NOAA/WDS Paleoclimatology - Pirotan Island - Stable Isotope Data

The stable isotopic analyses (d18O and d13C) of a coral Favia speciosa spanning forty two years (1948-1989), collected from the Pirotan island(22.6 N, 70E) in the Gulf of Kutch have been carried out to assess its potential for retrieving past environmental changes in this region. It is seen that the summer (minima) d18O variations in the coral CaCO3 are negatively correlated with seasonal (summer) monsoon rainfall in the adjoining region of Kutch and Saurashtra and a qualitative reconstruction of historical rainfall variations in this region can be obtained by analyzing the d18O in this species of coral. The observed mean seasonal range of d18O variations is 0.34 +/- 0.17 per mil (n=42), whereas the expected range calculated (from available SST and measured d18O of seawater) is ~1.1 +/- 0.15 per mil. The difference is due to the coarse resolution of sampling, which can be corrected. The seasonal range ind13C is ~1 per mil and is explained by changes in: a) the light intensity related to the cloudiness during monsoons and b) phytoplankton productivity.