首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
Two sediment cores of 70 and 252 cm length were recovered from Hjort Sø, a small lake on Store Koldewey, Northeast Greenland, and studied with a multidisciplinary approach in order to reconstruct the local environmental history and to test the relevance of proxies for paleoenvironmental information. The basal sediments from the longer core are dominated by clastic matter, which was likely deposited during deglaciation of the lake basin. These clastic sediments are overlain by gyttja, which is also present throughout the shorter core. AMS radiocarbon dating was conducted on plant macrofossils of 11 samples from the gyttja in both cores. A reliable chronology was established for both cores, which dated the onset of organic accumulation at 9,500 cal. year BP. The Holocene temperature development, with an early to mid Holocene thermal maximum, is best reflected in the grain-size composition. Nutrient availability was apparently low during the early Holocene and led to low productivity in the lake and its vicinity. From ca. 7,000 cal. year BP, productivity in the lake increased significantly, probably induced by external nutrient input from goose excrements. From this time, micro- and macro-fossil remains reflect relatively well the climate history of East Greenland, with a cooling during the middle Holocene, the medieval warming, and the Little Ice Age. The amount of organic matter in the sequence seems to be more affected by lake ice cover or by nutrient supply from the catchment than by temperature changes. The record from Hjort Sø thus reveals the difficulties in interpreting sedimentary records from high arctic regions.  相似文献   

2.
Terrace remnants close to the marine limit as well as two separate moraine ridges are observed in front of the glacier Albrechtbreen. The stacking of marine sediments from an original elevation of ca. 60–80 m a.s.l. into the Little Ice Age Moraine gives evidence for a considerably smaller glacier following the early Holocene deglaciation compared to that of the present. The outer moraine is composed of glacial diamicton. Radiocarbon datings of whale ribs, shell fragments and a log taken from sediment in front of Albrechtbreen indicate that the initial deglaciation occurred before 9, 400 B.P. and that the outer moraine was formed during a younger Holocene glacial advance. Lithological differences between the two moraine ridges suggest that the first ice advance occurred during a period with limited permafrost, whereas permafrost was more extensive during the Little Ice Age.  相似文献   

3.
Prediction of future Arctic climate and environmental changes, as well as associated ice-sheet behavior, requires placing present-day warming and reduced ice extent into a long-term context. Here we present a record of Holocene climate and glacier fluctuations inferred from the paleolimnology of small lakes near Istorvet ice cap in East Greenland. Calibrated radiocarbon dates of organic remains indicate deglaciation of the region before ~10,500 years BP, after which time the ice cap receded rapidly to a position similar to or less extensive than present, and lake sediments shifted from glacio-lacustrine clay to relatively organic-rich gyttja. The lack of glacio-lacustrine sediments throughout most of the record suggests that the ice cap was similar to or smaller than present throughout most of the Holocene. This restricted ice extent suggests that climate was similar to or warmer than present, in keeping with other records from Greenland that indicate a warm early and middle Holocene. Middle Holocene magnetic susceptibility oscillations, with a ~200-year frequency in one of the lakes, may relate to solar influence on local catchment processes. Following thousands of years of restricted extent, Istorvet ice cap advanced to within 365 m of its late Holocene limit at ~AD 1150. Variability in the timing of glacial and climate fluctuations, as well as of sediment organic content changes among East Greenland lacustrine records, may be a consequence of local factors, such as elevation, continentality, water depth, turbidity, and seabirds, and highlights the need for a detailed spatial array of datasets to address questions about Holocene climate change.  相似文献   

4.
Early and late Holocene water-level changes in Lake Annecy, France, were reconstructed from a sediment sequence from Annecy. Two early Holocene successive rises in lake level at ca. 8900-8700 BP are recorded. Another increase in lake level, beginning at ca. 780 BP, is documented. The higher lake-level conditions in Lake Annecy during the 9th millennium BP, i.e. between the Preboreal oscillation and the 8200 yr event, appear to coincide with a more widespread cooling period which has been recorded in western Europe, in the Greenland ice-sheet and the North Atlantic ocean. The rise in lake level at ca. 780 BP can be related to the early Little Ice Age.  相似文献   

5.
Earlier work in northeast Greenland has suggested a limited advance of the Greenland Ice Sheet during the Last Glacial Maximum (LGM). However, this concept has recently been challenged by marine geological studies, indicating grounded ice on the continental shelf at this time. New 10Be‐ages from the Store Koldewey island, northeast Greenland, suggest that unscoured mountain plateaus at the outer coast were covered at least partly by cold‐based ice during the LGM. It is, however, still inconclusive whether this ice was dynamically connected to the Greenland Ice Sheet or not. Regardless of the LGM ice sheet extent, the 10Be results from Store Koldewey add to a growing body of evidence suggesting considerable antiquity of crystalline unscoured terrain near present and Pleistocene ice sheet margins.  相似文献   

6.
小冰期气候的研究进展   总被引：18，自引：5，他引：13  
李明启  靳鹤龄  张洪 《中国沙漠》2005,25(5):731-737
小冰期是近2ka来的一个重要气候事件,又是目前全球变暖的背景事件,已成为古气候和古环境研究的热点。对此,科学工作者已经做了大量的研究。本文广泛综合前人研究的成果,介绍了小冰期的概况,认为1450-1890年是小冰期的时限,在此期间有三次冷期和两次暖期。冷期发生在1450-1510年、1560-1690年和1790-1890年,其中第二次冷期表现最甚;暖期发生在1510-1560年和1690-1790年。太阳活动和火山活动是小冰期气候变化的主要因素。并重点从冰芯、树轮、湖泊沉积、历史文献和沙漠地层等方面综述了近年来国内外对小冰期气候变化的研究现状。  相似文献   

7.
We present here a revised reconstruction of the Ross ice drainage system of Antarctica at the last glacial maximum (LGM) based on a recent convergence of terrestrial and marine data. The Ross drainage system includes all ice flowlines that enter the marine Ross Embayment. Today, it encompasses one-fourth of the ice-sheet surface, extending far inland into both East and West Antarctica. Grounding lines now situated in the inner Ross Embayment advanced seaward at the LGM (radiocarbon chronology in Denton and Marchant 2000 and in Hall and Denton 2000a, b), resulting in a thick grounded ice sheet across the Ross continental shelf. In response to this grounding in the Ross (and Weddell) Embayment, ice-surface elevations of the marine-based West Antarctic Ice Sheet were somewhat higher at the LGM than at present (Steig and White 1997; Borns et al. 1998; Ackert et al. 1999). At the same time, surface elevations of the East Antarctic Ice Sheet inland of the Transantarctic Mountains were slightly lower than now, except near outlet glaciers that were dammed by grounded ice in the Ross Embayment. The probable reason for this contrasting behavior is that lowered global sea level at the LGM, from growth of Northern Hemisphere ice sheets, caused widespread grounding of the marine portion of the Antarctic Ice Sheet, whereas decreased LGM accumulation led to slight surface lowering of the interior terrestrial ice sheet in East Antarctica. Rising sea level after the LGM tripped grounding-line recession in the Ross Embayment, which has probably continued to the present day (Conway et al. 1999). Hence, gravitational collapse of the grounded ice sheet from the Ross Embayment, accompanied by lowering of the interior West Antarctic ice surface and of outlet glaciers in the Transantarctic Mountains, occurred largely during the Holocene. At the same time, increased Holocene accumulation caused a slight rise of the inland East Antarctic ice surface.  相似文献   

8.
杨保  康兴成  施雅风 《地理科学》2000,20(5):397-402
据高分辨率的青海都兰树轮年表 ,将过去 2 0 0 0年的气候变化划分为 2 30’S以前的高温期 ,2 40’S～ 80 0’S冷暖波动强烈的低温期 ,810’S～ 10 70’S显著高温期 ,即中世纪暖期 ,10 80’S～ 1880’S的低温期 ,其中包括 142 0’S～1870’S的小冰期 ,以及 1890’S后的升温期。统计发现 11次极端高温或低温事件 ,以及几次大的突变事件全部出现于中世纪之前 ,指示 15 0’S～ 110 0’S期间气候运行的高度不稳定性。和中国东部、古里雅冰芯和青藏高原南部温度代用资料比较后发现 ,公元初至 3世纪前期的东汉暖期 ,3世纪后期至 7世纪初的魏晋南北朝冷期 (期间约380’S～ 46 0’S暖 ) ,中世纪暖期以及小冰期等几次重大的气候事件在中国东部、都兰和青藏高原南部序列中均存在。古里雅冰芯仅记录了前两次重要事件 ,中世纪暖期以及小冰期在该序列中表现微弱。 2 0世纪的升温在古里雅冰芯最显著 ,都兰、中国东部次之 ,而高原南部似乎不明显。  相似文献   

9.
中国热带西部的小冰期   总被引：1，自引：1，他引：1  
黄镇国  张伟强 《热带地理》2007,27(6):489-492
中国热带以约105°E为界分为东部和西部。热带西部主要是滇南地区。按照史书记载的25个冷冬降雪年份,小冰期为1498-1896年,期间有3个寒冷阶段(1498-1550年、1694-1826年、1868-1896年)和2个相对温暖阶段。热带西部的小冰期比东部地区历时短,寒冷阶段滞后,影响范围较小。小冰期时水旱灾害频仍。小冰期的寒冷阶段与太阳黑子活动的平静期有一定的相关性。热带东、西部小冰期的差异,主要是由于东部受东亚季风影响,西部受南亚季风影响。  相似文献   

10.
Age determinations of bivalve shells indicate that Bockfjorden, a fjord in north-western Spitsbergen, Svalbard, was deglaciated shortly before 10 Kya, and that the upper marine limit in this area, with an altitude of about 50 m a.s.l., has the same age. During most of the Holocene, the glaciers in Bockfjorden were less extensive than they are today. Their maximum Holocene extension occurred during the Little Ice Age. The initial shoreline emergence after the deglaciation was rapid, and former shorelines younger than 8.5 Ky are below the present sea level. A mid-Holocene transgression of the sea is traced as well as a transgression during the last thousand years.  相似文献   

11.
THE 'LITTLE ICE AGE': RE-EVALUATION OF AN EVOLVING CONCEPT   总被引：4，自引：0，他引：4  
ABSTRACT. This review focuses on the development of the ‘Little Ice Age’ as a glaciological and climatic concept, and evaluates its current usefulness in the light of new data on the glacier and climatic variations of the last millennium and of the Holocene. ‘Little Ice Age’ glacierization occurred over about 650 years and can be defined most precisely in the European Alps (c. AD 1300–1950) when extended glaciers were larger than before or since. ‘Little Ice Age’ climate is defined as a shorter time interval of about 330 years (c. AD 1570–1900) when Northern Hemisphere summer temperatures (land areas north of 20°N) fell significantly below the AD 1961–1990 mean. This climatic definition overlaps the times when the Alpine glaciers attained their latest two highstands (AD 1650 and 1850). It is emphasized, however, that ‘Little Ice Age’ glacierization was highly dependent on winter precipitation and that ‘Little Ice Age’ climate was not simply a matter of summer temperatures. Both the glacier‐centred and the climate‐centred concepts necessarily encompass considerable spatial and temporal variability, which are investigated using maps of mean summer temperature variations over the Northern Hemisphere at 30‐year intervals from AD 1571 to 1900. ‘Little Ice Age’‐type events occurred earlier in the Holocene as exemplified by at least seven glacier expansion episodes that have been identified in southern Norway. Such events provide a broader context and renewed relevance for the ‘Little Ice Age’, which may be viewed as a ‘modern analogue’ for the earlier events; and the likelihood that similar events will occur in the future has implications for climatic change in the twenty‐first century. It is concluded that the concept of a ‘Little Ice Age’ will remain useful only by (1) continuing to incorporate the temporal and spatial complexities of glacier and climatic variations as they become better known, and (2) by reflecting improved understanding of the Earth‐atmosphere‐ocean system and its forcing factors through the interaction of palaeoclimatic reconstruction with climate modelling.  相似文献   

12.
XU Juan 《地理学报》2004,14(3):289-295
A compilation of paleoclimate records from lake sediments, trees, ice cores, and historical documents provide a view of China and Arctic environmental changes in the last 600 years. Many of these changes have also been identified in sedimentary and geochemical signatures in deep-sea sediment cores from the North Atlantic Ocean, Arctic and Greenland and ice cores from the Qinghai-Tibet Plateau, confirming the linkage of environmental changes of different time scales between the Arctic and China. It is shown that the changes of precipitation, temperature and sea ice cover in Arctic were correlated with climate changes in China. This paper also developed a comparative research on the climate changes between Arctic and China both during the Little Ice Age (LIA) and the instrumental observation period. Cycles and trend of temperature variations during LIA and temperature and precipitation during the instrumental observation period are performed. We found some similarities and differences of environmental changes between Arctic and China.  相似文献   

13.
近600年来北极与中国气候变化的对比   总被引：2，自引：2，他引：0  
A compilation of paleoclimate records from lake sediments, trees, ice cores, and historical documents provide a view of China and Arctic environmental changes in the last 600 years. Many of these changes have also been identified in sedimentary and geochemical signatures in deep-sea sediment cores from the North Atlantic Ocean, Arctic and Greenland and ice cores from the Qinghai-Tibet Plateau, confirming the linkage of environmental changes of different time scales between the Arctic and China. It is shown that the changes of precipitation, temperature and sea ice cover in Arctic were correlated with climate changes in China. This paper also developed a comparative research on the climate changes between Arctic and China both during the Little Ice Age (LIA) and the instrumental observation period. Cycles and trend of temperature variations during LIA and temperature and precipitation during the instrumental observation period are performed. We found some similarities and differences of environmental changes between Arctic and China.  相似文献   

14.
中原地区晚全新世以来的环境变化   总被引：8，自引：0，他引：8  
施少华  杨怀仁 《地理学报》1992,47(2):119-129
本文利用丰富的历史资料和树木年轮资料,恢复了我国中原地区晚全新世2000余年以来的环境变化,建立了2200余年的降水变化序列。划分了晚全新世以来本地区的干湿和冷暖期。受晚全新世以来的季风环流的影响,本地区环境变化的基本模式是暖湿与冷干对应。然而,在小冰期时期特别是17世纪下半叶以后,这种模式有所改变,即冷湿对应。其主要原因作者认为有二:一是小冰期时期天气系统超常不稳定,这是由于地球气候系统的内外因素改变造成的;二是小冰期时夏季风锋面南移至中原一带,增加了本地区的降水。最后还讨论了晚全新世以来本地区季风变化的过程、机制以及它们所带来的环境变化。并提出了未来环境变化的可能趋向。  相似文献   

15.
The empirical mode decomposition method is used for analyzing the paleoclimate proxy δ18O from Greenland GISP2 ice core.The results show that millennium climate change trends in Greenland record the Medieval Warm Period (MWP) from 860AD-1350AD lasting for about 490 years,and the Little Ice Age (LIA) from 1350AD-1920AD lasting about 570 years.During these events,sub cooling-warming variations occurred.Its multi-scale oscillations changed with quasi-period of 3-year,6.5-year,12-year,24-year,49-year,96-year,213-year and 468-year,and are not only affected by ENSO but also by solar activity.The oscillation of intrinsic mode function IMF7,IMF8 and their tendency obviously appear in 1350AD which is considered as the key stage of transformation between MWP and LIA.The results give more detailed changes and their stages of millennium climate change in high latitude areas of the Northern Hemisphere.  相似文献   

16.
In october 1990 an automatic weather station was established at the Arctic Station (65° 15', 53°31'W), Qeqertarsuaq (Godhavn), Central West Greenland. The Station register parameters each 20 minutes, and the paramters have been described in an earlier paper in this journal by Nielsen et al.(1995). The present paper summarizes meteorological parameters during 1999.

During a field campaign in 1999, woody remains from Salix glauca were found on a nunatak, 515 m. a.s.l. on the Mittivakkat Glacier, South East Greenland. Radio carbon dating determined the age of a wood sample to AD 640. Together with analyses of macroscopic botanical remains and insect rests in peaty material found nearby, these results indicate, that a warmer climate prevailed near the glacier around AD 600. These findings are in accordance with temperature records based on studies of ice cores from the Greenland Ice sheet.  相似文献   

17.
Geografisk Tidsskrift—Danish Journal of Geography 110(2):337–355, 2010

In northern Greenland, the Cape Grinnell beach ridge plain offers a 9,000year multi-proxy record for isostatic recovery, storm history, and the hydrological changes related to precipitation and slope evolution. The chronology of uplifted beach ridges is constrained by ten geological 14C ages on shell and sea mammal bones and eleven upper limiting ages from archaeological sites that span the last 3,000 years. Beach ridges formed under the influence of open water storms with renewed frequency and intensity ca. 3 ka and 1 ka ago. A lack of shell may reflect cooler sea surface temperatures. The presence and absence of ice can be inferred by push-features. Three intervals of heightened precipitation produced extensive fan deltas: (a) after 9 ka BP (b) prior to 4.5 ka BP and (c) during the Little Ice Age (AD 1350–1900). Active solifluction lobes and colluvia cover beach ridge deposits that are between 9 and 7 ka old.  相似文献   

18.
Through the study of a late Holocene sample of small mammal remains from central Patagonia (Chubut province, Argentina) we document the regional extinction of four sigmodontines and one fossorial caviomorph rodent. This diversity loss is discussed in the light of two potential causes: Little Ice Age and human impact. We conclude that probably the latter was the main reason behind the current structure of small mammal communities.  相似文献   

19.
Abstract Small, stagnating ice caps at high latitudes are particularly sensitive to climatic fluctuations, especially with regard to changes in ablation season temperature. We conducted mass balance measurements and GPS area surveys on four small High Arctic plateau ice caps from 1999–2002. We compared these measurements with topographic maps and aerial photography from 1959, and with previously published data. Net mass balance (bn) of Murray Ice Cap was ?0.49 (1999), ?0.29 (2000), ?0.47 (2001), and ?0.29 (2002), all in meters of water equivalent (m w.eq.). The mass balance of nearby Simmons Ice Cap was also negative in 2000 (bn=?0.40 m w.eq.) and in 2001 (bn=?0.52 m w.eq.). All four ice caps experienced substantial marginal recession and area reductions of between 30 and 47% since 1959. Overall, these icecaps lost considerable mass since at least 1959, except for a period between the mid‐1960s and mid‐1970s characterized regionally by reduced summer melt, positive mass balance, and ice cap advance. The regional equilibrium line altitude (ELA) is located, on average, above the summits of the ice caps, indicating that they are remnants of past climatic conditions and out of equilibrium with present climate. The ice caps reached a Holocene maximum and were several times larger during the Little Ice Age (LIA) and their current recession reflects an adjustment to post‐LIA climatic conditions. At current downwasting rates the ice masses on the Hazen Plateau will completely disappear by, or soon after, the mid‐21st century.  相似文献   

20.
Geografisk Tidsskrift, Danish Journal of Geography 108(1):137–142, 2008

During field observations in August 2005 antler remains of a reindeer were found at a recently deglaciated site at about 500 m asl., and bones from a polar bear were found at about 300 m asl. along the margin of Mittivakkat Glacier, Southeast Greenland. Radio carbon dating determined the age of the samples to 720 14C years and 350 14C years, respectively. In August 2006 old surface vegetation covering peaty material became exposed due to ice recession close to the site where the antler was found. The radio carbon age of small roots from the material was determined to 1530 14C years, and is in agreement with dating of woody remains of Salix glauca found close by, at the top of a nearby nunatak in 1999. The antler indicates that reindeer lived in the area when the glacier began to advance from a position where it was close to or smaller than today. The vegetation surface and peaty material indicate that the climate was warmer before the onset of the Little Ice Age in Southeast Greenland than today.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号