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 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 pattern of strain accumulation and its release during earthquakes along the eastern Himalayan... more The pattern of strain accumulation and its release during earthquakes along the eastern Himalayan syntaxis is unclear due to its structural complexity and lack of primary surface signatures associated with large-to-great earthquakes. This led to a consensus that these earthquakes occurred on blind faults. Toward understanding this issue, palaeoseismic trenching was conducted across a ~3.1 m high fault scarp preserved along the mountain front at Pasighat (95.33°E, 28.07°N). Multi-proxy radiometric dating employed to the stratigraphic units and detrital charcoals obtained from the trench exposures provide chronological constraint on the discovered palaeoearthquake surface rupture clearly suggesting that the 15(th) August, 1950 Tibet-Assam earthquake (Mw ~ 8.6) did break the eastern Himalayan front producing a co-seismic slip of 5.5 ± 0.7 meters. This study corroborates the first instance in using post-bomb radiogenic isotopes to help identify an earthquake rupture.
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.
The Bay of Bengal receives large volume of sediments discharged through seven major rivers, the l... more The Bay of Bengal receives large volume of sediments discharged through seven major rivers, the largest of them being the Ganga and the Brahmaputra River systems (G-B). These sediments preserve records of the sediment discharged from these rivers. Sediment composition of the Bay of Bengal appears to be mainly governed by three processes, viz., detrital, biogenic and diagenetic, with detrital being the dominant in this region. Their input reveals physical and chemical erosion of the terrain over which they flow and is strongly dependent on the monsoon intensity, especially the southwest or summer monsoon. The sediment deposition in the Bay of Bengal is significantly influenced by the seven rivers draining into it with major contributor being the Ganga and Brahmaputra river system. The climate is one of the major driving force incontrolling sediment deposition in the Bay of Bengal with monsoon playing a pertinent role in it. To understand these processes, chemical and isotopic measurements were carried out in several surface sediments of various cores and depth profiles of two sediment cores from the Bay of Bengal. The sediments derived from the various river sources and distributed in the Bay of Bengal should mimic the signatures of their provenance. Sr and Nd isotopic composition measured on the silicate fraction of the surface sediments show strong influence of G-B rivers in the northern Bay of Bengal with high 87 Sr/ 86 Sr (0.725-0.735) and low ∈Nd (-18 to - 12). The samples from the western Bay of Bengal show mixed signature of Sr and Nd isotopes derived mainly from the rivers draining in the western continental margin of India. The samples from the Andaman Sea have least radiogenic Sr and more radiogenic ∈Nd, supposed to be influenced by sediments from the Irrawaddy River. The sediment core studies from the Bay of Bengal suggest the supply of low radiogenic 87 Sr/ 86 Sr from the Irrawaddy River to be a likely contributor for high radiogenic ∈Nd due to an enhanced NE Monsoon during LGM.
Geochimica et Cosmochimica Acta (2015), Dec 23, 2014
The concentration of dissolved Si and its isotope composition are measured in the Bay of Bengal (... more The concentration of dissolved Si and its isotope composition are measured in the Bay of Bengal (BoB) region of the northern Indian Ocean; the isotope data are the first data set from the northern Indian Ocean. The measurements are made in eight depth profiles closely along the 87°E transect (GIO1 section of the international GEOTRACES program) and in a few samples from the northern shelf of the bay. Dissolved Si in the water column varies from ~0.6 to ~152.5 μmol/kg, whereas the δ30Si data cover a range +1.2 to +3.6 ‰. The depth profiles of dissolved Si show generally lower values in the surface increasing with depth, whereas the pattern reverses in the case of δ30Si. These vertical distribution patterns of Si and δ30Si are similar to those reported in other oceanic regions and suggestive of the significant role of biological processes in governing Si biogeochemistry in the upper layers (top ~1500 m). In contrast, dissolved Si in near surface waters of the northern shelf and the so...
This article reports temporal changes in the measured oceanic geochemical properties of the Arabi... more This article reports temporal changes in the measured oceanic geochemical properties of the Arabian Sea and the equatorial Indian Ocean by reoccupying six stations investigated during the GEOSECS expedition in 1977 and 1978. Observed differences are interpreted in terms of plausible changes in the environment and climate that have occurred in response to natural or anthropogenic processes. The depth profiles of major parameters such as dissolved oxygen, ΣCO2, major nutrients (silicates, nitrates, and phosphates), and radiocarbon in dissolved inorganic carbon were measured during the cruises between 1994 and 1998 along with temperature and salinity. Most stations in the Arabian Sea show an increase in salinity by ∼0.2 to 0.3 salinity units in the top 400 m, whereas one station in the equatorial Indian Ocean showed a decrease in salinity by ∼0.1 units, indicating a likely change in the evaporation-precipitation (E-P) balance. The ΣCO2 increased by an average of 8 μM within the top 120...
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 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 pattern of strain accumulation and its release during earthquakes along the eastern Himalayan... more The pattern of strain accumulation and its release during earthquakes along the eastern Himalayan syntaxis is unclear due to its structural complexity and lack of primary surface signatures associated with large-to-great earthquakes. This led to a consensus that these earthquakes occurred on blind faults. Toward understanding this issue, palaeoseismic trenching was conducted across a ~3.1 m high fault scarp preserved along the mountain front at Pasighat (95.33°E, 28.07°N). Multi-proxy radiometric dating employed to the stratigraphic units and detrital charcoals obtained from the trench exposures provide chronological constraint on the discovered palaeoearthquake surface rupture clearly suggesting that the 15(th) August, 1950 Tibet-Assam earthquake (Mw ~ 8.6) did break the eastern Himalayan front producing a co-seismic slip of 5.5 ± 0.7 meters. This study corroborates the first instance in using post-bomb radiogenic isotopes to help identify an earthquake rupture.
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.
The Bay of Bengal receives large volume of sediments discharged through seven major rivers, the l... more The Bay of Bengal receives large volume of sediments discharged through seven major rivers, the largest of them being the Ganga and the Brahmaputra River systems (G-B). These sediments preserve records of the sediment discharged from these rivers. Sediment composition of the Bay of Bengal appears to be mainly governed by three processes, viz., detrital, biogenic and diagenetic, with detrital being the dominant in this region. Their input reveals physical and chemical erosion of the terrain over which they flow and is strongly dependent on the monsoon intensity, especially the southwest or summer monsoon. The sediment deposition in the Bay of Bengal is significantly influenced by the seven rivers draining into it with major contributor being the Ganga and Brahmaputra river system. The climate is one of the major driving force incontrolling sediment deposition in the Bay of Bengal with monsoon playing a pertinent role in it. To understand these processes, chemical and isotopic measurements were carried out in several surface sediments of various cores and depth profiles of two sediment cores from the Bay of Bengal. The sediments derived from the various river sources and distributed in the Bay of Bengal should mimic the signatures of their provenance. Sr and Nd isotopic composition measured on the silicate fraction of the surface sediments show strong influence of G-B rivers in the northern Bay of Bengal with high 87 Sr/ 86 Sr (0.725-0.735) and low ∈Nd (-18 to - 12). The samples from the western Bay of Bengal show mixed signature of Sr and Nd isotopes derived mainly from the rivers draining in the western continental margin of India. The samples from the Andaman Sea have least radiogenic Sr and more radiogenic ∈Nd, supposed to be influenced by sediments from the Irrawaddy River. The sediment core studies from the Bay of Bengal suggest the supply of low radiogenic 87 Sr/ 86 Sr from the Irrawaddy River to be a likely contributor for high radiogenic ∈Nd due to an enhanced NE Monsoon during LGM.
Geochimica et Cosmochimica Acta (2015), Dec 23, 2014
The concentration of dissolved Si and its isotope composition are measured in the Bay of Bengal (... more The concentration of dissolved Si and its isotope composition are measured in the Bay of Bengal (BoB) region of the northern Indian Ocean; the isotope data are the first data set from the northern Indian Ocean. The measurements are made in eight depth profiles closely along the 87°E transect (GIO1 section of the international GEOTRACES program) and in a few samples from the northern shelf of the bay. Dissolved Si in the water column varies from ~0.6 to ~152.5 μmol/kg, whereas the δ30Si data cover a range +1.2 to +3.6 ‰. The depth profiles of dissolved Si show generally lower values in the surface increasing with depth, whereas the pattern reverses in the case of δ30Si. These vertical distribution patterns of Si and δ30Si are similar to those reported in other oceanic regions and suggestive of the significant role of biological processes in governing Si biogeochemistry in the upper layers (top ~1500 m). In contrast, dissolved Si in near surface waters of the northern shelf and the so...
This article reports temporal changes in the measured oceanic geochemical properties of the Arabi... more This article reports temporal changes in the measured oceanic geochemical properties of the Arabian Sea and the equatorial Indian Ocean by reoccupying six stations investigated during the GEOSECS expedition in 1977 and 1978. Observed differences are interpreted in terms of plausible changes in the environment and climate that have occurred in response to natural or anthropogenic processes. The depth profiles of major parameters such as dissolved oxygen, ΣCO2, major nutrients (silicates, nitrates, and phosphates), and radiocarbon in dissolved inorganic carbon were measured during the cruises between 1994 and 1998 along with temperature and salinity. Most stations in the Arabian Sea show an increase in salinity by ∼0.2 to 0.3 salinity units in the top 400 m, whereas one station in the equatorial Indian Ocean showed a decrease in salinity by ∼0.1 units, indicating a likely change in the evaporation-precipitation (E-P) balance. The ΣCO2 increased by an average of 8 μM within the top 120...
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