It’s been another quiet week at Palmer Station, out here on the edge of Antarctica…
This week was punctuated by a set of intense storms. The one that came in on Wednesday was the most intense storm that we’ve had this season (see Jamie’s blog on the unusual winds this year here). Just before the storm hit we made a quick run out to one of our regular sampling stations. It was eerily quiet and the ice was drifting in. Within an hour of our return to station the wind was up over thirty knots and the ice was coming in fast. By the time the storm ended Arthur Harbor was chock-full of icebergs and large pieces of sea ice. This shut boating operations down for the rest of the week. The ice finally drifted out this morning with another (warm, wet) storm blowing from the east. Chances don’t look good for getting out before the next storm arrives on the tail end of this one.
We got cruised – “whale watched” in Conor’s words – by this humpback whale on our last sampling trip, just before Wednesday’s storm hit.
Cut off from boating for a few days we took the opportunity to complete some side projects. One that I’ve been particularly interested in doing is to take a look at the dense blooms of algae that form on top of the sea ice. I’ve written quite a bit in the past on the ice algae that grow below sea ice (see here). Wherever sea ice floods however, you also get a dense bloom at the ice surface. Although this does happen in the Arctic this is primarily an Antarctic phenomenon. The reason for this is that there is generally much more snow on Antarctic sea ice; the snow both insulates the ice and pushes it downward, making it warmer and more porous, and allowing seawater to infiltrate to the surface. The reason for that is largely geographic. One of the key distinctions between the Arctic and the Antarctic is that the latter is a continent surrounded by water. The ring of ice around the Antarctic continent in winter eventually gives way to open water, and open water means precipitation.
We couldn’t use a boat to get a fresh chunk of ice (on account of there being too much ice), fortunately it was easy enough to get in a drysuit and wrangle one close to shore.
Jamie keeps a lookout while I go wading after some algae-rich ice.
Scrape the snow off of any of these floes and this is what you find; a thick ice-top algal bloom.
Conducting experiments on ice algae is non-trivial and I’m fortunate to have spent a good portion of my time in graduate school dealing with the peculiarities of sea ice biota. One of the issues that we have to deal with is the semi-solid (emphasis on the semi for this slushy ice) nature of the sea ice matrix. The bacteria and algae that we want to separate out for further study are located in brine channels within the ice, we need to melt the ice to get them out. Simple enough, but consider that even for this very warm sea ice the salinity of the brine channels is roughly 37 ppt, while the bulk salinity of the ice (that is, the final salinity if you just let everything melt) is about 11 ppt (check out this open-access paper for a further explanation). Taking the sea ice microbes from 37 ppt to 11 ppt would have induced quite a shock. To avoid that we needed to melt slowly into a sterile, pH controlled, high salinity brine so that the final melt was about equal in salinity to the brine channels. That done we incubated the melt outside in clear bottles for a few hours to get everything acting like it was back on the ice floe.
Happy algae obtained from a carefully controlled melt. Surprisingly the algal community was fairly diverse, although that may be the result of recent seawater intrusion. The dominant diatom morphotype, the pennate diatoms with the long spines, is one that I haven’t observed in any other samples this season. Another interesting detail is the low abundance of bacteria. There are plenty there, they are the small dots scattered across the background, but are rare relative to the number of phytoplankton. There is some debate about a possible decoupling of primary production and bacterial production in really productive sea ice that I touch on in this open access paper. In this case bacteria might be inhibited by the high light conditions or by the ice algae themselves.
Once we felt that everything was acclimated we threw our complete analysis suite* at it; in addition to the core LTER measurements this includes measurement of photosynthetic efficiency, the reactive oxygen species superoxide and hydrogen peroxide, samples for RNA and DNA analysis, and lipid analysis. The main thing that I’m interested in learning from these samples is how the ice top algal community differs from that below or within the ice. The light regimes are completely different. Algae growing underneath the ice are generally thought to be low-light specialists. After all only a small fraction of the light that hits the ice surface makes it through into the water below. The light conditions at the ice surface by contrast are intense – too intense for most phytoplankton species to perform well. Given too much light the photosynthetic machinery of phytoplankton runs amok and starts to destroy the cell.
Experiments have demonstrated that low-light adapted ice algae are quickly destroyed by ice-top conditions. Given enough time however, the range of conditions that algae can adapt to is quite phenomenal. So are the ice algae at the surface the same as those underneath, but physiologically adapted to high light conditions? Or are they a different species (or assemblage of species) specially adapted to this ecological niche? So far all we know from yesterday’s effort is that they’re making quite a lot of the reactive oxygen species hydrogen peroxide and superoxide! We’ll learn more over the next few days as we complete more of our analyses. The real data however, RNA and DNA sequence abundances and the lipid profiles that Jamie is working on, will take months to develop…
Not all side projects undertaken while we wait out the weather and the sea ice conditions have been research related, however. Ashley and Chelsea, Rutgers undergraduates with the Schofield Palmer LTER group, found some time to get us all in the holiday spirit.
The chemis-tree; another US Antarctic Program infrastructure milestone.
Well, that’s the news from Palmer Station, where all the seals are fat, all the penguins are curious, and all the science is above average.
*Many thanks to both the Schofield and Ducklow Palmer LTER teams for going along with crazy idea #2 for the season (#1 being the sea ice station. #3 is still in development).
