Fate of Ayeyarwady and Thanlwin Rivers Sediments in the Andaman Sea and Bay of Bengal
Fate of Ayeyarwady and Thanlwin Rivers Sediments in the Andaman Sea and Bay of Bengal
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DOI：
10.1016/j.margeo.2020.106137
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发表时间：
2020-05
期刊：
影响因子：
2.9
通讯作者：
J. Liu;S. Kuehl;A. Pierce;Joshua R. Williams;N. Blair;C. Harris;D. W. Aung;Y. Aye
中科院分区：
文献类型：
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作者：
J. Liu;S. Kuehl;A. Pierce;Joshua R. Williams;N. Blair;C. Harris;D. W. Aung;Y. Aye
总体而言，现代的伊洛瓦迪和丹温河（萨尔温江）向海洋输送的沉积物超过6亿吨/年。为了了解伊洛瓦迪和Thanlwin河沉积物入海的命运，我们于2017年12月在安达曼海北方和孟加拉湾东部进行了为期14天的地球物理和地质调查。总体而言，获得了约1 500公里的高分辨率Chirp声纳剖面图和30个陆架沉积物岩心。本文介绍了经处理的高分辨率剖面图的结果以及沉积物分析。研究结果表明：（1）伊洛瓦迪河口附近陆架上几乎没有现代沉积物堆积。相比之下，在Martaban湾有一个主要的泥楔，其远端沉积中心厚度达60 m，向海沉积，延伸至Martaban凹陷约130 m水深。此外，2）没有证据表明现代沉积物已经积累或被运送到Martaban峡谷; 3）在孟加拉湾东部狭窄的缅甸西部大陆架周围有一个泥披覆物/毯子。泥质存款厚度在近岸达20 m，在-300 m水深处向斜坡逐渐变薄，并可能逃逸到安达曼海沟深处; 4）估算近海沉积的全新世沉积物总量约为1290 × 109吨。如果我们假设这主要是自中全新世高位以来积累的，（~6000 yr BP）与其他主要三角洲一样，陆架上的历史年平均沉积通量为215 Mt/yr，相当于现代Ayeyarwady-Thanlwin河流沉积物的~35%; 5）与亚洲其他大型河流系统（如长江和湄公河）不同，这项研究表明，受潮汐和季节性变化的季风风和波浪影响的当地水流控制的双向输送和沉积模式。有机碳生物标志物和同位素组成显示出一个逐渐变化的模式，沿陆架从河流到东部的马塔班湾和西部的孟加拉湾的运输。
Collectively, the modern Ayeyarwady (Irrawaddy) and Thanlwin (Salween) rivers deliver >600 Mt/yr of sediment to the sea. To understand the fate of Ayeyarwady and Thanlwin river-derived sediments to the sea, we conducted a 14-day geophysical and geological survey in the northern Andaman Sea and eastern Bay of Bengal in December 2017. Overall, ~1500-km of high-resolution Chirp-sonar profiles and 30 sediment cores from the shelf were acquired. This paper presents the results of the processed high-resolution profiles together with sediment analyses. Our findings indicate: 1) There is little modern sediment accumulating on the shelf immediately off the Ayeyarwady River mouths. In contrast, a major mud wedge with a distal depocenter, up to 60 m in thickness, has been deposited seaward in the Gulf of Martaban, extending to ~130 m water depth into the Martaban Depression. Further, 2) There is no evidence showing that modern sediment has accumulated or is transported into the Martaban Canyon; 3) There is a mud drape/blanket wrapping around the narrow western Myanmar Shelf in the eastern Bay of Bengal. The thickness of the mud deposit is up to 20 m nearshore and gradually thins to the slope at −300 m water depth, and likely escapes into the deep Andaman Trench; 4) The estimated total amount of Holocene sediments deposited offshore is ~1290 × 109tons. If we assume this has mainly accumulated since the middle Holocene highstand (~6000 yr BP) like other major deltas, the historical annual mean depositional flux on the shelf would be 215 Mt/yr, which is equivalent to ~35% of the modern Ayeyarwady-Thanlwin rivers derived sediments; 5) Unlike other large river systems in Asia, such as the Yangtze and Mekong, this study indicates a bi-directional transport and depositional pattern controlled by the local currents that are influenced by tides, and seasonally varying monsoons winds and waves. Organic carbon biomarkers and isotope compositions show a gradual changing pattern with the along-shelf transport from the river to the Gulf of Martaban in the east and to the Bay of Bengal in the west.