The timing of band formation and linear skeletal growth rate based on environmental changes were investigated using alizarin red S (ARS) in Porites lutea coral at Khang Khao Island, the Gulf of Thailand from November 10, 1999 to March 15, 2001. The X-radiograph of the vertical section of the Porites coral skeleton was examined and three pairs of density bandings including intermediate bandings were observed in one year, suggesting that additional factors other than sea surface temperature (SST) were associated during the process of band formation. We assumed that variation of salinity variations, nutrition/sedimentation load and light intensity may control the process of density band formation which may be influenced by the river run-off due to heavy rainfall. The coral skeleton was analyzed and measured from top to a depth of 47 mm by mass spectrometry and three cyclic changes in both oxygen and carbon isotopic values which reveal the abrupt changes of aquatic environment was observed. By using isotopic compositions, X-radiography and analyzing ARS line, the average annual growth rate of the Poritescoral was inferred at ~17.91 mm/year. Our results demonstrate that the density bands of coral and perhaps a useful proxy of extension rate could also be a potential indicator for reconstructing the past SSTs in rain-infested areas like the upper Gulf of Thailand.
Key words: Oxygen isotopes, carbon isotopes, Porites coral, density bands, skeletal growth, sea surface temperature, salinity, Khang Khao, Gulf of Thailand.
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