Diffuse
venting on the seafloor occurs where high-temperature fluids rising from
depth become mixed with cold seawater before they exit the seafloor. The
key difference between diffuse and focused vents is how much mixing with
seawater occurs before they are released. In other words, the plumbing
system of focused vents is well-sealed and transports hot fluid from depth
to the seafloor with little or no mixing and the vent fluid comes out
of one small pipe. On the other hand, the plumbing of diffuse vents is
leaky and allows seawater to mix with the vent fluid and this mixture
exits the seafloor over a larger area.
Because
of this mixing, diffuse vents are typically low in temperature, with fluids
cooler than 200°C
(by definition) and usually cooler than about 50°C.
Like the high temperature vents, the warm sulfide-rich water provides
the foundation for a diverse ecosystem of chemosynthetic organisms which
colonize these vent sites. After the 1998 eruption of Axial volcano, diffuse
vents were widespread on the new lava flow. White microbial residue along
the margins of cracks in the lava surface, in the recesses in lobate flows,
and outlining every skylight are evidence for diffuse venting and abundant
subsurface microbial growth throughout the lava flow area. Snowblower
vents are a unique kind of diffuse vent where white flocculent material
is blown out of the seafloor, evidence of a subsurface microbial bloom.
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