Garwood-bound/McMurdo-bound

It’s funny how one word can mean two exactly opposite things. I’m at McMurdo Station, waiting to kick off this year’s research program in Garwood Valley (one of the southern McMurdo Dry Valleys). My team and I arrived last Monday, and have spent the week assembling our camp gear, testing scientific instruments, and packing up food and supplies. We hit the ground running, with the goal of being Garwood-bound on Friday, January 6^th. But, weather (it’s been snowing quite a bit lately), coupled with a tight helicopter usage schedule, and mechanical problems with one of the big Bell 212 helos that we need to move our camp in, have kept us McMurdo-bound this weekend. The good news is, if the snow clears, we’re on the schedule for Monday, and can get rolling with our science! (The other good news is that the McMurdo galley has the best brunch below 65*S, so it’s a treat to be able to have a few more days of delicious chow before the menu changes to camp cuisine).

 This is the view out my lab window at McMurdo. That bright white space in the background is the direction I need to be flying, and those little flakes in the foreground are getting in the way!

What’s this season all about?

During the last glacial maximum (the LGM, which was the peak of the last ice age), about 20,000 years ago, Antarctica was a colder place than it is today. The ice sheets that cover the continent grew in the cold, and like giant glaciers, came pouring out of the high interior mountains of Antarctica and flowed down towards the coast. During the LGM, so much ice came flowing out of west Antarctica that it literally filled up the Ross Sea. The flood of ice spilled up into the valleys that surround the Ross Sea—so much ice was draining into the region that the glaciers flowed up hill!

But then the planet began to warm up again. The ice age was waning. The “grounding line,” which is the point where this wall of ice met the ocean, began to move back inland. Ice drained from some of the flooded valleys (but not all—Garwood being one that kept its ice). This is where Garwood Valley becomes important. Warming climate conditions stopped this flood of ice in its tracks, melting back ice that been streaming out of the West Antarctic ice sheet. Today, scientists are concerned that the West Antarctic ice sheet is experiencing so much warming that it may melt back catastrophically. When the ice melts, the water pours into the ocean, raising sea level.

This is a map from Conway et al. (1999) showing where the "grounding line" for the West Antarctic ice sheet is thought to have been over the last few thousand years. Garwood Valley is the green dot.

One of the big goals of this project is to help understand when, and under what temperature conditions, did the West Antarctic ice sheet flood into the Ross Sea region, and when, and under what temperature conditions did it get melted out. By Understanding the West Antarctic ice sheet’s response  to past warming, we can inform predictions about how it will respond to future warming.  

So, what’s a geologist doing all caught up in a story about glaciers and ice? As it turns out, Garwood Valley is a sticking point for the West Antarctic ice sheet as it came flooding out to sea. (Garwood is the green dot on that map). When the ice flooded into Garwood Valley, it dammed a tiny river that is fed by a glacier in the valley (the Garwood River). Like sticking a plug in a bathtub drain, the ice dam held back the water, causing a lake to rise in the valley. Eventually, a large delta grew in the lake where the river entered it, dropping off sediment every year during the summer melting season.

This is a satellite image of Garwood Valley. To the right is the modern Ross Ice Sheet (the sea). The tongue-shaped thing left of that is buried West Antarctic ice sheet ice. To the far left is the modern Garwood Glacier. Snaking its way down to the sea is the modern Garwood River.

This lake is one of the keys to figuring out when the ice flooded in, when the ice melted out, and what the temperatures in the Dry Valleys were like when all this happened. As the lake grew, algae living in the delta were buried, along with the shells of microscopic organisms that produce calcium carbonate shells. The age of these plant remains (algae and carbonates) can be determined by carbon dating, and by uranium-thorium dating. Since the lake deposits are actually sitting on top of the ice plug (more about that in another post), the lake deposits have to be younger than the ice flood, giving a minimum age for when the valley filled with ice.

 Right in the middle of this zoom you can see the deltas. The river bends around them. Looks pretty wet, doesn't it?  Thanks to Paul Morin and PGC for the great satellite images!

What happened to the lake? We can tell that the lake drained by cutting through the ice plug because the deltas get lower and lower as they get younger and younger. In order for the lake to drain, there has to be somewhere for the water to drain to. If the grounding line hadn’t moved past Garwood valley, the lakes could not have drained into the open ocean. So by dating when the lakes drained, we can learn when the ice had melted back past Garwood Valley.

 

Best of all, because the chemistry of the lake sediments can be used to figure out what temperature the water was, we can figure out what the climate was like when the ice filled the valley and when it left. I really like it when rocks can tell us something interesting about ice!

And, of course, if you don’t entirely believe the history I just told you, here’s one last bit of evidence. The ice that flooded the valley during the LGM is still there. It’s buried by delta sediments, and is rapidly melting away where it’s been cut into by the modern Garwood river. We’re trying to figure out just how fast this old ice is melting, so we can know how much longer it will be around, and what will happen to buried ice like it elsewhere in the Dry Valleys when temperatures start to rise.

This is the famous Garwood Valley "Ice Cliff." That's buried ice that got its start deep in West Antarctica, topped by layers of river-deposited sediment. I'm there in green, next to Andrew Fountain (from Portland State University), and Thomas Nylen (in blue). Thanks to Jim O’Connor of the USGS for the awesome photo, and for extensive amounts of insight in piecing together the geological history of the valley.   

Old Ice in Garwood Valley

I'm back from a week of tent camping in Garwood Valley--one of the southernmost Dry Valleys (more than 78 degrees South!). The mission was a great success. I'm starting a new project to study buried glaciers that flooded the valley more than 10,000 years ago. Unlike most glaciers from that era, which have long since melted, this ice is preserved under a thick sand cover.

Buried ice, to the right, in Garwood Valley. A 3 m tall weather station is next to the ice.

The ice is not stable, though. It formed under much colder conditions during the last glacial maximum and is now melting and sublimating away. It's particularly at risk of melting where the ice is exposed to the warm, dry summer atmosphere--so the "ice cliff" in the above photo is melting away like an ice cream cone on a hot afternoon. The melting of the buried ice, coupled with erosion by the Garwood river, means that this treasure trove of climate data from the recent past is quickly disintegrating.

A block of ice and sediment from the last glacial maximum that has tumbled from its perch into the Garwood river. Best not to be working on the cliff when one of these comes down.  

What we're trying to understand in Garwood is how thick was the ice in Antarctica 10,000 years ago and what was the climate like. This is important because Garwood is one of the few places in Antarctica that is currently undergoing rapid landscape change because of warm temperatures (relative to 10,000 years ago). It's like a crystal ball that we can use to look into the future of the Antarctic Dry Valleys to predict how the glaciers and permafrost soils will respond to a warmer world.

Well Met

Despite strong, gusty winds, we had a good day out at the weather stations (sometimes called "met" stations--short for "meteorology" stations). You might think that Thomas has a tough job, clinging to a 3 m tall mast, replacing sensors in the wind (and he sure does)...

Thomas Nylen at the Lake Vanda Met Station

...but my job's not only taking neat stereo images...

Thomas and Rae working on the Vanda Met Station, with "the Dais" cliffs in the background.

...It also involves making measurements of the Dry Valleys soils. Normally, it's nice to be low to the ground on a windy day. But with strong enough gusts, the sand on the valley floor begins to move and bounce--blown along by the gusts. This is called saltation, and is the process that piles up sand into dunes. On a really windy day, like last Thursday, the wind whips around any obstacle it in its way, making eddies of wind and sand, like eddies in a river. Any time I bent down to pick up one of my sensors, I became just such an obstacle. The wind would whip around me, and blast a column of sand right into my face. Not a fun way to collect a sediment sample!

Hailing frequencies open (from the field!)

Hello from Lake Hoare! This blog post comes to you live from the McMurdo Dry Valleys--Taylor Valley in particular. Camp is a gathering of huts (labs, cooking and eating spaces, generator, storage) and tents (for sleeping), situated at the toe of the Canada Glacier. Upvalley (to the west, away from the shores of the McMurdo Sound and the Ross Sea) is the Suess Glacier. In between these two giant ice conveyor-belts sits Lake Hoare, one of the famous ice-covered lakes of the McMurdo Dry Valleys.

We're celebrating the hundredth anniversary of the exploration of Taylor Valley this year, and explorers and scientists have been visiting the valleys regularly since (with particular interest in the Dry Valleys begining in the late 1950s). In one sense, the McMurdo Dry Valleys are very well understood. The valleys are "dry" because they are not covered by the Antarctic ice-cap (more than 99% of Antarctica is buried by the ice cap)--the glacier-like cap is held back from the Valleys by the tall Transantarctic Mountains that hem this side of the Ross Sea. The Dry Valleys aren't "dry," though.

As you can see in the picture, alpine glaciers (like the Canada) flow down the valley walls and spread across the valley floor. During summer months (December to February), the snouts and surfaces of these glaciers melt, generating streams that flow into low points between the glaciers, forming ponds and lakes. Because the average annual temperature in Talor Valley is -18*C (about 0*F), with summer air temperatures seldom rising above ~10*C (40*F), these ponds and lakes are perpetually covered by thick, floating ice covers. The Dry Valleys are "dry," though, in that they recieve very little precipitation: 3-50 mm of "water equivalent" snow per year ("water equivalent" means that you imagine melting that snow once it fell on the ground to form a height of water--just like when the weather report says that a storm dropped 1/2" of rain. Snow is puffy and low density, so it's difficult to describe how much fell unless you make this conversion.) One or two recorded rainfall events have occured in the whole history of the Dry Valleys (down at the coast), while some higher, inland areas have not seen substantial liquid water in millions of years.

What's missing from this short accounting of the history, geography, and climate of the Dry Valleys is permafrost (and biology--more about that later). Everything that you see in that photo that is not a glacier, lake, snow, or human structure is permafrost. Permafrost is nothing more than a ground surface that has remained below freezing, on average, for more than two years. Perennially frozen soil is my specialty, and is the reason that I've come all the way to Antarctica. Permafrost is the "dirt" in "Cold Dirt," and I'll be talking more