The sea floor at the site is gradually sloped at depths less than 90 m, but the deeper area is steppy, having gradual slopes over large areas that are near critical for diurnal internal waves and steep steps between those areas that account for much of the depth change. Large-amplitude nonlinear internal gravity waves incident on the site from the east were observed to change amplitude, horizontal length scale, and energy when shoaling. Beginning as relatively narrow solitary waves of depression, these waves continued onto the shelf much broadened in horizontal scale, where they were trailed by numerous waves of elevation (alternatively described as oscillations) that first appeared in the continental slope region. Internal gravity waves of both diurnal and semidiurnal tidal frequencies (internal tides) were also observed to propagate into shallow water from deeper water, with the diurnal waves dominating. The internal tides were at times sufficiently nonlinear to break down into bores and groups of high-frequency nonlinear internal waves.

A strong internal tide is generated in the Luzon Strait that radiates westward to impact the continental shelf of the South China Sea. Mooring data in 1500-m depth on the continental slope show a fortnightly averaged incoming tidal flux of 12 kW m−1, and a mooring on a broad plateau on the slope finds a similar flux as an upper bound. Of this, 5.5 kW m−1 is in the diurnal tide and 3.5 kW m−1 is in the semidiurnal tide, with the remainder in higher-frequency motions. Turbulence dissipation may be as high as 3 kW m−1. Local generation is estimated from a linear model to be less than 1 kW m−1. The continental slope is supercritical with respect to the diurnal tide, implying that there may be significant back reflection into the basin. Comparing the low-mode energy of a horizontal standing wave at the mooring to the energy flux indicates that perhaps one-third of the incoming diurnal tidal energy is reflected. Conversely, the slope is subcritical with respect to the semidiurnal tide, and the observed reflection is very weak. A surprising observation is that, despite significant diurnal vertical-mode-2 incident energy flux, this energy did not reflect; most of the reflection was in mode 1. The observations are consistent with a linear scattering model for supercritical topography. Large fractions of incoming energy can reflect depending on both the geometry of the shelfbreak and the phase between the modal components of the incoming flux. If the incident mode-1 and mode-2 waves are in phase at the shelf break, there is substantial transmission onto the shelf; if they are out of phase, there is almost 100% reflection. The observations of the diurnal tide at the site are consistent with the first case: weak reflection, with most of it in mode 1 and almost no reflection in mode 2. The sensitivity of the reflection on the phase between incident components significantly complicates the prediction of reflections from continental shelves. Finally, a somewhat incidental observation is that the shape of the continental slope has large regions that are near critical to the dominant diurnal tide. This implicates the internal tide in shaping of the continental slope.

In a recent study, satellite images have shown that internal solitons are active in the northern South China Sea (SCS). During the Asian Seas International Acoustic Experiment (ASIAEX) pilot studies, current profiler and thermistor chain moorings were deployed in the spring of 1999 and 2000 to investigate internal solitons northeast of Tung-Sha Island on the continental slope of the northern SCS. Most of the observed internal solitons were first baroclinic mode depression waves. The largest horizontal current velocity, vertical displacement, and temperature variation induced by the internal solitons were around 240 cm/s, 106 m, and 11 C, respectively, while the estimated nonlinear phase speed was primarily westward at 152 4 cm/s. The observed internal solitons could be categorized as four types.The first type is the incoming wave from deep water and can be described reasonably well with the KdV equation. The second and third types are in the transition zone before and close to the turning point (where the upper and lower layer depths are equal), respectively. These two types of solitons were generally near the wave-breaking stage. The fourth type of soliton is a second baroclinic mode and probably was locally generated. The time evolutions are asymmetric, especially at the middle depths. A temperature kink following the main pulse of the soliton is often seen. Higher order nonlinear and shallow topographic effects could be the primary cause for these features.The appearance/disappearance of internal solitons coincides mostly with spring/neap tide. The internal soliton is irregularly seen during the neap tide period and its amplitude is generally small. The time interval between two leading solitons is generally around 12 h. The first baroclinic mode of the semidiurnal tide has a larger amplitude than the diurnal tide and could redistribute its energy into the soliton.

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Abstract. Severe tropical storms play an important role in triggering phytoplankton blooms, but the extent to which such storms influence biogenic carbon flux from the euphotic zone is unclear. In 2008, typhoon Fengwong provided a unique opportunity to study the in situ biological responses including phytoplankton blooms and particulate organic carbon fluxes associated with a severe storm in the southern East China Sea (SECS). After passage of the typhoon, the sea surface temperature (SST) in the SECS was markedly cooler (∼25 to 26 • C) than before typhoon passage (∼28 to 29 • C). The POC flux 5 days after passage of the typhoon was 265 ± 14 mg C m −2 d −1 , which was ∼1.7-fold that (140-180 mg C m −2 d −1 ) recorded during a period (June-August, 2007) when no typhoons occurred. A somewhat smaller but nevertheless significant increase in POC flux (224-225 mg C m −2 d −1 ) was detected following typhoon Sinlaku which occurred approximately 1 month after typhoon Fengwong, indicating that typhoon events can increase biogenic carbon flux efficiency in the SECS. Remarkably, phytoplankton uptake accounted for only about 5% of the nitrate injected into the euphotic zone by typhoon Fengwong. It is likely that phytoplankton population growth was constrained by a combination of light limitation and grazing pressure. Modeled estimates of new/export production were remarkably consistent with the average of new and export production following typhoon Fengwong. The same modelCorrespondence to: C.-C. Hung (cchung@ntou.edu.tw) suggested that during non-typhoon conditions approximately half of the export of organic carbon occurs via convective mixing of dissolved organic carbon, a conclusion consistent with earlier work at comparable latitudes in the open ocean.