Earlier in the week we collected
a number of active layer and permafrost cores for a variety of uses, including
geophysics, biogeochemistry, and microbiology. These will be distributed to
team members and analyses performed back at their at home institutions.
However, we still have need of additional cores specifically for the purpose of
confirming presence of massive ice distributed across the subsurface of the BEO
landscape. Massive ice describes
features like ice wedges that are large in extent and consist mostly of ice.
The process of ice wedge formation begins during the winter when cold air and
ground temperatures cause the ground to contract and then crack with those
cracks filling with water that then freezes. The process repeats itself for
centuries to millennia with the end result being large ice formations in the
subsurface.
Previous geophysical surveys conducted
by the NGEE Arctic team have identified areas where ice wedges might be present
and several deep cores would be useful to verify what the LBNL geoscientists
are seeing in the electrical resistivity (ER) measurements, along with other
field techniques like ground penetrating radar (GPR). So, early one morning
John, Craig, Baptiste, and Ken loaded up the Big Beaver and using a snow machine
they pulled the sled-mounted rig out to the BEO where we would drill to 2
meters or more in search of ice.
Ice wedges are known to occur at
shallow depths along troughs of polygons. The drill rig was positioned over
such areas and cores carefully taken. This could take 30 minutes to an hour to
get intact cores to depth, but the presence of an ice wedge was pretty easy to
determine. What we typically observed while drilling was the presence of a dark
brown to black layer in the upper 20 cm of active layer that was rich in
organic matter. Drilling deeper we often saw a gray to much lighter mineral
soil, and then, upon drilling into an ice wedge, we observed white, almost pure
ice chips. The difference in coloration was, of course, quite striking.
Once an intact core was extracted
from the SIPRE device, we also saw these distinct layers of organic matter,
mineral soil, and then ice. I should note that we were joined by Shan Dou (red
parka), a PhD student in the Earth and Planetary Science Department at UC
Berkeley for this component of our field studies. She is working with Jonathan
Ajo-Franklin (LBNL) and has an interest in geophysics and subsurface properties
of permafrost environments. This was Shan’s first trip to the Arctic and I
really enjoyed working with her a few days before leaving Barrow. She will
remain in Barrow with John, Craig, and Baptiste for another few days as more
geophysical evaluation of the BEO is conducted. It’s a great opportunity for
her to be exposed to such a remarkable environment, work with a committed team
of scientists, and participate in the actual sampling of permafrost that will
form the basis of her PhD studies. I wish her and all the B.S., M.S., and Ph.D.
students working on the NGEE Arctic project good luck with the coming field
season!
