Glacial lakes appear remarkably gorgeous, with their clear, blue water. Glacial lakes, formed from the meltwater of retreating glaciers, are critical features of high-altitude mountain landscapes. These lakes are rapidly expanding due to climate change, increasing the risk of glacial lake outburst flood events that threaten downstream communities and ecosystems. Beyond their immediate hydrological significance, glacial lakes act as natural archives, preserving evidence of past environmental variability. The sediments within these lakes hold valuable records of glacial dynamics, offering crucial insights into Earth’s climatic history while also serving as vital freshwater reservoirs in fragile mountain regions.

The aquatic ecosystems of Ladakh are characterized by cold-arid climatic conditions and persistent nutrient limitation, resulting in low primary productivity and constrained ecosystem functioning. This study aims to evaluate ecosystem productivity and nutrient availability within this fragile high-altitude landscape. To achieve this, sediments from the sediment–water interface of Tsoltak glacial lake and its associated microhabitats was analyzed for biological proxies (diatoms, desmids, and pollen/spores), electrical conductivity (EC), and stable carbon (δ13C) and nitrogen (δ15N) isotopes. These aquatic systems are primarily fed by glacial meltwater and winter snow cover regulates ice-free duration, nutrient availability, and algal biomass, maintaining predominantly oligotrophic conditions. However, recent observations suggest a shift towards meso-oligotrophic conditions under prolonged summer seasons, reflected by moderate primary productivity dominated by diatom taxa such as Didymosphenia, Cymbella, Diatoma, and Pinnularia, and desmids including Cosmarium, Staurastrum dilatatum, and S. punctulatum. The pollen assemblage is dominated by Artemisia-Tanecetum-Apiaceae-Ephedra assemblage indicating desert steppe vegetation influenced by moist summers. The δ13C values of the sediment samples indicate a dominance of C3 and CAM vegetation, along with lower δ15N, indicating atmospheric nitrogen fixation in sediments. Overall, the integration of biological assemblages with EC and stable isotope proxies provides insights into primary productivity patterns and nutrient cycling processes within this Trans-Himalayan glacial lake ecosystem.

Landform geomorphology and glacial lake deposits in the largest drainage basin of the Ladakh Range i.e. Chang La-Tangtse basin were studied to infer their palaeoclimatic significance. The grain size, mineral magnetism, percentage loss on ignition (%LOI) and organic carbon stable isotope (delta C-13) data in combination with total organic carbon (TOC) supported by AMS C-14 (calibrated) dates of a 190 cm long section from the Chang La-Tsoltak palaeolake provides a climatic record since the last similar to 7075 cal yr BP. The chi lf, chi ARM, and SIRM values suggest that the catchment-derived palaeolake sediments predominantly contain magnetically "soft" minerals like magnetite and maghemite. The delta C-13 values range between -21 and -24 parts per thousand with an average of -22 parts per thousand which suggests a mixed C3-C4 plant signature and water stressed ecosystem. The relatively small variations in the delta C-13 values of organic matter in the entire lake profile suggest a stable climatic condition. The prominent effect of westerlies is seen between 7075 and 6040 cal yr BP with huge detrital influx at the lake bottom indi-cating a glacial advancement in the region. The affect of Mid-Holocene warm period is evident at 6040 cal yr BP with the advent of ISM. Paradigm shifts in the proxy values are observed at 5710, 4890, 3435, and 2800 cal yr BP. The influence of westerlies gradually reduces at 2800 cal yr BP. The landscape evolution and the climatic variations in the Trans-Himalaya are primarily governed by westerlies and do not correspond to the Indian monsoon variability records, particularly during the Mid-Holocene Thermal Maxima. Several other regions of the Ladakh Range also record similar climatic variations, indicating that the palaeolake sediments also reflect regional climate variations.

Gya river, one of the main tributary of Indus, hosts several scattered palaeoflood deposits. The chronology, genesis and spatiotemporal relationships of these scattered deposits can throw light to the regional and global climatic fluctuations and their implications for the evolution of the valley. The valley structure of the Gya river consists of a broad middle reach alternating with narrow valleys and gorges in the upper and lower reaches which can be blocked by the slightest of sediment discharge damming the entire valley. The geomorphological, sedimentological and chronological study in this valley reveals multiple short-lived lake phases at 21-19.9 ka, 13 ka and 4.5 ka in the broader reach of the river during the transition periods when climate rapidly fluctuates between cold-dry and warmwet. The damming in the valley is the result of the glacial lake outbursts in the head waters of the Gya catchment blocking the narrow lower reaches of the main channel by massive sediment. These lakes that are formed by valley damming contains similar to 10(8) m(3) of water which subsequently breach out causing significant geomorphic changes on reach scale along the Gya river channel.

In this communication we reconstruct climate variability of Ladakh, Trans-Himalaya region, on sub-century timescale spanning the last four millennia (similar to 4130 to 260 cal yr 'before present' (BP)). To achieve this objective, we measured a suite of physical, biotic and inorganic proxies of a lacustrine sequence. In general, between similar to 4130 to similar to 2640 cal yr BP proxy records reveal climate variability following a typical pattern of the northern hemispheric climate and appear to be dominated by westerlies. Thereafter, the Indian Summer Monsoon (ISM) forcing appears to dominate regional climate. The former period appears to have experienced human presence as evidenced by an invasive species of diatom -Didymosphenia and charcoal, likely originating from human activities on trading routes with Central Asia, China and Tibet. After similar to 2640 cal yr BP, when ISM started governing the climate of the Ladakh-Karakoram region, it probably induced high-frequency climate variability leading to disasters related to landslides, debris flows, avalanches etc., eventually reducing the intra-boundary trade. A similar situation appears to be gripping the region again as meteorologically recorded precipitation data from Ladakh reveals arrival of high-frequency monsoonal variability in the region with recurrent flash floods (e.g., 2010, 2013).

A multi-proxy study using mineral magnetism, sediment texture, total organic content, palynofacies and diatoms was conducted in one of the highest proglacial lake situated at North Pulu (5098 m a.s.l.) of Ladakh sector of NW Himalaya – a high-altitude cold arid desert. This study presents climatic variations that occurred between 5412 and 419 cal. yr BP (14C AMS chronology). Directly recharged by meltwater from Khardung glacier, this proglacial lake provides a complete record of past climatic variability due to continuous sedimentation and this attribute makes it an exceptionally important geochronological archive for climatic studies. This first high-resolution palaeolimnology record from Karakoram Himalayas shows intermittent warm and cold periods in which the cold events are short but sudden events recorded at 5700, 4600, 4400, 4200, 3800, 3500, 3000, 1800–1700, 1200, 910, 840 and 770–710 cal. yr BP. Between 5412 and 4840 cal. yr BP, an oxic lake condition existed with freeze–thaw action, prominent weathering, more sediment generation and less organic productivity. The following period till 4410 cal. yr BP was cold and dry, a transition phase to the next warmer phase. Between 4410 and 2064 cal. yr BP, climate ameliorated to somewhat moderate warm climate and relatively high lake levels. Glacial melting due to a warm climate resulted in high TOC%, and well-preserved OM indicating reducing conditions in the lake system. From 2064 to 1711 cal. yr BP cold conditions and from 1272 to 1182 cal. yr BP warmer conditions are seen with large appearance in Amphora ovalis indicating increased nutrients input and moderate water levels. This was followed by warmer climatic conditions between 1182 and 958 cal. yr BP. LIA in the region is experienced between 958 and 644 cal. yr BP with anoxic condition. Between 644 and 419 cal. yr BP, climatic condition was again warmer comparatively. However, this warming was not so severe and only had a regional impact.

The Ladakh Range in the Trans Himalaya houses sub-routes of the Silk route through its passes (La in local language) which may have been the main commercial and cultural passage to connect the central Asia and Tibetan region with the rest of India. A ca 6400-220 cal yr B.P. hydroclimatic record of two lakes viz Tsoltak lake and Yaya Tso near the Chang La and Hor La passes of Ladakh Range is presented here. The overall record (mineral magnetic analysis and microbiota) from the Ladakh range shows wetter conditions ca 6400 cal yr BP consistently declining till similar to 5000 cal yr BP and moderately wet and stable till similar to 4300 cal yr BP, followed by an arid cold phase (similar to 4300-4000 cal yr BP). This precedes two moderately wet phases (ca 4300-3500 cal yr BP and ca 1260-220 cal yr BP) and the peak arid conditions between 3500 and 2860 cal yr B P and 2230-855 cal yr BP, which may have affected the trade activities and had an adverse affect of cultural transitions during these periods across the Ladakh Range on the to and fro movements from this northern sub-route branch. The biotic assemblage is rich in Non Pollen Palynomorphs (76%) with minor amounts of pollens (24%). An improvement in the conditions since 855 cal yr BP and thereafter from 340 to 220 cal yr BP records the onset of the cold arid conditions again in the Ladakh Range. Presently due to contemporary deglaciation the Ladakh Range is becoming ice free and a number of lakes surrounded by herbaceous meadows are seen in the area due to glacial melt, likely to encourage the human settlements to soon occupy the higher reaches that will negatively affect the natural lake productivity.