Transcript PowerPoint Presentation - Black Smokers and Blue Ice

Antarctic Hydrothemal Vents
and Plate Tectonics
Steven Stevenoski
Principle Investigators
Dr. Gary Klinkhammer
Oregon State University
Marine Geophysics
Principle Investigators
Dr. Larry Lawver
University of Texas Institute for Geophysics
Marine Geophysics
Why Look For Vents in
Antarctica?
What are Vents?
•Located near regions of seafloor
spreading.
•Locations where porous rock is in
contact with the mantle.
•Areas where superheated water in
contact with the mantle is released
through the crust.
•A plume of dissolved minerals that
precipitate rapidly in the water column.
• When hot (350-400 deg C)
chemically enriched fluids first
emerge from a hydrothermal
vent they are buoyant because
they are hotter than the typical
deep-ocean (about 2 deg C).
• They are also saturated with
all kinds of minerals which
start to precipitate as soon as
the fluid is cooled forming thick
rising plumes of blue-black
sulfide mineral smoke –hence their common name of
'black smokers'.
• The plume that forms above
any hydrothermal vent can
typically rise 100-300m up
above the seafloor before it is
diluted enough and it no longer
goes on rising.
• Typically, by this stage, the
water which reaches this nonbuoyant stage represents a
10,000:1 dilution of vent-fluid
with ordinary seawater which
has been mixed in during the
turbulent ascent of the plume.
• Fortunately many of the
chemicals in vent-fluids are
concentrated up to 1 million
times more strongly than
ordinary seawater - so even
after all that dilution they still
contain 100 times more
material than ordinary
seawater.
• These plumes spread out over
kilometers and even tens of
kilometers downstream from
any vent-field - our record at
present is about 50km from
the source.
Where do you look for
vents in Antarctica?
• ZAPS, or zero angle photon
spectrometer, has been used to
look for Antarctic vents. The fiber
optic spectrometer gives scientists
a true picture of chemical changes
in water over time.
• Dählmann, A., Wallmann, K., Sahling,
H., Sarthou, G., Bohrmann, G.,
Petersen, S., Chin, C., Klinkhammer,
G.: Hot vents in an ice-cold ocean:
Indications for phase separation at the
southernmost area of hydrothermal
activity, Bransfield Strait, Antarctica,
Earth Planet. Sci. Lett. 193 (3-4), 381394 (2001)