Hakai Magazine

Coastal science and societies

Meltwater brings a lot of changes to the coast when glaciers and ice sheets dwindle. Photo by Colin Monteath/Minden Pictures

Melting Glaciers Do More Than Raise Sea Levels

The movement of meltwater from ice to the ocean carries some surprising cargo.

Authored by

by Amorina Kingdon

Article body copy

Novels and blockbuster movies that tackle climate change gravitate toward the dramatic, especially when it comes to melting ice. In these stories, mountainous glaciers crumble and cities flood as the sea rises. But a lot more happens in between the mountains and the sea, as meltwater passes through the liminal space of the coast. Here are five ways the slow, non-dramatic drip of melting ice changes our coastlines and oceans.

Released Toxicants

Glaciers, like many venerable objects, can act as time capsules. Like a dusty vinyl record holds an era’s songs, ice holds very old molecules—not just the H2O of snow, but traces of airborne particles like dust, ash, and chemicals that hitched a ride on falling flakes. In the Antarctic, Adélie penguins harbor consistent levels of the pesticide DDT even though it’s been widely banned since the 1970s. The source: glacier meltwater that trickles past the penguins on its way to the sea, eventually making its way into the penguins’ food webs. That means at least some of the ice now melting inland was once snow that fell before DDT was restricted in the 1970s. Many other once-airborne and now-banned pollutants are reappearing in glacier meltwater, such as PCBs and CFCs, the latter of which were a component of hairspray and other aerosols until they were phased out in the 1980s. Thanks, Van Halen.

Re-emerged Diseases

In 2016, an anthrax outbreak killed a young boy and decimated reindeer herds in Siberia. The source of the disease puzzled scientists since the area had been anthrax-free for 75 years. Eventually, they traced it to an anthrax-bacteria-ridden reindeer carcass once locked in the permafrost and now thawed due to climate change. The story raised fears that global warming might resurrect other once-vanquished diseases. Viruses can lurk in frozen bodies for a long time, which may not be an entirely bad thing. In 2005, researchers carefully reconstructed the virus that caused the 1918 flu pandemic from a corpse buried in the icy Alaskan ground, allowing the study of the virus’s genome for the first time. In reality, the chances of these diseases re-infecting humanity are very small, but millions of microbes live on and within ice sheets and glaciers.

Smothered Sea Life

As the volume of meltwater increases, it erodes more sand, dust, and rock. One Norwegian study projected that the volume of sediment in the meltwater of one mountain glacier will double between 2070 and 2100. Once deposited downstream, the extra sediment can change a river’s shape and function, causing channels to shift or widen, and waters to flood over the banks. And the impacts go all the way to the ocean. Sediment can smother animals living on the seafloor and murkier water means there is less light available for photosynthesizing phytoplankton. But those same sediments can also carry nutrients, which could fuel plankton growth. Either way, the extra sedimentation can cause ripples throughout marine food webs.

Flooded Rivers

Glacial lake outburst floods, or GLOFs, are one of the few fast and dramatic events in a field devoted to things that are literally glacially slow. GLOFs usually happen at the edges of the ice. When glaciers grind forward, they plow up the sediment leaving long ridge-like piles of sand and gravel—called moraines—at the glacier’s toe and along its sides. If the glacier then retreats, meltwater can pool in the open space between the ice and the moraine, forming a lake. But these new lakes can suddenly burst through weak spots in the melting ice or moraines, sending water barreling downstream. As well as delivering pulses of sediment, GLOFs can cause rivers to flood, widen, or alter course. The impacts can be significant in some mountainous regions where climate change is making GLOFs more common. In 2008, after 21 GLOFs tore down the coast of Chile from melting Andean glaciers, the water widened the country’s largest river by more than 40 meters and carried 25 million cubic meters (enough to fill 1,000 Olympic-sized swimming pools) of sediment downstream.

Changing Coastlines

When all this meltwater finally reaches the coast, it causes the sea to rise. Sea level rise is already subsuming coasts around the world, including many sandy or low-lying islands. But sometimes, if the coasts are steep, jagged, and formerly ice covered, melt can actually expose coastal features including whole islands. That’s because many glaciers and ice sheets spill over from the land into the sea. Their retreat reveals the underlying coastlines. And the more convoluted the terrain, the more dramatic the effect. Dozens of islands emerged in the past few decades as ice sheets receded along the crinkled edges of Greenland; Svalbard, Norway; and Novaya Zemlya, Russia. Cartographers scramble to keep up, but it can take several years to update digital maps and charts with high-tech satellite data, especially for remote places. With ice melt accelerating, just a few years can usher in a total sea change on the coast.