Today we passed the ½ way point: completed half our casts, half our stations, and half of our days at sea!
Spirits are high, not just
because of how far we have come, but also because we’re occupying a station on
top of the East Pacific Rise. The following comes from my interview of our
co-chief scientist, Dr. Chris German (Woods Hole Oceanographic Institute).
The image above shows the height
of the crust (or “ground”) above the earth’s mantle with continents in reds and
greens and seafloor features in blues. Lighter blues indicate more shallow
parts of the ocean. The 3 black arrows point to the East Pacific Rise which you
can see snaking down from North America nearly all the way to Antarctica. It is
the world’s FASTEST spreading mid-ocean ridge where fresh ocean crust forms.
Here’s a similar image our ship
generated of seafloor height as we arrived at the station. The red band is our
ridge, rising up over 1,000m above the rest of the seafloor (in blue). Previous
stations were in ~4,000m of water while this station on top of the ridge is
only 2,600m deep.
The East Pacific Rise spreads at
an average of 20 cm per year, but in actuality we believe lava spurts out to
the surface in large, 1 m blows once every 5 years. Chris says, “That’s kind of
cool, because everything we’re doing today is based on research work from 20
years ago – which is 4 or 5 eruptions back. So the seafloor probably isn’t the
same shape it was before.”
How did we know to come here?
Helium-3 (3He) is a
particularly special isotope because it is the heaviest atom that can escape
Earth’s gravity and fly off into outer space, never to return. There is no 3He
“laying around” on the Earth or in its atmosphere unless it was recently
released from inside our Earth. This means it can only come from volcanic
eruptions (above or below the ocean surface). It makes a perfect tracer because
it only has 1 source, and it is a noble gas. Digging deep in our minds, we
remember our Chemistry teachers telling us the noble gases are inert (as in
non-reactive) so the only way to change the 3He is through dilution.
No comments:
Post a Comment