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Ice‐associated phytoplankton blooms in the southeastern Bering Sea can critically impact the food web structure, from lower tropic level production to marine fisheries. By coupling pelagic and sea ice algal components, our 1‐D ecosystem model successfully reproduced the observed ice‐associated blooms in 1997 and 1999 at the NOAA/PMEL mooring M2. The model results suggest that the ice‐associated blooms were seeded by sea ice algae released from melting sea ice. For an ice‐associated bloom to grow and reach the typical magnitude of phytoplankton bloom in the region, ice melting‐resulted low‐salinity stratification must not be followed by a strong mixing event that would destroy the stratification. The ice‐associated blooms had little impacts on the annual primary production, but had significant impacts in terms of shifting phytoplankton species, and the timing and magnitude of the bloom. These changes, superimposed on a gradual ecosystem shift attributed to global warming, can dramatically alter the Bering Sea ecosystem.

[1] During a spring intermonsoon cruise in 2004, depth profiles of total and particulate 234 Th in the upper 100 m were collected at 36 stations in the southern South China Sea (SCS), covering a surface area of $1.0 Â 10 6 km 2 . Thorium-234 was sampled by using a modified small-volume MnO 2 co-precipitation technique, which allows mapping the 234 Th distribution with a high spatial resolution. A stratified structure of 234 Th/ 238 U disequilibria was generally observed in the upper 100 m water column, suggesting that the euphotic zone of the southern SCS in this season can be separated into two layers: an upper layer with low export production rates and a lower layer with high export production rates. At the same time, we observed extensive zones of 234 Th excess within the euphotic layer, which is possibly due to intense remineralization of particulate matter. Particulate organic carbon (POC) export was estimated from a three-dimensional steady state model of Th ratio on suspended particles. The POC export for this region varied from a low of À10.7 ± 1.5 mmolC m À2 d À1 to a high of 12.6 ± 1.1 mmolC m À2 d À1 , with an average of 3.8 ± 4.0 mmolC m À2 d À1 . A negative flux of POC export is interpreted as the result of lateral input of particulate matter from nearby waters. Regional patterns in POC export show enhanced fluxes along the western and southern boundaries of the study region, and a ''tongue'' of low export extending northwestward from $7°N 116°E to $10°N 111°E. This geographic distribution is consistent with the overall surface circulation pattern of the southern SCS in this season.

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