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Participant
Interview:
Ron Greene
Chemist
Oregon State University, Vents Program
Today I was able to satisfy
my own curiosity. Every time the CTD unit came back on deck Ron Greene
would be the first to start collecting samples in shiny copper tubes.
It was when he started vigorously tapping up and down their length with
a metal rod that I began to wonder what was going on.
I tracked down Ron Greene, a research assistant for John Lupton of the
NOAA Pacific Marine Environmental Laboratory (PMEL). The research group
he is with is studying the effects of hydrothermal venting in the Pacific
Ocean.
Ron grew up in Washington.
After graduating from college, he fished off the Washington/Oregon coast
for a living. After a few years Ron married, moved to Oregon and joined
the Helium Isotope Laboratory research group at PMEL. The group is comparing
the He isotope 3 and 4 ratio in the ocean to study the effects of hydrothermal
venting at spreading centers and to map deep ocean circulation and mixing.
It is at hot spots and seafloor vents that the mantle causes the enrichment
of He isotopes 3 and 4. 3He is three million times more rare than 4 He.
An increase in the amount of 3He in the deep ocean compared to the ambient
ocean water is due to the release of 3He from the mantle. So how does
this explain his vigorous tapping of the copper tubes?
It turns out that the earth's
air also has a similar ratio of 3He to 4He to that of deep ocean water
that hasn't been enriched. The special copper tubing is capped at both
ends to keep it very clean before it is filled with the samples of deep
ocean water. In the filling process both caps are removed and sample water
from the nisken bottle flows through the copper tube to flush it out.
Some air can cling to the inside of the tube walls as tiny bubbles during
the initial collection. To release these bubbles the tube is vigorously
tapped up and down its' length. In the lab work area the tubes are clamped
shut and when the tube is shaken it has a special metallic sound that
lets the scientist know all the air has been removed from the tube. The
tubes are sent back to the Newport, Oregon lab so the water samples can
be analyzed using a mass spectrometer.
How much the 3He to 4He
ratio of this deep ocean sample deviates from the Earth's air 3He to 4He
ratio is determined. Now the helium data is reported in units of delta
(3He)%. Why use 3He as a tracer? He is an inert gas that has stable isotopes
that are not affected by the living organisms in the ocean. It is only
changed by dilution. How do scientists like Ron use this information?
The deviation of 3He can help scientists locate the hydrothermal vents
and track the deep ocean currents. Scientists use this information to
study the Earth's climate and heat budget. Since it can take 500 years
for deep ocean water to reach the surface long term studies are needed.
Thank you Ron for explaining
a complicated study and satisfy my curiosity.
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