|Title||The significance of giant phaeodarians (rhizaria) to biogenic silica export in the California Current ecosystem|
|Publication Type||Journal Article|
|Year of Publication||2018|
|Authors||Biard T., Krause J.W, Stukel M.R, Ohman MD|
|Journal||Global Biogeochemical Cycles|
|Type of Article||Article|
|Keywords||california current ecosystem; carbon; Environmental Sciences & Ecology; export; Geology; global ocean; in situ imagery; living radiolarians; marine silica cycle; Meteorology & Atmospheric; north pacific-ocean; Northwestern Pacific; organic-carbon; Phaeodaria; radiolarian flux; Rhizaria; sargasso sea; sciences; sub-arctic pacific; surface waters|
In marine ecosystems, many planktonic organisms precipitate biogenic silica (bSiO(2)) to build silicified skeletons. Among them, giant siliceous rhizarians (>500 mu m), including Radiolaria and Phaeodaria, are important contributors to oceanic carbon pools but little is known about their contribution to the marine silica cycle. We report the first analyses of giant phaeodarians to bSiO(2) export in the California Current Ecosystem. We measured the silica content of single rhizarian cells ranging in size from 470 to 3,920 mu m and developed allometric equations to predict silica content (0.37-43.42 mu g Si/cell) from morphometric measurements. Using sediment traps to measure phaeodarian fluxes from the euphotic zone on four cruises, we calculated bSiO(2) export produced by two families, the Aulosphaeridae and Castanellidae. Biogenic silica export ranged from <0.01 to 0.63 mmol Si.m(-2).day(-1). These two families alone contributed on average 10% (range 0-80%) of total bSiO(2) export from the euphotic zone. Their proportional contributions increased substantially in more oligotrophic regions with lower bSiO(2) fluxes. Using the in situ Underwater Vision Profiler 5, we characterized vertical distributions of the giant phaeodarian family Aulosphaeridae to a depth of 500 m and inferred their contribution to bSiO(2) export in deeper waters. We found a significant increase of Aulosphaeridae export (<0.01 to 2.82 mmol Si.m(-2).day(-1)) when extended to mesopelagic depths. Using a global data set of in situ profiles, we estimated the significance of Aulosphaeridae to bSiO(2) export and revealed that they can act as major exporters of bSiO(2) to the mesopelagic zone in various regions.