Acantharian cysts were discovered in sediment trap samples from spring 2007 at 2000 m in the Iceland Basin.<br/>Although these single-celled organisms contribute to particulate organic matter flux in the upper mesopelagic,<br/>their contribution to bathypelagic particle flux has previously been found negligible. Four time-series sediment<br/>traps were deployed and all collected acantharian cysts, which are reproductive structures. Across all traps, cysts<br/>contributed on average 3–22%, and 4–24% of particulate organic carbon and nitrogen (POC and PON) flux,<br/>respectively, during three separate collection intervals (the maximum contribution in any one trap was 48% for<br/>POC and 59% for PON). Strontium (Sr) flux during these 6 weeks reached 3 mg m22 d21. The acantharian<br/>celestite (SrSO4) skeleton clearly does not always dissolve in the mesopelagic as often thought, and their cysts can<br/>contribute significantly to particle flux at bathypelagic depths during specific flux events. Their large size<br/>(, 1 mm) and mineral ballast result in a sinking rate of , 500 m d21; hence, they reach the bathypelagic before<br/>dissolving. Our findings are consistent with a vertical profile of salinity-normalized Sr concentration in the Iceland<br/>Basin, which shows a maximum at 1700 m. Profiles of salinity-normalized Sr concentration in the subarctic<br/>Pacific reach maxima at # 1500 m, suggesting that Acantharia might contribute to the bathypelagic particle flux<br/>there as well. We hypothesize that Acantharia at high latitudes use rapid, deep sedimentation of reproductive<br/>cysts during phytoplankton blooms so that juveniles can exploit the large quantity of organic matter that sinks<br/>rapidly to the deep sea following a bloom
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