Abstract
Severe tropical storms play an important role in triggering phytoplankton blooms, yet direct field observation of evidence of the effects of a typhoon is very rare. Sea surface temperature (SST), nitrate concentration, chlorophyll a (chl a) concentration, and particulate organic carbon (POC) flux were measured before and shortly after Typhoon Jangmi which affected the southern East China Sea (SECS) on September 28 ~ 29, 2008. In situ SST (27.5 ~ 28.0°C) on September 19 ~ 21, decreased to ~24.0°C (October 3 ~ 6) in the SECS 4 ~ 7 days after the passage of Typhoon Jangmi. In situ nitrate and chl a concentrations 7-days (on October 6) after the passage of Jangmi were 1.9 μM and 1.61 mg m^(-3), respectively, much higher than those (nitrate: 0.3 μM and chl a: 0.73 mg m^(-3)) concentrations before the typhoon (September 21). The enhanced chl a concentration is thus caused by a nutrient supply via vertical mixing or upwelling in the euphotic zone. The POC flux 7-days after Jangmi's passage was 552 ± 28 mg-C m^(-2) d^(-1), a ~2.5-fold increases before the typhoon (224 ± 33 mg-C m^(-2) d^(-1), on September 21). Our results suggest that typhoons indeed can stimulate efficient POC export out of the euphotic zone, while it is still poorly understood with regard to the total effects of a typhoon on nutrient dynamics and detailed carbon sequestration due to sampling difficulty. Therefore, successional sea-going observations ought to be conducted in the affected area after the passage of typhoons.
Highlights
Research has shown that tropical cyclones or dust storm events have pronounced affects on nutrient supply, phytoplankton activities, primary production, pollutant discharge, rainfall, and carbon cycling (Chang et al 1996, 2008; Babin et al 2004; Hung et al 2005, 2007, 2009, 2010a; Walker et al 2006; Zheng and Tang 2007; Shang et al 2008; Chou et al 2009, 2011; Huang et al 2011; Chen and Tang 2012; Jan et al 2013)
Sea-based experiments were conducted in the southern East China Sea (SECS) (25.5°N, 122.0°E, indicated as a blue asterisk in Fig. 1, water depth ~130 m, approximately 70 km northeast of Taiwan), on the research vessel Yang-Ming 66, with five separate cruises on 9/17, 9/19, 9/21, 10/3 and 10/6 in 2008
The observed cooling phenomenon in the SECS was primarily associated with the effect of Typhoon Jangmi (Fig. 2a)
Summary
Research has shown that tropical cyclones (e.g., typhoons in the Pacific and hurricanes in the Atlantic) or dust storm events have pronounced affects on nutrient supply, phytoplankton activities, primary production, pollutant discharge, rainfall, and carbon cycling (Chang et al 1996, 2008; Babin et al 2004; Hung et al 2005, 2007, 2009, 2010a; Walker et al 2006; Zheng and Tang 2007; Shang et al 2008; Chou et al 2009, 2011; Huang et al 2011; Chen and Tang 2012; Jan et al 2013). The SECS is not an oligotrophic region, yet there is no large river input into the region, and the satellite ocean color data in the study area are likely representative of the sea conditions unaffected by terrestrial materials (Liu et al 1995; Hung et al 2000, 2012). Even though an upwelling phenomenon (mainly below 150 m) off northeast Taiwan has been reported by Wu et al (2008a), the cold dome in the surface water on the shelf-break in the study area of the SECS has only been intermittently observed in summer (Chern et al 1990; Liu et al 1992; Gong et al 1995; Jan et al 2011)
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