Thursday, November 19, 2015

On Thin Ice: Big Northern Lakes Are Being Rapidly Transformed

As temperatures rise, the world’s iconic northern lakes are undergoing major changes that include swiftly warming waters, diminished ice cover, and outbreaks of harmful algae. Now, a global consortium of scientists is trying to assess the toll.

 Lake Baikal in March
For more than 25 million years, Lake Baikal has cut an immense arc from southern Siberia to the Mongolian border.  The length of Florida and nearly the depth of the Grand Canyon, Baikal is the deepest, largest in volume, and most ancient freshwater lake in the world, holding one-fifth of the planet’s above-ground drinking supply.  It’s a Noah’s Ark of biodiversity, home to myriad species found nowhere else on earth.  It’s also changing.  Records show that Baikal’s ice season is growing shorter and its ice thinning fast, due to heat-trapping greenhouse gases that are increasingly disrupting the climate.

Baikal’s surface waters are warming at an accelerating pace, rising at least 2 degrees Celsius (3.6 Fahrenheit) over the past quarter century — twice as fast as global air temperatures.  The ice season, which typically covered the lake from January through May, has been shortened by nearly three weeks since the mid-1800s, and the ice has thinned nearly 5 inches since 1949.  By the end of the century, scientists say that Baikal could be ice-free a month or more longer than today. 

This rapidly changing climate threatens the lake’s unique, cold-adapted creatures, including the iconic nerpa — the world’s only true freshwater seal — whose fertility drops in warmer winters. Fishermen complain that the omul — a once-bountiful species of whitefish — has already grown scarce. Rising temperatures may also factor into some mysterious new problems plaguing the lake in the past few years. The brilliant green underwater forests of endemic Baikal sponges are dying, victims of an unknown pathogen. And dense algal mats choke wide swaths of bottom near shore. 

“These mats smother everything underneath them, and of course that’s where the greatest biodiversity is in this lake,” said Wellesley College aquatic ecologist Marianne Moore. “It’s a real problem.” 

Baikal is just one of many large lakes worldwide showing signs of rapid change as a result of rising temperatures. Majestic water bodies like Baikal and North America’s Lake Superior are integral to regions such as Siberia and the Great Lakes, playing a key role in transport, fisheries, and tourism. They also store the bulk of our planet’s liquid freshwater. But the lake-rich northern latitudes, where the majority of these vital resources lie, are the fastest-warming regions on earth. 

Until recently, scientists had scant knowledge of how warming and weather extremes were affecting lakes.

More than three in four large lakes above the 40th parallel north, roughly the latitude of New York City and Madrid, have undergone summer surface temperature increases of 2.7 F or higher from 1985 to 2009, a new international research collaboration finds. Some lake temperatures rose more than twice that amount. Nearly all have experienced retreating winter ice, a loss that can interfere with internal circulation, reduce oxygen, and help create fertile breeding grounds for harmful algae. These changes, which appear to be accelerating, have potentially profound consequences for water supply, food, and aquatic life. 

Read more at On Thin Ice: Big Northern Lakes Are Being Rapidly Transformed

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