Posts Tagged ‘seaice’

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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.

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.

Another Day of Science and Mystery

September 27, 2009

Friday night was another overnight at the hut. We had dinner on station, which saved us the time we would otherwise have spent cooking and washing dishes at camp, and then headed out onto the ice. (A side note and brief glimpse into the mind of a couple of working scientists: Steve and Rich both profess to greatly enjoy doing dishes. Dishes, you see, unlike science, have a straightforward methodology and a well-defined endpoint. When you’re done doing a science experiment, it has already raised ten more questions which you must rush off to address; but when you’re done doing dishes, you can bask in a sense of closure and accomplishment.)

We got up around six A.M. the next day (my cot was next to the door, so as people went in and out I got several bracing facefuls of -28C air to drag me into alertness.) The sunlight is getting longer by about 20 minutes every day, so every time we go out we have to get up earlier in order to take measurements while the sites are still in shadow. Somehow, we managed to get the light dusting of snow swept off three sites and measure them all before the sun caught up with us–we made it with just a couple of minutes to spare:

From Pupsicles and Traverse Gear

The sun catches the edge of the site just moments after we complete our measurements.

It was all very dramatic, really. Rich tells me the measurements are excellent, and are showing exactly what we predicted they would show, which is gratifying. I’ll post graphs when Rich gets them all processed.

Having completed our Science and packed our gear, we went investigate a peculiar phenomenon which Steve had discovered earlier that morning:

From Pupsicles and Traverse Gear

Rich and Steve search the snow for tracks that might suggest how this happened.

That, if it’s not obvious, is a very frozen Weddell seal pup stuck in the ice like a flagpole. We investigated the area pretty thoroughly, and found evidence of the birth (blood, the afterbirth and umbilical cord, the outline left on the ice where the mother seal had been lying) but no identifiable footprints other than our own. The seal clearly froze while lying flat on the ice, as you can see from another angle:

From Pupsicles and Traverse Gear

'Flat-bottomed Seals': the less-successful predecessor to Queen's famous hit song

We thought someone from the seal research group might have set it up somehow, but those we’ve talked to deny it, and as I’ve said, there were no visible tracks. The other possibility is that the body was simply levered up by the action of the moving sea ice; if you look at the tail, you can see where some slabs of ice have been tilted upward.

Antarctica is a mysterious place.

As a bonus, we found what we think must be new-frozen frost flowers on the ice nearby:

From Pupsicles and Traverse Gear

Today's theme: things that are charming, fuzzy, and frozen.

Some Science Occurs

September 3, 2009

On Tuesday we managed to get a slightly earlier start heading out to the sea ice. It was still later than we’d planned; starting up a new project always seems to mean discovering several dozen things you forgot to bring.

The ride out was as bumpy as before, except this time we had the Analytic Spectral Device (for measuring albedos) along and thus had to be extra careful about excessive vibration.

We were looking for first-year sea ice that was bare of snow. We ended up near Tent Island, where our Kiwi friends had told us we might be able to find something sufficiently wind-scoured. No bare ice was immediately apparent, but we did find this iceberg trapped in the sea ice:


Click for larger version.



Say 'freeze'!

We investigated it, being careful to stay well clear of any possible falling ice. Icebergs are not to be trifled with; you can see the size of this one, and imagine how even a smallish piece of it might feel if it were to detach while you were underneath it.

Having found no bare ice even in the most wind-scoured of spots, and with the sun gradually sinking towards the horizon, we retraced our steps to an area which at least didn’t have very much snow and broke out our gear.



Rich uses the ASD to measure light levels. An overcast day is best for this, because the light comes in more evenly from all directions.



Me and the ice-coring device. Wrestling one of these down into the ice warms you up rather nicely, even at temperatures in the -30 range.



The snow was not very deep at all, but unfortunately even not-very-deep snow has quite a significant effect on albedo.

We got our albedo measurements, and we got our ice core, and we got very cold indeed.

On the way back we stopped in the sea ice hut the Kiwis have been using all winter, where they graciously fed us tea and cake. They also showed us their conductivity/temperature/depth sensor and the nifty hole in the sea ice–conveniently located within the warm confines of the hut–through which they lower it to get profiles of the ocean water below. Afterwards they kindly directed us to their own road back towards base, which felt orders of magnitude smoother than the route we’d been using and allowed us to get home in one hour instead of three despite being technically longer. An excellent day all round.

Scouting the Sea Ice

September 2, 2009

I was going to try and update this more frequently, wasn’t I? My apologies. It has been a long couple of days out on the sea ice.

Being out on the ice is a strange experience. Here at McMurdo, you can pretend you’re just in some small town in Alaska. Out on the ice, though, the vast expanse of frozen water stretches out around you and the landscape is considerably more alien. I still find it slightly unnerving to drive across the sea ice, despite the fact that it is demonstrably strong enough (at this time of year) to land enormous planes on and has no trouble with our little pisten bully.

On Monday we went out on a scouting trip to see what the terrain was like around the places we wanted to go. It turned out to be a very long commute, mostly due to the very uneven surface. Sea ice that has been around for a few seasons (which we call multi-year sea ice) collects hummocks of windblown snow called sastrugi. You can see a few in the foreground of this picture. They are usually of a concrete-like hardness, and since a pisten bully has no suspension aside from the spring-mounted driver’s seat, you have to go over them quite slowly to avoid shaking yourself and your equipment to bits.

We did see some interesting wind effects. In this picture, you can see the snow blowing over the ice on the right-hand side; on the left-hand side the wind is blocked by our parked pisten bully. In the middle Rich is conveniently blotting out the setting sun so that I can take the photo. (I need to do a proper introduction post for Steve, my advisor and the head of the project, and Rich, our collaborator; this blog is kind of me-centric, but they are the masterminds of this whole business.)

We concluded our scouting mission a bit before sunset, having gotten some good experience with ice driving and ideas of how long it took to drive out, and headed back to base. Next post: our scientific adventures on Tuesday.

Escaping the Snowball

August 22, 2009

So, how does a planet get itself out of a Snowball state? The short answer, as I mentioned in my last post, is “carbon dioxide.” When the Earth was frozen over, volcanic activity didn’t stop–volcanos kept pumping gases, including greenhouse gases such as CO2, into the atmosphere.

Now we get into the geochemical aspects, which are a bit outside my field, so please take my explanation with a grain of salt. Normally, CO2 that enters the atmosphere reacts with rocks on the Earth’s surface, creating carbonate minerals. This process gradually removes CO2 from the atmosphere. When the amount of CO2 in the atmosphere increases, the Earth warms, which speeds up the weathering process and removes CO2 more quickly. This CO2 feedback helps keep the Earth at a comparatively stable temperature over the long term (CO2 weathering is slow, so it can take thousands of years for CO2 to leave the atmosphere even at warmer temperatures.) Here’s a paper on the CO2 weathering feedback (link goes to PDF file) for those who are interested in a more in-depth treatment.

Much of this CO2 weathering process occurs when CO2 combines with minerals to form carbonates, such as calcium carbonate (the principal component of limestone, among other things.) This process is helped along when CO2 mixes with water in rain, rivers, and the ocean. However, on a Snowball Earth, little rain or snow would fall, and few, if any, rivers would flow. No CO2 could dissolve into the oceans, because they would be cut off from the atmosphere by a thick layer of ice. Instead of weathering out of the atmosphere, the CO2 would simply build up over time. As carbon dioxide levels increased, so would the greenhouse effect. Eventually, the CO2 would reach such high concentrations–hundreds of times modern levels, by some estimates (for example, Hoffman and others, 1998)–that the warming greenhouse effect would overcome the cooling effect of the light-reflecting ice.

When the greenhouse finally overcame the ice, it melted quickly, suddenly transforming most of the world’s surface from brilliantly reflective ice to dark, absorbent sea. Without the reflective effect of the ice, the greenhouse effect took over and the temperatures soared. At the same time, the massive amount of CO2 in the atmosphere began to dissolve into the ocean, where it precipitated out to form thick layers of carbonates. These “cap carbonates” are still visible today and form one piece of evidence for the Snowball Earth theory.

This is, of course, just one of several ideas about how the Snowball Earth scenario might have played out. It’s possible that, instead of Snowball Earth, there was a “Slushball” Earth, with open water at the equator. A Slushball Earth would have much less trouble supporting life, which would thrive in the areas of open ocean. On the other hand, that open ocean would act as a sink for CO2, and the Slushball might not be able to accumulate enough CO2 to overcome the albedo of the ice on the rest of the globe. Snowball Earth researchers continue to search for a model that will balance these various factors–account for sea-level glaciers at the tropics, provide a refuge for life, and permit enough CO2 buildup to initiate the return to a normal climate.

But you don’t have to take my word for it, as Levar Burton would say. Much more information on all these topics is available at SnowballEarth.org, which gives a good comprehensive overview of the whole business.

<A diagram from SnowballEarth.org, which gives a good graphical overview of the Snowball event.

A diagram from SnowballEarth.org, which gives a good graphical overview of the Snowball event.

Ice, albedo, and the Snowball Earth theory

August 4, 2009

Life on a planet is a fragile thing, particularly if the life is at all complex. Naturally, astrobiologists like to catalog the ways that life can be decimated or snuffed out entirely. Asteroids, comets, and bursts of high-energy gamma radiation are commonly cited catastrophes, but a planet can also run into trouble without any cosmic interference. One of these more self-contained scenarios is “runaway ice-albedo feedback.”

Albedo, if you aren’t familiar with the term, is just the amount of light that’s reflected from a surface relative to the total amount of light hitting it. You can measure it using a device that collects all the light coming down from the sky, then flips over to collect all the light being reflected back from the surface below it. Divide the latter by the former and you have your albedo. Dark-colored things have a low albedo–for instance, the open ocean has an albedo of around 0.06, meaning that it reflects only 6% of the light that hits it and absorbs the rest, which is mostly converted to heat. Light-colored things have a high albedo–for instance, sea ice has an albedo between 0.5 and 0.7, which goes up to 0.9 or higher when the sea ice is covered by snow. The relationship between albedo and absorbed heat will probably be obvious to anyone who has ever worn a black shirt on a hot, sunny summer day. Summer clothes tend to be light-colored because it maximizes your personal albedo and keeps you pleasantly cool.

Ice-albedo feedback occurs because ice and snow are highly reflective. Suppose a planet cools down a little, perhaps because of a reduction in solar output or the amount of CO2 in the air. The ice caps will grow a bit, which will reflect more sunlight back into space. With less sunlight being absorbed, the planet cools a bit more, the ice caps grow a bit more, and so on. (This works in the other direction, as well–the ice at the North Pole is melting faster because it exposes low-albedo ocean as it retreats.) Usually this feedback loop runs into some limit and stops. Theoretically, however, it can go into a “runaway” state. Computer models of this process suggest that once ice reaches 30 degrees latitude, the feedback becomes unstoppable and the entire planet freezes over very rapidly.

A diagram of a planet undergoing runaway ice-albedo feedback.

A diagram of a planet undergoing runaway ice-albedo feedback.

This fully-frozen state is fairly stable; the ice reflects most of the sunlight back into space, keeping the planet cold. In fact, when Mikhail Budyko first modeled this phenomenon in the 1960s, he concluded that it could never have happened on the Earth because there would have been no way to escape from it.

However, in recent decades an increasing amount of geological evidence seems to suggest that the entire Earth did freeze over, around 600 million years ago (and perhaps at other times before that.) How did the Earth transform from its frigid Snowball Earth alter ego back into the warm, pleasant planet we know today? Tune in next time to find out!


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