“It is a signal of large climate variability in the high latitudes,” Hakkinen said. “If this trend continues, it could indicate reorganization of the ocean climate system, perhaps with changes in the whole climate system, but we need another good five to 10 years to say something like that is happening.” Rhines said, “The subpolar zone of the Earth is a key site for studying the climate. It’s like Grand Central Station there, as many of the major ocean water masses pass through from the Arctic and from warmer latitudes. They are modified in this basin. Computer models have shown the slowing and speeding up of the subpolar gyre can influence the entire ocean circulation system.”
Satellite data makes it possible to view the gyre over the entire North Atlantic basin. Measurements from deep in the ocean, using buoys, ships and new autonomous “robot” Seagliders, are important for validating and extending the satellite data. Sea-surface height satellite data came from NASA’s Seasat (July, August 1978), U.S. Navy’s Geosat (1985 to 1988), and the European Space Agency’s European Remote Sensing Satellite1/2 and NASA’s TOPEX/Poseidon (1992 to present).
Hakkinen and Rhines were able to reference earlier data to TOPEX/Poseidon data, and translate the satellite sea-surface height data to velocities of the subpolar gyre. The subpolar gyre can take 20 years to complete its route. Warm water runs northward through the Gulf Stream, past Ireland, before it turns westward near Iceland and the tip of Greenland.
The current loses heat to the atmosphere as it moves north. Westerly winds pick up that lost heat, creating warmer, milder European winters. After frigid Labrador Sea winters, the water in the current becomes cold, salty and dense, plunges beneath the surface, and heads slowly southward back to the equator. The cycle is sensitive to the paths of winter storms and to the buoyant fresh water from glacial melting and precipitation, all of which are experiencing great change.
While previous studies have proposed winds resulting from the NAO have influenced the subpolar gyre’s currents, this study found heat exchanges from the ocean to the atmosphere may be playing a bigger role in the weakening current. Using Topex/Poseidon sea-surface height data, the researchers inferred Labrador Sea water in the core of the gyre warmed during the 1990s. This warming reduces the contrast with water from warmer southern latitudes, which is part of the driving force for ocean circulation.
The joint NASA-CNES (French Space Agency) Topex/Poseidon oceanography satellite provides high-precision data on the height of the world’s ocean surfaces, a key measure of ocean circulation and heat storage in the ocean.
NASA’s Earth Science Enterprise is dedicated to understanding the Earth as an integrated system and applying Earth System Science to improve prediction of climate, weather and natural hazards using the unique vantage point of space. NASA, the National Oceanic and Atmospheric Administration, and the National Science Foundation funded the study.
and was thinking of writing something up too :-) Definitely interesting in light of our current poll!
An article from a while back (which I linked to in a comment to a previous SciScoop article) is on abrupt climate change related to ocean currents.
It looks like more people are picking up on just how critical – and sensitive – that ocean current is…
Indeed it looks warmer. I wonder if the trans-polar drift current has weakened. That flows from the Bering Straits, along Russia, and splits in two with one current along the east coast of Greenland. Indeed, that part is shown in the map at the very bottom. But the velocity map shows movement to the north along the east coast.
Less cold water could affect the warmth. I hope the fellow didn’t only examine the north Atlantic and also examined the other currents in the area. After all, he should know…
It’s interesting that it is thought that warming would chill the East Coast. When climate was warmer, Vikings found the Canadian coast with grapes, trees worth harvesting as timber, and suitable for cattle. Now grapes tend to be down around Quebec.
An interesting thing about the north Atlantic area is implied in the Vinland map. The north coast of Greenland is shown rather well. This implies that the sea ice was further north or thin enough at least once for ships to travel around the north side of Greenland. Hiking across the ice would have been quite a task, particularly if you consider where the Greenland Viking colonies were.
Later maps do not show the north coast of Greenland, and it usually has a lot of sea ice year round. Also, the people who are used to living on ice, the Inuit arrived in Greenland as the climate cooled. Indeed, during the Little Ice age, Inuit were seen around the Irish coast. (Actually, the Thule Inuit displaced the Dorset Inuit around 1100 AD; the Stone-Age Dorset hunted land mammals, seals, and walrus without having bows and arrows.)
Labrador Sea water in the core of the gyre warmed during the 1990s. This warming reduces the contrast with water from warmer southern latitudes, which is part of the driving force for ocean circulation.
The obvious source of ocean heat is the Sun. If the Sun is getting hotter, warming would be expected. Climate simulations using a constant amount of heat from the Sun have trouble explaining recent warming, and perhaps more heat explains several things.
Ah, but what happens to the north Atlantic weather in warmer weather? The North Atlantic Oscillation (NAO) goes positive, as both the Azores high and Icelandic low increase in strength. Why? Well, if a moving high pressure cell is cold, why isn’t the above an Icelandic high and Azores low? Because the air is circulating up from the hot Equator, falling down on the Azores (causing higher pressure), some of the cool air flows north, and rises around Iceland’s longitude (causing low pressure). More heat, faster circulation toward the poles.
Actually, the Azores does not feed Iceland due to Earth’s rotation. There are pressure variations in NW North America and SE North America which are related to the Iceland circulation. These also are related to cold air flowing down the continent from the NW and warm air sweeping up from the Gulf of Mexico.
Indeed, there is a correlation between solar activity and the NAO. So it is hardly surprising that warmer water might be seen, and that the NAO would increasingly be positive, giving Europe milder winters.
You can see that recently the NAO index has been positive. Note also that the NAO was mostly negative during the global cooling period 1945-1975.
Something dramatic would have to happen to the ocean to chill all that hot air blowing across the Atlantic.