The Speciation of Particulate Iron and Carbon in the East Pacific Rise 15oS Near-field Hydrothermal Plume and Underlying Sediments
Tuesday, 16 December 2014
Particulate iron and carbon speciation were measured for water column and sediment samples collected at the East Pacific Rise ridge axis (15oS; Station 18) and approximately 80 km down-current (Station 20) during the US GEOTRACES Eastern Pacific Zonal Transect cruise. Water column particles were collected by in situ filtration (0.2 micron, polycarbonate) from above, within, and below the hydrothermal plume. Water column samples were handled in an anaerobic chamber and stored frozen under inert gas shipboard, and protected from ambient oxygen during analysis. The flocculant, top-layer of the sediments was sampled shipboard under ambient conditions and stored frozen until analysis. Iron and carbon speciation were measured using X-ray microprobe (10.3.2) and scanning transmission X-ray microscopy (STXM) instruments at the Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA, USA. Iron (1s and 2p) and carbon (1s) X-ray absorption near edge structure (XANES) spectroscopy and imaging for particles revealed that: (1) in comparison to the above plume sample, organic carbon is abundant in particles within and below the plume, as well as in surface sediments; (2) iron sulfides are not detectable in any water column sample investigated so far; (3) the fraction of non-sulfide reduced iron is highest in the below plume samples; and (4) the below plume sample is rich in free-living microbial cells.