PRELIMINARY RESULTS OF CHARACTERISTICS OF DENSITY BANDS OF PORITES CORAL FROM MEIJI REEF IN NANSHA AREA

The characteristics of density bands of Porites coral from Meiji reef in Nansha area are revealed by X-radiography of coral slabs and periodical changes of δ¹⁸O and δ¹³C in the skeletons. There are three typical patterns among varied density bands of both core MJO2 and core MJO3:(1) high-density bands and low-density bands with nearly equal widths were alternately arranged, and the width of the density band pair is about 4 mm; (2) fine density bands were alternately arranged with nearly equal widths (about 4 mm width of the density band pair) on the axis of maximum growth, while multiple fine density bands merged into one high or low density band beside the growth axis with 10 mm width of the compositive density band pair; (3) the density bands both on the axis of maximum growth and beside the axis are composed of fine density bands with 7 mm width high density band and 4 mm width low density band. The variations of δ¹⁸O of core MJO3 show that the density-band arrangement in the first pattern had no annual cycles since both high and low density bands ware not related to δ¹⁸O peak or trough values. But a couple of high and low wider density bands comprising fine densities seems to be annual.