Eddy-feature phytoplankton bloom induced by a tropical cyclone in the South China Sea

Abstract

This is the first report on an eddy-feature phytoplankton bloom induced by a tropical cyclone (the spiral structure of the bloom was coincident with that of a cold eddy) in the South China Sea (SCS). Applying satellite data, this report can furnish fresh evidence of the relationship between the bloom and the cold eddy. Tropical cyclone Linfa passed over the northern SCS from 16 to 21 June 2009. While it looped over for 2 days (from 17 to 19 June), a cold eddy, which lasted for 11 days in the looping area, was observed on 18 June. Subsequently, an eddy-feature phytoplankton bloom (central location: 18° N, 117.5° E) was detected on 22 June and it remained for 17 days. The character of both the cold eddy and the bloom was rotating counterclockwise, with two arms. High Ekman pumping velocity (>4.5 × 10⁻⁴ m s⁻¹) was estimated during the passage of Linfa (from 17 to 19 June). The monthly climatology of the mixed layer depth was about 20 m in June, and the maximum Ekman layer depth was about 346 m after Linfa. The analysis indicated that Linfa may have induced the cold eddy, where it looped around. With upwelling and entrainment, the eddy potentially provided nutrients to the bloom in the surface water. The results suggested that the sea surface current changes that Linfa induced had caused the bloom in an eddy feature. Tropical cyclones appear frequently in the SCS, which may affect the activities of mesoscale eddies in this area.

Acknowledgements

The present research was supported by the following grants awarded to D. Tang: (1) National Natural Science Foundation of China (40976091, 31061160190 and 40811140533); (2) Chinese Academy of Sciences (kzcx2-yw-226); (3) the CAS/SAFEA International Partnership Programme for Creative Research Teams (KZCX2-YW-T001 and KZCX2-YW-213); (4) Guangdong Natural Science Foundation, China (8351030101000002). NASA's Ocean Color Working group provided the MODIS data. Remote Sensing Systems provided the QuikScat wind-vector data. The Physical Oceanography Distributed Active Archive Center (PO.DAAC) provided the GHRSST and QuikScat wind speed data. We thank Dr Gad Levy of North West Research Associates, USA, Ms Pauline Lovell and Ms Stephanie King for their comments on the manuscript.