Multiyear ice

The helicopters started flying last Thursday and with their support we’re getting back on track with sampling. Friday we made it back out to Tent Island for our third sample there. It was great to make the trip in less than 10 minutes after all the hours we’ve spent driving that route! The only downside to this mode of transportation is the need for good weather. We had ambitious plans to fly to the Wilson-Piedemont glacier on the far side of McMurdo Sound Saturday for our first glacial ice sample, but fog grounded the helos for the day. Landing on glaciers is tricky business; the pilots are only willing to attempt it with good visibility. Tomorrow we’ll try again, hoping to net two large samples from a single trip. Time is running short – we leave November 2 – so we need to maximize every trip out!

The helicopter crews take Sundays off so we couldn’t fly yesterday. It was a warm (for Antarctica), sunny day so we decided to take a snowmobile trip to Turtle Rock, a little island tucked into a back pocket of McMurdo Sound. Turtle Rock is an interesting feature because it guards a bay full of sea ice which has not melted in many years. We call this ice “multiyear ice”. Until last year most of the ice in the south end of McMurdo Sound was multiyear ice, but a massive breakup of the ice last spring removed almost all of it. The ice that we have been working on so far is first year ice that only formed this winter.

We’ve done a little work on the microbiology of multiyear ice in the Arctic but a lot of questions remain. When sea ice forms in the fall it traps lots of bacteria from the seawater. These organisms aren’t adapted to life within the sea ice, but they persist there through the winter. When spring comes and the ice algae begin photosynthesizing these seawater bacteria are outcompeted by specialized sea ice bacteria that metabolize well under low temperatures and with a lot of organic carbon (produced by the ice algae). If sea ice survives that first summer to become multiyear ice however, what happens to those specialized sea ice bacteria? The ice algae use up the nitrogen, phosphorous, and other nutrients present in sea ice the first summer and can’t maintain the same level of photosynthesis in later years. The sea ice bacteria (which can perform better with little organic carbon) are long gone from the sea ice matrix. Does biological activity slowly grind to a halt, or is there a succession to a new microbial community adapted to low temperatures and low levels of nutrients?

Before we can answer these questions we need to acquire some cores of multiyear ice, something easier said than done. Reaching the multiyear ice behind Turtle Rock was easy enough but coring it proved quite difficult. First we had to reach the ice surface. It’s not uncommon to find a couple feet of hard, wind packed snow on top of the ice you want to core. In this case we had 7 feet of snow to tunnel through! Shelly and I cleared ourselves a pit large enough to work in and started coring. With limited space maneuvering the drilling equipment proved challenging, we were constantly climbing in and out of the pit to help lift the corer in and out of the hole. Multiyear ice can be 5 meters thick or more, after only two meters we had to quit for the day. With luck, time, and a couple of intrepid volunteers we might be able to finish that sampling effort before we leave. In the meantime we have more important objectives… collect our critical glacial ice samples and then start using the helicopters to access the ice edge for more frost flowers!