Prof. Jia-Jang Hung
National Sun Yat-Sen University, Chinese Taipei
Title: Biogeochemical Processes of Nutrient and Organic Carbon on the Internal-Waves Dominated Margin off Dongsha Atoll, North South China Sea
Abstract:
Internal
waves (IWs) are ubiquitous features and have pronounced impacts on carbon
biogeochemistry in marginal seas and deep oceans. In the northern South China Sea (NSCS), the IWs
generated frequently in the Luzon Strait and propagated westward to reach or
break down on the Dongsha continental shelf. To understand the biogeochemical
response of IWs impacts in the Dongsha margin, the study was conducted in several
cruises to measure hydrological (T, S, D) and biogeochemical (nutrients, Chl-a,
organic carbon) conditions from two transects covering the slope, shelf break
and shelf zones of Dongsha Atoll. We found that the surface water off Dongsha
Atoll was generally depleted with nutrients and its DIN/DIP ratio was quite low
and similar to the typical ratio of surface water in the South China Sea.
However, the concentrations of nutrients, Chl-a and particulate organic carbon
(POC) were enhanced after IWs lifted cold and nutrient rich water to the
surface. Meanwhile, the DIN/DIP ratio in the euphotic zone was elevated to
close to aphotic zone after lifting subsurface water to the surface layer. Such
features can be seen in both eastern transect (M1-M6) and northeastern transect
(NM1-NM4) particularly in the shallow zones near the Atoll. The effects of a down-welling occurrence (W2 moored station) on
biogeochemical distributions can be evaluated through a short-term observation
of T, DO and nutrients at 50 m during the passage of IWs. The down-welling IWs can transport DOC and POC into
subsurface layer and affect carbon budget significantly. In addition, the
moored station (the rmistor and trap array) show simultaneous changes of T and
Chl-a at 40, 100 and 150 m, indicating a significant effect of IWs on T and
phytoplankton abundance. The enhanced POC did not accumulate on shelf sediments
(<100 m), which
may imply a transport of Chl-a and POC toward north-western regions. Biological
pump (active and passive carbon transport) was also elevated under the impacts
of IWs in the Dongsha continental shelf.
Biography:
EDUCATION
Ph.D., 1984. University of Wisconsin-Madison
(Soil and Water Chemistry)
M.S., 1978.NationalTaiwanUniversity(Agricultural
Chemistry)
B.S., 1974.NationalChung-HsingUniversity(Soil and
Environmental Science)