Gulf Stream is slowing down faster than ever? Or?

[RobertEarl]

Calculations suggest that over the 20th century the North Atlantic meridional overturning circulation – the northward flow of warm surface water and the southward flow of deep, cold water – has slowed by between 15 and 20 per cent, said Professor Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research in Germany.

The scientists calculated that some 8,000 cubic kilometres of freshwater has flowed from Greenland into the Atlantic between 1900 and 1970, and this rose significantly to 13,000 cubic kilometres between 1970 and 2000.

http://www.independent.co.uk/environment/gulf-stream-is-slowing-down-faster-than-ever-scientists-say-10128700.html

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RE: Well, looking at the SST - Sea Surface Temperature maps tells us that warmer water is flowing further north into the Arctic than anytime in recent history. Indeed, the ice in the Arctic is melting from that induced warmer water.

Siberian Arctic waters are quite warm and Siberia is warmer than ever.

My theory is that the melt from Greenland and cold water from the Arctic that was formerly ice is flowing between Greenland and Canada and entering the Atlantic at the northwestern edge of the Gulfstream.

Being colder it sinks and the Gulfstream being warmer rises a bit. The flow into the Arctic at the Russian side of the Arctic is replacing the melted ice waters which are channeling between Greenland and Canada.

There is a clockwise flow going on in the Arctic as seen in Arctic SST maps.

Link to Arctic SST. not hot. Copy and Paste
weather.gc.ca/data/analysis/351_50.gif

Link to SST maps not hot. Copy and Paste
polar.ncep.noaa.gov/sst/rtg_high_res/"][/a]

[gratuitous]

1. Ted Cruz says

It's God stirring the waters. Vote for Ted!

[Warpy]

2. They need to know what's going on at the various depths.

Measuring surface temperature doesn't give the whole story.

[RobertEarl]

4. True

But the surface temps show warmer than usual waters flowing north of the gulfstream and cooler waters west of Greenland. The Arctic map takes some time to grok the locations but if you can find Greenland you are on your way.

The Gulfstream is warm water on the surface. The colder water sinks to deep locations.

The mixing of the cold water coming down from Greenland could slow the Gulfstream, but since Siberian waters are warmer, it seems doubtful.

[lpbk2713]

3. Thanks Obama.

[JayhawkSD]

5. Some problems with that.

"Siberian Arctic waters are quite warm and Siberia is warmer than ever."

Which is the Pacific and has nothing to do with the Gulf Stream, which is in the Atlantic. Inflow to the Arctic from the Bering Straight is relatively small, with much greater inflow coming from currents on the Atlantic side and from a couple of huge rivers in Russia. The Bering Straight is both narrow and very shallow.

"My theory is that the melt from Greenland and cold water from the Arctic that was formerly ice is flowing between Greenland and Canada and entering the Atlantic at the northwestern edge of the Gulfstream. Being colder it sinks..."

The problem is that, being melted ice, it would have a lower salinity, would be less dense, and therefor would not be able to sink below the more dense seawater. Freshwater stays on top of seawater regardless of temperature.

If you had read the article to which you linked, you would have noted that the cause of the slowdown appears to be freah water which is not sinking and is, in fact intefering with the normal sinking of cold water. You would also have read that the fresh water is from Greenland and not from the Arctic Ocean, and certainly has nothing to do with Siberia.

"There is a clockwise flow going on in the Arctic as seen in Arctic SST maps."

Yes, it's called the Beaufort Gyre, but that has nothing to do with where water is entering or leaving the Artic.

[Art_from_Ark]

6. Seawater on the ocean floor is generally less saline than seawater at the surface

Below the Sea Surface: Waters warmer than 10°C dominate the sea surface but do not extend much below 500 m within the ocean; tropical and subtropical surface water provide is just a veneer of warmth over a cold ocean; typical deep ocean temperature vary from ¨1° to 3°C. The sharp drop off in temperature with depth is called the thermocline. The warm surface water is generally saltier than the cooler deep or polar waters. The halocline marks the drop of salinity with depth that accompanies the thermocline. The surface water warmth overrides the saltiness in governing density, so that the warm surface water regions coincide with buoyant (less dense) water. In polar regions buoyancy of the surface layer is mainly a consequence of the freshness of the surface water. Deep cold waters derive their properties at the sea surface during winter at high latitude.

http://eesc.columbia.edu/courses/ees/climate/lectures/o_strat.html

[JayhawkSD]

7. Did you read the article that was linked?

"Freshwater is lighter than salty water which means that it tends to float on the surface of the ocean and in doing so disturbs the normal sinking of dense, cold saltwater to the ocean floor, which is the main driver of the Atlantic circulation."

Do those scientists not know what they are talking about?

The surface water is salty because it is warm and water has evaporated from it, leaving salt behind. The deeper water is less salty because it has not experienced the evaporation which causes the rise in salinity, not because it is fresh water which sank. The amount of sea water which circulates in the rising and falling currents is quite small compared to the immense volume of the oceans overall.

Also, this from The Water Encyclopedia.

When sea water freezes, much of the salt that it contains is frozen out, so that a layer of cold brine forms at the ocean surface. Being denser than the water below it, the brine sinks, entraining water as it does so, until it reaches a level where it has the same density as the surrounding sea water. This process takes place in several regions of the world's oceans, the most important being in the Greenland, Norwegian, and Labrador Seas in the Northern Hemisphere,

The deep water from the Greenland and Norwegian Seas fills up these basins until it spills over the ridges between Greenland, Iceland, and Scotland. From here it is forced to the right by the Coriolis force and follows the topography around the coast of southern Greenland and the Labrador Sea, eventually crossing under the Gulf Stream and flowing south along the east coast of the U.S. at depths between about 2,000 to 4,000 meters (1.3–2.5 miles).

So, here we have a deep, cold current which is saltier than the water above it.

There are many interlocking mechanism at work in ocean mechanics. I am suspicious pf the original article's explanation, thinking that it is an over-simplification. The Greenland melt "interfering with the normal sinking of cold seawater," strikes me as a simple answer which itself requires explanation. How does it cause that interference? That is not, in any case, the point at which the Gulf Stream turns cold and sinks, so how is that causing a failure at a point Rather far removed?