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 ~l%. and is explained by changes in: a) the light intensity related to the cloudiness during monsoons and b) phytoplankton productivity.