Sunday, February 7, 2016
Ice crystal halos
We saw several beautiful displays of halos in the Allan Hills. Halos form when ice crystals in the atmosphere (typically in cirrus clouds) scatter the light into different angles.
New snow leads to blowing snow
A couple days into our stay in the Allan Hills, it started to snow. In total, it snowed about a foot over a day. At first, the snow was beautiful, but then the wind picked up to 25 knots and it started to blow around. We were stuck in the tents for three days due to poor visibility from the blowing snow.
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| New snow at our campsite |
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| Blowing snow |
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| Blowing snow |
When the wind finally subsided, all the new snow had blown away. Similar to patterns that you would see in a desert (we are in fact in a desert!), the wind leaves dunes, wind scoops, and ripples on the surface.
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| Wind sculpting the snow surface |
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| Wind ripples on the ice surface |
The blowing snow left us with some nice big (2-3 ft) snow banks around our tents.
Finding old ice in the Allan Hills
What exactly were we doing in the Allan Hills?
Back in 2010, a group of scientists drilled an ice core in the Main Ice Field of the Allan Hills. They dated the ice to one million years old. That's really old ice! Most of our current ice core records, such as the recently-drilled core at the West Antarctic Ice Divide, date back only 100,000 years. The ice in the Allan Hills provides a unique opportunity to explore our climate history farther back in time.
Unfortunately, the million-year-old ice was found by itself. The ice directly above it was dated to 300,000 years old. That's not a continuous record of climate change, and as a result it's hard to put the observations that we make about the million-year-old ice into perspective. So the goal of our project was to trace this old ice back to where it came from and find a good place to drill a continuous, old ice core.
Why is there really old ice in the Allan Hills?
The Allan Hills is a blue ice region. The region is so windy and cold that the snow blows off the ice surface before it can melt or accumulate. As a result, old blue ice is exposed at the surface, hence why we call it a "blue ice region." Furthermore, the Allan Hills are a physical obstacle that the ice must flow over, which brings old ice at depth to the surface. The glacier velocities are so small (less than 10 feet per year) that it takes the ice a long time to move anywhere.
How do we map the old ice if it is below the surface?
Have you ever gotten an ultrasound or an x-ray? We use a similar technique to image the ice, except we use radio waves. We send radio waves down into the ice, and these waves reflect off of ice layers with different densities and/or chemistries. The waves return to the surface, where we record their travel time and phase characteristics. Through this technique, we can trace internal layers in the ice. Some of these layers are ash layers that have been dated, so we have a sense of the age of the ice.
Below is an image of our radar setup. We tow a sled with a transmitting and receiving antenna, with a central frequency of 7 MHz.
Did we find a place to drill a continuous ice core?
We think we did! We found a region upstream of the million-year-old ice where we think we can drill a continuous 1200-m ice core that should date back to at least ~400,000 years. We won't know the actual age of the ice until we drill it.
Back in 2010, a group of scientists drilled an ice core in the Main Ice Field of the Allan Hills. They dated the ice to one million years old. That's really old ice! Most of our current ice core records, such as the recently-drilled core at the West Antarctic Ice Divide, date back only 100,000 years. The ice in the Allan Hills provides a unique opportunity to explore our climate history farther back in time.
Unfortunately, the million-year-old ice was found by itself. The ice directly above it was dated to 300,000 years old. That's not a continuous record of climate change, and as a result it's hard to put the observations that we make about the million-year-old ice into perspective. So the goal of our project was to trace this old ice back to where it came from and find a good place to drill a continuous, old ice core.
Why is there really old ice in the Allan Hills?
The Allan Hills is a blue ice region. The region is so windy and cold that the snow blows off the ice surface before it can melt or accumulate. As a result, old blue ice is exposed at the surface, hence why we call it a "blue ice region." Furthermore, the Allan Hills are a physical obstacle that the ice must flow over, which brings old ice at depth to the surface. The glacier velocities are so small (less than 10 feet per year) that it takes the ice a long time to move anywhere.
How do we map the old ice if it is below the surface?
Have you ever gotten an ultrasound or an x-ray? We use a similar technique to image the ice, except we use radio waves. We send radio waves down into the ice, and these waves reflect off of ice layers with different densities and/or chemistries. The waves return to the surface, where we record their travel time and phase characteristics. Through this technique, we can trace internal layers in the ice. Some of these layers are ash layers that have been dated, so we have a sense of the age of the ice.
Below is an image of our radar setup. We tow a sled with a transmitting and receiving antenna, with a central frequency of 7 MHz.
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| Charging the batteries on the wood sled with the receiving antenna and red sled with the transmitting antenna |
We think we did! We found a region upstream of the million-year-old ice where we think we can drill a continuous 1200-m ice core that should date back to at least ~400,000 years. We won't know the actual age of the ice until we drill it.
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| Dragging the radar setup across a blue ice area |
Tuesday, February 2, 2016
Finally made it to the Allan Hills
After several bad weather days, we finally made it to the Allan Hills. The Allan Hills are a 45-minute flight from McMurdo across the McMurdo Sound and over the glaciers just north of the Dry Valleys. It took four Twin Otter flights to get all our gear there.
Once we landed in the "deep field," we were required to set up a tent and make contact with McMurdo before the plane could leave us behind. By the time the two Twin Otters returned with our second load of gear, we had set up two of our four tents, a Scott Tent and the Arctic Oven. Two of our tents were for sleeping, one was for the toilet, and the other was for cooking and science preparations.
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| Flying over the Mackay Glacier |
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| Flying over the mountains just before the Allan Hills |
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| The Twin Otter taking off |
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| The two Twin Otters lining up to unload our gear |
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