Dynamical impact of the Mekong River plume in the South China Sea
Dynamical impact of the Mekong River plume in the South China Sea
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DOI：
10.1029/2021jc017572
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发表时间：
2021-12
期刊：
影响因子：
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通讯作者：
Xi-bo Zeng;A. Bracco;F. Tagklis
中科院分区：
文献类型：
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作者：
Xi-bo Zeng;A. Bracco;F. Tagklis
在海洋表面附近，河流羽流影响分层、浮力和示踪剂、营养物和污染物的运输。然而，河流羽流对整个环流的影响程度通常没有受到很好的限制。这项工作的重点是南中国海（SCS）和量化的湄公河羽流，这是必然会显着改变的强度和季节性，在未来20年，如果超过百个大坝的建设按计划推进的动态影响。通过比较2011年和2016年之间有和没有河流输入的次中尺度允许和中尺度分辨模拟，量化了淡水通量对南海环流的动态影响。在夏季和初秋，当湄公河流量是在其高峰期，更大的层结通过增强斜压不稳定造成残留的中尺度环流。剩余环流的形状是一个正涡度和负涡度的涡列。次中尺度锋负责将淡水输送到近海，使残留中尺度环流的发展向东移动，并在次中尺度允许的情况下进一步加强残留涡旋串。总体而言，在河流输入的存在下，近地面的北向输送加强。与河流羽流相关的中尺度诱导和亚中尺度诱导的输送的意义在夏季风季节的下半期尤其重要，此时初级生产力具有次极大值。如果人类活动改变了湄公河羽流的强度和季节性，那么应该预料到环流的变化以及生产力的变化。我们通过一套区域海洋模拟来探讨湄公河羽流引起的淡水强迫如何影响南中国海的海洋环流。我们专注于动力学相关的河流羽在北方夏季。这次调查的动机是计划在湄公河流域及其主要支流沿着建造一百多座水电站大坝。这些水坝将大大减少湄公河的年平均流量及其季节性循环（最多可达一个数量级）和沉积物负荷。我们的研究结果表明，流域的整体环流可能会受到这些变化的影响，通过中尺度环流和流动的不稳定性特征的变化。提交给地球物理研究海洋杂志的手稿我们认为，南中国海沿着夏季急流路径的近海水域的生产力降低也可能是一个不希望的结果。
Near the ocean surface, river plumes influence stratification, buoyancy and transport of tracers, nutrients and pollutants. The extent to which river plumes influence the overall circulation, however, is generally poorly constrained. This work focuses on the South China Sea (SCS) and quantifies the dynamical impacts of the Mekong River plume, which is bound to significantly change in strength and seasonality in the next 20 years if the construction of over hundred dams moves ahead as planned. The dynamic impact of the freshwater fluxes on the SCS circulation are quantified by comparing submesoscale permitting and mesoscale resolving simulations with and without riverine input between 2011 and 2016. In the summer and early fall, when the Mekong discharge is at its peak, the greater stratification causes a residual mesoscale circulation through enhanced baroclinic instability. The residual circulation is shaped as an eddy train of positive and negative vorticity. Submesoscale fronts are responsible for transporting the freshwater offshore, shifting eastward the development of the residual mesoscale circulation, and further strengthening the residual eddy train in the submesoscale permitting case. Overall, the northward transport near the surface is intensified in the presence of riverine input. The significance of the mesoscale-induced and submesoscale-induced transport associated with the river plume is especially important in in the second half of the summer monsoon season, when primary productivity has a secondary maximum. Circulation changes, and therefore productivity changes, should be anticipated if human activities modify the intensity and seasonality of the Mekong River plume. Plain Language Summary We explore how the freshwater forcing induced by the Mekong River plume impact the ocean circulation in the South China Sea with a suite of regional ocean simulations. We focus on the dynamics associated to the river plume in boreal summer. The motivation for this investigation is the planned construction of more than hundred hydropower dams along the Mekong River Basin and its major tributaries. The dams will dramatically reduce the Mekong River annual mean flow and its seasonal cycle (up to an order of magnitude) and sediment loading. Our results suggest that the overall circulation of the basin may be impacted by these changes, through changes in the mesoscale circulation and instability characteristics of the flow. manuscript submitted to Journal of Geophysical Research Oceans We argue that a reduced productivity of the offshore water of the South China Sea along the pathway of the summer jet may be an undesirable outcome as well.