The search and rescue Hagglan had to be dug out after the big storm.
The second round of sampling went much better today, and now we have some ice cores to work on in the lab over the next couple of days. Things started a bit slow this morning, the storm that finally blew itself out last night left McMurdo in a bit of disarray. Our Piston Bully was fortunately parked in a sheltered spot, but the search and rescue team’s Hagglan tracked vehicle had to be dug out before we could depart (they’ve been showing us the ropes, today was our first chance to “fly solo”). Once on the ice things went pretty smooth. It was still a bit breezy but nothing like the heavy winds of the last five days and we were greeted with spectacular views of Mt. Erebus on the way out of town.
The six ice cores that we pulled from our first site, in the windbreak of Tent Island (seen in the background). In the windbreak very little snow has drifted over the ice.
We had two sampling sites picked out for collecting ice cores. One sits in a large windbreak behind Tent Island and as a result very little snow has drifted over it, just a couple of centimeters. The other site, about 1 km south, is outside of the windbreak. It has about 40 centimeters (about 16 inches) of snow on it. Snow does a couple of important things for sea ice. First, it is a great insulator. The top of the ice at our first site was -12C (10 F) while the top of the ice at the second site, with its insulating snow cover, was only -8 C (17.6 F). For bacteria and algae in sea ice this difference in temperature can have a huge impact. The warmer it is, they more they can do.
Digging out the ice at our second site. Outside of the Tent Island windbreak the snow has drifted pretty deep (Photo: Shelly Carpenter).
In addition to warmer temperatures sea ice algae and bacteria at this time of year are waiting for sunlight. Each day brings 15-20 minutes more sunlight, though the sun is still low on the horizon and the actual amount of light that hits the ground is still quite small. Soon, enough light will begin to penetrate the ice for algae to begin photosynthesizing. By the Antarctic summer the bottom of the ice in McMurdo Sound will be coated with slimy green algae. This alga is a major food source for fish, krill, and bacteria. Sea ice bacteria in particular are thought to respond quickly to the onset of spring photosynthesis within the ice. The ice algae give off a small amount of the carbon they fix during photosynthesis and this energy source drives the microbial response.
Flat Stanley struggles to move a large blog of ice. Come on Stanley, you can do it! (Is it just me or does Flat Stanley look worried in this photo?)
As you might guess the amount of light that gets through 40 cm of snow cover is much less than that which gets through 5 cm. So the biological community at site 2 is a little bit warmer, but also has a little less light for photosynthesis than site 1. Hopefully today’s samples will help us understand how the community responds to this. Snowfall patterns at high latitudes are changing dramatically, and Arctic sea ice in particular is thought to be accumulating more snow. If the algae and bacteria in sea ice begin responding to sunlight later in the spring this could have an interesting impact on the rest of the ecosystem.
Glad you were able to make it out and get samples. I’m enjoying reading about your adventure. Do you know how fast the green algae grows once it has enough light?
I checked a couple of sources and growth rates are all over the board depending on species and the light, temperature, and nutrients conditions. A good ballpark figure would be a specific growth rate of 0.05-0.10 per day (so 10-20 days for a population to double) (McMinn et al., 1999, Botanica Marina), however specific growth rates from 0.02-0.45 per day can be found. Most of these ice associated “algae” however are not green algae. The word “algae” is troublesome as it is used to refer to some single celled photosynthesizers taxonomically, but is also used to describe any photosynthetic cell that is not planktonic (is not floating free in the water column). So all cells, regardless of taxonomy, that are living on the seafloor, sea ice, anchor chains, rocks, etc. are algae. I personally don’t like this but that’s the convention! Most of the sea ice “algae” are in fact diatoms (class Bacillariophyceae, the true green algae are Chlorophyceae). To complicate the picture you can find true green algae in the fresher portions of sea ice, such as in melt ponds on the surface of summertime ice.