GOLF 4-3-9 Antarctica Expedition 2010

Location

We just returned from our first trip out to the Dry Valleys to retrieve our moorings at Lake Fryxell. We did the job we came to do, not entirely without hick-ups but it all worked out and we had a great adventure, learning lots.

You might know that the Dry Valleys represent the largest ice-free areas of Antarctica  and are amongst the driest places on earth. Glaciers converge on these valleys from many directions, but they melt and “dry up” way upslope, well before they can meet up and fill the valley floor with ice. The melt waters from the glaciers collects in the lowest points of these valleys and form permanently ice- covered lakes. 

One of the larger ones of these lakes, Lake Fryxell, is the target of our study.

The water that collects in the Dry Valley lakes has no other way to escape than by the evaporation (sublimation) of the top ice surface. The ice in these lakes can be very thick: The ice thickness in Lake Fryxell was six meters when we drilled into it in 2008. The underlying water is very stable and becomes layered (or stratified) because of a very strong density gradient due to high salinity waters in the deep portions of the lake and freshwater at the surface. There are also other strong chemical gradients in Lake Fryxell: The uppermost waters are rich in oxygen (oxic) but the lower layers have high hydrogen sulfide concentrations (sulfidic) and are void of oxygen (anoxic). Thus, in the water column there are chemical gradients corresponding to the density gradient and the region where these gradients are the steepest is referred to as the chemocline. Our experiments take advantage of the stratification because we can expose our “rocks” at three different depths, 8, 11, and 14 meters, corresponding to oxic, chemocline (the transition zone from oxygen to no oxygen sometimes referred to as the suboxic zone) and sulfidic conditions. Our 8 meter experiment will attract microbes that breathe (respire) oxygen to alter the rock, while the ones at 11 and 14 meters must respire other compounds in order to grow, such as nitrate (11 m) and sulfate (14 m). During these cellular respiratory processes reduced chemicals in the rock (i.e., the reductants, such as reduced forms of iron and manganese) are oxidized and the compounds being respired (oxidants) are then reduced. This is the mechanism by which all life forms gain cellular energy, oxidation and reduction. For us humans, we’re oxidizing organic compounds, such as sugars, proteins and fats, and reducing oxygen. Oxidizing a chemical compound with something like nitrate may sound less efficient than with oxygen. This is true, but remember that you can make an explosive out of nitrate as an oxidant (such as chicken-poop) and diesel oil as a fuel (such as diesel). We believe that nitrate based respiration may occur in the chemocline, but then, at 14 meters the oxidation of energy yielding compounds in the rock by sulfate, an even less efficient oxidant. Does the biological interaction with volcanic rocks stop at this point for lack of oxygen or nitrate? Or can microbes oxidize the iron and manganese by other means? Are there any differences in rock dissolution in oxic (8m), suboxic (11m) and anoxic (14m) environments? Lake Fryxell is a crucial experiment that helps us to explore the role of different oxidants in microbe-rock interaction. We have no idea yet what the results will be, but the samples are “in the bag” and they are currently being prepared for laboratory study.

If you wonder about where our mooring site is, you can google it on Google Maps: find it at 77.61195°S and 163.15224°E! To get to this site we have to walk about fifteen minutes on treacherous lake ice. There are some areas with smooth, flat ice or relatively easy to walk on snow, but most of the lake surface is frozen into unstable ice formations that can collapse under your step or that make you slip because they are so rugged. It is hard to walk the distance, but we also have to bring in heavy materials with sleds and an ATV, both of which are much more challenging than just walking…

It is quite interesting to explore how this unstable ice forms: In winter, extreme cold may thicken the ice on the lake to about six meters, while the dry and fierce winds ablate the ice from the top. This brings up to the surface a lot of dust, and rocks that were frozen in the ice. In the summer, when the sun begins to appear on the horizon, these rocks are heated and begin to melt into the ice often leaving behind an open (vertical) channel. Big rocks make big channels, small ones make thin channels that turn the ice into “styrofoam” that consists of irregular vertical columns of ice and a lot of channels in between. When you step on this styrofoam, you never know whether you are going to break through or whether it will support your weight. Later in the season, this ice is often underlain by a pool of melt water that can be several feet thick. There is a very good chance to get wet, but you probably will not drown—just get extremely cold very quickly.

We performed our own little experiment to see how this process could work. We took three rocks and placed them on top of the firm snow/ice, one white one, and two black ones. After three hours of sunshine, the white one was still on top while the dark ones had sunk in substantially! Dark materials warm up much easier than light ones, and that heat can be used to melt the ice underneath. This very process actually happens all over our planet with some dramatic consequences for our glaciers that are important to our climate as they radiate out to space a lot of solar heat. Humans produce a lot of fine dark particles (like the soot from diesel burning engines) that settle out from the atmosphere onto these glaciers which then melt them much faster than they would otherwise. This happens globally, but it is worst in temperate climate zones and areas that are closest to population centers (such as the European Alps).

Back to our moorings in Lake Fryxell. Once we figured out the logistics of getting to our dive site we started to drill into the ice. First we needed a hole to take our water samples and then we had to figure out how to free the rope with our mooring. The first hole was straightforward because we just had to widen a hole that the Limno team had drilled before. We did this with a Hotsy drill: a heated coil, very much like an old fashioned immersion heater, heats the water in a drill hole. This melts the ice around the narrow drill hole, widening it sufficiently that we can lower our Niskin bottles to sample the waters. Retrieving our mooring was not so straightforward: First, we had to drill a hole mechanically as close to the rope as possible, but without destroying it in the process. We drilled it half way down with the mechanical drill (Jiffy Drill) and then we began melting it with the Hotsy. We were making great progress, but the Hotsy drill promptly broke down just before we entirely freed the mooring. So what do you do when you are out there in the middle of a lake in the Antarctic Dry Valleys? You radio McMurdo station and they will send help by helicopter first thing the next day. Chantelle, (we named her the “Flying Hotsy Doctor of Antarctica”) fixed it in under an hour. Less than an hour of additional melting freed up the mooring, and we could pull it out, archive our two-year exposure samples and re-deploy the mooring again for our four-year experiment (to be pulled out in 2012).

This all took us about four days, and now we are back at McMurdo Station again. We are looking back to a fun time in Fryxell camp that we shared with eight other scientists, a lot of hard work and great company with common meals and lots of science exchanges. Good times doing science way down under!

Greetings from Hubert Staudigel (Hotel Sierra) and the G-439 team.