The effect of typhoon on particulate organic carbon flux in the southern East China Sea

C.-C Hung,S.-L Li,G.-C Gong,M.-A Lee,Y Chang,Y Yang,S.-J Huang,C -C Chung,E Laws,W.-C Chung,W.-R Yang,H.-Y Chen,W.-C Chou

doi:10.5194/bg-7-3007-2010

Abstract

Abstract. Severe tropical storms play an important role in triggering phytoplankton blooms, but the extent to which such storms influence biogenic carbon flux from the euphotic zone is unclear. In 2008, typhoon Fengwong provided a unique opportunity to study the in situ biological responses including phytoplankton blooms and particulate organic carbon fluxes associated with a severe storm in the southern East China Sea (SECS). After passage of the typhoon, the sea surface temperature (SST) in the SECS was markedly cooler (∼25 to 26 °C) than before typhoon passage (∼28 to 29 °C). The POC flux 5 days after passage of the typhoon was 265 ± 14 mg C m−2 d−1, which was ∼1.7-fold that (140–180 mg C m−2 d−1) recorded during a period (June–August, 2007) when no typhoons occurred. A somewhat smaller but nevertheless significant increase in POC flux (224–225 mg C m−2 d−1) was detected following typhoon Sinlaku which occurred approximately 1 month after typhoon Fengwong, indicating that typhoon events can increase biogenic carbon flux efficiency in the SECS. Remarkably, phytoplankton uptake accounted for only about 5% of the nitrate injected into the euphotic zone by typhoon Fengwong. It is likely that phytoplankton population growth was constrained by a combination of light limitation and grazing pressure. Modeled estimates of new/export production were remarkably consistent with the average of new and export production following typhoon Fengwong. The same model suggested that during non-typhoon conditions approximately half of the export of organic carbon occurs via convective mixing of dissolved organic carbon, a conclusion consistent with earlier work at comparable latitudes in the open ocean.

Highlights

Recent research has shown that typhoons can cause marked cooling of the sea surface, enhance nutrient pumping and result in phytoplankton blooms along storm paths of the typhoon and in adjacent areas (Babin et al, 2004; Bates et al, 1998; Chang et al, 1996; Chang et al, 2008; Lin et al, 2003; Shang et al, 2008; Walker et al, 2005; Zheng and Tang, 2007)
The POC flux after a typhoon was greater than that during non-typhoon periods, indicating that biogenic carbon sinking induced by a typhoon is more efficient than that during non-typhoon conditions
The enhanced POC export flux noted following typhoon Fengwong was attributed to a phytoplankton bloom, as evidenced by a dramatic increase in areal chl-a concentration

Summary

Introduction

Recent research has shown that typhoons (severe tropical storms referred to as tropical cyclones or hurricanes) can cause marked cooling of the sea surface, enhance nutrient pumping and result in phytoplankton blooms along storm paths of the typhoon and in adjacent areas (Babin et al, 2004; Bates et al, 1998; Chang et al, 1996; Chang et al, 2008; Lin et al, 2003; Shang et al, 2008; Walker et al, 2005; Zheng and Tang, 2007). Previous studies of typhoon induced phytoplankton blooms have been based largely on satellite remote sensing data, but it can often be difficult to obtain clear ocean color images during or shortly after typhoon passages because of extensive cloud cover. Sea-based measurements of pre- and post-typhoon phytoplankton biomass and biological activity are limited because of the dangers inherent in field work associated with typhoon events. In situ field observations on the effects of typhoons on biological processes are rare (Chang et al, 1996; Chen et al, 2003; Shiah et al, 2000; Zheng and Tang, 2007) and no reports of the effects of typhoon passage on ocean biogeochemistry, especially carbon export fluxes measured using floating sediment traps, have appeared. Hung et al.: The effect of typhoon on particulate organic carbon flux

Results

Discussion

Conclusion