A group of scientists are in the final stretch of a two-month journey to collect sea ice cores in Barrow Alaska and return to them to their home base in New Hampshire to study their three-dimensional pore structure. The final leg of the research mission will take them on a nearly 4,500-mile road trip from Fairbanks to Dartmouth College.
Dr. Rachel Obbard, a Dartmouth College professor who specializes in sea ice, is leading a National Science Foundation-funded project called Characterization of Brine Network Microstructure In First Year Arctic Sea Ice. To study the intricate networks of brine channels within the sea ice, Obbard and her team are attempting to transport the cores from the field to their lab without changing their temperature conditions. To do this they’ve engineered special transport boxes they call ICE-MITTs, or Ice Core Extraction while Maintaining In situ Temperature Transitions.
This month, Obbard talks to Field Notes about this sea ice project, the team’s two-week road trip to transport the ice cores, and their multiple stops along the way to bring Arctic science and engineering in to classrooms and beyond.
Field Notes (FN): What are sea ice brine networks and what roles do they play in the interface between sea ice, the ocean and the atmosphere?
Rachel Obbard (RO): You might picture sea ice as a solid layer of ice on the surface of the ocean. But it’s really not. It’s riddled with holes--like a sponge--that develop as the sea ice forms. This complex network of holes and vertical channels contain brine, or very salty water. They form as seawater freezes.
When the sea ice forms, its fresh water constituent freezes first. Salt water has a lower freezing temperature. So the crystals that begin to form are fresh, actually nearly fresh enough to drink. As they from, the remaining water around them gets saltier. As the crystals grow and connect with one another, they force the brine in to channels between the crystals.
FN: What do you hope to learn?
RO: My colleagues and I are trying to describe the three-dimensional geometry of the network of brine channels. Brine networks act as a conduit—both for gasses moving upward from the water in to the atmosphere and for water moving downward during the melt season. The presence of the brine pockets also affects everything from the reflectivity and thermal properties of the ice to its mechanical properties.
FN: As sea ice decreases and temperatures rise, why is it important to understand the structure of the brine networks?
RO: Sea ice extent and thickness in the Arctic has been decreasing since the 1970s. The decreased sea ice extent produces a positive feedback to the regional warming. When you have less sea ice, you have less of a reflective surface and the ocean absorbs more sunlight and gets warmer, which in turn makes more sea ice melt.
So, the sea ice plays a role in the regional climate, and by extension the global climate, and this role is changing. The scientists who use models to try to predict future change need to input certain parameters to their models—things like sea ice thickness, porosity, and so on. The better the information we can give them about the sea ice, the better they can identify the parameters they need for their models.
FN: You’ve spent the last six weeks in Barrow collecting ice cores. Please tell us more about your fieldwork there.
RO: We’ve been going out on the sea ice on snowmobiles and collecting sea ice cores at various sites. We take two 1-meter cores and put them in the specially engineered ICE-MITT boxes designed for this project. That makes it sound a lot easier than it is! Some times we have to drill about seven holes to get two good cores. We also collect a core from each site for shipping back the old-fashioned way, in a big box with ice packs.
We are collecting cores at sites that are different in terms of their oceanographic conditions. We believe that the ice formed in different conditions has different microstructure. So we’re testing, for instance, high-current areas versus low- or no-current areas, and shallow versus deeper waters. I want to make sure that the data we collect is representative and can be applied to the whole Arctic Basin.
FN: Tell us about the tools you and your team engineered to ensure the ice cores make it back to your lab in New Hampshire intact and at the correct temperature.
RO: The ICE-MITT looks a lot like a big footlocker. It’s for transporting sea ice cores. The trick for transporting sea ice cores is that when they are in the ocean, the bottom part of the core is relatively warm, say -2 Celsius, and the top is close to the current surface temperature. Today it’s -27 Celsius outside. So in one meter of ice, you have this huge temperature gradient.
Historically, people have put the cores in tubes, put those in a box with blue ice packs and shipped it. It all ends up at a single temperature, which is not the way it is in nature. Because we are studying brine channel geometry at such a fine scale and that geometry changes with temperature, we developed these ICE-MITT devices that hold the sea ice cores with one end warmer than the other.
FN: After you finish data collection, an entirely new and public component of the project begins. Tell us about that.
RO: The ICE-MITT boxes need to be plugged in most of the time. They can go about two hours without being plugged in or changing in temperature by more than a degree. So we are flying from Barrow to Fairbanks with them, and then driving from Fairbanks to New Hampshire with a U-Haul truck where we’ll have two generators that we can plug in the ten ICE-MITT boxes.
Along the way we have several stops planned. In Canada we’ll stop at the Telus World of Science in Edmonton, Alberta. In the U.S., we’ll meet with teachers and students at schools in Madison, Chicago and Detroit. We’ve been communicating with the teachers while in Barrow, and they’ve been following our blog.
It’ll take us two weeks to make the trip. It’s very tightly constrained because I have to start teaching on March 30, so we have to get back!