大面积低悬沙浓度高盐水终年占据秦皇岛外海的沉积动力分析

The protruding phenomenon which sea water with low suspended sediment concentration and high salinity dominates the sea area off the Qinhuangdao all year round, has never been definitely mentioned and delineated till now. However, being an exceptional case, the protruding phenomenon will be measured by three long-term bottom-mounted tripods equipped with acoustic Doppler current profiler (ADCP), acoustic Doppler velocimeter (ADV), and optical backscatter sensor (OBS), and numerically tested and simulated via the ECOMSED (Estuary, Coastal Ocean Model and SEDiment transport)..The proposal will focus on two key processes about sediment resuspension and long-term transport, which could maintain sea water clear and saline off the Qinhuangdao coast. The distinctive sediment resuspension process driven by strong winter monsoon, and the evident difference on resuspension between the exceptional area and other shallow areas will be demonstrated off the Qinhuangdao. How the dynamic factors, such as wind field, wave, tide and tidal current, circulation and even water and sediment exchange between the Bohai Sea and the Yellow Sea, etc. impact on sediment transport in the Bohai Sea, will also be manifested by this research. Finally the mechanism on sediment dynamics about clear saline water dominating the vicinity of Qinhuangdao all year round will be elucidated..The supplementary knowledge about marine sediment dynamics could be achieved, which has important theoretical value. It is crucial that keeping sea water clear and unpolluted at Qinhuangdao, the most famous coastal tourist resort. The research on water and sediment behavior at its adjacent waters will have practical significance and application value.

针对至今仍没有被明确指出的：大面积低悬沙浓度高盐水终年占据秦皇岛外海，甚至存在低悬沙浓度极值区这一特殊海洋现象，本申请拟进行多站位、长时序、全水深海床基水沙要素现场观测，并基于ECOMSED模式开展敏感性数值试验和数值模拟，对维持该海域低悬沙浓度、高盐特征的两个关键过程：沉积泥沙再悬浮以及悬沙的长期输运进行定量分析。.力图揭示研究海域在冬季强风作用下沉积泥沙的再悬浮特征，明确其与其它近岸浅海区再悬浮过程的显著差异；阐明各动力要素诸如：风场、波浪、潮汐潮流、环流以及黄渤海水沙交换等，以及底质沉积物类型在秦皇岛外海悬沙输运过程中的作用；最终揭示低悬沙浓度高盐水终年占据秦皇岛外海的沉积动力机制。该项目的研究可弥补现有海洋沉积动力过程认识的不足，具有一定理论价值。秦皇岛作为最著名的滨海旅游度假区，保持海域水体清澈、减少污染物聚集至关重要，因此对其邻近海域水沙行为的研究颇具实际意义。

本申请在终年占据秦皇岛外海的低悬沙浓度高盐水海域，分别于2017和2018年冬季以及2019年夏季进行了三个航次的多站位、长时序、全水深海床基水沙要素现场观测，同时利用ROMS模式的数值模拟结果，对维持该海域低悬沙浓度、高盐特征的两个关键过程：沉积泥沙再悬浮以及悬沙的长期输运进行了定量分析，并最终揭示低悬沙浓度高盐水终年占据秦皇岛外海的沉积动力机制：即使在冬季大风期，垂向上沉积物再悬浮强度低；水平方向上黄海暖流余脉携带的低悬沙浓度、高温、高盐大洋水在冬季持续输入本海域，局地效应和远场因素的共同叠加，最终造成该海域在冬季依然保持低悬沙浓度。.2017年2月至3月，在秦皇岛低悬沙浓度海域的22天海床基观测结果表明，在最强风作用下，泥沙再悬浮过程包括一个发生在高湍动能时期的湍动再悬浮事件，以及当波浪主导的底床切应力大于临界水平时的后续再悬浮事件。原位观测结果还表明，秦皇岛海域特殊低悬沙浓度区的局地成因是即使在速度高于14m/s的大风作用下，秦皇岛海域泥沙再悬浮强度仍然较弱。2018年1月至2月，在秦皇岛海域低悬沙浓度区的45天原位观测显示，由于固体冰面对水体的阻力系数较大，流速垂向分布结构由传统的无冰条件下的对数型转变为海冰条件下的抛物线型。由于海冰的屏蔽作用，水体一直处于低湍动能状态，即使在大风期。因此，泥沙再悬浮强度低，水体悬沙浓度几乎不受风场的作用，仅为无海冰覆盖期浓度的一半。数值模拟结果以及渤海海峡物质交换的研究均显示，来自黄海的高温高盐的低悬沙浓度水，在进入渤海海峡后，会先向左转，然后再向右转，之后沿20米等深线向西北方向流动，源源不断地到达秦皇岛外海。.该项目的研究可弥补现有海洋沉积动力过程认识的不足，具有一定理论价值。秦皇岛作为最著名的滨海旅游度假区，保持海域水体清澈、减少污染物聚集至关重要，因此对其邻近海域水沙行为的研究颇具实际意义。