Holocene Lake Level Research Articles

Holocene lake shrinkage on the northwestern Tibetan Plateau revealed by K-feldspar single-grain pIRIR dating of paleo-shorelines

As a vital component of the “Asian water tower”, lakes on the Tibetan Plateau (TP) significantly influence the regional ecosystems and economies and they are also an effective sentinel of climate change. However, the temporal and spatial patterns of lakes and the related hydroclimatic evolution on the northwestern TP (NWTP) remain unclear. We reconstructed the lake level variations of a non-glacier-fed lake, Longjue Co, on the NWTP, using optical dating of paleo-shorelines. The optically stimulated luminescence signals of quartz grains were unsuitable for dating due to high contributions of the medium component, and thus the post-infrared infrared stimulated luminescence signals (pIR50IR170, pIR50IR225) of K-feldspar single grains were used. Internal checks including dose recovery tests, residual dose tests, and anomalous fading tests showed that the pIR50IR170 signal was suitable for paleo-shoreline dating in Longjue Co. However, some of the samples were affected by the incomplete bleaching of pIRIR signals before deposition, and in this case the Minimum Age Model was used to constrain the ages. We also examined the dependence of the K-feldspar equivalent dose (De) on grain brightness and explored the possible mechanisms, and the brightest grains were then used for De calculations. The results show that Longjue Co reached its maximum Holocene level (+34 m) during the early Holocene (10.06 ± 1.39 ka), and then after ∼5 ka it commenced a shrinking trend, punctuated by two rapid lake level decreases. Reference to independent paleoclimate records suggests that the Holocene lake level variations of Longjue Co and the regional hydroclimate were mainly controlled by the Indian summer monsoon.

Middle to Late Holocene lake level variations recorded by shoreline tufa of Longmu Co Lake, northwestern Tibet Plateau

Tufa deposits have significant potential for reconstructing past lake-level fluctuations. Here, we conducted U-Th dating of tufa deposits exposed along the shoreline of Longmu Co Lake in the northwestern Tibetan Plateau to reconstruct its water level history during the middle-late Holocene. Our data demonstrate that Longmu Co Lake reached its highest level (61 m above the present level) at around 7.4 ka in response to the strengthened Indian Summer Monsoon and increased glacial meltwater; its lake level subsequently decreased due to solar insolation-induced decline in summer monsoon and glacial meltwater. Moreover, we find that the lake level experienced an abrupt decline at ~2.2 ka with a maximum amplitude of 13 m, probably owing to the rapid cooling of the local climate. The δ18O and δ13C of Longmu Co tufa also show a covariance trend, which supports the regional climate change reflected by the lake level fluctuation of Longmu Co. Additionally, we observed an inverse correlation between initial δ234U content in tufa and lake level variation, suggesting that initial calcium δ234U can serve as a proxy for reconstructing environmental changes. Our study therefore implies that lake tufa as a reliable archive for accurately reconstructing lake level changes.

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․

Holocene hydrological history of a Tibetan glacier-fed lake Taro Co in response to climate change

Lake hydrological fluctuations on the Tibetan Plateau (TP) are highly sensitive to global climate change, which can be reconstructed directly by dating paleoshorelines representing past lake-levels. In this study, we reconstructed the Holocene lake-level history of Taro Co lake system (Taro Co, Zabuye Salt lake and Lagkor Co) on the southwestern TP, based on seventeen optically stimulated luminescence ages of paleoshorelines. The results showed that lake-levels were at the broad highstands of ∼40 m above modern lake-level (amll) from 11.6 to 7.0 ka, during which the three lakes were integrated and formed a mega paleolake. After 7.0 ka, the mega paleolake fluctuantly contracted, and Lagkor Co and Zabuye Salt Lake probably became separated at ∼6.9 and ∼3.4 ka, respectively. Seven rapid millennial low lake stands were identified at 11.3–11.2 ka (14 m amll), 9.9–8.7 ka (< 28 m amll), 8.2–7.9 ka (6 m amll), ∼6.9 ka (5 m amll), ∼3.0 ka (8 m amll), 2.1–1.1 ka (< 6 m amll) and ∼0.4 ka (6 m amll). The large magnitude lake-level declines indicated that they reflected effective moisture in response to global millennial-scale climate events, e.g., the 11.1, 10.3, 9.4, 8.2 and 7.2 ka events in the early and middle Holocene, and the 4.2 ka and Little Ice Age events in the late Holocene. Holocene lake-level fluctuations were simultaneous with that of other lakes on the south-central TP. Comparisons with other paleoclimatic records suggested that the Holocene hydrological history of Taro Co was mainly dominated by both monsoonal precipitation and glacial meltwater supply, as well as evaporation and basin topography. Differences in meltwater supply probably led to different lake-level change histories for endorheic lakes in the lake system. In the future warming and wetting, Tibetan endorheic lakes would keep expanding, hence Taro Co lake system would be formed again through hydrological connections.

Holocene lake level variations of Dagze Co in central Tibetan Plateau revealed by OSL dates on palaeoshorelines

Lakes in the Tibetan Plateau (TP) provide indications of the past global climate change over this vast elevated highland. However, the patterns of Holocene lake-level variations in the central TP and their relevance to climate change are still unclear, especially for the middle and late Holocene. Located in the central TP, Dagze Co presents a number of distinct palaeoshorelines, thus making it ideal for investigating these patterns. In this study, we first identified these shorelines using remote sensing images, and then dated these shorelines using optically stimulated luminescence (OSL) dating. The results showed that high-resolution remote sensing images can successfully identify palaeoshorelines, alluvial fans, and remnant river channels surrounding the lake, which enhances our understanding of regional geomorphic processes. The OSL dating results showed that Dagze Co flowed westward to Cuowa Lake during a lake expansion stage in the early Holocene. The highest palaeoshoreline (40.6 m above the present lake level) formed between 6.1 and 5.5 ka, and the lake area was 2.8 times larger than present. The lake level declined between 5.5 and 3.4 ka in response to the weakened Indian summer monsoon (ISM) with substantially reduced summer rainfall. The lake level rose again and was sustained between 3.4 and 2.2 ka owing to slightly increased rainfall and increased water supply from glacial melt water. The lake level rapidly declined since 2.2 ka in response to decreased ISM rainfall and reduced meltwater supply. The lake level variations of Dagze Co was in a long-term decline pattern since the mid Holocene, similar to several other lakes in the TP influenced by the Asian Summer Monsoon (ASM).

Luminescence dating of shoreline sediments indicates a late deglacial lake-level rise of Selin Co on the central Tibetan Plateau

The palaeo-shorelines around the lakes on the Tibetan Plateau can be used to reconstruct water level variations, which serve as sensitive indicators of hydroclimate change. Extensive studies have been carried out to constrain the Holocene lake level fluctuations by dating shorelines with a variety of methods (e.g., luminescence, 14C, 10Be and U–Th series). In comparison, the timing of the lake level variations during the last glacial and subsequent deglaciation periods has been rarely studied. The driving factors of such changes, therefore, remain elusive. In this study, we performed a detailed luminescence dating investigation on six samples taken from a nearshore sedimentary outcrop in the south of Selin Co basin. The post-IR IRSL signals measured at 225 °C (pIRIR225) on sand-sized K-feldspar grains demonstrated a generally good behavior and yielded reliable chronologies, while the optically stimulated luminescence (OSL) signals of quartz showed systematical age underestimation, which was attributed to anomalous fading. Six pIRIR225 ages ranging from 15 to 10 ka suggested that the lake level of Selin Co during the last deglaciation reached up to 40–45 m high above the modern lake level. In view of the regional precipitation and temperature proxy records, we consider that the glacier meltwater supply has likely been the primary contributor to the lake highstands during the last deglaciation.

Late-Glacial and Holocene Lake-Level Fluctuations on the Kenai Lowland, Reconstructed from Satellite-Fen Peat Deposits and Ice-Shoved Ramparts, Kenai Peninsula, Alaska

Recent decades of warmer climate have brought drying wetlands and falling lake levels to southern Alaska. These recent changes can be placed into a longer-term context of postglacial lake-level fluctuations that include low stands that were as much as 7 m lower than present at eight lakes on the Kenai Lowland. Closed-basin lakes on the Kenai Lowland are typically ringed with old shorelines, usually as wave-cut scarps, cut several meters above modern lake levels; the scarps formed during deglaciation at 25–19 ka in a kettle moraine topography on the western Kenai Lowland. These high-water stands were followed by millennia of low stands, when closed-basin lake levels were drawn down by 5–10 m or more. Peat cores from satellite fens near or adjoining the eight closed-basin lakes show that a regional lake level rise was underway by at least 13.4 ka. At Jigsaw Lake, a detailed study of 23 pairs of overlapping sediment cores, seismic profiling, macrofossil analysis, and 58 AMS radiocarbon dates reveal rapidly rising water levels at 9–8 ka that caused large slabs of peat to slough off and sink to the lake bottom. These slabs preserve an archive of vegetation that had accumulated on a lakeshore apron exposed during the preceding drawdown period. They also preserve evidence of a brief period of lake level rise at 4.7–4.5 ka. We examined plant succession using in situ peat sequences in nine satellite fens around Jigsaw Lake that indicated increased effective moisture between 4.6 and 2.5 ka synchronous with the lake level rise. Mid- to late-Holocene lake high stands in this area are recorded by numerous ice-shoved ramparts (ISRs) along the shores. ISRs at 15 lakes show that individual ramparts typically record several shove events, separated by hundreds or thousands of years. Most ISRs date to within the last 5200 years and it is likely that older ISRs were erased by rising lake levels during the mid- to late Holocene. This study illustrates how data on vegetation changes in hydrologically coupled satellite-fen peat records can be used to constrain the water level histories in larger adjacent lakes. We suggest that this method could be more widely utilized for paleo-lake level reconstruction.

Holocene East African monsoonal variations recorded in wave-dominated clastic paleo-shorelines of Lake Abhe, Central Afar region (Ethiopia & Djibouti)

In tropical Africa, Late Pleistocene-Holocene climatic fluctuations heavily impacted the continental hydro-systems. The timing and magnitude of ‘African Humid Period’ hydrological dynamics (AHP; ~14.8 to ~5.5 ka BP) are not yet fully understood due to the extreme variability in African geomorphic patterns and the complex network of past air convergence boundary shifts. The investigation of the functioning of specific hydro-sedimentary basins is needed to improve our knowledge on the AHP spatial and chronological patterns over the continent. In this paper we present a revised Holocene lake level curve of Lake Abhe: an endorheic basin situated in the Afar Depression at the northern extremity of the East African Rift System (EARS). Located at the boundary of the Red Sea and the Indian and Atlantic Oceans' air moisture mass fluxes, the Lake Abhe watershed represents a system sensitive to changes in Northeast African hydro-climate. Based on numerous littoral lacustrine geomorphic features and 53 related radiocarbon ages on stromatolites and nearshore deposits, we have defined the main Holocene lake highstands proposing a detailed paleo-shoreline record. The first rise in water level is dated to ~11.1 ka cal. BP, while the Maximal Holocene Highstand Shoreline (~420 m a.s.l.) was rapidly reached around ~10 ka cal. BP. Evidence of the impact of the 8.2 ka North Atlantic cooling event is recognized with slow lake level regression until ~8.3 ka cal. BP and with an abrupt drop at ~8 ka cal. BP. The resurgence of humid conditions was recorded from ~7.7 ka cal. BP to ~4.6 ka cal. BP. Radiocarbon ages on littoral materials allow us to propose a Holocene subsidence rate of the Abhe basin axial valley. Furthermore, multiphase sill overflow incisions towards the downstream Hanle basin and transient fluvial connectivity with the upstream Ziway-Shala basin, indicate strong geomorphic controls on lake highstand elevations. In summary, Lake Abhe Holocene fluctuations are the result of combined hydro-climatic, tectonic and local geomorphic controls. However, the confrontation with others East African basins allows us to discuss the transport of moisture masses dynamics into the northern EARS during the Holocene.

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.

Holocene lake-level fluctuations of Selin Co on the central Tibetan plateau: Regulated by monsoonal precipitation or meltwater?

Over the Tibetan Plateau (TP), lakes as paleoenvironmental archives have been the most extensively investigated for their sensitivities to climate change on different timescales. Well-preserved shoreline and terrace remains surrounding these lakes provide critical geomorphological and sedimentary evidence that can be used to infer past lake levels over geological timescales. These features can offer an analogue for understanding how future lake-levels respond to global warming. In this study, we investigated a series of water level-related depositional profiles around the Selin Co basin from the central TP, by dating 28 samples using K-feldspar luminescence techniques. Combining the obtained chronological data with sedimentological, stratigraphic evidence and differential GPS survey observations, the Holocene history of lake-level fluctuations in Selin Co was inferred. The results show a stable highstand between 10 ka and 7 ka but a striking subsequent lake-level decline. This pattern appears to follow the solar insolation-forced changes in the intensity of the Indian summer monsoon (ISM), particularly during the early Holocene. However, such gradual weakening of ISM intensity after the early Holocene may not interpret the dramatically rapid shrinking of Selin Co, implying other components are largely underrecognized driving factors accounting for the effective moisture of lakes in the early Holocene. Here, we argue that the increased meltwater input from glaciers and permafrost, together with increased precipitation, might have resulted in the high lake level at 10–7 ka, as the high summer temperature during the early Holocene induced massive melting water flow into the lake. By 7 ka, the abrupt lake-level drop is likely related to the decreased meltwater owing to decreasing regional temperatures documented from glacier landforms, ice cores and lacustrine sediments. Therefore, we highlight that meltwater from glaciers and permafrost poured into lakes on the central TP, particularly during warm periods on the millennial timescales, might also dominate the Holocene high lake levels.

Holocene lake level, vegetation, and climate at the East Asian summer monsoon margin: A record from the Lake Wulanhushao basin, southern Inner Mongolia

Understanding the impact of Holocene climate variations in arid northern China will provide important insights into a better prediction of future water availability in this region. In this study, we present paleoenvironment data from the lacustrine-aeolian deposit sections and a lake sediment core from the Lake Wulanhushao basin, southern Inner Mongolia. Optically Stimulated Luminescence dating and elevation measurements on the outcrop sections provide an estimation of lake-level changes for the past 10.1 kyr. For the sediment core, multi-proxy analyses of pollen, grain size, loss-on-ignition, element, and chroma were undertaken. The pollen result indicates a tendency of moisture increase from 10.6 to 9.1 cal kyr B.P., providing moderate conditions for the gradual expansion of trees in the mountains. The highest moisture availability was reached from 9.1 to 5.6 cal kyr B.P. leading to the maximal arboreal extent. After then, aridification in the region was evidenced by the declined trees and the increase of desert components. Comparing with the pollen result, non-pollen proxies from the lake sediment core and the outcrop sections indicate a slightly different climate pattern. That is, the initiation of Holocene climate optimum in the lake catchment, suggested by a high lake level, increased biological production, and an enhanced chemical weathering occurred about 1.5 kyr earlier than the arboreal expansion in the distal mountains. While the climate patterns were more or less consistent as inferred from the lacustrine pollen records at the East Asian Summer Monsoon margin, catchment-specific responses to regional climate variations might explain this perplexing discrepancy between pollen and non-pollen proxies. Our study emphasizes the importance of multi-proxy analyses from various perspectives when investigating the local and regional responses to Holocene climate variations.

Pacific Southwest United States Holocene Droughts and Pluvials Inferred From Sediment δ18O(calcite) and Grain Size Data (Lake Elsinore, California)

Records of past climate can inform us on the natural range and mechanisms of climate change. In the arid Pacific southwest United States (PSW), which includes southern California, there exist a variety of Holocene records that can be used to infer past winter conditions (moisture and/or temperature). Holocene records of summer climate, however, are rare from the PSW. In the future, climate changes due to anthropogenic forcing are expected to increase the severity of drought in the already water stressed PSW. Hot droughts are of considerable concern as summer temperatures rise. As a result, understanding how summer conditions changed in the past is critical to understanding future predictions under varied climate forcings. Here, we present a c. 10.9 kcal BP 18O(calcite) record from Lake Elsinore, California, interpreted to reflect 18O(lake water) values as controlled by over-water evaporation from summer-to-early fall. Our results reveal three millennial scale intervals: 1) the highly evaporative Early Holocene (10.55-6.65 kcal BP), 2) the less evaporative Mid-Holocene (6.65-2.65 kcal BP); and, 3) the evaporative Late Holocene (2.65-0.55 kcal BP). These results are coupled with an inferred winter precipitation runoff (sand content) record from Kirby et al. (2010). Using these data together, we estimate the duration and severity of centennial-scale Holocene droughts and pluvials (e.g., high 18O(calcite) values plus low sand content = drought and vice versa). Furthermore, the coupled 18O(calcite) and sand data provide a generalized Holocene lake level history. The most severe, long-lasting droughts (i.e., maximum summer-to-early fall evaporation and minimum winter precipitation runoff) occur in the Early Holocene. Fewer, less severe, and shorter duration droughts occurred during the Mid-Holocene as pluvials became more common. Droughts return with less severity and duration in the Late Holocene. Notably, the Little Ice Age is characterized as the wettest period during the Late Holocene.

Late quaternary lake level changes of Taro Co and neighbouring lakes, southwestern Tibetan Plateau, based on OSL dating and ostracod analysis

Abstract The Late Quaternary lake history of Taro Co and three neighbouring lakes was investigated to reconstruct local hydrological conditions and the regional moisture availability. Ostracod-based water depth and habitat reconstructions combined with OSL and radiocarbon dating are performed to better understand the Taro Co lake system evolution during the Late Quaternary. A high-stand is observed at 36.1 ka before present which represents the highest lake level since then related to a wet stage and resulting in a merging of Taro Co and its neighbouring lakes Zabuye and Lagkor Co this time. The lake level then decreased and reached its minimum around 30 ka. After c. 20 ka, the lake rose above the present day level. A minor low-stand, with colder and drier conditions, is documented at 12.5 cal. ka BP. Taro Co Zabuye and Lagkor Co formed one large lake with a corresponding high-stand during the early Holocene (11.2–9.7 cal. ka BP). After this Holocene lake level maximum, all three lakes shrank, probably related to drier conditions, and Lagkor Co became separated from the Taro Co-Zabuye system at c.7 ka. Subsequently, the lake levels decreased further about 30 m and Taro Co began to separate from Zabuye Lake at around 3.5 ka. The accelerating lake-level decrease of Taro Co was interrupted by a short-term lake level rise after 2 ka BP, probably related to minor variations of the monsoonal components. A last minor high-stand occurred at about 0.8 ka before today and subsequently the lake level of Taro Co registers a slight increase in recent years.

Palynology of Lake Arin (Eastern Anatolia, Turkey) deposits and its relation with water level change of Lake Van: Preliminary findings

Palynological and lithological investigations of Lake Arin indicate mid-late Holocene lake level fluctuations both in Lake Arin and Lake Van. Pollen diagram and lithological features of sediments suggest unstable conditions during last 6 kyr BP for Lake Arin. Climatic changes and human impact have been both effective for destroying uppermost sediments of the lake. Semi-arid steppe vegetation dominance has been identified for Early Holocene around Lake Arin.

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 (&gt;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.

Holocene lake level variations of Longmu Co, western Qinghai-Tibetan Plateau

Longmu Co is surrounded by conspicuous regressive shorelines attesting to high-water levels in the past. In this study, we dated paleoshoreline sediments around the lake using optically stimulated luminescence (OSL), infrared stimulated luminescence (IRSL) and radiocarbon dating, then explored the forces that drove Holocene lake level variations. We found that: (1) OSL/IRSL ages are consistent with geomorphic sequences and some extant cosmogenic and U/Th shoreline ages. However, inorganic evaporite crust 14C ages are much older than corresponding OSL/IRSL ages due to varying lake reservoir effects and should be used with caution; (2) The highest lake levels of Longmu Co (~160–145 m above present) lasted from ~12.8 to ~11.3 ka. Two periods of abrupt lake level declines occurred at ~11.3 and ~7.4 ka (lake level dropped ~44 and ~45 m, respectively), with a gradual regression of ~18 m between these two intervals. The lake expanded moderately from ~7 to 5.5 ka, then declined once more after ~5.5 ka, with this regression accelerating during the last ~1.5 ka; (3) The deglacial lake level transgression was likely due to glacier melt waters. The Indian Summer Monsoon reached the Longmu Co watershed and brought precipitation during the early Holocene. Middle to late Holocene lake regression was caused by the retreat of the monsoon and consequent environmental deterioration.

Holocene climate changes in eastern Beringia (NW North America) – A systematic review of multi-proxy evidence

Reconstructing climates of the past relies on a variety of evidence from a large number of sites to capture the varied features of climate and the spatial heterogeneity of climate change. This review summarizes available information from diverse Holocene paleoenvironmental records across eastern Beringia (Alaska, westernmost Canada and adjacent seas), and it quantifies the primary trends of temperature- and moisture-sensitive records based in part on midges, pollen, and biogeochemical indicators (compiled in the recently published Arctic Holocene database, and updated here to v2.1). The composite time series from these proxy records are compared with new summaries of mountain-glacier and lake-level fluctuations, terrestrial water-isotope records, sea-ice and sea-surface-temperature analyses, and peatland and thaw-lake initiation frequencies to clarify multi-centennial- to millennial-scale trends in Holocene climate change. To focus the synthesis, the paleo data are used to frame specific questions that can be addressed with simulations by Earth system models to investigate the causes and dynamics of past and future climate change. This systematic review shows that, during the early Holocene (11.7–8.2 ka; 1 ka = 1000 cal yr BP), rather than a prominent thermal maximum as suggested previously, temperatures were highly variable, at times both higher and lower than present (approximate mid-20th-century average), with no clear spatial pattern. Composited pollen, midge and other proxy records average out the variability and show the overall lowest summer and mean-annual temperatures across the study region during the earliest Holocene, followed by warming over the early Holocene. The sparse data available on early Holocene glaciation show that glaciers in southern Alaska were as extensive then as they were during the late Holocene. Early Holocene lake levels were low in interior Alaska, but moisture indicators show pronounced differences across the region. The highest frequency of both peatland and thaw-lake initiation ages also occurred during the early Holocene. During the middle Holocene (8.2–4.2 ka), glaciers retreated as the regional average temperature increased to a maximum between 7 and 5 ka, as reflected in most proxy types. Following the middle Holocene thermal maximum , temperatures decreased starting between 4 and 3 ka, signaling the onset of Neoglacial cooling. Glaciers in the Brooks and Alaska Ranges advanced to their maximum Holocene extent as lakes generally rose to modern levels. Temperature differences for averaged 500-year time steps typically ranged by 1–2 °C for individual records in the Arctic Holocene database, with a transition to a cooler late Holocene that was neither abrupt nor spatially coherent. The longest and highest-resolution terrestrial water isotope records previously interpreted to represent changes in the Aleutian low-pressure system around this time are here shown to be largely contradictory. Furthermore, there are too few records with sufficient resolution to identify sub-centennial-scale climate anomalies, such as the 8.2 ka event. The review concludes by suggesting some priorities for future paleoclimate research in the region. • We summarize diverse Holocene paleoclimate records from Alaska and NW Canada. • Proxy types include midges, pollen, biogeochemistry, glaciers, isotopes, lake levels. • Early Holocene (11.5–8.0 ka) temperatures were highly variable, but cold on average. • Regional average temperature increased to a maximum between 7 and 5 ka. • Priorities for future paleoclimate research in the region are suggested.

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).

Holocene lake level fluctuations and environmental changes at Taro Co, southwestern Tibet, based on ostracod-inferred water depth reconstruction

Lake level change is an important indicator of changes in the hydrological status of lakes triggered by the influence of atmospheric circulation systems. Previous studies show that the interaction of the Indian monsoon and the Westerlies, and their influence on environmental changes in the Tibetan Plateau region, remain unclear. Here, we reconstruct the Holocene lake level history of a lake, Taro Co, in southwestern Tibet, based on the relationship between ostracod assemblages and water depth from 34 surface sediment samples spanning the depth range 0 to 125 m. Measurement and analysis of multi-proxy data from a 310 cm sediment core from Taro Co lead to the following conclusions: (1) From 10,200 to 9400 cal. a BP, the lake received large inflows of freshwater (mainly glacial melt water) resulting in a rapid rise in lake level. Following a cold and dry interval and low lake level from 9400 to 8800 cal. a BP, the lake maintained a high level between 8800 and 7500 cal. a BP. This was followed by a less warm and wet period until 6400 cal. a BP. From 6400 to 1200 cal. a BP, the lake probably overflowed after reaching a high level, and after 1200 cal. a BP, the lake level decreased and fluctuated around the modern depth of 60 m at the coring site. (2) The region experienced warm and wet conditions from 10,200 to 6400 cal. a BP, with a cold event at around 9000 cal. a BP, which probably resulted from the influence of the Indian monsoon. However, the inferred wet conditions between 6400 and 1200 cal. a BP are not observed in other records from the monsoon region; they are consistent with numerous records from the regions under the influence of the Westerlies, which probably indicate an interval of Westerlies-domination in the Taro Co region.

Holocene lake level history of the Tangra Yumco lake system, southern-central Tibetan Plateau

Massive carbonate banks representing ancient lacustrine deposits are exposed in the catchment of the lake Tangra Yumco (southern-central Tibetan Plateau) and nearby lake Xuru Co. Nine sediment samples were taken below and above these lacustrine deposits to determine periods of changing lake level using optically stimulated luminescence (OSL) applying a multiple-aliquot regeneration (MAR) protocol. According to facies and stratigraphy, samples below the carbonate banks indicate a rising and samples from above a falling lake level. The results indicate that the rising lake level of Tangra Yumco passed the sampling location at 10.5 and 2.1 ka while a falling lake level passed the sampling location at 0.9 ka. The rising lake level of Xuru Co passed the sampling location at 7.9 and 1.7 ka and a falling lake level at 0.5 ka showing a similar trend as at Tangra Yumco. Combining these results with recalculated cosmogenic nuclide ages and previously published feldspar luminescence data allows the establishment of a Holocene lake level reconstruction for Tangra Yumco, which is unique for the southern-central Tibetan Plateau. The lake level of Tangra Yumco crested a lake level highstand of 181–183 m above the recent lake level prior to 8.5 ka and has generally fallen after 8.5 ka, with a minor lake level rise at 2.1 ka. Lake level variations at Tangra Yumco occur simultaneously with other lakes on the Tibetan Plateau indicating that variations were controlled by monsoonal dynamics with a moist early Holocene and a successive reduction of available moisture thereafter. The average rate of the lake level rise between 10.5 and 8.5 ka is at least 0.05 m a−1 (compared with a modern value of 0.38 m a−1), providing valuable insights in the monsoonal impact on lake level change on the southern-central Tibetan Plateau.