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

摘要

Severe tropical storms play an important role in triggering phytoplanktonblooms, but the extent to which such storms influence biogenic carbon fluxfrom the euphotic zone is unclear. In 2008, typhoon Fengwong provided aunique opportunity to study the in situ biological responses includingphytoplankton blooms and particulate organic carbon fluxes associated with asevere storm in the southern East China Sea (SECS). After passage of thetyphoon, 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 notyphoons occurred. A somewhat smaller but nevertheless significant increasein POC flux (224–225 mg C m?2 d?1) was detected following typhoonSinlaku which occurred approximately 1 month after typhoon Fengwong,indicating that typhoon events can increase biogenic carbon flux efficiencyin the SECS. Remarkably, phytoplankton uptake accounted for only about 5%of the nitrate injected into the euphotic zone by typhoon Fengwong. It islikely that phytoplankton population growth was constrained by a combinationof light limitation and grazing pressure. Modeled estimates of new/exportproduction were remarkably consistent with the average of new and exportproduction following typhoon Fengwong. The same model suggested that duringnon-typhoon conditions approximately half of the export of organic carbonoccurs via convective mixing of dissolved organic carbon, a conclusionconsistent with earlier work at comparable latitudes in the open ocean.