Effects of settled diatoms on autumn phytoplankton blooms in the Pacific Arctic: A process study of sediment resuspension in the Chukchi shelf

Autumn phytoplankton blooms are increasingly observed in the Arctic Ocean due to more frequent strong wind events over open waters. A recent study on the Chukchi shelf suggested that diatoms in sediments can resuspend to the surface during such events, potentially acting as a seed population for blooms. To investigate how resuspended diatoms could influence the dynamics of autumn bloom, we conducted an in situ incubation experiment under two conditions: (1) only nutrients are supplied to and (2) nutrients and microalgae-containing bottom-sediments are inoculated to phytoplankton community. Both experimental conditions resulted in increased microalgal biomass, particularly diatoms. Sediment input enhanced initial biomass, accelerating the transition to the bloom state, whereas the photophysiological parameters, including the maximum specific growth rate and the maximum quantum yield of photosystem II, were similar in both treatments. When only nutrients were supplied, Arcocellulus spp. and common autumn diatoms in the Chukchi Sea, including Rhizosolenia spp. and Leptocylindrus spp., prevailed. Meanwhile, diatoms typically present on the seafloor, such as the Chaetoceros socialis complex, Chaetoceros spp., and Thalassiosira spp., dominated the assemblage when sediments were inoculated. These results indicate that sediment resuspension to the surface potentially influences autumn bloom characteristics, affecting bloom development rate, size structure, and diatom community diversity and composition.