The University of Washington, in partnership with Vulcan Inc. and the Paul G. Allen Family Foundation, launched a novel underwater ice float on its first mission to study ocean conditions underneath the Arctic Sea in late August.
The Arctic ice cover is currently undergoing profound changes. Not only is the ice cover shrinking in extent, but thick multi-year ice is disappearing, being replaced by thinner, seasonal "first-year" ice. The thinner ice transmits more sunlight into the ocean, which warms near-surface waters and increases photosynthesis within and beneath the ice. Massive plankton blooms recently discovered beneath the ice illustrate the potential for large changes in the Arctic ecosystem and chemistry with implications for CO2 absorption and ocean acidification.
The new UW ice float was developed to provide sustained real-time observations of physical, chemical and biological changes occurring at the underneath and along the Arctic ice. Lack of such observations precludes accurate modeling of the ongoing rapid change of polar climate. The float is designed to profile the upper 200 meters of ocean below the ice and to float just beneath the ice to measure its properties.
The float works like an underwater balloon, changing its buoyancy to move up and down in the water. It communicates by coming to the surface and sending information by satellite, much like a submarine. The float design and construction relied on the technical expertise of UW’s Applied Physics Laboratory and College of the Environment, including the 25 years of experience in underwater float development from principal investigator Eric D’Asaro and his team. The float design integrates buoyancy control, data collection, and satellite navigation and telemetry. The ice float adds an acoustic altimeter to measure ice thickness and roughness; optical sensors to measure the color and intensity of light; oxygen, chlorophyll and backscatter sensors to measure biological production; and a camera to take pictures of the ice bottom.
The float was tested at an ice camp on Baffin Island in May 2015 as shown in the photo, right, which shows APL/UW scientist Andrey Shcherbina setting up the UW ice float. The satellite antenna, camera, light sensor and altimeter can be seen at the top of the float.
It was then deployed in the Arctic Sea north of Alaska from the icebreaker U.S. Coast Guard Cutter Healy on August 23, 2015. As designed, the float drifted below the ice probing upward with the altimeter to detect open water and avoid ice, while measuring the ocean and ice properties. The photograph above, taken from 10 meters beneath the surface, shows the mix of ice and water in this particular area and highlights the challenge faced by the float in finding open water for surfacing to communicate data. In other locations data showed ice floes with thickness of up to 4 meters, typical for this region. Ocean temperatures were just above the freezing point, as expected since the ice is melting. Biological productivity was low, but a thin layer of chlorophyll occurred 50 meters below the surface, along with enhanced oxygen. As the melt season ends and new ice begins to form later this year, the float will monitor the evolution of these features, through late fall.
In the future, we envision fleets of underwater vehicles such as the UW ice float, as key tools for exploring the Arctic ice and ocean. These could provide the large sets of cross-disciplinary data necessary for improving regional and global climate models and predictions.