Yesterday we returned from our first field outing at a place called Marble Point. It’s on the Antarctic continent proper and is about a 30-minute helicopter flight from McMurdo Station on Ross Island. We arrived there on Dec. 29 on a nice sunny day with light winds. The flight over was spectacular as we followed the edge of the ice shelf and saw lots of penguins and seals below us. Marble Point is a rocky ice-free area in front of a huge piedmont glacier, a continental glacier that stretches for miles along the coast. After scouting areas to work and camp from the air, we were dropped off and spent about two hours setting up our camp (see figure). Then, we hiked out on Marble Point and began looking for abandoned penguin colonies. Fortunately, within an hour, we found one. They are recognized by concentrations of pebbles, which the penguins use to build their nests, that over time build up to form small mounds about 5-10 meters in diameter. Probing into the mounds we see evidence of a former colony—bones, eggshell fragments, and a distinct reddish brown soil (called ornithogenic or bird-caused soil) that acquires its characteristic color from penguin guano.
The abandoned colony is located on an old beach terrace that formed when sea level was higher. There are at least four of these beach terraces visible on the point and the colony is located on the highest one. In addition, the area is no longer used by penguins for breeding. Too much ice now persists around the point extending several miles out to sea. Adelie penguins need open water near their colonies so this one must have been occupied during a warmer period in the past compared to today, when the ice did not persist in the area through the summer months.
We sample the old colony by establishing a 1x1 meter test pit and excavate it in 5-cm levels. All the sediments from each layer is measured by volume using 14-liter buckets, then sieved through three stacked screens of different mesh sizes to separate out different sized fractions of rocks and soil. The top screen catches the larger rocks and pebbles and we can look through that in the field, remove and save any bone or other organic remains, and throw out the rest. The other two screens catch smaller particles and these we need to take back to our lab to sort by hand and with a stereomicroscope. We expect to find the smaller eggshell fragments in these sediments, plus bones of fish and parts of other organisms that were eaten by the penguins and preserved in the guano.
The screening goes very quickly as the sediments are so dry, everything falls through easily. It gets a little dusty (see figure) but it’s better than washing the sediments through the screens in the sea water like I had to do last year. In addition, we soon began to find lots of penguin bones and other remains in the sediments—it is a rich site and will provide lots of data. We bag up the sediments after completing each level and, over the course of three days, we excavate four test pits.
On New Year’s Day, we had time left over to hike around the area and look for new sites. We didn’t find any more, but we walked near the glacier (see figure), which was quite impressive, and saw more of the area. The weather stayed nice most of the time, with the temperature around 0 to –2 degrees C. When the winds picked up, it got colder but we still kept warm in all the layers of clothing. Our tents gave us adequate shelter as well and we slept well at night. On our last day there, a pair of Adelie penguins visited our camp. These birds are not breeding in the area, but are nonbreeders that wander around during the summer until they eventually start breeding at the colony where they were born, or one nearby. They also are very curious birds and perhaps were attracted to our tents. They stayed for about an hour and then moved on.
The helicopter picked us up on Jan. 2 and we returned to McMurdo to clean up and process our samples for a couple of days. It was quite a successful first outing and we leave again on Jan. 5, this time for Cape Crozier where we will be working near an active penguin colony that we will sample for diet information and try to determine the history of occupation there. So, my next update will follow that trip later next week.
Steve Emslie
