A 125 years (1879–2003 CE) record of seasonal δ18O changes in a Porites lutea coral from the Lakshadweep Archipelago, southeastern Arabian Sea

Abstract

We present a high-resolution δ¹⁸O record from two cores of living massive Porites lutea, covering a time period from 1879 to 2003 CE in the southeastern Arabian Sea to understand regional climate variability. The age models were established using annual banding counts and U-Th dating technique. Results show δ¹⁸O values range from −5.45 to −4.41 ‰ and feature a monthly-resolved, decreasing δ¹⁸O trend over the entire 125 years, coinciding with a gradual increase in instrumental SST record. A marked decreasing coral-δ¹⁸O pattern was noticed for more recent years, in agreement with published coral-δ¹⁸O records from the Indian Ocean, suggesting a rapid rate of warming. The most negative δ¹⁸O (for any given year) occurs during peak summer and the least negative δ¹⁸O during peak southwest (SW) monsoon times. The seasonal δ¹⁸O amplitude lies mostly ∼0.6–0.7 ‰, indicating a combined effect of decreased sea surface temperature (SST) and increased sea surface salinity (SSS) during the SW monsoon times. Ordinary least squares linear regressions (OLS) analysis performed using the coral-δ¹⁸O and Extended Reconstructed Sea Surface Temperature (ERSST) values for three distinct time periods (1879 to 1924, 1939 to 1958 and 1988 to 2003 CE) yield the following equations: δ¹⁸O = −0.24 (±0.01) × SST (°C) + 1.9 (±0.32), δ¹⁸O = −0.29 (±0.01) × SST (°C) + 3.5 (±0.48) and δ¹⁸O = −0.25 (±0.02) × SST (°C) + 2.4 (±0.63). The coral record is characterized by a stepwise decreasing δ¹⁸O pattern and a dampening of δ¹⁸O signal during strong El-Niño Southern Oscillations years.