Hydrothermal plumes sulphidic

The origin of microbes present in hydrothermal plumes is believed to be either from a subsurface biosphere maintained by the rapid mixing processes that take place during plume formation or from entrained seawater microbes (Winn etal., 1995 Cowen etal., 1998,1999). In the latter case, most of the organisms would not be able to grow, but a small segment of the population may thrive and multiply as plumes move away from the ridge crest. Similar forms to plume bacteria are common on rock surfaces near vents and on sulphide structures (Jannasch ... 

In comparison, Fe oxidation and deposition appear to be much less common in plumes. About half the Fe in the hydrothermal fluids combines with H2S and is rapidly transformed into Fe sulphides within a few seconds of release (e.g. Rudnicki Elderfield, 1993 James etal., 1995), and much of the Fe2+ that escapes sulphide precipitation is rapidly and spontaneously oxidized in well-oxygenated seawater making it difficult to evaluate the bacterial contribution to the redox transformations of hydrothermal Fe in plumes (Lilley etal., 1995 Winn etal., 1995). Nevertheless, high Fe/Mn particles and Fe-encrusted capsule forms have been observed in plumes at Axial Volcano (JDFR) the physicochemical characteristics of the capsules may be responsible for the passive or surface-enhanced deposition of iron (Cowen etal., 1999). Thiosulphate, the primary product of sulphide autooxidation, may also serve as a useful energy source, but this is yet to be documented in hydrothermal plumes (Winn etal., 1995 Cowen German, 2002). 

Scott, 1997). Where these deposits are relatively large, such as at the TAG mound on the Mid-Atlantic Ridge, they resemble ancient volcanic-hosted massive sulphide (VMS) deposits like those presently found in ophiolites (Rona Scott, 1993 Humphris etal., 1995 Mills, 1995 Goulding etal., 1998 Scott, 1997). Some of the metals at hydrothermal vents are discharged as black smoke along with gases and other dissolved ions, and are expelled into plumes above and away from the vents (see Section 2.4). 

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