The sea ice conditions have changed drastically in the past week. The sea ice is now too fragile and slushy for us to go sample there safely, leaving helicopter trips to the ice edge as our only opportunity to collect samples of ice, water, and microorganisms. Unfortunately, these trips have been few and far between because of changing weather conditions and demand on helicopter time. I haven’t had the chance to fly out yet, and my trip is third on the current list, so it may be that there won’t be enough time to make it happen. We’ll see!
Instead of sampling in the field, we’ve devoted much time this past week to analyzing what we’ve collected, using the capabilities of the Crary science lab, a “university lab on the ice”. Indeed, walking around Crary feels just like being inside a science building on a university campus. Three rooms and the entire aquarium are dedicated to the projects of our group. In the aquarium, a few of us have set up an experiment to pin down the causes of a weird shift in the populations of microorganisms that dominate the subglacial waters of Mc Murdo Sound. The balance of power is disputed between diatoms, tiny organisms with shells made of glass, and colonies of algae called Phaeocystis. This year, the Phaeocystis have taken over. Why is that? What decides who wins? We’re thinking that there could be reasons linked to (1) the physics and chemistry of the environment (how much light these species get, how warm or salty the water is, etc.), or (2) interactions among microbial species (presence or absence of bacteria either helpful or harmful to the Phaeocystis algae).
To find out about the influence of environmental conditions, we’ve measured the temperature, salinity, and light levels in the water at different places and times. That required lowering probes through holes in the ice on a rope down tens of meters, then hauling them back up. We’ve also taken samples of water at different depths by lowering an open Niskin bottle with a switch that closes it. The switch gets tripped by a “messenger”, a weight tied to the rope that we let fall down once the bottle is at the desired depth. We can then bring the water back to the lab to analyze its chemical and biological composition. We have yet to finish many of these analyses, but so far one interesting measurement has been that of light, which gets absorbed much more strongly in shallow waters than in deep waters. We think that’s because the shallow waters are full of algae capturing sunlight for photosynthesis. In deep water, there is not enough light and the algae can’t live there, so the water is more transparent.
To understand the biological relationships between algae and bacteria, we’ve set up that experiment in the aquarium. We’ve put Phaeocystis algae in bags full of seawater under three conditions: without many of the bacteria (killed using antibiotics), without the bacteria but with vitamin B12, and as is (control). This should help us understand if the bacteria are helpful to the algae (those bacteria are a natural source of vitamin B12), or harmful, or have no influence. If the bacteria are helpful, we should expect less algae in the antibiotic bag than in the others (control and antibiotic+B12), because the algae are deprived of bacterial B12. If the bacteria are harmful, we’d expect less algae in the control, in which the bacteria haven’t been killed by the antibiotics. If the bacteria have no influence, the three treatments should give the same results, in which case the answer to the diatom-Phaeocystis power struggle may lie in the environmental conditions instead. We hope to have an answer by next week!
We’ve turned our attention away from the sea ice for fun as well. Last night, two of us hiked up and skied down a trail leading inland toward Mt. Erebus. This trail took us near Castle Rock, a prominent local landmark that we could have climbed, but didn’t this time as it got late and cold. A good reason to go back… The return path faced the glorious and eerie Trans-Antarctic range backlit by the midnight sun. On the horizon to the north, we could see the orange glow of the oblique sunlight hitting iceberg cliffs contrasting with the deep blue ocean. Not a soul miles around (thousands of miles even, if it weren’t for the nearby stations). Just magical!