OSD Ocean Science Discussions OSD Ocean Sci. Discuss. 1812-0822 Göttingen, Germany 10.5194/osd-11-1191-2014 The shallow meridional overturning circulation of the South China Sea Zhang N. 1 Lan J. 1 Cui F. 1 Physical Oceanography Laboratory, and College of Physical and Environmental Oceanography, Ocean University of China, Qing dao, China 30 04 2014 11 2 1191 1212 Copyright: © 2014 N. Zhang et al. 2014 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://os.copernicus.org/preprints/11/1191/2014/osd-11-1191-2014.html The full text article is available as a PDF file from https://os.copernicus.org/preprints/11/1191/2014/osd-11-1191-2014.pdf

In this paper, the structure and formation mechanism of the annual-mean shallow meridional overturning circulation of the South China Sea (SCS) are investigated. A distinct clockwise overturning circulation is present above 400 m in the SCS on the climatological annual mean scale. The shallow meridional overturning circulation consists of downwelling in the northern SCS, a southward subsurface branch supplying upwelling in the southern SCS and a northward return flow of surface water. The formation mechanism is explored by studying causes of the branches constituting the meridional overturning circulation. The surface branch is driven by the annual mean zonal component of the wind stress which is predominantly westward. Another effect of the wind is Ekman pumping related subduction in the north hence the main source of downwelling there. The mixed layer depth reaches its maximum in winter and shoals in spring, which causes the thermocline to outcrop and ventilate. Part of the water mass from the bottom of the mixed layer subducts into the thermocline and flows southward along the isopycnals. The upwelling region is mainly along the Vietnam coast and in the open-ocean off it. In summer, the alongshore component of wind stress off Vietnam can cause coastal upwelling and the increase of alongshore wind off the coast can also cause great upwelling in the open-ocean off the Vietnam coast.

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