Diatom Resting Spore Formation and Carbon Export in the Southern Ocean

In the Southern Ocean, numerous observations suggest a strong attenuation of the vertical carbon flux with depth. This is probably due to efficient particle reprocessing by zooplankton and high remineralization rates by active bacterial communities in productive areas. Resting spore formation by diatoms is an ecological strategy frequently observed in neritic productive areas. Until recently, the impact of this process on biogeochemical cycles and more specifically carbon export was neglected.

We present chemical and diatom export fluxes from sediment trap deployments located in the vicinity of Subantarctic Islands: South Georgia, Crozet and Kerguelen. For each island system, an annual record of export is available in an HNLC site and a productive site. Carbon export appears to be low at the three sites (<100 mmol m^-2 yr^-1) with a two times increase between the HNLC and the productive areas. In the HNLC areas, the higher BSi:POC ratio is associated with a dominance of Fragilariopsis kerguelensis to the exported diatom community. We highlight the important contribution (40-60 %) of resting spores to carbon export at different depth horizons in the productive, naturally-fertilized areas, supporting their high transfer efficiency. This similar mechanism observed in the three island systems suggests that resting spore formation is a significant process driving carbon export in the Southern Ocean.