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Mukul Sharma Current Research Interests in Isotope Geochemistry

Near surface geochemistry of osmium

Seawater Os is derived from continental weathering, hydrothermal alteration of oceanic crust and from the dissolution of cosmic dust/micrometeorites. On average, 187Os/188Os ratio of MORB and cosmic material are nearly identical (~0.130) and about ten times lower than that of continental matter (~1.26). Therefore, variations in marine osmium isotopic composition could potentially provide quantitative insights into (1) the changes in the paleo-weathering rates, (2) the variations in the cosmic dust flux to the earth, and (3) glacial-interglacial variations in the source areas of eolian dust. Understanding the aqueous geochemistry of osmium, however, had been an intractable problem due to its low abundance and multiple oxidation states in natural waters. By developing a new osmium separation technique and combining it with highly sensitive negative thermal ionization mass spectrometry, I have been able to measure the concentration and isotopic composition of osmium in the oceans, rivers, and hydrothermal fluids. These results are very exciting and show that (1) the mean residence time of osmium in the oceans is about 40,000 years and roughly 80% of Os in the oceans is derived from the continents and the rest from hydrothermal alteration of basalt and dissolution of cosmic dust, (2) contrary to the general belief the Himalayan erosion has not provided sufficient osmium to affect the osmium evolution of the oceans, and (3) there is no net flow of osmium into the oceans via high temperature alteration of oceanic crust. This work has paved the way to examine in detail the geochemistry of Os in natural waters. I am working on the following problems: (A) Determination of the behavior of Os during sub-marine alteration of basalt; (B) Osmium and Iridium transport through estuarine environment; (C) Osmium isotopes of the Arsenic-enriched groundwater of Bangladesh; (D) Behavior of Re, Os, and Pt during weathering and soil formation: coupled 187Re-187Os, 190Pt-186Os systematics of laterites.


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