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

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 (similar to 25 to 26 degrees C) than before typhoon passage (similar to 28 to 29 degrees C). The POC flux 5 days after passage of the typhoon was 265 +/- 14 mg Cm-2 d(-1), which was similar to 1.7-fold that (140-180 mg Cm-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 Cm-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.