徐建^1,,
可菲¹,
KuhntWolfgang²,
HolbournAnn²,
张鹏¹,
崔瑞¹,
刘恒¹,
孙金梁¹
1. 西北大学地质学系大陆动力学国家重点实验室, 陕西 西安 710069
2. Institute of Geosciences, Christian-Albrechts-University of Kiel, D-24118 Germany

基金项目: 国家自然科学基金项目（批准号：41830539、40906032、41576045和41776060）、德国自然科学基金项目（批准号：KU649/28-1）和西北大学国家基础科学人才培养基金地质学科科学研究培训项目（批准号：XDCX2019-09和XDCX2020-01）共同资助


详细信息

作者简介: 徐建, 男, 42岁, 教授, 古海洋学专业, E-mail:jx08@live.cn

中图分类号: P72;P532

收稿日期:2020-06-28
修回日期:2020-08-25
刊出日期:2020-11-30

Stacked records of Timor Sea cores over the last 21 ka and their paleoceanographic significance

Xu Jian^1,,
Ke Fei¹,
Kuhnt Wolfgang²,
Holbourn Ann²,
Zhang Peng¹,
Cui Rui¹,
Liu Heng¹,
Sun Jinliang¹
1. State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi'an 710069, Shaanxi
2. Institute of Geosciences, Christian-Albrechts-University of Kiel, D-24118 Germany


MSC: P72;P532

--> Received Date: 28 June 2020
Revised Date: 25 August 2020
Publish Date: 30 November 2020


摘要
摘要:印尼穿越流是连接西太平洋和印度洋的唯一载体，与东亚季风和ENSO活动密切相关。帝汶海区是印尼穿越流的主要出口之一，该区不同钻孔末次冰期以来的古海洋学记录显示在长时间尺度上变化存在着很高的相似性。为了捕捉出口处印尼穿越流的平均信号，本研究将这些记录进行堆叠，并与其他海区的钻孔记录进行对比，探讨印尼穿越流对东亚季风和ENSO活动的响应。总体上，堆叠记录较为精准地复制了各个钻孔记录的信息。帝汶海区表层海水温度堆叠记录与其他海区钻孔记录对比显示末次冰期至12~6 ka期间帝汶海可能位于暖池范围内，而晚全新世时位于暖池的边缘；温跃层深度、海水温度和盐度堆叠记录揭示自末次冰期以来印尼穿越流温跃层流呈现逐渐强化的趋势。结合现代水文资料和堆叠记录与其他古海洋古气候记录的对比等，本文推测了不同时期ENSO的冷暖期状态以及东亚季风对印尼穿越流的影响方式和过程。
关键词: 堆叠记录/
印尼穿越流/
帝汶海/
东亚季风/
ENSO

Abstract:Indonesian Throughflow(ITF) is the unique conveyor transporting upper waters from the western Pacific to the Indian Ocean and hence regulates heat and fresh water budgets between the oceans. Change in the ITF, including its upper water stratifying, transporting volume and intensity, is closely related to East Asian monsoon and El Ni?o -Southern Oscillation(ENSO) activities. The Timor Passage is of key importance among exits of the ITF to the Indian Ocean. Study on cores from the Timor Sea thus provides insightful understanding of ITF history. In this study, we stack the records from the Timor Sea that we reconstructed in the past years and investigate changes in the ITF and its paleoceanographic significance. Motivation to stack Timor Sea records is firstly due to the fact that these records are alike in a common trend at a long-term timescale and their differences are very likely analogs of modern differences among coring sites. For instance, sea surface and thermocline temperatures from Core SO18460 were the lowest ones and those from Core SO18473 the highest ones in particular during the last glacial and deglaciation. This feature coincides with what we see in the modern profiles at the coring sites. Secondly, all of the records from which we try to get stacked records were performed in the same laboratory using the same methods, as is helpful for reducing the errors of stacked records due to inter-lab difference. Thirdly, a stacked record expresses more general information of the ITF outflow variability and provides an advantage for comparison with records from adjacent seas.
Our stacked Gs.ruber and P.obliquiloculata δ¹⁸O records well match those of SONNE cores, in particular SO18460 and SO18462. Obvious deviations are observed of stacked δ¹⁸O records from MD01-2378 δ¹⁸O records. Both of Gs.ruber and P.obliquiloculata δ¹⁸O in Core MD01-2378 are lighter than the stacked records but within the range of ±2σ(note that the error shading in Fig. 2 shows±1σ). Calculating errors using Student's-test at a confidence interval of 90% are 0.02 ‰ in average for both of Gs.ruber and P.obliquiloculata δ¹⁸O stacked records. Comparatively, data points of sea surface temperature(SST) and thermocline temperature(TT) of the Timor Sea cores are a bit of scattering at a certain age, in particular for the period prior to 15 ka, possibly due to amplification of signals in colder intervals. Standard Deviation(±1σ) and calculating error at a confidence interval of 90% are in average 0.64℃ and 0.56℃ for stacked SST, and 1.01℃ and 1.24℃ for stacked TT. However, the stacked records well display significant changes in the individual records. For instance, all of the individual SST records show lowest values at about 20~19 ka, which appears at 19.5 ka in the stacked SST. The stacked records of δ¹⁸O_sw represent records of the studied cores at very good precisions, with standard deviation and calculating error of 0.16 ‰ and 0.04 ‰ for stacked surface δ¹⁸O_sw, and of 0.22 ‰ and 0.06 ‰ for stacked thermocline δ¹⁸O_sw.
Stacked records of the Timor Sea cores in comparison with records from adjacent seas, the southern South China Sea(SCS), off Luzon Island, center of the Indo-Pacific Warm Pool(IPWP) and the Sulu Sea, show that stacked Timor Sea SST was comparable to SSTs from the center of the IPWP during the last glacial and last deglaciation. A remarkable pattern occurs to the stacked Timor Sea SST during the Holocene is that Timor Sea sustained SSTs over 28℃ merely during the period of 12 ka to 6 ka and then at around 28℃ towards the Late Holocene. This pattern is quite different from SSTs of other cores that are much higher than 28℃ over the entire Holocene. Given 28℃ defining the boundary of the IPWP, it indicates that the IPWP has been encompassing the Timor Sea during 12 ka to 6 ka and then shrank/shifted eastwards in its range to keep the Timor Sea only at its edge in the late Holocene. Taking together similar surface water δ¹⁸O(δ¹⁸O_sw) as well as similar temperatures occurred in the IPWP region during the last glacial, it indicates that uniform surface waters have developed in the IPWP region, except for the southern SCS. It possibly in turn indicates that all of the areas had been within or not within the warm pool during the last glacial. After ca. 14.5~12.5 ka, surface waters very clearly differentiated in between the center of the IPWP and the other areas. Surface waters in the Timor Sea had comparable level of salinity to those off the Luzon Island, and were more similar to surface waters in the Makassar Strait and the southern SCS other than those in the center of the IPWP. Thus, it is very likely that surface waters of the ITF outflow in the Timor Sea had been freshened en route by fresher surface waters in the Makassar Strait, with possible contribution of fresher surface waters from the southern SCS, as indicated by converging in salinity of surface waters in the southern SCS and the Makassar Strait during the Late Holocene. Remarkable features of the stacked Timor Sea TTs are that it reached highest level at 10.5 ka and then significantly decreased with two steps centering at 5.5 ka. The unchanged TTs in the southern SCS and the center of the IPWP indicate a relatively stable upper ocean thermal condition. In contrast, continuous decreasing of the stacked Timor Sea TT during 12 ka to 6 ka would suggest increasing transport of relatively cool thermocline waters from the IPWP. The staked Timor Sea TT then continuously decreased and approached to levels of the TTs in the southern SCS and the center of the IPWP after 6 ka, implying more intensified transport of ITF thermocline waters. Records of thermocline water δ¹⁸O reconstructions show that there were similar saline waters in the center of the IPWP, the southern SCS and the Makassar Strait during the last glacial. Comparatively, the Timor Sea had more saline waters. Starting from 12 ka, thermocline waters in the Timor Sea yielded and then kept comparable salinities to the waters from the western Pacific.
Comparison of modern hydrology profiles in the Timor Sea with local irradiance and ENSO indices indicates that SST is affected by irradiance and TT is very closely related to ENSO activities. Meanwhile, thermal gradient of upper waters between surface and thermocline is in a good relationship with ENSO activities on a long term. Comparison of stacked Timor Sea records with paleoceanographic and paleoclimatic records from other areas suggests that a La Ni?a -like state may have occurred during the last glacial, an enhanced La Ni?a -like state during 12 ka to 6 ka, and an El Ni?o -like state after 6 ka. In addition to influence of ENSO, the East Asian winter monsoon may also have played a role in affecting the ITF by intrusion of the South China Sea throughflow(SCSTF) waters into the Makassar Strait. In the modern days, winter monsoon driven SCSTF conveys low salinity surface waters from the SCS to the Makassar Strait either in the north via the Sulu Sea or in the south via the Java Sea, obstructing surface flow of the ITF and hence relatively enhancing the ITF thermocline flow.
Key words:stacked records/
Indonesian Throughflow/
Timor Sea/
East Asian monsoon/
ENSO



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