Paleohydrological Changes Research Articles

Holocene hydroclimate variability reconstructed from Lake Pangodi sediments in Estonia

Long-term hydroclimate variability recorded in lake sediments from Estonia provide information about environmental changes in northern Europe during the Holocene. Lake Pangodi is a semi-closed basin lake in southern Estonia with a large surface area to volume ratio, making it sensitive to effective moisture balance (precipitation minus evapotranspiration), which is recorded as changes in the lake level. Here we conducted a ground penetrating radar (GPR) survey, sedimentological analyses, radiometric dating and lake level modeling study to identify periods of lake-level high- and low-stands. The radiocarbon-dated sedimentary stratigraphic features on our radargram support the model results, suggesting that Lake Pangodi formed at ∼12.8 ka. The water levels were likely variable during the early Holocene, and the comparison of Lake Pangodi sediment facies and the lake level model show relatively stable lake water depth between ∼9.8 ka and ∼2.4 ka, and an increase towards modern. A notable reduction in lake levels occurred between ∼8.2 and ∼7.7 ka, likely due to a significantly reduced precipitation-evaporation balance. Our middle Holocene reconstruction suggests water column depths nearly 2.0 m lower than modern. This aligns with the results from studies conducted in the Baltic region, yet contrasts those from Scandinavia, suggesting different hydroclimate driving mechanisms during the Holocene variations in hydrogeological regimes. Our model detected the most abrupt rise of 1.7 m in water levels between ∼1.5 and ∼1.3 ka. This study highlights the need to develop proxies from single lake basins combining multiple methods for a better spatiotemporal resolution of paleo-hydrological changes.

Holocene Paleohydrological Changes Reflected in Lake-Level Fluctuations in Lake Annecy (French Pre-Alps): Climatic Significance and Archeological Implications

Lakes are threatened by contemporary climate change and human activities. Paleohydrological records provide important evidence for developing scenarios for future changes in the availability of freshwater resources. This study presents a synthesis of a sedimentological, archeological, and chronological dataset collected from Lake Annecy (eastern France) to reconstruct a lake-level record documenting the whole Holocene. This dataset shows a pronounced minimum in the lake level during the Holocene thermal maximum (HTM) (ca. 9000–7000 cal BP), preceded by a general lowering trend (early Holocene), and followed by a general rising trend (Neoglacial). On both the millennial and centennial scales, the Lake Annecy record appears to match the regional pattern of Holocene lake-level fluctuations established for West-Central Europe. In agreement with other extra-regional paleoclimatic records, it shows the dominant influence of orbital forcing. The high magnitude of the lake-level lowering (more than 5 m) during the HTM, with a 2–2.5 °C difference between the HTM and the pre-industrial mean summer temperatures, suggests possible drastic lake-level lowering phases in the near future depending on the IPCC scenarios following climate change. This would mean dramatic impacts on human activities and the preservation of exceptional archeological remains in regional lake basins.

Coordinated response of endemic gastropods to Late Glacial and Holocene climate-driven paleohydrological changes in a small thermal pond of Central Europe

The thermal spring-fed Lake Pețea located in NW Romania southeast of the city of Oradea harbors a unique endemic warm water biota. It is the only location in Europe where thermal water endemic melanopsid Microcolpia parreyssii (Philippi, 1847) lived along with the highly endangered warm-water relict neritid Theodoxus prevostianus. Lake Petea’s evolution was mainly controlled by major climate-driven hydrological changes also seen in regional records. The hydrological changes were mainly controlled by varying input of thermal water due to recurring increased/decreased recharge of the underground karst water system. The driving factor was warming connected to the interstadial GI 1 increasing recharge by melting of regional ice sheets in the Late Glacial. Conversely, during the Younger Dryas (H0) and the Holocene increasing/decreasing moisture availability was in control. Low stands created multiple bottlenecks reducing genetic variability seen in the appearance of extreme morphologies during next rapid climate melioration. The studied gastropods responded mostly similarly to changes controlling the availability of elements in shell construction and habitat reduction leading to changes in shape, density, size. Periods of lower lake levels and reduced warm water input are characterized by the emergence of elongated tightly coiled shells while globular, compressed loosely coiled shells develop at times of warmer water provision and increased Mg availability. In size there is a contrasting trend. Namely globose Th. prevostianus shells are larger than the elongated ones. Conversely globose, compressed Microcolpia are generally smaller than their elongated spindle-shaped counterparts. In this sense the development of dwarf morphotypes in warmer water habitats is characteristic of Lake Pețea melanopsids. This type of dwarfism i.e. the reduction of shell size is lacking though in Lake Pețea neritids. Our findings also confirm the presence of various ecophenotypes of Microcolpia in the pond degrading our endemic species Mi. parreyssii to a variety of Mi. daudebartii.

Paleohydrological changes during the Late Holocene recorded in the sediments of two mountain lakes in the Tatra Mountains (Central Europe)

Changes in local hydrological and climatic conditions over the last 5500 years have been reconstructed based on geochemical and paleobiological features recorded in the sediments of two mountain lakes. The lakes are located in the Tatra Mountains, in the highest mountain range of the Carpathians (Central Europe), which during the Holocene constituted an important climatic barrier. Because both studied lakes are relatively shallow, even relatively minor fluctuations in water level are clearly recorded both in the geochemical characteristics of the sediments and in the phyto- and zooplankton communities. The multiproxy records indicate several periods of high water stands: 5.4–5.2 ka, 3.5–2.7 ka, 1.4–1.0 ka and 0.5–0 ka, and prominent dry periods 2.7–2.1 ka and 1.7–1.5 ka. Comparison of the reconstructed water levels of the Tatra lakes with records from other European regions suggests that at the boundary of the Middle and the Late Holocene, the hydrological conditions in the Tatras were similar to those in Western and Central Europe. Later, beginning approximately 3500 years ago, records from the Tatras, the northern surroundings of the Pannonian Basin, and the southern part of the Carpathians were unified. In addition to changes in local and regional hydrology, the records from the studied lakes allowed us to reconstruct changes in lake productivity. Relatively high δ13C values, compared to the sedimentary organic matter of other lakes in the region, point to in-lake primary production as a major source of sedimentary organic matter in both lakes. The stable C:N ratio values suggest a constant proportion of organic matter coming from in-lake primary production and transported from the lake catchment. However, the amount of organic carbon and nitrogen and, most of all, differences in the composition of stable C and N isotopes indicate changes in the lake environment. These changes were correlated with some paleotemperature proxies from the region.

Hydroclimate reconstructions in the Suguta Valley, northern Kenya, during the Early-Middle Pleistocene Transition

The Early-Middle Pleistocene Transition (EMPT) between 1200 and 700 ka represents a major global climate transition from dominantly 41,000- to 100,000-year glacial cycles. The forces and mechanisms behind this transition and the response of African environments are not well understood. The active volcanism and tectonics of the East African Rift System add complexity to local environmental systems and can erase important proxy records, inhibiting studies of lacustrine dynamics. As a result, there is minimal understanding of how this transition impacted the region's lake systems. At Paleolake Suguta, in the northern Kenya Rift, however, flood basalts cap lacustrine EMPT-age deposits, preserving these strata and their valuable paleoenvironmental record. This research presents a high-resolution reconstruction of hydrological change from approximately 931 to 831 ka within the Suguta-Turkana Basin in the northern Kenya Rift. Paleolake dynamics are reconstructed from a 41 m sedimentary section using diatom morphology, sedimentology, and X-Ray Fluorescence elemental analysis. Results show that lake levels varied greatly during this part of the EMPT with two wetter phases and two drier phases developing over about 100 kyr. From ∼885–831 ka, especially, the Suguta-Turkana Basin exhibits rapid changes in paleohydrology, ranging between deep stratified lakes; shallow, well-mixed lakes; and complete desiccation, with some of these changes occurring on an order of hundreds of years. This EMPT Suguta-Turkana-Baringo record therefore provides valuable insight into hydroclimate variability at an overall resolution of several thousand years, allowing reconstruction of past environments during a period of poorly understood terrestrial environmental change.

Paleohydrologic history of pluvial lake San Agustin, New Mexico: Tracking changing effective moisture in southwest North America through the last glacial transition

Paleoclimate records across the Intermountain West region of North America show significant regional variation in timing and magnitude of wet conditions that accompanied the last glacial-interglacial transition. To understand the climate controls on paleohydrologic change, well-dated records are needed across the region. The Plains of San Agustin (New Mexico, USA) is a closed-basin watershed of the American Southwest influenced by both winter westerly and summer North American Monsoon precipitation. The flat valley floors of the Plains contain lake and groundwater discharge deposits that record multiple periods of past wet climate. We present a record of hydroclimate for the past 26,000 years based on radiocarbon, U–Th series, and OSL dating of these deposits and stratigraphic correlation across the three sub-basins of the lake system. We find that two major lake oscillations occurred, coincident with the global Last Glacial Maximum (∼23–18 ka) and with Heinrich Stadial 1 (∼17–14 ka). The LGM lake cycle created a deep lake in the lowermost sub-basin, fed by marsh/lake overflow in the upper sub-basins. The Heinrich Stadial 1 wet interval attained the highest recorded lake level between ∼17.0 and 15.3 ka, merging the lower two sub-basins into one lake. Both lake cycles agree well in timing and magnitude with other lake-based records from the southwestern U.S., supporting previous interpretations that a south-shifted cool season storm track brought a dipole-like pattern of enhanced moisture to the southwest at the expense of drier conditions in the northwest during the LGM and deglaciation. A transition from lake to groundwater discharge conditions followed during the Bølling-Allerød (14.7–12.9 ka) across the study area. Wet meadows prevailed in the lower sub-basin during the Younger Dryas (12.9–11.7 ka), with marsh and open lake conditions in the upper and middle sub-basins, respectively. During the early Holocene, discrete wet intervals are recorded by ages for wet meadow deposits in all sub-basins with centennial-millennial frequency at 9.9, 8.8, 8.2 ka. These events agree well with other Intermountain West records showing wetter-than-present conditions prior to 8 ka. Two additional wet periods, centered at 6.8 and 5.4 ka, occurred during the driest known interval of the middle Holocene, and likely were partly supported in the Plains of San Agustin by summer moisture associated with the peak strength of the North American Monsoon. Our record highlights that both winter and summer moisture support water resources in New Mexico watersheds.

Land-sea linkages on the Algerian Margin over the last 14 kyrs BP: Climate variability at orbital to centennial timescales

Past and present environmental conditions over the Holocene along the Algerian coast involve complex atmosphere-hydrosphere-biosphere interactions and anthropogenic activities on adjacent watersheds. Atlantic Ocean surface waters entering the western Mediterranean Sea at the Gibraltar Strait create the Algerian Current, which flows along the North African coast in a succession of strong and large-scale eddies. Deep-water upwelling plumes are other recurrent hydrological features of the Algerian margin affecting regional environmental features. However, vegetation and paleohydrological changes that have occurred over the Holocene have not yet been described. To bridge this gap, a suite of paleoclimate proxies was analysed in marine core MD04–2801 (2067 m water depth) at a secular-scale resolution over the last 14 kyrs BP. Terrestrial (pollen grains) and marine (dinoflagellate cysts or dinocysts) palynological assemblages, as well as sedimentological (grain-size analysis and XRD-based quantitative analysis of clay minerals) and biomarkers (alkenones and n-alkanes), were determined to explore the links between past sea surface hydrological conditions and regional environmental changes on nearby watersheds.The over-representation of heterotrophic dinocyst taxa (Brigantedinium spp.) indicates strong planktonic productivity in the study area. Results shows that the links between dryness on land and surface hydrological conditions are expressed by: (i) recurrent upwelling cells during the relatively dry climate conditions of the Younger Dryas (12.7 to 11.7 ka BP), the Early Holocene (11.7 to 8.2 ka BP) and from 6 ka BP onwards, (ii) enhanced fluvial discharges between 8.2 and 6 ka BP during the African Humid Period concomitant with the colonization of coastal lands by Mediterranean forest. Middle to Late Holocene transition around 4.2 ka BP characterizes by the intense event reffered to here as the Algerian Mega Drought (4.3 to 3.9 ka BP).

Late Quaternary hydroclimate and vegetation changes in an upland lake in southeastern Amazonia.

An integrated approach considering facies, isotopic, and palynological analyses of lake sediments from the Serra Norte de Carajás, southeastern Amazonia, is presented in this work to refine paleoclimate and paleohydrological changes based on upland lake sediments during the late Quaternary. The sediments have a fining-upward deposition cycle typical of upland swamps/lakes. The origin of organic matter is autochthonous mainly related to C3 terrestrial plants, macrophytes and algae. The pollen records of Hedyosmum during the Early Pleistocene suggest lower temperatures than those observed along Holocene. In the transitional period between the Pleistocene and the Holocene, rainfall decreased, causing the retraction of the flooded area, favoring the development of marshy conditions. The Late and Middle Holocene were marked by higher temperatures and lower humidity. Afterward, the increased pollen concentration from canga and forest vegetation, macrophytes, palms, and algae suggested increased humidity in the Early Holocene. The relative contribution of forest pollen along the records indicated that drier conditions were not strong enough for an extensive expansion of canga over forested areas.

Paleoecological and paleohydrological changes during the Eocene/Oligocene transition in the Qaidam Basin, NE Tibetan Plateau

The Eocene/Oligocene transition (EOT) at ∼34 Ma has been considered the most prominent climatic cooling event in the Cenozoic Era. However, few organic biomarker studies have attempted to reconstruct relevant terrestrial ecological and hydrological responses to an age characterized by drastic temperature changes. This research aims to reconstruct the paleoecological and paleohydrological evolution of the Qaidam Basin (QB) on the northeastern Tibetan Plateau (NE TP) between 40.2 and 29.9 Ma, based on analyses of n-alkane chain length distributions as well as compound-specific hydrogen isotopic compositions (δ2Halk). Research showed the presence of a sequence of pronounced ecological and hydrological variations at 35.0–33.1 Ma, including: 1) a significantly decreased input of bacteria, algae and aquatic plants, allied with a markedly increased input of terrestrial plants, reflected in a significant increase in carbon preference index (CPI) and the average chain length (ACL) ratio, as well as an abrupt decline in the relative ratio of mid- to long-chain length homologue (Paq) values and the ratio of low- to high- molecular-weight n-alkanes (L/H); and 2) drier climatic conditions, reflected in an 18.1‰ increase in δ2H31 values, as well as more positive hydrogen isotopic precipitation values (δ2Hp). These features demonstrate significant paleoecological and paleohydrological changes in the QB in response to the drier and cooler climate during the EOT.

Paleohydrological Changes in the Western Tibetan Plateau over the Past 16,000 years Based on Sedimentary Records of n‐Alkanes and Grain Size

AbstractBoth monsoons and westerlies have exerted influence on climate dynamics over the Tibetan Plateau (TP) since the last deglaciation, producing complex patterns of paleohydroclimatic conditions. Diverse proxy records are essential to forge a robust understanding of the climate system on the TP. Currently, there is a general lack of understanding of the response of inland lakes over the TP to climate change, especially glacier‐fed lakes. Paleohydrological reconstructions of such lakes could deepen our understanding of the history of lake systems and their relationship to regional climate variability. Here we use records of n‐alkanes and grain size from the sediments of Bangong Co in the western TP to reconstruct paleohydrological changes over the past 16,000 years. The Paq record (the ratio of non‐emergent aquatic macrophytes versus emergent aquatic macrophytes and terrestrial plants) is generally consistent with the variations in summer temperature and precipitation isotopes. The changes in grain‐size distributions show a similar trend to Paq but with less pronounced fluctuations in the early‐middle Holocene. The new data combined with previous results from the site demonstrate that: 1) Bangong Co experienced relatively large water‐level fluctuations during the last deglaciation, with a steadily high lake‐level during the early‐middle Holocene and a decreasing lake‐level in the late Holocene; 2) The lake level fluctuations were driven by both high summer temperatures via the melting water and monsoon precipitation. However, the dominant factor controlling lake level changed over time. The lake‐level history at Bangong Co deduced from the n‐alkanes and grain‐size records reveals the past hydrological changes in the catchment area, and stimulates more discussion about the future of glacier‐fed lakes under the conditions of unprecedented warming in the region.

Surface soil n-alkane molecular and δD distributions along a precipitation transect in northeastern China

Hydrogen isotope compositions of leaf wax long-chain n-alkanes (δDalk) buried in soils have the potential to provide records of continental paleoclimatic and paleohydrological changes. However, different factors and processes influence the δDalk signature, making interpretation of the soil isotope record complicated. The relative humidity/aridity and vegetation types (C3 vs C4 plants) are two major factors responsible for the soil δDalk variations. In most cases, the interaction between relative humidity/aridity and temperature cannot be separated. Here, we analyzed the δDalk compositions in surface soils along the Northeast China Transect (NECT), where the mean annual precipitation (MAP) varies from ca. 120 to 815 mm, yet the mean annual temperature changes little, providing a setting to test the role of relative humidity/aridity in soil δDalk variations, independent of temperature changes. At the same time, the western part of the NECT, which is mainly a grassland environment, provides a test of the effects of C3 and C4 grasses on soil δDalk changes. In the semi-humid eastern NECT region, the δDalk values and their apparent fractionation relative to precipitation exhibit a strong negative correlation with the aridity index and a close relationship with soil water content. This finding supports the idea that the soil δDalk values are mainly influenced by relative aridity and that the impact of evapotranspiration, including soil evaporation and transpiration-induced 2H enrichment of woody plant leaf water, plays a vital role in shaping soil δDalk. In the semi-arid and arid western NECT region, the δDalk values and their apparent fractionations show no relationship with any environmental factors. However, in the westernmost area, soil δDalk values tend to show a negative relationship with the increasing proportion of C4 plants. This pattern probably indicates that in the arid area the soil δDalk values vary more closely with plant types than with the environmental variables. This study provides new insights into deciphering the relationship between soil δDalk values and relative humidity/aridity, and it affirms the applicability of δDalk in paleo-hydrologic reconstructions.

Paleohydro-climatic changes revealed by anisotropy of magnetic susceptibility at the Heitugou section, Nihewan Basin, and its influences on human’s occupation

Paleohydro-climatic changes in the habitats of early humans are closely related to their evolution and occupation of specific niches. In the Nihewan Basin of North China, a large number of archaeological sites dating back to the early Pleistocene have been discovered which record the occupation history of human ancestors in the region. However, thus far, studies of the history of paleohydro-climatic changes in the Nihewan Basin and their influences on human occupation remain insufficient. Here, we report the results of a systematic investigation of variations in the anisotropy of magnetic susceptibility (AMS) and magnetic susceptibility stratigraphy in the Heitugou (HTG) section to partially rectify this paucity of data and interpretations. The HTG section is located in the eastern Nihewan Basin where, in 2006, a Paleolithic site was discovered and excavated at the bottom of the sequence. By comparing detailed magnetic susceptibility sequences in the HTG section with those of the nearby Xiaochangliang and Dachangliang sections, we found that the sedimentation of the HTG section began about 1.9 Ma, indicating that the HTG archaeological site possibly records the earliest human occupation of middle-to-high latitude North China. Our studies of the AMS in the HTG section indicate that it is characterized by a primary sedimentary magnetic fabric without significant disturbance, demonstrating its potential for tracing regional paleo-hydrological changes. In most samples dating between 1.9 Ma and 0.4 Ma, the maximum susceptibility axes ( K max) cluster along the SE-NW vector, suggesting hydrodynamic changes tracable in the study area were mainly influenced by the Huliu River. In addition, a relatively weak K max direction biased towards the SW-NE axis was also observed, possibly generated by the predominant flow of the Sanggan River. These two rivers – the Huliu and Sanggan – determined the paleohydrological changes in the eastern Nihewan paleolake basin. Meanwhile, AMS studies also suggest multiple-phase hydrodynamic changes in the Nihewan Basin. Around 1.9 Ma, a thick layer of gravel was deposited in the study area due to the emergence of the Huliu River, or tectonic subsidence of the Nihewan Basin. Strengthened hydrodynamic changes and higher water-levels of the Nihewan paleolake may have driven early human ancestors to occupy higher topographic locations. Between 1.9–1.8 Ma, the paleolake expanded and the hydrodynamic regime weakened accordingly, which may correspond with the enhancement of the summer monsoon cycle in East Asia. Between 1.8–1.5 Ma, the sedimentary hydrodynamic regime strengthened noticeably early on, and subsequently weakened continuously. During the period from 1.5–1.3 Ma, as the East Asian summer monsoon regime intensified, warmer and wetter climatic conditions resulted in deepening of the Nihewan paleolake, which may have subsequently weakened influences from fluvial input and was associated with decreased sedimentary hydrodynamics. Between 1.3–0.9 Ma, high-frequency fluctuations in the AMS are noted, indicating a dramatic change in lacustrine hydrodynamics possibly attributable to the Mid-Pleistocene Transition (MPT) event. After 0.9 Ma, the Nihewan paleolake deepened again. Relatively high-amplitude fluctuations during this period reflect a cyclicity of 100 ka, possibly indicating that it was controlled by global ice volume. In concordance with other Paleolithic sites in the Nihewan Basin that have been chronometrically investigated, our studies at Heitugou reveal that paleohydro-climatic changes had a significant influence on early hominin activities in the Nihewan Basin, which shaped the spatio-temporal distribution of Paleolithic sites there. For example, during the early Pleistocene, early humans lived mostly on lower lake terraces in the eastern Nihewan Basin, when the lake level was still quite low. Subsequently, they moved to topographically higher sites due to gradually increasing lake levels. During the Middle and Late Pleistocene, when the Nihewan paleolake shrank, early humans moved toward the upper reaches of the Sanggan River, and were widely distributed along river courses across the Nihewan Basin during the Late Pleistocene in order to maintain home ranges near permanent water sources.

The Holocene dynamics of moss communities in subalpine wetland ecosystems in the Eastern Carpathian Mountains, Central Europe

In this paper, we present high-resolution, contiguous plant macrofossil records taken from two glacial cirque mountain wetland ecosystems located in the subalpine zone of the Eastern Carpathians. We provide 1) a detailed reconstruction of plant succession from mountain peatland ecosystems; 2) a possible scenario of Holocene paleohydrological changes; 3) the presence of rare plants presently considered glacial relicts, e.g. Meesia triquetra; and 4) the peat forming potential of certain plants at altitudes above 1800 m a.s.l. At Gargalau, a gradual decrease of water level and isolation from ground water influence approximately 7000 cal yr BP trigged the colonization of minerotrophic Sphagnum species (S. teres, S. centrale and S. subsecundum). The decline of Sphagnum subsecundum ca. 3000 cal yr BP was most likely caused by an increase of water level and competiton with Sarmentypnum sarmentosum populations. In the Late Holocene, ca. 2000 cal yr BP, Selaginella selaginoides expansion was recorded, followed by the reappearance of Sphagnum populations, most likely due to a lowering of the water table. The Gropile ecosystem transformed from a shallow lake into peatland at ca. 4200 cal yr BP. The temporary presence of Warnstorfia exannulata in peat sediments ca. 2300, 1600, 1300–1200, and 700–600 cal yr BP may indicate an increase of water level and very wet habitat, or the presence of small ponds. Paleohydrological changes only partly agree at both studied wetlands, suggesting the importance of local climatic and morphological conditions on past vegetation development. According to our paleoecological data, Straminergon stramineum indicates wet stages in peatlands and cannot be considered a high peat-forming species in subalpine zones in European mountain ranges. Projected warm and dry conditions may trigger mountain peatland water tables in Eastern Carpathians to decline, potentially resulting in the expansion of moss species that demand more acidic and drier habitats, e.g. Sphagnum russowii.

Grain Size and Pollen of Sediments in Wanghu Lake (Central China) Linked to Hydro-Environmental Changes

Grain size of lake sediments is often measured in paleolimnological studies, especially investigations of past paleoclimatic and paleohydrologic changes. The implications of such measures, however, remain unclear, since watershed hydrology and the related transfer of materials to the lake are affected by local climate variables, hydrological shifts, and vegetation cover variables. Sediment from Wanghu Lake in the middle reaches of the Yangtze River have apparently been affected by land cover changes and lake-river system transitions caused by a sluice gate built at Fuchi in 1967. These changes influenced the watershed hydrology, thereby confounding paleoclimatic and paleohydrologic interpretations by proxy records in sediment cores. We collected sediment cores from the center of Wanghu Lake and analyzed trends in pollen and physical properties through sedimentary records to investigate land cover changes and hydrological transitions during the past 90 years. The grain size of the sediment core increased with precipitation and the significant relationships between pollen and grain size after 1967 indicated that sediment transfer to the lake was controlled by rainfall and land cover changes due to human-induced deforestation and farming in the lake catchment. Interestingly before 1967, there was no significant relationship between the pollen and grain size or between the precipitation and grain size, indicating that the sediment of WanghuLake was not simply from the lake catchment. The different relationships patterns before and after 1967 indicated that the sediments in the lake were not only transported following precipitation and discharge from the lake catchment but also came from the Yangtze River draining back into the lake during the flood seasons before 1967. These results highlight matters needing attention and the potential application of grain size of sediments for reconstructions of past hydro-environmental changes.

A biotic record of paleoenvironmental changes during the last interglacial-glacial cycle in a sub-Carpathian river valley; a case study of the Radymno loess section (SE Poland)

The studied Radymno loess section is located in the large, fore-Carpathian San River valley (Sandomierz Basin, SE Poland) and shows the sequence building the Pleistocene cover of middle terrace of the San River. Such sequence is quite rare in loess deposits because it combines different depositional environments: subaqueous – the late Eemian-Early Vistulian alluvial-swamp facies of loess with inserts of gyttja type, and subaerial – the Plenivistulian aeolian loess. The main goal of the study was to reconstruct the Late Pleistocene paleoenvironmental changes recorded in this section. For this purpose, pollen and fossil Ostracoda analyses were conducted. These data were supplemented with sedimentological and pedo-lithological analyses. Additionally, the results of earlier investigations published so far have been used: lithological and malacological analyses as well as luminescence (IRSL and TL) dating. Based on the analysis of many indicators, the paleoenvironmental changes have been correlated with those recorded in pollen diagrams obtained from other regions. This correlation indicates that in the Radymno section there is evidence of the vegetation succession typical of the Eemian Interglacial with climatic optimum and of the short-term oscillations in the Early Vistulian and then in the Lower Pleniglacial of Vistulian. The analysis of fossil Ostracoda, which were found in some parts of the profile, provided information about short-term paleohydrological changes, and especially about the functioning of surface water bodies in changing periglacial conditions of the bottom of the San River valley in MIS 5d – MIS 2. High humidity in the environment was caused mainly by floods and high groundwater level, which indirectly conditioned the formation of water bodies in the valley bottom. Correlation with palynological data indicated that these water bodies existed also under dry climate conditions. This proves that the local conditions of the studied area strongly modified the environmental changes dependent on paleoclimate.

Paleohydrological changes in southeastern China from 13.1 to 2.5 ka based on a multi-proxy peat record

Investigating the hydrological changes in the East Asian monsoon regions of China during the Holocene could provide important insights into the mechanism and future variability of the East Asian summer monsoon (EASM) rainfall. However, existing studies have revealed large inconsistencies in the spatiotemporal pattern of the hydrological changes in East China, probably due to different climatic sensitivities of various proxies, the uncertainties of sedimentary chronologies and unevenness of proxy record distributions. Thus, multi-proxy records with precise dating are needed, especially in southeastern China which is one of the key places to determine the spatiotemporal pattern with few hydrological records available. In this study, hopanoid flux, humification degree, the concentration of total organic carbon (TOC) and the atomic ratio between total organic carbon and total nitrogen (C/N) of organic matter were applied on Shuizhuyang (SZY) peat cores retrieved from southeastern China to reconstruct the paleohydrological changes spanning from 13.1 to 2.5 ka. Results of these proxies reveal a moderately dry period during 13.1–11.6 ka, followed by an interval of increasing aridity from 11.6 to 8.6 ka. The Holocene optimum (referred here as an effective moisture maximum) occurred at 8.6–4.4 ka before the climate became drier from 4.4 to 2.5 ka. The hydrological changes in SZY during the Holocene with a mid-Holocene Holocene optimum are consistent with the regional climate records in southeastern China. Such an overall arid-wet-arid pattern in Southeast China during the Holocene closely tracked the variations in the west-to-east sea surface temperature (SST) gradient in tropical Pacific. We preliminarily concluded the ENSO state and the western Pacific subtropical high (WPSH) position associated with variations in the thermal state of the tropical Pacific were primarily responsible for the hydrological changes in Southeast China during the Holocene. Our study added new evidence to the spatiotemporal pattern of hydrological changes in eastern China during the Holocene.

N-Alkyl lipid concentrations and distributions in aquatic plants and their individual δD variations

Aquatic plants are major input sources of autochthonous organic matter in lake sediments, but investigations on fatty acid (FA) and n-alkane distributions in aquatic plants are currently limited, greatly hindering the applications of their isotope geochemistry in lacustrine environments. Here, the reported n-alkyl lipid distributions of aquatic plants in globally studied lakes, together with newly obtained aquatic plant n-alkyl lipid data in Chinese lakes (Yunnan and Inner Mongolia), are used to understand their distribution characteristics. The results show that aquatic plants have predominantly mid-chain lipids (C23–C25n-alkanes and C22–C24 FAs), differing from that of terrestrial plants (dominant by long-chain lipids), but the long-chain n-alkanes (e.g., C27 and C29) and long-chain FAs (e.g., C26 and C28) also show high abundances in most samples. Submerged plants have high concentrations of long-chain n-alkanes (avg. 47 µg g−1) and long-chain FAs (avg. 170 µg g−1), close to those in terrestrial plants, indicating that submerged plants may make large contributions of long-chain n-alkyl lipids to lake sediments, while the contributions of long-chain n-alkyl lipids derived from algae to lake sediments may be small because of their low concentrations (avg. 2 µg g−1 for n-alkanes and 9 µg g−1 for FAs). We find that lipid molecular proxies (including ACL14–32 and ATR14–18) can be reliably used to distinguish the FAs sourced from algae and other plants, and Paq’ values can be utilized to distinguish the n-alkane sources between submerged plants and terrestrial plants. Aquatic plants do not have significant δD differences among different chain-length n-alkanes and FAs for each sample, suggesting that the offset between δD values of different chain-length n-alkyl lipids in lake sediments can help determine sedimentary lipid input sources and infer paleohydrological changes.

Mid- to- late Holocene hydroclimatic changes on the Chinese Loess Plateau: evidence from n-alkanes from the sediments of Tianchi Lake

We have reconstructed the history of mid-late Holocene paleohydrological changes in the Chinese Loess Plateau using n-alkane data from a sediment core in Tianchi Lake. We used Paq (the proportion of aquatic macrophytes to the total plant community) to reflect changes in lake water level, with a higher abundance of submerged macrophytes indicating a lower water level and vice versa. The Paq-based hydrological reconstruction agrees with various other lines of evidence, including ACL (average chain length), CPI (carbon preference index), C/N ratio and the n-alkane molecular distribution of the sediments in Tianchi Lake. The results reveal that the lake water level was relatively high during 5.7–3.2 ka BP, and decreased gradually thereafter. Our paleohydrological reconstruction is consistent with existing paleoclimate reconstructions from the Loess Plateau, which suggest a humid mid-Holocene, but is asynchronous with paleoclimatic records from central China which indicate an arid mid-Holocene. Overall, our results confirm that the intensity of the rainfall delivered by the EASM (East Asian summer monsoon) is an important factor in affecting paleohydrological changes in the region and can be considered as further evidence for the development of a spatially asynchronous “northern China drought and southern China flood” precipitation pattern during the Holocene.

Mineralogy and carbonate geochemistry of the Dali Lake sediments: Implications for paleohydrological changes in the East Asian summer monsoon margin during the Holocene

Hydrological variations in individual plateau lakes respond from both local hydrological processes and regional climatic changes. This study presents high resolution, absolutely-dated records of minerals in bulk samples and elements and stable isotopes of endogenic calcites from a sediment core from Dali Lake in Inner Mongolian Plateau, aiming to investigate the patterns and mechanisms of Holocene hydrological and climatic changes in the modern northern margin of the East Asian summer monsoon (EASM). Increases in the percentages of allogenic minerals (quartz, microcline and albite) and decreases in the percentages of endogenic/authigenic minerals (calcite, Mg-calcite and gypsum), together with decreases in the values of Ca and Mg concentrations and δ18O and δ13C of endogenic calcites indicate an excess of water input to the lake over evaporative losses, and vice versa. These data suggest that the hydrological balance of Dali Lake was controlled by strong evaporation before 9800 cal yr BP, and then the lake was supplied by significantly increased inflowing water between 9800 and 5900 cal yr BP. From 5900 to 4850 cal yr BP, the water input to the lake significantly decreased. Since 4850 cal yr BP, the inflowing water maintained a low level. In addition, the distinct characteristics of mineralogy and carbonate geochemistry of the Dali Lake sediments during the periods of high lake level between 9800–7700 and 7700–5900 cal yr BP imply that the lake was mainly fed by snow/ice melt water in the former period and then by regional precipitation in the latter period, which was further supported by the pollen records from the same sediment core. These results suggest that Holocene hydrological variations in the EASM margin were closely related to changes in regional temperature and precipitation which were ultimately controlled by changes in the Northern Hemisphere summer insolation, northern high latitude ice sheets, global sea level and physicochemical conditions of the North Atlantic and western tropical Pacific on orbital and millennial timescales. The datasets in this study support that the maximum EASM intensity occurred during the middle Holocene in the northern EASM regions.

Mikrofosylia pozapyłkowe w torfach Polesia Lubelskiego i ich wartość wskaźnikowa

<p>Artykuł stanowi pierwsze opracowanie typów mikrofosyliów pozapyłkowych (ang. non-pollen palynomorphs; NPP) występujących w próbkach palinologicznych z torfowisk Polesia Lubelskiego i stanowiących istotne bioindykatory zmian paleohydrologicznych w holocenie. Analizie na obecność NPP poddano torfy z trzech stanowisk: Płotycze, Mytycze i Durne Bagno. Oznaczono kilkanaście typów NPP wśród których występowały mikrofosylia pochodzenia zwierzęcego i grzybowego. Te same typy mikrofosyliów pozapyłkowych są powszechnie w torfowiskach Niżu Europejskiego. Większość z nich stanowią bowiem gatunki kosmopolityczne. Zidentyfikowane NPP w torfach Polesia Lubelskiego są zgodne z opisami zawartymi w międzynarodowych kluczach do oznaczania. </p>