Holocene climate forcings and lacustrine regime shifts in the Indian summer monsoon realm     

Sushma Prasad  Norbert Marwan  Deniz Eroglu  Bedartha Goswami  Praveen K. Mishra  Birgit Gaye  A. Anoop  N. Basavaiah  Martina Stebich  Arshid Jehangir 《地球表面变化过程与地形》2020,45(15):3842-3853

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.  相似文献   

Analysis and farmers’ perception of climate change in the Kashmir Valley,India     

Mahdi  S. Sheraz  Dhekale  B. S.  Jan  Rukhsana  Bhat  M. Anwar  Hussain  Ashaq  Jehangir  Intikhab Aalum  Sofi  Najeebul Rehman  Ahmed  Latief  Qureshi  Asif M. Iqbal  Aezum  Aziz Mujtaba  Bangroo  Shabir A.  Wani  Owais Ali  Bahar  F. A.  Mishra  S. K. 《Theoretical and Applied Climatology》2022,149(1-2):727-741

Theoretical and Applied Climatology - Analysis of climatic variables is important for the detection and attribution of climate change trends and has received considerable attention from researchers...  相似文献   

Environmetric and GIS techniques for hydrochemical characterization of the Dal lake,Kashmir Himalaya,India     

Shabir?A.?Khanday  Shakil?Ahmad?RomshooEmail author  Arshid?Jehangir  Arvind?Sahay  Prakash?Chauhan 《Stochastic Environmental Research and Risk Assessment (SERRA)》2018,32(11):3151-3168

This research explains the background processes responsible for the spatial distribution of hydrochemical properties of the picturesque eutrophic Himalayan Lake, Dal, located in Kashmir valley, India. Univariate and multivariate statistical analyses were used to understand the spatiotemporal variability of 18 hydrochemical parameters comprising of 12,960 observations collected from 30 sampling sites well distributed within the lake at a grid spacing of 1 km² from March 2014 to February 2016. Hierarchical cluster analysis (HCA) grouped all the sampled data into three clusters based on the hydrochemical similarities, Discriminant analysis also revealed the same clusters and patterns in the data, validating the results of HCA. Wilk’s λ quotient distribution revealed the contribution of ions, nutrients, secchi disk transparency, dissolved oxygen and pH in the formation of clusters. The results are in consonance with the Principal Component Analysis of the whole lake data and individual clusters, which showed that the variance is maximally explained by the ionic component (46.82%) followed by dissolved oxygen and pH (9.36%), nitrates and phosphates (7.33%) and Secchi disk transparency (5.98%). Spatial variability of the hydrochemistry of the lake is due to the variations in water depth, lake water dynamics, flushing rate of water, organic matter decomposition, and anthropogenic pressures within and around the Dal lake ecosystem. Overall, the water quality of the lake is unfit for drinking due to the presence of coliform bacteria in the lake waters.  相似文献   

Physical and chemical growth conditions of Ordovician organogenic deep-water dolomite concretions: implications for the δ¹⁸O of Early Palaeozoic sea water     

Reinhard Hesse  Jehangir Shah†  Shafiul Islam‡ 《Sedimentology》2004,51(3):601-625

The estimated depth of formation of authigenic dolomite concretions in the Middle Ordovician Cloridorme Formation, Quebec, ranges from < 1 m to 150–200 m below sea floor (mbsf) (mostly between < 1 and 25 mbsf), based on centre‐to‐margin variations in minus‐cement porosity (80–90% to 45–75%). Formation depths are > 350 mbsf (25–17% porosity) in the Lower Ordovician Levis Formation. Outward‐decreasing δ¹³C_VPDB values (10·2–0·8‰) suggest precipitation in the methane generation zone with an increasing contribution of light carbonate derived by advection from thermocatalytic reactions at depth. Anomalously low δ¹⁸O_VPDB values (centre‐to‐margin variations of ?0·4 to ?7·5‰) give reasonable temperatures for the concretion centres only if the δ¹⁸O of Ordovician sea water was negative (?6‰) and the bottom water was warm (> 15 °C). The 3–5‰ lower values for the concretion margins compared with the centres can be explained if, in addition, volcanic‐ash alteration, organic‐matter decomposition and/or advection of ¹⁸O‐depleted water lowered the δ¹⁸O of the pore water further by 2·0–4·0‰ during the first 25–200 m of burial. Reasonable growth temperatures for the margins of 17–20 °C are compatible with a lowering of the isotopic ratios by 1 to < 1·3‰ as a temperature effect. The systematic concentric isotope zonation of the concretions suggests that the well‐ordered near‐stoichiometric dolomite is a primary feature and not the result of recrystallization. Diagenetic dolomite beds of the Cloridorme Formation appear to have formed by coalescence of concretions, as shown by randomly sampled traverses that indicate formation at different subsurface depths. Growth of the Cloridorme dolomites was probably limited by calcium availability, at least 50% of which was derived from connate water, and the remainder by diffusion from sea water. Dolomite precipitation was favoured over calcite by very high sedimentation rates, the abundance of marine organic matter in the host sediment and a correspondingly thin sulphate reduction zone. Deep‐seated concretion growth in the Levis Formation required either internal sources for the participating ions (carbonate dissolution event) or porewater advection along faults.  相似文献   

Environmetric techniques in water quality assessment and monitoring: a case study     

Aadil Hamid  Salim Aijaz Bhat  Sami Ullah Bhat  Arshid Jehangir 《Environmental Earth Sciences》2016,75(4):321

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