Ecological Effect of Nonlinear Internal Wave Interaction on Chlorophyll Concentration on the Continental Shelf in the South China Sea

Abstract:

Ocean internal waves (IWs) occurred frequently and extensively in the northern South China Sea (SCS). We studied the effect of interacting nonlinear internal waves (IWs) on chlorophyll concentration variations in the northern South China Sea using the multi-sensors of the Envisat, ERS-2 and MODIS synthetically. Representative cases of the IWs spatial distribution in June in 2005, 2007 and 2009 provide the detailed analysis on the vicinity of the Dongsha Atoll. Unambiguously, results from the depth-integrated body force model, indicated that Luzon Strait was the main generation source of the large-scale IWs. Forcing of two parallel meridional ridges, Lan-yu and Heng-chun, played a more important role than adjacent regions (over 2 m²/s²). The chlorophyll (CHL) concentration enhancement detected by the ocean color sensors was consistent with the large-scale IWs activity from Luzon Strait. Our studies demonstrated that large-amplitude IW packets had a significant influence on the phytoplankton. In the vertical direction, CHL concentration lifting from sub-surface fluctuated along with the IWs activity, and was up to maximum (0.35 mg/m³) at the wave crest. Meanwhile, the peak value of CHL concentration decreased and the fluctuation disappeared with the spread of nonlinear IWs horizontally. A Deep Chlorophyll Maximum model (DCM) was introduced with this remote sensing inversion results, and the presence of IWs activities displace the top of the DCM and have an elevation where the effective light is just enough to produce a measurable response in the ocean color sensors. As further revealed, these large-scale IWs generated from Luzon Strait travelled long distance on the continental shelf in the SCS, significantly impacting vertical distribution, water masses and the ocean mixing.