Bottom Currents Observed in and Around a Submarine Valley on the Continental Slope of the Northern South China Sea

• Published in: Journal of Ocean University of China Vol. 15; no. 6; pp. 947 - 957
• Main Authors: Wu, Lunyu, Xiong, Xuejun, Li, Xiaolong, Shi, Maochong, Guo, Yongqing, Chen, Liang
• Format: Journal Article
• Language: English
• Published: Heidelberg Science Press 01.12.2016; Springer Nature B.V; First Institute of 0ceanography, State 0ceanic Administration, Qingdao266061, P. R. China%CN00C Deepwater Exploitation Co. Ltd., Shenzhen518067,P. R. China%College of Physical and Environmental 0ceanography, 0cean University of China,Qingdao266100, P. R. China
• Subjects: Bottom currents; Canyons; Continental slope; Earth and Environmental Science; Earth Sciences; Internal waves; Marine; Meteorology; Ocean currents; Oceanography; Submarine valleys; Submarines; Topography; Valleys; 中国; 凹陷地形; 剩余电流; 南海北部陆坡; 底部; 海底峡谷; 逆时针旋转; 露天边坡; South China Sea; ISEW, South China Sea; bottom currents; continental slope; South China Sea; valley
• ISSN: 1672-5182; 1993-5021; 1672-5174
• DOI: 10.1007/s11802-016-3054-1

Bottom currents at about 1000m depth in and around a submarine valley on the continental slope of the northern South China Sea were studied by a 14-month long experiment from July 2013 to September 2014. The observations reveal that bottom currents are strongly influenced by the topography, being along valley axis or isobaths. Power density spectrum analysis shows that all the currents have significant peaks at diurnal and semi-diurnal frequencies. Diurnal energy is dominant at the open slope site, which is consistent with many previous studies. However, at the site inside the valley the semi-diurnal energy dominates, although the distance between the two sites of observation is quite small （11 kin） compared to a typical horizontal first-mode internal tide wavelength （200 km）. We found this phenomenon is caused by the focusing of internal waves of certain frequencies in the valley. The inertial peak is found only at the open slope site in the first deployment but missing at the inside valley site and the rest of the de- ployments. Monthly averaged residual currents reveal that the near-bottom currents on the slope flow southwestward throughout the year except in August and September, 2013, from which we speculate that this is a result of the interaction between a mesoscale eddy and the canyon/sag topography. Currents inside the valley within about 10mab basically flow along slope and in the layers above the 10mab the currents are northwestward, that is, from the deep ocean to the shelf. The monthly mean current vectors manifest an Ek- man layer-like vertical structure at both sites, which rotate counter-clockwise looking from above.