High resolution hematite and goethite records from ODP 1143, South China Sea: Co-evolution of monsoonal precipitation and El Niño over the past 600,000 years
High resolution hematite and goethite records from ODP 1143, South China Sea: Co-evolution of monsoonal precipitation and El Niño over the past 600,000 years
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DOI：
10.1016/j.epsl.2007.09.022
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发表时间：
2007-12
影响因子：
5.3
通讯作者：
Y. Zhang;J. Ji;W. Balsam;Lianwen Liu;Jun Chen
中科院分区：
文献类型：
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作者：
Y. Zhang;J. Ji;W. Balsam;Lianwen Liu;Jun Chen
在热带季风区，降水的变率比气温的变率大，是一个重要的气候变量。然而，重建的长期降雨历史是稀缺的，因为缺乏可靠的代理。在这里，我们的文件，氧化铁矿物，特别是赤铁矿针铁矿的比例（Hm/Gt），是一个合理的沉淀代理。利用漫反射分光光度法，对大洋钻探计划（ODP）1143号钻探点（9°21.72′N，113°17.11′E，水深2777 m）的样品进行了赤铁矿和针铁矿的测量。为了确定赤铁矿和针铁矿的含量，我们通过去除氧化铁以生成天然基质来产生一组校准样品，向天然基质中添加已知百分比的赤铁矿和针铁矿。从这些校准样品中，我们开发了一个传递函数，用于确定赤铁矿和针铁矿浓度从样品的光谱反射率。应用这种方法ODP 1143沉积物（顶部34米的510米的采样间隔为10厘米），我们能够重建一个连续的降水历史东南亚过去600 kyr使用Hm/Gt比作为亚洲季风的降水变化的代理。该Hm/Gt代用指标的可靠性与华南石笋δ 18 O数据的一致性得到了证实。通过比较Hm/Gt的长期记录和赤道太平洋的表面温度梯度，我们发现近600 kyr以来季风降水和厄尔尼诺现象是相关的。类似厄尔尼诺现象的发展减少了东南亚的降水，而降水则因拉尼娜现象的加剧而增加。
Precipitation has a larger variability than temperature in tropical monsoon regions, thus it is an important climate variable. However, reconstructions of long-term rainfall histories are scarce because of the lack of reliable proxies. Here we document that iron oxide minerals, specifically the ratio of hematite to goethite (Hm/Gt), is a reasonable precipitation proxy. Using diffuse reflectance spectrophotometry, we measured samples from Ocean Drilling Program (ODP) 1143 drilling site (9°21.72′N, 113°17.11′E, 2777 m water depth) for hematite and goethite, whose formation processes are favored by opposing climate conditions. In order to determine the content of hematite and goethite we produced a set of calibration samples by removing the iron oxides to generate the natural matrix to which hematite and goethite in known percentages were added. From these calibration samples we developed a transfer function for determining hematite and goethite concentration from a sample's spectral reflectance. Applying this method to ODP 1143 sediments (top 34 m of a 510 m core with sampling interval of 10 cm) we were able to reconstruct a continuous precipitation history for SE Asia of the past 600 kyr using the Hm/Gt ratio as a proxy of the precipitation variability of Asian monsoon. The reliability of this Hm/Gt proxy is corroborated by its consistency with the stalagmite δ18O data from South China. Comparing long-term Hm/Gt records with the surface temperature gradient of equatorial Pacific Ocean, we found that monsoon precipitation and El Niño are correlated for the last 600 kyr. The development of El Niño-like conditions decreased SE Asia precipitation, whereas precipitation increases in response to La Niña intensification.