Young ice rafted up at the ice edge. The ice floe that we ultimately sampled is on the right. This photo is looking south toward the land-fast ice, you can see Mt. Discovery in the background.
Yesterday we finally made it out to where we can sample frost flowers, retracing Dan and Ryan’s track from Saturday out to Cape Royds. We were stopped from reaching the ice edge itself by an abrupt transition from ice over one meter thick to ice only 50 cm thick. In reality this is plenty of ice to support the weight of our vehicles, but McMurdo Station rules prevent vehicle travel on ice thinner than 76 cm (30 inches). So we parked our vehicles, shouldered packs, and headed to the ice edge to see what we could find. To understand what the ice edge looks like right now it’s necessary to understand the weather conditions over the last several days. We had an intense period of wind blowing primarily from the SE, followed by a couple of nicer but cool days, and finally a day of mild but persistent north wind. Yesterday was absolutely beautiful, possible the nicest day since we arrived.
Sampling frost flowers is as easy as scraping them from the ice surface with a clean shovel into a sterile plastic bin. Photo: Shelly Carpenter.
The period of strong SE winds cleared the ice edge of any recently formed ice, leaving an abrupt line between thicker, land-fast ice (ice that is anchored to the shoreline) and open water. In the open water ice still would have been forming, but the wind would have quickly driven this young ice out toward the open waters of the western Ross Sea. Once the SE winds ceased ice would have formed in place, some of it attached to the land fast ice and some of it drifting freely. Sunday’s mild north wind would have driven all of this ice south, against the thick land-fast ice. With nowhere to go this young ice would have “rafted up”, with some floes getting pushed underneath others. Think of a much scaled down version of the plate tectonics that gives rise to ocean trenches and mountain ranges. This is what we found at the ice edge yesterday.
Sampling the young ice underneath takes a little more effort, but the work still goes pretty quick. Photo: Shelly Carpenter.
A young ice flow that is rafted on top of another flow will quickly drain of salt, and presumably of many microorganisms. As a result this ice is of limited use to us for our current study. Fortunately we were able to find a large pan of young ice that had not rafted. Had the north wind been stronger we might not have found anything suitable in the area. Like all of the other floes we observed this one was completely covered with very salty several day old frost flowers. We did a quick check of the salinity of the frost flowers, the whole field was almost three times the salinity of seawater. Bacteria generally get transported with salt in sea ice. More salt means more bacteria, so this was perfect! We trekked back to our vehicles to collect our sampling gear and get to work.
This is a profile of the young ice that we sampled, with the top of the ice on the right and the bottom of the ice on the left. The growing ice front, or bottom horizon where the ice is adding thickness is defined by the white band. Below the white band frazil ice is accreating to the underside of the ice. As ice continues to accreate the band will move steadily downward driven by the movement of the freezing point lower in the ice column.
It didn’t take us very long to collect perhaps 500 kg of frost flowers, young ice, and water. It took much longer to haul these samples 2 km back to the vehicles. We had counted on being able to drive much closer to where we wanted to sample so we only brought one small sled for hauling. Not nearly enough unless we wanted to make a half-dozen trips! So we improvised a sled from a plastic containment berm that we use when fueling our saws and drills in the field. Not ideal, but it got the job done. However there are sore legs and sore backs all around this morning. Many thanks to Dan and Kevin (who volunteered to go out with us yesterday), we couldn’t have done it without them! We packed up just as the sun was setting and got back in time to eat a late dinner before turning in. This afternoon Shelly and I will begin the much longer process of melting and filtering all of this material and sorting out our field gear for the next excursion…
Putting our backs into it. Dan and I reenact some of the finer scenes of Antarctic exploration in an effort to get our samples back to the vehicles. Photo: Shelly Carpenter.
if the temp. in Antarctica were to rise by a couple degrees, what impact would that have on the ecosystem? Would it be good or bad?
I’m moving this question over to Antarctic Q&A, where questions and responses are a little more visible…
Jeff