Ishfaq Mir - Profile on Academia.edu (original) (raw)
Papers by Ishfaq Mir
Research Square (Research Square), Jul 14, 2023
Understanding historical pollution is essential since anthropogenic contamination is destroying t... more Understanding historical pollution is essential since anthropogenic contamination is destroying the Western Ghats' delicate ecosystem. The paleotoxicity in Honnamanakere Lake, southern India, is explored using a sediment core that has been radiocarbon dated and spans the last 753 years. With the exception of Ni, the core's Cr, Cu, Zn, Pb, and Hg contents rise from bottom to top. According to multivariate statistics, the sources of Cr, Cu, and Zn are agrochemical; the sources of Pb and Hg are atmospheric emissions; and the sources of Ni are mixed. From the bottom to the top of the core, the geoaccumulation index and enrichment factor both rise. The most serious threat to the water body comes from Cr and Ni, which are greatly enriched and highly contaminated. The toxic risk indices for Cu, Zn, Pb, and Hg indicate negligible toxic risk, low toxic risk for Cr, and moderate toxic risk for Ni. The water body and its biota are at a 49% hazardous risk from heavy metals, according to the mean probable-effects-levels quotient. Heavy metal enrichment, accumulation, and toxic risks have increased in the sediment core during the past 300 years, coinciding with the anthropogenic Industrial age.
Scientific Reports
This study presents spatial distribution, sources and toxicological risks of As, Cr, Cu, Hg, Ni, ... more This study presents spatial distribution, sources and toxicological risks of As, Cr, Cu, Hg, Ni, Pb, and Zn in the surface sediments from north-western Karnataka, southern India. Heavy metals (except Hg) are 1–5 times enriched than upper continental crust. High concentration of Cr, Ni, Cu, and Zn is in the central Kudalgaon, Devarayi, and Tavargatti and in the south-western Ganeshgudi area, whereas Arsenic is enriched in the north-eastern Alnavar, Kakkeri,Tavargatti and Pb, and Hg in the north-western Kapoli, Devarayi, Manjarpal villages. The ecological risk index, toxic risk index, and mean probable-effects-levels quotient of heavy metals suggest that ~ 40% of the area is prone to very high risk especially for Cr and As to the hydrological, biological, and ecological systems. Multivariate statistical analysis suggests possible geogenic sources for Ni, Cr, Cu, and Zn and anthropogenic sources such as emissions from vehicles and agricultural sectors for As, Hg, and Pb. This study is ...
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...
Journal of Earth System Science, 2009
Systematic studies on the suspended particulate matter (SPM) measured on a seasonal cycle in the ... more Systematic studies on the suspended particulate matter (SPM) measured on a seasonal cycle in the Mandovi Estuary, Goa indicate that the average concentrations of SPM at the regular station are ∼ 20 mg/l, 5 mg/l, 19 mg/l and 5 mg/l for June-September, October-January, February-April and May, respectively. SPM exhibits low-to-moderate correlation with rainfall indicating that SPM is also influenced by other processes. Transect stations reveal that the SPM at sea-end stations of the estuary are at least two orders of magnitude greater than those at the river-end during the monsoon. Estuarine turbidity maximum (ETM) of nearly similar magnitude occurs at the same location in two periods, interrupted by a period with very low SPM concentrations. The ETM occurring in June-September is associated with low salinities; its formation is attributed to the interactions between strong southwesterly winds (5.1-5.6 ms −1) and wind-induced waves and tidal currents and, dominant easterly river flow at the mouth of the estuary. The ETM occurring in February-April is associated with high salinity and is conspicuous. The strong NW and SW winds (3.2-3.7 ms −1) and wind-driven waves and currents seem to have acted effectively at the mouth of the estuary in developing turbidity maximum. The impact of sea breeze appears nearly same as that of trade winds and cannot be underestimated in sediment resuspension and deposition.
Surface sediment geochemistry for understanding the recent sedimentary environment in northwestern Karnataka, south India
Geosciences Journal
PAGES 4 th Open Science Meeting Can South-West monsoon intensification develop a reduced condition in the Bay of Bengal sediments?
Monsoon precipitation plays an important role in the socio-economic and agriculture development i... more Monsoon precipitation plays an important role in the socio-economic and agriculture development in the Asian region. Therefore, it is important to understand the monsoon dynamics and its impact on the benthic biogeochemistry. The Bay of Bengal (BOB) receives large quantity of suspended particulate matter and fresh water discharge from the Himalayas and Indian peninsula by a number of major rivers like Ganges-Brahmaputra, Krishna, Godavari, Cauvery and Irrawadi-Salween. The northern BOB receives maximum lithogenic flux during south-west (SW) monsoon that coincides with maximum river discharge from Ganges-Brahmaputra, Krishna-Godavari. In the present study, an attempt has been made to understand the impact of intensified SW monsoonal precipitation on the behaviour of redox-sensitive elements in a sediment core. Reconstruction of paleo-redox conditions in a radiocarbon (14C) dated sediment core (SK-218/1), covering the past 45 ka (thousand calendar years), collected from the western Ba...
Comparison of late Quaternary productivity variation in two contrasting basins of northern Indian Ocean using geochemical proxies (POSTER)
Can South-West monsoon intensification develop a reduced condition in the Bay of Bengal sediments?
Monsoon precipitation plays an important role in the socio-economic and agriculture development i... more Monsoon precipitation plays an important role in the socio-economic and agriculture development in the Asian region. Therefore, it is important to understand the monsoon dynamics and its impact on the benthic biogeochemistry. The Bay of Bengal (BOB) receives large quantity of suspended particulate matter and fresh water discharge from the Himalayas and Indian peninsula by a number of major rivers like Ganges-Brahmaputra, Krishna, Godavari, Cauvery and Irrawadi-Salween. The northern BOB receives maximum lithogenic flux during south-west (SW) monsoon that coincides with maximum river discharge from Ganges-Brahmaputra, Krishna- Godavari. In the present study, an attempt has been made to understand the impact of intensified SW monsoonal precipitation on the behaviour of redox-sensitive elements in a sediment core. Reconstruction of paleo-redox conditions in a radiocarbon (14C) dated sediment core (SK-218/1), covering the past 45 ka (thousand calendar years), collected from the western Bay of Bengal (Lat: 14o 02’N; Long: 82o 00’E) at a water depth of 3307 m, has been made based on geochemical analysis of redox-sensitive elements. The high U/Th ratio, Mo enrichment, Mo/U enrichment factor ratio, negative Ce-anomaly and lower Mn/Al and Fe/Al ratio, are all indicative of prevalence of sulfidic conditions in the benthic environment from 15.2 to 4.5 ka, peaking around 9.5 ka. Another event of smaller intensity and duration appears to have occurred around 20.5 ka. At this time, the U enrichment factor (3.1) was close to the Fe (II) – Fe (III) redox boundary and Mo/U enrichment ratio was nearly half that of the seawater, suggesting the prevalence of suboxic conditions. The major event centering around 9.5 ka corresponds to the previously recorded Southwest Monsoon intensification in response to increase in northern hemisphere summer insulation. However, productivity proxies – organic carbon and nitrogen contents – do not indicate marked increase in productivity at this time. It is proposed that as a result of large increase in lithogenic material supplied from land due to southwest monsoon intensification, which is evident by the very high concentrations of Al, Zr and Hf, the flux of fresh labile organic matter reaching the seafloor was higher, the degradation of which led to anoxia in the benthic environment. There is a strong positive correlation (R2=0.97) between Mo and Zr suggesting a coupling between lithogenic flux supplied by the monsoon and development of reducing condition during intensified monsoon between 4.5ka to 15.2ka. Our results suggest that temporal variability of the ballasting effect of the terrestrially-derived material could play a key role in benthic biogeochemistry and ecology of the Bay of Bengal. On the contrary, there is no correlation between Mo and Zr (R2=0.1) from 15.2ka to 45ka (except at 20.5ka) due to weaker monsoon during that period. Therefore, present data clearly shows that monsoon intensification can develop a reducing condition in the Bay of Bengal sediments.
Quaternary International, 2012
Aluminum, Titanium and Iron are the major lithogeneous contributors to the marine sediment and th... more Aluminum, Titanium and Iron are the major lithogeneous contributors to the marine sediment and their abundance varies strikingly with the intensity of monsoonal precipitation. Al and Ti concentration in a sediment core (SK-129/GC-05) from southeastern Arabian Sea exhibit very strong positive correlation (r=0.92, n=140) suggesting their lithogenous association, whereas, Ti and Fe does not correlate so strongly (r=0.44). This suggests that part of Fe is present as structurally unsupported and is evident by two fold increased Fe/Al ratio (0.87 average) compared to upper continental crust (0.44). The presence of structurally unsupported Fe is confirmed by the sequential leaching of Fe which is associated with different fractions such as exchangeable (0.98%), carbonate (1.98%), Fe-Mn oxide (30.8%), organic carbon (4.7%) and biogenic opal (11.4%) which together constitutes nearly 50% of the bulk Fe content. There is a good correlation between time series Fe/Al and differential solar insolation suggesting warmer and humid climatic condition resulting intense weathering of hinterland rocks, associated with increased monsoonal precipitation probably decoupled soluble Fe and its transportation to southeastern Arabian Sea.
Journal of the Geological Society of India, 2013
A 4.1m long sediment core from the Eastern Arabian Sea (EAS) is studied using multiple geochemica... more A 4.1m long sediment core from the Eastern Arabian Sea (EAS) is studied using multiple geochemical proxies to understand the variation of productivity and terrigenous matter supply during the past 100 ka. The temporal variation in element concentration and fluxes of CaCO 3, organic carbon (C org) and Barium excess (Ba exc) together in general indicate a higher productivity during the cold climate and highest during the Last Glacial Maximum (LGM) in particular. This cold climate-increased productivity coupling may be attributed to the shoaling of nutricline due to enhanced convective mixing resulting from the intensified winter monsoon. Increased linear sedimentation rates and fluxes of Al, Fe, Mg, Ti, Cr, Cu, Zn, and V during the cold period also suggest increased input of terrigenous matter supporting intensified winter winds. However, the presence of large abundance of structurally unsupported elemental content (e.g.: Mg-86%, Fe-82% and Al-53%) indicate increased input of terrigenous material which was probably enhanced due to intense winter monsoon.
Chemical Geology, 2013
Reconstruction of paleo-redox conditions in a radiocarbon (14 C) dated sediment core (SK-218/1), ... more Reconstruction of paleo-redox conditions in a radiocarbon (14 C) dated sediment core (SK-218/1), covering the past 45 ka (thousand calendar years), collected from the western Bay of Bengal (Lat: 14°02′N; Long: 82°00′E) at a water depth of 3307 m, has been made based on redox-sensitive element geochemistry. The high U/Th ratio, Mo enrichment, Mo/U enrichment factor ratio, Ce/Ce* b 1 and lower Mn/Al and Fe/Al ratios, compared to upper continental crust are all indicative of prevalence of suboxic condition in the benthic environment from 15.2 ka to 4.5 ka, peaking around 9.5 ka. The suboxic condition around 9.5 ka corresponds to the previously recorded southwest (SW) monsoon intensification in response to the increase in northern hemisphere summer insulation. However, productivity proxiesorganic carbon and nitrogen contentsdo not indicate marked increase in productivity at this time. It is proposed that as a result of large increase in lithogenic material supplied from land due to SW monsoon intensification, which is evident by the very high concentration of Al, Zr and Hf, the flux of fresh labile organic matter and these might have formed dense mineral matterbiogenic aggregates which sinks rapidly to the seafloor, and the degradation of labile organic matter might have led to the development of suboxic condition in the benthic environment. There exists a strong positive correlation (r = 0.98) between Mo and Zr during 15.2 ka to 4.5 ka suggesting a coupling between suboxic condition and lithogenic flux supply by the intensified SW monsoon. Our results suggest that temporal variability of the ballasting effect of the terrestrially-derived material could play a key role in benthic biogeochemistry and ecology of the Bay of Bengal. We also provide the first record of the nitrogen isotopic composition (δ 15 N) of sedimentary organic matter in the western Bay of Bengal, a region where the mesopelagic oxygen minimum zone (OMZ) is just short of being suboxic (denitrifying) today. The sedimentary δ 15 N fluctuated considerably in the past, especially during the Marine Isotope Stage 3. Oscillations in δ 15 N were apparently in concert with those in organic carbon and nitrogen contents and could be related to climatic changes (Heinrich and Dansgaard-Oeschger events) in the North Atlantic. The Dansgaard-Oeschger 12 event appears to have exerted the most intense effect on Bay of Bengal biogeochemistry when surface productivity, as inferred from the organic carbon and nitrogen contents, was the highest recorded in the core, and the δ 15 N reached up to 6.3‰. Considering the probable dilution by isotopically light terrigenous organic matter, it would appear that OMZ of the Bay of Bengal had turned denitrifying. However, the absence of suboxic conditions in the sediments at this time suggests a decoupling of the benthic processes with those in the mesopelagic water column.
Geochemistry and granulometry as indicators of paleoclimate, weathering, and provenance of sediments for the past 1,00,000 years in the eastern Arabian Sea
Journal of Asian Earth Sciences, 2022
Journal of Earth System Science, Aug 10, 2019
Sediment geochemistry is an important tool to understand the sediment provenance and weathering. ... more Sediment geochemistry is an important tool to understand the sediment provenance and weathering. The present study describes the geochemical distribution, the provenance and the degree of weathering in surface sediments in parts of Bandipora-Ganderbal areas, Kashmir valley, western Himalaya. Following the standard operating procedure of the Geological Survey of India, high-density sediment sampling over an area of 800 km 2 of toposheet Nos. 43J/11 and 43J/12 (part) was carried during the Field Season Programme of 2014-2015. A total of 200 stream and slope wash sediment samples collected on a 2 9 2 grid pattern, covering an area of 800 km 2 and 10 numbers of duplicate samples were used in this study. An analysis of major and trace element concentrations of the sediment samples revealed significant changes corresponding to different geological formations of the area. The correlation matrix of SiO 2 , Al 2 O 3 , TiO 2 , Fe 2 O 3 , MnO, K 2 O, Th and Y showed a positive correlation with each other and negative correlation with CaO, MgO and Sr, thereby indicating two dominant geological provenances of the sediments. Two dominant geochemical patterns revealed provenances from basaltic and carbonate rock formations in the area. Furthermore, an analysis of geochemical weathering indices (chemical index of alteration and chemical index of weathering) revealed a poor (27) to moderate (78) degree of weathering in this area. This observation is further substantiated by the immaturity of the soil sediments in the area.
Poster WISC
Comparison of late Quaternary productivity variation in two contrasting basins of northern Indian... more Comparison of late Quaternary productivity variation in two contrasting basins of northern Indian Ocean using geochemical proxies (POSTER). Abstract: A 4.1m long sediment core (SK-117/GC-08) raised from a water depth of 2500 m in the Eastern Arabian Sea (EAS) (Lat: 15˚29' N; Long: 72˚51' E) is studied for variation of productivity during the last 100 ka utilizing geochemical proxies. The temporal variation in element concentration and fluxes of CaCO3, organic carbon (Corg) and Barium excess (Baexc) together in general indicate a higher productivity during the cold climate and highest during the Last Glacial Maximum in particular. This cold climate-increased productivity coupling may be attributed to the shoaling of nutricline due to enhanced convective mixing resulting from the intensified winter monsoon during cold periods. A radiocarbon dated sediment core (SK-218/1) covering the past 45 ka is collected from the western Bay of Bengal (Lat: 14° 02′N; Long: 82° 00′E) at a wa...
Paleoceanographers have used several proxies for studying paleo-productivity of the of world ocea... more Paleoceanographers have used several proxies for studying paleo-productivity of the of world ocean
basins, eg., biological measures such as microfossil, sediment organic matter, biomarkers etc.
Geochemical proxies such as organic carbon, barium and calcium carbonate components have been
widely used to reconstruct palaeo export production. However, organic carbon has its own limitation
(preservation problems).
In the present study two sediment cores each from two contrasting basins of northern Indian Ocean,
viz Eastern Arabian Sea (EAS) and Western Bay of Bengal (WBOB), both experiencing similar
forcing by seasonally reversing Indian monsoons are studied for understanding the variation in
productivity during the late Quaternary. The study is important in terms of the role of tropical Indian
Ocean in regulating atmospheric carbon-dioxide on glacial-interglacial time-scale.
Monsoon precipitation plays an important role in the socio-economic and agriculture development i... more Monsoon precipitation plays an important role in the socio-economic and agriculture development in the Asian region. Therefore, it is important to understand the monsoon dynamics and its impact on the benthic biogeochemistry. The Bay of Bengal (BOB) receives large quantity of suspended particulate matter and fresh water discharge from the Himalayas and Indian peninsula by a number of major rivers like Ganges-Brahmaputra, Krishna, Godavari, Cauvery and Irrawadi-Salween. The northern BOB receives maximum lithogenic flux during south-west (SW) monsoon that coincides with maximum river discharge from Ganges-Brahmaputra, Krishna- Godavari. In the present study, an attempt has been made to understand the impact of intensified SW monsoonal precipitation on the behaviour of redox-sensitive elements in a sediment core.
Reconstruction of paleo-redox conditions in a radiocarbon (14C) dated sediment core (SK-218/1), covering the past 45 ka (thousand calendar years), collected from the western Bay of Bengal (Lat: 14o 02’N; Long: 82o 00’E) at a water depth of 3307 m, has been made based on geochemical analysis of redox-sensitive elements. The high U/Th ratio, Mo enrichment, Mo/U enrichment factor ratio, negative Ce-anomaly and lower Mn/Al and Fe/Al ratio, are all indicative of prevalence of sulfidic conditions in the benthic environment from 15.2 to 4.5 ka, peaking around 9.5 ka. Another event of smaller intensity and duration appears to have occurred around 20.5 ka. At this time, the U enrichment factor (3.1) was close to the Fe (II) – Fe (III) redox boundary and Mo/U enrichment ratio was nearly half that of the seawater, suggesting the prevalence of suboxic conditions. The major event centering around 9.5 ka corresponds to the previously recorded Southwest Monsoon intensification in response to increase in northern hemisphere summer insulation. However, productivity proxies – organic
carbon and nitrogen contents – do not indicate marked increase in productivity at this time. It is proposed that as a result of large increase in lithogenic material supplied from land due to southwest monsoon intensification, which is evident by the very high concentrations of Al, Zr and Hf, the flux of fresh labile organic matter reaching the seafloor was higher, the degradation of which led to anoxia in the benthic environment. There is a strong positive correlation (R2=0.97) between Mo and Zr suggesting a coupling between lithogenic flux supplied by the monsoon and development of reducing condition during intensified monsoon between 4.5ka to 15.2ka. Our results suggest that temporal variability of the ballasting effect of the terrestrially-derived material could play a key role in benthic biogeochemistry and ecology of the Bay of Bengal. On the contrary, there is no correlation between Mo and Zr (R2=0.1) from 15.2ka to 45ka (except at 20.5ka) due to weaker monsoon during that period. Therefore, present data clearly shows that monsoon intensification can develop a reducing condition in the Bay of Bengal sediments.
Systematic studies on the suspended particulate matter (SPM) measured on a seasonal cycle in the ... more Systematic studies on the suspended particulate matter (SPM) measured on a seasonal cycle in
the Mandovi Estuary, Goa indicate that the average concentrations of SPM at the regular station
are ∼20mg/l, 5mg/l, 19mg/l and 5mg/l for June–September, October–January, February–April
and May, respectively. SPM exhibits low-to-moderate correlation with rainfall indicating that SPM
is also influenced by other processes. Transect stations reveal that the SPM at sea-end stations
of the estuary are at least two orders of magnitude greater than those at the river-end during
the monsoon. Estuarine turbidity maximum (ETM) of nearly similar magnitude occurs at the
same location in two periods, interrupted by a period with very low SPM concentrations. The
ETM occurring in June–September is associated with low salinities; its formation is attributed to
the interactions between strong southwesterly winds (5.1–5.6ms−1) and wind-induced waves and
tidal currents and, dominant easterly river flow at the mouth of the estuary. The ETM occurring
in February–April is associated with high salinity and is conspicuous. The strong NW and
SW winds (3.2–3.7ms−1) and wind-driven waves and currents seem to have acted effectively at
the mouth of the estuary in developing turbidity maximum. The impact of sea breeze appears
nearly same as that of trade winds and cannot be underestimated in sediment resuspension and
deposition.
A 4.1m long sediment core from the Eastern Arabian Sea (EAS) is studied using multiple geochemica... more A 4.1m long sediment core from the Eastern Arabian Sea (EAS) is studied using multiple geochemical
proxies to understand the variation of productivity and terrigenous matter supply during the past 100 ka. The temporal
variation in element concentration and fluxes of CaCO3, organic carbon (Corg) and Barium excess (Baexc), together, in
general indicate a higher productivity during the cold climate and highest during the Last Glacial Maximum (LGM) in
particular. This cold climate-increased productivity coupling may be attributed to the shoaling of nutricline due to
enhanced convective mixing resulting from the intensified winter monsoon. Increased linear sedimentation rates and
fluxes of Al, Fe, Mg, Ti, Cr, Cu, Zn, and V during the cold period also suggest increased input of terrigenous matter
supporting intensified winter winds. However, the presence of large abundance of structurally unsupported elemental
content (e.g.: Mg-86%, Fe-82% and Al-53%) indicate increased input of terrigenous material which was probably
enhanced due to intense winter monsoon.
Aluminium, titanium and iron are the major lithogeneous contributors to the marine sediment and t... more Aluminium, titanium and iron are the major lithogeneous contributors to the marine sediment and their
abundance varies strikingly with the intensity of monsoonal precipitation. Al and Ti concentrations in
a sediment core (SK-129/GC-05) from southeastern Arabian Sea exhibit a very strong positive correlation
(r¼0.92, n¼140) suggesting their lithogenous association, whereas Ti and Fe does not correlate so strongly
(r ¼ 0.44). This suggests that part of Fe is structurally unsupported, as is evident by the two-fold increased
Fe/Al ratio (0.87 average) compared to upper continental crust (0.44). The presence of structurally
unsupported Fe is confirmed by the sequential leaching of Fe which is associated with different fractions
such as exchangeable (0.98%), carbonate (1.98%), FeeMn oxide (30.8%), organic carbon (4.7%) and biogenic
opal (11.4%) which together constitutes nearly 50% of the bulk Fe content. There is a good correlation
between time series Fe/Al and differential solar insolation, suggesting warmer and humid climatic
conditions resulted in intense weathering of hinterland rocks, associated with increased monsoonal
precipitation, which probably decoupled soluble Fe and transported it to the southeastern Arabian Sea.
Research Square (Research Square), Jul 14, 2023
Understanding historical pollution is essential since anthropogenic contamination is destroying t... more Understanding historical pollution is essential since anthropogenic contamination is destroying the Western Ghats' delicate ecosystem. The paleotoxicity in Honnamanakere Lake, southern India, is explored using a sediment core that has been radiocarbon dated and spans the last 753 years. With the exception of Ni, the core's Cr, Cu, Zn, Pb, and Hg contents rise from bottom to top. According to multivariate statistics, the sources of Cr, Cu, and Zn are agrochemical; the sources of Pb and Hg are atmospheric emissions; and the sources of Ni are mixed. From the bottom to the top of the core, the geoaccumulation index and enrichment factor both rise. The most serious threat to the water body comes from Cr and Ni, which are greatly enriched and highly contaminated. The toxic risk indices for Cu, Zn, Pb, and Hg indicate negligible toxic risk, low toxic risk for Cr, and moderate toxic risk for Ni. The water body and its biota are at a 49% hazardous risk from heavy metals, according to the mean probable-effects-levels quotient. Heavy metal enrichment, accumulation, and toxic risks have increased in the sediment core during the past 300 years, coinciding with the anthropogenic Industrial age.
Scientific Reports
This study presents spatial distribution, sources and toxicological risks of As, Cr, Cu, Hg, Ni, ... more This study presents spatial distribution, sources and toxicological risks of As, Cr, Cu, Hg, Ni, Pb, and Zn in the surface sediments from north-western Karnataka, southern India. Heavy metals (except Hg) are 1–5 times enriched than upper continental crust. High concentration of Cr, Ni, Cu, and Zn is in the central Kudalgaon, Devarayi, and Tavargatti and in the south-western Ganeshgudi area, whereas Arsenic is enriched in the north-eastern Alnavar, Kakkeri,Tavargatti and Pb, and Hg in the north-western Kapoli, Devarayi, Manjarpal villages. The ecological risk index, toxic risk index, and mean probable-effects-levels quotient of heavy metals suggest that ~ 40% of the area is prone to very high risk especially for Cr and As to the hydrological, biological, and ecological systems. Multivariate statistical analysis suggests possible geogenic sources for Ni, Cr, Cu, and Zn and anthropogenic sources such as emissions from vehicles and agricultural sectors for As, Hg, and Pb. This study is ...
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...
Journal of Earth System Science, 2009
Systematic studies on the suspended particulate matter (SPM) measured on a seasonal cycle in the ... more Systematic studies on the suspended particulate matter (SPM) measured on a seasonal cycle in the Mandovi Estuary, Goa indicate that the average concentrations of SPM at the regular station are ∼ 20 mg/l, 5 mg/l, 19 mg/l and 5 mg/l for June-September, October-January, February-April and May, respectively. SPM exhibits low-to-moderate correlation with rainfall indicating that SPM is also influenced by other processes. Transect stations reveal that the SPM at sea-end stations of the estuary are at least two orders of magnitude greater than those at the river-end during the monsoon. Estuarine turbidity maximum (ETM) of nearly similar magnitude occurs at the same location in two periods, interrupted by a period with very low SPM concentrations. The ETM occurring in June-September is associated with low salinities; its formation is attributed to the interactions between strong southwesterly winds (5.1-5.6 ms −1) and wind-induced waves and tidal currents and, dominant easterly river flow at the mouth of the estuary. The ETM occurring in February-April is associated with high salinity and is conspicuous. The strong NW and SW winds (3.2-3.7 ms −1) and wind-driven waves and currents seem to have acted effectively at the mouth of the estuary in developing turbidity maximum. The impact of sea breeze appears nearly same as that of trade winds and cannot be underestimated in sediment resuspension and deposition.
Surface sediment geochemistry for understanding the recent sedimentary environment in northwestern Karnataka, south India
Geosciences Journal
PAGES 4 th Open Science Meeting Can South-West monsoon intensification develop a reduced condition in the Bay of Bengal sediments?
Monsoon precipitation plays an important role in the socio-economic and agriculture development i... more Monsoon precipitation plays an important role in the socio-economic and agriculture development in the Asian region. Therefore, it is important to understand the monsoon dynamics and its impact on the benthic biogeochemistry. The Bay of Bengal (BOB) receives large quantity of suspended particulate matter and fresh water discharge from the Himalayas and Indian peninsula by a number of major rivers like Ganges-Brahmaputra, Krishna, Godavari, Cauvery and Irrawadi-Salween. The northern BOB receives maximum lithogenic flux during south-west (SW) monsoon that coincides with maximum river discharge from Ganges-Brahmaputra, Krishna-Godavari. In the present study, an attempt has been made to understand the impact of intensified SW monsoonal precipitation on the behaviour of redox-sensitive elements in a sediment core. Reconstruction of paleo-redox conditions in a radiocarbon (14C) dated sediment core (SK-218/1), covering the past 45 ka (thousand calendar years), collected from the western Ba...
Comparison of late Quaternary productivity variation in two contrasting basins of northern Indian Ocean using geochemical proxies (POSTER)
Can South-West monsoon intensification develop a reduced condition in the Bay of Bengal sediments?
Monsoon precipitation plays an important role in the socio-economic and agriculture development i... more Monsoon precipitation plays an important role in the socio-economic and agriculture development in the Asian region. Therefore, it is important to understand the monsoon dynamics and its impact on the benthic biogeochemistry. The Bay of Bengal (BOB) receives large quantity of suspended particulate matter and fresh water discharge from the Himalayas and Indian peninsula by a number of major rivers like Ganges-Brahmaputra, Krishna, Godavari, Cauvery and Irrawadi-Salween. The northern BOB receives maximum lithogenic flux during south-west (SW) monsoon that coincides with maximum river discharge from Ganges-Brahmaputra, Krishna- Godavari. In the present study, an attempt has been made to understand the impact of intensified SW monsoonal precipitation on the behaviour of redox-sensitive elements in a sediment core. Reconstruction of paleo-redox conditions in a radiocarbon (14C) dated sediment core (SK-218/1), covering the past 45 ka (thousand calendar years), collected from the western Bay of Bengal (Lat: 14o 02’N; Long: 82o 00’E) at a water depth of 3307 m, has been made based on geochemical analysis of redox-sensitive elements. The high U/Th ratio, Mo enrichment, Mo/U enrichment factor ratio, negative Ce-anomaly and lower Mn/Al and Fe/Al ratio, are all indicative of prevalence of sulfidic conditions in the benthic environment from 15.2 to 4.5 ka, peaking around 9.5 ka. Another event of smaller intensity and duration appears to have occurred around 20.5 ka. At this time, the U enrichment factor (3.1) was close to the Fe (II) – Fe (III) redox boundary and Mo/U enrichment ratio was nearly half that of the seawater, suggesting the prevalence of suboxic conditions. The major event centering around 9.5 ka corresponds to the previously recorded Southwest Monsoon intensification in response to increase in northern hemisphere summer insulation. However, productivity proxies – organic carbon and nitrogen contents – do not indicate marked increase in productivity at this time. It is proposed that as a result of large increase in lithogenic material supplied from land due to southwest monsoon intensification, which is evident by the very high concentrations of Al, Zr and Hf, the flux of fresh labile organic matter reaching the seafloor was higher, the degradation of which led to anoxia in the benthic environment. There is a strong positive correlation (R2=0.97) between Mo and Zr suggesting a coupling between lithogenic flux supplied by the monsoon and development of reducing condition during intensified monsoon between 4.5ka to 15.2ka. Our results suggest that temporal variability of the ballasting effect of the terrestrially-derived material could play a key role in benthic biogeochemistry and ecology of the Bay of Bengal. On the contrary, there is no correlation between Mo and Zr (R2=0.1) from 15.2ka to 45ka (except at 20.5ka) due to weaker monsoon during that period. Therefore, present data clearly shows that monsoon intensification can develop a reducing condition in the Bay of Bengal sediments.
Quaternary International, 2012
Aluminum, Titanium and Iron are the major lithogeneous contributors to the marine sediment and th... more Aluminum, Titanium and Iron are the major lithogeneous contributors to the marine sediment and their abundance varies strikingly with the intensity of monsoonal precipitation. Al and Ti concentration in a sediment core (SK-129/GC-05) from southeastern Arabian Sea exhibit very strong positive correlation (r=0.92, n=140) suggesting their lithogenous association, whereas, Ti and Fe does not correlate so strongly (r=0.44). This suggests that part of Fe is present as structurally unsupported and is evident by two fold increased Fe/Al ratio (0.87 average) compared to upper continental crust (0.44). The presence of structurally unsupported Fe is confirmed by the sequential leaching of Fe which is associated with different fractions such as exchangeable (0.98%), carbonate (1.98%), Fe-Mn oxide (30.8%), organic carbon (4.7%) and biogenic opal (11.4%) which together constitutes nearly 50% of the bulk Fe content. There is a good correlation between time series Fe/Al and differential solar insolation suggesting warmer and humid climatic condition resulting intense weathering of hinterland rocks, associated with increased monsoonal precipitation probably decoupled soluble Fe and its transportation to southeastern Arabian Sea.
Journal of the Geological Society of India, 2013
A 4.1m long sediment core from the Eastern Arabian Sea (EAS) is studied using multiple geochemica... more A 4.1m long sediment core from the Eastern Arabian Sea (EAS) is studied using multiple geochemical proxies to understand the variation of productivity and terrigenous matter supply during the past 100 ka. The temporal variation in element concentration and fluxes of CaCO 3, organic carbon (C org) and Barium excess (Ba exc) together in general indicate a higher productivity during the cold climate and highest during the Last Glacial Maximum (LGM) in particular. This cold climate-increased productivity coupling may be attributed to the shoaling of nutricline due to enhanced convective mixing resulting from the intensified winter monsoon. Increased linear sedimentation rates and fluxes of Al, Fe, Mg, Ti, Cr, Cu, Zn, and V during the cold period also suggest increased input of terrigenous matter supporting intensified winter winds. However, the presence of large abundance of structurally unsupported elemental content (e.g.: Mg-86%, Fe-82% and Al-53%) indicate increased input of terrigenous material which was probably enhanced due to intense winter monsoon.
Chemical Geology, 2013
Reconstruction of paleo-redox conditions in a radiocarbon (14 C) dated sediment core (SK-218/1), ... more Reconstruction of paleo-redox conditions in a radiocarbon (14 C) dated sediment core (SK-218/1), covering the past 45 ka (thousand calendar years), collected from the western Bay of Bengal (Lat: 14°02′N; Long: 82°00′E) at a water depth of 3307 m, has been made based on redox-sensitive element geochemistry. The high U/Th ratio, Mo enrichment, Mo/U enrichment factor ratio, Ce/Ce* b 1 and lower Mn/Al and Fe/Al ratios, compared to upper continental crust are all indicative of prevalence of suboxic condition in the benthic environment from 15.2 ka to 4.5 ka, peaking around 9.5 ka. The suboxic condition around 9.5 ka corresponds to the previously recorded southwest (SW) monsoon intensification in response to the increase in northern hemisphere summer insulation. However, productivity proxiesorganic carbon and nitrogen contentsdo not indicate marked increase in productivity at this time. It is proposed that as a result of large increase in lithogenic material supplied from land due to SW monsoon intensification, which is evident by the very high concentration of Al, Zr and Hf, the flux of fresh labile organic matter and these might have formed dense mineral matterbiogenic aggregates which sinks rapidly to the seafloor, and the degradation of labile organic matter might have led to the development of suboxic condition in the benthic environment. There exists a strong positive correlation (r = 0.98) between Mo and Zr during 15.2 ka to 4.5 ka suggesting a coupling between suboxic condition and lithogenic flux supply by the intensified SW monsoon. Our results suggest that temporal variability of the ballasting effect of the terrestrially-derived material could play a key role in benthic biogeochemistry and ecology of the Bay of Bengal. We also provide the first record of the nitrogen isotopic composition (δ 15 N) of sedimentary organic matter in the western Bay of Bengal, a region where the mesopelagic oxygen minimum zone (OMZ) is just short of being suboxic (denitrifying) today. The sedimentary δ 15 N fluctuated considerably in the past, especially during the Marine Isotope Stage 3. Oscillations in δ 15 N were apparently in concert with those in organic carbon and nitrogen contents and could be related to climatic changes (Heinrich and Dansgaard-Oeschger events) in the North Atlantic. The Dansgaard-Oeschger 12 event appears to have exerted the most intense effect on Bay of Bengal biogeochemistry when surface productivity, as inferred from the organic carbon and nitrogen contents, was the highest recorded in the core, and the δ 15 N reached up to 6.3‰. Considering the probable dilution by isotopically light terrigenous organic matter, it would appear that OMZ of the Bay of Bengal had turned denitrifying. However, the absence of suboxic conditions in the sediments at this time suggests a decoupling of the benthic processes with those in the mesopelagic water column.
Geochemistry and granulometry as indicators of paleoclimate, weathering, and provenance of sediments for the past 1,00,000 years in the eastern Arabian Sea
Journal of Asian Earth Sciences, 2022
Journal of Earth System Science, Aug 10, 2019
Sediment geochemistry is an important tool to understand the sediment provenance and weathering. ... more Sediment geochemistry is an important tool to understand the sediment provenance and weathering. The present study describes the geochemical distribution, the provenance and the degree of weathering in surface sediments in parts of Bandipora-Ganderbal areas, Kashmir valley, western Himalaya. Following the standard operating procedure of the Geological Survey of India, high-density sediment sampling over an area of 800 km 2 of toposheet Nos. 43J/11 and 43J/12 (part) was carried during the Field Season Programme of 2014-2015. A total of 200 stream and slope wash sediment samples collected on a 2 9 2 grid pattern, covering an area of 800 km 2 and 10 numbers of duplicate samples were used in this study. An analysis of major and trace element concentrations of the sediment samples revealed significant changes corresponding to different geological formations of the area. The correlation matrix of SiO 2 , Al 2 O 3 , TiO 2 , Fe 2 O 3 , MnO, K 2 O, Th and Y showed a positive correlation with each other and negative correlation with CaO, MgO and Sr, thereby indicating two dominant geological provenances of the sediments. Two dominant geochemical patterns revealed provenances from basaltic and carbonate rock formations in the area. Furthermore, an analysis of geochemical weathering indices (chemical index of alteration and chemical index of weathering) revealed a poor (27) to moderate (78) degree of weathering in this area. This observation is further substantiated by the immaturity of the soil sediments in the area.
Poster WISC
Comparison of late Quaternary productivity variation in two contrasting basins of northern Indian... more Comparison of late Quaternary productivity variation in two contrasting basins of northern Indian Ocean using geochemical proxies (POSTER). Abstract: A 4.1m long sediment core (SK-117/GC-08) raised from a water depth of 2500 m in the Eastern Arabian Sea (EAS) (Lat: 15˚29' N; Long: 72˚51' E) is studied for variation of productivity during the last 100 ka utilizing geochemical proxies. The temporal variation in element concentration and fluxes of CaCO3, organic carbon (Corg) and Barium excess (Baexc) together in general indicate a higher productivity during the cold climate and highest during the Last Glacial Maximum in particular. This cold climate-increased productivity coupling may be attributed to the shoaling of nutricline due to enhanced convective mixing resulting from the intensified winter monsoon during cold periods. A radiocarbon dated sediment core (SK-218/1) covering the past 45 ka is collected from the western Bay of Bengal (Lat: 14° 02′N; Long: 82° 00′E) at a wa...
Paleoceanographers have used several proxies for studying paleo-productivity of the of world ocea... more Paleoceanographers have used several proxies for studying paleo-productivity of the of world ocean
basins, eg., biological measures such as microfossil, sediment organic matter, biomarkers etc.
Geochemical proxies such as organic carbon, barium and calcium carbonate components have been
widely used to reconstruct palaeo export production. However, organic carbon has its own limitation
(preservation problems).
In the present study two sediment cores each from two contrasting basins of northern Indian Ocean,
viz Eastern Arabian Sea (EAS) and Western Bay of Bengal (WBOB), both experiencing similar
forcing by seasonally reversing Indian monsoons are studied for understanding the variation in
productivity during the late Quaternary. The study is important in terms of the role of tropical Indian
Ocean in regulating atmospheric carbon-dioxide on glacial-interglacial time-scale.
Monsoon precipitation plays an important role in the socio-economic and agriculture development i... more Monsoon precipitation plays an important role in the socio-economic and agriculture development in the Asian region. Therefore, it is important to understand the monsoon dynamics and its impact on the benthic biogeochemistry. The Bay of Bengal (BOB) receives large quantity of suspended particulate matter and fresh water discharge from the Himalayas and Indian peninsula by a number of major rivers like Ganges-Brahmaputra, Krishna, Godavari, Cauvery and Irrawadi-Salween. The northern BOB receives maximum lithogenic flux during south-west (SW) monsoon that coincides with maximum river discharge from Ganges-Brahmaputra, Krishna- Godavari. In the present study, an attempt has been made to understand the impact of intensified SW monsoonal precipitation on the behaviour of redox-sensitive elements in a sediment core.
Reconstruction of paleo-redox conditions in a radiocarbon (14C) dated sediment core (SK-218/1), covering the past 45 ka (thousand calendar years), collected from the western Bay of Bengal (Lat: 14o 02’N; Long: 82o 00’E) at a water depth of 3307 m, has been made based on geochemical analysis of redox-sensitive elements. The high U/Th ratio, Mo enrichment, Mo/U enrichment factor ratio, negative Ce-anomaly and lower Mn/Al and Fe/Al ratio, are all indicative of prevalence of sulfidic conditions in the benthic environment from 15.2 to 4.5 ka, peaking around 9.5 ka. Another event of smaller intensity and duration appears to have occurred around 20.5 ka. At this time, the U enrichment factor (3.1) was close to the Fe (II) – Fe (III) redox boundary and Mo/U enrichment ratio was nearly half that of the seawater, suggesting the prevalence of suboxic conditions. The major event centering around 9.5 ka corresponds to the previously recorded Southwest Monsoon intensification in response to increase in northern hemisphere summer insulation. However, productivity proxies – organic
carbon and nitrogen contents – do not indicate marked increase in productivity at this time. It is proposed that as a result of large increase in lithogenic material supplied from land due to southwest monsoon intensification, which is evident by the very high concentrations of Al, Zr and Hf, the flux of fresh labile organic matter reaching the seafloor was higher, the degradation of which led to anoxia in the benthic environment. There is a strong positive correlation (R2=0.97) between Mo and Zr suggesting a coupling between lithogenic flux supplied by the monsoon and development of reducing condition during intensified monsoon between 4.5ka to 15.2ka. Our results suggest that temporal variability of the ballasting effect of the terrestrially-derived material could play a key role in benthic biogeochemistry and ecology of the Bay of Bengal. On the contrary, there is no correlation between Mo and Zr (R2=0.1) from 15.2ka to 45ka (except at 20.5ka) due to weaker monsoon during that period. Therefore, present data clearly shows that monsoon intensification can develop a reducing condition in the Bay of Bengal sediments.
Systematic studies on the suspended particulate matter (SPM) measured on a seasonal cycle in the ... more Systematic studies on the suspended particulate matter (SPM) measured on a seasonal cycle in
the Mandovi Estuary, Goa indicate that the average concentrations of SPM at the regular station
are ∼20mg/l, 5mg/l, 19mg/l and 5mg/l for June–September, October–January, February–April
and May, respectively. SPM exhibits low-to-moderate correlation with rainfall indicating that SPM
is also influenced by other processes. Transect stations reveal that the SPM at sea-end stations
of the estuary are at least two orders of magnitude greater than those at the river-end during
the monsoon. Estuarine turbidity maximum (ETM) of nearly similar magnitude occurs at the
same location in two periods, interrupted by a period with very low SPM concentrations. The
ETM occurring in June–September is associated with low salinities; its formation is attributed to
the interactions between strong southwesterly winds (5.1–5.6ms−1) and wind-induced waves and
tidal currents and, dominant easterly river flow at the mouth of the estuary. The ETM occurring
in February–April is associated with high salinity and is conspicuous. The strong NW and
SW winds (3.2–3.7ms−1) and wind-driven waves and currents seem to have acted effectively at
the mouth of the estuary in developing turbidity maximum. The impact of sea breeze appears
nearly same as that of trade winds and cannot be underestimated in sediment resuspension and
deposition.
A 4.1m long sediment core from the Eastern Arabian Sea (EAS) is studied using multiple geochemica... more A 4.1m long sediment core from the Eastern Arabian Sea (EAS) is studied using multiple geochemical
proxies to understand the variation of productivity and terrigenous matter supply during the past 100 ka. The temporal
variation in element concentration and fluxes of CaCO3, organic carbon (Corg) and Barium excess (Baexc), together, in
general indicate a higher productivity during the cold climate and highest during the Last Glacial Maximum (LGM) in
particular. This cold climate-increased productivity coupling may be attributed to the shoaling of nutricline due to
enhanced convective mixing resulting from the intensified winter monsoon. Increased linear sedimentation rates and
fluxes of Al, Fe, Mg, Ti, Cr, Cu, Zn, and V during the cold period also suggest increased input of terrigenous matter
supporting intensified winter winds. However, the presence of large abundance of structurally unsupported elemental
content (e.g.: Mg-86%, Fe-82% and Al-53%) indicate increased input of terrigenous material which was probably
enhanced due to intense winter monsoon.
Aluminium, titanium and iron are the major lithogeneous contributors to the marine sediment and t... more Aluminium, titanium and iron are the major lithogeneous contributors to the marine sediment and their
abundance varies strikingly with the intensity of monsoonal precipitation. Al and Ti concentrations in
a sediment core (SK-129/GC-05) from southeastern Arabian Sea exhibit a very strong positive correlation
(r¼0.92, n¼140) suggesting their lithogenous association, whereas Ti and Fe does not correlate so strongly
(r ¼ 0.44). This suggests that part of Fe is structurally unsupported, as is evident by the two-fold increased
Fe/Al ratio (0.87 average) compared to upper continental crust (0.44). The presence of structurally
unsupported Fe is confirmed by the sequential leaching of Fe which is associated with different fractions
such as exchangeable (0.98%), carbonate (1.98%), FeeMn oxide (30.8%), organic carbon (4.7%) and biogenic
opal (11.4%) which together constitutes nearly 50% of the bulk Fe content. There is a good correlation
between time series Fe/Al and differential solar insolation, suggesting warmer and humid climatic
conditions resulted in intense weathering of hinterland rocks, associated with increased monsoonal
precipitation, which probably decoupled soluble Fe and transported it to the southeastern Arabian Sea.