Stable isotope variations in a coral (Favia speciosa) from the Gulf of Kutch during 1948-1989 A.D.: Environmental implications

Abstract

The stable isotopic analyses (δ18O and δ13C) of a coral Favia speciosa spanning forty two years (1948-89 A.D.), collected from the Pirotan island (22.6°N, 70°E) 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) δ18O 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 δ18O in this species of coral. The observed mean seasonal range of δ18O variations is 0.34 ± 0.17‰ (n = 42), whereas the expected range calculated (from available SST and measured δ18O of sea water) is ~ 1.1 ± 0.15‰. The difference is due to the coarse resolution of sampling, which can be corrected. The seasonal range in δ13C is ~ 1‰ and is explained by changes in: a) the light intensity related to the cloudiness during monsoons and b) phytoplankton productivity.