150 ka以来东南亚岛屿风化历史：来自深海钻孔MD98-2162的证据【封面文章】

The weathering history of Southeast Asian islands over the last 150 ka: evidence from deep sea core MD98-2162【Cover】

关键词:  印太交汇区  晚第四纪  化学风化  海洋沉积

Key words:  Indo-Pacific region  Late Quaternary  chemical weathering  marine sedimentation

摘要:

印度洋-太平洋交汇区（印太交汇区）岛弧化学风化可能对调节大气CO₂浓度变化起着重要作用。然而，目前该区域内岛屿风化历史和控制机制仍不清楚，主要体现在热带地区降水和温度的复杂变化及其与全球气候变化的关系难以区分，存在较多的争论。利用MD98-2162孔的主量元素、MD98-2162和MD01-2378孔的色度记录，并结合已有的总有机碳（TOC）含量等记录，研究印太交汇区风化和沉积输入演化对不同气候强迫因子的响应关系，结果表明：MD98-2162孔风化记录主要受控于源区降水变化，表现出显著的岁差周期；而MD98-2162和MD01-2378孔亮度（L^*）值与TOC含量主要受海平面变化影响，表现为偏心率周期。通过对比同钻孔的不同古气候代用指标，区分了热带地区降水和温度对不同地球轨道参数（岁差和偏心率）的不一致响应，结果表明晚第四纪以来热带地区可能不仅被动响应高纬气候，也可能发生主动变化，这仍需更多研究。

Abstract:

Background, aim, and scope Chemical weathering of island arcs in the Indo-Pacific region plays an important role in regulating atmospheric CO₂ changes. However, the history and control mechanisms of island weathering within this region are still in debate, mainly due to the controversial variations in precipitation and temperature and their relationship to global climate change are difficult to distinguish. To reveal the forcing factors of the island weathering in the Indo-Pacific region, this study reconstructed the weathering history of the islands in the region since the last 150 ka using marine sediment samples from core MD98-2162 and discusses the controlling factors of the weathering history. Materials and methods The sediment samples of core MD98-2162 were pretreated, and the clay-size major elements were measured by Thermo Icap 6300 ICP-AES. The chemical index of alteration (CIA) of core MD98-2162 were calculated by the four major elements, Al₂O₃, CaO, Na₂O and K₂O. In this study, the response of weathering and sedimentary input to different climatic drivers in the Indo-Pacific region was studied by using the major elements in core MD98-2162 and chroma of cores MD98-2162 and MD01-2378, and combined with the available total organic carbon (TOC) content. Results The CIA of core MD98-2162 ranged from 82 to 88, with an average of 85. Among the four components used in calculation, Al₂O₃ content is the highest, with an average content of 21.17%, and the distribution range is between 19.80%—22.80%. The average content of CaO and K₂O is 0.81% and 1.78%, and the distribution range is 0.40%—1.20% and 1.20%—2.20%, respectively. The content of Na₂O is the lowest, the average content is only 0.24%, and the distribution range is between 0.18%—0.36%. Discussion The high value state (CIA＞80) of core MD98-2162 reflects the intense chemical weathering in the hot, humid tropical climate of the provenance area. The variations of CIA of MD98-2162 and Kalimantan stalagmite δ¹⁸O show good consistent with a correlation coefficient of −0.23, and there is also a rough consistent between CIA and Kalimantan stalagmite δ¹⁸O in the last two deglacials (Termination Ⅰ and Termination Ⅱ) at the time of the minimal value point. The phenomenon confirms that the terrigenous weathering process recorded in core MD98-2162 is mainly controlled by precipitation. The L^* and TOC contents of core MD01-2378 and MD98-2162 are consistent with the Antarctic ice core, showing obvious glacial-interglacial fluctuation. The CIA and Kalimantan stalagmites δ¹⁸O have the same variation in precipitation, mainly showing the precession cycles, but there is no obvious glacial-interglacial fluctuation. Conclusions Our results show that the chemical weathering degree of core MD98-2162 is mainly determined by the precipitation changes in the provenance area and shows significant precession cycle variation; The L^* and TOC content of cores MD98-2162 and MD01-2378 are mainly influenced by sea-level changes and show eccentricity cycles. Recommendations and perspectives By comparing different paleoclimate proxies of the same core, we distinguish the inconsistent response of precipitation and temperature changes in the tropics to the changes of different Earth orbit parameters (precession and eccentricity). These results provide an example for studying climatic interactions between high and low latitudes.