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1.
Mongolian glaciers have been the subject of relatively little research, resulting in less geochronological constraint than other parts of Central Asia. The Khentey Mountains (latitude 47–51°N, longitude 105–112°E) are a typical landlocked mountain range exhibiting clear geomorphic evidence of late Quaternary glaciation. Yet, compared to western parts of Mongolia such as the Mongolian Altay, Gobi Altay, Khangay, and Khovsgol, glacial history of the Khentey Mountains is poorly understood. To address this, and permit comparison of the Khentey glacier–climate record with other alpine regions in Mongolia, we performed geomorphological mapping and cosmogenic 10Be surface‐exposure dating in two glaciated regions of the Khentey Mountains: Yestii and Khagiin Khar. Specifically, we measured 10Be in 34 samples collected from five moraine sequences, which, together with morphostratigraphy, correspond to four main glacial stages: (i) The My1 terminal moraine sequence for Yestii (21.0±4.9 ka) and the Mk1 moraine for Khagiin Khar (19.6±2.6 ka), both of which represent the Last Glacial Maximum; (ii) the Lateglacial Mk2 moraine, dated to 16.0±3.5 ka; (iii) the Mk3 moraine, dated to either 17.6±7.0 ka (Lateglacial) or 12.1±1.1 ka (Younger Dryas); and (iv) the currently undated Mk4 moraine (~2200 m a.s.l.), to which we assign a Holocene age. Our results suggest that the timing of maximum glacier extent in Mongolia was regionally variable. In the Khentey Mountains, maximum glaciation occurred during Marine Isotope Stage (MIS) 2, whereas the maximum occurred during MIS 3 in Khangay and Khovsgol and during MIS 4 in the Altay. The MIS 2 glacial maximum in the Khentey Mountains coincided with the global sea level minimum during the Last Glacial Maximum, and was followed by at least three glacial re‐advances during the Lateglacial to possibly the Holocene.  相似文献   

2.
Evidence of a dynamic Holocene glacial history is preserved in the terrestrial and marine archives of St. Jonsfjorden, a small fjord‐system on the west coast of Spitsbergen, Svalbard. High‐resolution, remotely sensed imagery from marine and terrestrial environments was used to construct geomorphological maps that highlight an intricate glacial history of the entire fjord‐system. The geomorphology and stratigraphy indicate an early Holocene local glacier advance constrained to the Lateglacial–early Holocene transition. Identification and 14C dating of the thermophilous bivalve mollusc Modiolus modiolus to 10.0±0.12 cal. ka BP suggest a rapid northward migration of the species shortly after deglaciation. Further evidence enhances the understanding of the onset and subsequent climax of the Neoglacial‐Little Ice Age in inner St. Jonsfjorden. The present‐day terminus of Osbornebreen, the dominating glacier system in St. Jonsfjorden, is located over 8.5 km up‐fjord from its Neoglacial maximum extent. Cross‐cutting relationships suggest subsequent advances of all the smaller glaciers in the area following the break‐up of Osbornebreen. Glacial deposits, landforms and their cross‐cutting relationships observed in both terrestrial and marine settings imply a complex and highly dynamic environment through the later part of the Holocene.  相似文献   

3.
The deglaciation history and Holocene environmental evolution of northern Wijdefjorden, Svalbard, are reconstructed using sediment cores and acoustic data (multibeam swath bathymetry and sub-bottom profiler data). Results reveal that the fjord mouth was deglaciated prior to 14.5±0.3 cal. ka BP and deglaciation occurred stepwise. Biomarker analyses show rapid variations in water temperature and sea ice cover during the deglaciation, and cold conditions during the Younger Dryas, followed by minimum sea ice cover throughout the Early Holocene, until c. 7 cal. ka BP. Most of the glaciers in Wijdefjorden had retreated onto land by c. 7.6±0.2 cal. ka BP. Subsequently, the sea-ice extent increased and remained high throughout the last part of the Holocene. We interpret a high Late Holocene sediment accumulation rate in the northernmost core to reflect increased sediment flux to the site from the outlet of the adjacent lake Femmilsjøen, related to glacier growth in the Femmilsjøen catchment area. Furthermore, increased sea ice cover, lower water temperatures and the re-occurrence of ice-rafted debris indicate increased local glacier activity and overall cooler conditions in Wijdefjorden after c. 0.5 cal. ka BP. We summarize our findings in a conceptual model for the depositional environment in northern Wijdefjorden from the Late Weichselian until present.  相似文献   

4.
Glacial landforms and sediments mapped in three presently unglaciated mountain massifs, the Nanhuta Shan, the Hsueh Shan and the Yushan, support the concept of repeated, multi-stage glaciations in the Taiwanese high mountain range during the late Pleistocene. New results from surface exposure dating using in situ produced cosmogenic 10Be measured in samples taken from erratic and moraine boulders in Nanhuta Shan at altitudes between 3100 and 3500 m are presented here. The results confirm independent and previously reported Optically Stimulated Luminescence (OSL) ages and 10Be exposure ages from glacial deposits in the same area and suggest a Lateglacial and early Holocene glaciation, the so called Nanhuta glacier advance with two substages at about 12–15 ka and 9.5 ka BP. The respective equilibrium line altitudes (ELA) were calculated at 3340 m and 3440 m with corresponding ELA depressions of 610 ± 100 m and 510 ± 100 m relative to the present day (theoretical) ELA, which is estimated to be at about 3950 ± 100 m in Taiwan. Large-scale erosional landforms indicate a much wider glacier extent during an earlier stage, which is not dated in Nanhuta Shan so far. Luminescence dating from near Hsueh Shan suggests an age of marine isotope stage (MIS) 4 for this stage.  相似文献   

5.
A sudden release of large volumes of water during a glacier outburst flood (GLOF) is a major hazard worldwide. Here, we identify the sedimentary signature of glacial and non‐glacial processes, including GLOFs, based on lacustrine sediments from the distal glacier‐fed Lake Buarvatnet in western Norway. Historically documented GLOFs in 2002 CE and during the 1980s CE are identified in the 210Pb‐ and 14C‐dated sediments. These events have the same sedimentary signature as 12 earlier events throughout the Holocene interpreted to represent previous GLOFs in the catchment. The GLOFs are interpreted to have occurred during periods when the glacier extent was similar to the modern positions, and the events are thus used to pinpoint past positions of the glacier terminus and, hence, the equilibrium line altitudes (ELAs). The results indicate that the glacier Svartenutbreen, located at the eastern part of Folgefonna, had a similar size in 2002 CE as c. 8200–8300 cal. a BP, corresponding to the 8.2 ka event in the North Atlantic region. The regrowth of Sørfonna after the Holocene Thermal Optimum occurred at c. 6900 cal. a BP and Svartenutbreen was at modern size and extent in the periods c. 6400, c. 5450, c. 4850, c. 3850, c. 3550 and c. 1650 cal. a BP. Since 1650 cal. a BP, we infer that the glacier was larger than the 2002 CE glacier extent until 1910 CE when a GLOF occurred. Svartenutbreen has been retreating since 1910 CE, which led to the ice damming of the two historical GLOFs in the 1980s and 2002 CE separated by a glacier advance in the 1990s CE. The findings are discussed and compared to other regional glacier reconstructions in Norway, and emphasize the value of identifying and utilizing GLOFs as an indicator of past ELA variability.  相似文献   

6.
Quaternary glaciation of Mount Everest   总被引：1，自引：0，他引：1  
The Quaternary glacial history of the Rongbuk valley on the northern slopes of Mount Everest is examined using field mapping, geomorphic and sedimentological methods, and optically stimulated luminescence (OSL) and 10Be terrestrial cosmogenic nuclide (TCN) dating. Six major sets of moraines are present representing significant glacier advances or still-stands. These date to >330 ka (Tingri moraine), >41 ka (Dzakar moraine), 24–27 ka (Jilong moraine), 14–17 ka (Rongbuk moraine), 8–2 ka (Samdupo moraines) and ～1.6 ka (Xarlungnama moraine), and each is assigned to a distinct glacial stage named after the moraine. The Samdupo glacial stage is subdivided into Samdupo I (6.8–7.7 ka) and Samdupo II (～2.4 ka). Comparison with OSL and TCN defined ages on moraines on the southern slopes of Mount Everest in the Khumbu Himal show that glaciations across the Everest massif were broadly synchronous. However, unlike the Khumbu Himal, no early Holocene glacier advance is recognized in the Rongbuk valley. This suggests that the Khumbu Himal may have received increased monsoon precipitation in the early Holocene to help increase positive glacier mass balances, while the Rongbuk valley was too sheltered to receive monsoon moisture during this time and glaciers could not advance. Comparison of equilibrium-line altitude depressions for glacial stages across Mount Everest reveals asymmetric patterns of glacier retreat that likely reflects greater glacier sensitivity to climate change on the northern slopes, possibly due to precipitation starvation.  相似文献   

7.
We reconstructed a chronology of glaciation spanning from the Late Pleistocene through the late Holocene for Fish Lake valley in the north‐eastern Alaska Range using 10Be surface exposure dating and lichenometry. After it attained its maximum late Wisconsin extent, the Fish Lake valley glacier began to retreat ca. 16.5 ka, and then experienced a readvance or standstill at 11.6 ± 0.3 ka. Evidence of the earliest Holocene glacial activity in the valley is a moraine immediately in front of Little Ice Age (LIA) moraines and is dated to 3.3–3.0 ka. A subsequent advance culminated at ca. AD 610–900 and several LIA moraine crests date to AD 1290, 1640, 1860 and 1910. Our results indicate that 10Be dating from high‐elevation sites can be used to help constrain late Holocene glacial histories in Alaska, even when other dating techniques are unavailable. Close agreement between 10Be and lichenometric ages reveal that 10Be ages on late Holocene moraines may be as accurate as other dating methods. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

8.
The timing of glaciation in the Lahul Himalaya of northern India was ascertained using the concentrations of cosmogenic 10Be and 26Al from boulders on moraines and drumlins, and from glacially polished bedrock surfaces. Five glacial stages were identified: Sonapani I and II, Kulti, Batal and Chandra. Of these, cosmogenic exposure ages were obtained on samples representative of the Batal and Kulti glacial cycles. Stratigraphical relationships indicate that the Sonapani I and II are younger. No age was obtained for the Chandra glacial advance. Batal Glacial Stage deposits are found throughout the valley, indicating the presence of an extensive valley glacial system. During the Kulti Stage, glaciers advanced ca. 10 km beyond their current positions. Moraines produced during the Batal Stage, ca. 12–15.5 ka, are coeval with the Northern Hemisphere Late‐glacial Interstadial (Bølling/Allerød). Deglaciation of the Batal Glacial Stage was completed by ca. 12 ka and was followed by the Kulti Glacial Stage during the early Holocene, at ca. 10–11.4 ka. On millennial time‐scales, glacier oscillations in the Lahul Himalaya apparently reflect periods of positive mass‐balance coincident with times of increased insolation. During these periods the South Asian summer monsoon strengthened and/or extended its influence further north and west, thereby enhancing high‐altitude summer snowfall. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

9.
Quantitative glacial chronologies of past glaciations are sparse in the Himalaya, and mostly absent in the Kashmir Himalaya. We used cosmogenic 10Be exposure dating, and geomorphological mapping to reconstruct glacial advances of the Thajwas Glacier (TG) in the Great Himalayan Range of the Kashmir Himalaya. From 10Be exposure dating of ten moraine boulders, four glacial stages with ages ～20.77 ± 2.28 ka, ～11.46 ± 1.69 ka, ～9.12 ± 1.39 ka and ～4.19 ± 0.78 ka, were identified. The reconstructed cosmogenic radionuclide ages confirmed the global Last Glacial Maximum (gLGM), Younger Dryas, Early Holocene, and Neoglaciation episodes. As per area and volume change analyses, the TG has lost 51.1 km2 of its area and a volume of 2.64 km3 during the last 20.77 ± 2.28 ka. Overall, the results suggested that the TG has lost 64% of area and 73% of volume from the Last glacial maximum to Neoglaciation and about 85.74% and 87.67% of area and volume, respectively, from Neoglaciation to the present day. The equilibrium line altitude of the TG fluctuated from 4238 m a.s.l present to 3365 m a.s.l during the gLGM (20.77 ± 2.28 ka). The significant cooling induced by a drop in mean ambient temperature resulted in a positive mass balance of the TG during the gLGM. Subsequently the melting accelerated due to the continuing rise of the global ambient temperature. Paleo-glacial history reconstruction of the Kashmir Himalaya, with its specific geomorphic and climatic setting, would help close the information gap about the chronology of past regional glacial episodes.  相似文献   

10.
Forty-four boulders from moraines in two glacial valleys of Mount Erciyes (38.53°N, 35.45°E, 3917 m), central Turkey, dated with cosmogenic chlorine-36 (36Cl), indicate four periods of glacial activity in the past 22 ka (1 ka = 1000 calendar years). Last Glacial Maximum (LGM) glaciers were the most extensive, reaching 6 km in length and descending to an altitude of 2150 m above sea level. These glaciers started retreating 21.3 ± 0.9 ka (1σ) ago. They readvanced and retreated by 14.6 ± 1.2 ka ago (Lateglacial), and again by 9.3 ± 0.5 ka ago (Early Holocene). The latest advance took place 3.8 ± 0.4 ka ago (Late Holocene). Using glacier modeling together with paleoclimate proxy data from the region, we reconstructed the paleoclimate at these four discrete times. The results show that LGM climate was 8–11 °C colder than today and moisture levels were somewhat similar to modern values, with a range between 20% more and 25% less than today. The analysis of Lateglacial advance suggests that the climate was colder by 4.5–6.4 °C based on up to 1.5 times wetter conditions. The Early Holocene was 2.1–4.9 °C colder and up to twice as wet as today, while the Late Holocene was 2.4–3 °C colder and its precipitation amounts approached to similar conditions as today. Our paleoclimate reconstructions show a general trend of warming for the last 22 ka, and an increase of moisture until Early Holocene, and a decrease after that time. The recent glacier terminates at 3450 m on the northwest side of the mountain. It is a remnant from the last advance (possibly during the Little Ice Age). Repeated measurements of glacier length between 1902 and 2008 reveal a retreat rate of 4.2 m per year, which corresponds to a warming rate of 0.9–1.2 °C per century.  相似文献   

11.
With accelerated melting of alpine glaciers, understanding the future state of the cryosphere is critical. Because the observational record of glacier response to climate change is short, palaeo‐records of glacier change are needed. Using proglacial lake sediments, which contain continuous and datable records of past glacier activity, we investigate Holocene glacier fluctuations on northeastern Baffin Island. Basal radiocarbon ages from three lakes constrain Laurentide Ice Sheet retreat by ca. 10.5 ka. High sedimentation rates (0.03 cm a?1) and continuous minerogenic sedimentation throughout the Holocene in proglacial lakes, in contrast to organic‐rich sediments and low sedimentation rates (0.005 cm a?1) in neighbouring non‐glacial lakes, suggest that glaciers may have persisted in proglacial lake catchments since regional deglaciation. The presence of varves and relatively high magnetic susceptibility from 10 to 6 ka and since 2 ka in one proglacial lake suggest minimum Holocene glacier extent ca. 6–2 ka. Moraine evidence and proglacial and threshold lake sediments indicate that the maximum Holocene glacier extent occurred during the Little Ice Age. The finding that glaciers likely persisted through the Holocene is surprising, given that regional proxy records reveal summer temperatures several degrees warmer than today, and may be due to shorter ablation seasons and greater accumulation‐season precipitation. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

12.
We present a well‐dated, high‐resolution and continuous sediment record spanning the last c. 24 000 years from lake Bolshoye Shchuchye located in the Polar Ural Mountains, Arctic Russia. This is the first continuous sediment succession reaching back into the Last Glacial Maximum (LGM) ever retrieved from this region. We reconstruct the glacial and climate history in the area since the LGM based on sedimentological and geochemical analysis of a 24‐m‐long sediment core. A robust chronology was established using a combination of AMS 14C‐dating, the position of the Vedde Ash and varve counting. The varved part of the sediment core spans across the LGM from 24 to 18.7 cal. ka BP. We conclude that the lake basin remained ice‐free throughout the LGM, but that mountain glaciers were present in the lake catchment. A decrease in both glacial varve preservation and sedimentation rate suggests that these glaciers started to retreat c. 18.7 cal. ka BP and had disappeared from the catchment by 14.35 cal. ka BP. There are no indications of glacier regrowth during the Younger Dryas. We infer a distinct climatic amelioration following the onset of the Holocene and an Early to Middle Holocene thermal optimum between 10–5 cal. ka BP. Our results provide a long‐awaited continuous and high‐resolution record of past climate that supplements the existing, more fragmentary data from moraines and exposed strata along river banks and coastal cliffs around the Russian Arctic.  相似文献   

13.
Cosmogenic nuclide surface exposure dating of boulders and erratics provides new constraints for a glacial chronology in the source area of the Urumqi River, Tian Shan, China. 10Be exposure ages of 15.0 ± 1.3–17.1 ± 1.5 ka from the Upper Wangfeng (UWF) moraines agree well with their previous relative age assignments to marine isotope stage (MIS) 2, but are younger than published AMS 14C and electron spin resonance (ESR) ages (from 22.8 ± 0.6 to 37.4 ka). This difference may result from variations in techniques, or could reflect the impact of surface erosion and sediment/snow cover on surface exposure dating. 10Be ages from the Lower Wangfeng (LWF) moraines (18.7 ± 1.8 and 16.2 ± 1.5 ka) are indistinguishable from the UWF exposure ages, but are significantly younger than previously reported thermoluminescence (TL) and ESR ages (37.7 ± 2.6–184.7 ± 18 ka). Either these two groups were formed during the same period (MIS 2) and there are problems with TL and ESR ages, or the moraines were of very different ages and the similar exposure ages result from different degrees of degradation. Erratics on rock steps and a drumlin along >8 km of the main glacial valley above the UWF have internally consistent and slightly decreasing 10Be exposure ages indicating glacier retreat >2.5 m a?1 after MIS 2 and before middle or late Holocene glacier re‐advances. This retreat rate is similar to rates observed from modern glaciers. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

14.
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   

15.
We present a chronology of late Pleistocene deglaciation and Neoglaciation for two valleys in the north‐central Brooks Range, Alaska, using cosmogenic 10Be exposure dating. The two valleys show evidence of ice retreat from the northern range front before ～16–15 ka, and into individual cirques by ～14 ka. There is no evidence for a standstill or re‐advance during the Lateglacial period, indicating that a glacier advance during the Younger Dryas, if any, was less extensive than during the Neoglaciation. The maximum glacier expansion during the Neoglacial is delimited by moraines in two cirques separated by about 200 km and dated to 4.6 ± 0.5 and 2.7 ± 0.2 cal ka BP. Both moraine ages agree with previously published lichen‐inferred ages, and confirm that glaciers in the Brooks Range experienced multiple advances of similar magnitude throughout the late Holocene. The similar extent of glaciers during the middle Holocene and the Little Ice Age may imply that the effect of decreasing summer insolation was surpassed by increasing aridity to limit glacier growth as Neoglaciation progressed. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

16.
Only a few chronological constraints on Lateglacial and Early Holocene glacier variability in the westernmost Alps have hitherto been obtained. In this paper, moraines of two palaeoglaciers in the southern Écrins massif were mapped. The chronology of the stabilization of selected moraines was established through the use of 10Be cosmic ray exposure (CRE) dating. The equilibrium line altitude (ELA) during moraine deposition was reconstructed assuming an accumulation area ratio (AAR) of 0.67. Ten pre‐Little Ice Age (LIA) ice‐marginal positions of the Rougnoux palaeoglacier were identified and seven of these have been dated. The 10Be CRE age of a boulder on the lowermost sampled moraine indicates that the landform may have been first formed during a period of stable glaciers at around 16.2±1.7 ka (kiloyears before AD 2017) or that the sampled boulder experienced pre‐exposure to secondary cosmic radiation. The moraine was re‐occupied or, alternatively, shaped somewhat before 12.2±0.6 ka when the ELA was lowered by 230 m relative to the LIA ELA. At least six periods of stable ice margins occurred thereafter when the ELA was 220–160 m lower than during the LIA. The innermost dated moraine stabilized at or before 10.9±0.7 ka. Three 10Be CRE ages from a moraine of the Prelles palaeoglacier indicate a period of stationary ice margins at or before 10.9±0.6 ka when the ELA was lowered by 160 m with respect to the end of the LIA. The presented 10Be CRE ages are in good agreement with those of moraines that have been attributed to the Egesen stadial. Assuming unchanged precipitation, summer temperature in the southern Écrins massif at ~12 ka must have been at least 2 °C lower relative to the LIA.  相似文献   

17.
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   

18.
The transition phase from Lateglacial to Holocene climate conditions was accompanied by a pronounced reorganization of climate patterns in the Northern Hemisphere. Evidence of Alpine palaeoglaciers provides a basis for understanding climate downturns during a time of generally warming conditions. In this context a series of well‐preserved and previously undated moraines were investigated in the small Falgin cirque located in the central Alpine Langtaufers Valley (South Tyrol, Italy) and in the neighbouring Hinteres Bergle cirque of the Radurschl Valley (North Tyrol, Austria). Both localities are situated in the driest area of the eastern Alps. They lie well above prominent moraines associated with the Younger Dryas (YD) cold phase and represent the first moraines below Little Ice Age (LIA) positions. The corresponding equilibrium line altitude of the palaeoglaciers in both cirques was 100–120 m lower than during the LIA. Surface exposure dating (10Be) of the inner Falgin moraines shows a mean stabilization age of 11.2±0.9 ka, which is similar to the deglaciation age of 10.9±0.8 ka for the Hinteres Bergle cirque. The ages indicate glacier activity most likely during the earliest Holocene or the YD/Holocene transition. These findings point to a climate with mean summer temperatures about 1.5 °C lower than during the 20th century in the Alps.  相似文献   

19.
Latest Pleistocene and Holocene glacier variations in the European Alps   总被引：1，自引：0，他引：1  
In the Alps, climatic conditions reflected in glacier and rock glacier activity in the earliest Holocene show a strong affinity to conditions in the latest Pleistocene (Younger Dryas). Glacier advances in the Alps related to Younger Dryas cooling led to the deposition of Egesen stadial moraines. Egesen stadial moraines can be divided into three or in some cases even more phases (sub-stadials). Moraines of the earliest and most extended advance, the Egesen maximum, stabilized at 12.2 ± 1.0 ka based on 10Be exposure dating at the Schönferwall (Tyrol, Austria) and the Julier Pass-outer moraine (Switzerland). Final stabilization of moraines at the end of the Egesen stadial was at 11.3 ± 0.9 ka as shown by 10Be data from four sites across the Alps. From west to east the sites are Piano del Praiet (northwestern Italy), Grosser Aletschgletscher (central Switzerland), Julier Pass-inner moraine (eastern Switzerland), and Val Viola (northeastern Italy). There is excellent agreement of the 10Be ages from the four sites. In the earliest Holocene, glaciers in the northernmost mountain ranges advanced at around 10.8 ± 1.1 ka as shown by 10Be data from the Kartell site (northern Tyrol, Austria). In more sheltered, drier regions rock glacier activity dominated as shown, for example, at Julier Pass and Larstig valley (Tyrol, Austria). New 10Be dates presented here for two rock glaciers in Larstig valley indicate final stabilization no later than 10.5 ± 0.8 ka. Based on this data, we conclude the earliest Holocene (between 11.6 and about 10.5 ka) was still strongly affected by the cold climatic conditions of the Younger Dryas and the Preboreal oscillation, with the intervening warming phase having had the effect of rapid downwasting of Egesen glaciers. At or slightly before 10.5 ka rapid shrinkage of glaciers to a size smaller than their late 20th century size reflects markedly warmer and possibly also drier climate. Between about 10.5 ka and 3.3 ka conditions in the Alps were not conducive to significant glacier expansion except possibly during rare brief intervals. Past tree-line data from Kaunertal (Tyrol, Austria) in concert with radiocarbon and dendrochronologically dated wood fragments found recently in the glacier forefields in both the Swiss and Austrian Alps points to long periods during the Holocene when glaciers were smaller than they were during the late 20th century. Equilibrium line altitudes (ELA) were about 200 m higher than they are today and about 300 m higher in comparison to Little Ice Age (LIA) ELAs. The Larstig rock glacier site we dated with 10Be is the type area for a postulated mid-Holocene cold period called the Larstig oscillation (presumed age about 7.0 ka). Our data point to final stabilization of those rock glaciers in the earliest Holocene and not in the middle Holocene. The combined data indicate there was no time window in the middle Holocene long enough for rock glaciers of the size and at the elevation of the Larstig site to have formed. During the short infrequent cold oscillations between 10.5 and 3.3 ka small glaciers (less than several km2) may have advanced to close to their LIA dimensions. Overall, the cold periods were just too short for large glaciers to advance. After 3.3 ka, climate conditions became generally colder and warm periods were brief and less frequent. Large glaciers (for example Grosser Aletschgletscher) advanced markedly at 3.0–2.6 ka, around 600 AD and during the LIA. Glaciers in the Alps attained their LIA maximum extents in the 14th, 17th, and 19th centuries, with most reaching their greatest LIA extent in the final 1850/1860 AD advance.  相似文献   

20.
Shells of the helicid Cepaea nemoralis were studied using taphonomic, isotopic and morphometric measurements to estimate late glacial–Holocene (~ 12.1–6.3 cal ka BP) environmental conditions in northern Spain. Higher taphonomic alteration among Holocene shells suggests lower sedimentation rates or higher shell-destruction rates than during glacial conditions. Shells preserved the aragonitic composition despite differing degree of skeleton damage. Shell δ13C values were ? 10.3 ± 1.1‰, ? 8.2 ± 2.3‰, and ? 7.3 ± 1.6‰ for modern, Holocene and late-glacial individuals, respectively. Higher δ13C values during the late-glacial and some Holocene periods imply higher water stress of C3 plants and/or higher limestone contribution than today. Intrashell δ13C values were higher during juvenile stages suggesting higher limestone ingestion to promote shell growth. Shell δ18O values were ? 1.1 ± 0.7‰, ? 0.9 ± 0.8‰ and ? 0.1 ± 0.7‰ for modern, Holocene and late-glacial specimens, respectively. A snail flux-balance model suggests that during ~ 12.1 ? 10.9 cal ka BP conditions were drier and became wetter at ~ 8.4 ? 6.3 cal ka BP and today. Intrashell δ18O profiles reveal that glacial individuals experienced more extreme seasonality than interglacial shells, despite possible larger hibernation periods. Shell size correlated positively with δ18O values, suggesting that growth rates and ultimate adult size of C. nemoralis may respond to climate fluctuation in northern Spain.  相似文献   

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