Posts Tagged ‘ice surface’

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.

Audited by Emperors

September 23, 2009

I made a comment in a previous post about gangs of ne’er-do-well Adelie penguins vandalizing our site. That was, of course, a joke; there are no roving gangs of Adelie penguins out here. There are roving gangs of Emperor penguins.

From Penguin Day

The Emperors are here to inspect our work.

Backing up a bit: yesterday dawned cold and cloudy, perfect for taking measurements, so we headed out to the study site and got there around 1:00pm. The ice surface has been changing a lot in the past week or so. The snow crust is becoming thinner, probably eroded by high winds. Wandering away from our camp a ways, we found that the bare blue ice we’ve been hoping to find ever since we got here had finally begun to emerge from beneath its snowy blanket. As we explored we noticed a number of distinctive black-and-white forms in the distance.

From Penguin Day

Bare blue ice has never been so exciting. That's my boot for scale.

We selected a good site and set up our instrument, and soon acquired company in the form of fifteen Emperor penguins who sauntered up to watch. Apparently this phenomenon is fairly common: small groups of non-breeding individuals will break off from the main colony and wander aimlessly for large distances, stopping to inspect anything that catches their interest. (This is also exactly what the penguins say about scientists.)

From Penguin Day

An attentive audience of Emperor penguins watches Rich take albedo measurements.

Evidently the penguins decided our scientific endeavours were worthy of closer investigation, because when we set up the instrument at our original, carefully-groomed site for comparison measurements, we had a devil of a time keeping the entire group from marching directly across it.

From Penguin Day

Rich tries to convince the penguins to move slightly further away.

By keeping myself between the penguins and the study site, I managed to avert their repeated efforts to get penguin prints (and penguin excreta) all over our nice clean ice. Fortunately they tend to follow each other, so by discouraging the foremost penguin I could get the others to bypass the site as well. The penguins took it all with good humor and hung around for a while after we were done taking measurements.

From Penguin Day

Rich and Steve take measurements; meanwhile, the penguins stop their advance on our site to pose for a group photo.

Around six o’clock we retired to our hut to make dinner and bed down for the night. I don’t think I have told you about the ice hut we recently acquired (I’ve been shockingly lax about updating this week, for which I apologize.) The hut sleeps five in reasonable comfort and makes a good staging area for equipment during the day:

From Penguin Day

Our home away from home.

It’s also heated and equipped with solar panels for electricity. Evidently the penguins thought it was pretty nifty too, because shortly after dinner we heard their distinctive trumpeting just outside the door. We thought they might come in for cocoa, but they just wanted to get out of the wind. For obvious reasons, the side of the hut that’s out of the wind is also the side of the hut where we set up our pee bucket toilet facilities, so for most of the night any of us who went out to answer a call of nature found ourselves doing so in front of fifteen interested penguins.

Meghan, the wilderness safety person who came out to the hut to ensure we didn’t do ourselves an injury somehow, says that she heard the penguins near the hut until the wee hours of the morning; then they marched around it, perhaps to see if any of us were interested in joining them, and struck off into the night.

More photos at my Picasa album; this time I added the link under the pictures. I haven’t included the link to the album on previous posts, but a lot of them have additional photos on Picasa as well.

Frost Flowers Revisited

September 17, 2009

Somebody asked about frost flowers (thanks, MeghanC!) This gives me an excuse to pontificate upon them a bit. Here’s a great picture of frost flowers from a New Scientist gallery:

Those of you who haven’t spent a lot of time hanging out in the polar regions may not be familiar with the sequence of events involved in the formation of sea ice (apologies if I’ve explained this one before…) As the winter begins and the ocean cools down, little bits of ice begin to form at the surface of the water; these are called frazil or grease ice. Eventually they stick together into a flat sheet, called nilas ice. Pockets of seawater (brine) get trapped between the crystals as they freeze.

As the ice gets colder, water freezes onto the walls of the brine pockets. When water freezes, it tends to exclude any non-water substances, so the brine within the pockets gets saltier. Water also expands as it freezes, so some of the salty brine is pushed out of the ice. Part of it goes downward, and the sinking of this cold, dense, salty water has interesting effects on ocean currents. Part of it goes upward through whatever channels it can find:

Experimenting with hand-drawn diagrams this time, as you can see.

The ice continues to freeze, and the brine being pushed out of the pockets forms a thin layer across the ice. This layer is very salty, so it stays liquid even at very low temperatures:

Frost flowers form at temperatures below -15C (or lower, depending on who you ask.) Seawater, of course, can never get colder than -1.8C. This means that under frost-flower-forming conditions, the ocean is quite a lot warmer than the air. The brine layer on the surface of the newly-formed ice is also comparatively warm, and it gives off water vapor. The vapor re-condenses and forms crystals on top of the briny “bumps” we saw earlier:

The flowers continue to grow, and some of the brine travels up them via capillary action, making them very salty compared to most sea ice:

That, anyway, is the short version of how frost flowers form. They may have some effects on the atmosphere because salts from the ocean are caught in their delicate fronds where the salts can easily be picked up by wind. They may also, as we are now seeing, have some effect on ice albedo both by themselves and by capturing snow that blows across the ice.