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1.
Frozen ground phenomena in the Northern Foothills, Northern Victoria Land, Antarctica, include large–scale polygons, 15–20 m in diameter, and small frost mounds, 1–5 m high. The polygons are most widespread on terrain formed upon Younger Drift and are usually surrounded by interpolygon furrows or troughs, 10–30 cm deep and 10–100 cm wide. The troughs contain shallow wedges of sandy gravel (sand wedges) near the surface but excavations into underlying permafrost indicate that small ice wedges or ice veins are locally present. Field and anecdotal evidence suggest that thermal contraction cracking is active under today's climate. Frost mounds occur in association with a number of perennially frozen lakes in the region. In most cases they appear related to frost and icing blister activity caused by the episodic injection of free water from below. The debris–covered nature of the centre of Enigma Lake is best explained in terms of basal ice accretion beneath the lake–ice cover.  相似文献   

2.
Stratigraphic changes in diatom assemblages from four small lakes on northeastern Ellesmere Island, high Arctic, Canada, provide a proxy lake-ice cover and paleoenvironmental record. Low absolute diatom abundances and a benthic Fragilaria (sensu lata) dominated assemblage during the postglacial (< 7.6 ka B.P.) to mid-Holocene record the moderating effects of locally retreating glaciers. Around 5.5 ka B.P. diatom concentrations begin to rise, reaching their highest levels (109 valves per g dry sediment) between 4.2 and 3 ka B.P., interpreted to be the warmest period in this region. Topoclimatic differences between lakes on Hazen Plateau and those lower in Lake Hazen Basin account for the initial decline in diatom abundances in the upper lakes after 3 ka B.P. This change is thought to reflect a lowering of the regional snowline, accordant with widely recognized Neoglacial advances on Ellesmere Island and Greenland. Lakes in lower Lake Hazen Basin maintained extensive summer ice free conditions until ~ 1.9 ka B.P., after which diatom abundances declined, suggesting prolonged summer lake-ice cover through the remainder of the recovered Holocene record. Differences between the records presented here and those from coastal areas of the Canadian high Arctic highlight the unique topoclimatic characteristics and continentality of the Lake Hazen region, and possible effects that local marine environments may have had on coastal records. Such differences serve to demonstrate the inherent geographic variability of paleoenvironmental records from the high Arctic.  相似文献   

3.
东南极中山站附近湖冰与固定冰热力学过程比较   总被引：2，自引：0，他引：2       下载免费PDF全文
2006年对东南极中山站附近湖冰和固定冰的热力学过程进行了系统观测.基于观测数据比较湖冰和固定冰热力学生消过程;分析湖冰和固定冰温度对气温变化的响应规律;计算不同深度层湖冰和固定冰的垂向热传导通量.结果表明:观测的湖泊和海岸区均在2月底至3月初形成连续冰层;湖冰9月底至10月初达到最大冰厚,早于固定冰1-2个月,湖冰最...  相似文献   

4.
Wedge-like structures filled with silty sand penetrate Quaternary fluvial and aeolian sediments and, in places, Tertiary bedrock on the Ordos Plateau, North China. The wedges reflect thermal contraction cracking of either permafrost or seasonal frost during the Late Pleistocene and early Holocene. Wedges of about 1 m in depth form polygonal nets of 2-3 m in diameter(type B). They contrast with wedges of 3-4 m in depth that form polygons of 10-15 m in diameter(type A).This review focuses upon the highly variable size of the inferred polygon nets and discusses the problem of differentiating between seasonally and perennially frozen ground, or between seasonal frost and permafrost.  相似文献   

5.
The permafrost history of the high northern latitudes over the last two million years indicates that perennially frozen ground formed and thawed repeatedly, probably in close synchronicity with the climate changes that led to the expansion and subsequent shrinkage of continental ice sheets. The early stages of the Pleistocene are the least known and the changes that occurred in the Late Pleistocene and early Holocene are the best known.
Evidence that permafrost is degrading in response to the current global warming trend is difficult to ascertain. The clearest signals are probably provided by changes in permafrost distribution in the sub-Arctic regions. at the extreme southern fringes of the discontinuous permafrost zone.  相似文献   

6.
Observational evidence such as outflow channels and valley networks suggest that in the past there was flowing water on Mars. The images of fluvial features on Mars logically suggest that there must exist downstream locations in which the water pooled and the sediment load deposited (i.e. lakes). Sediments and morphological features associated with the martian paleolakes are believed to occur in Valles Marineris, and several large basins including Amazonis, Chryse and Elysium planitia. As Mars became progressively colder over geological time, any lakes on its surface would have become seasonally, and eventually perennially ice-covered. We know from polar lakes on Earth that ice-covered lakes can persist even when the mean annual temperature falls below freezing. Thus, the most recent lacustrine sediments on Mars were probably deposited in ice-covered lakes. While life outside of the Earth's atmosphere has yet to be observed, there is a general consensus among exobiologists that the search for extraterrestrial life should be based upon liquid water. The inference that there was liquid water on Mars during an earlier epoch is the primary motivation for considering the possibility of life during this time. It would be of enormous interest from both an exobiological and paleolimnological perspective to discover lakes or the evidence of former lakes on another planet such as Mars. Limnology would then become an interplanetary science.  相似文献   

7.
Measurements of dissolved N2, O2, Ar, CO2, and CH4 were made in perennially ice-covered Lake Hoare. Results confirm previous reports that O2 concentrations in the upper water column exceed atmospheric equilibrium and that N2 and Ar are supersaturated throughout the water column. The mean supersaturation of N2 was found to be 2.0 (+/- 0.37) and Ar was 3.8 (+/- 1.1). The ratios of N2/Ar (20.3 +/- 13.8), and O2/Ar (22.5 +/- 4.0) at the ice-water interface are consistent with those previously measured, suggesting that bubble formation is the main process for removing gas from the lake. However, the saturations of N2 and Ar greatly exceed those previously predicted for degassing by bubble formation only at the ice-water interface. The data support the hypothesis that removal of gas by bubbles occurs in the water column to a depth of 11 m in Lake Hoare. CO2 concentration increases from near zero at the ice-water interface to 80-100 times saturation at and below the chemocline at c. 28 m. There is considerable variability in the gas concentrations throughout the water column; samples separated in depth by one metre may vary by more than 50% in gas content. It is likely that this phenomenon results from the lack of turbulent mixing in the water column. Methane (c. 2 micrograms l-1) was detected below the chemocline and immediately above the sediment/water interface at a depth of 30 m. Samples from lakes Vanda, Joyce, and Miers, also show supersaturations of O2, N2, and Ar at levels similar to levels found in Lake Hoare.  相似文献   

8.
In two of the perennially ice-covered lakes in the McMurdo Dry Valleys, lakes Hoare and Bonney in the Taylor Valley, bottom water has 14C ages of 2.7 ka and 10 ka (respectively), rendering 14C ages of bottom sediments highly problematic. Consequently, we tested the effectiveness of thermoluminescence (TL) zeroing in polymineral fine silt material from several depositional environments around and on the lake (stream suspensions, ice-surface sand dune, and silty sand from near the top of the more-than-3m-thick ice). We also conducted TL and infrared-stimulated-luminescence (IRSL) dating tests on material from three box cores recovered from the bottom of Lake Hoare, in a transect away from the abutting Canada Glacier. We observed effective zeroing of light-sensitive TL in suspended silt from one input stream and less effective zeroing from another stream. We observed effective zeroing of light-sensitive TL also in silt from a glacier-proximal eolian ice-surface dune and from sand from within the upper 5 cm of ice. In contrast, in box-core 1, the bottom sediment yielded minimum TL apparent ages of 1500-2600 yrs, with no discernable stratigraphic depth trend. IRSL dating applied to the same box-core samples produced significantly lower age estimates, ranging from ~600 ± 200 yrs to 1440 ± 270 yrs top-to-bottom, an improvement over the depth-constant ~2200 yrs TL ages. In two other cores closer to the Canada Glacier, IRSL ages from ~600 ± 200 yrs (top) to ~ 2900± 300 yrs (at depth) were measured. Not only are the IRSL ages a significant improvement over the TL results, but the near-core-top IRSL ages are also a dramatic improvement over the 14C results (~2.7 ka). IRSL dating has a demonstrated potential to supplant 14C dating for such antarctic lacustrine deposits.  相似文献   

9.
Three lakes, informally named Lakes Inqua, Instaar and Mercer, from the Jackman Sound area in Southern Baffin Island were cored. The elevation of the three lakes are 36 m above high tide (aht), 10 m aht and 1 m aht. The cores from Lakes Inqua and Mercer penetrated the marine/lacustrine boundary; the core from Lake Instaar is estimated to have come within ca. 5 cm of this boundary. In addition, grab samples and water samples were retrieved from the lakes. The cores have been 14C dated (AMS). Emergence of the three lake basins from the sea occurred approximately 8650 BP (Lake Inqua), 8630 BP (Lake Instaar) and 7900 BP (Lake Mercer, averaged date). This suggests a very rapid rate (>5 m/100 yrs) of glacio-isostatic rebound for this area. Down-core analyses of diatom assemblages indicate that the paleolimnology in the three lakes was similar. The diatom analyses suggest a change in climate between approximately 8000 and 6000 BP, which is also reflected in the marine record from the same area, and the onset of the neoglacial period around 4500 to 3800 BP. A decrease in diatom-inferred pH is evident in the lakes' development and can probably be related to the general change of the watershed vegetation with time.  相似文献   

10.
ABSTRACT. This paper critically appraises the evidence for a succession of ice-dammed lakes in the central Strait of Magellan ( c. 53°S) c. 17 000–12 250 cal. yr BP. The topographic configuration of islands and channels in the southern Strait of Magellan means that the presence of lakes provides compelling constraints on the position of former ice margins. Lake shorelines and glacio-lacustrine sediments have been dated by their association with a key tephra layer from Volcan Reclús (c. 15 510–14 350 cal. years bp ) and by 14C-dated peats. The timing of glacial lake formation and associated glacier readvances is at odds with the rapid and widespread glacier retreat of the Patagonian ice fields further north after c. 17 000 cal. yr bp , suggesting rather that the lakes were coeval with the Antarctic Cold Reversal and persisted to the Late-glacial/Holocene transition. This apparent asymmetrical latitudinal response in glacier behaviour may reflect overlapping spheres of northern hemisphere and Antarctic climatic influence in the Magellan region.  相似文献   

11.
Chemical weathering and associated soil development trends on glacial forelands are commonly assumed to exhibit increases with time elapsed since glaciation. However, this gross trend is complicated by several other factors including elevation, aspect, and microtopography. This paper demonstrates that on the glacial foreland at Storbreen, Jotunheimen, Norway, chemical weathering and associated soil development trends show significant elevational influences. We sampled soils at shallow depths (0–1, 1–5, and 15–20 cm) at two sites on a moraine dated to 1750 at its elevational extremes of 1155 m (site L) and 1385 m (site H). The two moraine sites also differed developmentally from an adjacent 9000-year-old surface (site T) at an intermediate elevation, 1205 m. Analyses were conducted on the fine-earth fractions. Extractable elemental composition exhibited detectable differences between the same-age soils at different elevations with the lower site L tending to have measured parameters intermediate between the high site H and the older site T. Weathering, as indicated by mineralogy, was more pronounced at the 9000-year-old site T and least evident at the high elevation site H. In addition, elevation under the conditions of the field research may inhibit pedogenesis as indicated by the chemical data. Site H, for example, showed little variation with depth and had in general, less organic matter accumulation, smaller C:N ratio, greater pH, and lesser amounts of the measured extractable elements than the soil at site L. Site T generally had smaller pH and larger levels of the measured elements than the other sites. It was concluded that elevation has a significant control on weathering and pedogenesis that may mask the effects of age in this cold and wet environment.  相似文献   

12.
内蒙古呼伦贝尔草原湖泊变化研究   总被引：1，自引：0，他引：1  
内蒙古呼伦贝尔地区湖泊数量多,面积大,占内蒙古湖泊总面积的58％.近年来该地区湖泊趋于萎缩,但是已有研究主要关注大型湖泊,缺乏对该地区湖泊整体,尤其是小型湖泊(<1 km2)的研究.通过利用Landsat系列(TM、ETM+、OLI)卫星数据,参照该地区湖泊图集、湖泊名录以及Google Earth高清影像,分析了19...  相似文献   

13.
汶川地震造成泥石流形成条件的改变,其次生灾害堰塞湖的危害已开始显现。如何对震后潜在性泥石流堰塞湖进行判识,成为迫切需要解决的问题。选取岷江上游映秀至汶川段为研究区,通过分析震后泥石流形成条件的变化、典型泥石流堰塞湖的危害及松散物质储量,选取潜在性泥石流堰塞湖的判识指标,利用模糊物元可拓模型,建立潜在性泥石流堰塞湖的综合判识模式。通过判识,研究区形成泥石流堰塞湖可能性高的一级支沟有17条,主要集中分布在映秀镇至草坡乡段,此段将是今后受堰塞湖危害的高危地段。  相似文献   

14.
《Polar Science》2009,3(4):262-271
We investigated the vertical structure of physicochemical properties in 27 lakes at Skarvsnes and Langhovde, Syowa Oasis, East Antarctica, from December 2003 to February 2004. The lakes were classified into three types based on their origin and geographical characteristics: non-marine relic lakes, marine relic and lotic lakes, and marine relic and lentic lakes. We describe the physicochemical characteristics of each lake type. When the non-marine relic lakes were partly covered with ice, the water column was stratified beneath the ice. In the non-marine relic lakes, during the season with no ice cover, physicochemical parameters were uniform throughout the water column, probably due to frequent vertical mixing induced by wind force and thermal convection within the shallow basins. Similarly, in marine relic and lotic lakes, lake waters appeared to be completely mixed because of a large inflow of meltwater from glaciers and outflow to other lakes and the coastal sea. In the marine relic and lentic lakes, except for Lake Himebati-ike, the lake water was vertically stratified with a strong halocline. In Lakes Suribati-ike and Hunazoko-ike, salinity was very high (up to 20%) due to evapoconcentration. Lake Suribati-ike is a meromictic lake, with a monimolimnion developed below 10 m water depth.  相似文献   

15.
Glacial landscapes of the Land of Great Masurian Lakes and Suwa?ki Lakelands in northeast Poland are characterized by very high abundance of lakes. These two areas were surveyed for lakes containing laminated sediments. Using bathymetry as a criterion, 60 small, deep lakes, representing preferred conditions for formation and preservation of lacustrine non-glacial varves, were selected for gravity coring. We found laminated sediments in 24 of the lakes, 15 in the Land of Great Masurian Lakes and 9 in the Suwa?ki Lakeland. Seven of these 24 sediment records were laminated in the topmost part only. Analysis of lake morphometric variables showed that the relation between surface area and maximum water depth can be used to identify lakes with laminated sediments. Most of the newly discovered lakes with laminated deposits have surface areas ≤0.3 km2 and maximum depths of 15–35 m. Multivariate statistical analysis (Linear Discriminant Analysis) of the lake dataset identified the morphological features of lake basins and their catchments that largely control preservation of laminated sediments. Microscopic and geochemical analyses revealed a biogenic (carbonaceous) type of lamination typical for lakes in northeast Poland. Such lakes are characterized by a spring-summer lamina that is rich in calcium carbonate and an autumn-winter lamina composed of organic and minerogenic detritus. This pattern may be modified by multiple periods of calcite deposition during a single year or substantial contribution of clastic material. Laminations and high sedimentation rates offer the possibility of high-resolution investigation of past climate and environmental changes through application of myriad biological, isotopic and geochemical proxies.  相似文献   

16.
Paleolimnology of the McMurdo Dry Valleys,Antarctica   总被引：1，自引：0，他引：1  
The McMurdo Dry Valleys presently contain more than 20 permanent lakes and ponds, which vary markedly in character. All, with the exception of a hypersaline pond, have a perennial ice-cover. The dry valley lakes, and lakes in other ice-free regions of continental Antarctica, are unique on this planet in that they consistently maintain a thick year-round ice cover (2.8–6.0 m) over liquid water. The persistent ice covers minimize wind-generated currents and reduce light penetration, as well as restricting sediment deposition into a lake and the exchange of atmospheric gases between the water column and the atmosphere. From a paleolimnological perspective, the dry valley lakes offer an important record of catchment and environmental changes. These lakes are also modern-day equivalents of periglacial lakes that were common during glacial periods at temperature latitudes. The present lakes are mostly remnants of larger glacial lakes that occupied the valleys in the past, perhaps up to 4.6 Ma ago. Two of the valleys contain evidence of being filled with large glacial lakes within the last 10000 years. Repeated drying and filling events since then have left a characteristic impression on the salt profiles of some lakes creating a unique paleo-indicator within the water column. These events are also marked in the sediments by the concentration and dilution of certain chemical constituents, particularly salts, and are also corroborated by carbonate speciation and oxygen isotope analysis. Stratigraphic analysis of dry valley lake sediments is made difficult by the occurrence of an old carbon reservoir creating spurious radiocarbon dates, and by the high degree of spatial variability in lake sedimentation. From a biological perspective, the lakes are relatively simple, containing various taxa of planktonic and benthic microorganisms, but no higher forms of life, which is an advantage to paleolimnologists because there is no bioturbation in the sediments. Useful biological paleo-indicators found in the sediments include cyanobacterial filament sheaths, diatom frustules and other eukaryotic algal cells, protozoan cysts, photosynthetic pigments, and minerals (e.g. carbonates) associated with microbial activity. Future work will benefit from fully characterizing the connection between the ice covers, environmental conditions, and paleo-indicators, thereby allowing refinement of inferences made concerning the paleoenvironment. New dating techniques need to be tested in this environment to overcome the problems associated with radiocarbon dating. The establishment of a detailed and focused paleolimnological campaign is proposed.  相似文献   

17.
西藏扎布耶盐湖水位波动规律初探   总被引：3，自引：2，他引：1  
齐文  郑绵平 《地理科学》2006,26(6):693-700
文章探讨扎布耶北湖1991年1月至2003年12月水位变化的季节性波动、长期变化和周期变动的规律。该湖水位的季节性波动在1991~1996年表现为单峰模式,高水位出现于4月,由冰雪与冻土融水补给引起;1997~2003年表现为双峰模式,高水位分别出现在4月和8~9月(雨季),反映近年来气温上升和降水增加的影响。数学模型表明水位波动表现出8.2年的周期,幅度达0.48 m。1991~2003年水位共上升0.25 m,但大多数年份表现出平均0.06~0.08 m/a下降趋势,1998~1999年的水位上涨是水位由单峰模式变为双峰模式转折点。  相似文献   

18.
Summary. The East Pacific Rise at 12–15° S is topographically smooth with a crestal horst or linear volcanic peak marking the present axis of spreading. The Galapagos Rise at 14–17° S is topographically rough with a possible central graben marking the extinct spreading axis. The seafloor spreading magnetic anomalies on the East Pacific Rise are of low amplitude, but fracture-zone anomalies at 13–14° S have amplitudes of up to 1250 nT. Anomalies of this amplitude at the magnetic equator must be formed within the fracture zone by some combination of block reversal boundaries, anomalously-high magnetic intensities, and/or anomalously-large thicknesses of the magnetic layers within the fracture zone. Magnetization and major-element chemical analyses of basalts dredged from four locales along the fracture zone indicate that the large magnetic-anomaly amplitudes are caused by the high iron and titanium content of these ferrobasalts. The magnetic-anomaly profiles from the Galapagos Rise and its fracture-zone system are of normal amplitude and are extremely difficult to correlate internally or with the geomagnetic timescale.
Eighty-one heat-flow measurements indicate that the values measured are controlled by sediment thickness. Where the thickness of the sediment blanket is greater than 100 m, high heat flow is measured and possibly is representative of the total heat transfer at the seafloor. Where the sediment thickness is less than 100 m, seawater circulation in the oceanic crust is thought to remove most of the heat convectively; thus causing low conductive heat-flow values to be measured by the usual heat-flow apparatus. The heat loss by convective processes is probably a function also of topographic roughness and sediment permeability.  相似文献   

19.
利用卫星海冰密集度资料和船基海冰走航观测数据分析了2012年12月至2013年3月南极罗斯海海冰密集度、厚度和浮冰尺寸等参数的时空变化特征。12月下旬罗斯海西侧浮冰区南北向宽约1 000 km,沿雪龙船航线平均密集度在5成以上,平均海冰厚度为100 cm,平均冰上积雪厚度为16 cm,高密集度区域主要为尺寸较小的块浮冰(2—20 m)和小浮冰(20—100 m),低密集度区域主要为大尺寸浮冰(500—2 000 m)。1月和2月罗斯海大部分海域无海冰覆盖,3月海冰迅速冻结,下旬即覆盖整个罗斯海。SSMIS和AMSR2两种卫星遥感数据均能较好反映航线上的真实海冰密集度状况,AMSR2产品与观测符合更好。与1978—2012的气候平均值相比,观测区在2012年夏季冰情偏重。本文的分析结果可帮助我们了解罗斯海海冰的时空特征,为中国后续罗斯海科考提供参考。  相似文献   

20.
As many as 2500 interdune lakes lie within the Nebraska Sand Hills, a 50000 km stabilized sand sea. The few published data on cores from these lakes indicate they are typically underlain by less than two m of Holocene lacustrine sediments. However, three lakes in the southwestern Sand Hills, Swan, Blue, and Crescent, contain anomalously thick marsh (peat) and lacustrine (gyttja) sediments. Swan Lake basin contains as much as 8 m of peat, which was deposited between about 9000 and 3300 years ago. This peat is conformably overlain by as much as 10.5 m of gyttja. The sediment record in Blue lake, which is 3 km downgradient from Swan lake, dates back to only about 6000 years ago. Less than two m of peat, which was deposited from 6000 to 5000 years ago, is overlain by 12 m of gyttja deposited in the last 4300 years. Crescent Lake basin, one km downgradient from Blue Lake, has a similar sediment history except for a lack of known peat deposits. Recently, a 8-km long segment of a paleovalley was documented running beneath the three lakes and connecting to the head of Blue Creek Valley. Blockage of this paleovalley by dune sand during two arid intervals, one shortly before 10500 yr BP and one in the mid-Holocene, has resulted in a 25 m rise in the regional water table. This made possible the deposition of organic-rich sediment in all three lakes. Although these lakes, especially Swan, would seem ideal places to look for a nearly complete record of Holocene climatic fluctuations, the paleoclimatic record is confounded by the effect dune dams have on the water table. In Swan Lake, the abrupt conversion from marsh to lacustrine deposition 3300 years ago does not simply record the change to a wetter regional climate; it reflects the complex local hydrologic changes surrounding the emplacement and sealing of dune dams, as well as regional climate.  相似文献   

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