High Lake Levels Research Articles

A Fuller Great Salt Lake Would Likely Narrow an Environmental Health Gap

Pacific Islander and Hispanic residents of Salt Lake City would benefit most from higher lake levels and reduced dust pollution.

Causes and consequences of natural and anthropogenically induced late Holocene hydrological variations on the largest freshwater system in the Lesser Caucasus (Lake Sevan, Armenia)

Although Lake Sevan is the largest freshwater reservoir in the Caucasus, no paleohydrological or paleoenvironmental investigations have been carried out on profundal sediments so far. Here we present high-resolution sedimentological results from a 141 cm-long sediment core covering the past 4870+190/-245 cal a BP. The chronology is based on a combination of 137Cs/210Pb and radiocarbon dating supported by paleomagnetic secular variation stratigraphy, providing new inclination and declination data for the Caucasus. The time frame covered by this sequence is characterized by a long-term lake level rising trend superimposed by smaller-scale hydrological variations which is in agreement with the rest of the Lake Sevan basin. In the presented sedimentary sequence, the superimposed hydrological variations seem to be coherent with the Hallstatt and Eddy cycles.A distinct shift towards wetter conditions is observed between 2500 and 2000 cal a BP resulting in a very high lake level. An artificial lake level drop of about 20 m in the 20th century led to anoxic conditions similar to the ones during a low lake level at 4870+190/-245 cal a BP. This study shows that under natural conditions Lake Sevan was able to recover from this oxygen deficit when the lake level increased, implying that this would also happen to the artificially lowered lake today if the lake level were raised.

Soil Genesis of Alluvial Parent Material in the Qinghai Lake Basin (NE Qinghai–Tibet Plateau) Revealed Using Optically Stimulated Luminescence Dating

Alluvial parent material soil is an important soil type found on the Qinghai–Tibet Plateau (QTP) in China. However, due to the limited age data for alluvial soils, the relationship between alluvial geomorphological processes and soil pedogenic processes remains unclear. In this study, three representative alluvial parent material profiles on the Buha River alluvial plain in the Qinghai Lake Basin, northeast QTP, were analyzed using the optical luminescence (OSL) dating method. Combined with physical and chemical analyses of the soil, we further analyzed the pedogenic process of alluvial soil. The alluvial parent material of the Buha alluvial plain predominately yielded ages between 11.9 and 9.1 ka, indicating that the alluvial soil began to form during the early Holocene. The development of the alluvial soil on the first-order terrace presents characteristics of entisol with multiple burial episodes, mainly between 8.5 and 4.0 ka, responding to the warm and humid middle Holocene and high lake levels.

Reconstruction of late Holocene palaeoenvironmental and palaeohydrological changes using multi-proxy analysis of Sattal lake sediments, Kumaun lesser Himalaya, India

The present study aims to investigate the palaeoenvironmental changes around Sattal Lake, Kumaun Lesser Himalaya spanning the last 1670 years. Based on multi proxy analysis (i.e., grain size, mineral magnetism, clay mineralogy, Total Organic Carbon (TOC) and carbon isotopes), supported by a robust radiocarbon chronology, three major environmental phases were identified. Warm, wet phases occurred between 1,150–650 cal yr BP and 260 cal yr BP to the present. These phases coincide closely with the Medieval Climatic Anomaly (MCA) and modern warming, respectively. These warm/wet events were due to elevated precipitation, resulting in high lake levels and an expansion of the lake margin, which were marked by lower δ13C values, comparatively higher sand concentration, TOC values and magnetic susceptibility (χlf). The inference of a modern warm phase is supported by high resolution instrumental data. The MCA, which is marked by elevated amounts of coarse grained (sand) detrital material, is inferred to be an interval of strengthened of monsoonal intensity, which correlates with available monsoon records from various continental paleoclimate archives. Following the MCA a cold and dry phase was observed to occur between 610 and 260 cal yr BP, corresponding to the Little Ice Age (LIA). The LIA, which was characterized by high silt and clay concentration, high δ13C, low TOC and reduced magnetic susceptibility (χlf), is inferred to represent an interval of low lake levels, likely reflecting an episode of weakened monsoonal intensity.

The impact of climate change upon intestinal parasites in central Europe during the 4th millennium BCE

The Neolithic period in Europe was subject to marked climatic variations during the fourth millennium BCE in the Alpine arc, marking the transition between the recent Atlantic and the Subboreal. This phase is characterized by falling temperatures and rising humidity in the Northern Hemisphere. Within this phase, between 3700 and 3250 BCE, a more intense phase takes place, known as Rootmoos 2 or Piora 2. This phase is characterized by a significant drop in lake water levels. This climatic change had repercussions on lakeside dwellers, notably through the modification and adaptation of their diet and subsistence modes. Intestinal parasites (helminths), found by human and animals via parasitic markers, seem to respond over time to these climatic variations. At first sight, low lake level phases are characterized by significant proportions of Trichuris at the expense of Diphyllobothrium, as well as an increase in Fasciola. These phases therefore seem to favour parasites indicative of agropastoral activities. During periods of high lake levels, Diphyllobothrium increase in number, pointing to a higher frequency of fishing practices. In sum, during periods of cooler/wetter climate, Neolithic lakeside populations seem to focus more on fishing produce, which may be a response to a destabilization of previously established agropastoral systems, marking a return to more opportunistic behaviour with the exploitation of products from the direct environment. This pilot study tends to evaluate if the evolution of parasitic communities in the 4th millennium BCE could therefore be used to complete our understanding of the effects of climatic variations on societies, both as a direct consequence of environmental destabilization (effect on the hosts) and the result of the behavioural adaptation of the inhabitants, even if it is still difficult to determine the importance of the influence of each factor on these variations. Despite some remaining challenges in the current study, the integration of paleoparasitic data into broader paleoenvironmental models appears promising. Future research can continue to develop along this path.

Response of aquatic ammonia-oxidizing archaea to thermal stratification and nutrient levels since the Last Glacial Maximum in the deep lake Fuxian, southwestern China

Ammonia-oxidizing archaea (AOA) are the critical nitrifier in lake ecosystems and participate in the global nitrogen cycle. However, the response of aquatic AOA to long-term climate change remains unclear. Here, we obtained a continuous sediment record from a deep, oligotrophic lake (Lake Fuxian, China) and reconstructed changes in AOA productivity over the past 26 thousand years (cal ka BP) using a multi-proxy approach. AOA productivity (estimated using diagnostic archaeal lipids) was low during the Last Glacial Maximum (LGM) before peaking during the cold-dry Heinrich event 1 (H1, 17.7–15.9 cal ka BP). As the Indian Summer Monsoon (ISM) intensified and the climate became warmer and wetter, aquatic AOA productivity progressively declined. We show that a combination of factors modulates millennial-scale AOA productivity. In particular, low lake levels under cold-dry climate conditions strengthen lake mixing and nutrient upwelling, promoting AOA productivity; in contrast, high lake levels during warm-humid climate conditions weaken upwelling, resulting in reduced AOA blooms. Changes in terrestrial nutrient availability also exert a secondary control on aquatic primary production and by extension, AOA productivity. We also show that anthropogenic human activities can potentially alter AOA productivity levels due to climate and land-use change.

Climate Change and Indigenous Subsistence in the Thompson River Watershed (British Columbia) in the Late Holocene

ABSTRACT The Indigenous peoples of the Thompson River watershed on the northern Columbia Plateau traditionally subsisted in winter on dried salmon, dried roots and berries from upland meadows, and game. A summed probability distribution (SPDF) based on 54 radiocarbon ages from twenty-eight winter villages and summer fishing camps along that river exhibits volatile activity in anti-phase with an SPDF derived from 77 radiocarbon ages from twenty-six sites in the neighbouring uplands in the 2500–500 cal BP interval. Activity levels on the riverbanks decline after ∼2000 cal BP, increase rapidly from ∼1600 cal BP to ∼1350 cal BP, fall dramatically in the next century, then rise again after ∼700 cal BP, echoing patterns at other upriver fisheries on the northern Columbia plateau. Periods of increased activity on the Thompson riverbank are linked to robust runs of sockeye salmon, prompted by cooler/wetter phases of regional climate, and marked by higher lake levels, glacial advances, and increased rates of coastal upwelling in the northeast Pacific. Less reliable salmon harvests in the intervening periods are indicated by increases in activity in the uplands, with a concomitant greater reliance on roots and game in the local diet.

Holocene paleoenvironmental history of Jackson Lake (Grand Teton National Park, USA) deduced from CHIRP seismic reflection and radiocarbon-dated sediment cores

Sedimentary records from Jackson Lake (Grand Teton National Park, Wyoming, USA) provide an opportunity to investigate the Late Quaternary tectonic and hydroclimatic history of a region known to have considerable earthquake hazard potential. Here, we present a new paleoenvironmental reconstruction for Jackson Lake using high-resolution Compressed High-Intensity Radar Pulse (CHIRP) seismic reflection data and sediment cores from Moran Bay, which is adjacent to the active Teton fault on the southwestern lake margin. Three seismic units (SU) are present within Moran Bay. The lowermost SU-1 defines the acoustic basement, which is characterized by a sharp reflector of variable relief above material with a very low signal-to-noise seismic response; direct sampling reveals this unit to be glaciogenic in origin. SU-2 contains diverse acoustic facies that onlap, downlap, and drape underlying strata. Prominent in SU-2 are faulted, folded, and slumped reflections with mixed amplitude characteristics, as well as reflections organized into prograding clinoforms, which suggest a history of deformation and slope instability in fluvio-deltaic and shallow lacustrine environments. A local unconformity separates SU-2 and SU-3, and above this boundary clinoform packages backsteps towards the hinterland. A bi-directionally tapering package of low-moderate amplitude, continuous to semi-continuous reflections onlap the clinoform; this unit was fully cored (13.8 m), allowing the unit boundary to be sampled and dated. Radiocarbon ages indicate that the core spans ca. 10.4 calibrated kiloyears before present (cal ka BP) to present. Retrogradational stacking of deltaic clinoforms are best explained by increased accommodation in Moran Bay around ca. 10 ka, consistent with a major earthquake and hanging wall subsidence on the Teton fault. Two turbidites identified in the strata align temporally (ca. 10.3 ± 0.4 cal ka BP and ca. 8.3 ± 0.3 cal ka BP) with earthquakes on the Teton fault that have been identified in terrestrial and lacustrine paleoseismic records. From ca. 10.4–6.6 cal ka BP core sediments are relatively rich in clay with highly variable magnetic susceptibility and organic carbon content. Deposition during this period was influenced by an evolving stream network and a relatively dry paleoclimate. From ca. 6.6–2.7 cal ka BP core sediments have higher sand and organic carbon contents, suggesting variable fluvial discharge and climate instability. The youngest core records produced a sharp increase in sedimentation rate, sand and organic carbon content, propelled by greater effective moisture, higher lake levels, and increasing watershed vegetation density. Based on clinoform rollover position, water levels at ∼2,046, ∼2,049, ∼2,053, and 2063 m asl characterized Moran Bay during the Holocene. Together, the seismic and core data records indicate a complex and dynamic Holocene lacustrine evolution controlled by fault motion and water level changes.

Assessing alternative lake management actions for climate change adaptation.

Lake management actions are required to protect lake ecosystems that are being threatened by climate change. Freshwater lakes in semiarid regions are of upmost importance to their region. Simulations of the subtropical Lake Kinneret project that rising temperatures will cause change to phytoplankton species composition, including increased cyanobacteria blooms, endangering lake ecosystem services. Using lake ecosystem models, we examined several management actions under climate change, including two alternatives of desalinated water introduction into the lake, hypolimnetic water withdrawal, watershed management changes and low versus high lake water level. To account for prediction uncertainty, we utilized an ensemble of two 1D hydrodynamic-biogeochemical lake models along with 500 realizations of meteorological conditions. Results suggest that supplying desalinated water for local use, thus releasing more natural waters through the Jordan River, increasing nutrient flow, may reduce cyanobacteria blooms, mitigating climate change effects. However, these results are accompanied by considerable uncertainty.

The influence of multidecadal climate variability and abrupt landscape change on terrestrial ecosystem composition and fire regime in the upper Columbia River basin - A high-resolution Holocene perspective

High-resolution paleoclimatic and paleoecologic datasets from a small lake in eastern Washington (USA) help elucidate Holocene environmental dynamics in the interior Pacific Northwest. Round Lake lies near the ecotone between sagebrush steppe and dry pine forest, making it highly sensitive to changes in precipitation-evaporation (P-E) balance. We present isotopic, sedimentological, and paleoecological data from a single sedimentary sequence analyzed at sufficient resolution to detect sub-decadal climatic variability. During the early Holocene (11,000–8500 cal yr BP), when summer insolation was higher than present, Round Lake experienced persistent aridity that led to reduced forest cover and small, probably frequent surface fires. Sub-centennial hydroclimate fluctuations during this period were muted, as indicated by low multi-decadal variability in δ18Ocarbonate records from the region. Oxygen isotopes indicate increased cool-season moisture during the middle Holocene (8500-5300 BP), but stratigraphic evidence suggests intermediate and variable lake levels. The deposition of the Mazama tephra (ca. 7600 cal yr BP) immediately preceded to a protracted expansion of steppe at the expense of forest. Increased hydroclimate variability and fire activity following ash deposition likely restricted conifer taxa even when elevated cool-season moisture would have facilitated their growth. The late Holocene was marked by persistently high lake levels, as indicated by the lithostratigraphic and pollen records. Comparatively large multidecadal variations in precipitation, which peaked during the last millennium, were also prominent features of late-Holocene hydroclimate, and may have been related to the strengthening of the El Niño Southern Oscillation and Pacific Decadal Oscillation. Pinus and Pseudotsuga show a 60–100 year lag in their response to hydroclimatic variations inferred from the oxygen isotope records. These results highlight how millennial-to-decadal scale hydroclimate conditions, along with abrupt landscape change, influence ecology in a water-stressed region of western North America.

Possible role of anthropogenic climate change in the record-breaking 2020 Lake Victoria levels and floods

Abstract. Heavy rainfall in eastern Africa between late 2019 and mid 2020 caused devastating floods and landslides throughout the region. These rains drove the levels of Lake Victoria to a record-breaking maximum in the second half of May 2020. The combination of high lake levels, consequent shoreline flooding, and flooding of tributary rivers caused hundreds of casualties and damage to housing, agriculture, and infrastructure in the riparian countries of Uganda, Kenya, and Tanzania. Media and government reports linked the heavy precipitation and floods to anthropogenic climate change, but a formal scientific attribution study has not been carried out so far. In this study, we characterize the spatial extent and impacts of the floods in the Lake Victoria basin and then investigate to what extent human-induced climate change influenced the probability and magnitude of the record-breaking lake levels and associated flooding by applying a multi-model extreme event attribution methodology. Using remote-sensing-based flood mapping tools, we find that more than 29 000 people living within a 50 km radius of the lake shorelines were affected by floods between April and July 2020. Precipitation in the basin was the highest recorded in at least 3 decades, causing lake levels to rise by 1.21 m between late 2019 and mid 2020. The flood, defined as a 6-month rise in lake levels as extreme as that observed in the lead-up to May 2020, is estimated to be a 63-year event in the current climate. Based on observations and climate model simulations, the best estimate is that the event has become more likely by a factor of 1.8 in the current climate compared to a pre-industrial climate and that in the absence of anthropogenic climate change an event with the same return period would have led lake levels to rise by 7 cm less than observed. Nonetheless, uncertainties in the attribution statement are relatively large due to large natural variability and include the possibility of no observed attributable change in the probability of the event (probability ratio, 95 % confidence interval 0.8–15.8) or in the magnitude of lake level rise during an event with the same return period (magnitude change, 95 % confidence interval 0–14 cm). In addition to anthropogenic climate change, other possible drivers of the floods and their impacts include human land and water management, the exposure and vulnerability of settlements and economic activities located in flood-prone areas, and modes of climate variability that modulate seasonal precipitation. The attribution statement could be strengthened by using a larger number of climate model simulations, as well as by quantitatively accounting for non-meteorological drivers of the flood and potential unforced modes of climate variability. By disentangling the role of anthropogenic climate change and natural variability in the high-impact 2020 floods in the Lake Victoria basin, this paper contributes to a better understanding of changing hydrometeorological extremes in eastern Africa and the African Great Lakes region.

ENSO-driven hydroclimate changes in central Tibetan Plateau since middle Holocene: Evidence from Zhari Namco’s lake sediments

The Tibetan Plateau, often referred to as the “Asian Water Tower”, holds immense significance as a critical water source for billions of people in surrounding regions. Its unique location and extreme environmental conditions contribute to the formation of some of the world largest lakes, crucial components of the regional water cycle. These lakes not only store vast freshwater resources but also play a vital role in regulating the flow and quality of rivers, maintaining a delicate balance in the local ecosystem. Recent decades have witnessed rapid expansion of many plateau lakes, primarily attributed to glacial melt. However, evaluating the contribution of climate forcings to these changes remains challenging. In this study, we reconstructed Zhari Namco's lake-level changes between 5.3 ka and 1.3 ka based on optically stimulated luminescence dating, a period with relatively stable glacial amount on the Tibetan Plateau. Our analysis employed sediment grain size distribution, organic matter contents and their stable carbon isotopes. In contrast to recent expansions, our findings reveal a declining trend in Zhari Namco's lake level since the middle Holocene, consistent with intermittent paleo-shoreline records from major central Tibetan Plateau lakes. This regional decline is likely the result of a weakening of the Indian Summer Monsoon. In addition to the long-term drying trend, we identified high-frequency fluctuations in Zhari Namco's lake level on centennial timescale. Further comparison with hydroclimate records from the tropics suggests that centennial high lake levels correlate with increased monsoonal precipitation during periods when ENSO activities were reduced. This study sheds lights on the historical dynamics and driving mechanisms of Zhari Namco's lake levels, providing valuable insights for predicting the impacts of future climate change on the Tibetan Plateau's water cycle.

Climate change has driven multidecadal declines in lake levels in central Alberta, Canada

Timoney, KP. 2024. Climate change has driven multidecadal declines in lake levels in central Alberta, Canada. Lake Reserv Manage. 40:205–220. This study examined water level data from 5 lakes in central Alberta to determine the timing and rates of change and to identify the causes for those changes. Over the past century, the estimated average levels of Beaverhill and Cooking lakes declined ∼3 m. Highest lake levels were observed ca. 1902–1904. Lake levels varied widely over the decades, punctuated by periods of high or low water conditions embedded within the longer term declines. Over the past 50 yr, average rates of lake drawdown were as follows: Miquelon −6.8 cm/yr, Cooking −4.4 cm/yr, Beaverhill −4.4 cm/yr, Hastings −0.9 cm/yr, and Ministik −0.7 cm/yr. Over time, annual temperature, evaporation, and net evaporation increased while annual precipitation, runoff, and Palmer Drought Severity Index (PDSI) decreased. Annual precipitation was significantly correlated with the levels of all 5 lakes, and with annual runoff and PDSI. Net evaporation was significantly correlated with temperature, runoff, PDSI, and the levels of all lakes but Ministik. Annual runoff was significantly correlated with the levels of all 5 lakes and PDSI. Conversely, neither annual temperature nor evaporation was correlated significantly with the annual lake levels. Annual levels of all 5 lakes were significantly correlated with each other. The lake level declines are part of a larger pattern of declining levels observed in other lakes in western North America over many decades. In central Alberta, data from several sources indicate accelerated rates of drawdown since the late 1970s to early 1980s at some lakes and accelerated declines since the mid to late 1990s at other lakes.

Demography and threats to population growth of Cirsium pitcheri, a threatened dune plant, in Wisconsin.

Multi-year and multi-site demographic data for rare plants allow researchers to observe threats and project population growth rates and thus long-term persistence of the species, generating knowledge, which allows for effective conservation planning. Demographic studies across more than a decade are extremely rare but allow for the effects of threats to be observed and assessed within the context of interannual environmental variation. We collected demographic data on the Threatened plant Cirsium pitcheri in two sites from 2011-2022. These sites were chosen because one exhibited the presence of non-native seed predators while the other did not, and we hypothesized that we would see declines and potentially extinction of the population threatened by predation. Over the course of our study, we observed additional threats, such as human trampling and high lake levels, which led to significant erosion, sand burial, and storm damage to plants. We find high interannual variation in vital rates and population growth rates for both populations, which mask the overall effects of predation. We observed dramatic declines in plant survivorship and population growth rates in both sites in the years with high lake levels. We conclude that high lake levels, which are expected to become more frequent with climate change, pose a significant threat to all near-shore populations of C. pitcheri.

Lake-Level-Fluctuation Control on Shale Oil Enrichment of the Salinized Lacustrine Organic-Rich Shale in the Paleogene Biyang Depression, East China

The paleolake level, which is controlled by the moisture balance (precipitation minus evaporation) within the lake basin, is a significant factor in determining the deposition of lacustrine organic-rich shale (LORS) across geological time, and hence influences shale oil enrichment. However, the impact of lake-level-fluctuations on shale oil enrichment of LORS is not well understood. Based on an integration of bulk geochemistry, organic petrography, pyrolysis gas chromatography, and element compositions, we address this issue using the Paleogene Biyang Depression in East China as an example. High lake levels, combined with anoxic–suboxic conditions, brackish–saline water, high productivity, and low detrital influx, are favorable for LORS deposition, which is characterized by a large distribution area and thickness, a high potential for oil generation and emplacement, and a high free shale oil content. In contrast, LORS deposited during low lake levels, with suboxic–dysoxic conditions, fresh–brackish water, low productivity, and high detrital influx, has a small distribution area and thickness, a low potential for oil generation and emplacement, and a low free shale oil content (a comparable maturity was present in all the studied LORS). Our data suggests that the elevated lake level led to higher salinity, stronger reduction conditions, higher productivity, and lower clastic inflow in the paleolake, forming LORS with higher shale oil potential. It has a positive effect on shale oil enrichment of LORS. The findings are also applicable to regional shale oil exploration.

Climatic fluctuations over the Holocene in southern Iberia (Sierra Nevada, Spain) reconstructed by fossil cladocerans

A combination of microfossil assemblages, abundance of fossil ephippia and mean body size provides the longest paleoclimatic reconstruction based on cladoceran subfossils in the Iberian Peninsula. Species turnover in Laguna de Río Seco (Sierra Nevada, southern Spain) was controlled by changes in lake levels in response to fluctuations in hydroclimatic variability over the last ∼8600 years. Our archive documents a wet period in the Early and Middle Holocene (∼8600–5000 cal yr BP), characterized by eurytopic and plant-associated species. A drier stage occurred from ∼5000 cal yr BP and implied a reduction in lake level and higher occurrence of species highly adapted to more ephemeral environments. Proportions of total chydorid ephippia (TCE), indicating rates between asexual and sexual reproduction, are well-correlated with a progressive trend towards aridification. Lower TCE was registered before ∼5000 cal yr BP as a result of a favourable environment under higher lake level, while higher TCE started with the upcoming arid stage (∼5000 cal yr BP) due to environmental stress. Besides these hydrological signatures, data on Daphnia size broadly indicate a warmer period ∼8600–4000 cal yr BP and a colder stage ∼4000–255 cal yr BP. Further investigations using this indicator in the Sierra Nevada will provide more precise reconstructions of past climatic conditions in southern-latitude and alpine ecosystems.

Historical flood reconstruction in a torrential alpine catchment and its implication for flood hazard assessments

Flood marks and descriptions of past floods in archival records are valuable sources of information to complement the often short – and sometimes lacunary – systematic records provided by gauge stations, especially in mountain and smaller catchments for which the network of recording stations is still fragmentary. Yet, historical accounts of floods are only rarely used to calculate discharge during past floods and to complement estimates of flood frequency and magnitude. This is because the definition of flood types and the reconstruction of past topography of the now urbanized riverscapes is often challenging. Here, we employ an approach by which we combine (i) archival (1331–1965) and continuous gauge (1966–2020) records of past floods, (ii) information on past topography and mitigation measures found on topographic maps and contemporary documents specifying the dimensions of contemporary engineering plans and (iii) a hydraulic model to derive a c. 700-year history of flood activity and related discharges for the Saltina River, Brig-Glis (Valais, Swiss Alps). Periods of increased flood activity match with flood-rich episodes in the Rhone River and high lake levels at Lago Maggiore (Ticino), and the time series passes stationarity tests since at least 1828 CE. For a total of 32 floods occurring prior to the installation of the gauge station in 1966, we provide discharges following a descriptive classification, and demonstrate that major floods occurred in 1755 (∼140 m3s−1), 1828 (∼160 m3s−1), and 1921 (∼120 m3s−1). We also evidence that the construction of mitigation measures has contributed to a reduction in flood frequency, but that the occurrence of extraordinary floods has again been on the rise since the early 21st century.

Sedimentary evolution and lake level fluctuations of Urmia Lake (north‐west Iran) over the past 50 000 years; insights from Artemia faecal pellet records

AbstractA 25 m long sediment core from hypersaline Urmia Lake (north‐west Iran) was studied for the Late Quaternary depositional history and palaeoclimate variations using the abundance and compositional characteristics of Artemia faecal pellets. Sediment analysis is supported by scanning electron microscopy – energy dispersive X‐ray spectroscopy, organic and inorganic carbon content measurements, and stable isotopes (δ13C and δ18O) from faecal pellet carbonates. The imprecise chronology of the core back to 50 kyr bp is supported by ten radiocarbon ages from faecal pellets and bulk sediments. The palaeoenvironmental record is subdivided into four periods: (i) During much of Marine Isotope Stage 3, a period of lake level lowering is characterized by a decreasing amount of faecal pellets, and an increasing amount of coated grains, sulphate minerals and reworked shell fragments. (ii) During late Marine Isotope Stage 3 and early Marine Isotope Stage 2 a lake level lowstand and a lake floor exposure is interpreted based on the relatively low abundance of pellets, which are multicoloured and appear together with volcanic lithics and rounded sulphate minerals. (iii) During late Marine Isotope Stage 2 the record is devoid of pellets but dominated by large sulphate crystals suggesting a prolonged low lake level. (iv) During Marine Isotope Stage 1 a relative lake level highstand is rapidly established with sediments that are highly abundant in fresh pellets. The modern lake level lowstand is represented by a salt crust. The δ13C and δ18O records measured from faecal pellet carbonates suggest a link with the precipitation versus evaporation balance in the lake over time. From bottom to top the linear trend towards more negative delta values illustrates the increasing amount of precipitation arriving at the lake from the Late Pleistocene to the Holocene. Two prominent isotope minima during the Late Pleistocene and one prominent minimum in the early Holocene mark relative high lake levels, which can also be linked to Lake Van in Turkey.

Holocene hydroclimate and dust activity, as reconstructed from the sediments of Lake Bayanchagan, on the northern margin of the East Asian summer monsoon

Abstract The sediments of closed-basin lakes on the margin of the East Asian summer monsoon (EASM) are valuable archives of past changes in hydroclimate and dust activity and thus potentially can help us to understand future climate changes. We present high-resolution, well-dated records of the grain size and carbonate mineralogy from Lake Bayanchagan, northern China, spanning the last 11.5 ka. Grain-size endmember (EM) analysis distinguished four EMs, each linked to different sediment transport processes. EM1 (0.4–0.6 μm) and EM3 (14–102 μm) reflect the strength of regional dust activity, whereas EM2 (1.3–31 μm) represents variations in local hydrodynamic conditions related to lake-level changes and EM4 (68–500 μm) is associated with local dust activity. Our results show that a high lake level and weakened dust activity occurred during 10–5.8 ka, as indicated by increased EM2 and decreased EM3, respectively. After 5.8 ka, EM2 decreased as the three other EMs increased, and dolomite appeared in the sediments while calcite decreased—indicating both a decline in lake level and strengthened dust activity. The fluctuations in lake level and dust activity are in good agreement with precipitation variations reconstructed from other records, which are in turn correlated to movement of the EASM rainfall belt, in response to temperature changes.

Early-Middle Holocene high lake levels of Rinqen Shubtso on the southern Tibetan Plateau and the formation mechanisms

The lake-level highstands on the southern Tibetan Plateau (TP) during the Early-Middle Holocene have traditionally been attributed to increased monsoonal precipitation. However, there has been limited discussion and evaluation regarding how the elevated shoreline indicates the formation of mega-paleolakes and the effects of glacial meltwater on rising lake levels. In this study, we conducted an investigation into the well-preserved paleoshorelines of Rinqen Shubtso, a closed-basin lake system located on the southern TP. By utilizing 14C dating and analyzing shoreline elevations, the Holocene lake-level fluctuation history of Rinqen Shubtso was reconstructed. Through examining strontium (87Sr/86Sr) and oxygen isotopes (δ18O), as well as Rb/Sr ratios in tufa samples from the shoreline, we evaluated the relative contribution of glacial meltwater and East Asian Monsoon precipitation to the lake-level expansion throughout this period. Our findings indicate that prior to 8.5 cal ka BP, the lake level reached its highest elevation before experiencing a rapid drop by approximately 44 m within a short timeframe. Subsequently, maintaining a stable highstand between 8.5 and 5.8 cal ka BP before gradually declining to its present elevation thereafter. We argue that the glacial meltwater induced by rising temperature due to solar insolation likely played a significant role in contributing to these large amplitude high lake levels prior to 8.5 cal ka BP, whereas the maximum East Asian Monsoon precipitation was responsible for sustaining high water levels during 8.5–5.8 cal ka BP when the mean latitudinal position of the summer Intertropical Convergence Zone shifted northward until reached its northernmost point at 8.5 cal ka BP. Following 5.8 cal ka BP, with the weakening of summer monsoon precipitation observed, gradually decreased lake level occurred accordingly. Our results provide valuable insights into understanding past changes in lake level, which are of great importance to predicting future lake variations on the TP.