The Case of the Salty Pond

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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2 Responses to “The Case of the Salty Pond”

  1. Solomon Says:

    That pingo is most odd but also quite beautiful.

  2. Marla Says:

    I predict mirabilite jewelry at souvenir stands in the far off future.

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