Mechanism for initiation of the offshore phytoplankton bloom in the Taiwan Strait during winter: a physical–biological coupled modeling study J. Wang1, H. Hong1, Y. Jiang1, and X.-H. Yan1,2 1State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen 361005, Fujian, China 2College of Earth, Ocean and Environment, University of Delaware, Newark, Delaware, 19716, USA
Received: 31 Jul 2013 – Revised: 14 Aug 2013 – Accepted: 20 Aug 2013 – Published: 05 Sep 2013
Abstract. In situ observations showed phytoplankton blooms appear during winter in the
Taiwan Strait (TWS), but the mechanism for bloom initiation was unclear.
With the use of a coupled physical–biological numerical model, we find the
winter bloom is triggered by the relaxation of the northeasterly monsoon.
Thus, the aim of this study is to investigate the mechanism for bloom
formation using the model. The model results show the weakening of the
northeasterly wind generates a current that carries the fresh eutrophic
Min-Zhe coastal water (MZCW) off the west coast of the TWS; then a stable
stratification is formed in the upper ocean of the western strait, which
significantly limits the turbulence. Via diagnostic analysis of the model
output, we illustrate that the reduced turbulence allows the phytoplankton
to accumulate within the upper layer of the western strait, which leads to
an increase in chlorophyll. The analysis is further verified by the critical
turbulence theory about the bloom. In addition to reduced turbulence, the
lag between zooplankton and phytoplankton responses to the offshore
extension of the MZCW is responsible for the formation of the bloom at the
front. Therefore, we propose the observed offshore bloom in winter in the
TWS is induced by the stable water stratification and the biological
processes during the relaxation of the northeasterly wind.
Citation: Wang, J., Hong, H., Jiang, Y., and Yan, X.-H.: Mechanism for initiation of the offshore phytoplankton bloom in the Taiwan Strait during winter: a physical–biological coupled modeling study, Biogeosciences Discuss., 10, 14685-14714, doi:10.5194/bgd-10-14685-2013, 2013.