Code 613.1 Branch Seminar: Jen-Ping Chen, I-I Lin, and I-Chou Lin

Department of Atmospheric Sciences, National Taiwan University
The role of Asian dust as an atmospheric forcing in the biogeochemical cycle and primary production in the Northwest Pacific Ocean and neighboring Seas (Yellow/East China Sea and South China Sea) has long been speculated. Dust may contribute to ocean biogeochemistry in various ways. Firstly, the nutrients in the dust may stimulate phytoplankton growth by adding nutrient to the water. Secondly, if nutrients is present in the ocean in abundance, the deposited iron in the dust may stimulates nutrient uptake and leads to higher primary production. Thirdly, if the ocean is devoid of nutrients, the iron deposited may stimulate atmospheric nitrogen fixation. However, due to the lack of observational evidences, it remains unclear what specific role does Asian dust plays and to which extent such processes can be quantified. This research combines multiple remote sensing data sets including SeaWiFS ocean color data, MODIS aerosol optical thickness (AOT), together with a regional dust storm model TAQM/kosa to systematically investigate dust episodes and associated ocean biogeochemistry responses. High correlation between the monthly chlorophyll concentration and AOT was found in the Northwest Pacific to the southeast of Japan. But the simulated daily dust deposition correlates less well with the chlorophyll concentration, and the location of maximum correlation is further south at more remote areas. These discrepancies are still under investigation, but most likely they are due to the time lag of response to the dust input, as well as different sensitivity of biological response at different locations. Inaccuracy of model simulation may also be one of the main causes.