Holocene Lake-level Changes Research Articles

Middle to late Holocene lake level changes of Lake Sevan (Armenia) – Evidence from macro and micro plant remains of Tsovinar-1 peat section

In the Caucasus, peat deposits exposed near Lake Sevan (Armenia) provide a Middle to Late Holocene record of lake level fluctuations. The Tsovinar-1 section at the southern shore of Lake Sevan in the Armenian Highlands reveals a well-dated and divers pollen and carpo-flora covering a time span from 6000 BC to 900 AD. The abundances of pollen of forest taxa in relation to steppe vegetation indicate climatic changes through time. In parallel, the presence and number of fossils of aquatic and wetland plants, both in micro and macro floras, provide information about the presence of water and allows estimating changes of water depth. Characteristic taxa pointing to deeper water at Tsovinar-1 are Myriophyllum sp., Ceratophyllum demersum, and several species of Potamogeton. In shallow water, Persicaria amphibia,Sparganium sp., and Typha sp. dominate. In fluctuating water and wetlands those plants are replaced by Menyanthes trifoliata, Ceratophyllum submersum, Alisma sp., and others. High lake levels can be inferred at 6000−5000 BC, 1700−900 BC and 200−900 AD and are associated with humid climate and the development of forest vegetation. Low lake levels occurred at 4000−2600 BC and 600 BC−100 AD corresponding to epochs of decreased humidity and expanded steppe vegetation. Macro and micro remains of plants from the Tsovinar-1 site serve as reliable sources of information for determining environmental changes over time, which are in accordance with archaeological data from the region showing the effects of lake level changes on human activities․

The Driving Forces Underlying Spatiotemporal Lake Extent Changes in the Inner Tibetan Plateau During the Holocene

The Inner Tibetan Plateau (ITP), the central and western part of the Tibetan Plateau (TP), covers about one-fourth of the entire TP and contains more than 800 endorheic lakes larger than 1 km2. These lakes are important water reservoirs and sensitive to TP climate changes. They regulate regional water circulations, and further influence local ecosystems. Many lakes in ITP are surrounded by conspicuous paleoshorelines indicating much higher past lake levels. Previous studies found that lakes in the western ITP (west of ∼86°E) apparently expanded to higher levels than those to the east during the Holocene high lake level stage, however, there is no in-depth study on the reasons for the spatial differences of high lake levels within the ITP. In this study, we first identify Holocene lake level (or lake extent) changes over the ITP by combining published lake level variation data with our reconstruction of Dagze Co lake level variations. We then investigate spatial differences in the magnitude of lake expansions and explore the underlying forces driving these differences using the transient climate evolution of the last 21 ka (TraCE-21ka) and Kiel Climate Model (KCM) simulation results. We find that lakes in the ITP expanded to their highest levels during the early Holocene when the Indian summer monsoon (ISM) greatly intensified. After the mid-Holocene, lake levels fell as a result of the weakening of the ISM. The early Holocene northward shift of the westerly jet and a positive phase of the Atlantic multidecadal oscillation (AMO) resulted in the intensification of southwesterly winds on the southwest TP flank. Concurrently, westerly winds over the TP weakened, causing a differential increase in water vapor transport to the ITP with higher precipitation levels in the southwestern ITP and lower levels to the northeast. These wind-driven differential precipitation levels caused lakes in the southwestern ITP to expand to higher levels than those in the central, northern and northeastern ITP. During the early Holocene, expansion of lakes in the northwestern ITP was enhanced by an increase in glacier melt water besides the increased summer rainfall associated with the intensified ISM.

A Complicated Groundwater Flow System Supporting Ridge-and-Swale Wetlands in a Lake Michigan Strandplain

Beach ridges and wetland swales formed in embayments along Great Lakes shorelines during Holocene lake-level changes. Vegetation differences among swales suggested influence from differing groundwater flow systems. We characterized the hydrology across 79 ridge/swale wetlands in the Manistique/Thompson embayments of Lake Michigan using chemical and physical methods. Cross-sections were built from geologic data, and nested piezometers were installed across three ridges/swales where upwelling was noted. Stainless steel piezometers driven in 30 swales were sampled and water analyzed for specific conductance, alkalinity, and major ions. Surface water from 11 swales was analyzed. Water dominated by Ca-Mg-HCO3 was prevalent across the strandplain, with specific conductance generally less than 100 μS/cm. Conductivity, Ca, Mg, and HCO3 in groundwater were greater at identified groundwater discharges; where an amalgamated beach ridge forms a surficial groundwater divide; and swales nearer Lake Michigan that likely receive greatly mineralized water from a deeper aquifer. Repositioning of the shoreline as the embayments filled over the past 4700 years, coupled with isostatic rebound and changes in lake water levels, altered head differentials and changed the sources of discharge from local, intermediate, and deep flow systems over time. Extant plant communities are consistent with the groundwater dependence of these wetlands.

Preliminary Analysis of Middle Holocene Lake-Level Change of Ancestral Lake Michigan, Wentworth Woods, Cook County, Illinois

Study of past lake-level change and isostasy in the upper Great Lakes has demonstrated the need to reconstruct relative lake-level history at each outlet during the Nipissing phase of ancestral Lakes Huron, Michigan, and Superior. Although elevation and age data exist for the Port Huron/Sarnia and Sault outlets of Lake Huron and Lake Superior, respectively, no paleohydrograph has been created for southern Lake Michigan near the Chicago outlet. The Wentworth Woods area of the Cook County Forest Preserve, Illinois, contains more than 30 beach ridges that formed during the rise and fall from the peak elevation of the Nipissing phase. These relict shorelines were vibracored to recover basal foreshore sediments that can be used as a proxy for lake-level elevation at the time of individual shoreline formation. In addition, sand samples from soil pits and vibracores were collected for optically stimulated luminescence age determinations. This report addresses the sedimentological data used to determine the elevation of the conjoined upper Great Lakes (Lake Nipissing) when each beach ridge formed. The age data will be presented in future reports.

Late Pleistocene to present lake-level fluctuations at Pyramid and Winnemucca lakes, Nevada, USA

AbstractA new lake-level curve for Pyramid and Winnemucca lakes, Nevada, is presented that indicates that after the ~15,500 cal yr BP Lake Lahontan high stand (1338 m), lake level fell to an elevation below 1200 m, before rising to 1230 m at the 12,000 cal yr BP Younger Dryas high stand. Lake level then fell to 1155 m by ~10,500 cal yr BP followed by a rise to 1200 m around 8000 cal yr BP. During the mid-Holocene, levels were relatively low (~1155 m) before rising to moderate levels (1190–1195 m) during the Neopluvial period (~4800–3400 cal yr BP). Lake level again plunged to about 1155 m during the late Holocene dry period (~2800–1900 cal yr BP) before rising to about 1190 m by ~1200 cal yr BP. Levels have since fluctuated within the elevation range of about 1170–1182 m except for the last 100 yr of managed river discharge when they dropped to as low as 1153 m. Late Holocene lake-level changes correspond to volume changes between 25 and 55 km3 and surface area changes between 450 and 900 km2. These lake state changes probably encompass the hydrologic variability possible under current climate boundary conditions.

Potential forcing mechanisms of Holocene lake-level changes at Nam Co, Tibetan Plateau: Inferred from the stable isotopic composition of shells of the gastropod Radix

The timing of lake-level fluctuations on the Tibetan Plateau and their relationship with climatic changes is still under debate, and the main reason for this is the lack of suitable archives for reconstructing the paleohydrology and paleoclimatology of the lakes. Here, we present the results of analyses of the shell geochemistry of Radix sp. from an exposed terrace of Nam Co lake on the south-central Tibetan Plateau. Optically stimulated luminescence (OSL) dating reveals that deep-water lacustrine sediments formed between ca. 4.4 and 2.2 ka, suggesting a high and stable lake level significantly above the present. The results of Sr/Ca, δ13C and δ18O analyses of the fossil shells of Radix sp. indicate that during the mid- to late-Holocene, lake-level variations in Nam Co were mainly controlled by variations in the Indian Summer Monsoon. A trend of decreasing evaporation also played an important role. Comparison with other results suggests a consistent pattern of mid- to late-Holocene lake-level changes across a large area of the Tibetan Plateau and adjacent regions to the south, which had a similar causal mechanism. Finally, our results indicate that fossil shells of the gastropod Radix sp. of the lakes on the Tibetan Plateau are a valuable archive for reconstructing the regional paleohydrology and paleoclimatology.

Asynchronous Holocene Asian monsoon vapor transport and precipitation

Millennial-scale variations in the Asian monsoon vapor transport are always associated with long-term changes in monsoon rainfall according to the conventional understanding. However, recent advances in monsoon studies suggested that regional monsoon rainfall has different responses to monsoon vapor transport. This paper presents a comparison between monsoonal vapor and precipitation records along the path of the Asian summer monsoon vapor transport. Pedogenic carbonate δ18O values in both surface sediment and Holocene eolian and lacustrine sediments from the Shiyang River drainage basin were used to investigate the variations of the Asian monsoon vapor transport. Meanwhile, Holocene lake-level changes of the terminal lake were reconstructed to reflect the monsoon precipitation variability. The results show that millennial-scale monsoon vapor transport is in accordance with low-latitude summer insolation, while the increasing summer monsoon rainfall during the early Holocene lags the monsoon water vapor transport. In addition, the relatively cold oceans left over from glacial periods and slow melting of ice sheets may temper the onset of the rainfall. These findings can provide insights into the interpretation of the asynchronous Holocene records from lakes and caves in East Asia.

Comparison of grain-size distributions between nearshore sections and a deep-water sediment core from Dali Lake, North China, and inferred Holocene lake-level changes

The grain-size distribution of the sediments of closed lake basins is sensitive to lake-level changes and thus to changes in regional climate. Deep-water areas of lakes potentially yield high resolution, continuous records of sedimentation and lake-level changes. In contrast, the marginal areas of lake basins accumulate sediment in a wave-dominated, high-energy environment and may be more sensitive to lake-level changes than deep-water environments, but they might also be more affected by sedimentary hiatuses. Here, we present grain-size data from two sections of exposed nearshore sediments of Dali Lake, North China, and compare them with previously published results from a sediment core from the lake center. We used the grain size-standard deviation method to distinguish various grains-size components of the nearshore sediments, and compared the results with those from surface sediments from various depths in order to investigate past lake-level changes. Combining the grain-size results with a radiocarbon chronology, we defined four lake-level stages during the Holocene: (1) An intermediate lake level from early Holocene to 10.0 cal ka BP. (2) A high lake level from 10.0 to 6.6 cal ka BP. (3) A decline to an intermediate lake level from 6.6 to 1.0 cal ka BP. (4) An abrupt fall to a low lake level from 1.0 cal ka BP to the present when the marginal section was covered with eolian sand. Our results indicate that the total amplitude of lake-level variation during the Holocene was greater than 45 m. This record of lake-level change is in good agreement with previous results obtained from the lake center, and it indicates that the grain-size standard deviation method may be well suited for lake-level reconstruction from nearshore sediments. Moreover, the marginal sections provide evidence of an abrupt short-lived lake-level decline more clearly than the deep-water core.

Multiple drivers of Holocene lake level changes at a lowland lake in northeastern Germany

Many German lakes experienced significant water level declines in recent decades that are not fully understood due to the short observation period. At a typical northeastern German groundwater‐fed lake with a complex basin morphology, an acoustic sub‐bottom profile was analysed together with a transect of five sediment cores, which were correlated using multiple proxies (sediment facies, μ‐XRF, macrofossils, subfossil Cladocera). Shifts in the boundary between sand and mud deposition were controlled by lake level changes, and hence, allowed the quantification of an absolute lake level amplitude of ~8 m for the Holocene. This clearly exceeded observed modern fluctuations of 1.3 m (AD 1973–2010). Past lake level changes were traced continuously using the calcium‐record. During high lake levels, massive organic muds were deposited in the deepest lake basin, whereas lower lake levels isolated the sub‐basins and allowed carbonate deposition. During the beginning of the Holocene (>9700 cal. a BP), lake levels were high, probably due to final melting of permafrost and dead‐ice remains. The establishment of water‐use intensive Pinus forests caused generally low (3–4 m below modern) but fluctuating lake levels (9700–6400 cal. a BP). Afterwards, the lake showed an increasing trend and reached a short‐term highstand at c. 5000 cal. a BP (4 m above modern). At the transition towards a cooler and wetter late Holocene, forests dominated by Quercus and Fagus and initial human impact probably contributed more positively to groundwater recharge. Lake levels remained high between 3800 and 800 cal. a BP, but the lake system was not sensitive enough to record short‐term fluctuations during this period. Lake level changes were recorded again when humans profoundly affected the drainage system, land cover and lake trophy. Hence, local Holocene water level changes reflect feedbacks between catchment and vegetation characteristics and human impact superimposed by climate change at multiple temporal scales.

Records of repeated drought stages during the Holocene, Lake Iznik (Turkey) with reference to beachrock

The cement fabrics, subsurface nature and optically stimulated luminescence age of beachrocks along the shores of Lake Iznik in NW Turkey were studied within the context of Holocene lake level changes. With a maximum thickness of 1.5 m, the low-angle (average 5–10°) beds are composed of coarse grains and small gravels and extend up to 5 m offshore at their most lakeward extremities. Cement textures on and around the poorly-rounded grains are made up of micrite envelopes and meniscus bridges as well as acicular aragonite rims. Geoelectrical resistivity sections taken from a representative location along the beach where the beds have maximum thickness showed that the sand-buried beds are followed up to about 24 m landward. Based on the OSL ages of 33 samples, the cemented beds occurred at four drier periods of the following: Pre- and Early Holocene (dated to 15–9 ka), Holocene Climatic Optimum (7.9–5.6 ka), Middle Holocene (4.9 ka–2.8 ka) and Late Holocene (2.0 ka–0.9 ka).

Littoral landforms and pedosedimentary sequences indicating late Holocene lake-level changes in northern central Europe — A case study from northeastern Germany

A multidisciplinary study was carried out at Lake Großer Fürstenseer See (LFS) in order to explore the potential of littoral sediments, palaeosols and landforms as indicators of historical lake-level changes. This research was initiated to investigate the extent to which lakes in northern central Europe responded hydrologically to climatic and land-use changes in the last millennium. Specific landforms investigated comprise lake terraces, beach ridges, local basins/peatlands and dunes, revealing a wealth of sedimentary sub-environments at the lakeshore. Eleven sections were recorded with subsequent sedimentological–pedological, geochronological (OSL, 14C) and palaeobotanical (pollen, macro remains) analyses. Most of the pedosedimentary littoral sequences show a succession of basal glacial sand, intermediate palaeosols and lacustrine sand on top. A broader number of (semi-)terrestrial buried palaeosols along the lakeshore were systematically identified and analysed, providing evidence for changing hydrological conditions during the late Holocene. Additional historical data from the last centuries (e.g. maps, aerial photos, public records) allow the lake-levels reconstructed from geoarchives to be connected with modern gauging data. All local data sources available enable a tracing of lake level changes of the LFS during the last millennium, comprising periods of relatively low (c. 1200AD, 2000s AD) and relatively high water levels (c. 1250–1450AD, c. 1780AD, 1980s AD). The amplitude of lake-level changes during the last c. 1000years amounts to c. 3m, so that the fluctuations of the last 30years recorded by lake-level monitoring only reflect a small amount of the potential variability. Regional climate and local land-use history suggest that the Medieval lake-level dynamics of LFS were primarily governed by climate and secondarily influenced by human impact on the drainage system. At present the lake level is additionally influenced by the impact of highly water-consuming pine plantations in the catchment area. The regional significance of the local development at LFS can be demonstrated by comparison with other regional and supra-regional lake-level data. The present study underlines the potential of a closer examination of the littoral zone for lake-level reconstructions with high altitudinal precision.

Biomarker-based reconstructions of Holocene lake-level changes at Lake Gahai on the northeastern Tibetan Plateau

Holocene hydrological changes in regions dominated by the westerlies significantly differ from those by the Asian summer monsoon. The high-elevated northeastern Tibetan Plateau, located in between, is likely influenced by the interactions of both circulation systems. Here, we attempt to use biomarkers, n-alkanes and alkenones, to reconstruct Holocene lake-level changes at Lake Gahai in the Qaidam Basin. We choose a sediment core drilled at the lake shore, where biomarkers would be sensitive to lake-level changes. The n-alkane records show high average chain length (ACL), high carbon preference index (CPI), and low proportion of aquatic macrophyte (Paq) values at 7–2 kyr (thousand calibrated years ago) with peaked values around 6 kyr, whereas low ACL, low CPI, and high Paq values occurred after 2 kyr and before 7 kyr. No alkenones were detected at 7–2 kyr, suggesting that lake level at this period was incapable of constantly reaching to the coring site. Therefore, combined results provide unambiguous evidence of relatively low lake level at 7–2 kyr, probably lowest at ~6 kyr. Holocene lake-level changes in this marginal region thus display a different pattern from either of the core regions dominated by the westerlies (anti-phase) and the Asian summer monsoon (out-of-phase). We suggest that in the arid marginal region, temperature-induced evaporation could significantly affect regional hydrological balance, resulting in the discrepancy with the Holocene long-term precipitation decreasing trend in Asian monsoon-dominated regions.

Persistence of Artemisia steppe in the Tangra Yumco Basin, west-central Tibet, China: despite or in consequence of Holocene lake-level changes?

The closed Tangra Yumco Basin underwent the strongest Quaternary lake-level changes so far recorded on the Tibetan Plateau. It was hitherto unknown what effect this had on local Holocene vegetation development. A 3.6-m sediment core from a recessional lake terrace at 4,700 m a.s.l., 160 m above the present lake level of Tangra Yumco, was studied to reconstruct Holocene flooding phases (sedimentology and ostracod analyses), vegetation dynamics and human influence (palynology, charcoal and coprophilous fungi analyses). Peat at the base of the profile proves lake level was below 4,700 m a.s.l. during the Pleistocene/Holocene transition. A deep-lake phase started after 11 cal ka BP, but the ostracod record indicates the level was not higher than ~4,720 m a.s.l. (180 m above present) and decreased gradually after the early Holocene maximum. Additional sediment ages from the basin suggest recession of Tangra Yumco from the coring site after 2.6 cal ka BP, with a shallow local lake persisting at the site until ~1 cal ka BP. The final peat formation indicates drier conditions thereafter. Persistence of Artemisia steppe during the Holocene lake high-stand resembles palynological records from west Tibet that indicate early Holocene aridity, in spite of high lake levels that may have resulted from meltwater input. Yet pollen assemblages indicate humidity closer to that of present potential forest areas near Lhasa, with 500–600 mm annual precipitation. Thus, the early mid-Holocene humidity was sufficient to sustain at least juniper forest, but Artemisia dominance persisted as a consequence of a combination of environmental disturbances such as (1) strong early Holocene climate fluctuations, (2) inundation of habitats suitable for forest, (3) extensive water surfaces that served as barriers to terrestrial diaspore transport from refuge areas, (4) strong erosion that denuded the non-flooded upper slopes and (5) increasing human influence since the late glacial.

Reconstruction of Holocene lake-level changes in Lake Igelsjön, southern Sweden

Pollen and sediment stratigraphic analyses of a transect of core sequences are used to reconstruct Holocene lake-level changes in Lake Igelsjön, southern Sweden. The pattern of changes seen in the records is related to climatic/hydrological changes and agrees principally with the pattern characteristically found in lakes in southern Sweden. However, compared with an earlier study based on isotopic analysis of lake sediments by Hammarlund et al. (2003), some significant differences are found in the early Holocene, and possible explanations for these differences are discussed.

Summed radiocarbon probability density functions cannot prove solar forcing of Central European lake-level changes

It has been argued that Central European lake levels were driven by solar activity. This interpretation rests on the comparison of a score record of radiocarbon dates with the 14C residual curve. This score record is a variant of a cumulative probability density function (CPF). In this paper it is argued that this method is not valid because the shape of the CPF is determined by the calibration curve. This hypothesis is tested by a set of null models. An alternative interpretation is given according to which only few episodes of Holocene lake-level changes were climatically driven, while most of the time non-climatic factors were dominating. On a more general level some methodological issues of CPFs are discussed and exemplified by the comparison of dendrochronological results from archaeological settlements and a CPF created using radiocarbon dates from the same settlements.

Fine resolution of early hominin time, Beds I and II, Olduvai Gorge, Tanzania

Reconstructing paleoenvironments and landscapes within lake-centered, hominin-yielding basinal sequences requires a resolution of time-rock units finer than but complementary to that provided by the present tephrostratigraphy. Although indispensable in providing an absolute time frame at Olduvai, the average 15,000–20,000 year intervals between successive tuff units lack the time resolution to construct a sufficiently contemporary paleolandscape within sedimentary intervals away from the interleaved tuffs. Such control is essential to construct valid paleogeographies in which to contextualize contemporaneous paleoanthropological sites and the traces of hominin land use they contain. Within Beds I and II of the Olduvai Basin a Sequence Stratigraphic analysis has achieved a relative time framework in which time-rock units, “lake-parasequences,” each generated by a major advance and withdrawal of the lake system, are recognizable for average periods of about 4000 years duration. Within each of these time slices at least two paleogeographic landscapes are identifiable, reducing the time constraints of an individual landscape reconstruction to a few thousand years. Within the sedimentary succession both highly incised and less incised unconformities are identifiable to provide sequence boundaries. Within each sequence the higher frequency lake-parasequences can be identified by (1) a disconformable base, (2) accretion of sediment during lake transgression and at maximum, (3) a disconformable top caused by lake withdrawal, and (4) a soil profile generated beneath that disconformable land surface. Individual lake-parasequences can be recognized in lake marginal and fan settings, and their imprint can also be seen in the lake setting where, for example, maximum flooding might be marked by a layer of dolomite. Lower Bed II parasequences represent time intervals of <5000 years, while parasequential periods between Tuffs IB and IC in Bed I are <4300 years. Analogous Holocene lake-level changes of the same order in East Africa have a period close to 4200 years. The estimated period is close to that defined by Stadial/Interstadial Dansgaard-Oeschger Events recorded in the Greenland Ice record, which force cycles of period similar to lake-parasequences, both in the Arabian Sea and Lake Malawi. Lake-parasequences not only aid construction of landscapes, they also allow contextualization of individual paleoanthropological occurrences. For instance, a parasequence lies between Leakey’s Level 1 and her butchered Deinotherium occurrence at FLK N. However, elephantid and giraffid skeletons associated with stone artifacts at VEK, uncovered by OLAPP excavations, are situated on the same land surface as a possibly butchered rhinocerid at KK. To complement the existing absolute radiometric time framework, relative Sequence Stratigraphic techniques might be applied to any lake-centered, hominin-yielding basinal sequence, not only those found within East Africa. Because they are climatically controlled, and might plausibly be related to globally driven Dansgaard-Oeschger Events, lake-parasequences and their associated sequences might be correlatable between various East African basins in the Plio-Pleistocene in the same way as they presently are for the Holocene.

The sedimentary and palynological records of Serpent River Bog, and revised early Holocene lake-level changes in the Lake Huron and Georgian Bay region

Serpent River Bog lies north of North Channel, 10 m above Lake Huron and 15 m below the Nipissing Great Lake level. A 2.3 m Holocene sequence contains distinct alternating beds of inorganic clastic clay and organic peat that are interpreted as evidence of successive inundation and isolation by highstands and lowstands of the large Huron-Basin lake. Lowstand phases are confirmed by the presence of shallow-water pollen and plant macrofossil remains in peat units. Twelve 14C dates on peat, wood and plant macrofossils combined with previously published 14C ages of lake-level indicators confirm much of the known early Holocene lake-level history with one notable exception. A new Late Mattawa highstand (8,390 [9,400 cal]–8,220 [9,200 cal] BP) evidenced by a sticky blue-grey clay bed is tied to outburst floods of glacial Lake Minong during erosion of the Nadoway drift barrier in the eastern Lake Superior basin. A subsequent Late Mattawa highstand (8,110 [9,040 cal]–8,060 [8,970 cal] BP) is attributed to enhanced meltwater inflows that first had deposited thick varves throughout Superior Basin. Inundation by the Nadoway floods and possibly the last Mattawa flood were likely responsible for termination of the Olson Forest (southern Lake Michigan). A pollen diagram supports the recognized progression of Holocene vegetation, and defines a subzone implying a very dry, cool climate about 7.8–7.5 (8.6–8.3 cal) ka BP based on the Alnus crispa profile during the Late Stanley lowstand. A new date of 9,470 ± 25 (10,680–10,750 cal) BP on basal peat over lacustrine clay at Espanola West Bog supports the previous interpretation of the Early Mattawa highstand at ca. 9,500 (10,740 cal) BP. The organic and clastic sediment units at these two bogs are correlated with other records showing coherent evidence of Holocene repeated inundation and isolation around northern Lake Huron. Taken together the previous and new lake-level data suggest that the Huron and Georgian basin lakes were mainly closed lowstands throughout early Holocene time except for short-lived highstands. Three of the lowstands were exceptionally low, and likely caused three episodes of offshore sediment erosion which had been previously identified as seismo-stratigraphic sequence boundaries.

A new water-level history for Lake Ontario basin: evidence for a climate-driven early Holocene lowstand

Piston cores from deep-water bottom deposits in Lake Ontario contain shallow-water sediments such as, shell-rich sand and silt, marl, gyttja, and formerly exposed shore deposits including woody detritus, peat, sand and gravel, that are indicative of past periods of significantly lower water levels. These and other water-level indicators such as changes in rates of sedimentation, mollusc shells, pollen, and plant macrofossils were integrated to derive a new water-level history for Lake Ontario basin using an empirical model of isostatic adjustment for the Great Lakes basin to restore dated remnants of former lake levels to their original elevations. The earliest dated low-level feature is the Grimsby-Oakville bar which was constructed in the western end of the lake during a near stillstand at 11–10.4 (12.9–12.3 cal) ka BP when Early Lake Ontario was confluent with the Champlain Sea. Rising Lake Ontario basin outlet sills, a consequence of differential isostatic rebound, severed the connection with Champlain Sea and, in combination with the switch of inflowing Lake Algonquin drainage northward to Ottawa River valley via outlets near North Bay and an early Holocene dry climate with enhanced evaporation, forced Lake Ontario into a basin-wide lowstand between 10.4 and 7.5 (12.3 and 8.3 cal) ka BP. During this time, Lake Ontario operated as a closed basin with no outlets, and sites such as Hamilton Harbour, Bay of Quinte, Henderson Harbor, and a site near Amherst Island existed as small isolated basins above the main lake characterized by shallow-water, lagoonal or marsh deposits and fossils indicative of littoral habitats and newly exposed mudflats. Rising lake levels resulting from increased atmospheric water supply brought Lake Ontario above the outlet sills into an open, overflowing state ending the closed phase of the lake by ~7.5 (8.3 cal) ka BP. Lake levels continued to rise steadily above the Thousand Islands sill through mid-to-late Holocene time culminating at the level of modern Lake Ontario. The early and middle Holocene lake-level changes are supported by temperature and precipitation trends derived from pollen-climate transfer functions applied to Roblin Lake on the north side of Lake Ontario.

Controls on lake level in the early to mid Holocene, Hawes Water, Lancashire, UK

This study presents a new interpretation of the evidence for Holocene lake-level changes from Hawes Water in NW England constrained by detailed stratigraphic data, radiocarbon chronology and palaeo-environmental evidence. Lake levels are seen to decline gradually from the start of the Holocene through to 9960 cal. yr BP, in response to lake infilling and the prevailing dry climatic conditions. Low lake levels then persist until 6000 cal. yr BP, punctuated by two transgressive phases. Rising sea levels during the Holocene high-level sea stand are thought to be responsible for a major rise in lake level at 6000 cal. yr BP driven by changes in the local water-table. The rise in lake level is coincident with a rise in anthropogenic activity across the site, possibly reflecting the migration of coastal Mesolithic communities inland in response to rising sea levels.

Multiple factors causing Holocene lake-level change in monsoonal and arid central Asia as identified by model experiments

Lake-level records provide a rich resource of information about past changes in effective moisture, but water-balance fluctuations can be driven by a number of different climate variables and it is often difficult to pinpoint their exact cause. This understanding is essential, however, for reconciling divergent paleo-records or for making predictions about future lake-level variations. This research uses a series of models, the NCAR CCSM3, a lake energy-balance and a lake water-balance model, to examine the reasons for lake-level changes in monsoonal Asia and arid central Asia between the early (8.5 ka), middle (6.0 ka) and late (ca. 1800 AD) Holocene. Our results indicate that the components of the lake water balance responsible for lake-level changes varied by region and through time. High lake levels at 8.5 and 6.0 ka in the monsoon region were caused by the combined effects of low lake evaporation and high precipitation. The low lake evaporation resulted from low winter solar radiation and high summer cloud cover. Precipitation associated with the mid-latitude westerlies increased from the early to middle Holocene and maintained high lake levels throughout most of arid central Asia ca. 6 ka. The modeled evolution of lake level in arid central Asia from the mid to late Holocene was spatially heterogeneous, due to different sensitivities of the northern and southern parts of the region to seasonally-changing insolation, particularly regarding the duration of lake ice cover. The model results do not suggest that precipitation and lake evaporation changes compete with one another in forcing lake-level change, as has been hypothesized.