High-resolution carbon and oxygen isotope records from a scleractinian (Porites) coral of Lakshadweep Archipelago

A 17-year-long delta C-13 and delta O-18 record from a scleractinian coral (Porites spp.) of Bangaram island (Lakshadweep Archipelago) is based on a nearly-monthly sample interval. This live coral head of Porites spp. was recovered from the lagoon of Bangaram (Lakshadweep) island at similar to 20 m water-depth. The skeletal delta C-13 and delta O-18 values varied approximately in phase and exhibit a positive relationship with each other. High-density (monsoon) bands are characterized by enriched delta O-18 values and low-density (nonmonsoon) bands by depleted delta O-18 values. Coral delta C-13 and delta O-18 primarily reflects local oceanographic and climatic variability. The high-density bands were formed during the southwest monsoon (JuneSeptember) because of increased turbidity and cloud cover, whereas low-density bands were deposited during the non-monsoon months (October-May). Temporal changes in coral-derived sea surface temperature (SST) show a good agreement with instrumental SST record. The delta O-18 values in monsoon and non-monsoon bands are mainly due to the sea surface temperature (SST) changes, controlled by monsoon-induced upwelling and insolation changes. Coral-derived SST values clearly show warming events during summer 1993 and 1998. Spectral analysis of delta O-18 data reveals a teleconnection between the local SST and tropical Pacific climate variability. Enriched delta O-18 values for the monsoon months of 1984, 1985, 1993 and 1997 are probably indicative of cooler surface water due to the stronger upwelling at the studied location. Generally higher delta C-13 values correlate with enriched delta O-18 values of the monsoon bands. This increase in delta C-13 during the southwest monsoon months is attributed to a decrease in endosymbiotic photosynthesis. Alternatively, an increase in biological production, due to monsoon-induced upwelling, may have resulted in the delta C-13 enrichment of dissolved inorganic carbon (DIC) in surface waters. However, other possibilities, such as higher delta C-13 values due to coral mass-spawning events during monsoon times cannot be ruled out. A progressive decrease of 0.5%, in delta C-18 from 1985 to 2001 may be due to the changes inphotosynthesis and/or changing food habits from autotrophy to heterotrophy as the coral grew in size. (C) 2009 Elsevier Ltd and INQUA. All rights reserved.