Quantification of Typhoon-Induced Phytoplankton Blooms Using Satellite Multi-Sensor Data

Jiayi Pan,Lei Huang,Adam Devlin,Hui Lin

doi:10.3390/rs10020318

Abstract

Using satellite-based multi-sensor observations, this study investigates Chl-a blooms induced by typhoons in the Northwest Pacific (NWP) and the South China Sea (SCS), and quantifies the blooms via wind-induced mixing and Ekman pumping parameters, as well as pre-typhoon mixed-layer depth (MLD). In the NWP, the Chl-a bloom is more correlated with the Ekman pumping than with the other two parameters, with an R2 value of 0.56. In the SCS, the wind-induced mixing and Ekman pumping have comparable correlations with the Chl-a increase, showing R2 values of 0.4~0.6. However, the MLD exhibits a negative correlation with the Chl-a increase. A multi-parameter quantification model of the Chl-a bloom strength achieves better results than the single-parameter regressions, yielding a more significant R2 value of 0.80, and a lower regression rms of 0.18 mg·m−3 in the SCS, and the R2 value in the NWP is also improved compared with the single-parameter regressions. The multi-parameter quantification model of Chl-a blooms is more accurate in the SCS than in the NWP, due to the fact that nutrient profiles in the NWP are uniform from surface to a deep depth (300 m). Thus, the Chl-a blooms are more correlated with the upper ocean dynamical processes in the SCS where a shallower nutricline is found.

Highlights

Tropical cyclones occur frequently over the tropical and subtropical oceans, accompanied by strong winds that can significantly influence upper ocean dynamics [1,2,3,4,5]
High correlations are found between the Chl-a increase (∆Chl) and the Ekman pumping parameter (LEKM) using a linear regression for both the Northwest Pacific (NWP) and the South China Sea (SCS)
The linear regression suggests that in the NWP, the typhoon-induced Chl-a increase is correlated with the Ekman pumping parameter with a regression rms of 0.024 mg·m−3 and an R2 value of 0.56, while in the SCS, the R2 value is 0.47 and the rms is 0.27 mg·m−3

Summary

Introduction

Tropical cyclones (a rapidly rotating storm system) occur frequently over the tropical and subtropical oceans, accompanied by strong winds that can significantly influence upper ocean dynamics [1,2,3,4,5]. Strong cyclonic systems that form in the Northwest Pacific are known as typhoons. The strong forcing of tropical cyclone or typhoon winds produces two kinds of dynamic responses in the upper ocean, namely turbulent mixing and upwelling, both of which can induce a decrease of sea surface temperature (SST). Typical cyclone-induced SST decreases range from 1 to 6 ◦C [1], though more intensive cooling (9 ◦C) was observed for Typhoon Kai-Tak in the South China Sea (SCS) [6]. The range of temperature drop depends on typhoon intensity and translation speed, and the ocean response is much different for fast- and slow-moving typhoons [2,8]

Methods

Results

Conclusion