• D Lal

      Articles written in Journal of Earth System Science

    • Annual fallout of32Si,210Pb,22Na,35S and7Be in rains in India

      D Lal V N Nijampurkar G Rajagopalan B L K Somayajulu

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      The concentration of radioisotopes7Be,35S were measured in Bombay since 1956 and22Na,210Pb,32Si since 1963. In Khandala and other stations such measurements have been made at irregular periods since 1961. In addition several measurements especially that of32Si were made in 1970. Data available todate from Indian stations is summarised and critically analysed.

      We conclude that appreciable amounts of35S,22Na and32Si, over and above their production by cosmic rays, were produced during the high yield Russian tests as evidenced by their fallout between 1962–66. Based on the bomb produced excess the half period for their removal from the stratosphere is deduced to be less than 1 year. The ‘excess’ contribution of32Si due to bombs is, however, small; about 1% of its inventory in the oceans.

      The present study shows that for stations where orogeny is the principal mechanism of precipitation, the annual fallout is independent of the annual rainfall.

    • Particle accelerator measurements of10Be in marine accumulations: Intercomparison with beta counting method

      P Sharma B L K Somayajulu D Lal W Wolfli G Bonani Ch Stoller M Suter J Beer

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      Cosmogenic beryllium-10 activities have been measured in marine accumulations of up to ∼6 m.y age by conventional beta counting technique and by accelerator mass spectrometry. The two sets of data at10Be levels of 109–1010 atoms/g agree within the absolute errors of the two methods. The detection limit for10Be by the accelerator mass spectrometry is about five orders of magnitude lower than that with the beta counting method.

    • Tracing quartz through the environment

      D Lal J R Arnold

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      Quartz, SiO2, a pure mineral with tight crystal structure, is widespread in rocks and soil. Cosmic rays produce10Be (t1/2=1·5×106, yr) and26Al (t1/2=7·05×105 yr) in quartz exposed at or near the earth’s surface. The use of accelerator mass spectrometry permits measurement of these nuclides in samples exposed at sea level for typical periods.In situ production makes interpretation relatively straightforward. Potential applications include age determination, measurement of erosion and deposition rates, and use as a tracer for continental weathering processes.

    • Preferential solution of234U from recoil tracks and234U/238U radioactive disequilibrium in natural waters

      N Hussain D Lal

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      A mathematical model to calculate the234U/238U activity ratio (AR) in an aqueous phase in contact with rock/soil is presented. The model relies on the supply of238U by dissolution and that of234U by dissolution and preferential release from radiation damaged regions (recoil tracks). The model predicts that values of234U/238U AR>1 in the aqueous phase can be obtained only from weathering “virgin” surfaces. Thus, to account for the observed steady-state supply of234U excess to the oceans by the preferential leaching model, ‘virgin’ rock/soil surfaces would have to be continually exposed and weathered. The238U concentration and234U/238U AR in continental waters allow us to estimate the exposure rates of “virgin” rock/soil surfaces.

    • A critical analysis of processes governing the nutrient profiles in the ocean

      R Ramesh D Lal

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      We have theoretically considered the problem of interpretation of nutrient profiles in the upper ocean (100–2000m). We compare the experimental depth profiles of nonconservative tracers, both stable and radioactive, with solutions of one-dimensional steady state transport equations of increasing complexity including situations not encountered in the real oceans. Apart from gaining insight into the nutrient transport processes, this analysis is useful in offering a way to obtain operational estimates of depth dependent/independent eddy diffusivity and dissolution fluxes in the ocean. These parameters are essential for estimating new production, total production and burial of carbon in the sediments.

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