Acantharian cysts: high flux occurrence in the bathypelagic zone of the Scotia Sea, Southern Ocean

The abundance and flux of acantharian cysts were recorded for a period of 12 months from December 2012 to 2013 in a sediment trap deployed at 1500 m in the north-eastern Scotia Sea, Southern Ocean. Acantharia (radiolarian protists) are found globally, have very dense celestite skeletons, and form cysts which can sink rapidly through the water column. However, they are highly soluble in seawater and have rarely been found to contribute significantly to fluxes of particulate organic carbon (POC) in mesopelagic or bathypelagic zones. We measured fluxes of acantharian cysts of up to 2706 ind. m−2 day−1, which we estimate to drive a POC flux of 5.1 mg C m−2 day−1. These acantharian cyst fluxes are unprecedented in the literature, and accounted for 17% of the annual POC flux at this site (0.5–26.0%). The high fluxes of acantharian cysts (and associated high POC fluxes) measured highlight the pressing need for further research into the life cycles of Acantharia to understand what drives the mass flux of their cysts, and to determine the contribution of Acantharia to the biological carbon pump.