One of my tasks this week while in Barrow is to collect a
series of soil samples from low- and high-center polygons. A colleague,
Elizabeth Herndon, a former post-doc at ORNL, now Assistant Professor at Kent
State University requested samples of active layer soils for a geochemistry study
that she is doing across a latitudinal transect. My guess is that samples
provided by the NGEE Arctic project represent the northern anchor to that
transect.
I was glad to help and therefore set about to formulate a
strategy whereby soil cores could be collected from frozen soil using a slide
hammer and a split-core sampler. I organized everything into a small sled and
walked several kilometers with sled in tow to our NGEE Arctic “intensive” field
site on the Barrow Environmental Observatory (BEO). Two or three inches of
fresh snow made this a fairly easy task.
Once representative polygons had been located, cores were
collected from several different micro-topographic positions across the
polygons including centers, rims, and troughs. The cores varied in length from
15 to 30 cm and in composition with generally an organic-rich upper layer and a
deeper layer of mineral soil. There were obvious differences in these
characteristics among micro-topographic positions in the landscape.
Fortunately, the split-core design of the sampler facilitated retrieval of the
soil core and made it fairly easy to visualize the sample and record a quick
characterization into my lab notebook. Photographs were taken of all cores.
One interesting observation made while collecting 15 soil
cores was that these active layer soils were freezing from the top, down, and
also from the bottom, up. This is not entirely surprising given the nature of
permafrost, but what it meant for many of the samples is that the middle
portion of the soil core was still thawed. This can lead to a soil appearing
frozen and presumably devoid of biological activity when, in reality, this
layer can be warmer than soils above and below it with maintenance of possible microbial
metabolism into the winter. The question that many scientists are trying to
answer, including those on the NGEE Arctic team, is what significance might
this make to annual carbon budgets of tundra ecosystems and CO2 and
CH4 fluxes either during the fall-winter transition or to fluxes in
the early spring? We are currently conducting chamber-based measurements of
carbon fluxes in the field, coupled with controlled freeze-thaw experiments in
the laboratory. What we hope to provide is a multi-scale, quantitative
assessment of this phenomenon and representation of such in models.
At the end of the day all soil cores were loaded into the
sled and everything was pulled back to the road and a waiting vehicle. The
cores were placed into a freezer at the Barrow Arctic Research Center (BARC)
and will be shipped to Elizabeth in a few days. It will be interested to see
the results of her analysis.
