Land and ocean temperature percentiles for January-August 2015. Graphic: NOAA

[cf. Why some scientists are worried about a surprisingly cold ‘blob’ in the North Atlantic Ocean – ‘The fact that a record-hot planet Earth coincides with a record-cold northern Atlantic is quite stunning’]

By Lisa Sorg
4 November 2015

(Coastal Review) – There it is, hanging out in the northern Atlantic Ocean, off the southern tip of Greenland, a patch of unusually cold, fresh water in an otherwise warming, salty sea. It’s described, inelegantly, as the big, blue blob because of its color on maps of sea temperatures.

Scientists who are studying the mechanisms behind this cooling phenomenon, suggest that ocean circulation — what they call the Atlantic meridional overturning circulation, or AMOC — in this part of the world is slowing down. And if you think of the ocean as a living organism, like a human, when circulation decreases in one part, it affects the entire system. This slowing and cooling, which some scientists say is happening decades ahead of schedule, could affect sea level rise on the East Coast, and climate patterns and marine life worldwide.

In St. John’s, Newfoundland, Canada, at 47 degrees latitude north, professors Brad deYoung and Entcho Demirov live at the southern edge of change. “The North Atlantic is an area that is very dynamic,” says Demirov, an associate professor of physics and physical oceanography at Memorial University of Newfoundland. “You have to look at the size of the cold water spot, not just horizontally but vertically. Then we have to determine what caused it, what’s the impact and how long will it persist.”

Like many scientists, deYoung attributes, at least in part, the slowing of the AMOC and the formation of the blue blob to two main factors: freshwater flowing from a melting Greenland ice sheet and river runoff from a warmer Arctic. A similar situation is unfolding near Antarctica, where melting ice is chilling part of the ocean. This is happening even though average sea surface temperatures globally set a record high.

“We’re still disentangling climate change and other variabilities to understand what’s happening,” says deYoung, a professor in the physics and physical oceanography department at Memorial.

The ocean’s underlying mechanism is a conveyor belt of warm water that circulates from southern latitudes to the north and then returns cooler waters back toward the equator again. For example, this motion is responsible for the Gulf Stream, which flows northward off the Southeast coast before veering across the Atlantic. Its warm waters help keep Western Europe temperate even though it is located farther north than the U.S. The churn of ocean waters also fosters marine habitats for zooplankton, fish and other aquatic life.

But an influx into the ocean of cold, fresh water, which has less salt and thus is less dense, disrupts the motion and heat exchange. If that persists, over time, a lethargic conveyor belt will no longer move water. A breakdown of the Gulf Stream could translate to colder weather in Western Europe, higher sea levels along portions of the N.C. coast and changes in marine ecosystems. Some fish could die; others could migrate. And because of the interconnectedness of the ocean currents, the effects could be international in scope.

“We can turn off the AMO circulation by adding fresh water, which could shut it down,” deYoung says. Although that is unlikely, he adds, “It is still possible that we can substantially disrupt circulation on a larger scale in the ocean.” […]

Many scientists did not expect the recent shifts to happen so quickly. “I thought the AMOC would change slowly, but the oscillation has been quite dramatic over short periods,” deYoung says. “We like to think of climate as an elephant moving slowly along. But the ocean system is not that simple. We’re open for more surprises.” [more]

Changes in Atlantic Sooner Than Expected



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