Sea ice redux

We were supposed to sample the regular LTER stations by Zodiac yesterday, but this was the view of Arthur Harbor as of yesterday evening:

No possible way to get a zodiac through all that.  We’ll have to wait until the wind comes up (but not too much…) and blows it out.  In lieu of our regular sampling routine we made another visit to our ice station.  The ice station has been essential this year, and we feel truly lucky to have it.  We’ve made only three forays by zodiac to the regular sampling stations, but we’ve made it to the ice station six times.  Originally we only planned to visit once or twice.

Scientifically this has the potential to be a real coup.  We’ve managed to observe the onset of the spring bloom underneath the ice, in comparison with the delayed onset in open water, and a transition of the under-ice phytoplankton population from potentially mixotrophic cryptophytes to phototrophic diatoms.  Today we observed the plot thicken further still.  We knew that something was different because our filters were clogging much faster than usual, but we didn’t know what until we got back to the lab.

When we visited the ice station a week ago the phytoplankton community was largely composed of centric diatoms like these:

I spent quite a while on the microscope yesterday evening and couldn’t find a single centric diatom.  Or rather I couldn’t find a single live centric diatom.  Here’s a typical view from a water sample taken below the ice yesterday.

The large blob in the center of the image is, I’m willing to bet, the remains of one of these diatoms.  You can see a stream of cytoplasm trailing off to the right, and the bright area is what remains of the nucleus (the stain used to make the image fluoresces when bound to DNA).  They’re difficult to make out in this image, but the stream and the remainder of the cell are heavily colonized by bacteria.  While all the centric diatoms died off a number of chain-forming pennate diatoms remained, like the Chaetoceros to the left in this image.  So there was some kind of selective mortality.  At this stage we have no way of determining the cause, but my guess is a viral attack – the algal equivalent of a flu epidemic.  Phytoplankon viruses haven’t received a lot of study as of yet, in large part because of the difficulty in studying them and the complexity of phytoplankton ecology, but they probably play a major role in phytoplankton population dynamics, and by proxy the marine carbon cycle.

Later today we’ll have a sense of how much carbon the bacterial population is taking up as a result of this early collapse of the phytoplankton bloom (how much bacterial production is occurring).  My guess is it will be up quite a bit from the last time that we sampled.  Phytoplankton are the primary source of food for marine bacteria, and aged or infirm phytoplankton are quickly colonized by marine bacteria that specialize in scavenging these cells.  Cell lysis is the final step in this process, and the high quality biomass inside phytoplankton cells can fuel a lot of bacterial production.  Bacterial abundance is up and it was likely bacteria, and all the goopy cytoplasm from lysed diatoms, that clogged our filters yesterday.

Macroscopically it was an exciting sampling day as well.  The southern elephant seals seem to be abundant this year.  No one knows if the numbers are really up, or if they’ve arrived  a little earlier than usual, or if they’re just being more sociable than normal, but they’re all over the ice and the station.  Usually they don’t take much notice of people, but we attracted the attention of a small (fortunately) one yesterday.  On land elephant seals move in 10 m lurching “sprints” with very long rest periods; not the most graceful creatures out of the water.  We could see this one making a beeline towards us from a long way off, and had plenty of time to ponder what to do if it tried to join our sampling operation.  As it got closer we were relieved to see that it wasn’t a mature bull (which get territorial and can top out at well over 3 tons).  We made a line of ski poles and snowshoes, which was enough to deflect its course around us.

Shortly after the elephant seal departed we were joined by the juvenile crabeater seal pictured below, the first of that species that I’ve seen this season (thanks to the birders for clarifying that this was a crabeater and not a leopard seal – despite the predation of the latter on the former the two species are closely related and difficult to tell apart).

Our last visitor was this Adélie penguin which, like most penguins, seemed mostly confused that we were not also penguins.

If you like pictures of Adélie penguins, and really, who doesn’t, Palmer Station’s seasonal penguin cam is now operational.  Check it out to view all the stages in the penguin life cycle in all their glory…