Indian summer monsoon variability during the last 20 kyr: Evidence from peat record from the Baspa Valley, northwest Himalaya, India (original) (raw)
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Scientific reports, 2017
We provide the first continuous Indian Summer Monsoon (ISM) climate record for the higher Himalayas (Kedarnath, India) by analyzing a (14)C-dated peat sequence covering the last ~8000 years, with ~50 years temporal resolution. The ISM variability inferred using various proxies reveal striking similarity with the Greenland ice core (GISP2) temperature record and rapid denitrification changes recorded in the sediments off Peru. The Kedarnath record provides compelling evidence for a reorganization of the global climate system taking place at ~5.5 ka BP possibly after sea level stabilization and the advent of inter-annual climate variability governed by the modern ENSO phenomenon. The ISM record also captures warm-wet and cold-dry conditions during the Medieval Climate Anomaly and Little Ice Age, respectively.
High frequency abrupt shifts in the Indian summer monsoon since Younger Dryas in the Himalaya
Scientific reports, 2018
In order to quantify the Indian summer monsoon (ISM) variability for a monsoon dominated agrarian based Indian socio-economy, we used combined high resolution δC, total organic carbon (TOC), sediment texture and environmental magnetic data of the samples from a ~3 m deep glacial outwash sedimentary profile from the Sikkim Himalaya. Our decadal to centennial scale records identified five positive and three negative excursions of the ISM since last ~13 ka. The most prominent abrupt negative ISM shift was observed during the termination of the Younger Dryas (YD) between ~11.7 and 11.4 ka. While, ISM was stable between ~11 and 6 ka, and declined prominently between 6 and 3 ka. Surprisingly, during both the Medieval Warm Period (MWP) and Little Ice age (LIA) spans, ISM was strong in this part of the Himalaya. These regional changes in ISM were coupled to southward shifting in mean position of the Intertropical Convergence Zone (ITCZ) and variations in East Asian monsoon (EAM). Our rainfa...
Quaternary Science Reviews, 2015
In contrast to the East Asian and African monsoons the Indian monsoon is still poorly documented throughout the last climatic cycle (last 135,000 years). Pollen analysis from two marine sediment cores (NGHP-01-16A and NGHP-01-19B) collected from the offshore Godavari and Mahanadi basins, both located in the Core Monsoon Zone (CMZ) reveals changes in Indian summer monsoon variability and intensity during three contrasting climatic periods: the Holocene, the Heinrich Stadial (HS) 2 and the Marine Isotopic Stage (MIS) 5/4 during the ice sheet growth transition. During the first part of the Holocene between 11,300 and 4200 cal years BP, characterized by high insolation (minimum precession, maximum obliquity), the maximum extension of the coastal forest and mangrove reflects high monsoon rainfall. This climatic regime contrasts with that of the second phase of the Holocene, from 4200 cal years BP to the present, marked by the development of drier vegetation in a context of low insolation (maximum precession, minimum obliquity). The historical period in India is characterized by an alternation of strong and weak monsoon centennial phases that may reflect the Medieval Climate Anomaly and the Little Ice Age, respectively. During the HS 2, a period of low insolation and extensive iceberg discharge in the North Atlantic Ocean, vegetation was dominated by grassland and dry flora indicating pronounced aridity as the result of a weak Indian summer monsoon. The MIS 5/4 glaciation, also associated with low insolation but moderate freshwater fluxes, was characterized by a weaker reduction of the Indian summer monsoon and a decrease of seasonal contrast as recorded by the expansion of dry vegetation and the development of Artemisia, respectively. Our results support model predictions suggesting that insolation changes control the long term trend of the Indian monsoon precipitation, but its millennial scale variability and intensity are instead modulated by atmospheric teleconnections to remote phenomena in the North Atlantic, Eurasia or the Indian Ocean.
Abrupt changes in Indian summer monsoon strength during 33,800 to 5500 years B.P
Geophysical Research Letters, 2015
Speleothem proxy records from northeastern (NE) India reflect seasonal changes in Indian summer monsoon strength as well as moisture source and transport paths. We have analyzed a new speleothem record from Mawmluh Cave, Meghalaya, India, in order to better understand these processes. The data show a strong wet phase 33,500-32,500 years B.P. followed by a weak/dry phase from 26,000 to 23,500 years B.P. and a very weak phase from 17,000 to 15,000 years B.P. The record suggests abrupt increase in strength during the Bølling-Allerød and early Holocene periods and pronounced weakening during the Heinrich and Younger Dryas cold events. We infer that these changes in monsoon strength are driven by changes in temperature gradients which drive changes in winds and moisture transport into northeast India.
Quaternary Research, 2013
A 4.9-m-thick lake sequence, formed due to the landslide damming of a stream in the semiarid Garhwal Himalaya, was studied to understand past monsoonal variations in the region. The Optically Stimulated Luminescence (OSL) chronology indicates that the lake existed between~12 and~7 ka ago. Chronologically constrained trends of sand percent, organic phosphorus (OP), apatite inorganic phosphorus (AIP) and parameters of environmental magnetism were measured in the paleolake profile. Measured proxies indicate that the Indian summer monsoon ameliorated in the early Holocene after 12 ka cooling, and it appears that all the proxies from the lake have captured this globally recognized early Holocene warming. Four phases of wet conditions (intensified monsoon) are recognized at~11.5 ka,~11-10.5 ka,~10-9 ka and~8-7 ka with maximum uncertainties of 1000 years. The wet phases are characterized by high magnetic susceptibility, increased OP and reduced AIP. In an attempt to understand the primary forcing of the sharp fluctuations in monsoonal activity in the region, we show that changes in magnetic susceptibility match variations of residual atmospheric δ 14 C, suggesting a role for solar variability as an explanation of climatic variability.
Quaternary Research, 2011
Stable isotope analysis along with radiocarbon and luminescence dating of late Pleistocene lacustrine deposits at Burfu in the higher central Himalaya are used to interpret hydrologic changes in the lake basin. From 15.5 ka to~14.5 ka the Burfu lake was largely fed by melting glaciers. A warming event at 14.5 ka suggests an enhanced monsoon and increased carbonate weathering. From~13.5 ka to~12.5 ka the isotopic data suggest large-amplitude climate variability. Following this, the isotope data suggest a short-lived, abrupt cooling event, comprising a~300-yr intense cool period followed by a~500-yr interval of moderate climate. A shift in isotope values at~11.3 ka may signify a strengthening monsoon in this region. The inferred climatic excursions appear to be correlative, at least qualitatively, with global climatic events, and perhaps the Burfu lake sequence provides regional evidence of globally recorded excursions. This study also suggests a potential use of radiocarbon ages in specific environments as a paleoenvironmental proxy.
CATENA, 2018
To understand the present day climate change impacts on ecosystem, knowledge of the rapid climatic events occurred within the last few thousand years is crucial. Indian summer monsoon (ISM) dominated eastern Himalayan vegetation is sensitive to even a minor change in climate parameters, hence suitable for studying climate-plant interactions. We reconstruct a~2400 years climatic history of the Darjeeling area, eastern Himalaya combining pollen, phytoliths, non-pollen palynomorphs (NPPs), δ 13 C signatures, sediment texture and total organic carbon (TOC) records from a lacustrine deposit to explore ecosystem response to climate change and to understand the possible forcing mechanisms behind it. This study is centred on two northern hemispheric late Holocene climatic events namely Medieval Warm Period (MWP) and Little Ice Age (LIA). Although considerable variations exist globally for these warm (moist) and cool (dry) periods with respect to their timing, duration, and hydroclimatic dynamics, our results identify a humid climatic phase at the beginning of the last millennium, a pre-MWP less humid phase, while MWP was wetter than the former phase and a wet LIA in the Darjeeling Himalaya. Our results indicate that this climatic variability also induced changes in the regional vegetation. During 364 BCE to 131 CE, the region was humid harbouring a dense broad-leaved evergreen forest; a comparatively drier condition prevailed between 131 CE and 624 might be the reason behind the thinning in the forest cover. A wet phase is observed during 1118 CE. A further increase in monsoonal strength is apparent between 1367 CE and 1802. Considering the available records from the eastern Himalaya and peninsular India it is inferred that centennial scale variations in frequencies of "active dominated" and "break-dominated" periods govern the internal dynamics of the ISM, and considered to be the key forcing mechanism behind the differential behaviour of the ISM over these regions.
We review the available reconstructions of the Indian summer and winter monsoons using well-dated natural climatic archives such as tree-rings, corals, ice-cores, speleothems and ocean sediments. Oxygen isotopic analyses of cellulose from annual growth rings of teak trees on an intra-annual scale hold high promise for reconstructing rainfall during both monsoons. Oxygen isotopic variations in corals and ice-cores seem to re-spond to atmospheric and ocean processes and may not yield direct reconstructions of monsoonal precipi-tation. Oxygen isotopic variations in speleothem and multiple proxies from ocean sediments consistently show that monsoon precipitation increased during the Holocene. The connection between insolation changes and monsoon needs to be carefully reassessed.