ABSTRACT A total of 61 samples, from six vertical profiles between surface and 1800 m from the Ar... more ABSTRACT A total of 61 samples, from six vertical profiles between surface and 1800 m from the Arabian Sea, have been analysed for uranium concentration to assess its behaviour in oxic and sub-oxic waters. These samples cover a wide range of dissolved oxygen concentration, from 0.14 to 230 μM. Uranium concentration in most of the samples fall in the range of 3.2 ± 0.2 μg l–1. In general, uranium exhibits a conservative behaviour in the Arabian Sea water column and denitrification processes do not seem to influence its abundance. The mean uranium/salinity ratio in waters with dissolved oxygen 100 μM, and in waters from other oceanic regions (9.34 ± 0.56) × 10–8 g g–1. In one of the profiles (18°N, 64°E) collected during summer monsoon (SK115/6; August 1996), two samples from 300 and 600 m have uranium concentration ∼10–15% lower than that expected based on salinity. Further studies are needed to confirm these results and to characterize the process(es) contributing to depletion of uranium at these depths.
Atmospheric transport of chemical constituents from the Indo-Gangetic Plain (IGP) to the Bay of B... more Atmospheric transport of chemical constituents from the Indo-Gangetic Plain (IGP) to the Bay of Bengal is a conspicuous seasonal feature that occurs during the late NE-monsoon (December-March). With this perspective, aerosol composition and abundance of mineral dust have been studied during November 2009 - March 2010 from a sampling site (Kharagpur: 22.3 N, 87.3E) in the IGP, representing the atmospheric outflow to the Bay of Bengal. The chemical composition of PM2.5 suggests the dominance of nss-SO42- (6.9 – 24.3 µg m-3); whereas the abundance of mineral dust varied from 3 to 18 µg m-3. The concentration of aerosol iron (FeTot) and its fractional solubility (Fews % = Fews/FeTot *100, where Fews is the water-soluble fraction of FeTot) varied from 60 to 1144 ng m-3 and from 6.7 to 26.5 %, respectively. A striking similarity in the temporal variability of total inorganic acidity (TIA = NO3- + nss-SO42-) and Fews (%) provides evidence for acid processing of mineral dust (alluvium) during atmospheric transport from the IGP. The contribution of TIA to water-soluble inorganic species [(nss-SO42- + NO3-)/ΣWSIS], mass ratios of Ca/Al and Fe/Al, abundance of dust (%) and Fews (%) in the IGP-outflow are similar to the aerosol composition over the Bay of Bengal. With the rapid increase in anthropogenic activities over south and south-east Asia, the enhanced fractional solubility of aerosol iron (attributed to acid processing of mineral dust) has implications to further increase the air-sea deposition of Fe to the surface ocean.
ABSTRACT We report here temporal changes in the measured oceanic geochemical properties of the Ar... more ABSTRACT We report here 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 nearly two decades earlier in 1977 and 1978. Observed differences are interpreted in terms of plausible changes in environment and climate that have occurred in response to natural or anthropogenic processes. The depth-profiles of major parameters such as dissolved oxygen, CO2, major nutrients (silicate, nitrate and phosphate), 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 show a decrease in salinity by ~ 0.1 units, indicating a likely change in the evaporation-precipitation (E-P) balance. The CO2 show average increase by 8 M within the top 1200 m of the Arabian Sea. The depth-profiles of nitrate and dissolved oxygen for the central Arabian Sea stations show significant variations, while only marginal changes are seen for silicate and phosphate relative to the GEOSECS data. Decrease in 14C of surface waters is due to steady decrease in atmospheric 14C concentration since GEOSECS and 14C increase in sub-surface waters is attributed to the downward vertical diffusion of bomb-radiocarbon interpreted in terms of atmosphere to ocean transfer and lateral advection of water masses.
The High Resolution Stereo Camera (HRSC) has been orbiting the planet Mars since January 2004 onb... more The High Resolution Stereo Camera (HRSC) has been orbiting the planet Mars since January 2004 onboard the European Space Agency (ESA) Mars Express mission and delivers imagery which is being used for topographic mapping of the planet. The HRSC team has ...
U–Th decay series isotopes, δ18O and Si measurements in the river estuarine waters and sediments ... more U–Th decay series isotopes, δ18O and Si measurements in the river estuarine waters and sediments of the polluted Hooghly estuary as well as the surface waters of the Bay of Bengal, its high salinity end member, are reported. Dissolved Si indicates that there are probably two mixing regimes, dissolved U behaviour is nonconservative and δ18O behaves conservatively in the overall
ABSTRACT Laboratory inter-comparison is one of the methods used for regularly assessing the accur... more ABSTRACT Laboratory inter-comparison is one of the methods used for regularly assessing the accuracy of the analytical data produced by laboratories for particular measurements. A working group at the 2010 GEOTRACES Asia Planning Workshop in Taipei recommended that a Ra inter-comparison experiment be conducted in the surface sea water of the Asian coastal region. In May 2011, we organized the Asian Ra Inter-comparison experiment. Analytes included 223Ra, 224Ra, 226Ra, 228Ra, and 228Th. Nine laboratories joined this activity. One sample set was collected in the coastal region of the Yellow Sea, near Qingdao, China (YS1, YS2) and another in Tolo Harbor of Hong Kong (HK1, HK2). These waters are relatively high in Ra and low in suspended matter and can be considered representative of coastal waters in the region. The results show that most of the data reported by different labs is within two standard deviations of the mean. Radium extraction efficiencies based on two Mn-fiber columns attached in series averaged 95–99%. Results for 226Ra, 223Ra, and 228Th in the Asia Inter-comparison are considerably less scattered than in the GEOTRACES Atlantic Inter-comparison. For 228Ra the Asia and GEOTRACES results are similar; but for 224Ra, the Asia results are considerably more scattered than the GEOTRACES results.
Measurements of five cosmogenic 32Si vertical profiles in Atlantic waters (27°N to 60°S) are pres... more Measurements of five cosmogenic 32Si vertical profiles in Atlantic waters (27°N to 60°S) are presented. The amounts of dissolved SiO2 extracted range from 2 to 54 g; the amounts of water from which SiO2 was extracted range between 540 kg and 270,000 kg. In additon, SiO2 recovered from four surface particulate composites (64°N to 61°S) were also analyzed for 32Si.
The 228Ra concentrations of the Dead Sea waters range from 0.13 to 1.48 dpm kg-1, two to three or... more The 228Ra concentrations of the Dead Sea waters range from 0.13 to 1.48 dpm kg-1, two to three orders of magnitude higher than those of ocean waters and lake waters. However, the 228Ra/226Ra activity ratios, (0.12-1.29) × 10-2, are in the range reported for the hydrosphere. The surface waters of the Dead Sea are enriched in 228Ra by a factor of about three over the near-bottom waters. There is a factor of about two spatial variability in the mid-depth Ra concentrations at the two profile stations. The near-bottom 228Ra gradients yield vertical eddy diffusivity coefficient (K) of 2.0 and 0.4 cm2 s-1 at profile locations 1 and 2 respectively. These values are comparable to those measured in oceans and lakes.
Radiometric and compositional studies of a gravity core from the Tapti salt marsh region is repor... more Radiometric and compositional studies of a gravity core from the Tapti salt marsh region is reported. The sediment accumulation rate of 3 mm/yr. Determined by the 210Pb excess method is indicative of the apparent rate of sea level rise in the region (as a lower ...
ABSTRACT Daily variability in the chemical composition of atmospheric PM2.5 and PM10 has been stu... more ABSTRACT Daily variability in the chemical composition of atmospheric PM2.5 and PM10 has been studied from an urban site (Ahmedabad) in western India over a span of 30 days during winter. The PM2.5 and PM10 mass concentrations ranged from 32 to 106 μg m− 3 and 121 to 327 μg m− 3, respectively. On average, PM2.5 constitutes ~ 33% of PM10, indicating dominance of coarse mode aerosols in the urban atmosphere. The particulate EC and OC show higher abundances in PM2.5 (average: 3.0 ± 0.9 and 18.3 ± 5.9 μg m− 3 respectively) whereas those in PM10 are 4.4 ± 2.4 and 29.8 ± 11.2 μg m− 3 respectively. A linear increasing trend and representative OC/EC ratio of 6.2 indicate their primary source from biomass burning emissions. The water-soluble organic carbon (WSOC: 4.0–14.7 μg m− 3) and its linear relationship with K+ (0.6–1.7 μg m− 3) in PM2.5 further support biomass burning emissions as a dominant source for carbonaceous aerosol. Among water-soluble inorganic species, SO42− is the most abundant (range: 3.2–22.5 μg m− 3); almost all of it occurs in fine mode (PM2.5) and exhibits near-quantitative neutralization with NH4+ (r = 0.98, slope: 1.3). The water-soluble Ca2+ and Mg2+ mainly abundant in the coarse mode, suggest significant contribution from mineral dust. Documenting large temporal variability in the chemical composition of coarse and fine mode aerosol is essential in order to assess the changing regional emission scenario over mega-cities and their down-wind transport.
ABSTRACT A total of 61 samples, from six vertical profiles between surface and 1800 m from the Ar... more ABSTRACT A total of 61 samples, from six vertical profiles between surface and 1800 m from the Arabian Sea, have been analysed for uranium concentration to assess its behaviour in oxic and sub-oxic waters. These samples cover a wide range of dissolved oxygen concentration, from 0.14 to 230 μM. Uranium concentration in most of the samples fall in the range of 3.2 ± 0.2 μg l–1. In general, uranium exhibits a conservative behaviour in the Arabian Sea water column and denitrification processes do not seem to influence its abundance. The mean uranium/salinity ratio in waters with dissolved oxygen 100 μM, and in waters from other oceanic regions (9.34 ± 0.56) × 10–8 g g–1. In one of the profiles (18°N, 64°E) collected during summer monsoon (SK115/6; August 1996), two samples from 300 and 600 m have uranium concentration ∼10–15% lower than that expected based on salinity. Further studies are needed to confirm these results and to characterize the process(es) contributing to depletion of uranium at these depths.
Atmospheric transport of chemical constituents from the Indo-Gangetic Plain (IGP) to the Bay of B... more Atmospheric transport of chemical constituents from the Indo-Gangetic Plain (IGP) to the Bay of Bengal is a conspicuous seasonal feature that occurs during the late NE-monsoon (December-March). With this perspective, aerosol composition and abundance of mineral dust have been studied during November 2009 - March 2010 from a sampling site (Kharagpur: 22.3 N, 87.3E) in the IGP, representing the atmospheric outflow to the Bay of Bengal. The chemical composition of PM2.5 suggests the dominance of nss-SO42- (6.9 – 24.3 µg m-3); whereas the abundance of mineral dust varied from 3 to 18 µg m-3. The concentration of aerosol iron (FeTot) and its fractional solubility (Fews % = Fews/FeTot *100, where Fews is the water-soluble fraction of FeTot) varied from 60 to 1144 ng m-3 and from 6.7 to 26.5 %, respectively. A striking similarity in the temporal variability of total inorganic acidity (TIA = NO3- + nss-SO42-) and Fews (%) provides evidence for acid processing of mineral dust (alluvium) during atmospheric transport from the IGP. The contribution of TIA to water-soluble inorganic species [(nss-SO42- + NO3-)/ΣWSIS], mass ratios of Ca/Al and Fe/Al, abundance of dust (%) and Fews (%) in the IGP-outflow are similar to the aerosol composition over the Bay of Bengal. With the rapid increase in anthropogenic activities over south and south-east Asia, the enhanced fractional solubility of aerosol iron (attributed to acid processing of mineral dust) has implications to further increase the air-sea deposition of Fe to the surface ocean.
ABSTRACT We report here temporal changes in the measured oceanic geochemical properties of the Ar... more ABSTRACT We report here 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 nearly two decades earlier in 1977 and 1978. Observed differences are interpreted in terms of plausible changes in environment and climate that have occurred in response to natural or anthropogenic processes. The depth-profiles of major parameters such as dissolved oxygen, CO2, major nutrients (silicate, nitrate and phosphate), 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 show a decrease in salinity by ~ 0.1 units, indicating a likely change in the evaporation-precipitation (E-P) balance. The CO2 show average increase by 8 M within the top 1200 m of the Arabian Sea. The depth-profiles of nitrate and dissolved oxygen for the central Arabian Sea stations show significant variations, while only marginal changes are seen for silicate and phosphate relative to the GEOSECS data. Decrease in 14C of surface waters is due to steady decrease in atmospheric 14C concentration since GEOSECS and 14C increase in sub-surface waters is attributed to the downward vertical diffusion of bomb-radiocarbon interpreted in terms of atmosphere to ocean transfer and lateral advection of water masses.
The High Resolution Stereo Camera (HRSC) has been orbiting the planet Mars since January 2004 onb... more The High Resolution Stereo Camera (HRSC) has been orbiting the planet Mars since January 2004 onboard the European Space Agency (ESA) Mars Express mission and delivers imagery which is being used for topographic mapping of the planet. The HRSC team has ...
U–Th decay series isotopes, δ18O and Si measurements in the river estuarine waters and sediments ... more U–Th decay series isotopes, δ18O and Si measurements in the river estuarine waters and sediments of the polluted Hooghly estuary as well as the surface waters of the Bay of Bengal, its high salinity end member, are reported. Dissolved Si indicates that there are probably two mixing regimes, dissolved U behaviour is nonconservative and δ18O behaves conservatively in the overall
ABSTRACT Laboratory inter-comparison is one of the methods used for regularly assessing the accur... more ABSTRACT Laboratory inter-comparison is one of the methods used for regularly assessing the accuracy of the analytical data produced by laboratories for particular measurements. A working group at the 2010 GEOTRACES Asia Planning Workshop in Taipei recommended that a Ra inter-comparison experiment be conducted in the surface sea water of the Asian coastal region. In May 2011, we organized the Asian Ra Inter-comparison experiment. Analytes included 223Ra, 224Ra, 226Ra, 228Ra, and 228Th. Nine laboratories joined this activity. One sample set was collected in the coastal region of the Yellow Sea, near Qingdao, China (YS1, YS2) and another in Tolo Harbor of Hong Kong (HK1, HK2). These waters are relatively high in Ra and low in suspended matter and can be considered representative of coastal waters in the region. The results show that most of the data reported by different labs is within two standard deviations of the mean. Radium extraction efficiencies based on two Mn-fiber columns attached in series averaged 95–99%. Results for 226Ra, 223Ra, and 228Th in the Asia Inter-comparison are considerably less scattered than in the GEOTRACES Atlantic Inter-comparison. For 228Ra the Asia and GEOTRACES results are similar; but for 224Ra, the Asia results are considerably more scattered than the GEOTRACES results.
Measurements of five cosmogenic 32Si vertical profiles in Atlantic waters (27°N to 60°S) are pres... more Measurements of five cosmogenic 32Si vertical profiles in Atlantic waters (27°N to 60°S) are presented. The amounts of dissolved SiO2 extracted range from 2 to 54 g; the amounts of water from which SiO2 was extracted range between 540 kg and 270,000 kg. In additon, SiO2 recovered from four surface particulate composites (64°N to 61°S) were also analyzed for 32Si.
The 228Ra concentrations of the Dead Sea waters range from 0.13 to 1.48 dpm kg-1, two to three or... more The 228Ra concentrations of the Dead Sea waters range from 0.13 to 1.48 dpm kg-1, two to three orders of magnitude higher than those of ocean waters and lake waters. However, the 228Ra/226Ra activity ratios, (0.12-1.29) × 10-2, are in the range reported for the hydrosphere. The surface waters of the Dead Sea are enriched in 228Ra by a factor of about three over the near-bottom waters. There is a factor of about two spatial variability in the mid-depth Ra concentrations at the two profile stations. The near-bottom 228Ra gradients yield vertical eddy diffusivity coefficient (K) of 2.0 and 0.4 cm2 s-1 at profile locations 1 and 2 respectively. These values are comparable to those measured in oceans and lakes.
Radiometric and compositional studies of a gravity core from the Tapti salt marsh region is repor... more Radiometric and compositional studies of a gravity core from the Tapti salt marsh region is reported. The sediment accumulation rate of 3 mm/yr. Determined by the 210Pb excess method is indicative of the apparent rate of sea level rise in the region (as a lower ...
ABSTRACT Daily variability in the chemical composition of atmospheric PM2.5 and PM10 has been stu... more ABSTRACT Daily variability in the chemical composition of atmospheric PM2.5 and PM10 has been studied from an urban site (Ahmedabad) in western India over a span of 30 days during winter. The PM2.5 and PM10 mass concentrations ranged from 32 to 106 μg m− 3 and 121 to 327 μg m− 3, respectively. On average, PM2.5 constitutes ~ 33% of PM10, indicating dominance of coarse mode aerosols in the urban atmosphere. The particulate EC and OC show higher abundances in PM2.5 (average: 3.0 ± 0.9 and 18.3 ± 5.9 μg m− 3 respectively) whereas those in PM10 are 4.4 ± 2.4 and 29.8 ± 11.2 μg m− 3 respectively. A linear increasing trend and representative OC/EC ratio of 6.2 indicate their primary source from biomass burning emissions. The water-soluble organic carbon (WSOC: 4.0–14.7 μg m− 3) and its linear relationship with K+ (0.6–1.7 μg m− 3) in PM2.5 further support biomass burning emissions as a dominant source for carbonaceous aerosol. Among water-soluble inorganic species, SO42− is the most abundant (range: 3.2–22.5 μg m− 3); almost all of it occurs in fine mode (PM2.5) and exhibits near-quantitative neutralization with NH4+ (r = 0.98, slope: 1.3). The water-soluble Ca2+ and Mg2+ mainly abundant in the coarse mode, suggest significant contribution from mineral dust. Documenting large temporal variability in the chemical composition of coarse and fine mode aerosol is essential in order to assess the changing regional emission scenario over mega-cities and their down-wind transport.
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Papers by R. Rengarajan