Last week’s successful sampling efforts have left us with a lot to do this week. On Monday Dan and I went back out to the ice edge to sample mature first year ice, the final sample in our four part set of ultra-large samples from this area. Completing that was a huge relief, although melting and filtering all of that ice (900 kg total between frost flowers, young sea ice, and first year ice) is going to be quite a task. We still have to aquire some equally large samples from glaciers in the Dry Valleys, but logistically this should be much simpler. Sampling at the ice edge went off okay despite the fact that the motor we normally use to power the coring equipment wouldn’t work. This sort of thing is pretty normal in the cold, so we switched to a smaller backup motor and finished up pretty quick.
Jeff at Barne Glacier. Photo: Dan Mahon.
Ahead of schedule we decided to do a little reconnaissance of some cracks in the ice near Barne Glacier, an impressive glacier that flows into McMurdo Sound from Mt. Erebus. The absence of multiyear ice from McMurdo Sound and the abnormally warm winter have left the McMurdo Sound sea ice more difficult to travel over than in normal years. One of Dan and Jen’s jobs prior to the start of the summer season is to map out safe travel routes over the sea ice and identify problematic cracks. Fractures are everywhere on sea ice. Most are not dangerous but some can become wide cracks (essentially small leads) over time if the winds and tides exert enough stress on the ice. A crack can widen to a half meter of more overnight and then be camouflaged under a layer of snow.
The route we’ve been taking out to the ice edge is in danger of being blocked off by a crack just like this, right now it can only be crossed safely in a couple of spots. Normally an alternate route can be found inside of (east of) Tent and Inaccessible Islands, heading north past Cape Evans and the Barne Glacier. Right now this passage is blocked by a large crack south of Tent Island that might heal in the coming weeks, but we confirmed another impassible crack at the Barne Glacier effectively shutting off this route. We were very lucky to get such good access to the ice edge early in the season; the summer science groups will start arriving next week and some that work around McMurdo Sound will be hard pressed to reach their normal study areas.
The Barne Glacier was as beautiful up close as it looked like it might be from a distance. At the base of the glacier the sea ice pulls away, leaving an easy access point for seals. Seals were lying all around the ice at the base of the glacier and we could see a number breathing through the thin ice there. After the glacier we headed to our second objective for the day, a site near Tent Island where we are taking periodic ice cores for a time series of microbial community composition during the seasonal transition. Here’s where the day got a little bit interesting. We were within sight of being done and back to McMurdo in time for dinner (which rarely happens when we head out) when the ice corer become very stuck in the ice. As I mentioned earlier the large motor that we normally use wouldn’t start in the cold. This motor drives the corer slowly, but with a tremendous amount of torque. Instead we were using a much smaller, faster, and weaker motor. Midway through drilling the core barrel stuck in the ice, firmly frozen in place. This happens sometimes with very cold ice.
There's not way we're rotating this corer out, time to start digging...
The next couple of hours unfolded comically as we went to more extreme lengths to get the core barrel back out of the ice. After about thirty minutes we realized that no tool at our disposal was going to get the barrel to back out by turning, so we decided to excavate. This was a little unnerving, core barrels are expensive and made of fiberglass, so they are easily damaged. The last time I saw one get dug out in a similar situation it sustained serious damage. We slowly but surely chainsawed and picked a pit around the corer and eventually got it free. Totally exhausted we finished up and headed for home.
