Temperature calibration of Gulf of Mexico corals

Abstract

High-resolution proxy records of climate are limited and have poor coverage of the tropical ocean-atmosphere system. One particular area in which climate records are lacking is the northern Gulf of Mexico. Four coral cores were collected for measurement of extension, density, and isotopes ([]¹⁸O, []¹³C). The coral oxygen isotope signature was calibrated against high-resolution daily temperature and salinity data sets spanning 1990-1997. Coralline estimates of water temperature demonstrate only ~60% of the amplitude of the actual temperature range and are offset by >15°C. The amplitude reduction appears to be the result of sampling resolution in conjunction with the manner in which these corals precipitate skeletal CaCO₃. The net effect of annual skeletal extension upon the []¹⁸O isotopic signature was examined and there appears to be no relationship between summer []¹⁸O values and extension rate. However, there is a statistically significant relationship between winter []¹⁸O values and extension rate, indicating that faster coral growth leads to a higher resolution []¹⁸O temperature signal. The values of []¹⁸O lag []¹³C by about two months, coinciding well with maxima in insolation and water temperature. Overall, these corals prove to be reliable indicators of temperature change in this region.