Anthropogenic contamination is damaging the fragile Western Ghats making it necessary to understa... more Anthropogenic contamination is damaging the fragile Western Ghats making it necessary to understand the historical pollution. Radiocarbon dated sediment core covering the past 753 years is investigated to reconstruct the paleoclimate and paleotoxicity in Honnamanakere Lake, southern India. Increased sedimentation, weathering, organic carbon, and clay fraction during the medieval and modern warm periods indicate stronger southwest monsoon rainfall than during the little ice age. A decrease in silt content at the core location during warm periods suggests high lake levels. Cr, Cu, Zn, Pb, Hg except Ni content is increasing from bottom to top of the core. Multivariate statistics suggest natural sources for organic carbon and weathering products, agrochemical sources for Cr, Cu, Zn, atmospheric sources for Pb and Hg, and mixed sources for Ni. The enrichment factor and geoaccumulation index are increasing from the bottom to top of the core. Cr and Ni are significantly enriched and extrem...
Centennial–scale palaeoenvironmental variability has been deduced during past eight millennia usi... more Centennial–scale palaeoenvironmental variability has been deduced during past eight millennia using multi–proxy study (textural analysis, environmental magnetic parameters, stable carbon isotopes, palynofacies and elemental concentration), from Khangok–Padam in Zanskar Valley, northwest Himalaya. The multi–proxy record from this morainal lake spanning last ~8200 cal years BP has revealed four hydroclimatic phases. The overall progressively improving hydroclimatic trend is indicated by multi proxy study: sediment size/texture (as a proxy for the energy condition and depositional environment), mineral magnetism (proxy for sediment flux or lithogenic input and lithologic variation), carbon isotope signature (δ13Corg) preserved in organic constituents of sediments (a proxy for palaeovegetation and climate change), elemental geochemistry (proxy for weathering and erosion) and selected samples for palynofacies data (a proxy for changes in biological organic matter). This improving hydrocl...
The coastal sediments in the northern Bay of Bengal has undergone contamination due to the heavy ... more The coastal sediments in the northern Bay of Bengal has undergone contamination due to the heavy metal contribution from rivers. To evaluate the status of contamination in the inner shelf region of the Bay of Bengal, a sediment core chronologically constrained using 210Pb dating technique from the northwest Bay of Bengal was investigated for several trace elements. To assess sediment quality, enrichment factor (EF), geo-accumulation index (Igeo), and Modified Nemerow Pollution Index (MPI) were derived. The influence on ecology by individual contaminants and combined contaminants was evaluated using the potential ecological risk factor (Eri) and modified ecological risk index (MRI). The single-element pollution indices indicated that the sediment has no significant pollution by individual elements. However, the multi-elemental approach shows slight pollution in the sediment core. The ecology is at low risk by contaminants present in the sediment. Comparison of the elemental values of shelf sediment with adjacent riverine and estuarine samples demonstrates the role of estuarine environment and/or high riverine flux of sediments causing either removal or dilution of trace elements during its transport from the river to the sea.
We analyzed a sediment core from the equatorial Arabian Sea, chronologically constrained by accur... more We analyzed a sediment core from the equatorial Arabian Sea, chronologically constrained by accurate accelerator mass spectrometry (AMS) radiocarbon dates on selected planktonic foraminiferal species, for paleoproductivity variations corresponding to the variations in the Indian Ocean Equatorial Westerlies (IEW). The IEW in turn are positively correlated to the Southern Oscillation Index (SOI), which is a measure of El Niño, Southwest monsoon (SWM), and east African rainfall (EAR). The productivity data show that Indian and east African rainfalls declined from 35,000 calendar yr BP up to the last glacial maximum (LGM), with the maximum El Niño frequency during the last glacial period. From ∼14,500 to ∼2000 calendar yr BP (i.e. core top), we find strengthening SWM and EAR along with declining El Niño frequency.
We provide the first continuous Indian Summer Monsoon (ISM) climate record for the higher Himalay... more 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.
The lakes of the Himalaya are degrading due to increase in toxic heavy metal loading. This study ... more 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 137Cs and 210Pb 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.
We present here radiocarbon dates obtained using a liquid scintillation system installed at the P... more We present here radiocarbon dates obtained using a liquid scintillation system installed at the Physical Research Laboratory (PRL), which has been in operation for the past three years for14C measurements of oceanographic and geochemical samples from India.
Anthropogenic contamination is damaging the fragile Western Ghats making it necessary to understa... more Anthropogenic contamination is damaging the fragile Western Ghats making it necessary to understand the historical pollution. Radiocarbon dated sediment core covering the past 753 years is investigated to reconstruct the paleoclimate and paleotoxicity in Honnamanakere Lake, southern India. Increased sedimentation, weathering, organic carbon, and clay fraction during the medieval and modern warm periods indicate stronger southwest monsoon rainfall than during the little ice age. A decrease in silt content at the core location during warm periods suggests high lake levels. Cr, Cu, Zn, Pb, Hg except Ni content is increasing from bottom to top of the core. Multivariate statistics suggest natural sources for organic carbon and weathering products, agrochemical sources for Cr, Cu, Zn, atmospheric sources for Pb and Hg, and mixed sources for Ni. The enrichment factor and geoaccumulation index are increasing from the bottom to top of the core. Cr and Ni are significantly enriched and extrem...
Centennial–scale palaeoenvironmental variability has been deduced during past eight millennia usi... more Centennial–scale palaeoenvironmental variability has been deduced during past eight millennia using multi–proxy study (textural analysis, environmental magnetic parameters, stable carbon isotopes, palynofacies and elemental concentration), from Khangok–Padam in Zanskar Valley, northwest Himalaya. The multi–proxy record from this morainal lake spanning last ~8200 cal years BP has revealed four hydroclimatic phases. The overall progressively improving hydroclimatic trend is indicated by multi proxy study: sediment size/texture (as a proxy for the energy condition and depositional environment), mineral magnetism (proxy for sediment flux or lithogenic input and lithologic variation), carbon isotope signature (δ13Corg) preserved in organic constituents of sediments (a proxy for palaeovegetation and climate change), elemental geochemistry (proxy for weathering and erosion) and selected samples for palynofacies data (a proxy for changes in biological organic matter). This improving hydrocl...
The coastal sediments in the northern Bay of Bengal has undergone contamination due to the heavy ... more The coastal sediments in the northern Bay of Bengal has undergone contamination due to the heavy metal contribution from rivers. To evaluate the status of contamination in the inner shelf region of the Bay of Bengal, a sediment core chronologically constrained using 210Pb dating technique from the northwest Bay of Bengal was investigated for several trace elements. To assess sediment quality, enrichment factor (EF), geo-accumulation index (Igeo), and Modified Nemerow Pollution Index (MPI) were derived. The influence on ecology by individual contaminants and combined contaminants was evaluated using the potential ecological risk factor (Eri) and modified ecological risk index (MRI). The single-element pollution indices indicated that the sediment has no significant pollution by individual elements. However, the multi-elemental approach shows slight pollution in the sediment core. The ecology is at low risk by contaminants present in the sediment. Comparison of the elemental values of shelf sediment with adjacent riverine and estuarine samples demonstrates the role of estuarine environment and/or high riverine flux of sediments causing either removal or dilution of trace elements during its transport from the river to the sea.
We analyzed a sediment core from the equatorial Arabian Sea, chronologically constrained by accur... more We analyzed a sediment core from the equatorial Arabian Sea, chronologically constrained by accurate accelerator mass spectrometry (AMS) radiocarbon dates on selected planktonic foraminiferal species, for paleoproductivity variations corresponding to the variations in the Indian Ocean Equatorial Westerlies (IEW). The IEW in turn are positively correlated to the Southern Oscillation Index (SOI), which is a measure of El Niño, Southwest monsoon (SWM), and east African rainfall (EAR). The productivity data show that Indian and east African rainfalls declined from 35,000 calendar yr BP up to the last glacial maximum (LGM), with the maximum El Niño frequency during the last glacial period. From ∼14,500 to ∼2000 calendar yr BP (i.e. core top), we find strengthening SWM and EAR along with declining El Niño frequency.
We provide the first continuous Indian Summer Monsoon (ISM) climate record for the higher Himalay... more 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.
The lakes of the Himalaya are degrading due to increase in toxic heavy metal loading. This study ... more 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 137Cs and 210Pb 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.
We present here radiocarbon dates obtained using a liquid scintillation system installed at the P... more We present here radiocarbon dates obtained using a liquid scintillation system installed at the Physical Research Laboratory (PRL), which has been in operation for the past three years for14C measurements of oceanographic and geochemical samples from India.
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