The Laurence M. Gould departed for Punta Arenas last night, taking Colleen with it and leaving Jamie and I on our own until reinforcements arrive in two weeks (you can check out Jamie’s blog here for more on what we’re up to this season). That should work out fine although we’ll be very busy on sampling days – when and if we get sampling days. We were supposed to get out today but the weather isn’t cooperating.
Shortly after the Gould departed the wind started to increase. Right now the Gould is getting 50 kt winds at the southern edge of the Drake Passage (sorry Colleen!), we’re getting a steady 35 kt wind the blew all night and should last through today. I’m nervous about what that will do to our sampling plan. So far the land fast ice where our ice station is has held together; it’s a nearly a meter thick and pretty well anchored to the land. Sometime this season it’s going to give out though, and I’m hoping that we can sample from it a couple more times before that happens.
The flip side is that when the ice goes away we’ll be able to start using the zodiacs to sample at our regular stations, at least until the ice blows back in. The worst case scenario is being in the awkward position of too much ice for the zodiacs, but no solid land fast ice from which to sample. To get an idea of how fast things can change compare the ice conditions in the following pictures to the conditions when the Gould departed:
The fast departure of the ice underscores an important ecological concept that is central to this region. The timing of the switch from ice covered to open water conditions has a major impact on the strength and timing of the spring phytoplankton bloom; the annual ecological event from which everything else derives (think of it like a burst of new green grass in the Serengeti).
In the springtime Antarctic phytoplankton are limited in growth only by the absence of light. Nutrients have been replenishing all winter, there are no grazers around (yet), and the phytoplankton are relatively indifferent to temperature. Right now at Palmer Station we have nearly 18 hours of daylight, what keeps the phytoplankton bloom from exploding right now is the ice. Only 6 % of the light that hits the surface of the fast ice in Arthur Harbor is making its way down into the water. That’s enough to support the growth of specialized ice algae and low-light adapted phytoplankton just below the ice, but not a major bloom deeper in the water column. At just 10 m depth only about 0.01 % of the light that hits the surface remains; it is essentially totally dark.
So as soon as the ice departs the phytoplankton are primed to start growing. In Arthur Harbor the wind is driving the ice away, does this mean a bloom is about to start? Not necessarily. For phytoplankton, what the wind gives it also takes away. A strong wind induces strong vertical mixing in the water column. This impact of vertical mixing on phytoplankton has been studied in places like the North Atlantic for a very long time. Some phytoplankton can swim, but none can swim fast enough to outpace vertical mixing. Under a stiff, sustained wind phytoplankton in the surface are mixed deep into the water column. If they don’t go too deep that’s fine. Below a certain point they can’t photosynthesize enough to meet their metabolic demands (we usually take this to be the 1 % light level), but like all organisms they have energy stores and can wait to get mixed back above this depth. Pushed deep enough however, at what we call the critical depth a phytoplankton cell has insufficient energy stores to make it back to the surface. Under these conditions, although phytoplankton may be growing at the surface, the formation of the bloom will be suppressed.
So what does this have to do with timing? It’s no surprise that the strongest storms happen in the winter. In low sea ice years, with less land fast ice and an earlier retreat of both land fast and pack ice, the surface of the Antarctic ocean is exposed to late winter storms and strong mixing. Phytoplankton that have been overwintering safely in the stable water column below the ice start to grow, but are constantly mixed down below the critical depth. Eventually this stock of phytoplankton is depleted (or much reduced), leaving insufficient numbers to initiate the bloom when conditions finally calm down. This idea has been explored in a number of studies, including this great 1998 paper led by Kevin Arrigo at Stanford and this 2006 study led by Hugh Ducklow at the Lamont-Doherty Earth Observatory. This latter study is particularly interesting because it implicates the Southern Annual Mode (SAM) in determining the strength of the spring bloom. As the plot at right shows it’s clear that SAM isn’t the only thing that determines ice duration, extent, and the strength of the bloom, but it has a clear and logical role.
More recent studies have extended the link between sea ice and SAM to higher trophic levels, including krill. One of my favorite Palmer LTER papers is this 2013 paper by Grace Saba et al., which does a great job of illustrating the link and exploring the idea in the context of climate change. A negative phase in the SAM during the winter and springs leads to low wind and high ice conditions (a double bonus for phytoplanton). These conditions set the stage for a strong bloom and good krill recruitment (a large number of juvenille krill being “recruited” to the sexually mature, adult size class). A positive SAM during the winter and spring leads to low ice, high wind, and a taxonomically different and overall smaller phytoplankon bloom. This leads to fewer krill with a direct negative impact on penguins, seals, seabirds, and whales.
This post is getting long (this is what happens when a sampling day gets weathered out) so I want to end by wrapping it back around to the current season. As I described in a previous post things are a little different this year. The SAM index has generally been positive with some dips into the negative. Only for the month of October was the mean SAM negative, and not very. Despite this there is a definite positive sea ice anomaly. This seems to be driven by the strong, persistent El Niño in the equatorial Pacific that shows no sign of abating any time soon. Regardless of SAM, ice conditions are good this year, in a few weeks we’ll see what that means for the spring bloom when the ice clears out for good!
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!
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We’re off to a rough start this season! Two of our instruments are down, including our flow cytometer – annoying, but we can deal with it – and Colleen’s instrument for measuring superoxide. That’s a real problem. Colleen is only with us for five more days. When she leaves the instrument stays, but we will no longer have a skilled operator! Measuring superoxide is not trivial and I was supposed to spend a good chunk of this week learning how to do it. That’s going to be tricky with no instrument. Fortunately the instrument tech at Palmer this season is handy with a soldering iron and seems to have some ideas. We’ll see how that plays out tomorrow.
The one piece of good news this week is that the big storm last Sunday didn’t do much damage to the land-fast sea ice near Palmer Station. At least for now we can do a little science on the ice. This afternoon Jamie Collins, Nicole Couto, and I went out with the SAR team to establish a sea ice sample site near the station. Hopefully we can get a couple weeks of sampling at this site before the sea ice deteriorates.
Being able to do some science on the sea ice at Palmer Station is actually a pretty big deal and an unexpected bonus for this season. In some ways this is a very logical place to study ice. Palmer Station is the United States’ premier polar marine research station, and you can find dozens of papers describing the ecological importance of sea ice in this region. It’s been years however, since anyone was able to routinely access sea ice from the station. Considering the amount of ecological research that takes place here this actually seems a little silly; the single most important feature is virtually ignored for practical reasons. Working on ephemeral, dynamic sea ice requires a set of skills, equipment, and intrepidness that simply doesn’t exist in this day and age within the US Antarctic Program.
Our very small adventure today (on relatively thick, static ice) is reason to hope that that might eventually change. There isn’t a lot of institutional knowledge about sea ice at Palmer Station, but Station staff and management are open minded and seem eager to learn. As a further indication the Cold Regions Research and Engineering Lab recently provided new recommendations for sea ice operations at McMurdo Station, a major step toward a rational, data-based policy for traveling and working on ice (which I’ll link it I can find, too tired to search now… must fix flow cytometer…).
Hopefully we can get some good science done on the sea ice this season. In the Arctic large, under ice phytoplankton blooms are a major source of new carbon to the ecosystem. In the Antarctic blooms of algae at the ice-water interface are an essential food source for juvenile krill – adult krill being the major food source for virtually everything else down here. Getting some indication of when, where, and how often these events occur along the West Antarctic Peninsula will tell us a lot about how these ecosystems function, and what will happen to them as the ice season and range continues to decline.
We arrived at Palmer Station last Thursday morning after a particularly long trip down from Punta Arenas. Depending on the weather the trip across the Drake Passage and down the Peninsula to Anvers Island typically takes about four days. This time however, the Laurence M. Gould had science to do and a NOAA field camp to put in at Cape Shirreff on Livingston Island. This was a particularly welcome event as it gave us an opportunity to get off the boat and get a little exercise unloading 5 months of supplies for the NOAA science team.
Since arriving at Palmer Station the activity has been nonstop. In addition to lab orientations and water safety training there is the seemingly never-ending job of setting up our lab and getting instruments up and running. Yesterday evening following the weekly station meeting we did manage to go for a short ski on the glacier out behind the station. I’m glad we did because today the weather took a real turn for the worse; winds are gusting to 55 knots and strengthening. This is a real concern for us because wind strength and direction are the primary determinant of the presence and condition of sea ice in this area. As I wrote in my previous post we are hoping for sea ice to be either very solid, so we can sample from it or clear out completely, so we can get the zodiacs in the water. We’ll have to wait until the storm passes to see what conditions are like but very likely it will be neither!