4Ma来澳大利亚西海岸带的环境变化历史及其与印尼贯穿流的联系

印尼贯穿流在热带甚至全球气候系统的变化中起着重要的作用，而澳大利亚西海岸带（西澳海岸）是研究印尼贯穿流变化历史的理想地区。本次研究通过国际大洋发现计划（IODP）356航次沉积岩芯的基于长链烯酮和正构烷烃指标，重建了4百万年（Ma）来低分辨的西澳海岸南北区域的海表温度、长链烯酮生产藻种属和陆源高等植物输入的演变历史，从而分析区域气候的时空变化趋势，及其与印尼贯穿流强度变化的相关性。结果表明，2~4Ma西澳海岸表现出海表温度逐步下降的趋势以及几个较为明显的降温事件，与临近海域温度数据以及全球底栖有孔虫的δ¹⁸ O曲线有着较好的对应。1Ma以来西澳海岸整体升温，这可能与印尼贯穿流的开启和增强带来的区域升温相关。长链烯酮C₃₇/C₃₈比值表明，1~4Ma西澳海岸南、中、北部站位的长链烯酮生产藻基本没有交流，而0~1Ma交流较为剧烈。这种现象与印尼贯穿流强度的变化相符，表现为贯穿流强度越强交流越明显。4Ma以来，西澳海岸南、北站位的陆源高等植物输入历史表现出相反的变化特征，这种差异性可能由不同环境对不同区域性气候的复杂响应模式所致。通过中部和北部站位的数据，我们进一步探讨了季风影响下的澳大利亚大陆干湿情况和印尼贯穿流变化的关系。结果表明，2~2.5Ma印尼贯穿流的减弱或者关闭降低了整个澳大利亚大陆的湿度，但0~1Ma印尼贯穿流的增强并未导致澳大利亚大陆的湿润，这种现象可能表明了该区域不同时期的气候驱动机制的改变。

History of environmental changes on the Western Australia Shelf over the past 4 million years and its indication on the Indonesian Throughflow

The Indonesian Throughflow(ITF), an important component of the global thermohaline conveyor, exerts a major control on global climate. The Western Australia Shelf located on the southeastern edge of the Indian-Pacific Warm Pool is an ideal area for investigation on history of variation in the ITF strength. Here we reconstruct low-resolution records of sea surface temperature, alkenone-producer communication and terrestrial plant organic input over the last 4 million years(Ma), based on analysis of alkenones and n-alkanes in 126 samples from marine sediment cores obtained from the Western Australia Shelf(sites U1459~1464, covering a latitudinal range of 28°~18°S) by the International Ocean Discovery Program(IODP)Expedition 356. Sites U1459~U1460 are in the northern part of the Perth Basin and sites U1461~U1464 are in the Northern Carnarvon Basin and Roebuck Basin. The chronostratigraphic framework of all the cores is mainly based on the biostratigraphy(calcareous nannofossil and benthic foraminiferal assemblages)and magnetostratigraphy. According to our results, sea surface temperature at the Western Australia Shelf shows decreasing trend at 2~4Ma with some further cooling events, consistent with the temperature record in the nearby region and the global benthic δ18 O record. Over the last 1Ma, sea surface temperatures at the studied region increased, probably caused by the strengthening of the ITF. The alkenone C37/C38 records show no communication on alkenone-producers among northern, middle and southern sites at 1~4Ma, but intensive communication at 0~1Ma, resembling with the strengthening of the ITF over the last 1Ma. The organic input from terrestrial plants indicated by the ratio of long-chain and short-chain n-alkanes show different variations between southern and middle-to-northern sites, probably caused by regional moisture evolution responding to the climate forcing. Although weaken ITF strength at 2~2.5Ma reduced the moisture in the northern Australia continent, intensified ITF strength at 0~1Ma didn't lead to wet condition in the northern Australia continent, tentatively suggesting a change in the regional climatic forcing mechanism at those two periods.