Oceanic bottom mixed layer in the Clarion-Clipperton Zone: potential influence on deep-seabed mining plume dispersal
Oceanic bottom mixed layer in the Clarion-Clipperton Zone: potential influence on deep-seabed mining plume dispersal
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DOI：
10.1007/s10652-023-09920-6
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发表时间：
2023-04
影响因子：
2.2
通讯作者：
S. Chen;R. Ouillon;Carlos Muñoz-Royo;T. Peacock
中科院分区：
文献类型：
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作者：
S. Chen;R. Ouillon;Carlos Muñoz-Royo;T. Peacock
海底混合层是一种混合良好、层结较弱的湍流边界层。在海底附近，BML对于研究海洋混合、能量耗散、颗粒循环和沉积物-水相互作用具有内在的重要性。虽然预计将在热带太平洋东北部的克拉里昂-克利珀顿区开始深海海底多金属结核采矿，但关于海底界线的形式及其对深海海底采矿活动产生的沉积物羽流扩散的潜在关键影响的知识空白尚未得到解决。在这里，我们报告了最近的实地观察，从德国采矿许可证地区的CCZ的BML本地的结构和变化。从海底延伸出的准均匀的位温剖面显示，存在一个时空可变的边界层，局部平均厚度约为250米。在11个月的记录中，该区域的深层水平流的平均速度为3.5厘米，最大速度为12厘米，位于底部以上18.63毫秒。近底流最初有一个净东南流，然后是向西和向南的流动与复杂的反气旋流型的发展。理论预测和历史数据表明，广泛的一致性，平均BML厚度，但不能解释所观察到的局部BML厚度的异质性。我们假设，深压异常引起的通过表面中尺度涡旋和深海热锋可以影响BML厚度，除了当地的地形效应。然后用一个简化的输运模型研究海底边界层对深海海底采矿引起的沉积物羽流输运中湍流扩散和沉积物沉降之间相互作用的影响。在一系列现实的参数值，BML对羽流演变的影响可以有很大的不同，突出强调，解决BML将是准确的数值模拟羽流扩散的关键一步。
The oceanic bottom mixed layer (BML) is a well mixed, weakly stratified, turbulent boundary layer. Adjacent to the seabed, the BML is of intrinsic importance for studying ocean mixing, energy dissipation, particle cycling and sediment-water interactions. While deep-seabed mining of polymetallic nodules is anticipated to commence in the Clarion-Clipperton Zone (CCZ) of the northeastern tropical Pacific Ocean, knowledge gaps regarding the form of the BML and its potentially key influence on the dispersal of sediment plumes generated by deep-seabed mining activities are yet to be addressed. Here, we report recent field observations from the German mining licence area in the CCZ that characterise the structure and variability of the BML locally. Quasi-uniform profiles of potential temperature extending from the seafloor reveal the presence of a spatially and temporally variable BML with an average local thickness of approximately 250 m. Deep horizontal currents in the region have a mean speed of 3.5 cm sand a maximum speed of 12 cm sat 18.63 ms above bottom over an 11 month record. The near-bottom currents initially have a net southeastward flow, followed by westward and southward flows with the development of complex, anticyclonic flow patterns. Theoretical predictions and historical data show broad consistency with mean BML thickness but cannot explain the observed heterogeneity of local BML thickness. We postulate that deep pressure anomalies induced by passing surface mesoscale eddies and abyssal thermal fronts could affect BML thickness, in addition to local topographic effects. A simplified transport model is then used to study the influence of the BML on the interplay between turbulent diffusion and sediment settling in the transport of deep-seabed mining induced sediment plumes. Over a range of realistic parameter values, the effects of BML on plume evolution can vary significantly, highlighting that resolving the BML will be a crucial step for accurate numerical modelling of plume dispersal.