SOURCE: The Guardian

DATE: June 7, 2019

SNIP: The demise of an entire ocean is almost too enormous to grasp, but as the expedition sails deeper into the Arctic, the colossal processes of breakdown are increasingly evident.

The natural thaw that starts with spring’s warm weather is being amplified by manmade global heating. The Arctic has heated up by 2C above pre-industrial levels, twice the global average. Some hotspots, including parts of the Fram strait, have warmed by 4C. There are variations from year to year, but the trend is clear and accelerating. Sea ice is melting earlier in the spring and freezing later in the autumn. Each summer it thins more and recedes further, leaving greater expanses of the ocean exposed to 24-hour sunlight. This is driving back the frontiers of ice and fragmenting one of the planet’s most important climate regulators. It is also creating a series of feedbacks that are accelerating the Arctic melt. Several are only partially understood.

Since the start of the satellite era in 1979, the summer Arctic has lost 40% of its extent and up to 70% of its volume. Other scientists calculate the rate of decline at 10,000 tonnes a second. Much of the multiyear ice is now gone. Most of what is left is the younger, thinner layer from the previous winter, which is easier for the sun to melt and the wind to push around. [Scientists] expect ice-free summers in 20 to 40 years, which would allow ships to cruise all the way to the north pole.

If the Arctic were a patient, doctors would be alarmed by its vital signs. As well as hot flushes, asthma and contamination (the researchers are following up on studies that suggest the Fram strait has one of the highest levels of microplastics in the world), the ocean has also been diagnosed with a weakening of its immune system. For centuries, the Arctic’s distinctive character has been shaped by a layer of cold, relatively fresh water just below the surface, produced by melting ice and glaciers. This has insulated the sea ice from the warmer, denser, saltier waters of the Atlantic currents that flow in the depth. But this stratification is collapsing as temperatures rise.

The oceanic shift was outlined in a landmark study published last year in Science, which found that the water density and temperature of the Fram strait and Barents Sea were increasingly like those of the Atlantic, while further east, Russia’s Laptev sea was starting to resemble what the Barents used to be. “The polar front is shifting,” the lead author, Dr Sigrid Lind, of the Institute of Marine Science and the University of Bergen, told the Guardian this year. “The Arctic as we know it is about to become history. It will go when stratification breaks down completely and the Atlantic takes over the whole region.”

This has not happened for more than 12,000 years, but the shift is well under way. First to succumb, according to Lind, will be the Barents Sea, which will have no fresh water by 2040, then the Kara sea. The consequences will be far-reaching. The food chain is already affected. Atlantic species of cod, herring and mackerel are moving northwards. For the next 20 to 30 years this could boost fishing catches, but forecasts by Norway suggest boom will turn to bust later as the waters grow too warm for fish larvae.

For humanity, the biggest impact is on the weather. The area between the cold pole and the warm equator is a ramp that propels weather fronts across continents. Its incline has always varied from season to season as the icecap expands in winter and shrinks in summer, providing a global pulse that pumps sea and air currents around the world. But that frozen heartbeat is warming and weakening as the Arctic becomes more like the Atlantic. Lind speculates that ocean destratification is the key driver for ice loss, which in turn affects the jet stream, weakens the polar vortex and can lead to heatwaves in the southern US and cold weather extremes in Asia. “The rules of the game are changing. We seem to be seeing large-scale weather pattern changes connected to the shrinking Arctic. As the Arctic becomes history, we need to understand how it affects the globe.”