Lake Water Salinity Research Articles

Controls on the occurrence of beach‐bar sandstone in a Neogene saline lake basin, southwestern Qaidam Basin, China

To identify the developmental characteristics and controlling factors of the beach-bar sandstone in saline lake basins in the Qaidam Basin, China, the lithology and bedding structure of some representative outcrops of the Neogene saline lake basins were comprehensively investigated by means of experimental test data of local drilling cores, casting thin sections, and grain size, together with field outcrops in the basin and the modern salt lake deposition record of Qinghai Lake. Two types of sand bodies in the saline lake basins, that is, delta sand bodies and shore-shallow lake beach-bar facies were revealed. Neogene saline lake basins were found to host widespread beach-bar sand bodies. Lithologically, the sand bodies were composed of fine-grained sandstone and siltstone, with wavy bedding, low-angle cross-bedding, and bimodal cross-bedding. The beach-bar sandstone was characterized by multi-layer superimposition, lateral migration, and NW–SE wide-coverage continuation. Drilling data showed that beach-bar sand bodies extended from 10 to 35 km in width and most of them occurred 3–15 km away from braided river delta front. It has been predicted that the total area of beach-bar sand bodies of 14 sand groups in the Neogene spread across 5,000 km2. Four factors, that is, lake water salinity, terrigenous input, palaeogeomorphology, and monsoons, controlled the construction of the beach-bar sand bodies developed in the Neogene saline lake of the Qaidam Basin. We can conclude that the settling velocity and transport distance of the sand bodies were affected by the water body salinity in such saline lake basins. Also, the distribution range of the beach-bar sand bodies was affected by the clastic input from a terrigenous provenance. Furthermore, the wide-coverage distribution and local enrichment of the beach-bar sandstone were affected by palaeogeomorphology, and the distribution direction of the beach-bar sandstone was affected by the driving effect of NW monsoons. We propose a deposition model of the beach-bar sandstone in saline lake basins that can predict favourable beach-bar sand body regions, to support the major discoveries of lithologic traps in southwestern Qaidam, China.

The Significance of Subtlety: Contrasting Lithic Raw Materials Procurement and Use Patterns at the Oldowan Sites of Barranco León and Fuente Nueva 3 (Orce, Andalusia, Spain)

Situated in southern Spain’s Guadix-Baza basin, Barranco León and Fuente Nueva 3 (Orce, Andalusia, Spain) are two of the most important western European Oldowan archeological sites. After 30 years of quasi-uninterrupted excavations, these two occurrences have yielded exceptional lithic and faunal records in precisely dated stratigraphic situations, providing a wealth of information about the oldest presence of hominins outside of Africa (1.4 and 1.3 Ma, respectively). Recently, excavations and multidisciplinary research have allowed to discern new patterns of lithic raw material procurement and use patterns practiced by the Orce hominins that enable us to clearly distinguish different behavioral schemes between these two sites; in spite of their spatial proximity. This paper explores new data from the lithic collections in relation to hominin technical and economic behavior, highlighting subtle but significant differences in their exploitation of local limestone and flint clasts more than a million years ago. During this period of the late Early Pleistocene, these sites were situated on the shores of an ancient saline lake and fresh water sources were available. This favorable environmental situation, while attractive to the hominins, also supported life for an abundance of large mammals, including competitive large carnivores, underlining questions of expedience as an influence on techno-morphology in these early stone toolkits. This paper analyzes these themes, highlighting updated information from these and other key European late Early Pleistocene sites.

Organic geochemistry and controlling factors of alkaline source rocks within sequence stratigraphic framework in the Fengcheng Formation, Mahu sag, Junggar Basin, NW China

The Fengcheng Formation (P1 f) source rock, which was deposited in an alkaline water body, is one of the most significant source rocks in the Mahu sag, Junggar Basin. However, its evolution and mechanism of organic matter accumulation are still not understood. Using seismic, core, and log data, P1 f is divided into 3 third-order sequences, i.e., SQ1, SQ2, and SQ3, from bottom to top. Pyrolysis data of core samples shows that SQ1 and SQ3 mainly are characterized by poor to fair source rocks, with Type III to Type II2 kerogen, while SQ2 mainly are characterized by fair to good to excellent source rocks, with Type II2 to Type I kerogen. The biomarker parameters of 40 source rock samples from different sequences suggest that the reducibility of sedimentary water is characterized by SQ2 > SQ1 > SQ3. The organic matter contribution in different sequences is obviously different. SQ1 organic matter contain more bacteria and algae than that of SQ2 and SQ3, and terrigenous higher plants may have contributed to SQ3 organic matter. Lake level changes and water salinity dominate organic matter origin, accumulation, and preservation. During SQ1 deposition, the lake level was the highest, the salinity of sedimentary water was moderate, and the organic matter contained more conventional algae sources. During SQ2 deposition, the lake level was the lowest and the salinity was the highest, and the organic matter contained special algae characterized by C29 regular steroids. The lake level of SQ3 was higher than that of SQ2, the salinity was the lowest, and terrigenous higher plants may have contributed to organic matter during this period.

The influence of Early Cretaceous paleoclimate warming event on sedimentary environment evolution and organic matter sources in Yin'e Basin: Evidence from petrology and molecular geochemistry

The lacustrine organic-rich fine-grained sedimentary rocks of the Early Cretaceous Bayingebi Formation are widely distributed in the Yin'e Basin and they have become important source rocks for oil and gas exploration. To reveal the influence of paleoclimate warming event on sedimentary environment evolution and organic matter sources, the petrological and molecular geochemical analyses of the upper member of the Bayingebi Formation (K1b2) were carried out using optical microscopy, X-ray diffraction, scanning electron microscopy, Rock-Eval pyrolysis and gas chromatography–mass spectrometry, in order to establish the paleoecological models of the Early Cretaceous freshwater and saline lakes. The oil shale and dark mudstone of K1b2 are both in the immature-early mature stage and have good potential for hydrocarbon generation, with a dominance of type I and type II1 kerogen. Two types of primary dolomite were found in this formation: microcrystalline dolomite with uniform structure, and the microbially originated spherical dolomite aggregates. The K1b2 can be divided into four units based on its lithology and logging curve characteristics. Unit II was deposited in the peak of lake development, under the warm-humid paleoclimate with abundant annual precipitation. There was greater influx of freshwater than other units, which resulted in the unstable stratification of the water column and less reducing condition of the lake bottom water body. Lower aquatic organisms and vascular plants were unprecedentedly prosperous, which were indicated by short-term thriving phenomena of telalginite, and the large input of terrestrial OM and highest abundance of the OM compared to other units. A lake water salinization event occurred during the sedimentation period of Unit III under the cooling climate, causing a transition from a freshwater lake to a high-salinity lake with reducing condition and stable stratification of the water column. Salinity of lake water increased the competitiveness of salt-tolerant algae and bacteria. The salty environment is beneficial for the thriving of single to halophilic genus of microorganism and lead to significantly lower abundance of telalginite. The biological sources of OM were mainly bacteria, algae and emergent plants, with limited contribution of terrestrial higher plants. The anoxic alkaline environment and high salinity condition at the lake bottom were beneficial for the formation of carbonate minerals and the preservation of OM. This were characterised by medium abundance of OM and high hydrocarbon generation potential. The study on the petrological and molecular geochemical characteristics of these organic-rich fine-grained sedimentary rocks is of great significance for investigating the genetic mechanisms and resource potential of oil and gas.

Intestinal ion regulation exhibits a daily rhythm in Gymnocypris przewalskii exposed to high saline and alkaline water

Naked carp (Gymnocypris przewalskii), endemic to the saline-alkaline Lake Qinghai, have the capacity to tolerate combinations of high salinity and alkalinity, but migrate to spawn in freshwater rivers each year. In this study, we measured the drinking rate over a 24 h period for naked carp exposed to saline-alkaline lake waters with salinities of 15 (L15) and 17 (L17). We also assessed the daily feed intakes of naked carp exposed to L15 and fresh water (FW). Additionally, we studied the daily expression of acid–base regulation and osmoregulation related genes and proteins in the intestine of naked carp exposed to saline-alkaline lake waters. Our results revealed that the drinking rate at night was significantly higher than in daytime when exposed to either L15 or L17, while feed intakes in daytime were significantly higher than at night. The relative expression of Na+/K+-ATPase α (NKA-α), solute carrier family members 26A6 (SLC26A6) and 4A4 (SLC4A4) in the intestine of naked carp exposed to L17 at night was higher than in daytime. Specifically, NKA-α mRNA expression at 4:00 was 7.22-fold and 5.63-fold higher than that at 10:00 and 16:00, respectively, and the expression at 22:00 was 11.29-fold and 8.80-fold higher than that at 10:00 and 16:00, respectively. Similarly, SLC26A6 mRNA expression was greatest at 22:00, exceeding that observed at 4:00, 10:00 and 16:00 by 3.59, 4.44 and 11.14-fold, respectively. Finally, the expression of NKA-α and SLC26A6 protein at the single cell level was also higher at night than during the day, which was 1.65-fold and 1.37-fold higher at 22:00 respectively compared to 16:00. Overall, the present findings revealed that naked carp drinks at night and feeds during the day, demonstrating that intestinal ion regulation exhibits a daily rhythm when exposed to high saline and alkaline lake water.

Effects of Ice Freeze-Thaw Processes on U Isotope Compositions in Saline Lakes and Their Potential Environmental Implications

The dissolved uranium (U) content in the water column of saline lakes varies little between ice-free seasons throughout the whole water column. Such uniformity allows for the potential absolute dating and/or paleohydrologic interpretations of lake sediments and biogenic shell materials using U isotopes. Before using these methods in cold regions, however, it is necessary to evaluate the effects that ice freeze-thaw processes have on the distribution of U isotopes in saline lake waters, and to determine the amount of variation in U isotopic values when such processes occur. In this paper, we collected ice and dissolved water samples from six lakes with variable salinity in February 2021. Five groundwater and three water samples from rivers into Qinghai Lake were sampled in November 2020. The sampled water was analyzed for dissolved concentrations of 238U and the activity ratio of 234U/238U ([234U/238U]AR). The results show that the 238U concentration of ice samples was less than that of the underlying water. The [234U/238U]AR of ice in the five saline lakes was similar to that of the underlying water with less than a 10‰ variation, suggesting no observable fractionation between ice and dissolved water. Thus, the ice freeze-thaw processes have almost no effect on the uranium content and [234U/238U]AR of the sampled saline lakes, which were characterized by a limited recharge volume from surface runoff, groundwater, and ice volume, namely the close saline lake in arid alpine background. The results from the indoor freeze-thaw experiments also showed that the U isotopic composition of Qinghai Lake waters and ice were similar with the 238U concentration of the ice was about 40% of that of the dissolved lake water, supporting the data obtained from natural saline lakes. The above results provide important insights into whether it is feasible to use U isotopes for absolute dating and/or paleohydrologic analysis of lake sediments or biogenic shell materials. In addition, the results are important for evaluating the [234U/238U]AR and uranium concentrations in seawater when there exists a process of melting polar ice, and for determining the initial delta 234U variations needed for dating of coral and other fossil materials.

Hydrogeochemical characteristics of the Indus river water system

ABSTRACT The Indus River is the most prominent freshwater source of the northwestern part of the Indian subcontinent. Glacier/snow melting during the summer season is the main source of water. Here, we are presenting the major ion chemistry of the Indus river water, its tributary rivers, including small streams (nallahs), mainly in the territory of India, to know the overall quality of water, and geochemical processes controlling the solute acquisition and sources of elements in the catchment region. The analytical results indicate that the water samples are mildly acidic to alkaline in nature and have Ca2+ and Mg2+ dominance in cationic and HCO3 - and Cl- in anionic composition. Overall, alkaline-earth elements (Ca2+ + Mg2+) dominate over alkalis (Na+ + K+), and weak acids (HCO3 -) exceed strong acids (SO4 2- + Cl-) in the river/stream water samples. The hydrogeochemical diagrams, molar ratios, and statistical analysis suggest that carbonate and silicates minerals’ weathering mainly control the solute acquisition process with negligible contribution from marine or anthropogenic sources. Most of the surface water samples are fit for drinking and domestic uses except the hot spring and saline lake waters.

Precipitation dynamics on the Tibetan Plateau during the Late Quaternary – Hydroclimatic sedimentary proxies versus lake level variability

Two of the largest and deepest endorheic lakes on the Tibetan Plateau, Nam Co and Tangra Yumco, were targeted to infer Late Quaternary (24 ka) responses of their hydrological balance to environmental dynamics. For this purpose, high-resolution multi-proxy records were used to obtain information on lake level variations and how these are related to direct precipitation proxies. Allochthonous minerogenic input as reflected by potassium (K), is directly linked to precipitation driven by variations in Indian Summer Monsoon. Negatively correlated elements such as Ca, Sr and Mg and associated carbonate mineral phases represent autochthonous sediment production, which is coupled to evaporation in these closed systems. δ 13 C and δ 18 O of bulk carbonates represent lake water conditions, i.e., salinity and lake water volume, interpreted as precipitation-evaporation (P/E) balance. In combination with geomorphological features, i.e., lake level terraces and paleo-shorelines, the multy-proxy data set from Nam Co is used to reconstruct lake level dynamics. Low lake levels of >90 m below the recent one between 20 and 16 ka cal BP are associated with most enriched δ 18 O carb values and the precipitation of aragonite and high-Mg calcite in a shallow lake with highly dynamic allochthonous minerogenic input. Similar conditions are observed between 13.1 and 11.4 ka cal BP matching the Younger Dryas chronozone. Between 15.5 and 13.1 ka cal BP as well as during the Early Holocene (11.4 to 8.0 ka cal BP) distinctly depleted δ 18 O carb and δ 13 C carb coupled with high rates of allochthonous minerogenic input suggest substantial strengthening in precipitation. After 9.4 ka cal BP, the terrigenous input and thus precipitation is significantly reduced, whereas δ 18 O carb reveals only a slight enrichment trend and thus a slowly but steady decrease in lake level througout the Mid- to Late Holocene. The decoupling of this relation between precipitation and lake level suggest that lake level terraces of large endorheic lakes on the TP and also δ 18 O carb records are not a direct indicator of (monsoonal) precipitiation, whereas the allochtonous minerogenic input can be directly linked to precipitation dynamics. This is supported by the comparison to regional archives from the Arabian Sea and the northern Bay of Bengal, showing the very same pattern in precipitation variability. The presented monsoon precipitation record from Nam Co additionally reveals a link to supra-regional atmospheric circulation components as it is oscillating in- and anti-phase to El-Niño strength and frequency. A distinct precipitation change at 2 ka cal BP seems to have affected all archives, however leaving space for future studies to find the cause of this Late-Holocene climatic shift. • First Late Quaternary lake level reconstruction for Nam Co, one of the best and most investigated lakes on the TP • Presentation of a robust paleo-precipitation proxy, i.e., allochthonous minerogenic input into the Tibetan lakes • Decoupling of lake level and precipitation proxy suggests e.g., paleo shorelines do not trace paleo-monsoonal variability • Robustness of the paleo-precipitation proxy supported by excellent temporal match of the variability to regional archives • Supra-regional link between paleo-precipitation on the Tibetan Plateau and the Tropical Pacific (El Niño variability)

Decadal changes in size, salinity, waterbirds, and fish in lakes of the Konya Closed Basin, Turkey, associated with climate change and increasing water abstraction for agriculture

ABSTRACT The Konya Closed Basin (KCB) in Turkey has a cold semiarid to warm Mediterranean climate and hosts the largest Turkish freshwater lake, Lake Beyşehir, and the iconic saline Lake Tuz. Using published as well as our own ground-truth and remote sensing data, we provide (1) a brief description of the paleoenvironmental changes in the KCB; followed by (2) a detailed description of the changes in land use, crop farming, groundwater and surface water levels, and climate; and (3) associated changes in lake water surface area and salinity as well as in waterbird and fish communities during the past 40 years. The KCB is intensively farmed, and the farming of mainly water intensive crops has increased substantially, especially since 2000. This, combined with climate warming, has led to a substantial rate of reduction of the groundwater level (up to 1 m/yr) and the surface area of the lakes and wetlands, followed by an increase in salinisation, and even complete loss of several wetlands. Three globally threatened waterbird species face extinction in the basin, and 18 of the 62 previous breeding species have already been lost. The KCB has 38 fish species, of which 74% are endemic and 61% are considered threatened or near threatened. Modelling projections using various climate and land use scenarios predict serious additional reductions of the water level in the future due to climate change, leading to deterioration (or complete loss) of lake ecosystems and the services they provide.

Vegetation dynamics of Kisima Ngeda freshwater spring reflect hydrological changes in northern Tanzania over the past 1200 years: Implications for paleoenvironmental reconstructions at paleoanthropological sites

Kisima Ngeda (KN), a spring on the northern margin of saline Lake Eyasi, Tanzania, sustains an Acacia-Hyphaene palm woodland and Typha swamps, while the surrounding vegetation is semi-desert. To study the vegetation changes associated with this spring, which represents a plausible modern analog for the fossil springs documented in the nearby paleoanthropological and archaeological sites of Olduvai Gorge, we analyzed the pollen content of a 43 cm-long sediment core that documents vegetation changes since the last ~1200 years (from cal yrs. C.E. 841 to 2011). Our results show that (1) Hyphaene palms, which require meso-halophytic soil conditions were most abundant in the area of the coring site until cal yrs. C.E. ~1150 when the groundwater supplying the KN spring was likely lower than at present, allowing intrusions of saline lake waters. (2) From cal yrs. C.E. ~1200, a peat began to develop, the palm woodland was replaced by a Mimosaceae woodland, and the increased presence of Typha pollen indicates the presence of more wetlands. (3) From cal yrs. C.E. 1600, the groundwater level of the KN spring increased and reached its highest level in the last 1200 years. (4) Peaks of wetland expansion, which reflect increased groundwater flow and level in response to amplified rainfall in the recharge area (Mt Oldeani, Ngorongoro Highlands), occurred at cal yrs. C.E. ~1200–1400 and ~1650–2011. These outflows of groundwater at Kisima Ngeda were linked to the intensity and frequency of positive Indian Ocean Dipole (IOD) events, which trigger heavy rains in eastern Africa. We conclude that the Kisima Ngeda hydrological system, which has been active for more than 1200 years, responds rapidly to regional climate change driven by changes in the sea surface temperatures (SSTs) of the Indian Ocean. Yet, it is also capable of remaining active during dry intervals as inferred from the Kisima Ngeda record prior to cal yrs. C.E. 1200. Our results support the hypothesis that this type of system helped to maintain Plio-Pleistocene hominin populations and activities in the arid lowlands of the rift on a multi-decennial scale.

Origin and enrichment of borates in a Late Paleozoic alkaline lake-playa deposit, Junggar Basin, NW China

Reedmergnerite (NaBSi3O8) and searlesite (NaBSi2O6·H2O) are rare borates minerals over the world. In the Late Paleozoic Fengcheng Formation of the NW Junggar Basin, NW China, the two borates, especially reedmergnerite, occur as locally abundant minerals of potential economic interest. Here, petrology, minerology, and boron isotopes of different reedmergnerite occurrences in the Fengcheng Formation were systematically studied to explore its enrichment mechanism in sedimentary rocks. Reedmergnerite in the Fengcheng Formation is a temperature-controlled (crystallizing at 55–180 ℃, mainly at 90–110 ℃) and diagenetic replacive mineral. In the lake center deposits of the Fengcheng Formation, reedmergnerite is confined within sodium carbonate beds or nodules and shows a clear replacement of sodium carbonate minerals. In the lake slope deposits, reedmergnerite is also very abundant and mainly replaces calcite or dolomite-ankerite within sub-horizontal fractures or shortite/eitelite crystal molds, occasionally seen replacing bedded searlesite or growing both replacively and displacively in organic-rich matrix. No significant reedmergnerite is found in the lake margin deposits. Boron isotopes of reedmergnerite-bearing samples (–0.04‰ to + 7.69‰) are higher than those of lacustrine mudstone samples (–14.2 to + 2.79‰) and overlap those of ignimbrite samples (+2.37 to + 3.87‰). Boron for diagenetic reedmergnerite formation was primarily inherited from the original hydrothermal fluids that flowed into lakes and its concentration was influenced by lake water pH and salinity. Potential early boron reservoirs were searlesite, sodium carbonates, organic matter and tuff materials. Fluids responsible for reedmergnerite replacement were weakly acidic. CO2 generated by organic matter degradation-maturation and carbonate dissolution acted as a mineralizer to promote reedmergnerite formation at a lower temperature range than the previously synthetic temperatures (>270 ℃). Enrichment of reedmergnerite in sedimentary rocks requires a primary volcanic-related evaporated lake with high organic productivity, and meanwhile a deep burial environment, at best reaching the depth of oil generation window.

Evaluating organic geochemical proxies for application to coastal lake sediments along the Gulf Coast of Florida for paleotempestology

Organic geochemical proxies (OGPs) preserved in coastal lake sediments have recently been used to reconstruct millennia-long hurricane records. Although OGPs (δ13C, δ15N and C/N) appear to be a more sensitive indicator of past storm events than traditional proxies used in paleotempestology, the method has not been tested in many lakes with modern data. In this study, we measured the δ13C, δ15N and C/N values of particulate organic matter (POM), along with the salinities and stable isotopic compositions of water (δ18O and δD), in two coastal lakes on seasonal or much shorter time scales throughout a 3-year period. This work was intended to develop a better understanding of the dynamics of OGPs in these lakes. The time-series data not only show that geochemical properties of these lakes varied seasonally, reflecting variations in lake biological and environmental conditions, but displayed unique variation patterns in response to storms that caused either seawater flooding or freshwater flooding of the lakes. The data show that seawater flooding led to higher δ13C and δ15N values, with either lower or no change in the C/N ratios of the POM, generally consistent with a previously proposed conceptual model for detecting seawater flooding events. The data also show that freshwater flooding reduces δ15N and increases the C/N values of POM, in addition to lowering the salinity, δ18O and δD of lake water. These time-series modern data demonstrate the feasibility of detecting past storm events that were large enough to cause either seawater or freshwater flooding by examining variation patterns of multiple OGPs in coastal lake sediments. Applying this understanding to a sediment core from one of the study lakes (Mullet Pond, Florida), we reconstructed a centuries-long record of storms based on the variation patterns in OGPs together with 210Pb ages. The OGP-based storm record suggests that 30 flooding events, including 15 seawater flooding and 15 freshwater flooding incidents, occurred over the last 165 years. Almost all of these flooding events can be matched (within the dating uncertainty) to the historic hurricanes that are known to have passed within 150 km of the study site. This further confirms that OGPs preserved in sediments in coastal lakes of Florida or similar regions may be used as reliable recorders of past storm activity.

Salinity-controlled isomerization of lacustrine brGDGTs impacts the associated [formula omitted] terrestrial temperature index

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are microbial molecular fossils ubiquitous in natural environments. The correlation between the Methylation Index of brGDGTs (the MBT5ME' paleothermometer) and temperature offers an important tool for reconstructing past terrestrial temperatures. However, factors other than temperature could also affect the distribution of brGDGTs in lacustrine systems, hampering the quantitative application of this paleothermometer. Here we investigated brGDGT distributions in contemporary sediments collected from 52 lakes in mid-latitude Asia. Combined with published brGDGT data from other lakes across the globe, we have found a strong salinity control on the relative abundance of 5-methyl brGDGTs versus their late-eluting isomers (including 6-methyl, 7-methyl, and unknown isomers). This allows the development of novel indices based on the isomerization of brGDGTs for tracing past lake water salinity. We also demonstrate that salinity-controlled isomerization of pentamethylated and hexamethylated brGDGTs can significantly impact the MBT5ME' paleothermometer, potentially leading to an overestimation of past temperature, but the temperature signal can be extracted out of the MBT5ME' index after correcting the salinity effect. As demonstrated in application to a Lake Qinghai (China) sediment core spanning the last 18 kyr, our finding could facilitate the simultaneous retrieval of reliable temperature and salinity records using brGDGTs in lacustrine settings, in particular for lakes that have experienced large salinity changes during the geological past.

Late Quaternary environmental changes of Lake Urmia basin (NW Iran) inferred from sedimentological and magnetic records

The ongoing changes affecting Lake Urmia (NW Iran) are revealed by the lake water level decrease (~7 m in the last 20 yr) that was attributed to natural and anthropogenic causes but the exact impact of these factors on the state of the lake is still not identified. Indeed, lack of detailed record of environmental evolution of the lake in the past limits the understanding of actual and future processes. Our project aims to obtain a high-temporal resolution record of environmental changes in the lake area for the last ~30 kyrs. Sediment cores have been obtained from the recently dried out part of the lake near Urmia City, and surface and ground waters have been measured for electric conductivity. This paper presents results of water and sediments analyses. Six 14C AMS dating on organic fractions provide a chronological framework and indicate that the record covers the last ~30 cal kyr BP. During this period, evaporitic conditions were prevailing in the lake. The electric conductivity of brines from the sediment highlights changes in the lake water salinity. The data indicate a lake-level low stand at ~30 cal kyr BP that was followed by a water level rise and establishment of lacustrine conditions for the next ~9 kyr, this phase representing the highest lake level recorded since that time to date. From the LGM, the lake experienced several fluctuations of the water level. The relatively long-term lacustrine condition established during the Early Holocene before the water level decrease between ~5.5 and 4.9 cal kyr BP. Sediments from the two dry events at ~30 cal kyr BP and at 5.5–4.9 cal kyr BP are characterized by the presence of greigite, which indicates anaerobic early diagenetic conditions in the sediment.

Hudson Strait ice dam collapse: An explanation for the onset of the Younger Dryas cold climate in Europe in only one year

The Younger Dryas cold climate event in Europe began abruptly at about 12,679 years BP. The abruptness of the onset was caused by the rapid collapse of a dynamic ice dam that had existed because of ice stream flow across the east end of Hudson Strait in northern Canada. The resulting flood of icebergs into the southern half of the Northern Gyre adjacent to the Gulf Stream converted western Europe’s mild climate to an arctic climate. The collapse event was caused by the last large accumulation of glacial ice in the thick ice dome of Hudson Bay. The accumulation created a pressure gradient that forced an ice stream flow eastward in Hudson Strait. A highly saline sub-glacial lake had formed earlier in the western part of the strait. The ice stream flow entrained saline lake water in a network of channels at the seabed between the lake and the ice dam, melting and extending the network eventually to and beneath the ice dam. This detached much of the ice dam from its frozen bed and caused its catastrophic collapse and the onset of the Younger Dryas in only one year.

Hydrogeochemistry and fractionation of boron isotopes in the inter-dune aquifer system of Badain Jaran Desert, China

Groundwater flow systems can be topography-controlled in arid, mountainous, and/or permeable areas. Previous theoretical studies indicated that local groundwater flow systems were usually less developed or even did not exist in recharge-controlled flow systems, and the whole flow system was dominated by regional groundwater flow system. However, the occurrence and role of local groundwater flow systems in real recharge-controlled aquifer systems are rarely addressed. The Badain Jaran Desert is featured by hyper dry climate, mega sand dune-lake landscapes, and highly permeable loose sediments, making it an ideal natural laboratory to address these issues. In this study, the local groundwater flow system and its interaction with saline lake water in the desert inter-dune aquifer are investigated via hydrogeochemical and isotopic approaches. The stable boron isotopic compositions reveal the existence of local groundwater flow systems in the hyper arid climate condition. The fresh local flow systems regulate not only the lake water volume and the lake water-groundwater mixing process, but also the ion contents and isotopic compositions of saline groundwater and lake water. Lake water-groundwater interaction manifests as fresh groundwater discharge and saline lake water intrusion. This study demonstrates that boron fractionation is applicable in deciphering groundwater flow patterns and lake water-groundwater interaction in the arid aquifer systems.

An eogenetic karst in lacustrine carbonates and its influence on reservoir development: A case study of the Eocene Dongying Depression, Bohai Bay Basin, East China

Research on eogenetic karsts has mostly focused on oceanic settings but rarely targeted lacustrine settings. This study describes an eogenetic karst formed in a saline lacustrine setting in the upper 4th member of the Shahejie Formation (Es4s), Dongying Depression, China. Limestones were deposited on a landmass-attached carbonate platform characterized by boundstones and grainstones interbedded with micrites. Tectonic uplift at the end of Es4s caused the karstification in a saline lake shore setting over approximately 2 Ma. During the exposure period, pervasive macroporosity developed in intervals within the top 20 m below the unconformity. Caves formed along the periphery of the platform, and they are mainly at 0.2–1.3 m in height and are filled with wackestone sediments without turbulent flow features. The caves are interpreted as the result of mixing dissolution on the margin of a mixing zone of saline lake-water and fresh-water. Sponge-like intervals occur in interior areas and range from 0.5 to 2.5 m in height, and they present a spongy porosity with pyrite crusts, pervasive pyrite framboid disseminations and occasional cements. The sponge-like dissolution pores are analogous to the Swiss-cheese texture forming in modern and fossil mixing zones and are probably caused by microbially-mediated dissolution in a mixing zone where mixing rate is limited because of reduced circulation in saline lake phreatic water. A small number of sub-vertical conduits (turbulent flow paths) and pervasive fissures are generated due to dissolution by meteoric water. The dissolution effects are strongly influenced by primary lithofacies. Spongy dissolution and caves develop almost in boundstone and grainstone layers, which is probably because they maintained a high permeability after shallow burial and thus become the preferential diffuse flow paths. According to this model, the boundstone and grainstone intervals that developed along the periphery of the platform could be favorable reservoirs for future petroleum exploration.

The Impact of Climate Change on the River Jordan-Lake Kinneret (Israel) Ecosystem

The long-term record of River Jordan-Lake Kinneret ecosystem indicates some significant climate condition changes: water temperature increase, decline in rainfall, and diminishing river discharges and lake water inflows accompanied by a reduction in nitrogen and a slight increase in phosphorus in the Lake upper layers (Epilimnion). Lake Water level decreased, Prolongation of Residence Time was documented, nutrient inputs and dynamics modifications resulting water quality deterioration. As a result of temperature elevation and nitrogen deficiency, the biomass of Peridinium spp significantly reduced and was replaced by Cyanobacterial biomass enhancement. Dryness trend expressed as enhanced frequency of drought seasons initiated an elevation of lake water salinity. It has been suggested that these changes in the phytoplankton community structure are caused by regional climate change. This study evaluates a multi-annual respective approach although the summer is the most critical. The objective of this research is evaluate the background of the ecosystem structure modification aimed at define future potential management design.

Abrupt Freshening Since the Early Little Ice Age in Lake Sayram of Arid Central Asia Inferred From an Alkenone Isomer Proxy

AbstractHydroclimatic variations of arid central Asia (ACA) significantly impact regional ecosystems and human civilizations. Here we present a lake water salinity record of the last 3,000 years from Lake Sayram in the core area of ACA using a new alkenone isomer‐based RIK37 index. Our record shows an abrupt decrease in salinity by more than 5‰ since the “early” Little Ice Age (LIA) (about CE 1150), which can be attributed to the combined effect of regional wetting, cooling, and topographic features. Combined with other moisture records in the region, we find two periods of relatively wet conditions during CE 1150–1550 and 1850 to present, which may be linked to Arctic sea ice expansion due to natural variability and, from CE 1950, anthropogenically induced warming. The wet conditions during CE 1206–1260 may have favored the spread of the Mongol Empire across the entire core area of ACA.

Volcanic activity controls cholera outbreaks in the East African Rift.

We hypothesized that Cholera (Vibrio cholerae) that appeared along Lake Kivu in the African Rift in the seventies, might be controlled by volcano-tectonic activity, which, by increasing surface water and groundwater salinity and temperature, may partly rule the water characteristics of Lake Kivu and promote V. cholerae proliferation. Volcanic activity (assessed weekly by the SO2 flux of Nyiragongo volcano plume over the 2007–2012 period) is highly positively correlated with the water conductivity, salinity and temperature of the Kivu lake. Over the 2007–2012 period, these three parameters were highly positively correlated with the temporal dynamics of cholera cases in the Katana health zone that border the lake. Meteorological variables (air temperature and rainfall), and the other water characteristics (namely pH and dissolved oxygen concentration in lake water) were unrelated to cholera dynamics over the same period. Over the 2016–2018 period, we sampled weekly lake water salinity and conductivity, and twice a month vibrio occurrence in lake water and fish. The abundance of V. cholerae in the lake was positively correlated with lake salinity, temperature, and the number of cholera cases in the population of the Katana health zone. V. cholerae abundance in fishes was positively correlated with V. cholerae abundance in lake water, suggesting that their consumption directly contaminate humans. The activity of the volcano, by controlling the physico-chemical characteristics of Lake Kivu, is therefore a major determinant of the presence of the bacillus in the lake. SO2 fluxes in the volcano plume can be used as a tool to predict epidemic risks.