Rengasamy Alagarsamy - Academia.edu (original) (raw)
Papers by Rengasamy Alagarsamy
Science of The Total Environment, 2018
We report the analysis and geographical distribution of anthropogenically impacted marine surfici... more We report the analysis and geographical distribution of anthropogenically impacted marine surficial sediments along a 3,700 km transect around the continental shelf of India. Sediments have been studied using a mixed analytical approach; high sensitivity electron paramagnetic resonance (EPR), chemical analysis and environmental magnetism. Indian coastal marine deposits are heavily influenced by monsoon rains flushing sediment of geological and anthropogenic origin out of the subcontinental river systems. That is, climatic, hydro-, geo-and anthropogenic spheres couple strongly to determine the nature of Indian coastal sediments. Enrichment of Ni, Cu and Cr is observed in shelf sediments along both east and west coasts associated with industrialised activities in major urban areas. In the Gulf of Cambay and the Krishna and Visakhapatnam deltaic regions, levels of Ni and Cr pollutants (≥ 80 and ≥ 120 ppm respectively) are observed, sufficient to cause at least medium adverse biological effects in the marine ecosystem. In these areas sediment EPR spectra differ in characteristic from those of less impacted ones. Modelling enables deconvolution of EPR spectra. In conjunction with environmental magnetism techniques, EPR has been used to characterise species composition in coastal depositional environments. Paramagnetic species can be identified and their relative concentrations determined. EPR g-values provide information about the chemical and magnetic environment of metals. We observe g-values of up to 5.5 and large g-shifts indicative of the presences of a number of para and ferrimagnetic impurities in the sediments. EPR has enabled the characterisation of species composition in coastal depositional environments, yielding marine sediment environmental 'fingerprints'. The approach demonstrates the potential of EPR spectroscopy in the mapping and evaluation of the concentration and chemical speciation in paramagnetic metals in sediments from marine shelf environments and their potential for source apportionment and environmental impact assessment.
Thirty-five surface sediment samples from the Indian continental shelf were recovered offshore fr... more Thirty-five surface sediment samples from the Indian continental shelf were recovered offshore from the mouths of the major rivers (Brahmaputra, Ganges, Narmada, Tapti, Godavari, Krishna and Cauvery) discharging into the coastal region of both east and west coast, were analysed using ICP–AES for selected major (i.e. Al, Ca, Fe, K, Ti, Mg and Na) and trace elements (e.g. Ba, Co, Cr, Cu, Ga, Ni, P and V), after total dissolution. The main objectives are to understand the processes controlling major and trace elements in the surface sediments and to identify natural and anthropogenic sources in the coastal environment using statistically regressed elemental concentrations to establish regional baseline levels. Metal enrichments observed close to the major urban areas in the east and west coast are associated with the industrialized activities areas rich in Cu and Co in both the east and west coast sediments. Normalization of metals to Al indicated that high enrichments factors in the o...
Mineral magnetic and geochemical analyses were carried out on surface sediments from the continen... more Mineral magnetic and geochemical analyses were carried out on surface sediments from the continental shelf of India. The purpose of this study is to examine the environmental assessment of heavy metal concentrations and its impact in the coastal environment using magnetic techniques and to gain an understanding on the factors controlling metal concentrations and distributions in the east and west coast of India. The strong relationships between Anhysteretic Remanent Magnetization (χARM) and heavy metals can be explained by the role of iron oxides controlling metal concentrations, though the link is also reinforced by the strong tendency of χARM to be associated with the finer particle sizes. Higher values of magnetic susceptibility, IRM20 mT and SIRM are associated with the east coast shelf sediments suggest the presence of high ferrimagnetic content, which can be derived from the weathering products of the Deccan Basalts. χARM can be used as a normalizer for particle size effects i...
The trace metal geochemistry in Indian and Chinese rivers in the Asian region was studied to unde... more The trace metal geochemistry in Indian and Chinese rivers in the Asian region was studied to understand its variation on a global scale in terms of climate, geo-logical conditions and anthropogenic impact. The average particulate trace metal concentration of Indian rivers (~300–1000 mg g–l) is higher than that of Chinese riv rs (~150–300 mg g–l) and the global average (~170–350 mg g–l). Molar ratios of alkaline and alkaline earth metals to Fe and Al (i.e. segregation factor, SF) were calculated in Indian bed sediment and in suspended matter of Chinese rivers to determine metal reactivity over the drainage basin. The segregation factors for bed sediment in Indian rivers were generally < 1, except for the Tapti ( ~ 1.7) and the Godavari (1.4) systems. Regional and watershed differences in segregation fact rs were observed, reflecting variable weathering rates due to differing mineralogy, preferential removal of alkaline and alkaline–earth metals relative to oxide-forming elements (...
The trace metal geochemistry in Indian and Chinese rivers in the Asian region was studied to unde... more The trace metal geochemistry in Indian and Chinese rivers in the Asian region was studied to understand its variation on a global scale in terms of climate, geological conditions and anthropogenic impact. The average particulate trace metal concentration of Indian rivers (-300-1000 μg h - 1 ) is higher than that of Chinese rivers (-150-300 μg g - 1 ) and the global average (-170-350 pg g - 1 ). Molar ratios of alkaline and alkaline earth metals to Fe and Al (i.e. segregation factor, SF) were calculated in Indian bed sediment and in suspended matter of Chinese rivers to determine metal reactivity over the drainage basin. The segregation factors for bed sediments in Indian rivers were generally <1, except for the Tapti (-1.7) and the Godavari (1.4) systems. Regional and watershed differences in segregation factors were observed, reflecting variable weathering rates due to differing mineralogy, preferential removal of alkaline and alkaline-earth metals relative to oxide-forming elem...
Microchemical Journal, 2010
Downcore variation of rare-earth elements (REEs) in the authigenic Fe-Mn oxides of a sediment cor... more Downcore variation of rare-earth elements (REEs) in the authigenic Fe-Mn oxides of a sediment core (covering a record of last ~40 kyr) from the Andaman Sea, a part of Indian Ocean show distinctive positive Ce and Eu anomalies. These positive Ce anomalies (Ce*=1.1~1.8) are ascribed to be due to oxidation of deep sea sediments. The large positive Eu anomalies (i.e., Eu* >1.8 to 3.2) occur within a time span near the glacial/interglacial transition (~7,000-14,000 yr BP) which could be due to the past hydrothermal activity or to the effects arising from sea level changes. During glacial times, the Andaman Sea was almost completely isolated due to low sea level, leading to a reduction in sediment supply from the Ayeyarwady river. The variations of metal abundances (i.e., Ca, Al, Mn, and Fe) in the authigenic fraction provided independent information to evaluate the water column physicochemical changes during the glacial/interglacial transition period. The studied sediment core record changes in riverine inputs and reflect depositional changes related to sea level fluctuations and climatic events over the past 40 kyr in the Andaman Sea.
The trace metal geochemistry in Indian and Chinese rivers in the Asian region was studied to unde... more The trace metal geochemistry in Indian and Chinese rivers in the Asian region was studied to understand its variation on a global scale in terms of climate, geological conditions and anthropogenic impact. The average particulate trace metal concentration of Indian rivers (~300-1000 µ µg g -l ) is higher than that of Chinese rivers (~150-300 µ µg g -l ) and the global average (~170-350 µ µg g -l ). Molar ratios of alkaline and alkaline earth metals to Fe and Al (i.e. segregation factor, SF) were calculated in Indian bed sediment and in suspended matter of Chinese rivers to determine metal reactivity over the drainage basin. The segregation factors for bed sediments in Indian rivers were generally < 1, except for the Tapti (~ 1.7) and the Godavari (1.4) systems. Regional and watershed differences in segregation factors were observed, reflecting variable weathering rates due to differing mineralogy, preferential removal of alkaline and alkaline-earth metals relative to oxide-forming elements (Fe and Al), and a regional climatic shift north to south from temperate to sub-tropical conditions. Elevated levels of lead in Chinese rivers and of cobalt and zinc in Indian rivers indicated anthropogenic inputs of these heavy metals.
In this Chapter, two sediment cores from an abyssal site, close to the base of the Oman Margin co... more In this Chapter, two sediment cores from an abyssal site, close to the base of the Oman Margin continental slope (see Figs. 3.8 i&ii) were chosen as examples of organic rich sediments underlying oxygenated waters. The Oman Margin sediments also provide a good opportunity to study the past variations in the Indian Ocean monsoon because the sediments there accumulate rapidly (>10 cm ky -1 ) and can be well dated and contain multiple proxy records of past monsoon variation (Overpeck et al.1996). In the context of the present study, the sediments were expected to be 'diagenetically-active' and therefore, to provide an ideal opportunity to study suboxic diagenesis. The chapter is divided into separate Results and Discussion sections in order to facilitate access to the data (see Appendix B in .1.1 to B.1.7.1).
Many coastal regions of India were affected by the tsunami caused by a magnitude 9 earthquake off... more Many coastal regions of India were affected by the tsunami caused by a magnitude 9 earthquake off Sumatra on 26th December 2004. This report presents the observations of post-tsunami reconnaissance survey conducted by the National Institute of Oceanography, Dona Paula, Goa, India, along the most affected coastal stretch of Tamil Nadu, Pondicherry and southern Andhra Pradesh. The surveyed coastal tract is about 450 km long and lies between Vedaranyam (Tamil Nadu) in the south and Krishnapatnam (Andhra Pradesh) in the north. The objective of the study was to observe and document the readily available and perishable data, which contains information about the nature and impact of the phenomenon. This information is expected to be helpful for planning, preparedness and identifying further research needs. To fulfill the above objective, the survey covered various aspects of tsunami such as run-up, inundation, tsunami transported sediments, tsunamigenic structural failures and other damage...
ABSTRACT Downcore variation of rare-earth elements (REEs) in the authigenic Fe-Mn oxides of a sed... more ABSTRACT Downcore variation of rare-earth elements (REEs) in the authigenic Fe-Mn oxides of a sediment core (covering a record of last ~40 kyr) from the Andaman Sea show distinctive positive Ce and Eu anomalies. These positive Ce anomalies (Ce*=~1.1 to 1.8) are ascribed to be due to oxidation of deep sea sediments, which differs significantly from other observations in the western North Atlantic. The large positive Eu anomalies (i.e., Eu* >1.8 to 3.2) occur within a time span near the glacial/interglacial transition (~7,000-14,000 yr BP) which could be due to the past hydrothermal activity or to the effects arising from sea level changes. During glacial times, the Andaman Sea was almost completely isolated due to low sea level, leading to a reduction in sediment supply from the Ayeyarwady river. The variations of metal abundances (i.e., Ca, Al, Mn, and Fe) in the authigenic fraction provided independent information to evaluate the water column physicochemical changes during the glacial/interglacial transition period. The studied sediment core record changes in riverine inputs and reflect depositional changes related to sea level fluctuations and climatic events over the past 40 kyr in the Andaman Sea.
During the austral summer 2004, an intensive multidisciplinary survey was carried out in the Indi... more During the austral summer 2004, an intensive multidisciplinary survey was carried out in the Indian Ocean sector of the Southern Ocean to study the main hydrographic features and the associated productivity processes. This sector includes circumpolar zones and fronts with distinct hydrographic and trophic regimes, such as the Subtropical Zone, Subtropical Frontal Zone, Sub Antarctic Zone, Polar Frontal Zone, Northern
Polar Record, 1992
Physico-chemical and biological studies during the austral summer of 1986–87 in the ice-edge and ... more Physico-chemical and biological studies during the austral summer of 1986–87 in the ice-edge and a region offshore of Antarctica indicated significant spatial differences in concentrations of nutrients, dissolved oxygen (DO), Ca, Mg, and chlorophyll a, and in the rates of primary production. The waters within the ice-edge region were richer in nutrients and DO and showed a four-fold increase in chlorophyll a(1.98 mg m-3) and a 10-fold increase in primary productivity (0.74 mg C m-3 h-1) as compared with offshore waters. In the ice-edge region, Mg was high (1319 mg kg-1), whereas values of Ca (421.7 mg kg-1) were within the normal range. Offshore Ca (423.8 mg kg-1) and Mg (1297 mg kg-1) were within the expected limits. In the ice-edge region, Ca/Cl varied from 0.0202 to 0.0229, with a mean of 0.0220, and Mg/Cl varied from 0.0637 to 0.0737, with a mean of 0.0687. These figures were slightly higher than those offshore (Ca/Cl: 0.0205 to 0.0224, mean 0.0214; Mg/Cl: 0.0630 to 0.0693, mean...
Microchemical Journal, 2009
ABSTRACT
Marine Pollution Bulletin, 1993
Following the enormous oil spills resulting from the 1990-91 military conflict in the Gulf, fears... more Following the enormous oil spills resulting from the 1990-91 military conflict in the Gulf, fears were expressed concerning dissipation of oil from the Gulf into the Arabian Sea and Indian Ocean. To investigate contamination of the northern Arabian Sea, two sampling cruises were undertaken during 1991. The sampling strategy was designed to investigate the most likely path of outflowing water from the Gulf. Floating tar balls were enumerated and analyses were performed to measure petroleum residues in water, sediment and biota samples. Concentrations were within the ranges reported for comparable pre-war surveys and collectively the results indicate that in the areas investigated, negligible contamination has occurred due to the Gulf oil spills. It is considered probable that the prevailing physical oceanographic conditions within the Gulf favoured containment of the spilled oil.
Marine Environmental Research, 2009
Marine Ecology Progress Series, 2009
During the austral summer 2004, an intensive multidisciplinary survey was carried out in the Indi... more During the austral summer 2004, an intensive multidisciplinary survey was carried out in the Indian Ocean sector of the Southern Ocean to study the main hydrographic features and the associated productivity processes. This sector includes circumpolar zones and fronts with distinct hydrographic and trophic regimes, such as the Subtropical Zone, Subtropical Frontal Zone, Sub Antarctic Zone, Polar Frontal Zone, Northern Subtropical Front , Agulhas Retroflection Front, Southern Subtropical Front, Subantarctic Front, Surface Polar Front, and SubSurface Polar Front. Seasonal variations in the solar irradiance and day length, stratification, lack of micronutrients like iron and increased grazing pressure are the major factors that influenced or constrained biological production in this region. Even though there are broad differences in these controlling factors in time and space between the zonal regions, the upper 1000 m of the water column of the main zones viz. (STZ, STFZ, SAZ, PFZ) supported almost identical standing stocks of mesozooplankton (0.43, 0.47, 0.45 and 0.49 ml m -3 , respectively) during the austral summer. This unexpected similarity can be explained either through the functioning of the microbial loop within STZ,STFZ and SAZ or the multivorous foodweb ecology within the PFZ. Dominance of ciliates in the microzooplankton community may be one facor resulting in the maintenance of a high mesozooplankton standing stock in SAZ. In contrast to the zones, frontal regions showed wide differences in hydrography and biological characteristics. The SSTF and SPF were far more biologically productive than that of NSTF and ARF.
Science of The Total Environment, 2018
We report the analysis and geographical distribution of anthropogenically impacted marine surfici... more We report the analysis and geographical distribution of anthropogenically impacted marine surficial sediments along a 3,700 km transect around the continental shelf of India. Sediments have been studied using a mixed analytical approach; high sensitivity electron paramagnetic resonance (EPR), chemical analysis and environmental magnetism. Indian coastal marine deposits are heavily influenced by monsoon rains flushing sediment of geological and anthropogenic origin out of the subcontinental river systems. That is, climatic, hydro-, geo-and anthropogenic spheres couple strongly to determine the nature of Indian coastal sediments. Enrichment of Ni, Cu and Cr is observed in shelf sediments along both east and west coasts associated with industrialised activities in major urban areas. In the Gulf of Cambay and the Krishna and Visakhapatnam deltaic regions, levels of Ni and Cr pollutants (≥ 80 and ≥ 120 ppm respectively) are observed, sufficient to cause at least medium adverse biological effects in the marine ecosystem. In these areas sediment EPR spectra differ in characteristic from those of less impacted ones. Modelling enables deconvolution of EPR spectra. In conjunction with environmental magnetism techniques, EPR has been used to characterise species composition in coastal depositional environments. Paramagnetic species can be identified and their relative concentrations determined. EPR g-values provide information about the chemical and magnetic environment of metals. We observe g-values of up to 5.5 and large g-shifts indicative of the presences of a number of para and ferrimagnetic impurities in the sediments. EPR has enabled the characterisation of species composition in coastal depositional environments, yielding marine sediment environmental 'fingerprints'. The approach demonstrates the potential of EPR spectroscopy in the mapping and evaluation of the concentration and chemical speciation in paramagnetic metals in sediments from marine shelf environments and their potential for source apportionment and environmental impact assessment.
Thirty-five surface sediment samples from the Indian continental shelf were recovered offshore fr... more Thirty-five surface sediment samples from the Indian continental shelf were recovered offshore from the mouths of the major rivers (Brahmaputra, Ganges, Narmada, Tapti, Godavari, Krishna and Cauvery) discharging into the coastal region of both east and west coast, were analysed using ICP–AES for selected major (i.e. Al, Ca, Fe, K, Ti, Mg and Na) and trace elements (e.g. Ba, Co, Cr, Cu, Ga, Ni, P and V), after total dissolution. The main objectives are to understand the processes controlling major and trace elements in the surface sediments and to identify natural and anthropogenic sources in the coastal environment using statistically regressed elemental concentrations to establish regional baseline levels. Metal enrichments observed close to the major urban areas in the east and west coast are associated with the industrialized activities areas rich in Cu and Co in both the east and west coast sediments. Normalization of metals to Al indicated that high enrichments factors in the o...
Mineral magnetic and geochemical analyses were carried out on surface sediments from the continen... more Mineral magnetic and geochemical analyses were carried out on surface sediments from the continental shelf of India. The purpose of this study is to examine the environmental assessment of heavy metal concentrations and its impact in the coastal environment using magnetic techniques and to gain an understanding on the factors controlling metal concentrations and distributions in the east and west coast of India. The strong relationships between Anhysteretic Remanent Magnetization (χARM) and heavy metals can be explained by the role of iron oxides controlling metal concentrations, though the link is also reinforced by the strong tendency of χARM to be associated with the finer particle sizes. Higher values of magnetic susceptibility, IRM20 mT and SIRM are associated with the east coast shelf sediments suggest the presence of high ferrimagnetic content, which can be derived from the weathering products of the Deccan Basalts. χARM can be used as a normalizer for particle size effects i...
The trace metal geochemistry in Indian and Chinese rivers in the Asian region was studied to unde... more The trace metal geochemistry in Indian and Chinese rivers in the Asian region was studied to understand its variation on a global scale in terms of climate, geo-logical conditions and anthropogenic impact. The average particulate trace metal concentration of Indian rivers (~300–1000 mg g–l) is higher than that of Chinese riv rs (~150–300 mg g–l) and the global average (~170–350 mg g–l). Molar ratios of alkaline and alkaline earth metals to Fe and Al (i.e. segregation factor, SF) were calculated in Indian bed sediment and in suspended matter of Chinese rivers to determine metal reactivity over the drainage basin. The segregation factors for bed sediment in Indian rivers were generally < 1, except for the Tapti ( ~ 1.7) and the Godavari (1.4) systems. Regional and watershed differences in segregation fact rs were observed, reflecting variable weathering rates due to differing mineralogy, preferential removal of alkaline and alkaline–earth metals relative to oxide-forming elements (...
The trace metal geochemistry in Indian and Chinese rivers in the Asian region was studied to unde... more The trace metal geochemistry in Indian and Chinese rivers in the Asian region was studied to understand its variation on a global scale in terms of climate, geological conditions and anthropogenic impact. The average particulate trace metal concentration of Indian rivers (-300-1000 μg h - 1 ) is higher than that of Chinese rivers (-150-300 μg g - 1 ) and the global average (-170-350 pg g - 1 ). Molar ratios of alkaline and alkaline earth metals to Fe and Al (i.e. segregation factor, SF) were calculated in Indian bed sediment and in suspended matter of Chinese rivers to determine metal reactivity over the drainage basin. The segregation factors for bed sediments in Indian rivers were generally <1, except for the Tapti (-1.7) and the Godavari (1.4) systems. Regional and watershed differences in segregation factors were observed, reflecting variable weathering rates due to differing mineralogy, preferential removal of alkaline and alkaline-earth metals relative to oxide-forming elem...
Microchemical Journal, 2010
Downcore variation of rare-earth elements (REEs) in the authigenic Fe-Mn oxides of a sediment cor... more Downcore variation of rare-earth elements (REEs) in the authigenic Fe-Mn oxides of a sediment core (covering a record of last ~40 kyr) from the Andaman Sea, a part of Indian Ocean show distinctive positive Ce and Eu anomalies. These positive Ce anomalies (Ce*=1.1~1.8) are ascribed to be due to oxidation of deep sea sediments. The large positive Eu anomalies (i.e., Eu* >1.8 to 3.2) occur within a time span near the glacial/interglacial transition (~7,000-14,000 yr BP) which could be due to the past hydrothermal activity or to the effects arising from sea level changes. During glacial times, the Andaman Sea was almost completely isolated due to low sea level, leading to a reduction in sediment supply from the Ayeyarwady river. The variations of metal abundances (i.e., Ca, Al, Mn, and Fe) in the authigenic fraction provided independent information to evaluate the water column physicochemical changes during the glacial/interglacial transition period. The studied sediment core record changes in riverine inputs and reflect depositional changes related to sea level fluctuations and climatic events over the past 40 kyr in the Andaman Sea.
The trace metal geochemistry in Indian and Chinese rivers in the Asian region was studied to unde... more The trace metal geochemistry in Indian and Chinese rivers in the Asian region was studied to understand its variation on a global scale in terms of climate, geological conditions and anthropogenic impact. The average particulate trace metal concentration of Indian rivers (~300-1000 µ µg g -l ) is higher than that of Chinese rivers (~150-300 µ µg g -l ) and the global average (~170-350 µ µg g -l ). Molar ratios of alkaline and alkaline earth metals to Fe and Al (i.e. segregation factor, SF) were calculated in Indian bed sediment and in suspended matter of Chinese rivers to determine metal reactivity over the drainage basin. The segregation factors for bed sediments in Indian rivers were generally < 1, except for the Tapti (~ 1.7) and the Godavari (1.4) systems. Regional and watershed differences in segregation factors were observed, reflecting variable weathering rates due to differing mineralogy, preferential removal of alkaline and alkaline-earth metals relative to oxide-forming elements (Fe and Al), and a regional climatic shift north to south from temperate to sub-tropical conditions. Elevated levels of lead in Chinese rivers and of cobalt and zinc in Indian rivers indicated anthropogenic inputs of these heavy metals.
In this Chapter, two sediment cores from an abyssal site, close to the base of the Oman Margin co... more In this Chapter, two sediment cores from an abyssal site, close to the base of the Oman Margin continental slope (see Figs. 3.8 i&ii) were chosen as examples of organic rich sediments underlying oxygenated waters. The Oman Margin sediments also provide a good opportunity to study the past variations in the Indian Ocean monsoon because the sediments there accumulate rapidly (>10 cm ky -1 ) and can be well dated and contain multiple proxy records of past monsoon variation (Overpeck et al.1996). In the context of the present study, the sediments were expected to be 'diagenetically-active' and therefore, to provide an ideal opportunity to study suboxic diagenesis. The chapter is divided into separate Results and Discussion sections in order to facilitate access to the data (see Appendix B in .1.1 to B.1.7.1).
Many coastal regions of India were affected by the tsunami caused by a magnitude 9 earthquake off... more Many coastal regions of India were affected by the tsunami caused by a magnitude 9 earthquake off Sumatra on 26th December 2004. This report presents the observations of post-tsunami reconnaissance survey conducted by the National Institute of Oceanography, Dona Paula, Goa, India, along the most affected coastal stretch of Tamil Nadu, Pondicherry and southern Andhra Pradesh. The surveyed coastal tract is about 450 km long and lies between Vedaranyam (Tamil Nadu) in the south and Krishnapatnam (Andhra Pradesh) in the north. The objective of the study was to observe and document the readily available and perishable data, which contains information about the nature and impact of the phenomenon. This information is expected to be helpful for planning, preparedness and identifying further research needs. To fulfill the above objective, the survey covered various aspects of tsunami such as run-up, inundation, tsunami transported sediments, tsunamigenic structural failures and other damage...
ABSTRACT Downcore variation of rare-earth elements (REEs) in the authigenic Fe-Mn oxides of a sed... more ABSTRACT Downcore variation of rare-earth elements (REEs) in the authigenic Fe-Mn oxides of a sediment core (covering a record of last ~40 kyr) from the Andaman Sea show distinctive positive Ce and Eu anomalies. These positive Ce anomalies (Ce*=~1.1 to 1.8) are ascribed to be due to oxidation of deep sea sediments, which differs significantly from other observations in the western North Atlantic. The large positive Eu anomalies (i.e., Eu* >1.8 to 3.2) occur within a time span near the glacial/interglacial transition (~7,000-14,000 yr BP) which could be due to the past hydrothermal activity or to the effects arising from sea level changes. During glacial times, the Andaman Sea was almost completely isolated due to low sea level, leading to a reduction in sediment supply from the Ayeyarwady river. The variations of metal abundances (i.e., Ca, Al, Mn, and Fe) in the authigenic fraction provided independent information to evaluate the water column physicochemical changes during the glacial/interglacial transition period. The studied sediment core record changes in riverine inputs and reflect depositional changes related to sea level fluctuations and climatic events over the past 40 kyr in the Andaman Sea.
During the austral summer 2004, an intensive multidisciplinary survey was carried out in the Indi... more During the austral summer 2004, an intensive multidisciplinary survey was carried out in the Indian Ocean sector of the Southern Ocean to study the main hydrographic features and the associated productivity processes. This sector includes circumpolar zones and fronts with distinct hydrographic and trophic regimes, such as the Subtropical Zone, Subtropical Frontal Zone, Sub Antarctic Zone, Polar Frontal Zone, Northern
Polar Record, 1992
Physico-chemical and biological studies during the austral summer of 1986–87 in the ice-edge and ... more Physico-chemical and biological studies during the austral summer of 1986–87 in the ice-edge and a region offshore of Antarctica indicated significant spatial differences in concentrations of nutrients, dissolved oxygen (DO), Ca, Mg, and chlorophyll a, and in the rates of primary production. The waters within the ice-edge region were richer in nutrients and DO and showed a four-fold increase in chlorophyll a(1.98 mg m-3) and a 10-fold increase in primary productivity (0.74 mg C m-3 h-1) as compared with offshore waters. In the ice-edge region, Mg was high (1319 mg kg-1), whereas values of Ca (421.7 mg kg-1) were within the normal range. Offshore Ca (423.8 mg kg-1) and Mg (1297 mg kg-1) were within the expected limits. In the ice-edge region, Ca/Cl varied from 0.0202 to 0.0229, with a mean of 0.0220, and Mg/Cl varied from 0.0637 to 0.0737, with a mean of 0.0687. These figures were slightly higher than those offshore (Ca/Cl: 0.0205 to 0.0224, mean 0.0214; Mg/Cl: 0.0630 to 0.0693, mean...
Microchemical Journal, 2009
ABSTRACT
Marine Pollution Bulletin, 1993
Following the enormous oil spills resulting from the 1990-91 military conflict in the Gulf, fears... more Following the enormous oil spills resulting from the 1990-91 military conflict in the Gulf, fears were expressed concerning dissipation of oil from the Gulf into the Arabian Sea and Indian Ocean. To investigate contamination of the northern Arabian Sea, two sampling cruises were undertaken during 1991. The sampling strategy was designed to investigate the most likely path of outflowing water from the Gulf. Floating tar balls were enumerated and analyses were performed to measure petroleum residues in water, sediment and biota samples. Concentrations were within the ranges reported for comparable pre-war surveys and collectively the results indicate that in the areas investigated, negligible contamination has occurred due to the Gulf oil spills. It is considered probable that the prevailing physical oceanographic conditions within the Gulf favoured containment of the spilled oil.
Marine Environmental Research, 2009
Marine Ecology Progress Series, 2009
During the austral summer 2004, an intensive multidisciplinary survey was carried out in the Indi... more During the austral summer 2004, an intensive multidisciplinary survey was carried out in the Indian Ocean sector of the Southern Ocean to study the main hydrographic features and the associated productivity processes. This sector includes circumpolar zones and fronts with distinct hydrographic and trophic regimes, such as the Subtropical Zone, Subtropical Frontal Zone, Sub Antarctic Zone, Polar Frontal Zone, Northern Subtropical Front , Agulhas Retroflection Front, Southern Subtropical Front, Subantarctic Front, Surface Polar Front, and SubSurface Polar Front. Seasonal variations in the solar irradiance and day length, stratification, lack of micronutrients like iron and increased grazing pressure are the major factors that influenced or constrained biological production in this region. Even though there are broad differences in these controlling factors in time and space between the zonal regions, the upper 1000 m of the water column of the main zones viz. (STZ, STFZ, SAZ, PFZ) supported almost identical standing stocks of mesozooplankton (0.43, 0.47, 0.45 and 0.49 ml m -3 , respectively) during the austral summer. This unexpected similarity can be explained either through the functioning of the microbial loop within STZ,STFZ and SAZ or the multivorous foodweb ecology within the PFZ. Dominance of ciliates in the microzooplankton community may be one facor resulting in the maintenance of a high mesozooplankton standing stock in SAZ. In contrast to the zones, frontal regions showed wide differences in hydrography and biological characteristics. The SSTF and SPF were far more biologically productive than that of NSTF and ARF.