Relationship between phytoplankton bloom and wind stress in the sub-polar frontal area of the Japan/East Sea

Abstract

The seasonal dynamics of phytoplankton blooms in the central Japan/East Sea (JES) show pronounced year-to-year variability based on Sea-viewing Wide Field-of-view Sensor (SeaWiFS; 1997∼2003) and Moderate Resolution Imaging Spectroradiometer (MODIS)/Terra (2000∼2003) observations. Wind seems to strongly influence this variability. To study the relationship between wind and bloom initiation, we analyzed daily, remotely sensed wind stress data (Active Microwave Instrument–wind [AMI–wind], NASA Scatterometer [NSCAT], and Quick Scatterometer [QuickSCAT]: 1997∼2003) and daily chlorophyll concentrations based on ocean color data (SeaWiFS and MODIS). The results agreed well with the hypotheses; in spring, blooms began 6∼15 days after wind stress weakened. Fall blooms started 3∼9 days after wind strengthened. We also simulated seasonal changes using a simple light–nutrient model using two values for the respiration ratio: 10% and 20%. The use of 20% seemed to reproduce the timing of the spring bloom quite well but underestimated the absolute level of chlorophyll concentration. On the other hand, using 10% produced a better estimation of the chlorophyll concentration but failed to match the timing. Neither of the model runs reproduced the timing of the fall bloom well.