Thursday, May 1, 2014
More Cores; This Time Looking for an Ice Wedge…
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!