In a joint project 1997-2000 the University of Hamburg (Germany) and the Ocean University of Qingdao (China) have investigated the circulation, water mass structure, sediment transport, nutrient fluxes, and phytoplancton dynamics of the Bohai Sea. A hierarchy of coupled circulation, transport and production models for the seasonal scale has been developed and tested against field data from two ship cruises in autumn 1998 and in spring 1999. The main objective of the project was the qualitative and quantitative description of the mass and matter fluxes in the Bohai Sea. In addition to annual averages, seasonal variability as a consequence of meteorological forcing, riverine inputs and light availability has been studied. Particular interest was directed to local and global fluxes of salt (fresh water), suspended particulate matter, nitrogen and phosphorus. It turned out that the astronomical tides enhance all mixing processes and propagate dissolved and suspended material through the residual currents. Beyond the tides the main external forcing is by the atmospheric fluxes of momentum and heat resulting in a strong seasonal signal. The hitherto dominating SPM and nutrient input by the Yellow River is weakening due to the decreasing freshwater discharge. This means that the atmospheric input of nutrients becomes more important. The models of the 3D hydrodynamics, of SPM transport, nutrient dynamics and primary production reproduce the natural situation as far as observational data are available. This is especially true for the simulation of the flow and mass fields for scales from hours to years.
The circulation models will allow now reliable scenario calculations in the decadal range provided the atmospheric forcing and the river discharges are available. For the biogeochemical fluxes and primary production modelling more field data is necessary. Besides of a longterm monitoring, specific multiship experiments are neede for identification and quantification of the major chemical and biological processes. These campaigns should be accompanied by high resolving remote sensing and modelling of ocean and atmosphere dynamics. |
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