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SUMMARY:Hydrothermal sediments are a source of water column Fe and Mn in t
 he Bransfield Strait\, Antarctica - Dr Rachel Mills ( Southampton Universi
 ty)
DTSTART:20140218T163000Z
DTEND:20140218T173000Z
UID:TALK49568@talks.cam.ac.uk
CONTACT:Natalie Roberts
DESCRIPTION:Sediments from the top of Hook Ridge\, a submarine volcanic ed
 ifice in the Central Basin of the Bransfield Strait\, Antarctica\, supply 
 significant Fe and Mn to the overlying water column. Low-temperature hydro
 thermal fluids advect through these sediments and\, in places\, subsurface
  H2S is present at high enough concentrations to support abundant Scleroli
 num sp.\, an infaunal tubeworm that hosts symbiotic thiotrophic bacteria. 
  Pore water Fe and Mn content is high within the subsurface ferruginous zo
 ne\; 14-18 times higher than values measured at a nearby\, background site
  of equivalent water depth. Sequential extraction of the sediment demonstr
 ates that there is a significant enrichment in a suite of reactive\, authi
 genic Fe minerals in the upper 0-5 cm of sediment at one site. At a site w
 ith only minor authigenic mineral surface enrichment we infer that leakage
  of pore water Fe and Mn from the sediment leads to enriched total dissolv
 able Fe and Mn in bottom waters\, which have a distinct Eh signature over 
 several km laterally at the depth of Hook Ridge. We hypothesize that the m
 ain mechanism for Fe and Mn efflux from the sediment is breach of the surf
 ace oxic layer by the abundant Sclerolinum sp.\, supplemented by episodic 
 enhancements by physical mixing and resuspension of sediment in this dynam
 ic volcanic environment.  We propose that Hook Ridge sediments are an impo
 rtant source of Fe and Mn to the deep waters of the Central Basin in the B
 ransfield Strait\, where concentrations are sustained by the benthic flux\
 , and that Fe is stabilised in the water column as either colloidal phases
  or ligand- bound dissolved species.  Entrainment of this water mass into 
 the Drake Passage and thereby the Antarctic Circumpolar Current could prov
 ide a significant metal source to this HNLC region of the Southern Ocean i
 f mixing and upwelling occurs before removal of this metal pool to underly
 ing sediments.  Sediment-covered volcanic ridges are common within rifted 
 margins\, and may play a previously overlooked role in the global Fe cycle
 . 
LOCATION:Harker 1 seminar room\, Department of Earth Sciences
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