Given the uncertainties in projecting future precipitation seasonality and droughts in the Indian Summer Monsoon realm (ISMr) in a heterogeneous global warming scenario, understanding past hydroclimate responses to regional/hemispheric co(di)vergent temperature trends and shifting teleconnections is crucial. This study presents a comprehensive hydroclimate overview of the past 5 cal ka in the ISMr by integrating existing records with new data from the amplifier Manasbal Lake (NW Himalaya). Our findings identify two major reorganizations of seasonal precipitation pathways linked to temperature trends in high-latitude and tropical regions, which triggered asynchronous prolonged droughts (PDs) in the NW Himalaya (3.9-2.9 cal ka) and the core monsoon zone (CMZ) (4.6-3.9 and 1.2-0.6 cal ka). The first reorganisation, around similar to 5 cal ka, coincided with simultaneous cooling in both high-latitude and tropical regions, driving a southward shift of the winter westerlies and resulting in winter droughts in the NW Himalaya (5-2.9 cal ka). Concurrently, a northward-shifted ISM caused a PD in the CMZ (4.6-3.9 cal ka). Within this interval, diminishing east-west ISM rainfall (3.9-2.9 cal ka) and reduced winter precipitation culminated in a severe PD in Manasbal Lake. The second reorganisation (similar to 1.2 cal ka), coincided with divergent temperature trends-cooling in the high-latitude Northern Hemisphere and warming in the tropics, and increased ENSO activity causing a second PD in the CMZ (1.2-0.6 cal ka). Our results highlight the importance of considering the complexities in regional temperature trends in refining predictive climate models.

Lipid biomarkers, including n-alkanes, C20 highly branched isoprenoids (HBI), and the pristane-to-phytane (Pr/Ph) ratio in sedimentary organic matter (OM), serve as key proxies for reconstructing past environmental conditions and assessing ecological dynamics in aquatic systems. This study examines surface sediment and vegetation samples from Manasbal Lake and compares the lipid biomarker signatures with previously published data from Renuka and Ahansar Lakes in the NW Himalaya. In Manasbal Lake, aquatic macrophytes exhibit Paq values > 0.4 and average chain length (ACL) values between 25.5 and 27.3, while terrestrial plants show Paq values < 0.4 and ACL values between 27.3 and 30.5.The surface sediments from Manasbal Lake show elevated ACL and terrestrial/aquatic ratio (TAR) values near the eastern inlet, indicating significant terrigenous input via runoff, while Paq > 0.5 in the eastern and western regions suggests enhanced autochthonous productivity and anthropogenic influence. A carbon preference index (CPI) > 1 supports the effective preservation of biogenic OM. The weak correlation between n-alkane distributions and sediment grain size suggests that OM deposition is independent of hydrodynamic sorting. Comparative analysis reveals that Manasbal and Ahansar lakes receive substantial terrestrial and aquatic OM contributions, whereas OM in Renuka Lake is largely microbial. The redox-sensitive Pr/Ph ratio suggests anoxic conditions favour OM preservation. The presence of C20 HBI isoprenoids highlights periphytic algal contributions in these aquatic systems. These findings underscore the utility of lipid biomarkers in tracing OM sources, intrabasinal distribution, and transformation. This data will help in developing strategies for protecting aquatic systems under anthropogenic and environmental pressures.

Microplastic (MP) contamination in freshwater systems is a prevalent and persistent environmental issue, yet their occurrence and distribution remain poorly constrained. The present study examines the MPs abundance in sediment and water samples and factors controlling their distribution in the Manasbal Lake, north-western (NW) Himalaya. Additionally, the study investigates the relationship between heavy metals and the distribution of MPs in sediment, as well as their potential interactions. The MPs counts in lake surface sediment and water samples varied from 840 nkg−1 to 4020 nkg−1 and 13 nL−1 to 89 nL−1, respectively. The MPs distribution in Manasbal Lake exhibited spatial heterogeneity, with the greatest abundance observed in the eastern and northeastern areas near lake inlets. Grain size and land use appear to collectively modulate the variability of MPs in Manasbal Lake sediments. Five main MPs types were identified: beads/pellets, fragments, fibres, foams, and films, with beads being the predominant type. Polypropylene, polyethylene, and polystyrene are the dominant constituents of the observed MPs, with domestic sewage suggested as the predominant source for their abundance in the lake. Furthermore, the contamination factor for heavy metals indicated a high level of lead contamination in surface sediments, while copper and cobalt showed moderate contamination near the lake inlet. The SEM-EDS analysis illustrated the presence of toxic elements such as Hg, Zn, Pb, Cr, Cd, Ni, and Cu to the surface of MPs. This study expands the baseline characterization of MPs in freshwater systems and enhances our understanding of the potential sources and factors influencing MP distribution.

The conventional approach of using modern values of lake hydrochemistry and sediment composition as key parameters for identifying proxies for environmental reconstruction is complicated by regional climate, catchment geology, lake morphometry and anthropogenic input. In contrast to modern studies from lakes in the north-temperate regions, reliable proxy indicators for past environmental change from tropical lake systems are still lacking. In this study, we compare new surface geochemical and mineralogical data from the Manasbal Lake, Kashmir (India), with other lakes situated in climatically and geomorphologically distinct regimes with varying degrees of pollution (Tso Moriri in north-western Himalaya and Lonar in central India). We characterise external (e.g., geology and weathering), internal (e.g., lake water mixing and evaporation) factors and human activities influencing sediment composition and spatial distribution of proxies in each of these lakes to evaluate the usefulness of some of the commonly used proxies, as well as ascertain conditions where they might be applicable. Our results show that (i) morphometric parameters (such as lake size, water depth and catchment vs. lake area) variably influence the spatial distribution of sediments and proxies on the lake bottom highlighting the limitations of using single cores for long-term palaeoclimate reconstruction; (ii) hydrochemical proxies (such as Na+/Na++Ca2+ and Mg/Ca) can delineate endogenic (Lonar and Tso Moriri lakes) versus allogenic (Manasbal Lake) influence on modern sediment characteristics; (iii) the compilation of heavy metal data (e.g., Fe, Zn, Mn, Cr and Ni) from all three lake basins with varying degrees of pollution highlights the limitations of using them to characterise weathering conditions in these basins; and (iv) human impact must be precluded before using the most promising endogenic minerals (calcite, aragonite, gypsum and pyrite) as palaeoenvironmental/palaeoclimate indicators. The first multiproxy approach (elemental, mineral and isotopic data) from the Indian sub-continent comprehends the factors controlling proxy behaviour in lakes from different climatic and geographically distinct regions. Assessing the impact of human activities is crucial before using elemental data and endogenic minerals as indicators for paleoenvironmental or paleoclimate conditions. Emphasising the importance of modern proxy calibration enhances the accuracy of long-term paleoclimate reconstructions. image

Diversity of Plant Functional Types (PFTs) along a sediment core drilled in Lonar Crater Lake, Central India, is analysed, based on previously published pollen data for a total of 115 depth levels and covering the past 9.2 kyr. Our results support concepts of a dominantly humid period persisting until ca. 5 ka, succeeded by a significantly drier phase with weaker monsoon, including various prominent drying pulses. Throughout the Holocene, plant diversity at Lonar was composed of a variable proportion of herbaceous PFTs (ca. 40–60%) and mainly angiosperm woody PFTs. Changes in herbaceous diversity account for a considerable part of the observed PFT data variability. PCA analysis reveals a total of four partly alternating diversity associations (DAs) interpretable in terms of vegetation spanning from drier Savanna and dry deciduous forest to (semi-) evergreen woody vegetation, mainly recorded in older strata. It is shown that the succession of the DAs is largely triggered by climate change inferred from other proxies. Correlation analysis with geochemical data testifies that the diversity signal obtained is largely unaffected by sedimentary processes and detrital inflow, highlighting the potential of this archive to reflect ‘true’ diversity signals, rather than artefacts of sedimentary processes. While warm and humid conditions promoted diversity, drying and weak monsoon tended to cause diversity loss. In contrast, the relative diversity of dry herbs increased during drier periods. Short-term variability in our data is evident in varying diversity percentages of single PFTs and their ratios. Changing ratios of dry on mesic herbs, the relation of shrub and tree diversity, tropical on temperate PFTs, and total plant diversity are likely related to solar cycles. Evidence for recurrent cooling episodes through solar forcing comes from the observed coincidence of Grand Solar Minima and minima in the tropical/temperate PFT ratio.

Holocene history of the Indian monsoon reconstruction using environmental magnetism has emerged as an effective paleoclimate proxy with its fast, efficient, and repeatable measuring procedures. In this chapter, we have made an attempt to provide a broad synthesis of the available sediment magnetic records obtained from the loess-paleosols (central Himalaya), lake (western India), delta and lagoon sequences (eastern coast Godavari and Iskapalli). Variations in magnetomineralogical S-ratio values of sediment archives were combined and stacked as a surrogate for Holocene paleomonsoon change. High S-ratio results from low weathering rates were attributed to more wet conditions, while low S-ratios were related to dry conditions from intense low temperature oxidation. Combining the S-ratio data from diverse environments collectively revealed three broad climate phases with minor oscillations during the past 20 ka. These are (i) a step-wise intensification of the SW monsoon since the Last Glacial Maximum with its peak level at ∼9.0 ka, (ii) the prevalence of a prolonged dry spell along the eastern coast and western India at ∼3.5 ka that led to the collapse of the Harappan civilization, and (iii) reduction of monsoon rainfall during the period of global cooling events such as Last Glacial Maximum, Younger Dryas, and Little Ice Age. We observed that instead of the concentration-specific magnetic susceptibility (χ), the combined remanence S-ratio seems to be a more sensitive proxy responding to the monsoon variability both at centennial and millennial time scales.

In recent decades, the ecologically sensitive region of NW Himalaya, a transition zone between the westerlies and the Indian summer monsoon (ISM), has witnessed extreme precipitation events as well as an increase in seasonal temperatures, the impact of which on the lacustrine systems is unknown. In this study, we use a two-pronged approach involving (1) reconstruction of precipitation pathways and moisture sources using the HYSPLIT model during years with extreme (seasonal) precipitation in NW Himalaya; and (2) documentation of the impact of climate extremes on limnology and sediment characteristics by comparing mu-XRF and mineralogical data from a Manasbal Lake sediment core (Kashmir) with the lake monitoring data. Our results show that (a) the most significant change in precipitation pathways is observed during summer when the Bay of Bengal branch of the ISM, in addition to the Arabian Sea branch, also contributes to the regional precipitation; (b) moisture pathways from the Bay of Bengal and the Arabian Sea at different levels also indicate that moisture availability at mid tropospheric level plays an important role in creating extreme wet conditions over Kashmir during the summer monsoon season. In the years with above normal spring precipitation, back trajectories from the Arabian Sea and the Middle East carry more moisture at 1.5 km and 5 km levels; (c) the sub-decadal extremes in seasonal tem-perature and precipitation can be linked to drier events preserved in the core demonstrating the high sensitivity of the lake systems to short term climate variability; (d) changes in hydrochemistry resulting from inflow of groundwater can provide insights into prolonged anoxia and hypolimnion ventilation; (e) the lake level appears to be insensitive to isolated extreme rainfall events, and anomalous winter and spring warming observed in recent decades. The results of this study have wider implications for understanding changes in moisture path-ways and sources during prolonged extreme events, and their impact on lacustrine systems.

An unresolved issue in the vegetation ecology of the Indian subcontinent is whether its savannas, characterized by relatively open formations of deciduous trees in C 4 -grass dominated understories, are natural or anthropogenic. Historically, these ecosystems have widely been regarded as anthropogenic-derived, degraded descendants of deciduous forests. Despite recent work showing that modern savannas in the subcontinent fall within established bioclimatic envelopes of extant savannas elsewhere, the debate persists, at least in part because the regions where savannas occur also have a long history of human presence and habitat modification. Here we show for the first time, using multiple proxies for vegetation, climate and disturbances from high-resolution, well-dated lake sediments from Lonar Crater in peninsular India, that neither anthropogenic impact nor fire regime shifts, but monsoon weakening during the past ~ 6.0 kyr cal. BP, drove the expansion of savanna at the expense of forests in peninsular India. Our results provide unambiguous evidence for a climate-induced origin and spread of the modern savannas of peninsular India at around the mid-Holocene. We further propose that this savannization preceded and drove the introduction of agriculture and development of sedentism in this region, rather than vice-versa as has often been assumed.

Extreme climate events have been identified both in meteorological and long‐term proxy records from the Indian summer monsoon (ISM) realm. However, the potential of palaeoclimate data for understanding mechanisms triggering climate extremes over long time scales has not been fully exploited. A distinction between proxies indicating climate change, environment, and ecosystem shift is crucial for enabling a comparison with forcing mechanisms (e.g. El‐Niño Southern Oscillation). In this study we decouple these factors using data analysis techniques [multiplex recurrence network (MRN) and principal component analyses (PCA)] on multiproxy data from two lakes located in different climate regions – Lonar Lake (ISM dominated) and the high‐altitude Tso Moriri Lake (ISM and westerlies influenced). Our results indicate that (i) MRN analysis, an indicator of changing environmental conditions, is associated with droughts in regions with a single climate driver but provides ambiguous results in regions with multiple climate/environmental drivers; (ii) the lacustrine ecosystem was ‘less sensitive’ to forcings during the early Holocene wetter periods; (iii) archives in climate zones with a single climate driver were most sensitive to regime shifts; (iv) data analyses are successful in identifying the timing of onset of climate change, and distinguishing between extrinsic and intrinsic (lacustrine) regime shifts by comparison with forcing mechanisms. Our results enable development of conceptual models to explain links between forcings and regional climate change that can be tested in climate models to provide an improved understanding of the ISM dynamics and their impact on ecosystems. © 2020 John Wiley & Sons, Ltd.

We present late Quaternary lake level reconstruction from the high altitude Tso Moriri Lake (NW Indian Himalaya) using a combination of new and published data from shallow and deep water cores, and catchment geomorphology. Our reconstruction indicates two dramatic lake level increases – a late glacial (ca. 16.4–12.6calkyrB.P.) rise of 65m, and a 47m rise during the early Holocene wet phase (ca. 11.2–8.5calkyrB.P.) which are separated by the Younger Dryas (YD) event. We decouple the role of precipitation seasonality and snow melt using a combination of proxies sensitive to the Indian Summer Monsoon (ISM), and a regional spatio-temporal transect that provides information on the eastward penetration of the winter westerlies. A comparison of shallow and deep water cores shows that (i) the first lake level increase (~65m, ca. 16.4–12.6calkyrB.P.) is caused by melt water inflow triggered by the increasing summer insolation; (ii) the second lake level increase (~47m, 11.2–8.5calkyrB.P.) is largely caused by a rise in annual precipitation coupled with reduced summer evaporation; (iii) in contrast to the onset of ISM (Bay of Bengal branch) at ca. 14.7ka in lower elevations in NE India, the hydroclimatic influence of ISM in the high altitude Himalaya is seen only between 12.7 and 12calkyrB.P., though the influence of solar insolation (via increased snowmelt) is visible from 16.4calkyrB.P. onwards; (iv) the eastward penetration of westerlies in Indian Himalayas is strongly influenced by the strength of the Siberian High.

High resolution reconstructions of the India Summer Monsoon (ISM) are essential to identify regionally different patterns of climate change and refine predictive models. We find opposing trends of hydrological proxies between northern (Sahiya cave stalagmite) and central India (Lonar Lake) between 100 and 1300CE with the strongest anti-correlation between 810 and 1300CE. The apparently contradictory data raise the question if these are related to widely different regional precipitation patterns or reflect human influence in/around the Lonar Lake. By comparing multiproxy data with historical records, we demonstrate that only the organic proxies in the Lonar Lake show evidence of anthropogenic impact. However, evaporite data (mineralogy and δ18O) are indicative of precipitation/evaporation (P/E) into the Lonar Lake. Back-trajectories of air-mass circulation over northern and central India show that the relative contribution of the Bay of Bengal (BoB) branch of the ISM is crucial for determining the δ18O of carbonate proxies only in north India, whereas central India is affected significantly by the Arabian Sea (AS) branch of the ISM. We conclude that the δ18O of evaporative carbonates in the Lonar Lake reflects P/E and, in the interval under consideration, is not influenced by source water changes. The opposing trend between central and northern India can be explained by (i) persistent multidecadal droughts over central India between 810 and 1300CE that provided an effective mechanism for strengthening sub-tropical westerly winds resulting in enhancement of wintertime (non-monsoonal) rainfall over northern parts of the Indian subcontinent, and/or (ii) increased moisture influx to northern India from the depleted BoB source waters.

We use multiple proxies (δ13Corg, δ15Norg, C/N, amino acids, biogenic silica) from the catchment, lake surface and core sediments to (i) identify the factors influencing conventional lacustrine primary productivity (LPP) indicators (isotopic covariance, C/N) in the sediments from the pristine high altitude Tso Moriri Lake during the late Quaternary, (ii) compare C/N and bulk organic isotopic data from the core with available biogenic silica and amino acid data to test the applicability of conventional LPP indicators during the late Quaternary, and (iii) evaluate the degree of sensitivity of LPP to climate change. Our results show that climate driven changes in water salinity and source water changes have influenced the isotopic (δ13C, δ15N) content of the lake water and hence the isotopic composition of bulk organic matter. Erosion has also played a role in masking the LPP as the catchment sediments from this high altitude lake have low C/N thereby casting doubt on the effectiveness of this parameter as an LPP indicator. Independent LPP indicators in Tso Moriri sediments clearly indicate that it is driven by climate change and increases during warmer periods. However, our data show that the LPP in recent times is not much higher than during the early Holocene, ruling out any impact of recent warming on LPP and therefore the possibility of large carbon sequestration in high altitude oligotrophic lakes.

High resolution isotopic (δ18O and δ13C) investigations on endogenic carbonates (calcite/aragonite) from Tso Moriri Lake, NW Himalaya show dramatic fluctuations during the late glacial and the early Holocene, and a persistent enrichment trend during the late Holocene. Changes in this lake are largely governed by the [input (meltwater+monsoon precipitation)/evaporation] (I/E) ratio, also reflected in changes in the carbonate mineralogy with aragonite being formed during periods of lowest I/E. Using new isotopic data on endogenic carbonates in combination with the available data on geochemistry, mineralogy, and reconstructed mean annual precipitation, we demonstrate that the late glacial and early Holocene carbonate δ18O variability resulted from fluctuating Indian summer monsoon (ISM) precipitation in NW Himalaya. This region experienced increasing ISM precipitation between ca. 13.1 and 11.7calka and highest ISM precipitation during the early Holocene (11.2–8.5calka). However, during the late Holocene, evaporation was the dominant control on the carbonate δ18O. Regional comparison of reconstructed hydrological changes from Tso Moriri Lake with other archives from the Asian summer monsoon and westerlies domain shows that the intensified westerly influence that resulted in higher lake levels (after 8calka) in central Asia was not strongly felt in NW Himalaya.

In the present study, we report the results of comprehensive amino acid (AA) analyses of four Indian lakes from different climate regimes. We focus on the investigation of sediment cores retrieved from the lakes but data of modern sediment as well as vascular plant, soil, and suspended particulate matter samples from individual lakes are also presented. Commonly used degradation and organic matter source indices are tested for their applicability to the lake sediments, and we discuss potential reasons for possible limitations. A principal component analysis including the monomeric AA composition of organic matter of all analysed samples indicates that differences in organic matter sources and the environmental properties of the individual lakes are responsible for the major variability in monomeric AA distribution of the different samples. However, the PCA also gives a factor that most probably separates the samples according to their state of organic matter degradation. Using the factor loadings of the individual AA monomers, we calculate a lake sediment degradation index (LI) that might be applicable to other palaeo-lake investigations.

We present the results of our investigations on the radiocarbon dated core sediments from the Lake Tso Moriri, NW Himalaya aimed at reconstructing palaeohydrological changes in this climatically sensitive region. Based on the detailed geochemical, mineralogical and sedimentological analysis, we recognise several short-term fluctuations superimposed upon seven major palaeohydrological stages identified in this lake since similar to 26 cal ka. Stage I (>20.2 cal ka): shallow lake characterised by input of coarse-grained detrital sediments; Stage II (20.2-16.4 cal ka): lake deepening and intensification of this trend ca. 18 cal ka; Stage III (16.4-11.2 cal ka): rising lake levels with a short term wet phase (13.1-11.7 cal ka); Stage IV (11.2-8.5 cal ka): early Holocene hydrological maxima and highest lake levels inferred to have resulted from early Holocene Indian monsoon intensification, as records from central Asia indicate weaker westerlies during this interval; Stage V (8.5-5.5 cal ka): mid-Holocene climate deterioration; Stage VI (5.5-2.7 cal ka): progressive lowering of lake level; Stage VII (2.7-0 cal ka): onset of modern conditions. The reconstructed hydrological variability in Lake Tso Moriri is governed by temperature changes (meltwater inflow) and monsoon precipitation (increased runoff). A regional comparison shows considerable differences with other palaeorecords from peninsular India during late Holocene. (C) 2014 Elsevier Ltd and INQUA. All rights reserved.

A better understanding of past variations of the Indian Summer Monsoon (ISM), that plays a vital role for the still largely agro-based economy in India, can lead to a better assessment of its potential impact under global climate change scenarios. However, our knowledge of spatiotemporal patterns of ISM strength is limited due to the lack of high-resolution, continental paleohydrological records. Here, we reconstruct centennial-scale hydrological variability during the Holocene associated to changes in the intensity of the ISM based on a record of lipid biomarker abundances and compound-specific stable isotopic composition of a 10 m long sediment core from saline alkaline Lonar Lake, situated in the core 'monsoon zone' of central India.We identified three main periods of distinct hydrology during the Holocene in central India. The period between 10.1 and 6 cal ka BP was likely the wettest during the Holocene. Lower average chain length (ACL) index values (29.4-28.6) and negative delta C-13(wax) values (-34.8 parts per thousand to -27.8 parts per thousand) of leaf wax n-alkanes indicate the dominance of woody C-3 vegetation in the catchment, and negative delta D-wax values (concentration weighted average) (-171 parts per thousand to -147 parts per thousand) suggest a wet period due to an intensified monsoon. After 6 cal ka BP, a gradual shift to less negative delta C-13(wax) values (particularly for the grass derived n-C-31) and appearance of the triterpene lipid tetrahymanol, generally considered as a marker for salinity and water column stratification, mark the onset of drier conditions. At 5.1 cal ka BP an increasing flux of leaf wax n-alkanes along with the highest flux of tetrahymanol indicate a major lowering of the lake level. Between 4.8 and 4 cal ka BP, we find evidence for a transition to arid conditions, indicated by high and strongly variable tetrahymanol flux. In addition, a pronounced shift to less negative delta C-13(wax) values, in particular for n-C-31 (-25.2 parts per thousand to -22.8 parts per thousand), during this period indicates a change of dominant vegetation to C-4 grasses. In agreement with other proxy data, such as deposition of evaporite minerals, we interpret this period to reflect the driest conditions in the region during the last 10.1 ka. This transition led to protracted late Holocene arid conditions after 4 ka with the presence of a permanent saline lake, supported by the sustained presence of tetrahymanol and more positive average delta D-wax values (-122 parts per thousand to -141 parts per thousand). A late Holocene peak of cyanobacterial biomarker input at 1.3 cal ka BP might represent an event of lake eutrophication, possibly due to human impact and the onset of cattle/livestock farming in the catchment.A unique feature of our record is the presence of a distinct transitional period between 4.8 and 4 cal ka BP, which was characterized by some of the most negative delta D-wax values during the Holocene (up to -180 parts per thousand), when all other proxy data indicate the driest conditions during the Holocene. These negative delta D-wax values can as such most reasonably be explained by a shift in moisture source area and/or pathways or rainfall seasonality during this transitional period. We hypothesize that orbital induced weakening of the summer solar insolation and associated reorganization of the general atmospheric circulation, as a possible southward displacement of the tropical rainbelt, led to an unstable hydroclimate in central India between 4.8 and 4 ka.

As part of ongoing research on Holocene lacustrine sediments of Lonar Crater Lake (central India), pollen assemblages in lake surface sediment and soil samples were studied to unravel pollen–vegetation relationships, including pollen transport processes in tropical dry deciduous forest vegetation. Furthermore, palynological results were compared with geochemical proxies and spatial features of the lake sediments and the vegetation. The obtained data reveal strong differences in pollen assemblages and pollen concentrations between and within the studied trapping media. Local arboreal vegetation is adequately represented in the soil samples, but is less represented in the lake surface sediment samples. The composition of the lacustrine pollen assemblages is mainly influenced by patterns of transport through surface and channel runoff. Besides the relevance of our new data for reliable interpretation of fossil pollen spectra extracted from Lonar sediment cores, the results of this study are of general importance for the understanding of Quaternary pollen assemblages from tropical lacustrine archives, as well as for the implementation and selection of suitable approaches for quantitative pollen based environmental reconstructions in south Asia and beyond.

We report the results of our investigations on the catchment area, lake surface sediments, and hydrology of the high altitude alpine Tso Moriri Lake, NW Himalayas (India). Our results indicate that the lake is currently alkaline, and thermally stratified with an oxic bottom layer. Results from hydrochemistry and isotopic composition (delta O-18 and delta D) of inflowing streams and lake waters show that Tso Moriri Lake is an evaporative lake with contributions from both westerly source (snow melt) and Indian summer monsoon precipitation. Geochemical and mineralogical investigations on the catchment and lake surface sediments reveal the presence of authigenic aragonite in modern lake sediment. The lithogenic components reflect the inflow and sorting processes during transport into the lake, whereas the authigenic carbonate fraction can be linked to the changes in ([precipitation+meltwater]/evaporation) (I/E) balance within the lake. The spatial variability in grain size distribution within the lake surface sediments shows that the grain size data can be utilised as a proxy for transport energy and shoreline proximity in the lake basin. We have evaluated the applicability of commonly applied environmentally sensitive proxies (isotopes, mineralogy, weathering indices) for palaeoenvironmental reconstruction in the Tso Moriri Lake. Our results show that the commonly used weathering index (Rb/Sr) is not applicable due to Sr contribution from authigenic carbonates. The useful weathering indices in Tso Moriri Lake are the Si/Al and the Chemical Proxy of Alteration (CPA). Since the carbonates are formed by evaporative processes, their presence and isotopic values can be used as indicators of I/E changes in the lake.

The basin-scale spatial variability in lipid biomarker proxies in lacustrine sediments, which are established tools for studying continental environmental change, has rarely been examined. It is often implicitly assumed that a lake sediment core provides an average integral of catchment sources. Here we evaluated the distribution of lipid biomarkers in a modern ecosystem and compared it with the sedimentary record. We analyzed lipid biomarkers in terrestrial and aquatic organisms and in lake surface sediments from 17 locations within the saline-alkaline Lonar crater lake in central India. Terrestrial vegetation and lake surface sediments were characterized by relatively high average chain length (ACL) index values (29.6-32.8) of leaf wax n-alkanes, consistent with suggestions that plants in drier and warmer climates produce longer chain alkyl lipids than plants in cooler and humid areas. A heterogeneous spatial distribution of ACL values in lake surface sediments was found: at locations away from the shore, the values were highest (31 or more), possibly indicating different sources and/or transport of terrestrial biomarkers. In floating, benthic microbial mats and surface sediment, n-heptadecane, carotenoids, diploptene, phytol and tetrahymanol occurred in large amounts. Interestingly, these biomarkers of a unique bacterial community were found in substantially higher concentrations in nearshore sediment samples. We suggest that human influence and subsequent nutrient supply resulted in increased primary productivity, leading to an unusually high concentration of tetrahymanol in the nearshore sediments. In summary, the data showed that substantial heterogeneity existed within the lake, but leaf wax n-alkanes in a core from the center of the lake represented an integral of catchment conditions. However, lake level fluctuation may potentially affect aquatic lipid biomarker distributions in lacustrine sediments, in addition to source changes. (C) 2013 Elsevier Ltd. All rights reserved.