From the American Geophysical Union: Study suggests no slowing of Atlantic ‘conveyor belt’ current
The Atlantic meridional overturning circulation (AMOC), which carries warm water to high northern latitudes near the surface and returns cold water in the deep ocean to the Southern Hemisphere, affects and is affected by global climate change. There has been debate as to whether the AMOC has begun slowing down due to global warming, but research on AMOC variability based on instrumental records is limited. One possible indicator of change in the AMOC is the North Brazil Current (NBC), a strong current that flows northward in the tropical South Atlantic, connecting the North and South Atlantic oceans, and plays an important role as a major pathway for surface return flow in the AMOC.
Zhang et al. calculate how the NBC varies on multidecadal time scales based on a record of 50 years of observations off the coast of Brazil. They find that NBC transport changes are correlated with Labrador Sea deep convection (important for deepwater formation) and with a broad pattern of sea surface temperature anomalies in the Atlantic (sometimes referred to as the Atlantic Multidecadal Oscillation or Atlantic Multidecadal Variability), both of which have previously been linked to AMOC fluctuations. The researchers therefore suggest that observed NBC variability is a useful indicator of AMOC variations. They confirm this using a climate model simulation. Furthermore, the authors note that although some studies have suggested that the AMOC is slowing down due to global warming, the NBC shows multidecadal variability but no significant slowing trend over the past 50 years.
Source:
Journal of Geophysical Research-Oceans, paper doi:10.1029/2010JC006812, 2011
Title:
“Multidecadal variability of the North Brazil Current and its connection to the Atlantic meridional overturning circulation”
Authors:
- Dongxiao Zhang
- Joint Institute for the Study of the Atmosphere and Ocean, University of Washington, Seattle, Washington, USA; NOAA Pacific Marine Environmental Laboratory, Seattle, Washington, USA;
- Rym Msadek
- AOS Program, Princeton University, Princeton, New Jersey, USA; NOAA Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey, USA;
- Michael J. McPhaden
- NOAA Pacific Marine Environmental Laboratory, Seattle, Washington, USA;
- Tom Delworth
- NOAA Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey, USA.
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and they wonder how Pacific lion fish got in the Caribbean….
….same way other circumtropical fish did
(face palm)
So, AMOC is not running amok? That’s a relief.
How can this conveor belt slow? It’s a function of the 2nd Law of Thermodynamics; temperature moves toward equality. Entropy. The same reason for the existence of the jet streams.
If a continental land mass were to eventually cut off the conveyor belt, that’s one thing. But it’s not spontaneously going to stop on its own. It is a physical mechanism for transferring heat from a warmer area to a colder area.
The flow of warm currents face a severe bottleneck through the the Indonesian archipelago, the waters there considered inland seas and the only deep water being the Wetar Trench that runs besides Timor.
Smokey says:
May 22, 2011 at 7:16 pm
How can this conveor belt slow? It’s a function of . . .”
Would not the assumption be that if the high latitudes warm (and are they not supposed to warm first?) in contrast to the low latitude zone, then the temperatures would be moving “toward equality” and the flow would slow?
Insofar as this does not appear to be happening, it is one more indicator that, so called, global warming isn’t happening.
Is it possible for the Antarctic Ice Sheet/Sea Ice to grow to the point of cutting off the AMOC return current?
The warm current passing by the north of Australia seems problematical – everywhere else the currents flow inimpeded by land masses except in nth Oz. I get the impression that the author’s are not familiar with 3D structures…….
“New NASA measurements of the Atlantic Meridional Overturning Circulation, part of the global ocean conveyor belt that helps regulate climate around the North Atlantic, show no significant slowing over the past 15 years. … Willis found evidence that the circulation had sped up about 20 percent from 1993 to 2009.”
See: http://www.appinsys.com/GlobalWarming/GW_4CE_NATCGulfStream.htm
Interesting also how the idealized conveyor belt figures get the North Atlantic flow backwards -i.e. the warm flow should be northward on the western side of the Atlantic (the Gulf Stream).
Good point, The Indonesian flowthrough must be resistive and restrict the quantity
that exits this area to the North of WA. It does this slowly in La Nina episodes when the sea height is higher due to the strong easterly effect of the trade winds. The diagram is directional and not quantitative, but it seems odd that this bottleneck allows free passage of AMOC.
On another point, I can see how the warm Atlantic component might sink when it reaches high latitudes, but how does the Pacific component rise when it also reaches high latitudes ?
And it’s a darn good thing it isn’t slowing. It would take a major sudden influx of fresh cold water into the north atlantic to shut down the AMOC such as occurred to bring on the cooling of the Younger Dryas period when Lake Agassiz suddenly drained. There is evidence this has also happened other times. See:
http://www.nature.com/nature/journal/v464/n7289/full/nature08954.html
As it stands, even though Greenland is melting and releasing lots of cold fresh water into the N. Atlantic, it is hardly enough to make a dent in the massive amount of warm salty water flowing from the tropical Altantic area. Recent studies also suggest that warm water is spilling into the Atlantic from the Indian Ocean around the southern tip of Africa:
http://www.worldweatherpost.com/2011/04/28/water-currents-of-south-africa-could-stabilize-climate-in-europe/
This should help to keep the current nice and warm and easily counter act the cold fresh water pouring off of a melting Greenland.
Oh moon, out of step or back, jittery star lit, tarried thee be by this floppy minded magma magnet, and a cometary frockfull of fickles, by these things doth fate be wrought.
Hanging in there! yeah. 20 thousand years and still going strong.
But isn’t the anthropogenic global warming going to cut this current off and soon turn the overheated world into an icebox…..or something like that????
Because heat stops convection….or something like that????
Wait. …. I think I get it. Sort of. Or not. Hmmm
Gore can explain.
Alan Cheetham says:
May 22, 2011 at 8:26 pm
Interesting also how the idealized conveyor belt figures get the North Atlantic flow backwards -i.e. the warm flow should be northward on the western side of the Atlantic (the Gulf Stream).
See the image here:
Page 3, Figure 2: Thermal infrared image of the Gulf Stream
http://er.jsc.nasa.gov/SEH/Ocean_Planet/activities/ts2siac2.pdf
The image shows you are correct. However, the warm water off the coast of North America doesn’t seem to get near as far north as most diagrams (idealized drawings) suggest. I’ve searched to find a satellite image that does show this warm water reaching across the N. Atlantic to Norway – or even close. Still looking.
John F Hulquist;
Would not the assumption be that if the high latitudes warm (and are they not supposed to warm first?) in contrast to the low latitude zone, then the temperatures would be moving “toward equality” and the flow would slow?>>>
Well yes…but no.
If all you consider is a theoretical uniform forcing from increased CO2, then T at high lats would increase more than T at low lats which in turn reduces the “inequality”. The reasoning being that “forcing” is measured in watts/m2 which varies with T raised to the power of 4 (T^4), so a given increase in watts/m2 results in a greater increase in T at cold temps (high lats) than at warm temps (tropics).
But there are more factors to consider. First of all, “forcing” cannot be uniform. For CO2 to absorb and re-radiate, it can only work on what is coming up from the surface. At high latitudes it has perhaps 250 watts/m2 coming at it, while at the tropics it might be 450 watts/m2 or more. Beyond that, the tropics are net absorbers of energy while the high lats are net losers of energy. That condition is created by wind and water moving energy from the tropics to the poles. But where is it written that because it is moving in that direction (from tropics to poles) that it actually gets there? Since P in watts/m2 varies with T^4, any increased energy absorbed at the tropics means much higher radiance to space of the water and wind carrying it…so maximum radiance to space as a consequence of warming might well be at middle latitudes instead, with the extra energy mostly exhausted by the time the wind/water gets all the way to the poles.
Hence one has to ask, is the strength of the conveyor belt showing that warming is not occuring? Or is the strength of the conveyor belt showing that warming kicks of processes that serve to mitigate the warming and keep both tropics and poles relatively stable?
Alan Cheetham says:
May 22, 2011 at 8:26 pm
“Interesting also how the idealized conveyor belt figures get the North Atlantic flow backwards -i.e. the warm flow should be northward on the western side of the Atlantic (the Gulf Stream).”
Good point! It does seem contrary. Perhaps it does not show the surface/near surface Gulf Stream Current that flows north to Cape Hatteras and thence to the Grand Banks but only the underlying deep cold N to S current?
AMOC isn’t the driver and the North Atlantic isn’t the center of the universe:
http://wattsupwiththat.com/2011/05/22/arctic-cycles-amopdo-corresponds-to-arctic-station-group/#comment-666101
NBC, this is new to me. I thought we had the climate and all her processes nailed.
I see the cold current has whisked my country clean off the map.
( about 1200 miles east of Oz )
This explains our (Broome, W.A.) above average temperatures in the sea between here and Indonesia for the previous 2 years. Since the beginning of the last wet season, this changed and since the end of December, our mean temperatures are below the long term mean, March was much colder http://pindanpost.com/2011/04/19/cold/ than normal, and April more than 2 C colder than last year and the year before.
Warwick Hughes has a new post up about the Australian temperatures over the last few months.
R Gates said, This should help to keep the current nice and warm and easily counter act the cold fresh water pouring off of a melting Greenland.
Do you have more information or is this the output of a computor program?
@ur momisugly R Gates
Could you provide estimates, please, of how much water is melting from Greenland per unit time. And then some relationship of that volume to objects we can understand?
Thanks,
R.Gates jumped in the water with his belt and whistle… LOL
Meanwhile this notion of conveyor belt was quite beaten up recently through realizing that there are many regional circulations… ref?
The Atlantic ‘conveyor belt’ current is a fascinating feature of Earth’s climate. I don’t see how you could claim to understand or predict the climate without detailed knowledge of its pace.
How much heat would that current transport per year? I am quite interested in that amount. Could that amount possibly be large enough to act as negative feedback?
I think the “Argonne National Laboratory” wins this this week’s prize for “Lousy Unhelpful Scientific Diagram”.
New Zealand was clearly inconvenient and so got wiped off the globe, which is criminal considering how beautiful that country is.