Major contribution of diatom resting spores to vertical flux in the sub-polar North Atlantic

The mass sinking of phytoplankton cells following blooms is an important source of carbon to the ocean's interior, with some species contributing more to the flux of particulate organic carbon (POC) than others. During the 2008 North Atlantic Bloom Experiment in the Iceland Basin, we examined plankton community composition from surface waters and from sediment traps at depths down to 750 m. Samples collected with neutrally buoyant Lagrangian sediment traps captured a major flux event. Diatoms comprised ≥99% of cell flux into the sediment traps, with vegetative cells and resting spores of the genus Chaetoceros contributing 50–95% of cell flux. Resting spores of one species, identified as Chaetoceros aff. diadema, were dominant, comprising 35–92% of cell flux. The flux of resting spores ranged from 2 to 63 mg C m−2 day−1 and was significantly correlated with POC flux (p=0.003). Over the course of 10 days, the flux of resting spores increased by 26 fold, suggesting that the cells sank en masse, possibly in aggregates. In contrast, vegetative cells of C. aff. diadema sampled from surface waters during the period preceding the flux event generally comprised