The role of sex in the sedimentation of a marine diatom bloom

A longitudinal transect in the Atlantic sector of the Southern Ocean extending from the ice‐covered Weddell Sea across the Antarctic Circumpolar Current and into the Polar Frontal Zone was studied repeatedly during the austral spring. The centric diatom Corethron criophilum was found at most stations in variable numbers, but in the Polar Frontal Zone I encountered a large bloom undergoing a mass sexual phase. This event apparently triggered downward transport of empty diatom cell walls in numbers that suggest the phenomenon is significant for the vertical silica flux and the formation of monospecific layers of this important diatom species in Southern Ocean sediments. Comparison of the cell‐wall dimensions of such a monospecific layer with those in the plankton in the sexual phase reveals a characteristic signature that may indicate the provenance of these layers.