SEASONAL AND DIEL VARIATION IN THE OPEN OCEAN CONCENTRATION OF MARINE SNOW AGGREGATES

MARINE snow, generally defined as aggregated particles of diameter greater than 0.5 mm, is thought to play an important role in oceanic biogeochemical cycles1. Recent studies have focused on its unusual physical, biological and chemical properties but its temporal variability has received scant attention 2-6. Here we report observations of the abundance, volume concentration and size distribution of marine snow over a five-month period at a single site in the Northeast Atlantic. At a depth of 270 m, marine snow particles demonstrated strong seasonal and diel variability. Volume concentrations in spring were about 20 times those in summer and autumn with late morning concentrations up to three times higher than at other times of the day. Our results suggest that the marine snow forms as a result of highly dynamic interactions in the particle pool. We believe that the mid-water biota and their migratory behaviour are responsible for the diel variability; they are therefore likely to have a significant influence on marine snow concentrations and hence on open-ocean material flux.