Understanding Arctic Sea Ice in a Period of Rapid Climatic Change

By Andrew R. Mahoney, Geophysical Institute, University of Alaska Fairbanks and Martin Robards, Wildlife Conservation Society

Sea ice is the thin floating skin that forms on the surface of the ocean as it freezes. Though few of us encounter sea ice in our daily lives, the shrinking and thinning of the Arctic ice pack as a result of regional warming has global implications that will be felt by all of us. Sea ice plays a fundamental role in the global climate system (Barry et al. 1993) and provides critical habitat for a wide range of species (Laidre et al. 2015, Melnikov et al. 2001). At the same time, the increasing extent of open water in summer is making its mark on offshore oil exploration and development, global shipping routes, and the geopolitical landscape in the North (Blunden 2012). However, for those people who live at the shores of the Arctic Ocean, sea ice is more than just a component of the global climate and ecosystems, or a subject of discussion in boardrooms and conferences. For Inuit, the shrinking Arctic ice pack is changing a way of life that relies on sea ice as a source of food and clothing and a place to call home (Gearheard et al. 2013, ICC 2015). 

woman in red parka kneeling by a hole in ice
Marguerite Tibbles collecting water data

Photo courtesy of Trevor Haynes, Wildlife Conservation Society

Over the last three decades, satellite records show that the amount of sea ice in the Arctic Ocean at the end of summer has decreased by approximately 40% (Serreze and Stroeve 2015), exposing an area of previously ice-covered ocean one and a half times the size of Alaska.

Historical observations recorded in ice charts and ship log books indicate that this loss of ice is unprecedented in at least 150 years (Mahoney et al. 2011 and 2008). Sea ice helps keep the Polar Regions cool by reflecting the majority of solar energy back into the atmosphere. Thus, any reduction in ice extent creates a self-reinforcing cycle whereby the retreating ice edge exposes more ocean during the summer, allowing more heat to be absorbed, which accelerates the loss of ice and rate of warming. Scientists call this process the “ice-albedo-feedback” (Perovich et al. 2007). Partly due to the loss of sea ice in the North, the Arctic has warmed on average by 0.6 °C (1.1 °F) per decade (Comiso and Hall 2014), faster than any other region on Earth. The loss of sea ice also has profound ecological implications that extend well beyond the Arctic.

The seasonal expansion and contraction of the ice pack sets an annual rhythm to the ecology of the Polar Regions and the Inuit way of life. At the beginning of each winter, new ice forms around the margins of the old and the ice-covered area of the ocean grows. The southward advance of the ice edge has annually driven most of the summer visitors away leaving behind only those species adapted to the polar winter. For example, ringed seals and polar bears have remained while walrus, bowhead whales, and guillemots migrate southward with the ice edge. These differences in behavior are becoming increasingly blurry as winter ice conditions ameliorate. Conversely, in spring when the ice retreats north, it has historically provided a platform for tens of thousands of female walrus and their calves during summer. Now with the ice retreating so far north, it lays over waters too deep for them to forage. These female walrus and their calves now come ashore in vast congregations that endanger the young animals that can be trampled as the herd comes and goes.

In addition to the charismatic wildlife so visible on and around sea ice, pockets of liquid brine trapped within sea ice provide a winter habitat for ice algae. Sheltered from grazing krill and located at the top of the water column, these algae are positioned at the front of the line ready to take advantage of the sunlight when it returns in spring. Released by melt into nutrient-rich waters, the algae multiply rapidly and provide the foundation of a food chain that supports the entire Arctic Ocean ecosystem (Arrigo et al. 2008). The life cycles of the Arctic’s year-round residents and its migratory summer visitors are timed to take advantage of this seasonal pulse of food. Thus, when female polar bears emerge from their dens with cubs, they feed on seals fattened by fish that eat the krill that thrive on the algae, which also feed the bowhead whales during their migration to their summer feeding grounds. In fact, the algal bloom that accompanies the retreating ice edge is so abundant that its leftovers nourish the seafloor, supporting vast populations of clams that are gorged on by bottom-feeding walrus.

All of these relationships between life and ice are well known to the Inuit, whose subsistence activities have long been timed to take advantage of this abundance (Gearheard et al. 2013). The close connection with sea ice places the Inuit on the frontlines of rapid Arctic change. Indeed, they are at the forefront of observing and experiencing the repercussions of these changes. Furthermore, a long history of traditional ecological knowledge about sea ice presents a rich context for the suite of contemporary changes affecting their own uses as well as that of the wildlife they rely on for food security. 

a group of men in a low boat in the ocean
A whaling party waits in their umiaq for a bowhead whale to surface in the open lead near Barrow, Alaska.

Photo courtesy of Andrew Mahoney

man in a white parka standing on large block of ice looking toward the ocean
A hunter watches for whales at the edge of the shorefast ice near Barrow, Alaska.

Photo courtesy of Andrew Mahoney

The emergence of new weather patterns, species assemblages, and behaviors have all been astutely observed and increasingly documented by local experts (Krupnik 2010, Krupnik and Jolly 2002, Gearheard et al. 2006). In concert, residents of Arctic coastal communities are facing impacts related to the changes that directly affect their traditional way of life. For example, the delayed formation of sea ice in fall is leading to increased wave energy reaching the coast during storms, resulting in increased erosion of village sites (ACIA 2005). At the same time, the reduced stability of shore-fast ice increases the risk of detachment and endangerment of hunters during the spring hunting season (Druckenmiller et al. 2013), while the early onset of the spring melt is shortening the ice-based hunting season and impacting the health of ice-dependent seals (Gearheard et al. 2006).

While these changes in sea ice may bring some new opportunities for local communities (e.g., new species assemblages including more temperate whales and salmon, or new industries), the current pace of change is without recent precedent and poses significant challenges for effective adaptation. Current models predict that the Arctic will experience effectively ice-free summers (<1 million square kilometers) as early as 2040 (Wang and Overland 2012). Understanding and planning for the impacts of this will require science that responds to the priorities of local communities and incorporates the expertise of their indigenous knowledge holders. By doing so, we may help support the resilience of local communities and the iconic wildlife of the Arctic.

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Last updated: March 6, 2017