Geophysicist Andy Mahoney balanced a cylinder of ice on the top of his boot for a moment as he extracted it from a drill barrel. The balancing act kept loose snow lying on top of the sea ice Mahoney stood on from attaching itself to the extracted ice’s surface. The ice core looked like art: layers contrasted with other layers one atop another, and bubbles were suspended within the ice. The extracted ice core will help Mahoney understand the sea ice off the shore of Barrow, Alaska. He’ll use it to examine ice microstructure, “The structure inside of sea ice— the structure of the ice crystals and the arrangement of the liquid brine pockets that occupy the spaces between the ice crystals as the sea ice forms.”
“Microstructural properties turn out to be very important… It affects physical properties of the ice, like its strength and its albedo. And then, from an operational perspective, the porosity of the ice: how easily liquid can transport through the ice— that’s a critical consideration if you want to clean up an oil spill, which of course is becoming a topic of increasing concern up here in the Arctic.”
Mahoney, an assistant research professor in the University of Alaska Fairbanks Geophysical Institute, does much of his sea ice science near Point Barrow, Alaska, the northernmost tip of the U.S.A. Sea ice there impacts the lives of local residents and also can both affect and be affected by climate and weather conditions ranging through the Northern Hemisphere.
Data gathered from the physically extracted ice core will be used to compare to other collected data including new electrical measurements ice scientists are developing that could peek at the ice’s microstructure without physically drilling for a core. Drilling isn’t easy. Mahoney says you can do it by hand but an electric drill is more efficient. Near Barrow he might use a snowmobile to tow a generator onto the landfast ice (ice connected to shore) for drilling. A cordless drill is the “Preferred method if we’re flying out to a site by helicopter where weight and equipment payload in a concern.”
Once he’s reached the spot where he wants to drill Mahoney readies the equipment and gets out a saw. During the drilling process the ice core will spin in the barrel, twisting dizzily before it’s finally extracted, so Mahoney must mark the orientation of the ice before drilling. He does that by scoring the ice with a saw. “I used a saw to put a notch that was lined up North/South. So when I pulled the ice out, I could work at which direction it was oriented. I put a groove along it, a little bit like a credit card slot,” Mahoney said. “If we handle the core in the future we can easily remember which direction was North when we took the core.”
The ice core will have to come out in pieces. That’s alright as long as the scientists know which part of the ice faces north. In time the core will also be purposefully cut apart for transport and study. The drill in use had a four foot long barrel [1.2 meters], and on this occasion Mahoney was using to to extract a core from sea ice that was about 5 feet thick [1.5 meters]. It was early spring. Mahoney explained “Even though it is a nice day and we are standing without gloves on, the surface of the ice is still minus 10 degrees C right now [-10° Celsius = 14° Fahrenheit]. And so the cold brittle ice will have a tendency to break.” Though he cannot mark every piece that breaks, he can align the broken edges to determine the core pieces’ cardinal directions.
When he collects a core Mahoney explained that he measures three things. First, a measurement of the ice thickness: “As a geophysicist, that is one of the most important things; it tells us how much ice there is and if we are in the process of trying to look at how the ice is changing over time, one of the things that we are concerned about is the thinning of the ice. So we take all the ice thickness measurements we can.” Second, he measures the freeboard. That is the height of the ice sticking above the water as opposed to the ice submerged in water. Gathering this data can help validate and corroborate emerging technologies built to take this difficult measurement remotely (such as from a satellite). Third, he measures the depth of the snow atop the ice core. Snow depth “Is strongly linked to how quickly the ice can grow. The snow acts as an insulating layer on top of the ice.” When deep snow protects the ice from frigid winter winds it reduces sea ice growth. Yet when the sun returns, snow’s high albedo (highly reflective white surface) works to bounce sunlight’s heat away from the ice, reducing summertime melt. Mahoney summed it up: “The role of snow and sea ice is very complex.”
Once the core is out of the hole and laid out on a cradle in the correct orientation the scientists photograph it. Mahoney puts a notch along the whole length’s original North-facing side for future orientation, and the core is photographed again before being readied for transport to land.
The core segments are packed in thick plastic bags and transported back to a lab freezer in nearby Barrow. The core will be sliced into 5 centimeter long sections. “We will cut sections out of it and look at those sections in more detail to confirm what direction the crystals are oriented in and take some measurements,” including ice crystal size and the size of the brine pockets between the crystals.
Each core segment will then be melted so the salt content or salinity of the water can be measured using a probe. “How much of the sea salt was in the sea water originally? How much of that gets trapped in the ice? That can tell us a bit about how old the ice is, how fast the ice grew and a lot of the other properties of the sea ice: its strength, it’s ability to be a habitat for microorganisms, a lot of that is dependent on the salinity of the sea ice.” Some is sent to another lab for isotope analysis. The data gained during the process will add to a growing body of information which benefits Mahoney’s work as well as other scientists’.
Laura Nielsen 2015
Frontier Scientists: presenting scientific discovery in the Arctic and beyond
Drilling sea ice– extracting a sea ice core