南沙美济礁滨珊瑚骨骼密度条带的变化

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

结合珊瑚骨骼X射线照片和δ18O、δ13C的年际变化,对南沙群岛美济礁滨珊瑚骨骼岩心的密度条带进行了分析,发现其密度带变化模式多样,初步可归纳为如下3种类型:(1)宽度相近的高低密度条纹均匀、相间地排列,一对高低密度条带平均宽约4 mm;(2)在骨骼主生长轴上由近于均匀分布的细密度条带组成,高低密度条带对平均宽约4 mm,但在主生长轴的两侧,多条细密度条带合成一条较宽的密度条带,高低密度条带对平均宽约10mm;(3)主生长轴上和其两侧的骨骼密度条带均由细密度条带组成,合成的高低密度条带宽分别约7和4 mm。与滨珊瑚骨骼δ18O的对比分析表明,第1种类型的细密度条带对不代表骨骼一年的伸长量,因为高低密度带和δ18O的峰值和谷值之间不存在统计学上的关系。第2种和第3种类型中由细条带组成的宽的高低密度条带对很可能是年周期性的。

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 δ^18O 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 δ^18O 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 δ^18O peak or trough values.But a couple of high and low wider density bands comprising fine densities seems to be annual.