The multiproxy record from Loch Assynt indicates relatively continuous, sub-aqueous sedimentation during the last ～17,000 years, providing an approximate age for the initiation of modern Loch Assynt and supporting recent dates of moraine retreat lines in the Loanan Valley from about 14–15 ka BP. Pollen and chironomid sampling provides further insights to the history of this relatively deep water body and compliment existing high-resolution palaeo-precipitation records for the mid to late Holocene interval from speleothem archives within the loch catchment.  相似文献   

18.
Lake Ladoga in northwestern Russia is Europe's largest lake. The postglacial history of the Ladoga basin is for the first time documented continuously with high temporal resolution in the upper 13.3 m of a sediment core (Co1309) from the northwestern part of the lake. We applied a multiproxy approach including radiographic imaging, (bio‐)geochemical and granulometric analyses. Age control was established combining radiocarbon dating with varve chronology, the latter anchored to a correlated radiocarbon age from a lake close by. The age‐depth model reveals the onset of glacial varve sedimentation at 13 910±140 cal. a BP, when Lake Ladoga was part of the Baltic Ice Lake. Linear extrapolation of published retreat rates of the Scandinavian Ice Sheet provides a formation age of the Luga moraine close to Lake Ladoga's southern shore of 14.5–15.9 cal. ka BP, older than previously assumed. Varve sedimentation covers the Bølling/Allerød interstadial, the Younger Dryas stadial and the Early Holocene. Varve‐thickness variations, conjoined with grain‐size and geochemical variations, inform about the relative position of the Scandinavian Ice Sheet and the climate during the deglaciation phase. The upper limit of the varved succession marks the change from glaciolacustrine to normal lacustrine sedimentation and post‐dates the drainage of the Baltic Ice Lake as well as the formation of the Salpausselkä II moraine north of Lake Ladoga, by c. 250 years. The Holocene sediment record is divided into three periods in the following order: (i) a lower transition zone between the Holocene boundary and c. 9.5 cal. ka BP, characterized by mostly massive sediments with low organic content, (ii) a phase with increased organic content from c. 9.5 to 4.5 cal. ka BP corresponding to the Holocene Thermal Maximum, and (iii) a phase with relatively stable sedimentation in a lacustrine environment from c. 4.5 cal. ka BP until present.  相似文献   

19.
Studies of lake sediments on Sejerø in southern Kattegat indicate a treeless arctic environment with the dwarf shrub Salix polaris, herbs and wetland mosses. The mean July temperature was around 8 to 10°C. An AMS radiocarbon age determination of a Salix twig yielded an age of around 36 000 14C yr BP, which is in accordance with previous conventional dating of bulk sediment samples. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

20.
Articulated molluscs, sea urchins and barnacle fragments close to the Vedde Ash Bed in a shallow marine deposit on the west coast of Norway have been 14C dated. The weighted mean of four dates from a sediment slice 8 cm thick centred on the Vedde Ash Bed is 10920 ± 24 14C yr BP. The most accurate 14C age of the Vedde Ash from terrestrial plant macrofossils is 10310 ± 50 yr BP. The difference is the 14C reservoir age for coastal water at the west coast of Norway during the mid‐Younger Dryas and equals 610 ± 55 yr. This is 230 yr older than the reservoir age for the Bølling/Allerød and for the present day in this area. The result supports earlier conclusions of a higher reservoir age for the Younger Dryas in the North Atlantic and Nordic Seas, although our reservoir age of 610 ± 55 yr is a few hundred years younger. This suggests that the 14C reservoir age at Vedde Ash time may increase from coastal water towards the open North Atlantic and Nordic Seas. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

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