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Keeping Ice Cool Posts

Flow

What does the word flow bring to mind? Maybe a river? Water coming out of a sink? What about pouring syrup out of a jar? If it didn’t already, ice sheets should also come to mind. Ice isn’t stationary, it slides! Here’s maps of surface ice velocity for both Greenland and Antarctica.

Velocity of the Greenland and Antarctic ice sheets for the period 2015-2016. Mouginot et al. (2017)

Take a minute to really look at these maps. The first time I saw maps of velocity for Greenland and Antarctica I was surprised by what I saw. You might guess that the velocity would be fastest near the ice margins (the edge of the ice where it meets the ocean) and progressively slower towards the middle of the ice sheet. This is sort of the case, but there is a lot of variability. Do you notice the very fast flowing areas that resemble streams within the ice, almost like veins? Fittingly, glaciologists call these “ice streams”.  Some of these streams start very far in the interior (near the middle of the ice sheet). While it’s all ice, these streaming areas move orders of magnitude faster than ice adjacent to the streams. Remember, you can see these streams when looking at a velocity map, however if you just look at a picture of an ice sheet from space (see below), you can’t really identify where the ice is moving fast and slow.

What dictates exactly where and how these ice streams develop is not entirely known. Some of it has to do with topography of the bed below the ice and some has to do with how slippery the bed is. What’s important, is that these ice streams are like a conveyor belt transporting ice to the ocean where it eventually melts. Warming the ice sheet only causes the ice to flow faster, contributing to sea level rise.

If you’re curious to look more closely at ice flow, take a look at this video showing just how dynamic the Antarctic ice sheet is.  

 

Here’s a thought to leave you with. What causes the ice to flow this way? Why doesn’t ice sit complacently at rest, like a pile of sand or rocks? On the other hand, why does an ice sheet last at all? Why doesn’t the ice immediately flow off the land like water would? I’ll give you a hint, this has to do with viscosity. Let’s pick this idea back up next time. 

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Glaciology venturing to the desert

A trip to the desert may sound like the wrong place for a glaciology group to go, but that’s exactly what we did the other weekend. After packing up the radar that we usually use on the Greenland ice sheet, I drove down with my research group to the Mojave Desert. Situated in an abandoned part of Southern CA about 100 miles outside of Las Vegas, the Mojave is home to sand dunes the size of small mountains, and buried lava tubes. 

These sand dunes may not be ice, but they actually have some similar material properties and could provide a setting to conduct similar tests to an ice sheet (minus a long and expensive trip to Antarctica or Greenland). Instead of using radar to map out the bed and layers of an ice sheet, the radar could be used to map out the layers of sand and the transition from sand to bed rock at the bottom of the dune. If successful, the dunes could be a useful place to do initial tests before implementing new techniques on an ice sheet.

The testing was only preliminary since the fieldwork was done in conjunction with a weekend geophysics class field trip, however initial processing of the data suggests that we can detect the bed of the sand dunes. If further processing shows that dunes work to test our radar, maybe we will be back to the desert again. Here’s some more photos I took over the trip.

Driving up to the sand dunes
Climbing sand dunes isn't easy!
Morning view outside the guesthouse
In the lava tube
A little exploring during lunch, my first joshua tree!
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A Trip North

Mark your calendars, July 10th, 2019 will be my first time stepping foot on an ice sheet! (Of course the exact day may vary depending on the optimal weather window). I will be going to the Greenland Ice sheet where I will spend a month camped out on Store Glacier doing fieldwork testing some of our radar experiments and designs. While I’m out there collecting data, this will also be your chance to experience research life on an ice sheet vicariously through me so get excited for lots of Greenland blogs and stories to come.

Store Glacier (credit: Aberystwyth University)

The field team will consist of myself and some of my research group members here at Stanford as well as our collaborators from the Scott Polar Research Institute at the University of Cambridge. We will be working to characterize the glacier’s englacial and basal structure and hydrological processes using radar echo sounding techniques. We’ll also be using this opportunity to test our radar experimental designs.

Store Glacier Terminus - Credit: Sam Doyle
Crevasses on Store Glacier - Credit: Sam Doyle

We’ll be helicoptered out from the small village of Uummannaq (see map above) and spend the time split between two field sites on store glacier (both well upstream of the terminus — the part where the glacier flows into the ocean). We’ll be camping in tents directly on the ice the entire time and all of our food will be shipped out with us and will have to preserve well.

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The Northern Counterpart

So far I’ve talked about Antarctica, but what about Greenland, the other ice sheet on Earth? Well, let’s begin an exploration of it! Greenland and Antarctica are the only two ice sheets on Earth. In simple terms, this means they are the two places where a very large amount of ice has been sitting on land for a very long time. (There is also a lot of sea ice in the Arctic, but remember that sea ice floats on water). Together, Antarctica and Greenland contain ~99% of all the freshwater on earth. If all the ice in the Greenland ice sheet melted, global sea level would rise about 6 m (20 ft). If all of the Antarctic Ice sheet melted, sea level would rise about 60 m (200 ft.) 

Antarctic
Arctic

Note: Sea ice is excluded from the images above. Only land ice (i.e. ice sheets) are shown.

What do you notice in the maps above? You can see Greenland is significantly smaller than Antarctica. Remember, Antarctica is roughly the size of the US? Well Greenland is about 3 times the size of Texas. Also notice Antarctica is close to centered over the South pole. On the other hand, Greenland is more offset from the North Pole. Another spatial difference is that in the Antarctic, there is land surrounded by water, whereas in the Arctic, there is water surrounded by land. This geographic difference in the arrangement of land vs. water gives rise to many differences in the climates of the two regions as well as other things.

In general, the Arctic is warmer, with temperatures typically between -43 and 5 degrees C (-45 and 41 degrees F), with temperatures up to 10 degrees C (50 degrees F) along the coast in the summer. The Antarctic is much colder, holding the world record of -89.2 degrees C (-128.6 degrees F) for the coldest temperature recorded on Earth in 1983! More typically, temperatures reach about -80 degrees C (-112 degrees F) in the interior in the winter, to between 5 degrees C (41 degrees F) and 15 degrees C (59 degrees F) along the coast in the summer.

While these temperatures might seem extremely cold, that’s what’s normal. However, especially in the Arctic, new record high temperatures are being recorded. And this warming trend is greater than the normal variability.

To put this in perspective, here’s a video showing surface temperature changing over the last 150 years. Notice the increasingly warm temperatures recorded in the Arctic over time.

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Below the surface

“What we see is only a fractional part of what it really is” – While I’m pretty sure this quote wasn’t written about Antarctica, it certainly is applicable. Here’s a glimpse below the surface.

Are you wondering what on earth you’re looking at? Well you can bring your complaints to me because I actually made this plot the other week as part of my research. We are looking at data collected by an airborne radar survey (data provided by NASA Operation Ice Bridge). This image shows us a slice through the ice sheet, allowing us to see more than 4 km (2.5 miles) down below the surface. In fact, this image even shows a lake (yes unfrozen water!) below the ice sheet. This is called Lake Vostok and it is comparable in size to North America’s Lake Ontario yet completely hidden below the surface of the ice. Without imaging below the surface, we would never know that unfrozen lakes exist below ice sheets. Can you find the lake in the image.

The red line traces the surface of the ice and the blue line traces the bottom of the ice sheet. See where the blue line dips down and then gets very flat? That is the lake surface (below the ice sheet). And how do we know it is not frozen? Reflectivity of water is much higher than ice and the radar detects very high reflectivity values over this area. How does a radar make this image of the subsurface?… to be continued next time.

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Applying the Unit Lens to Antarctica

What do the following have in common?

  • The length of your last bike ride
  • The temperature outside today
  • Your age

All these measurements have units. Miles, degrees Fahrenheit, years. In fact units define a measurement. I could also tell you that the units are meters, kelvin, and seconds, and the measurement would have to reflect this change.

Antarctica is a place of enormity, however it’s pretty easy to forget about this mysterious snowy continent. Check out any world map. Often Antarctica is completely missing or hugely distorted!

So if world maps are this misleading, how does the size of Antarctica actually compare to other parts of the world? I think comparing Antarctica to the continental US really puts it to scale. Antarctica is over 5 million square miles.

Image from NASA.gov

But what about the ~2.5 miles (4 km) of snow blanketing Antarctica? Maybe your mind conjures up images of snowy mountains like somewhere you ski in the winter? In fact that really isn’t the right image to have in your head.

Mountains (~10 feet)

Vs.

Antarctica (~13,000 feet)

Antarctica has snow that is up to 2.5 miles (~4 km) deep where as mountains get snow on the order of feet (meters) deep. So Antarctica has snow that is 1000% times deeper than mountain snow. This is comparing ~10 feet (mountains) to ~13000 feet (Antarctica). So essentially Antarctica is our “living proof” of what ice age conditions were like.

To help picture what 2.5 miles (~4 km) of snow is like, here’s a cross section revealing what Antarctica would look like if you cut it in half along the West to East black line in the inset. 

Source: J.W. White et al. 2007

This much snow applies a massive amount of weight on the continent below. You can see all this weight even pushes the level of the continent below sea level in some places (see the solid black horizontal line).

At this point you’re probably wondering about a very good question: How do we know how deep the ice is? How can we “see” through 2.5 miles (~4 km) of ice to know what the continent looks like beneath? Remember this is ground no human has ever set foot on.

Stay tuned for more on this next time!

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The Southern most desert in the world is…?

Yep, it’s Antarctica. Counter to what you might think, it doesn’t rain or snow very much there. Deserts are defined by their aridity. Many deserts are also in very warm places but as you now know, not all are! 

I think this begs two questions: First, why? What about the climate of Antarctica makes it so dry? Second, how can there be so much snow then? Okay, let’s dive in.

The Climate of Antarctica: To understand why Antarctica is so dry, I think it’s helpful to compare Antarctica to places we’re more familiar with. Let’s start on the west coast of the US. All along the west coast are very tall mountain ranges. Now let’s compare this to the precipitation (rain and snowfall) along the west coast.

Topography of Western US

What do you notice? West (left) of the mountain ranges precipitation is very high (blue and purple). East of the mountain ranges, it is much much drier (orange and yellow). Why is this? Let’s think about what is happening to the air. The flow of air is predominantly from west to east. The air starts off very moist over the Pacific Ocean and then reaches the west coast. The air is forced up and over the mountains, squeezing the moisture out of the air parcel causing it to rain or snow. By the time the air gets to the other side of the mountains, most of the moisture is gone.

How does this compare to Antarctica? It’s similar, but the air is also a lot colder in Antarctica to begin with. Here, moist air over the ocean must rise up to the top of ice that is miles high (like one big mountain). In the process, most of the moisture is lost so that by the time the air gets to the interior of the continent, it is very dry. Additionally, since it’s a very cold climate, the air can’t hold much water to begin with. Check out the map of Antarctic precipitation (mostly snowfall in this case). Notice the high precipitation along the coast and the much lower precipitation in the interior.

Average precipitation (mostly snowfall) in Antarctica (mm of water equivalent/year)

Thinking about snow accumulation: How is there so much snow in Antarctica if it hardly ever snows? Well it also is very cold so the snow can’t melt. I just did some rough calculations, and if it snows ~50 mm/yr in the middle of Antarctica and the ice is ~4 km (2.5 miles) thick, that means it takes on the order of 78,000 years to build up that much ice! In fact, ice cores that scientists have drilled tell us that there is probably ice that is over 2.7 million years old currently in Antarctica! This is a comparable time scale to that of human evolution. 

In fact, paleoclimate data suggests that glaciation on Antarctica began around 35 million years ago. I think the main point to realize is that the Antarctic climate is very unique and what we see today is the result of millions of years of snowfall and glacial processes.

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Are we there yet?

Have you every tried typing Antarctica into Google maps? Well I just did and it isn’t very helpful.

Let me fill in the gaps of google maps. Antarctica is over 8,800 miles (~14,200 km) from Stanford. This a little further than traveling from Stanford to Mumbai India. Researchers often get to Antarctica by first flying to the southern tip of Chile or Tasmania and then flying to one of the field stations you see pictured below.

A few of these stations operate year round but most are seasonal. These stations are usually jumping off points to then go to a field site for actual data collection.

So other than scientists and people operating the stations, what lives in Antarctica? As you may recall from March of the Penguins or Happy Feet, Antarctica is home to lots of penguins. In fact approximately 12 million of them are found across the continent (five species: emperor, Adélie, chinstrap, gentoo and macaroni). 

There are no polar bears in Antarctica. This is a common misconception but polar bears only live in the arctic. (Did you catch this error in the cartoon?) Antarctica is also home to many types of sea-creatures including lots of whales.

It’s also the driest place in the world. Yes you read that right. By definition, Antarctica is a desert. In the Antarctic interior, it is so arid that the snow fall equivalent is as low as 51 mm (~2 inches) of rain per year making it drier than the Sahara. How can Antarctica possibly be this dry? More next time!

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