High-resolution Oxygen and Carbon Isotopic Records of a Modern and a Fossil Coral from the Lakshadweep Archipelago

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ABSTRACT We report here δ18O and δ13C records of a modern Porites and a fossil Favia coral from the Lakshadweep Island to decipher seasonal changes in seawater characteristics. The modern coral was obtained by underwater drilling of a live Porites colony of Kavaratti Island, whereas fossil Favia coral was collected from a nearby location of the same island. Our interpretation is mainly based on high-precision isotopic measurements of 378 samples. The skeleton δ18O values of Porites coral, representing a period of 25 years (between 1984 and 2008 AD), vary between – 5.1‰ and – 4.37‰ vs VPDB, whereas δ18O values of a >400 yrs old fossil Favia coral exhibit significantly greater δ18O values, ranging from – 4.75 to – 3.39‰ vs VPDB. A plot of δ18O time series of modern Porites coral with the available sea surface temperature (SST) record of the study area exhibits an inverse relationship between coral δ18O and regional SST changes, suggesting temperature as the dominant factor for controlling δ18O in seasonal bands of corals. Seasonal variations in δ13C values in both the scleractinian corals were probably influenced mainly by variations in δ13C of dissolved inorganic carbon (DIC). However, carbon isotopic records also indicate the effects of biological (metabolic) processes on their δ13C. The greater seasonal amplitude recorded in δ18O and δ13C values of Favia coral than in Porites coral implies a marked difference in their metabolic processes.

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