Frost Flowers Revisited

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.

Antarctica, Macabre and Sublime

We’d originally planned to stay in on Wednesday and analyze our results from previous trips. When we learned the forecast was for clouds, though, we realized it might be our last chance for a while to make good measurements, and headed out to the ice. Upon getting to our planned site, however, we found that the day was beautifully bright and sunny, with barely a hint of the “partly cloudy” the day’s forecast had promised.

SCIENCE INTERLUDE: Why, you may well ask, do we need cloudy days for our measurements? Here’s a series of pictures I took on Wednesday, showing the same patch of ice from different angles:

You can see that the amount of light reflecting from it is radically different depending on what direction you’re looking. If we tried to determine the amount of light reflecting from the surface, we’d get similarly variable results. So we need a cloudy day, when the light is diffused and comes in equally from all directions.

END SCIENCE INTERLUDE
Given the weather, it was clear that the day was entirely inappropriate for taking measurements. Happily, that made it an ideal day for a hike. We parked the pisten bully on some multi-year sea ice near an outcropping called Turk’s Head and set off to explore.

Our first discovery was something that looked a bit like a rock sticking out above the ice, but upon closer inspection proved to be the frozen corpse of a small Weddell seal. A little more searching turned up two others. Below is an image of the third one, which shows evidence of having been scavenged, probably by large gull-like birds called skuas. (Skuas are a big problem around McMurdo in the summer, apparently–they’ll divebomb anyone who appears to be carrying food.)

I later learned that the head was probably removed by local biologists.

Bits of dead seal scattered around the ice nearby had protected the ice beneath them from the sun, leading to these strange structures with a small stem of shaded ice holding up a scrap of frozen skin.

Fungoid, alien forms gradually emerge from beneath a residue of death.

Rich and Steve deemed the loose scree on the side of Turk’s Head to be suitable for climbing, so up the slope we went.

Unsettlingly steep, but lots of fun nonetheless.

We ran around on the top for a while admiring the view and plummeting down snow slopes so I could practice stopping an uncontrolled slide using an ice axe (a useful life skill.)

Tent, Inaccessible, Big Razorback and Little Razorback islands. From here you can see that they are actually parts of the rim of an ancient volcanic caldera. They say it's extinct, but you can tell it's merely biding its time beneath the ice.

As we descended, the pressure ridges in the sea ice showed up beautifully in the low light of the sunset. Pressure ridges are formed, as the name suggests, when currents and winds press huge slabs of ice up against each other. The combination of pressure, wind, and sun creates these grotesque and fantastical forms–I’m a bit vague on the specific mechanisms.

Ominous eldritch being or Muppet?

The ice fog rolling in at sunset produced a sundog, a circular rainbow around the sun:

The sundog touches down in the ice fog around Tent Island.

Curse You, Frost Flowers

Another sea ice day on Friday. We admired some Fata Morgana mirages on the way out:

Some nice sastrugi (snow dunes) with a band of mirage in the background

A mysterious cyclopean edifice in the distance

We returned to our previous sample spot and attempted to get better measurements by removing the snow:

Janitorial duty on the sea ice

The crust of snow was pretty well stuck on to the ice, requiring us to shovel, sweep, and then kneel down and scrape with spatulas and ice axes until the ice was more or less clear. We tasted the snow and found it was salty, which means that a lot of it actually started out as frost flowers. Frost flowers are fluffy, rather ethereal-looking crystals that form on new sea ice; they are pretty fascinating, scientifically. If anyone requests it in the comments I’ll write up a post about how they form.

Nifty as frost flowers are, they are making our life difficult. As you may recall from my previous post Salt, Sea Ice and Science we are looking at the way the albedo of sea ice changes when the salt in brine pockets forms crystals. Unfortunately, it’s very hard to see anything useful through a layer of frost flower remains. Hence our janitorial activities.

I am reminded that I promised equipment pictures in that post I just linked. You’ve seen the field equipment, of course, but I shall have to do a post about lab technique and some pictures of my impressive array of beakers.

The Altered Nature of Things

One of the weirdest things about the extreme cold is the way familiar substances begin to betray your expectations. Plastics stiffen and become brittle after just a few seconds’ exposure to the outside air. Metal burns to the touch. Moving parts freeze together or shrink apart. Batteries dwindle to a fraction of their former capacity and LCDs update sluggishly. The various vital fluids of vehicles freeze and coagulate. I can’t even imagine how much more bizarre and difficult it is at the South Pole, where ambient temperatures regularly dip below -100F.

We had a lot of this out in the field today. My issues with spectacles persist (frosting over completely, attempting to freeze to my face, what have you) and the goggles do nothing don’t help very much. (The little fan died their first day out, as I sort of expected it to do.) Our ice corer nearly got stuck in the ice. And our electronic thermometer, which we use to take the temperature of ice cores, refuses to function properly when it gets too cold. This meant I spent quite a while with it stuck down the front of my pants, nestled against my belly, trying to get it warm enough to give a reading–like an emperor penguin incubating an egg, as my advisor put it.

Speaking of penguins, I saw my first sign of the local wildlife today. Small clouds of steam, puffing up from a crack in the sea ice once a second or so: a Weddell seal at a breathing hole. We didn’t see the actual seal, of course. Weddell seals are fascinating creatures. They live under the sea ice, so they have to breathe through any cracks or holes in the ice they can find. They keep them open by chewing away at the ice as the holes freeze over. Any hole in the ice is likely to attract a Weddell seal; Antarctic divers often find themselves suddenly sharing their diving hole with a half-ton of blubbery, snorting Weddell, and our Kiwi friends say that their little hut on the sea ice has been visited (and splattered with seal snot) more than once.

A Weddell seal breathing hole in a sea ice crack.

It seems like a precarious lifestyle, being dependent upon the ever-shifting sea ice just to be able to breathe. Antarctic animals are a resilient and determined lot.

Home, Icy Home

So, I arrived in McMurdo on schedule on Monday, but I had some trouble getting my laptop onto the ‘Net. Here’s a post I wrote on the plane coming down, and here are some pictures from the journey and of the station itself.

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Currently on the plane to McMurdo, just about at the midpoint between there and Christchurch. It is a very loud plane; everyone is wearing earplugs, so there’s not a great deal of conversation with one’s seatmates. So I thought I’d take this opportunity to tell you about the International Antarctic Centre and the “Antarctic Attraction” museum. (Incidentally, Antarctic Attraction would be a great name for a romance novel. A parka ripper, if you will.)

Christchurch evidently takes great pride in its status as “gateway to the Antarctic”. The tourist information center downtown even includes a small “Antarctic shop.” The actual International Antarctic Centre is out by the airport, and acts as a base for the New Zealand, U.S. and Italian Antarctic programs. I don’t know much about the Italian Antarctic program, but the Kiwi and American programs are quite neighborly, with New Zealand’s Scott Base being located just a couple of miles from McMurdo. (Our team actually has an invitation to dinner there tomorrow night.) According to my Lonely Planet Antartica guidebook, both bases sit on land to which New Zealand has laid claim. The status of Antarctic territorial claims and the Antarctic treaty are pretty fascinating topics in and of themselves, which I’ll address in another post.

The CDC (Clothing Distribution Centre) where they issued our gear is in the International Antarctic Centre right across from the Antarctic Attraction, so my advisor and I decided to go investigate and see how much they’d gotten right. (Most of it, as it turned out.)

The Little Blue penguins are indifferent to their admirers.

We got there just as they were feeding the Little Blue penguins. Twenty or so birds–rescued from predators, car accidents, or parental abandonment–make up the museum’s Little Blue penguin colony. It is worthwhile to note that while Little Blue penguins are widespread on the New Zealand coast, they are found nowhere in the Antarctic. Evidently the Antarctic Attraction felt that any penguins were better than no penguins at all.

Feeding a recalcitrant penguin. Since they are all rescues, they tend to be invalids to a greater or lesser degree. A few have missing or paralyzed flippers and therefore a tendency to swim in circles.

The Antarctic Attraction also features a simulated Antarctic storm, taking place inside a refrigerated Antarctic landscape held at around -5 C/20 F. The windchill gets down to about -25C/-20F during the storm, which is respectably nippy but distinctly unimpressive to Alaskan sensibilities. I found the ice slide much more entertaining.

Museum visitors relax after their harrowing artificial ordeal.

Once upon a time, clipart dinosaurs roamed the Antarctic.

Everybody loves penguins! Remember, penguins in the Antarctic, polar bears in the Arctic. It is interesting to ponder whether, if introduced to the opposite pole, either species would thrive.

More bits of exhibit.