Archive for October, 2009

The Case of the Salty Pond

October 28, 2009

At the end of our last post, we had just made a successful landing in Garwood Valley:

From Science and Aesthetics at Garwood

Karen and the helo tech unload our Garwood gear.

We started our hike up the hill. Before you can go to the Dry Valleys, you are required to watch several videos about how to minimize your environmental impact on the slow-regenerating ecosystem of the Valleys, where tire tracks may last for decades and life is rare and delicate. So I was very careful not to step on the peculiar lichen-like growths we found among the rocks, or their peculiar algae-like cousins frozen into the ice of the ponds.

From Science and Aesthetics at Garwood

I've taken a lichen to this valley! ...please don't kill me, the bad puns are a hereditary condition.

From Science and Aesthetics at Garwood

Mitten for scale--it was warm enough not to have to wear them all the time.

This part of the valley is full of these little ponds in deep holes. I never was quite clear on what created the unusual topography. In any case, we investigated a couple of others and finally crested a hill to see the pond that we’d been looking for. The dry air and winds of the valley had gradually sublimed away the ice on its surface, leaving behind a layer of hydrated sodium sulfate–mirabilite.

Unfortunately, the winds had also stained the surface with thick layers of dust.

The pond was small, perhaps five meters across (I think–I’m kicking myself for not taking a photo with a size reference.) The clear patches weren’t nearly big enough to get good albedo measurements–and even what looks nice and white from a distance was mixed in with enough dust to muddy our results. Rich was also concerned about taking measurements at the bottom of a hole, because the ASD records light from every direction, so the light reflected from the dark hillsides could also be an issue if we took measurements too close to them.



Raised surfaces near the ASD can reflect light onto the sensor.

Disappointed, we had a snack and considered our options. We decided to take a couple of ice cores, one from the mirabilite pond and one from a pond with no crust, and then spend the rest of our day in the valley scouting around for better surfaces to measure.

From Science and Aesthetics at Garwood

The ice of this pond was so clear you could see several feet down, all the way to the bottom in some places.

The first notable feature we found was an entire cliff that seemed to be made mostly of mirabilite. Mirabilite, remember, forms only at -8 degrees C, so we’re not sure exactly how this structure formed in the first place. We actually found mirabilite, or its dehydrated form sodium sulfate, lurking below the soil in quite a few different places in the valley.

From Science and Aesthetics at Garwood

An impressive mirabilite outcrop.

A bit further along we discovered this formation, which we think is a pingo, or ice hill. Pingos are levered upwards gradually over many years, as water seeps in below them, freezes, and expands. The gap beneath this ice slab is a couple of feet high. Pingos are frequently found in the Arctic, but I suspect there just isn’t enough exposed ground for them to be common in the Antarctic.

From Science and Aesthetics at Garwood

We ended up near the mouth of the valley, where it meets the sea ice, and spent a little time investigating there. Here’s a ground-level look at the kind of surfaces we would have had to navigate if we’d decided to make the traverse:

From Science and Aesthetics at Garwood

Things you do not want to drive over in a Pisten Bully.

Finally, as our scheduled pickup time began to draw close, we made our way back to the study site. We never did find a better pond, but we think we may simply be too early in the season; with a little more time and sunshine making the ice sublime away, more ponds might have suitable crusts that we could measure. We’ll be back next year to find out. On the way back to the landing site we found some ventifacts:

From Science and Aesthetics at Garwood

Wind does strange, strange things given enough time.

From Science and Aesthetics at Garwood

Waddles the stuffed penguin hides out in a ventifact.

The helicopter lifted away, and we bade farewell to Garwood Valley–and the Antarctic Continent, lurking tantalizingly beyond the hills. (Since McMurdo is on Ross Island, this had been the only time on the trip that we actually set foot on the continent itself.) With any luck, next year will give us more opportunities to improve our measurements here–perhaps we’ll even get time to hike upvalley and look for Garwood’s single resident mummified seal.

I do encourage you to go check out my Garwood Valley album–I took many more photos than I could fit in one post.

From Science and Aesthetics at Garwood

A fond farewell to Garwood and the continent.

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Getting to Garwood

October 20, 2009

Last you heard from me, I was languishing in Crary Lab (the scientific heart of McMurdo Station) awaiting appropriate weather conditions for helicoptering over to Garwood Valley. A few helo flights made it to other nearby valleys—Taylor Valley, for instance, which is probably the best-known of the group and contains a fairly permanent camp which is staffed during summer. Garwood, however, had slightly different weather conditions and no available shelter should anything go wrong.

I’ll take a moment here for a parenthetical discussion of our original Garwood plans. Initially, you see, we’d hoped to drive there. This sort of ground-based expedition is locally referred to as a “traverse”—such as the “South Pole traverse”, a caravan of tractors that drags fuel and supplies to the Pole. To get to Garwood, we would have driven a couple of tracked vehicles across the sea ice and along the coast until we reached Garwood.

Along the way, we would have had to get across ice that had melted and re-frozen into fantastical structures. Some aerial photos from the previous year, showing sea-ice features whimsically named by some creative individual involved in taking them, gave us a small idea of what to expect:


'The Marshes of Insanity.'


'The Rivers of Woe.'


'The Wall of Despair.' We would have had to find a gap in this ten-foot ice wall, through to the 'Straits of Impunity', in order to actually enter the valley.

Our stalwart compatriots in the Field Safety department spent many hours working out a way to accomplish the traverse in a way that would be both safe and scientifically successful. Alas, as we planned it became clear that the mission was logistically unfeasible, and we returned to the less adventurous, but more efficient method of helicopter flights.

On Tuesday, the 12th of October, the weather finally looked good enough to try it. Myself, Rich, and Karen—our field safety person, who did much of the original traverse planning—donned our helicopter helmets, packed our bags, and lifted off in a Bell 212 bright and early that morning. I was thoroughly excited to be on my first helicopter flight. The sea ice went past beneath us at a good clip, and we arrived at Garwood Valley around half an hour after we left McMurdo.


Our first glimpse of Garwood.

The weather was marginal, though, with turbulence making us all a bit queasy on our way out. At Garwood, winds in excess of fifty knots were roaring down into the valley and up the other side. When our pilot went in for a banking turn that would allow us to get a better look at the study site, the wind flung the helo upwards and then shoved it down practically into free fall. Our pilot pulled us out without too much difficulty–McMurdo’s helicopter pilots are among the best–but it was clear that landing was out of the question.

But the trip was not entirely in vain; we had taken as many photos as we could during that single pass over the valley. We could see the pond we wanted, tantalizingly close and showing what we thought to be just the salt crust we wanted.


A reconnaissance photo of Garwood's saline ponds.

We were eager to get back, and Wednesday obligingly dawned as clear and calm as we could hope for. This time the valley was dead calm, and the helicopter landed without a hitch and left us to enjoy a day whose sunny and windless weather made it feel nigh-tropical to our cold-adapted senses. The pond was just a couple of hundred meters from our landing site, over some hills whose steep sides hadn’t been apparent from the aerial photos, and we set out optimistically to examine it at close quarters.

Tune in next time for The Case of the Salty Pond!

Long on Airline Miles, Short on Internet

October 18, 2009

Oh dear. Has it really been over a week since I updated?

It has certainly been a very hectic week. We did finally make it out to the Dry Valleys, and then spent the next few days in the time-consuming process of getting ready to leave and packing up the lab. I said my tearful goodbyes to Antarctica on Friday, and I’m currently in Sydney en route to Seattle. I’ll be posting about our Dry Valleys experiences, the ins and outs of the McMurdo sewage system, and various other interesting topics as soon as possible once I get back to my home and reliable Internet access.

Conditional Approval

October 11, 2009

In my previous post, I said we’d be heading out to the Dry Valleys on a helicopter on Saturday. I had hoped to have all kinds of excellent pictures to show you by now. Alas, the weather was not with us, and all helicopter flights on Saturday were cancelled. There are no flights on Sunday—it’s a coveted day of respite from McMurdo’s six-day workweek—so we’ve been rescheduled for tomorrow. Unfortunately, if things go as predicted by the weather staff, tomorrow may be even worse for flying.

This kind of weather-related delay is pretty much par for the course in Antarctica. You may recall that some time back I said I’d be leaving on the 9th of October, and you may note that I am in fact still here. This is because the flight with the helicopter pilots on it was delayed five days, by weather and mechanical issues, so the helicopter schedule was also pushed back. I am beginning to learn that, whatever your plans may be, Antarctica has final say in when they happen.

Dealing with weather is an interesting part of daily life at McMurdo. There are three official designations for local weather:

Condition 3 is the default. In Condition 3, station life proceeds as normal.

Condition 2 means that the weather has become somewhat hazardous. The weather forecasters will officially designate Condition 2 if one or more of the following apply:

  • Wind speed between 55 and 63 miles per hour, or
  • Wind chills between -75F and -100F, or
  • Visibility of 1/4 mile or less.

In Condition 2, travel outside the station is restricted, and if Condition 2 is called because of low visibility you’re encouraged to use a buddy system when traveling between buildings.

Condition 1 essentially shuts down the station. Condition 1 means:

  • Wind speed above 63 miles per hour, or
  • Wind chills below -100F, or
  • Visibility of less than 100 feet.

For the most part, once Condition 1 goes into effect, you’re not supposed to leave the building you’re in. I am told they train people to navigate in Condition 1 by putting a white plastic bucket over their head; the effect is evidently similar. If severe weather lasts long enough, the safety staff will string ropes between buildings so that people can get to meals or go to work.

While I’ve been here, we’ve had Condition 2 a few times—earlier in September the wind chills went below -75F on a fairly regular basis, and once or twice blowing snow has reduced visibility enough to be considered Condition 2. We’ve yet to experience Condition 1. Personally, I almost wish we would; if the weather is going to continue delaying us, we might as well get some excitement out of it.

Sealing the Tent Island study site

October 9, 2009

Tomorrow morning we’re getting on a helicopter and flying to Garwood Valley, then coming back in the afternoon. This makes me tremendously excited, and we’ve been very busy getting ready. There will undoubtedly be lots of pictures from the trip.

In the meantime, here are some photos from yesterday’s trip out to our Tent Island study site to retrieve our datalogger. The weather was sunny and calm, and the Weddell seals were out in force. Most of these are pregnant females; they’ll have their pups soon.

From Sealing the Study Site

Two Weddell seals bask in the warm (by Antarctic standards) spring sunshine.

You can hear the seals under the ice. They make noises that are difficult to describe–something like the sound effects for a science fiction movie.

From Sealing the Study Site

Rich does his relaxed-seal impression.

From Sealing the Study Site

A frost flower decorates the seals' icy stomping grounds (or galumphing grounds, as the case may be.)

From Sealing the Study Site

The seal is dubious.

From Sealing the Study Site

Weddell seals often lie in one spot for hours at a time, long enough to melt their outline into the ice. (As you can see, they also don't bother with separate toilet facilities.)

From Sealing the Study Site

A seal bids us farewell.

Results!

October 7, 2009

It’s a tremendous amount of fun to go out on the ice, take data, and drink in the Antarctic sites. Eventually, however, the question must arise: what is it all for? Do we have anything to show for it?

The answer, in this case, is yes. Rich has spent a couple of days diligently analyzing our albedo data, and we’ve found that, just as we expected, colder sea ice has a higher albedo, probably due to the crystallization of salts in the brine pockets. Here’s a graph of the albedo at a wide range of wavelengths of light. The graph shows three measurements at cold temperatures below the crystallization point (-23 degrees Celsius.) As you can see, the albedos get steadily higher as the temperatures drop and salt crystallizes in more brine pockets.



Rich's analysis of our albedo measurements. Click for larger image.

Rich also spent a day in our cold room, while the helpful freezer technicians changed the temperature from above -23 to below -23 and back. Here are his Highly Magnified brine pockets (as mentioned previously) in the process of going from liquid brine to crystallized hydrohalite:





The hydrohalite is behaving just as we want it to. This is an unusual thing in science.

It may not look like much, but the minute changes visible in those photos are really quite tremendously exciting. Rich’s long hours in the cold, drafty, noisy freezer have not been spent in vain.

Ice from a Dry Valley

October 6, 2009

Some of the weirdest places on what is arguably the world’s weirdest continent are located just across McMurdo Sound from Ross Island.



A USGS map of the Dry Valleys in relation to Ross Island, highlighting two of the largest and best-studied valleys. Click for larger version.

These are the Dry Valleys, so called because they are some of the few places on the continent that are free of ice and snow. Almost no snow or rain falls here, and what does fall is blown away or evaporated by the constant strong winds. The valleys are so dry and cold that NASA used them as a testing ground for the Viking Mars lander.

The winds that blow through the Dry Valleys are called katabatic winds. Katabatic winds arise from air simply flowing downhill off of a continent. The center of Antarctica is at high altitude due to the kilometers of ice that have built up there, and is also very cold. Cold air is denser than warm air, so the cold air from the middle of the continent naturally wants to flow downhill toward the edges. Places like the Dry Valleys act as bottlenecks, where the winds are forced through a narrow place and therefore have to blow even faster.

The wind is the main source of erosion in the Dry Valleys. It picks up tiny grains of sand that carve the rocks into strange forms called ventifacts:



Ventifact image courtesy the Exploratorium's website.

But the Dry Valleys aren’t entirely dry. They’re home to a number of lakes and streams, some of which are fresh and some of which are extremely salty. Some are frozen right to the bottom, others are liquid below their covering of ice. Some have distinct horizontal layers of water of different salinities.

We are interested in one lake in particular, in Garwood Valley. This lake is one of the high-salinity ones, and we’re hoping to use it to get an idea of how a particular type of ice on Snowball Earth might look.

So far, you may recall, we’ve been looking at what happens when crystals of hydrohalite form within sea ice. Here on modern Earth, those crystals don’t last long; the sea ice warms up, dissolving them. On Snowball Earth, though, the temperatures would be around -30C even in the tropics. The hydrohalite would remain crystallized indefinitely.

In the tropics of the Snowball, where evaporation would exceed precipitation, the ice around the hydrohalite would gradually sublime (that is, transition from solid ice to water vapor without going through a liquid phase in between.) With the ice sublimed away, the hydrohalite would be left behind on the surface. Like table salt, it would reflect a lot of light, and it might have a quite significant effect on the albedo.

We can’t observe this effect on modern sea ice, of course, because it doesn’t stay cold enough for long enough. We can try the next best thing, though: salty lakes in the Dry Valleys. We know of one lake in particular that develops a crust, not of hydrohalite, but of another low-temperature salt called mirabilite that we hope might have similar qualities.

Our first helicopter flight to the Dry Valleys leaves on the 10th of October; then we get a day to crunch data collected on that flight before we go out again. I may not get much time to write in between, but I’ll try to post lots of pictures. In between now and then I’ll see if I can get in a post about other weird things in the Dry Valleys, including Blood Falls, cryptobiotic soils, and ancient mummified seals.

The Ridiculous and the Slime

October 2, 2009

I don’t think I’ve talked much yet about my own personal corner of our project. This is actually a bit of science I tacked on at the last minute—it wasn’t in the original grant—and I’m hard pressed now to recall quite how I even came up with it.

You may recall that the effect we’re looking for in the sea ice depends on the formation of hydrohalite crystals inside brine pockets. Rich has actually got a nifty microscope setup in our cold room to look at the brine pockets now (pictures of which will be posted here as soon as I can pilfer them from his collection.)



Rich's tablet displays a highly magnified (and perhaps thoroughly educated) view of some brine pockets.

The brine pockets, as I explained earlier, are there because seawater got trapped in the ice when it was in the process of freezing. However, as you are well aware, seawater isn’t just a collection of water and salts. It is also home to a staggering number of microorganisms, some of which are inevitably trapped in the ice with the seawater as it freezes.



(From an essay by J. Deming and C. Krembs on NOAA’s website.)

Some diatoms (diatoms are a type of algae) living inside a brine pocket.

The brine pockets don’t provide a particularly hospitable environment for things to live. As the ice gets colder, the brine pockets also get colder, as well as smaller and saltier. Sharp pointy ice crystals may form. Some of the creatures that get caught up in these brine pockets try to protect themselves from freezing by secreting things that reduce the melting point of water, keeping it liquid at lower temperatures. One of these is a slimey substance called EPS (which stands for “expolymeric substance” or “exopolysaccharide”, but I usually just think of it as “slime.”)

Now, this substance obviously has the potential to mess up our nice simple salt-water physics. Changing the behavior of the water and salt in the brine pocket is exactly what the diatom wants it to do, after all. When our colleague Bonnie Light observed natural sea ice in the lab, she found that not all hydrohalite precipitated at the expected temperature—some brine pockets developed hydrohalite crystals earlier than others (Light, Maykut and Grenfell, 2003.) The difference could, perhaps, be due to EPS content of some brine pockets. So while Steve and Rich are investigated albedos, I’m collecting ice to see how much EPS it might contain.

The process starts when I take an ice core:



You remember this bit.

We strap it to the top of the pisten bully and take it back to the cold lab, where Steve and I cut it into manageable bits.



Even with a couple of layers of gloves, my hands get awfully cold doing this. Presumably my squid hat is also getting pretty chilly, but it remains stoic.



Manageable bits.

If there are any organisms in the sample—algae or bacteria—I don’t want to shock them too much by exposing them to very different temperatures or salinities. If I shock them, they might explode (or ‘lyse’ in biologist-speak.) When I’m starting out the critters are in brine pockets that started out between -15C and -30C, depending on what day we took the core and what depth they were at. The brine pockets they’re in are very salty at that temperature, so I mix up some very salty artificial brine and dump the samples into that to melt.





Lots of Instant Ocean and some distilled water.

Once the samples are melted, I filter them.



The filters are rather delicate and finicky.




This is very similar to a setup that Steve carted around Siberia for two months for snow research. Note handpowered vacuum pump.

There are a couple of common ways to look at EPS. One of them uses the filters plain; for the other, you dye them with something called Alcian blue that binds to the EPS:



Blue. Like a glacier! Well, sort of.

Eventually, you end up with something like this, which I’ll put back in the freezer until it can make it onto a cargo flight back to the States.



All that work for something that fits in a 1.5mL tube with room to spare.