In the northeastern South China Sea, fast westward moving nonlinear internal waves (NLIWs) emanate nearly daily from the Luzon Strait during spring tide. Their propagation speed of about 2.9 meters per second is faster than NLIWs previously observed in the world's oceans. The amplitudes of these waves reach 140 meters or more, and they are the largest free propagating NLIWs observed to date in the interior ocean. These NLIWs energize the top 1500 meters of the water column, moving water up and down at timescales as short as 20 minutes. While their associated energy density and energy flux are the largest observed to date, the exact source of these giant waves has yet to be determined.

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Our long-term goal is to locate the source of non-linear internal waves (NLIWs) in the northern South China Sea (SCS), study their generation mechanism and establish the capability to predict its generation time and propagation path. OBJECTIVES In 2005, locate NLIWs with satellite image analysis and field data collection, and study their characteristics. In 2006, study the evolution of NLIWs from internal tide. In 2007, study their generation mechanism, and derive a model to predict their generation and propagation.

The La Niña of 2007/2008 was particularly strong, so was the southward flow of the cold, nutrient-rich Changjiang (Yangtze River) Diluted Water (CDW) when the winter monsoon started to blow in the fall. Here we use shipboard data in 2008 in two transects, one in the southwestern East China Sea and one in the southern Taiwan Strait, to show that as late as April in 2008 the CDW was still clearly identifiable when the winter monsoon had weakened. Waters as cold as 16 °C with a salinity lower than 30 still occupied the southwestern East China Sea. Waters of 17 °C and S < 32 could also be found off the coast of China in the central Taiwan Strait. The concentration of NO3 + NO2 was higher than 18 μmol L−1 at both places, which was as much as 40 times higher than the northward moving South China Sea (SCS) water to the east. As a result, the Changjiang River plume may be a significant source of nutrients, particularly N, to the oligotrophic, N-poor SCS, especially in the La Niña years. Indeed, colder and more turbid CDW was more intense and went farther south in 2008 compared with the normal springs of 2006, 2007 and 2009.