Impact of Typhoon Morakot on chlorophyll a distribution on the inner shelf of the East China Sea

Abstract

To study typhoon-induced variations in chlorophyll a (chl a) distribution, 2 surveys were conducted on the inner shelf of the East China Sea, and 3 remote sensing images were selected before and after the passage of Typhoon Morakot. Chl a was predominantly present in coastal waters and the euphotic zone during normal, pre-typhoon conditions at a concentration >0.7 mg m-3. After the passage of the typhoon, the chl a concentration drastically declined to <0.5 mg m-3, except for in the surface layer in coastal areas, where the concentration of chl a was >1.0 mg m-3 due to the abundant fresh water supply from typhoon-induced runoff. Remote sensing data indicated that under normal conditions, the concentration of surface chl a was ~1.0 mg m-3, whereas it increased to >10.0 mg m-3 post-typhoon. A typhoon-initiated chl a increase showed a delay of ~4 to 7 d. A 3-stage conceptual model is proposed to describe the time-evolution of chl a. The first stage is the normal, pre-typhoon condition. The second stage is the typhoon-active period, when chl a generally decreases due to the presence of opposing factors, such as increasing turbidity and cloud cover, while in the coastal surface water layer, chl a is increased due to the fresh water supply. The third stage is the post-typhoon condition, when the opposing factors disappear and an increase in nutrient supply causes an increase in chl a. © Inter-Research 2013.