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961.
青藏高原上分布着大量的大陆性冰川,其对区域及全球气候变化响应极其敏感.工业革命以来,随着全球升温速率加快(特别是北半球),青藏高原部分地区的冰川在近百年显著退缩.冰前湖沉积物是最直接的冰川变化记录载体之一,但其沉积速率如何响应冰川及气候变化,能否反演冰川进退过程却知之甚少.本文依据~(210)Pb和~(137)Cs限定藏南冰前湖枪勇错QY5沉积岩芯的年龄,计算出不同深度沉积物的沉积速率,且与前人(QY-3)的沉积速率进行对比,揭示了近百年来枪勇错流域冰川变化历史及其与气温之间的关系.结果表明,枪勇错QY5近百年来的平均沉积速率为0.21 cm/a,比湖心(QY-3)快2倍左右,但两者的变化基本同步,高沉积速率对应温度上升期,是冰川退缩的直接响应:(1)1900—1960年,枪勇错沉积速率整体增加且变幅较大,与1890—1950年之间西藏温度波动式升高相对应,反映枪勇冰川总体处于退缩状态;(2)1960—1985年,沉积速率低且变幅较小,同期气温下降,枪勇冰川退缩程度相对较低且保持平稳;(3)1985年以来,枪勇错沉积速率呈上升趋势,是全球增暖下冰川显著退缩的直接响应.在短时间尺度内冰前湖沉积速率所揭示的枪勇冰川变化主要受控于温度,降水量对冰川变化的影响较小,但冰川对温度变化的响应滞后5~10 a.由于全球变暖和冰川对温度响应的滞后,在未来几十年高原冰川的融化速率可能会加快,亚洲水塔将面临着新的挑战. 相似文献
962.
The glacial deposits at the Boyne Bay Limestone Quarry near Portsoy, a key Quaternary Site of Special Scientific Interest, comprise (i) a sandy, partly weathered diamicton (Craig of Boyne Till Formation, CBTF) resting on decomposed bedrock, (ii) a central, variably glaciotectonised assemblage of dark clay, diamicton and sand, with rafts of sand and weathered diamicton (Whitehills Glacigenic Formation, WGF), and (iii) an upper dark sandy diamicton (Old Hythe Till Formation, OHTF). The CBTF was probably derived from the west or southwest, and the WGF from seawards. Structures within the OHTF conform to deposition by east‐ or southeast‐moving ice from the Moray Firth, but some erratics indicate derivation from the south. The CBTF is believed to pre‐date the last (lpswichian) interglacial, but the WGF and OHTF both post‐date the early Middle Devensian, and are probably of Late Devensian age. It is proposed that the OHTF was deposited by ice from inland which was directed eastwards near the coast by a vigorous glacier in the Moray Firth, and that the complex, Late Devensian glacial history of the south coast of the Moray Firth as a whole is the result of the interplay of these two contemporary ice‐masses. British Geological Survey. © NERC 2000. 相似文献
963.
Excavations of deposits filling a closed basin within glacial drift at Church Moss, Davenham, near Northwich (Cheshire, England) revealed a sequence of Late‐glacial and Early Holocene sediments. Analyses of pollen and plant and invertebrate macrofossils were undertaken, together with loss‐on‐ignition analyses and a programme of AMS radiocarbon dating, to provide a record of changing biostratigraphy and climatic and ecological regimes. The infilling of features identified as frost‐cracks in the till flooring the basin gave remains that reflected conditions of extreme cold towards the end of the Devensian. The pollen record from a 3.5 m sequence of peat towards the deepest part of the basin, supported by radiocarbon dates, shows that organic deposition was initiated during the Late‐glacial Interstadial and continued into the early part of the Holocene. There was some evidence for a cool episode during the interstadial, with amelioration prior to the rapid onset of the tundra conditions of the Loch Lomond Stadial. Following the stadial, amelioration was rapid. There was evidence from both central and marginal sequences for a mosaic of fen dominated by sedges and often also mosses, with short‐lived small pools through much of the succession. Change to terrestrial conditions proceeded intermittently, probably as a result of subsidence caused by solution of underlying salt‐bearing strata. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
964.
Palaeoenvironment in Java island and its surrounding areas since the last interglacial stage was reconstructed initially using previous studies by various researchers. The karst area in Gunung Sewu on Java island was also examined by the authors in order to reconstruct the palaeoenvironment through the process of karstification. Summarizing the evidence related to palaeoclimate in the various areas made it clear that the palaeoclimatic condition was cooler and drier at the Last Glacial Maximum 18 000 yr BP, than today. Formation of dry valleys in Gunung Sewu was conditioned by lowering of sea-level, and establishment of a cool and extremely dry climate. Subsequent to the initial reconstruction, the results of the estimated palaeoclimate at 18 000 yr BP were plotted at the respective points where the samples were obtained, and maps for northern winter and northern summer were constructed showing the estimated streamlines of monsoon circulations, polar frontal zones and intertropical convergence zones, in order to better explain the distribution of the palaeoclimate conditions of the area. ©1997 John Wiley & Sons, Ltd. 相似文献
965.
J. J. MAGNUSON K. E. WEBSTER R. A. ASSEL C. J. BOWSER P. J. DILLON J. G. EATON H. E. EVANS E. J. FEE R. I. HALL L. R. MORTSCH D. W. SCHINDLER F. H. QUINN 《水文研究》1997,11(8):825-871
The region studied includes the Laurentian Great Lakes and a diversity of smaller glacial lakes, streams and wetlands south of permanent permafrost and towards the southern extent of Wisconsin glaciation. We emphasize lakes and quantitative implications. The region is warmer and wetter than it has been over most of the last 12000 years. Since 1911 observed air temperatures have increased by about 0·11°C per decade in spring and 0·06°C in winter; annual precipitation has increased by about 2·1% per decade. Ice thaw phenologies since the 1850s indicate a late winter warming of about 2·5°C. In future scenarios for a doubled CO2 climate, air temperature increases in summer and winter and precipitation decreases (summer) in western Ontario but increases (winter) in western Ontario, northern Minnesota, Wisconsin and Michigan. Such changes in climate have altered and would further alter hydrological and other physical features of lakes. Warmer climates, i.e. 2 × CO2 climates, would lower net basin water supplies, stream flows and water levels owing to increased evaporation in excess of precipitation. Water levels have been responsive to drought and future scenarios for the Great Lakes simulate levels 0·2 to 2·5 m lower. Human adaptation to such changes is expensive. Warmer climates would decrease the spatial extent of ice cover on the Great Lakes; small lakes, especially to the south, would no longer freeze over every year. Temperature simulations for stratified lakes are 1–7°C warmer for surface waters, and 6°C cooler to 8°C warmer for deep waters. Thermocline depth would change (4 m shallower to 3·5 m deeper) with warmer climates alone; deepening owing to increases in light penetration would occur with reduced input of dissolved organic carbon (DOC) from dryer catchments. Dissolved oxygen would decrease below the thermocline. These physical changes would in turn affect the phytoplankton, zooplankton, benthos and fishes. Annual phytoplankton production may increase but many complex reactions of the phytoplankton community to altered temperatures, thermocline depths, light penetrations and nutrient inputs would be expected. Zooplankton biomass would increase, but, again, many complex interactions are expected. Generally, the thermal habitat for warm-, cool- and even cold-water fishes would increase in size in deep stratified lakes, but would decrease in shallow unstratified lakes and in streams. Less dissolved oxygen below the thermocline of lakes would further degrade stratified lakes for cold water fishes. Growth and production would increase for fishes that are now in thermal environments cooler than their optimum but decrease for those that are at or above their optimum, provided they cannot move to a deeper or headwater thermal refuge. The zoogeographical boundary for fish species could move north by 500–600 km; invasions of warmer water fishes and extirpations of colder water fishes should increase. Aquatic ecosystems across the region do not necessarily exhibit coherent responses to climate changes and variability, even if they are in close proximity. Lakes, wetlands and streams respond differently, as do lakes of different depth or productivity. Differences in hydrology and the position in the hydrological flow system, in terrestrial vegetation and land use, in base climates and in the aquatic biota can all cause different responses. Climate change effects interact strongly with effects of other human-caused stresses such as eutrophication, acid precipitation, toxic chemicals and the spread of exotic organisms. Aquatic ecological systems in the region are sensitive to climate change and variation. Assessments of these potential effects are in an early stage and contain many uncertainties in the models and properties of aquatic ecological systems and of the climate system. © 1997 John Wiley & Sons, Ltd. 相似文献
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968.
玉龙山东麓更新世冰川作用 总被引:34,自引:7,他引:27
利用1:10000地形图和航空照片,对玉龙山东麓更新世冰川作用遗迹进行了调查和填图。据冰川与冰水沉积物的钙质胶结物和冰湖相钙板的ESR测年结果,初步划分4次冰期,即0.7 ̄0.6Ma BP的玉龙冰期。其中最早一次冰期为规模较大的山麓冰川,后2次冰期为规模较大的山谷冰川。 相似文献
969.
970.
Tracy A. Mashiotta David W. Lea Howard J. Spero 《Earth and Planetary Science Letters》1999,170(4):113-432
Laboratory culturing experiments with living Globigerina bulloides indicate that Mg/Ca is primarily a function of seawater temperature and suggest that Mg/Ca of fossil specimens is an effective paleotemperature proxy. Using culturing results and a core-top Neogloboquadrina pachyderma calibration, we have estimated glacial–interglacial changes in sea surface temperature (SST) using planktonic Mg/Ca records from core RC11-120 in the Subantarctic Indian Ocean (43°S, 80°E) and core E11-2 in the Subantarctic Pacific Ocean (56°S, 115°W). Our results suggest that glacial SST was about 4°C cooler in the Subantarctic Indian Ocean and 2.5°C cooler in the Subantarctic Pacific. Comparison of SST and planktonic δ18O records indicates that changes in SST lead changes in δ18O by on average 1–3 kyr. The glacial–interglacial temperature change indicated by the Subantarctic Mg/Ca records suggests that temperature accounts for 40–60% of the foraminiferal δ18O change. We have used the Mg/Ca-based SST estimates and δ18O determinations to generate site-specific seawater δ18O records, which suggest that seawater δ18O was on average 1‰ more positive during glacial episodes compared with interglacial episodes. 相似文献