Lin¹, I.-I., W. Timothy Liu², Chun-Chieh Wu ³, George T. F. Wong⁴, Chuanmin Hu⁵, Zhiqiang Chen⁵, Wen-Der Liang¹, Kon-Kee Liu¹, and Yih Yang¹

¹National Center for Ocean Research, P.O. Box 23-13, Taipei, 10617, Taiwan, ²Jet Propulsion Laboratory, NASA, Pasadena CA 91109-8099, USA, ³Department of Atmospheric Sciences, National Taiwan University, Taipei, Taiwan, ⁴Department of Ocean, Earth and Atmospheric Sciences, Old Dominion University, Norfolk, Virginia 23529-0276, USA and ⁵College of Marine Sciences, University of South Florida, St. Petersburg, Florida 33701, USA

The fertilisation of the sea by a tropical cyclone

Traditionally accepted mechanisms of nutrient supply to the upper ocean are insufficient for supporting the new production in the oligotrophic ocean estimated from geochemical tracers^1-3. This paradox, whose resolution is critical for a full understanding of the global carbon cycle, has generated an intensive search for sources of allochthonous nutrients to the upper ocean^3-9. Episodic injections of nutrients as a result of enhanced vertical mixing and upwelling across the nutricline pumped by tropical cyclones, is a possibility that has been much speculated yet largely undocumented by direct observations^10-13. Here we use a combination of newly available remote sensors and show that the impact of a moderate cyclone can be far reaching. In July 2000, tropical cyclone Kai-Tak transgressed through the South China Sea (SCS). It caused up to 300 times increase in phytoplankton biomass and 9°C reduction of sea surface temperature. A minimum of 0.8 Mt of carbon, equivalent to 2-4% of the annual new production in the oligotrophic SCS, has been generated. Given that there are in average 14 tropical depressions/cyclones passing SCS annually, their contribution to the SCS carbon cycle is significant.