Lake-level Record Research Articles

Holocene paleolakes of Lake Canyon, Colorado Plateau: Paleoclimate and landscape response from sedimentology and allostratigraphy

Middle and late Holocene paleoclimate can be inferred from lake-level fluctuations recorded in the sediment of two, fresh, groundwater‐controlled paleolakes in Lake Canyon, southeast Utah. The record from Lake Canyon contributes proxy climate data for the region as well as insight into climate controls on sedimentation. The paleolakes were formed immediately upcanyon of side-stream confluences where disproportionately large volumes of alluvium were focused into the bedrock canyon. Excellent exposure allows a depositional facies model to be developed and allostratigraphic units to be defined. A facies-based proxy for the past shoreline position is applied to the allostratigraphy and radiocarbon-based chronostratigraphy to produce a record of lake level through time that is corroborated by diatom proxy data. The earliest known lake formed during an episode of aggradation that began just before 5180 14 C yr B.P., and an arroyo-cutting event drained the lake before 3050 14 Cy r B.P. The Lake Canyon record for the past 3 k.y. is composed of wet-dry cycles that have a periodicity of ~520 yr, matching cycles resolved by the regional tree-ring record and the timing of the Medieval Warm Period and Little Ice Age. Lake level rose after 420 14 C yr B.P. and aggradation continued until an advancing arroyo headcut drained the upper lake in A.D. 1915. Fluvial and lacustrine aggradation in Lake Canyon accompanied shifts to wetter climate when sediment stored in upper reaches of the drainage basin was delivered to the canyon, whereas arroyo cutting in the canyon is more a function of sediment supply and internal complex-response mechanisms than dry climate conditions. Correlation with other records is hindered by differences in resolution and the influence of local controls on alluvial stratigraphy. The Lake Canyon record confirms that episodes of high flood frequency in Holocene time have been wetter overall, but not all wet periods have been marked by high flood frequency.

A direct comparison between the historical record of lake level and the δ18 O signal in carbonate sediments from Lake Turkana, Kenya

We compared oxygen isotopic profiles from authigenic calcite in nine freeze cores from Lake Turkana, Kenya, with the historical record of lake levels for the past 105 years. 210Pb dating of the cores indicates that sediment in two of the cores spans the complete historical record. We observed spatial variability in 6180 and 617C values between cores and an offset from expected isotopic equilibrium values in several of the cores. Both of these characteristics can be explained by proximity to river input. In model calculations of lake level, we muted the spatial variability of the S1*O dataset by using a normalized and stacked record. There is good agreement between the lake level history modeled using the normalized and stacked record and the historical record of lake level. The lake level record derived from the S180 data indicates that lake level fluctuated by 15 m during the last century. Our model calculations indicate that S’*O records can be used to generate quantitative lake level curves even using datasets with significant spatial variability. The isotopic composition of carbonates has been used in numerous lacustrine studies to determine paleoclimatic information. Fluctuations in the isotopic record preserved in carbonates are created mainly by variations in the temperature and composition of the water in which the carbonate formed. In turn, these variations can be caused by climatic changes in the lake basin. Carbonates are therefore potentially an archive of the paleoenvironment of a lake basin. In tropical or closed-basin settings, shifts in the oxygenstable isotopic composition (S180) of carbonates are often attributed to shifts in the evaporation-to-input (E : Z) ratio of a lake. Previous workers have used the relationship between changes in the S180 value of carbonates and the E: Z ratio of a lake basin to discuss qualitative changes in paleo-lake levels. Although the relationship between the &*O composition of lake water and the various inputs and outputs to a basin has been described quantitatively (Gat 1984; Phillips et al. 1986; Benson and White 1994), only one quantitative comparison between a historical lake level record and lake level determined from the aI80 composition of carbonates has been attempted (Li 1995).

Sedimentation history of the Selenga Delta, Lake Baikal: simulation and interpretation

The computer simulation of a Lake Baikal seismic profile located in the Selenga River Delta area resulted in a lake level record of the last 600 kyr. This curve demonstrates several low-magnitude episodes and both a dramatic 300 m fall and a more than 150 m increase of the lake level relative to present situation. The greatest change in paleo-lake depth at 300 ka corresponds in time with the major glaciation in the Eastern Siberia and is probably the response of the lake to this climatic phenomenon. The results of this study conform with existing hypotheses on the regional tectonic history and climatic events.

The hydrology of Lake Bosumtwi, a climate-sensitive lake in Ghana, West Africa

Lake Bosumtwi, lying in a million-year-old meteor crater, is hydrologically closed in spite of the wet, humid climate in this part of Ghana. To understand this geographical enigma, a water-balance model that describes both the historical lake-level record and the full range of lake levels observed in terrace deposits around the lake was developed. The water-balance model shows that the reception of rainfall by and evaporation from the lake surface are the dominant constituents of the water balance. Prior to 1969, the average rainfall of 1550 mm year −1 was generally equal to lake evaporation, and the average annual rise of 30 cm year −1 was produced mostly by runoff from the small watershed around the lake. Since 1969, with a decreased rainfall of 1380 mm year −1, the combination of rainfall and runoff has nearly equaled lake evaporation, resulting in a nearly steady lake level. Long-term simulations show that stochastic climatic variations very similar to those observed in this century could produce the full range of lake levels observed in terrace deposits. The low salinity of about 1‰ suggests that dissolved solutes were removed by lake overflow in the recent geological past.

Carbonate deposition, Pyramid Lake Subbasin, Nevada: 4. Comparison of the stable isotope values of carbonate deposits (tufas) and the Lahontan lake-level record

In this paper, the fundamental importance of changes in hydrologic balance and hydrologic state on the δ 18O and δ 13C values of water and dissolved inorganic carbon (DIC) in lakes of the Lahontan basin is illustrated. Abrupt changes in δ 18O and δ 13C values of carbonate deposits (tufas) from the Pyramid Lake subbasin, Nevada, coincide with abrupt changes in lake-level and hydrologic state. Minima in lake-level at ∼26,000, ∼15,500 and ∼12,000 yr B.P. are associated with relatively heavy δ 18O and δ 13C values; maxima in the lake-level record at ∼14,000 and ∼10,500 yr B.P. are associated with relatively light δ 18O and δ 13C values. We believe that the correlation between maxima and minima in the lake-level and δ 18O records reflect the fundamental effect of lake-level dynamics on the δ 18O value of lake water. Evaporation increases the δ 18O value of lake water, whereas, streamflow discharge and on-lake precipitation decrease the δ 18O value. Variation in the δ 18O value of lake water, therefore, indicates change in the hydrologic balance; increases in δ 18O accompany decreases in lake volume and decreases in δ 18O accompany increases in lake volume. Covariance of δ 13C and δ 18O indicates that change in δ 13C values of DIC also accompany change in lake volume. We offer the hypothesis (first put forward by J.A. McKenzie) that change in the productivity (photosynthesis) respiration balance is responsible for much of the observed variation in δ 13C. Most Great Basin lakes, including Lake Lahontan, experienced changes in hydrologic state during the late Wisconsin. When a lake becomes hydrologically open, the residence time of water decreases. The greater the rate of spill, the greater the volume of evaporated ( 18O-enriched) water removed from the spilling lake and the more negative the δ 18O value of water remaining in the spilling lake. The concentration of DIC, as well as the concentrations of photosynthesis limiting nutrients (e.g., phosphorus, nitrogen, silica, molybdenum) decrease as spill increases. Increasing rates of spill, therefore, lead to overall decreases in photosynthetic rates relative to respiration rates and, as a consequence, the δ 13C values of DIC become more negative.

Late Quaternary Lake-Level Record from Northern Eurasia

Lake records from northern Eurasia show regionally coherent patterns of changes during the late Quaternary. Lakes peripheral to the Scandinavian ice sheet were lower than those today but lakes in the Mediterranean zone were high at the glacial maximum, reflecting the dominance of glacial anticyclonic conditions in northern Europe and a southward shift of the Westerlies. The influence of the glacial anticyclonic circulation attenuated through the late glacial period, and the Westerlies gradually shifted northward, such that drier conditions south of the ice sheet were confined to a progressively narrower zone and the Mediterranean became drier. The early Holocene shows a gradual shift to conditions wetter than present in central Asia, associated with the expanded Asian monsoon, and in the Mediterranean, in response to local, monsoon-type circulation. There is no evidence of mid-continental aridity in northern Eurasia during the mid-Holocene. In contrast, the circum-Baltic region was drier, reflecting the increased incidence of blocking anticyclones centered on Scandinavia in summer. There is a gradual transition to modern conditions after ca. 5000 yr B.P. Although these broad-scale patterns are interrupted by shorter term fluctuations, the long-term trends in lake behavior show a clear response to changes in insolation and glaciation.

Recent lake-level and outflow variations at Lake Viljandi, Estonia: validation of a coupled lake-catchment modelling scheme for climate change studies

Changes in the depth of Lake Viljandi between 1940 and 1990 were simulated using a lake water and energy-balance model driven by standard monthly weather data. Catchment runoff was simulated using a one-dimensional hydrological model, with a two-layer soil, a single-layer snowpack, a simple representation of vegetation cover and similarly modest input requirements. Outflow was modelled as a function of lake level. The simulated record of lake level and outflow matched observations of lake-level variations ( r = 0.78) and streamflow ( r = 0.87) well. The ability of the model to capture both intra- and inter-annual variations in the behaviour of a specific lake, despite the relatively simple input requirements, makes it extremely suitable for investigations of the impacts of climate change on lake water balance.

Change in the size of Walker Lake during the past 5000 years

In 1984, a 12-m sediment core (WLC84-8) was taken from the deepest part of Walker Lake. Samples of the core were analysed for diatoms, pollen, carbonate mineralogy, magnesium content, δ 18O and δ 13C values of the total inorganic fractin, δ 18O and δ 13C values of Limnocythere ceriotuberosa, δ 13C values of the total organic fraction, grain size, and magnetic susceptibility. The data indicate that Walker Lake became shallow and probably desiccated between ⩾5300-4800 and 2700-2100 yr B.P.. Each of the organic and inorganic proxy indicators of lake size discussed in this paper was useful in determining the presence of the shallow-lake intervals. However, none of the indicators was useful in determining the cause of the shallow-lake intervals. Instead, the types of fish living in Walker Lake prior to 1940 were used to demonstrate that shallow-lake intervals resulted from diversion of the Walker River and not from climatic aridity. Major changes in mineralogy and magnesium content of carbonates and major changes in diatom populations with time were found to be a function of the chemical evolution of Walker Lake combined with changing lake size. The stable isotopes of oxygen and carbon were found to be good indicators of lake volume changes. A lake-level record for Walker Lake constructed from stable-isotope data was found to be similar to a lake-level record constructed using tufa and tree-stump data. Both records indicate relatively high lake levels between 4800−2700 yr B.P., at 1250 yr B.P., and within the last 300 yr. Substantial declines in lake level occurred ∼2000 and ∼1000 yr B.P.

A record from Lake Cardiel of climate change in southern South America

SOUTHERN South America, the only continental land mass lying between 38° S and the Antarctic Circle, presents a rare opportunity to reconstruct terrestrial records of palaeoclimate in an area that is subject to shifts of polar and mid-latitude wind and pressure belts. In the bulk of this region (Patagonia) are many hydrographically closed lakes which, despite the palaeoclimatic significance of the region and the proven utility of lake level records in reconstructing past climates1,2, have escaped detailed study. Using sedimentary and geomorphic evidence, together with 14C dating, we present here a detailed lake level record for Lake Cardiel (Fig. 1). The highest level of the past >21,000 years occurred at about 9,780 BP, reminiscent of tropical lakes rather than those in northern mid-latitudes1,2. The Lake Cardiel record corroborates and clarifies the timing of the wetness record inferred from pollen studies in Patagonia.

An 18,000-Year Record of Vegetation, Lake-Level and Climatic Change from Tigalmamine, Middle Atlas, Morocco

Pollen, stable istotope and sedimentological analyses of a 21 m-long radiocarbon-dated core of calcareous lake sediments from the Middle Atlas moun- tains, Morocco, provide an 18,000-year record of change in lake level and local vegetation attributable to climatic, ecological and anthropogenic causes. Herb-rich grassland persisted for nearly 10,000 years, except for a period between 14,000 and 12,000 BP when scattered oaks were present. Oak forest replaced the grassland 8500 years ago and Cedrus atlantica (Endl.) Carriere arrived in the area about 4000 years ago. These vegetational changes probably

Late Quaternary Chronology of Tufa Deposits, Walker Lake, Nevada

Walker Lake, a terminal desertic lake in Mineral County, Nevada, has fluctuated greatly in lake level throughout its long history due to changes in climate and drainage. In its Late Pleistocene high stand, Walker Lake formed the southernmost embayment of pluvial Lake Lahontan. Calcareous tufa and other shoreline deposits of Pleistocene and Holocene ages provide a valuable record of past lake levels. Studies of tufa morphology and stable isotope character, closely integrated with sedimentologic data, show great promise for elucidating the post-glacial climatic history of the Great Basin. Three prominent shoreline carbonate deposits below 1250 m have been studied in the field and with stable isotope and radiocarbon analyses. The oldest deposit (18,000 radiocarbon yrs B.P.) consists of massive, bowl-shaped tufa heads outcropping from conspicuous wavecut and fan-deltaic terraces. Three "bigheads" are covered by alluvial fan deposits, which in turn are coated by an "encrusting tufa" of 3 cm average thickness. This encrusting tufa, dated at 2150 yrs B.P. and exhumed during the historic drop in lake level, coats virtually every undisturbed boulder around the entire lake. The third deposit, a 2 mm "outer rind," coats the first two deposits and has modern pre A-bomb or A-bomb radiocarbon levels depending on sample elevation. The $$\delta^{13}C$$ values for the bighead deposits average $$3.41 \pm 0.10\%0$$, and the $$\delta^{18}O$$ values average $$-1.47 \pm 0.61\%0$$. The $$\delta^{13}C$$ and $$\delta^{18}O$$ values for the encrusting tufas average $$3.21 \pm 0.12\%0$$ and $$-0.68 \pm 0.25\%0$$, respectively, and the $$\delta^{13}C$$ and $$\delta^{18}O$$ values for the outer rinds average $$3.09 \pm 0.17\%0$$ and $$-0.10 \pm 0.34\%0$$, respectively. Isotopic paleotemperatures for the two Holocene deposits range from 27 to 35°C, the same as shoreline values measured in July and August. Our results indicate late Pleistene low stands below 1222 m circa 18,000 yrs B.P., a post-Pleistocene period of desiccation during which alluvial fans formed, another rise to 1250 m, another period of desiccation circa 2000 yrs B.P., a rise to the historic high stand of 1244 m and, since 1880, a drop to 1206 m.

Late Cainozoic history of vegetation, fire, lake levels and climate, at Lake George, New South Wales, Australia

The results of pollen, spore, algal and charcoal particle analyses from an 18 m core sample, dating fromca. 730000-0 a before present (B.P.), from Lake George are described along with an account of a five year study of modern pollen-rain from the same site. Also, pollen analyses of two isolated samples, dating about 4-7 Ma B.P., in a separate core from the same location are reported for comparison. The sedimentary sequence is dated by means of magnetostratigraphy and radiocarbon. The microfossil record from Lake George provides the longest relatively continuous Quaternary continental sequence yet available from Australia and may document one of the world’s longest combined record of vegetation, bush-fires, lake levels and climates together with the record of accompanying plant migrations, redistributions and extinctions. It is so far the only chronologically secure Late Cainozoic palynological database available in Australia that spans the entire Brunhes Chron. The altitudinal shifts of vegetation belts inferred from the palynological sequence suggest significant past changes in terrestrial temperatures of the order of glacialinterglacial cycles. It is revealed that the upper treeline was depressed by 1200-1500 m and 300-600 m, respectively, during the glacial maxima and the cool-temperate intervals, and reverted during the interglacials. Assuming an average lapse rate of 0.7 °C per 100 m, the drop in mean temperature for the warmest month (January) with respect to the present during the glacial maxima and the cool-temperate periods respectively may have been about 8—10 °C and 2—4 °C. A series of about eight glacial-interglacial cycles (phases I-XIX ) are recognized during the Brunhes Chron at Lake George broadly corresponding to stages 1-19 of the deep sea18O palaeotemperature record. A correlation between the palaeotemperature sequence and the former lake levels at Lake George is presented for the relatively more continuous section, ca. 350000-0 a B.P., with a view to resolve past precipitation changes. It is inferred that periods of considerably lower precipitation than at present prevailed during the glacial maxima. Conversely, periods of higher precipitation than at present occurred for some considerable lengths of time during the interglacials. In general terms, the precipitation levels increased during both interglacials and interstadials with respect to glacial maxima. The plant microfossil evidence indicates thatEucalyptus-dominated, dry sclerophyll (low, open) forests, now growing in the lake catchment, and probably elsewhere in southeastern Australia are the result of a comparatively recent development. It is shown that the relatively ‘ fire-sensitive’Casuarina-dominated forests, combined several equally or more ‘fire-sensitive’ rainforest taxa, dominated the vegetation for at least half a million years during all but the last two interglacials. The relatively ‘fire-tolerant’,Eucalyptus-dominated forests started to expand onwards from the last interglacial, some 130000 years ago, in conjunction with large increases in the amount of charcoal in the sediment. Since then, not only did the amount of charcoal remain at a generally high level but the overall dominance of open, eucalypt forest is maintained throughout during the warmer periods except for a cool-temperate interstadial interval (zone D) during the last glacial. The ‘fire-sensitive’Casuarina(under 23 μm type) as well as all the rainforest taxa declined at the end of the last glacial and finally disappeared from the lake catchment during the Holocene, culminating in the total extinction ofCasuarinatype under 23 μm during the last few hundred years. Some of the changes in flora during the Brunhes Chron were undoubtedly the result of long-term climatic change but most appear to have been precipitated through increased fire-frequencies only during the last 130000 years (with the maximum impact occurring during the last 10000 years), probably on account of the bush-firing activities of early man in Australia. This presupposes the presence of the Aboriginal people some 90000 years earlier than the oldest available archaeological evidence for human occupation of the Australian continent, a proposition that remains to be tested by future archaeological investigations. In biogeographical terms, the studies reveal that a number of Gondwanic taxa, commonly seen during the late Tertiary in southeastern Australia, survived well into the Pleistocene and finally disappeared during the late Brunhes from Lake George.

Global maps of lake-level fluctuations since 30,000 yr B.P.

This paper presents selected world maps of lake-level fluctuations since 30,000 yr B.P. These are based on a literature survey of 141 lake basins with radiocarbon-dated chronologies. The resulting patterns are subcontinental in scale and show orderly variations in space and time. They reflect substantial changes in continental precipitation, evaporation, and runoff, which are due to glacial/interglacial fluctuations in the atmospheric and oceanic circulations. In the tropics, high lake levels are essentially an interglacial or interstadial phenomenon, although there are important exceptions. Since extensive lakes during the Holocene corresponded with relatively high sea-surface temperatures, and therefore presumably with high evaporation rates on land, they are interpreted as the result of higher precipitation. Tropical aridity culminated in most areas at, or just after, the glacial maximum, although the present day is also characterized by a below-average abundance of surface water. In extratropical regions the mapped patterns are more complex. They vary markedly with latitude and proximity to major ice sheets. In these areas, evidence is at present insufficient to evaluate the relative contributions of precipitation and temperature to the observed lake-level record.

Recent changes in the level of Lake Naivasha, Kenya, as an indicator of equatorial westerlies over East Africa

A previously unpublished record of lake levels from Lake Naivasha, Kenya from 1880 to 1976 has been analysed and shows little similarity to the level record from nearby Lake Victoria. Level changes from year to year of the two lakes show no significant correlation (at 5%) and spectral analysis of the two records shows no common significant peaks. Both lakes show significant correlations between their level changes and the strength of the North Atlantic winter circulation, with the correlation coefficients in opposing directions indicating important, but different, large scale climatic links. Lake Naivasha's major level increases occur during May and September. Lake Victoria's level increases mainly in May with a small December increase. East African rainfall is generally during April and November, corresponding with Lake Victoria's changes. Rainfall records from Kenyan highland areas, however, show an August rainfall peak and little rainfall in November. Rainfall amounts from Equator, a highland meteorological station, for July, August and September are highly correlated (at 1% significance level) with the change in Naivasha's level during September. Winds at the highland stations are westerly during August while the lower level stations experience the drier S.E. Trades. The level changes of Lake Naivasha indicate changes in the extent of the penetration of moist air from West Africa between the Trade winds and the 200 mb easterly jet.