Effect of 1998 El Niño on the distribution of phytoplankton in the South China Sea

Abstract

The present study analyzed interannual variation of phytoplankton/Chlorophyll‐a (Chl‐a) distribution in the South China Sea (SCS) for the period from 1997 to 2005 using SeaWiFS‐derived Chl‐a data and other oceanographic data. The results show high spatial variation of Chl‐a concentrations in the SCS and revealed an anomalous event in 1998. High Chl‐a concentrations in the southwestern SCS in the summer season (June to August) may be related with strong Ekman Pumping and strong wind stress, whereas a jet‐shape high Chl‐a region offshore in western SCS was associated with coastal upwelling driven by offshore Ekman transport and Vietnamese offshore current. Chl‐a concentrations in 1998 summer in the SCS were the lowest among the 7 years and were particularly low in the western SCS. At the same season, the jet‐shape Chl‐a region offshore of southeast Vietnam almost disappeared, and southwesterly monsoon winds and offshore current were relatively weaker in 1998. This anomalous event of low phytoplankton biomass in the SCS coincided with an El Niño year in 1998.

Comparison of phytoplankton blooms triggered by two typhoons with different intensities and translation speeds in the South China Sea

“…Ekman pumping velocity (EPV) is an important index of vertical upwelling movements in the upper ocean. EPV was estimated based on daily and monthly wind data (Stewart 2002, Zhao & Tang 2007. In order to eliminate the influence of typhoons on chl a and Fig.…”

Strong enhancement of chlorophyll a concentration by a weak typhoon

“…In the summer, there was a high chl a concentration off Vietnam (Fig. 5b), because southwest -northeast monsoon winds are roughly parallel to the coastline southeast of Vietnam and favorable wind-direction and strong winds can lead to coastal upwelling in coastal areas and Ekman upwelling in offshore areas (Zhao & Tang 2007). The impact of Hagibis on the chl a concentration in the middle of the SCS (the box in Fig.…”

Summer Monsoon Impacts on Chlorophyll-a Concentration in the Middle of the South China Sea: Climatological Mean and Annual Variability

“…Corresponding author: SUN Liang, sunl@ustc.edu.cn monsoon system has a significant impact on the dynamics of marine systems for the entire SCS (Hu et al, 2000;Ning et al, 2004;Zhao and Tang, 2007;Gao and Wang, 2008;Tan and Shi, 2009). Prominent responses of the upper ocean to the summer monsoon are especially evident in the middle of the SCS.…”

“…Hence, our study area is focused mainly on the middle of the SCS, including the prominent monsoon zone and the wide continental shelf south and north of the SCS. Previous studies have shown that sea surface temperature (SST) and Chlorophyll-a (Chl-a, an index of phytoplankton biomass) are two important indicators of the responses of upper ocean conditions to atmospheric forces, e.g., typhoons and monsoons (Zhao and Tang, 2007;Gao and Wang, 2008;Sun et al, 2009Sun et al, , 2010Yang et al, 2010). Although several studies on the spatial and temporal variation of SST and Chl-a have been conducted in the middle of the SCS (Gao and Wang, 2008;Tang et al, 2006;Tan and Shi, 2009), it is still unclear what the quantitative relationship is between the oceanic conditions, variations, and monsoon variability.…”

“…Although several studies on the spatial and temporal variation of SST and Chl-a have been conducted in the middle of the SCS (Gao and Wang, 2008;Tang et al, 2006;Tan and Shi, 2009), it is still unclear what the quantitative relationship is between the oceanic conditions, variations, and monsoon variability. In the present study, compared with previous studies in the middle of the SCS (Zhao and Tang, 2007;Gao and Wang, 2008;Tan and Shi, 2009), we use a longer time series of satellite-derived data to examine the effects of the SCS summer monsoon on the climatological mean state of Chl-a and SST in the middle of the SCS and on their annual variabilities during the period between 19982008. We also apply an SCS summer monsoon index (SCSSMI) to better understand the quantitative relationship between oceanic conditions (e.g., SST, Chl-a) and the annual variability of the monsoon.…”