The LeConte Glacier in southeast Alaska is a 21-mile long fast-flowing tidewater glacier, which terminates abruptly in a fjord––spilling its contents into the ocean. The glacier sheds ice from its 200-meter face in calamitous calving events when large blocks of ice drop into LeConte Bay. Researchers seeking to collect data on the glacier’s submarine melt rate needed a way to get close enough to the terminus to collect the data they needed—the solution: a fleet of robotic kayaks sent into waters too dangerous for human researchers to enter.
The November 2019 study, which was published in the journal Geophysical Research Letters, was led by Rebecca Jackson, an assistant professor of physical oceanography at Rutgers University, and a team of researchers from Oregon State University, University of Alaska Southeast, University of Oregon and University of Alaska Fairbanks.
Tidewater glaciers are glaciers that reach all the way to the ocean. At their border with the sea, they melt either through calving or through submarine melting.
Submarine melt matters because it is a significant contributor to glacier melt and is sensitive to rises ocean temperature and shifts in ocean circulation. It’s also more difficult to observe directly than surface melt because it occurs on the underside of glaciers. It can take place through two processes. The first is more easily detectable and comes from the drainage of freshwater discharge due to upstream melt on the glacier. It creates fast-moving plumes of water entering the ocean at the glacier’s terminus. The second type of submarine melting is the slower and harder to measure process of ambient melting where a glacier melts directly into the sea.
Ambient submarine melting is hard to measure: as a result it is typically estimated using laboratory experiments and models. The idea that emerged from theory and lab experiments suggested that ambient melting was responsible for only a small amount of total terminus melting.
Jackon’s study used autonomous kayaks to study plumes created by ambient melting at LeConte. The glacier has been recorded moving at velocities of up to 18 meters per day along its one kilometer-wide terminus. The kayaks were deployed along the length of LeConte over a seven-day period in September 2018. As they cruised close to the steep face of the glacier, they used complex instruments to observe water velocity, temperature, and salinity. The near-glacier data they gathered was supplemented with data collected downstream aboard a research vessel.
Plumes created by ambient melt only exist within 400 meters of a glacier’s terminus and as such were difficult to access without technology given the risks created by the glacier. The autonomous kayaks were essential to this project because of the hazards of working directly next to a glacier’s terminus, where calving pieces of ice can crash into the water without warning, producing life-threatening waves––or in the case of LeConte, from below the surface, too. The glacier is known for “shooter” icebergs that calve beneath the water and launch up to the surface, propelled by their buoyancy.
A shooter glacier emerging from below the surface at Dawes Glacier, another glacier in Alaska. Source: AdventureM/ Youtube
Glaciologist and founding director of The Dasht Foundation, Faezeh M. Nick, who was not involved with the study, told GlacierHub “The autonomous kayaks taking measurements in front of the calving glaciers sound very promising. It has been very risky and expensive to get this kind of data at glacier fronts. It would be very beneficial if these kayaks are not too expensive and are robust enough to be used at several locations.”
The kayaks used in the study were developed at the University of Oregon and are called Robotic Ocean Surface Samplers (ROSS). They were designed to function in harsh conditions, to be resilient in the face of unforeseen challenges due to redundancies of critical systems, and to be inexpensive enough that they could be used in areas with high risk of being lost.
The kayaks’ base component is a commercially available Mokai gas-powered kayak. The researchers then built upon it, adding in the necessary control electronics, communications systems, and scientific instruments needed for the tasks it would be sent to accomplish.
Kayaks have historically been associated with Indigenous peoples of the Arctic, though in earlier times were only found in the areas further north. Monitoring climate impacts in Alaska has brought scientific and Indigenous technologies together as people strive to understand the changes taking place on the planet.
The data gathered by the autonomous kayaks show that ambient melting is a significant contributor to total melting at a glacier’s terminus and represents a large part of the total submarine melt flux. It revealed that ambient melt has been underestimated by a factor of up to 100.
“We need these types of measurements being performed in front of several other glaciers in different regions before making a new statement about the general pattern or magnitude of submarine melt and its effect on sea-level rise,” Nick said. This finding increases scientists’ understanding of submarine glacier melt and opens the door for further research to establish a generalizable melt parameter for modeling ocean‐glacier interactions. As scientists’ understanding of glacier melt dynamics improves through studies like this one, they are one step closer to being able to generate predictive models on critical issues like sea-level rise with greater accuracy.