December 24, 2018
By Elizabeth Hunke and Andrew Roberts
The Earth’s polar oceans are cold enough that it’s possible to walk on seawater turned to ice. About nine million square miles of ice rest float on top of the world’s high-altitude seas and oceans. Looking like plates, sheets and mounds of fractured alabaster on a surface of shimmering blue, sea ice is more than a beautiful phenomenon—it influences Earth’s climate, wildlife and the people who must contend with it year-round.
Long ago frequented by just a few rugged groups living in the high north, the polar regions are now home to more people than ever. Their interests range across commercial shipping, mining and energy development; recreational fishing, hunting and tourism; scientific research; and military bases and defense operations.
Sea ice creates challenges for all these activities. It makes navigation hazardous for shipping, for instance, while thick ice complicates the operation and safety of U.S. Navy submarines. On the other hand, disappearing Arctic ice is changing hunting and fishing practices, as well as the ocean’s acoustic properties.
To address these challenges and support these varied interests, arctic researchers use satellites, aircraft and ships to monitor how far sea ice extends, how thick it is in various locations and other topographic characteristics, and even its color. Other field research looks at the physical and biological processes that influence how ice forms, moves and changes hue.
From the mountains of data provided by this research, we have developed computer models to forecast the spread and thickness of the ice. Starting in the 1990s, our Los Alamos National Laboratory team created and continues to develop a software package known as CICE that calculates the physics of sea ice and models how ice freezes, melts and moves across the ocean’s surface, influenced by external forces such as the ocean’s currents and the ever-shifting wind. The latest version of the software program, released by the Los Alamos-led CICE Consortium in late 2018, models land-fast ice, which becomes attached to coastlines and the sea floor.
This work has practical applications. Together, the models and real-world monitoring provide insight into how sea ice interacts with the Earth’s climate. Coupling this software with ocean and atmospheric models, the Navy produces predictions of the ice used in forecasts by the National Oceanic and Atmospheric Association and the National Ice Center. Along with a number of other nations, Canada’s Environment Department likewise uses CICE to forecast conditions in the Arctic Ocean and its marginal seas. These forecasts include land-fast ice prediction, which they contributed to the CICE codes.
Land-fast ice is an interesting phenomenon. When it attaches to the shore and when it disintegrates affect the length of shipping, hunting and fishing seasons. It can also block river channels, causing floods during spring runoffs. Given this impact, predicting the behavior of land-fast sea ice can directly benefit all kinds of human activity around the polar region.
The new version of CICE also includes a sophisticated description of the sea ice ecosystem, including different types of algae that live there and the nutrients they feed on. The model also simulates dissolved gases that are generated in the sea ice and interact with the atmosphere and the clouds.
Conversely, these organisms and chemical processes have an impact on the sea ice. For example, the ecosystem in sea ice can change color, becoming darker or lighter. Pure white sea ice reflects more sunlight, keeping temperatures frigid during winter. Darker ice absorbs more sunlight, warming the waters, melting and thinning the sea ice, and curtailing its spread as the oceans warm around the shrinking ice.
The CICE software also helps earth-system scientists better understand how sea ice influences climate around the world. When sea ice forms, most of the salt drains into the ocean water below it. Now denser from all that salt, that water sinks deeper into the ocean, then migrates toward the equator while warmer equatorial waters circulate into the polar regions. The relatively fresh ice moves to other locations, and as it warms it suppresses the ocean’s circulation by capping the ocean with a lightweight layer of fresher meltwater. In this way, changes in the amount of sea ice can alter the global “conveyor belt” of heat.
With the CICE program, a wide range of researchers study how sea ice grows and melts, crumples and moves, and interacts with global climate patterns—work they can do from a cozy chair in front of a computer screen. We hope the end results will be a better understanding of how sea ice keeps the polar regions cool and helps modulate the global climate.
Elizabeth Hunke and Andrew Roberts are sea ice scientists in the Fluid Dynamics and Solid Mechanics group in the Theoretical Division at Los Alamos National Laboratory. The CICE Consortium is supported through the U.S. Department of Energy’s Office of Science, the U.S. Department of Defense, the National Science Foundation, the National Oceanic and Atmospheric Administration and Environment and Climate Change Canada.