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    • Keywords


      Oxygen isotope ratio; Rayleigh distillation model; IsoGSM2 prediction; rainout fraction.

    • Abstract


      Oxygen isotope ratios (¹⁸O/¹⁶O) of surface seawater and rainwater samples from the Indian Ocean region (10◦N–60◦S) during austral summer collected onboard ORV Sagar Nidhi during 2011–2013 have been measured along with salinity, sea surface temperature and relative humidity. The rainwater is isotopically lighter (by 4.6±2.70/00) compared to the equilibrium condensation of the vapour arising from the seawater at the ambient condition. The isotopic composition of the vapour at high altitude responsible for the rain formation at the sampling location is estimated from a global atmospheric water isotope model (IsoGSM2). The apparent deficit of ~5⁰/₀₀ can be explained by invoking a high degree of rainout (on average, about 70% of the overhead atmospheric moisture) during transport of the source vapour to the sampling location undergoing a Rayleigh fractionation. The required rainout fraction is higher (~80%) in the latitude belt 40◦–60◦S compared to the equatorial belt (~60%). The pattern of variation in the rainout fraction with latitude is consistent with the well-known evaporation/precipitation processes inthe Indian Ocean.

    • Author Affiliations


      K Prasanna1 2 Prosenjit Ghosh2 3 S K Bhattacharya2 P Rahul2 Kei Yoshimura4 N Anilkumar5

      1. Birbal Sahni Institute of Palaeosciences, Lucknow 226 007, India.
      2. Centre for Earth Sciences, Indian Institute of Science, Bengaluru, India.
      3. Divecha Centre for Climate Change, Indian Institute of Science, Bengaluru, India.
      4. Atmosphere and Sea Research Institute and Institute of Industrial Science, The University of Tokyo, Tokyo, Japan.
      5. National Centre for Antarctic and Ocean Research, Vasco da Gama, Goa, India.
    • Dates

    • Supplementary Material

  • Journal of Earth System Science | News

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