The changing Arctic Ocean

The vast frozen surface of the Arctic Ocean, often referred to as the polar ice cap, separates the atmosphere from the underlying ocean, reflects incoming radiation from the sun back out to space, and provides a unique habitat for creatures ranging in size from microbes to 1500 pound (680 kg) polar bears. While the amount of Arctic sea ice has waxed and waned with the seasons for all of recorded human history, a large fraction would always persist throughout the year. This old, multiyear sea ice reached thicknesses of several meters and resisted melting, even in the polar summer (Eicken et al., 1995). As temperatures have increased in recent decades, much of this old ice has disappeared and been replaced by thinner first-year ice that melts earlier in spring (Maslanik et al., 2011). Earlier melt has allowed the surface ocean to absorb more solar radiation, delaying the onset of freeze-up in the fall. As a result, a positive feedback has developed in which rising Arctic Ocean temperatures have been accompanied by a markedly thinner and less extensive sea ice cover and an ever-lengthening open water season, which allows the ocean to absorb more radiation, further increasing the temperature (Perovich, 2011). Estimates suggest that the volume of sea ice in the Arctic today is only 20% of that present just a few decades ago (Laxon et al., 2013). Scientists are no longer debating if the Arctic Ocean will eventually become ice-free in summer—they are debating when, with estimates ranging from 20 to 50 years from now (Wang and Overland, 2009). For some, the loss of Arctic sea ice is a unique opportunity. Improved access to ice-free Arctic waters has sparked interest in the development of a viable Arctic commercial fishery. It has also fuelled interest from energy companies wishing to explore the shallow continental shelves for fossil hydrocarbons. Already, a more predictably ice-free Northwest Passage (Smith and Stephenson, 2013), a northern gateway between the Atlantic and Pacific oceans, has resulted in increased commercial ship traffic in Arctic waters. As all of these activities ramp up, it is essential that strategies are developed and implemented to minimize environmental degradation (Pew, 2013). For others, the loss of Arctic sea ice looks to be a disaster in the making, particularly for indigenous populations that rely on the ocean for their food. Access to the interior ice pack for hunting is hampered as shore-fast ice diminishes and pack ice retreats further from shore. Subsistence whaling is becoming more difficult as the sea ice historically used as a reliable hunting platform disappears (Struzik, 2012). Newly ice-free waters are encouraging the northward migration of non-native animals, such as killer whales, that compete with native species and indigenous humans for food (Higdon, Hauser and Ferguson, 2012). And coastal populations are rapidly losing valuable land to erosion (Solomon, 2005; Kittel et al., 2011) caused by intense wave action from frequent and stronger storms (Hakkinen, Proshutinsky and Ashik, 2008) with more intense storm surges (Vermaire et al., 2013) in increasingly ice-free waters. Yet the consequences of Arctic sea ice loss extend far beyond the subsistence and commercial activities of humans there will be profound ecological implications as well. Some of these are already apparent, such as habitat reduction for large mammals like ringed seals and polar bears that require stable sea ice in spring/ summer for reproduction and feeding (Stirling and Derocher, 2012). But most consequences are still playing out and our ability to either understand or predict them is limited. This is particularly true for the smallest Arctic inhabitants on which the rest of the marine ecosystem relies.