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Hydrothermal
plumes are created and sustained by the heat of volcanic processes along
the Mid-Ocean Ridge system that circles the globe. Hydrothermal systems
consists of circulation
zones where seawater interacts with rock, thereby changing chemical
and physical characteristics of both the seawater and the rock. The altered
seawater, called hydrothermal
fluid, is injected back into the ocean at hydrothermal vent fields and
forms hydrothermal plumes. These plumes are often black or white with the
color coming from mineral particles that precipitate rapidly as hot hydrothermal
fluids (with temperatures as high as 340oC) mix with cold seawater (usually
about 1-2oC) at or just below the vent orifice. Some hydrothermal fluids
may be cooler and nearly absent of particles, but the hottest plumes are
generally colored black and are called "black
smokers."
Hydrothermal plumes can be detected
in seawater overlying vent fields, and beyond, because they have a distinctly
different physical and chemical signature from the surrounding seawater.
The heat and particle content of hydrothermal plumes are two readily measurable
parameters. These parameters are usually elevated relative to unaffected
seawater, and measurable differences can be detected as far as tens to hundreds
of kilometers away from the vent fields. The NOAA-VENTS Plume Studies Group
has pioneered methods for measuring
and mapping hydrothermal plumes based on the detection of these temperature
and particle anomalies.
The distribution
and intensity of hydrothermal plumes is variable in both space and time.
Volcanic activity on the seafloor can produce enormous and profound changes
in hydrothermal discharge. The importance of this impact was first realized
with the discovery of a "megaplume"
in 1986, and subsequent verification of fresh lava flows on the seafloor
in the same area. Since that time, a major objective of the NOAA-VENTS
program has been to monitor for and respond to volcanic events occurring
on mid-ocean ridges off the west coast of the United States to assess
the impact of these events on the ocean environment, particularly with
respect to the thermophile
and hyperthermophile microbial community they release into the ocean,
and to track the subsequent evolution of hydrothermal systems.
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