The TKE dissipation rate in the northern South China Sea Iossif Lozovatsky & Zhiyu Liu & Harindra Joseph S. Fernando & Jianyu Hu & Hao Wei Received: 5 February 2013 /Accepted: 19 September 2013 /Published online: 19 October 2013 # Springer-Verlag Berlin Heidelberg 2013 Abstract The microstructure measurements taken during the summer seasons of 2009 and 2010 in the northern South China Sea (between 18°N and 22.5°N, and from the Luzon Strait to the eastern shelf of China) were used to estimate the averaged dissipation rate in the upper pycnocline 〈ε p 〉 of the deep basin and on the shelf. Linear correlation between 〈ε p 〉 and the estimates of available potential energy of internal waves, which was found for this data set, indicates an impact of energetic internal waves on spatial structure and temporal variability of 〈ε p 〉. On the shelf stations, the bottom boundary layer depth-integrated dissipation b ε BBL reaches 17–19 mW/m 2 , dominating the dissipation in the water column below the surface layer. In the pycnocline, the integrated dissipation b ε p was mostly ∼10–30 % of b ε BBL . A weak dependence of bin-averaged dissipation ε on the Richardson number was noted, according to ε ¼ ε 0 þ ε m 1þRi=Ri cr ð Þ 1=2 , where ε 0 + ε m is the background value of ε for weak stratification and Ri cr =0.25, pointing to the combined effects of shear instability of small-scale motions and the influence of larger-scale low frequency internal waves. The latter broadly agrees with the MacKinnon– Gregg scaling for internal-wave-induced turbulence dissipation. Keywords Turbulence . Internal waves . South China Sea 1 Introduction The northern South China Sea (SCS) has a deep (>2,000 m) central basin and a wide continental shelf of depths less than 200 m. In recent years, the deep northern basin of SCS has been actively investigated for generation, propagation, and breakdown of large-amplitude nonlinear internal waves (NLIW) (e.g., Orr and Mignerey 2003; Duda et al. 2004; Gawarkiewicz et al. 2004; Duda and Rainville 2008; Huang et al. 2008; Ramp et al. 2010; Alford et al. 2010; Farmer et al. 2011). Internal waves (IW) and mixing in this region are strongly affected by barotropic tide and main patterns of SCS circulation, which are coupled to short-term variations of atmospheric forcing. In particular, such powerful events as tropical cyclones (typhoons) in the western Pacific and China Seas, frontal dynamics, and the bottom topography that con- trols water exchange between shallower and deeper basins play key roles. The tidal currents in SCS rotate clockwise, being driven by the diurnal O 1 and K 1 constituents over the upper slope and the semidiurnal constituent M 2 over the shelf (Beardsley et al. 2004). The semidiurnal S 2 constituent is also enhanced on the shelf, but it is always weaker than O 1 and K 1 . Mesoscale eddies of various sizes have been observed in the northern SCS, near Dongsha Islands, and to the west of the Luzon Strait. High-amplitude NLIW generated in the Luzon Strait region propagate northwestwards (Huang et al. 2008; Simmons et al. 2011). Basic characteristics of NLIW have been obtained using SAR images (e.g., Liang et al. 1995; Hsu et al. 2000; Liu and Hsu 2004; Huang et al. 2008) and mooring measure- ments (e.g., Duda et al. 2004; Yang et al. 2004; Lien et al. 2005; Chang et al. 2006; Duda and Rainville 2008; Alford Responsible Editor: Pierre De Mey I. Lozovatsky : H. J. S. Fernando Environmental Fluid Dynamics Laboratories, Department of Civil & Environmental Engineering and Earth Sciences, University of Notre Dame, Notre Dame, IN 46556, USA Z. Liu : J. Hu State Key Laboratory of Marine Environmental Science, and Department of Physical Oceanography, College of Ocean & Earth Sciences, Xiamen University, 422 Siming South Road, Xiamen 361005, China H. Wei College of Marine Science and Engineering, Tianjin University of Science & Technology, Tianjin 300457, China Z. Liu (*) Room C3-416 Xiping Building, Xiangan Campus, Xiamen University, Xiamen 361102, China e-mail: zyliu@xmu.edu.cn Ocean Dynamics (2013) 63:1189–1201 DOI 10.1007/s10236-013-0656-7