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Terrestrial cosmogenic nuclide (TCN) dating has emerged as one of the most useful techniques in the last two decades for quantifying geomorphological processes and building the chronology of late Quaternary glacial advances/retreats. The chronology based on TCN and optically stimulated luminescence (OSL) dating of glacial landforms from the northwestern (NW) Himalaya suggests that glaciers responded to a complex interaction between temperature and moisture essentially derived from either of the climate systems, the Indian Summer Monsoon (ISM) and the Mid‐latitude Westerlies (MLW). The discrepancies between the TCN ages obtained on moraine boulders/bedrock surfaces, and the OSL ages on the stratigraphically equivalent deposits, highlighted the need for a detailed investigation. The present study attempts to build the chronology of Quaternary glaciation events in the Karakoram and Ladakh Ranges using TCN dating of stratigraphically constrained moraine boulders and striated bedrock surfaces. The TCN ages from glacially eroded surfaces (GES) having prominent striations are narrowly clustered around the Marine Isotopic Stage‐2 (MIS‐2). Agreement between GES TCN ages and OSL ages on the stratigraphically equivalent moraines suggests negligible geological inheritance. The glacial advance during MIS‐2 can be attributed to the combined effect of reduction in north hemispheric insolation and enhanced westerly precipitation. However, relict non‐glacial surfaces and moraine boulders with minimal ice flow modifications yield wide age distributions, most likely suggesting denudational events (interglacials) and/or contribution from tributary valley flanks. Plain Language Summary: Quaternary glacial advances and retreats in the northwestern (NW) Himalaya respond to a complex interaction between climatic parameters, that is, temperature and moisture essentially derived from the two contrasting weather systems viz., the Indian Summer Monsoon (ISM) and the Mid‐latitude Westerlies (MLW). In this study, we employed terrestrial cosmogenic nuclide dating of stratigraphically constrained moraine boulders and striated bedrock surfaces to understand the dynamics of late Quaternary glaciation in the Karakoram and Ladakh ranges. The exposure ages obtained from glacially eroded surfaces (GES) show a narrow cluster around the Marine Isotopic Stage‐2 (MIS‐2), a period when the northern hemispheric insolation was low resulting in a temperature decline. The glacial advance during MIS‐2 is attributed to the combined effect of temperature reduction and enhanced westerly precipitation. Key Points: New insight into the Quaternary glacial history of NW Himalaya based on 40 10Be exposure ages of boulders and bedrock surfacesGlacially eroded surface ages suggest that Marine Isotopic Stage‐2 glacier advances were driven by enhanced westerlies and reduced insolationRelict non‐glacial surface/boulder ages indicate denudational events during the interstadial and/or contribution from tributary valleys [ABSTRACT FROM AUTHOR]

Variations in lake-levels and hydrology are connected to climatic dynamics over the Trans-Himalaya and Tibetan Plateau (TP). Pangong Tso, a ~140 km long hypersaline lake, is sensitive to changes in air temperature, precipitation and snow-glacier melt over the southwestern TP. The incised tributaries entering the lake expose deltaic sequences constituting topset, foreset and bottomset. Sedimentology, chronology and diatom analysis of delta sediments; and stable isotopic and sclerochronological analysis of gastropods helped delineate the Late-Holocene variation in lake levels, surface temperature and salinity. The elevation of the topsets is considered as representing past lake high-stands from where molluscs were also recovered. Three phased lake level changes are observed during the past 3 ka. The first high-stand (+1.4–3.0 m) was at ~2.8–2.0 ka when lake surface salinity and temperature were 4.67–6.01 ppt (parts per thousand) and 5°C–7°C, respectively, against the modern average values of 7.7 ± 0.09 ppt and 16.1°C ± 2.0°C. Followed by a brief decline, another high-stand (+3.0–3.6 m) is observed at 1.1 ka when the salinity is reduced to 4.03–5.72 ppt and lake surface temperature to 5°C–8°C. A corresponding increase in freshwater diatom concentration is also observed here. The third phase over the past 1 ka witnessed a fall of ~3.6–6 m in lake level that is attributed to an abrupt rise in aridity over the TP. We demonstrate that lake level variation in the region is a function of the variability of the Indian Summer Monsoon (ISM) and the westerlies, however during the high-stand, the hydrology of the lake was dominated by ISM precipitation. [ABSTRACT FROM AUTHOR]

Wildfire is an integral component of the terrestrial ecosystem that plays a significant role in regulating the vegetation cover. The paleofire records stored in lacustrine, peat, or marine sedimentary deposits along with environmental proxy records provide temporal information on fire activity and contemporary climatic conditions on a regional scale. A ~2.8m long peat sedimentary profile from Stagmo, Indus Valley, Ladakh Himalaya was examined for sedimentology and charcoal microfossil contents to investigate fire characteristics and reconstruct wildfires which are compared with paleoclimatic changes and past human activities to assess their significance in biomass burning. Charcoal count (CC) analysis provides a suitable method for investigating climatic and vegetation changes with human intervention when no direct evidence is available in the Late-Holocene Trans Himalaya records. The results bring new insight into the interaction between vegetation, fire, and human activity in the Ladakh Himalaya during the past ~2.8 cal kyr BP. An event characterized by high CC at ~2.8 cal kyr BP is distinct from the whole sequence and cannot easily be explained as only the result of a climatic event. This first high charcoal count phase (2.81–2.55 cal kyr BP) could be a natural response to the expansion of forest and dense vegetation with human management interruption. This paleo wildfire event likely corresponds with the time of the Tibetan Plateau's immediate human occupation. In the second phase, a relatively low charcoal count (1.65–1.54 cal kyr BP) is supported by the high fuel availability during a transitional phase. The third phase of wildfire reconstruction in Ladakh Himalaya is identified at ~1.38 cal kyr BP. This phase can be correlated with the intensified Indian Summer Monsoon (ISM) advancing to Trans-Himalaya leading to increased human settlement in the region. [ABSTRACT FROM AUTHOR]

A 1.3-m-long sediment core from the Penzi-la pass, Zanskar Valley, provides a record of hydroclimatic conditions and abrupt climate changes over short time scales since the mid-Holocene. These climatic changes of centennial time scale are crucial to understanding the hydroclimatic variability in northwestern (NW) Himalaya. Relatively higher δ13C values complemented by total organic carbon, loss on ignition, grain size parameters, and lower Rubidium/Strontium ratios during the Late Northgrippian imply that the area had a dry climate during the period from ~6200–4500 cal yr BP. Subsequently, a relatively stable hydroclimatic environment was experienced between ~4500 and 3400 cal yr BP. After ~3400 cal yr BP the multiproxy data show gradual strengthening of hydroclimatic conditions, however, this trend is interrupted by high-amplitude abrupt reversals (dry events) with a stepwise decreasing intensity at ~3300, 2600, 1700, and 400 cal yr BP. The two most important climatic events of the last millennia (i.e., Medieval Climate Anomaly and the Little Ice Age) were also recorded from the sedimentary archive. Overall, our data show a progressive increase in the moisture availability in the Zanskar Valley and are in agreement with the late Holocene climatic trends of central and western Himalaya. [ABSTRACT FROM AUTHOR]

The lakes of the Himalaya are degrading due to increase in toxic heavy metal loading. This study reports the last 50-year heavy metal pollution loading in the Rewalsar Lake, Himachal Pradesh, India. Sediment cores were recovered to study the pollution loading in the lake sediments. The Cs and Pb isotope-based sedimentation rate suggest rapid sedimentation in the lake during the last ~50 years. The concentrations of Mn, Cu, Zn, Cd, Pb, Co, Ni, Cr metals in the lake sediments owe its contributions both to the natural and anthropogenic sources. Prior to ca 1990 AD, metal loading was dominated by the lithogenic input, whereas post ca 1990 AD the metal loading was controlled by the anthropogenic factors. The Pb concentration in the lake gradually increased during 1990-2004 and then decreased significantly till present. The higher concentration of Pb seems to be derived from the fossil fuel burning, while the Cr concentration in the lake indicates the use of fertilizer in the catchment area. The lowest concentrations of elements around ca 1990 AD seem to have occurred due to channelization of the lake feeding system. [ABSTRACT FROM AUTHOR]

In the northwestern Himalaya (Ladakh and Karakoram), the spatial and temporal changes in the late Quaternary glaciation were modulated by a combination of two contrasting moisture sources (viz., the Indian Summer Monsoon and the mid-latitude westerlies). The inferences about their relative contribution to glacier expansion are based on the ages obtained on moraines. Since the moraines suffer from poor preservation and chronological uncertainty, the present study, therefore, resorted to a near-continuous relict proglacial lake succession in order to reconstruct the continuous pattern of glacier fluctuations during Marine Isotopic Stage-2 (MIS-2). Since the AMS radiocarbon ages (both organic and inorganic matter) suffered from various complexities such as dead carbon contribution and hard water effect, the paleohydrological inferences in this study were drawn primarily based on optical ages (along with sedimentological and geochemical analysis). The proglacial lake sedimentation was modulated by the temporal changes in meltwater discharge. This is attributed to the waning and waxing of proximal valley glaciers. Evidence accrued from the lake sediment supported by the published moraine chronology suggests that valley glaciers expanded during the onset of MIS-2 and persisted until around the Last Glacial Maximum (LGM). The beginning of MIS-2 is marked by the onset of cooling (~ 30 ka), which led to a marginal advance in the glaciers. Additionally, early MIS-2 was characterised by millennial-scale climatic fluctuations. For example, a short-lived increase in humidity was observed between 30.2 ka and 29.3 ka, followed by a reversal towards a drier climate between 29.3 ka and 28.1 ka. During the early part of MIS-2, glaciers were driven by the decrease in temperature, whereas the enhanced moisture contribution during mid MIS-2 was responsible for extensive glacier growth. We hypothesise that the enhanced moisture was contributed by the mid-latitude westerlies, with subordinate contribution from the Indian Summer Monsoon (ISM). This we attribute to the southward positioning of the Intertropical Convergence Zone (ITCZ) during MIS-2. • A relict proglacial lake deposit was used to understand glacial boundary conditions. • The OSL method provided more robust chronology than the 14C method. • Evidence of MIS-2 glaciation was observed in the lacustrine sedimentation. • Increase in wetness observed during mid MIS 2 was due to enhanced westerlies. [ABSTRACT FROM AUTHOR]

• Multi-proxy based Late Holocene vegetation climate variability. • Evidence of aridity (∼3070 to 2890 cal yr BP) by high alpine dessert steppe. • Strengthening of ISM at ∼2630 to 2130 and ∼2890 to 2630 cal yr BP. • The first evidence of Cerealia at ∼2700 cal yr BP indicates human settlement. Unlike other parts of the world, the high-resolution past climate (monsoonal) record of Northwestern Himalaya is limited and such paucity of data on climatic records hinders the past climatic understanding which further reduces the possibility of future prediction. In this study, high-resolution centennial to millennial-scale regional vegetation changes and associated climatic variability (Indian Summer Monsoon) is being reconstructed from a sedimentary profile of Shakti Wetland, Ladakh Northwestern Himalaya deposited during the Late Holocene. The reconstructed climate and vegetation record is based on a multi-proxy approach which are pollen, non-pollen palynomorphs (NPP), stable isotopes (δ13C org , δ15N bulk), total organic carbon (TOC), and total nitrogen (TN) derived from sedimentary profile spanning the last ∼ 3200 cal yr BP. A substantial variability in the ISM strengths was found throughout the profile covering the time span of ∼ 3230–740 cal yr BP. The peak warm and wet condition occurred during ∼ 2890 to 2630 cal yr BP, inferred from the rise in an alpine meadow, dry steppe, and marshy taxa. This interval is characterized by relatively lower δ15N suggesting increased nitrification. The first evidence of Cerealia pollen indicated that human settlement near the study area might have initiated around ∼ 2700 cal yr BP. Pollen data show a mixed forest type vegetation from ∼ 2630–2130 cal yr BP. The increase in alpine taxa suggests a wet phase from ∼ 1280 to 740 cal yr BP which globally corresponds to the Medieval Climate Anomaly (MCA). In addition, spectral analysis on the δ13C proxy shows multiple periodicities during the last ∼ 3200 cal yr BP reinforcing the idea of solar control on climate variability of Ladakh. [ABSTRACT FROM AUTHOR]

[Display omitted] • Geochemistry of a core (0.8–7.2 kyr) from the eastern Arabian Sea was studied. • Provenance and chemical weathering show the minimal change between 7.2 and 2.6 kyr. • Changes in weathering patterns were observed during the Roman Warm Period. • Transition from oxic to reduced bottom water condition was observed since ∼4.2 kyr. Major and trace elemental geochemistry of a sediment core (SSK40/GC10; water depth ∼ 50 m) from the eastern Arabian Sea (17° 59.89123 N, 72° 22.45161 E) have been investigated to reconstruct the continental weathering pattern and ocean redox state between 7.2 and 0.8 kyr BP (kyr, hereafter). The covariations of Fe/Al with K/Al and Ti/Al ratios indicate that the western-flowing Indian rivers (e.g., Narmada, Tapi, and Mahi) and eolian supply from the Thar regions are the major sediment suppliers to this location. Factor analysis of the geochemical dataset identifies four major factors explaining about 80 % of the total variance. Down-core profiles of several detrital proxies (Fe/Al, Ti/Al, V/Al, and Co/Al) show that the sediment sources were nearly uniform until 2.6 kyr. In contrast, changes in provenance indices, K/Al ratios, and CIA* (modified Chemical Index of Alteration) have been observed in the upper part of the core. The period of these weathering changes (2.6–1.6 kyr) mostly overlaps with the Roman Warm Period, indicating a weathering-climate linkage. Variations in the Ba/Al ratios and enrichment factors of U (EF-U) and Mo (EF-Mo), along with TOC/Al, and S/Al trends, indicate a fluctuating oceanic (bottom water) redox state during the studied period. These trends point to a shift from oxic to anoxic bottom water condition since ∼4.2 kyr. The timing of this change is synchronous to the earlier reported drought phase at the beginning of the Meghalayan stage, underscoring climatic control on the bottom water redox state. [ABSTRACT FROM AUTHOR]

Stable isotopic compositions of carbon (C) and nitrogen (N) in lake sediments have the potential to decipher natural and anthropogenic influences in a region, which has undergone significant cultural changes in the recent past. In this study, using carbon (δ13C) and nitrogen (δ15N) isotopic compositions of organic matter along with C isotopic ratio of black carbon (δ13C BC) in sediments collected from a lake in the Lesser Himalaya, an attempt has been made to decipher the biogeochemical changes in the lake under natural and anthropogenic stresses along with fire history of the region. The sediment core, dated using 210Pb and 137Cs, went back to 1949 AD, where isotopic compositions and elemental ratios (TOC/TN) suggested that the lake biogeochemistry was largely controlled by in-lake primary productivity. A noticeable change in isotopic compositions and elemental ratios was observed in the early 1970s, possibly due to increased input of soil organic matter from the catchment, which coincided with the urbanization and other human interventions in the region. At the same time, a consistent increase in differences between the measured and Suess effect corrected δ13C of organic matter from the early 1970s to 2016 AD indicated towards the increased utilization of fossil fuel-induced atmospheric CO 2 by the lake biota. Also, a sudden shift in δ13C BC in the early 1970s showed an increase in fossil fuel-induced black C in the region during that time. Overall, a comparison of the current study with other lakes in the region revealed the effect of land use change and population growth on the lake biogeochemistry, which was clearly recorded in elemental contents and stable isotopic composition of different components of lake sediments. However, the response of each lake depended on the location (i.e., distance from the city) and size of the catchment. The larger lakes in the region appeared to have suffered the anthropogenic stress through both atmospheric and terrestrial routes, whereas the smaller and secluded lake, as in the present study, was largely influenced via atmospheric factors. • Evidence of natural to anthropogenic transition in lake sediments from the Himalayan region using stable isotopes. • First measurements of black carbon concentrations and isotopic compositions in lake sediment from the Indian side of the Himalaya. • Evidence of the effect of fossil fuel induced CO 2 on the biota of Himalayan lake. [ABSTRACT FROM AUTHOR]