After a tough couple of weeks things are starting to look up. I’ve got the flow cytometer up and running, and Colleen’s instrument received a complete makeover (thanks to the über instrument tech at Palmer) and is producing good data. The big question is whether I can gain enough proficiency over the next two days to keep it going after Colleen leaves on Sunday.
The operational instrument status comes just in time; yesterday we went back to the sea ice station that we established on Tuesday to do some science. In addition to collecting some pretty novel data it was a good chance to practice the measurements we’ll be making all season for the Palmer LTER. It felt good to get out but hopefully for most of the season it will be a little warmer, however. That it would be cold in early spring in Antarctica is kind of a no-brainer, but that didn’t keep it from surprising me yesterday. And the downside to doing fieldwork cold is that it takes longer, so you end up getting colder, and things take even longer…
In addition to making all the core LTER measurements (see the end for descriptions); chlorophyll a, nutrients (inorganic nitrogen and phosphorous), primary production, bacterial production, dissolved organic carbon, particulate organic carbon, bacterial abundance, photosynthetically active radiation, and UV, we took multiple RNA and DNA samples (my main focus for this trip), large amounts of water for lipidomics (Jamie’s project) and samples to measure hydrogen peroxide. This last measurement was a consolation prize since we couldn’t measure superoxide – the two species have some similarities – and it gives us some indication of what to expect now that Colleen’s instrument is up and running.
So what did we find? It’s early in the season, and there isn’t that much happening yet below the ice. Everything is driven by light, and it’s pretty dark under there. But things are starting to happen, and all the action is near the ice. We measured only two depths in the water column (and that still took us over three hours), just below the ice and 2 meters further down. Even over that short distance there was a big difference in what’s going on. The concentration of hydrogen peroxide – a byproduct of photosynthesis – was much higher near the ice, and there were about four times as many bacteria just beneath the ice than 2 meters below it.
Hopefully, if the weather’s good we’ll get a chance to go back out on Monday. If the ice holds together for just a couple more weeks we’ll be able to document the transition from an ice-covered to an ice-free state, and get the data to test some hypotheses about how bacteria and phytoplankton respond to this transition. In the meantime yesterday’s bitterly cold wind has given way to calm conditions and outside the snow is falling. The woodstove in the Palmer Station galley is putting out a nice glow and the stress of fieldwork is dissipating for a moment…
As promised here’s a quick description of the core LTER measurements:
Chlorophyll a: The principal (but certainly not only) photosynthetic pigment in phytoplankton. Oceanographers having been measuring the concentration of chlorophyll a in the water for a long time as a measure of phytoplankton biomass, and as an estimate of how much primary production is happening.
Primary production: The amount of carbon dioxide that is being taken up by phytoplankton and converted into organic carbon. The whole food web depends on primary production, and much of our work is focused on what aspects of the ecosystem control the amount that happens.
Bacterial production: Sort of the inverse of primary production, this is the amount of organic carbon taken up by bacteria. We can’t measure this directly so we estimate it from the uptake of certain carbon compounds that we can track.
Dissolved organic carbon: One of the most mysterious types of carbon out there (see this article for some indication why). This is organic carbon in pieces small enough for bacteria to take them up.
Particulate organic carbon: Phytoplankton die, they become particulate organic carbon. It’s sad.
Bacterial abundance: The number of bacteria in the water, measured on our now operational flow cytometer.
Nutrients: Nutrients in the ocean are operationally divided into macro and micro categories, depending on their biologically relevant concentrations. We measure nitrogen and phosphorous, the principal macronutrients.
Photosynthetically active radiation (PAR): In addition to nutrients phytoplankton need light to grow. PAR is the part of the electromagnetic spectrum that can actually be used in photosynthesis. Too little PAR (like under thick, snow covered ice) and you get very little photosynthesis. Too much PAR (like at the surface of the ocean during the Antarctic summer) also produces very little photosynthesis!