Sea ice, some of it more than a meter (~ 3.3 ft) thick, continues to linger in and around Arthur Harbor.
In many years, persistent sea ice is a significant source of frustration to early-season scientists at Palmer: Conditions like we’re seeing now generally preclude access via small boat to the regular Palmer LTER sampling locations at stations “B” and “E.” (View a description of the two stations in an older post.)
This season, however, the sea ice — which supports unique microbial communities at the base of many Antarctic food webs — is serving as an object of science rather than an obstacle. While we await the right combination of wind and warmer temperatures to blow the ice out to sea, the scientists of Palmer LTER’s Microbial Ecology and Biogeochemistry and Phytoplankton and Bio-optics components are sampling through the ice to characterize the frigid waters below.
It turns out that most of what we know about ice-attached and under-ice microbial communities in polar regions comes from (1) various locations in the Arctic and (2) studies in and around McMurdo Sound. (McMurdo, site of the largest U.S. research station in Antarctica, is 3,800 km, or 2,370 miles, from Palmer Station — on opposite side of the continent!)
The relative lack of information about sea ice microbial communities in West Antarctica makes it difficult to say how they will be affected by the very rapid shifts in climate currently underway here (see, for example, work by Bromwich et al. and Meredith and King). There have been some studies on sea ice West Antarctica, but the literature is not extensive. (A group of scientists at NASA generated some controversy recently with an analysis that found the overall mass of Antarctic sea ice is growing, despite global warming; in that study, however, the authors found that sea ice on the West Antarctic Peninsula was still very much losing mass.)
This uncertainty made us even more excited about the opportunity to sample from the ice here at Palmer. On Tuesday, we established a sampling station in the middle of Arthur Harbor, just off Palmer Station. We revisited the site the following day (on Wednesday) to make the first in what we hope will be a series of measurements. We collected samples and made measurements at two depths: Just below the underside of the ice (at around 1 m from the ice surface), and then at 3 m.
Sampling the ice
From both of these depths, we collected water for some basic, recurring measurements that form the basis for the LTER study. These parameters include particulate chlorophyll a, dissolved organic carbon, particulate organic carbon, bacterial and phytoplankton cell size and community composition, rates of primary and bacterial production, oxygen-18 (an isotope of oxygen), and basic macronutrients (nitrate and phosphate). We also made a profile of photosynthetically active radiation (PAR), the specific wavelengths of light that phytoplankton need to carry out photosynthesis. My field team partner Jeff has a great description of the importance of each of these on his blog.
In addition, we collected water for several special projects:
First, Jeff collected material onto several filters for DNA and RNA analysis, which will form the basis of his research here this season.
Second, Colleen Hansel, a scientist at Woods Hole Oceanographic Institution, used some of the water to measure concentrations of hydrogen peroxide generated by the microbes living under the ice. (Colleen is happens to be a member of my Ph.D. thesis committee at WHOI.) She is an expert in the measurement and environmental function of certain reactive oxygen species (“ROS”), including hydrogen peroxide and superoxide.
Third, I brought large volumes of water back to station, where I filtered it to collect biomass (organic material from bacteria and phytoplankton) for lipidomics analysis as part of my Ph.D. research. Lipidomics is a fancy word for the analysis of large quantities of lipid data (lipidomics is the lipid equivalent of genomics or metabolomics). It turns out that the molecules Colleen studies (and in which Jeff is interested) belong to the same overall class of oxygen-containing molecules produced as a result of many environmental stressors in the ocean. (See also a separate and very lengthy Wikipedia entry that addresses the production of ROS in marine microbes, here.) I am interested in two other kinds of ROS (specifically, chemical compounds called hydroxyl radical and singlet oxygen) because these compounds are what cause much of the “direct” damage to the lipids of marine microbes when they are subjected to the stress of ultraviolet radiation. When these ROS compounds react with lipids, they can cause the lipids to break apart into smaller fragments. Some of these lipid fragments are the sorts of “infochemical” compounds that are the object of my research (and much of the research going on in my lab right now).
Very early impressions
It’s too early to say what the lipid data will tell us (I will analyze the samples back in my lab in Woods Hole). But, it’s interesting to note that Colleen did measure modest quantities of hydrogen peroxide in the water samples we brought back from the ice station. In fact, the concentration was much higher just on the underside of the ice than it was at 3 m depth; this makes sense since algae produce hydrogen peroxide as a byproduct of photosynthesis, and photosynthesis depends largely on light (see plot to right). We also measured more bacteria in samples from just underneath the ice — though the rates of bacterial production, essentially a measure of how active the bacteria are, did not differ between the two depths.
All in all, however, things were pretty subdued from a microbial perspective: The core that came out of the hole didn’t have much brown or green color, which would serve as first-order visual evidence of an impending algal bloom. Things will start cranking soon, though (see photo from last season).
Science summary: LTER science is well underway down here at Palmer Station, but there’s no evidence yet of an algal bloom. Although I promised I’d formally introduce the members of our field team (Jeff, Colleen, Nicole, Ashley, and Chelsea), I’m going to hold off until next time. I’ve already indirectly introduced you in this post to Jeff, Colleen, and Nicole.
A feathered observer, and some other images
On a final note, I can say our work this week drew the interest of at least one (feathered) member of the Palmer community. After giving our efforts at the ice station a thorough inspection, this lone Adélie penguin (see below) followed us nearly all the way back onto land. No word yet on whether we passed whatever evaluation he or she was conducting.