香港西贡滨珊瑚REE的地球化学特征及其与海平面变化的关系

Geochemistry of REE in a Porites coral from Sai Kung,Hong Kong and its relationship with sea level rise

用ICP-MS技术测定了位于珠江口西岸香港西贡滨珊瑚在1991～2002年(分辨率达到0.5a)的稀土元素(REE)含量。实验结果显示香港滨珊瑚REE具有Ce负异常、重稀土富集这种典型的海水相分布模式。香港滨珊瑚中REE含量处于目前已见报道中的高值范围,与巴布亚新几内亚珊瑚的REE含量相当。通过与不同地区的比较,香港珊瑚高REE含量很可能就是毗邻的珠江水体高REE的直接反映,而且同南海北缘半封闭边缘海的性质有关。香港珊瑚REE的来源主要为珠江口及其相邻的陆缘沉积物。此外,1991～2002年香港珊瑚REE含量年际下降趋势十分明显,Ce负异常和重稀土富集的程度也呈加剧的趋势,分布模式向海水相转化。REE含量与海平面的年际变化之间有显著的负相关关系(r=-0.7～-0.9),而且重稀土与海平面的相关系数优于轻稀土。上述结果揭示了热带滨珊瑚对近期全球变暖、极冰融化和海水膨胀所引起的海平面快速上升的响应。

Inductively coupled plasma mass spectrometry has been used to produce a high resolution Porites coral record of rare earth elements （REE）, from Sai Kung, Hong Kong, the west coast of Pearl River Estuary, which spans from 1991 to 2002. The distribution pattern of REE in the coral is similar to seawater, whose characteristics are Ce negative anomaly and heavy REE enrichment on the basis of standard of shale in Post-Archaean average Australian sedimentary rock （PAAS）. The REE contents in Hong Kong coral are much higher than reported results from other areas, except corals from Misima Island, Papua New Guinea, which are affected by an open-cut gold mining. The high REE contents in Hong Kong coral are a direct response to high REE contents in the Pearl River and nearby surface sedimentary deposit, indicating a severe terrestrial influence and a closed marginal sea effect. Moreover, the decreasing trend of annual REE contents in the coral from Sai Kung, Hong Kong is very apparent, with severer Ce negative anomaly and heavy REE enrichment, from 1991 to 2002. REE composition in the coral is significantly negatively correlated with sea level, and heavy REE linear correlation coefficients are better than light REE. These results are associated with sea level rising caused by globe warming and polar ice melting.