Environmental significance of carbon and oxygen isotope ratios of banded corals from Lakshadweep, India

Abstract

The stable isotope ratios (δ¹⁸O and δ¹³C) of the coral Porites compressa from the Lakshadweep islands, eastern Arabian Sea, preserve environmental parameters related to monsoon-induced upwelling. The oxygen isotopic ratios in P. compressa record the seasonal drop in sea surface temperature (SST) during the monsoon season. An earlier calibration of the coralline δ¹⁸O with observed changes in SST is used to estimate past SST changes and to evaluate the relationship with upwelling and rainfall. The seasonal variations in carbon isotope ratios seem to be controlled by photosynthesis of the algal symbiont, which in turn is modulated by monsoon activities; sedimentation, sediment suspension, water current and turbidity. Both δ¹⁸O and δ¹³C in this species do reflect the monsoon clearly.