海洋地质与环境重点实验室知识库

基于2012年7月东海陆架温度、盐度、浊度、叶绿素a浓度以及悬浮体粒度等实测数据，结合同期海表面高度异常和HYCOM流场数据，分析不同水团内悬浮体物质组成和粒度分布特征并探究其影响因素，探讨以台湾暖流为主体的东海陆架垂向环流对悬浮体分布及输运的影响及作用机制，厘清台湾暖流表层水和台湾暖流深层水分别对悬浮体分布的影响。研究结果显示：

（1）夏季，东海陆架共存在长江冲淡水、苏北沿岸流、东海冷涡、台湾暖流表层水、台湾暖流深层水以及台湾海峡暖水六个水团。台湾暖流是东海陆架控制性水团，几乎占据了整个东海外陆架，以其为主体构成东海陆架垂向环流体系。环流共包括四个环节：近岸表层水形成离岸流；外陆架上层海域台湾暖流表层水形成下降流；外陆架底层海域台湾暖流深层水形成向岸流；近岸海域台湾暖流深层水形成上升流。

（2）夏季东海陆架悬浮体由两部分构成，即小于128μm以无机悬浮体为主的颗粒和大于128μm以浮游生物为主的颗粒，其平均体积浓度分别为3.5μL/L和8.4μL/L。悬浮体空间分布受到该海域水团类型的制约。长江冲淡水、台湾暖流表层水、台湾暖流深层水、台湾海峡暖水以及东海冷涡的悬浮体粒径均呈双峰分布，峰值位于27.7—74.7μm和391μm；苏北沿岸流影响海域悬浮体粒径呈单峰分布，小颗粒端含量极低。悬浮体粒度组成及其空间分布差异与水团挟带的无机颗粒、营养盐输送以及水体界面阻隔密切相关。其中，长江冲淡水挟带大量无机颗粒和营养盐进入东海，致使其无机颗粒和浮游生物含量均为研究区最高；苏北沿岸流经长距离扩散后挟带的无机颗粒大多已经沉降，因此无机颗粒含量在研究区最低，而其挟带的丰富营养盐，致使浮游生物含量为次高值；台湾暖流表层水、台湾暖流深层水、东海冷涡以及台湾海峡暖水中悬浮体均以无机颗粒为主，其中前三个水团的水体界面处浮游生物含量较高。

（3）夏季东海陆架海区存在强烈的跃层，跃层所在层位层结较强，垂向扩散较弱，能够有效抑制底层再悬浮物质向表层的扩散。此外，跃层还能够抑制底层营养盐向表层的扩散，导致跃层位置成为大颗粒浮游生物高含量区。由于研究区跃层所处层位均较深，其对浮游植物垂向分布的影响较弱。

（4）东海陆架近岸表层水向外海扩散形成离岸流，离岸流可以将近岸表层悬浮体向东输运到外海海域。位于东海外陆架上层海域的台湾暖流表层水不利于浮游植物的生长，其向下凹陷形成下降流；下降流可以将上层 “洁净”水体向下输运，致使低悬浮体区呈舌状向下凹陷；此外，下降流还可以抑制跃层的抬升，进而抑制底层悬浮体向表层输运。自外海向近岸入侵的台湾暖流深层水在东海外陆架底层形成向岸流，向岸流能够抑制近岸下层悬浮体向外海的扩散。向岸入侵的台湾暖流深层水在近岸形成上升流，上升流可以汇聚底层海域的悬浮体，致使其中心海域悬浮体含量较高，而且有利于小颗粒悬浮体向表层的扩散；上升流还可以将底层丰富的营养盐输运到表层海域，促进表层浮游植物的生长；此外，上升流还可以抬升跃层，进而间接促使底层悬浮体向表层输运。近岸向上凸起的台湾暖流深层水与外海向下凹陷的台湾暖流表层水之间形成了向岸倾斜的海洋锋，该锋能够抑制近岸悬浮体向外海的扩散。

本项研究可为开展陆架海区海洋环境调查和工程建设等提供资料参考，为查明东海陆架区陆源沉积物输运扩散机制、揭示海底沉积物来源和成因机制等提供理论依据。

Based on temperature, salinity, turbidity, chlorophyll a and suspended particle size data obtained in the East China Sea (ECS) shelf in July 2012, combined with the Sea Level Anomaly (SLA) and HYCOM data during the sampling, the composition and particle size distribution of suspended particulate matter (SPM) were analyzed, and the influence factors were explored. In addition, the effects of the vertical circulation on the distribution and transport of SPM were explored in the East China Sea shelf. The effects of the Taiwan Warm Current Surface Water (TWCSW) and Taiwan Warm Current Deep Water (TWCDW) on the distribution of SPM were clarified. The results showed that:

(1) In summer, there were six water masses in the study area: Changjiang Diluted Water (CDW), coastal current off north Jiangsu (NSCC), TWCSW, TWCDW, Taiwan Strait warm water (TWSWC) and East China Sea Cold Eddy (ECSCE).The Taiwan Warm Current (TWC) was controlled water mass, which occupied almost the whole of the East China Sea outer shelf and formed the vertical circulation. The vertical circulation was consisted of four parts: the near-shore surface water formed offshore current, the TWCSW formed downwelling, the TWCDW formed onshore flow in bottom area of the East China Sea outer Shelf and an upwelling in the nearshore.

(2) The SPM were consisted of two parts in ECS shelf in summer. The fine component (＜128μm) of SPM were inorganic particles, while the coarse component (＞128μm) of SPM were almost plankton, and the average volume concentrations were 3.5μL/L and 8.4μL/L, respectively. The spatial distribution of SPM was restricted by different water masses. The particle size spectra of the CDW, TWCSW, TWCDW, TWSWC and ECSCE all showed bimodal feature and two peaks always located at 27.7—74.7μm and 391μm, respectively. The particle size spectra presented unimodal feature, and the fine component of SPM was extremely low in the NSCC. The composition and distribution of SPM were closely related to the transport of inorganic particles, nutrients and the barrier of water interface. In summer, the enormous terrigenous material and nutrients carried by the CDW contributed to the highest content of inorganic particle and plankton in the CDW, respectively. The settlement of fine inorganic particles after long-distance transport led to the lowest content of inorganic particles in the NSCC. In addition, the nutrients carried by the NSCC resulted in the secondary high value of plankton. As for the TWCSW, the TWCDW, the ECSCE and the TWSWC, the SPM was mainly composed of inorganic particle, and where plankton only existed in the water interface of the first three water masses.

(3) In summer, there was a thermocline in the ECS shelf, which had strong thermocline and weak diffusion, and effectively inhibited the diffusion of bottom resuspended matter to the surface. In addition, the thermocline can also inhibited  the diffusion of nutrient from bottom layer to surface layer, which was beneficial to the growth of plankton, resulted in the high content of plankton in thermocline. Because the thermocline was very deep, it had little influence on the vertical distribution of phytoplankton.

(4) The near-shore surface water mass formed offshore curren, which transported of near-shore surface SPM eastward. The TWCSW formed downwelling in the upper of the East China Sea outer shelf, which transported of clean water downward, resulted in the low SPM region to be tongue-shape downward depression. Furthermore, the concentration of Chorophyll-a was low in the downwelling. The downwelling can also inhibited the rise of the thermocline, so that it can indirectly inhibited the transport of SPM from the bottom to the surface. The TWCDW formed onshore flow in the ECS outer shelf, which can restrained the eastward diffusion of the underlying SPM. The TWCDW formed upwelling in near-shore. The upwelling can converged the SPM in the bottom, resulted in the content of SPM was high in the upwelling center. In addition, the upwelling was beneficial to the diffusion of fine SPM to the surface. The upwelling can transported the rich nutrients from the bottom to the surface, which promoted the growth of the phytoplankton. In addition, the upwelling indirectly promoted the upward transport of bottom SPM by lifted the thermocline. The ocean front formed by the TWCSW and TWCDW can inhibited the eastward diffusion of near-shore SPM.

This study can provided information reference for marine environment investigation and engineering construction. In addition, it provided a theoretical basis for identifying the transport and diffusion mechanism of terrigenous sediments and revealing the origin and genesis mechanism of seabed sediments in the East China Sea shelf.