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Little Manitou Lake is a topographically closed, hypersaline lake that occupies a long, linear glacial meltwater channel in the northern Great Plains of western Canada. Most of the modern and late Holocene sediment in the lake has been generated from within the basin itself, either by endogenic inorganic precipitation or by other authigenic processes. These endogenic and authigenic precipitates, composed of mainly very soluble sulfate salts and sparingly soluble carbonates, provide an explicit record of the past chemical and hydrological fluctuations that have occurred in the lake. Although detailed chronostratigraphy is incomplete, preliminary14C dating indicates an age of about 2000 years for the oldest sediment recovered from the basin.Five subsurface sedimentary facies are identified in offshore cores. From the base these are: (i) structureless, gray clay, (ii) gypsiferous mud, (iii) structureless, organic-rich mud, (iv) finely laminated aragonitic mud, and (v) Na and Mg sulfate salts. The lithostratigraphy and variation in the mineralogical composition of the sediment indicate that Little Manitou Lake experienced significant water level changes and compositional fluctuations during the past several millennia. The basal clays indicate a relatively deep, freshwater lake existed about 2000 years ago, but was soon followed by a period of low water/playa sedimentation and a negative hydrological budget in the basin. Water levels gradually increased after about 1500 years ago in response to a cooler and wetter climate. This resulted in development of a meromictic, saline to hypersaline lake characterized by periodic carbonate (aragonite) whitings. Water levels again decreased about 1000 years ago, resulting in a breakdown of meromixis and initiation of subaqueous evaporitic salt precipitation. Although the brine in Little Manitou Lake has fluctuated between Na-SO4 and Mg-Na-SO4 -Cl types during the past 1000 years, water levels and overall salinities have remained relatively constant.Palliser Triangle Global Change Contribution No. 16. 相似文献
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Analyses of pollen, plant macrofossils, sediment mineralogy, geochemistry, and lithology of cores from Chappice Lake, southeastern Alberta, provide an outline of paleohydrological changes spanning the last 7300 radiocarbon years. Situated near the northern margin of the Great Plains, Chappice Lake is currently a small (1.5 km2), shallow (<1 m), hypersaline lake. Results of this study suggest that the lake has experienced significant changes in water level and chemistry during the Holocene.From 7300 to 6000 BP the lake oscillated between relatively high stands and desiccation. From 6000 to 4400 BP it was smaller than present and ponded highly saline water. Although extreme water level variations of the preceding period had ceased, pronounced seasonal fluctuations persisted. Between 4400 and 2600 BP, lake level was more stable but gradually rising. Carbonates were a major component of the sediments deposited during this interval. A large, relatively fresh lake existed from 2600 to 1000 BP. Illite was the dominant mineral deposited during this period, but since then has been a minor constituent in a mineral suite dominated by detrital silicates. A series of low-water, high-salinity stands occurred between 1000 and 600 BP, although these low stands were not as pronounced as low-water intervals in the middle Holocene. Relatively high water levels were sustained from 600 BP until the late 1800s. The lake declined significantly in the last one hundred years, notably during the historically documented droughts of the late 1800s, 1920s, 1930s, and 1980s.The timing of paleohydrological events at Chappice Lake corresponds closely with well documented Holocene climatic intervals, such as the Hypsithermal, Neoglaciation, Medieval Warm Period, and Little Ice Age. In addition, historic lake-level fluctuations can be related directly to climate. As a result, the Chappice Lake sedimentary succession offers a rare opportunity to obtain a high-resolution, surrogate record of Holocene climate on the northern Great Plains, and to observe the response of lake chemistry and biota to significant environmental change.Geological Survey of Canada Contribution No. 45191, Palliser Triangle Global Change Contribution No. 2This publication is the first of a series of papers presented at the Conference on Sedimentary and Paleolimnological Records of Saline Lakes. This Conference was held August 13–16, 1991 at the University of Saskatchewan, Saskatoon, Canada. Dr. Evans is serving as Guest Editor for this series. 相似文献
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William M. Last 《International Journal of Salt Lake Research》1993,2(1):47-58
Remarkably high rates of sedimentation (up to nearly 60 kg m−2 yr−1) are documented for offshore areas of Freefight Lake, a deep, hypersaline, meromictic lake in the northern Great Plains of
Canada. Most material in the offshore sediment traps consists of soluble and suparingly soluble endogenic salts. Deposition
of allogenic sediment is minor. The observed high sedimentation rates are in response to several mechanism: (i) freeseout
precipitation of salts from the mixolimnion; (ii) redistribution of shallow water endogenic precipitates by turbidity flows
and interflow processes; and (iii) precipitation of salts from within the monimolimnion Because the bottom water mass of the
lake is essentially isothermal and isochemical, large scale temperature induced remobilization of these salts at or near the
sediment-water interface is unlikely. Similarly, the morphology of the basin suggests that resuspension of bottom sediment
by waves in the offshore areas of the basin is negligible. Although the sedimentation rates observed in Freefight Lake are
extraordinarily high and considerably greater than other modern lacustrine sedimentation rates documented in the literature
to date, the observed rates are entirely compatible with suggested accumulation rates of ancient evaporite sequences.
Palliser Tringle Global Change Contribution Number 6. 相似文献
5.
Sediment cores from Chappice Lake, a hypersaline, groundwater-fed lake in southeastern Alberta, have been used in previous studies to reconstruct Holocene climate using lake levels as a source for proxy climate data. This assumes that the lake is fed by a shallow groundwater system sensitive to changes in climate. In this study we use the dynamics and chemistry of groundwater entering the lake to test this hypothesis.Groundwater inputs calculated from historical records using a simple water budget were highest during periods when the precipitation deficit was high. Over specific time intervals, the expected relationship between lake volumes and climate were not always found. Feedback loops between lake levels and groundwater input, and time lags within the system are the mechanisms proposed to explain these discrepancies.Field measurements suggest discharge of a local surficial groundwater system. Slug tests reveal a high conductivity system (K = 10-5 m/s) surrounding the lake. Hydraulic heads measured in standpipe, multilevel and minipiezometers installed around Chappice Lake show that the lake is situated in a closed hydraulic head contour. Hydraulic heads and water table elevations show strong annual fluctuations corresponding to seasonal changes in recharge. Horizontal hydraulic gradients measured in areas of groundwater springs indicate a strong horizontal component of flow towards the lake. Vertical hydraulic gradients are low and indicate the upward flow of water consistent with the discharge of a shallow, surfical groundwater system.Groundwater sampled from deposits surrounding Chappice Lake and springs feeding the lake have compositions similar to both shallow surficial aquifers and bedrock aquifers suggesting that the lake may be receiving inputs from both sources. However, evaporation simulations using PHRQPITZ, show that the evaporation of water typical of bedrock aquifers result in a mineral assemblage and brine composition different from that found at Chappice Lake. This suggests that discharge of a regional groundwater system can be eliminated as a dominant source over the lake's history. Evaporation simulations suggest that evaporation of groundwater from shallow surficial deposits can best explain the present mineral assemblage and brine chemistry and were likely the dominant source of water to the lake.Bedrock and shallow surficial groundwater sources have different chemistries and isotopic compositions. In hydrogeological settings such as Chappice Lake where more than one source may contribute to the lake, the relative importance of the different sources may change with changes in climate. If the source water composition to the lake changes, identifying changes in climate or hydrology based on changes in the composition of the lake preserved in sediment core will be made more difficult. This may complicate paleoclimate and paleohydrological reconstructions that rely on mineralogical and isotopic data. 相似文献
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William M. Last 《Journal of Paleolimnology》1990,4(3):219-238
In the western part of the Canadian Prairies, there are thousands of small, closed-basin saline lakes. Most of these lakes are ephemeral, filling with water during the spring and drying completely by late summer. Ceylon Lake, located in southern Saskatchewan, is typical of many of these shallow ephemeral lacustrine basins. The stratigraphic sequence recovered from this salt playa can be subdivided into six distinct facies types: (a) icelaid gravelly clay loam diamicton; (b) fluvial massive bedded to laminated sand; (c) lacustrine laminated calcareous clay and silt; (d) lacustrine laminated gypsiferous clay and silt; (e) lacustrine black, anoxic, nonlaminated, organic-rich mud; and (f) lacustrine salt. The crystalline salt facies, which can be up to 9 meters thick, is comprised mainly of sodium and sodium + magnesium sulfates, with smaller and more variable proportions of other sulfates, halides, carbonates, and insoluble clastic detritus.Although a variety of postdepositional processes have significantly altered the nature and stratigraphic relationships in the basin, the sediment fill does record, in a general way, the fluctuating depositional, hydrological, and geochemical conditions that existed in the basin since deglaciation. The Ceylon Lake basin originated about 15 000 years ago as meltwater from the retreating glacial ice cut a major spillway system in the drift and bedrock. The initial (early Holocene) phases of lacustrine sedimentation in Ceylon Lake occurred in a relatively deep freshwater lake. By about 6000 years B.P., the lake had become much shallower with numerous episodes of complete drying and subaerial exposure. The most recent 5000 years of deposition in the basin have been dominated by evaporite sedimentation. The composition of the soluble salts deposited during this time indicates some degree of cyclic sedimentation superimposed on an overall gradual shift from a sodium dominated brine to one of mixed sodium and magnesium. 相似文献
7.
We present a paleolimnological record spanning the Holocene from a small lake on Russell Island (Lake PW02), in the central
Canadian Arctic Archipelago (74.07° N, 97.77° W, 182 m asl). Fragilarioid diatom types in the genera Pseudostaurosira, Staurosira and Staurosirella constitute >90% of valves in fossil samples. Using modern biogeographic data which specify the temperature optima of the
Fragilarioid diatom taxa, we present new inferences about the timing of paleoclimatic changes in the central Arctic islands.
The early Holocene was characterized by maximum values for sediment organic matter, and lower ratios of Staurosirella pinnata to Staurosira construens v. venter, suggesting warm summer air temperatures between about 9500−6500 cal year BP. Influxes of biogenic silica and diatom valves
decreased following 4000 cal year BP, the sediment accumulation rate slowed and diatom taxa of the littoral zone diversified,
suggesting cooler summers and more persistent lake ice. Variations in the species composition of the assemblages indicate
paleoclimatic changes that are in broad agreement with other paleoenvironmental records from the Arctic including melt records
from the Agassiz Ice Cap. Although autecological data remain incomplete for Fragilarioid taxa, our results indicate differences
in these taxa in responses to paleoenvironmental change and underline the potential for the increased use of these taxa in
paleoenvironmental reconstructions. The record from Lake PW02, as in other records from Arctic lakes with low algal diversity
throughout the Holocene, shows a pronounced increase in diatom diversity since the 1920s, and diatom production since the
1970s far exceeds any recorded during the Holocene. 相似文献
8.
淀山湖太湖形成的古生物证据 总被引：3，自引：0，他引：3
通过对湖泊周围钻孔样品的微体古生物分析,根据化石群的生态特征,结合岩性、孢粉、14C等资料探讨晚更新世中期以来淀山湖、太湖沉积环境的演变过程,并比较其异同。现代湖泊的形成于全新世晚期。 相似文献
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Qinghai Lake and Zhuye Lake, ~400 km apart, are located in the northwest margin of the Asian summer monsoon. Water of these two lakes mostly comes from the middle and eastern parts of the Qilian Mountains. Previous studies show that the Holocene climate changes of the two lakes implied from lake records are different. Whether lake evaporation plays a role in asynchronous Holocene climate changes is important to understand the lake records. In this paper, we used modern observations beside Qinghai Lake and Zhuye Lake to test the impact factors for lake evaporation. Pan evaporation near the two lakes is mainly related to relative humidity, temperature, vapor pressure and sunshine duration. But tem-perature has different impacts to lake evaporation of the two lakes, which can affect Holocene millennial-scale lake level changes. In addition, differences in relative humidity on the millen-nial-scale would be more significant, which also can contribute to asynchronous lake records. 相似文献
11.
青海湖是国内最大的内陆湖泊,位于青藏高原东北缘,因其处在东亚夏季风、印度季风和西风带的交替控制区域,对气候变化十分敏感,成为古环境变化研究的热点地区。有关青海湖的形成演化、环境变化和水文变化的研究也存在多种观点。本研究再分析了青海湖已报道的古环境指标和气候模式模拟的夏季、冬季温度和降水变化,力图更加全面地理解青海湖全新世以来的古环境变化。研究发现早全新世11~8 ka夏季降水量和表面蒸发量较大,冬季降水稀少,湖泊水位只有十余米深,使得青海湖周边风沙活动频繁。并且,早全新世的气候不稳定,经历了频繁和较大幅度的波动。全新世气候适宜期出现在8~6 ka,古环境指标指示这一时期为温暖湿润的气候环境,湖盆内植被以森林草原为主,湖泊水位不断上升。青海湖地区的夏季降水自6 ka开始减少,然而冬季降水增加,同时夏季温度和蒸发量减少,使得湖区植被组成由森林草原向高山草甸转变,湖区大范围形成古土壤。湖区古环境条件在晚全新世距今1.5 ka开始恶化,冬季和夏季降水同时减少,湖泊水位下降,风沙活动再次加强。 相似文献
12.
Massimiliano Tardio Francesca Sangiorgi Henk Brinkhuis Maria Letizia Filippi Marco Cantonati André F. Lotter 《Journal of Paleolimnology》2006,36(3):315-318
This paper documents the discovery of peridinioid organic walled dinoflagellate cysts in Holocene sediments of the freshwater, low-alkalinity, high mountain Lake Nero di Cornisello (Adamello mountain range, Trentino, Italy). Among the three main cyst morphotypes found in the samples, the dominant one is acavate, with a smooth and light brown colored wall, with a clear conical shape, elongated with a pointy to rounded end in the antapical-ventral part, with the epicyst broader than the hypocyst and displays a typical peridinioid archeopyle. Comparison with data available in literature, besides pointing out the general scarcity of observations on dinocysts in lakes sediments, suggested a strong morphological similarity with the marine genus Brigantedinium. This finding pinpoints the need for more detailed studies on cysts in freshwater environments offering a new tool for paleoenvironmental interpretations. 相似文献
13.
The extraction of paleohydrological and paleoclimatological information from a modern hydrological system, shown to represent unique and extreme hydroclimatological conditions, is illustrated by an example from the Mojave River drainage basin in southern California. The Mojave River allows only the most extreme floods to reach its terminal basin in the Silver Lake playa and to form ephemeral lakes. All the other floods are lost by transmission into the alluvial aquifer along its 200 km channel. This filtering out of regular floods by the river provides an essential tool in establishing a physical link between atmospheric and hydrologic conditions. We demonstrate such a link between anomalous, present-day atmospheric circulation patterns over the North Pacific Ocean, extreme storms in southern California that produced the heaviest precipitation on record, the largest floods of record in the Mojave River watershed, and ephemeral lakes in its terminal playa. This physical link determines the possible cause of the formations of perennial, short-duration, shallow lakes in Silver Lake playa during the late Holocene and characterizes the hydroclimatic conditions that prevailed during these lacustrine episodes. Hydrological simulations of this river and its filtering character demonstrate that these lakes could have formed only if the most extreme modern storms and floods were more frequent in at least an order of magnitude during specific time episodes. We conclude that such extreme hydroclimatic conditions occurred more frequent in past episodes during which the Holocene lakes formed. In turn, this conclusion indicates that the cause of these storms and floods, i.e. the anomalous atmospheric circulation pattern, must have been more frequent. This research outlines a way to extract information on Holocene climates in hydrologic settings that demonstrate a unique cause and effect relationship. 相似文献
14.
钠硼解石是一种常见的硼酸盐,主要分布在南美和我国青藏高原盐湖中,以及土耳其西阿纳托里亚（ＷｅｓｔＡｎａｔｏｌｉａ）硼矿和美国西部Ｋｒａｍ ｅｒ硼矿中。它是青海盐湖硼矿的主要矿石类型。由于自然界未发现在水体中析出的钠硼解石,因而,其成因仍是不清楚的。从放置３ 年、８ 年和１４ 年的小柴旦湖矿坑水、湖表卤水和扎仓茶卡湖表卤水获得了钠硼解石,从而查明钠硼解石是在稳定平衡条件下的低浓度、弱碱－ 碱性、富硼的硫酸钠亚型水体中形成的。这对于阐明钠硼解石矿床的成因及其人工控制再生均有重要的意义 相似文献
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16.
Lidia Romero-Viana Ramon Julià Antonio Camacho Eduardo Vicente Maria Rosa Miracle 《Journal of Paleolimnology》2008,40(2):703-714
Lake La Cruz is a meromictic, karstic lake with annually laminated sediment formed by summer pulses of calcite deposition.
The aim of this study was to explore the potential use of the laminated sediment from Lake La Cruz as a quantitative climate
proxy, by calibrating lamina thickness against instrumental climate data. Statistical analysis of the relation between lamina
thickness and the meteorological dataset indicated a high correlation between calcium carbonate lamina thickness and rainfall
from December to March (r = 0.725, P < 0.01, n = 35). Winter rainfall anomalies in the area are, in turn, highly negatively correlated with the North Atlantic Oscillation
index (NAO, r = −0.832; P < 0.01; n = 53). We propose a regression model to infer past winter rainfall from calcium carbonate laminae thickness. These results
highlight new possibilities for paleoenvironmental research using calcite laminated sediment records as climate proxies, especially
to study past rainfall variability. 相似文献
17.
Lake Simcoe is a large lake 45 km across and in places over 30 m deep, located between Lake Huron and Lake Ontario, in the
glaciated terrain of southern Ontario, Canada. Seismostratigraphic analysis of high-resolution seismic reflection profiles,
together with lakebed sediment sampling and pollen study, revealed distinctive sequences in the sediments beneath Lake Simcoe,
Ontario. A surface unit (Blue Sequence) of soft Holocene mud (low-amplitude surface reflection, discontinuous parallel internal
reflections) lies in the deeper basins of the lake. The underlying unit (Green Sequence) is characterized by high-amplitude
parallel internal reflections; basal sediments of this sequence consist of clay rhythmites with dropstones. The Green Sequence
was deposited by lacustrine sedimentation in proglacial Lake Algonquin; sedimentation persisted until the basin was isolated
from other glacial lakes at about 10 14C ka at the Penetang post-Algonquin phase. Subsequent erosion of the uppermost portion of the Green Sequence is attributed
to wave action in a low-level early Holocene lake, possibly closed hydrologically and coeval with closed lowstands in the
Huron and Georgian Bay basins. Two sequences with high-amplitude surface reflections and chaotic internal reflections (Purple
and Red Sequences) lie below the Green Sequence. Northeast-southwest trending ridges, tens of metres in height, on the Red
Sequence (the lowermost of these two units) are interpreted to be drumlins. An erosion surface descends into narrow valleys
50–80 m deep beneath the lake in bays to the west and south of the main lake basin. These depressions are interpreted as subglacial
tunnel channels cut by rapid flows of meltwater. The sediments of Purple Sequence are interpreted as channel-fill sediments
rapidly deposited during waning stages of the meltwater drainage. The Red Sequence is correlated with the Newmarket Till of
the last glacial maximum identified beneath the Oak Ridges Moraine to the south. 相似文献
18.
Relationships among conductivity, temperature, total dissolved solids (TDS), and density were determined for hypersaline brine (TDS, 83 g kg–) from Mono Lake. A theoretical estimate of density based on ionic composition and calculated partial molar volumes compared well with actual measurements (difference, 390 ppm). However, an empirically derived equation of state based on temperature and conductivity provides the most accurate density estimates (residual errors, 190 ppm) and can be used with data collected with CTD profilers. 相似文献
19.
扎陵湖、鄂陵湖对黄河源头年径流的影响 总被引：15，自引：0，他引：15
黄河源头扎陵湖、鄂陵湖为吞吐湖泊，是黄河源头二大主要湖泊。对黄河源头年径流具有滞蓄、调节作用。利用黄河源头控制站黄河沿站和下游吉迈、唐乃亥、循化3个测站水文资料，依据年径流在地区上的变化特点，分析了扎、鄂二湖对黄河源头径流影响。①扎、鄂二湖滞蓄，改变了源头径流年内分配，使其均匀化；②在枯水年份，入湖水量小，加上湖面强烈蒸发，使得湖泊以下黄河沿站年径流量更小，致使枯水程度加剧，加大了年径流年际变化；③黄河沿站与下游吉迈站年径流丰、平、枯程度对比分析，二站丰、平、枯水年同步出现机率为78．8％，扎、鄂二湖没有改变源头黄河沿站年径流丰、枯规律，是年调节湖泊，不是多年调节湖泊。 相似文献
20.
Walter L. Loope Timothy G. Fisher Harry M. Jol Ronald J. Goble John B. Anderton William L. Blewett 《Geomorphology》2004,61(3-4):303-322
Causal links that connect Holocene high stands of Lake Superior with dune building, stream damming and diversion and reservoir impoundment and infilling are inferred from a multidisciplinary investigation of a small watershed along the SE shore of Lake Superior. Radiocarbon ages of wood fragments from in-place stumps and soil O horizons, recovered from the bottom of 300-ha Grand Sable Lake, suggest that the near-shore inland lake was formed during multiple episodes of late Holocene dune damming of ancestral Sable Creek. Forest drownings at 3000, 1530, and 300 cal. years BP are highly correlated with local soil burial events that occurred during high stands of Lake Superior. During these and earlier events, Sable Creek was diverted onto eastward-graded late Pleistocene meltwater terraces. Ground penetrating radar (GPR) reveals the early Holocene valley of Sable Creek (now filled) and its constituent sedimentary structures. Near-planar paleosols, identified with GPR, suggest two repeating modes of landscape evolution mediated by levels of Lake Superior. High lake stands drove stream damming, reservoir impoundment, and eolian infilling of impoundments. Falling Lake Superior levels brought decreased sand supply to dune dams and lowered stream base level. These latter factors promoted stream piracy, breaching of dune dams, and aerial exposure and forestation of infilled lakebeds. The bathymetry of Grand Sable Lake suggests that its shoreline configuration and depth varied in response to events of dune damming and subsequent dam breaching. The interrelated late Holocene events apparent in this study area suggest that variations in lake level have imposed complex hydrologic and geomorphic signatures on upper Great Lakes coasts. 相似文献