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.
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?
@ 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.
So the ice is not melting after all…
Thar ya go John A, NZ restored. I can’t quite work out how the water passes over Borneo.
Had no time to read whole of the article, but I welcome it. I think no natural climate change can be understood without understanding what is going in the North Atlantic. I wrote about some aspects of it in my post:
http://wattsupwiththat.com/2011/05/20/indirect-solar-forcing-of-climate-by-galactic-cosmic-rays-an-observational-estimate/#comment-665614
and our resident ‘know everything expert’ responded with usual phraseology, nothing to do with sun.
We know that the conveyor does stop, or slow drastically, at times we have scant data about though it may be a reason why ice ages can be severe in NW Europe. Climate change is probably not a reason for the conveyor changes. Could be tectonic plate speed changes. Give me a grant and I will assemble a team of scientists to study the problem(sarc).
So, essentially, oceans drive climate but oceans are rivers driven by the rotational and gravitational forces of the planet and steered by the movements of land upon the tectonic plates.
Note to next doomsday workshop: How to stop all tectonic plate movement to save us all from catastrophic change? “Make reference to Japan, and the children.” dumdeedum.
Alan Cheetham says:
May 22, 2011 at 8:26 pm
I was going to ask/rant about this.
Is this a case of graphics artists using bogus drawings produced by previous graphics artists who didn’t live near the Atlantic and don’t know about the Gulf Stream? Perhaps they knew better but simplified the drawing to make it look less busy.
It would be nice to find a good source or perhaps someone here has tools, skills, and time to come up with a more accurate sketch.
BTW, http://www.anl.gov/OPA/frontiers/d8ee2.html doesn’t work (File not found). I might Email them and ask about what they did with the Gulf Stream and if other parts of the map are wrong.
Well I think the Coriolis effect may have a bit to do with all this…..
TomRude wrote (May 22, 2011 at 11:35 pm)
“Meanwhile this notion of conveyor belt was quite beaten up recently through realizing that there are many regional circulations… ref?”
While I suspect you might mean referee (you did mention a whistle):
Yes, please share the reference.
DR says:
May 23, 2011 at 6:18 am
Well I think the Coriolis effect may have a bit to do with all this…..
More than a bit. If what I’ve been looking into is correct, the Earth’s ocean circulation isn’t driven by a ‘heat engine’ after all, but by internal tides deriving their energy from the rotation of the planet, and the topography of mid ocean ridges – the Coriolis effect.
http://tallbloke.wordpress.com/2011/05/23/how-solar-energy-gets-mixed-into-the-deep-ocean-internal-tides/
Sediment studies from the Gulf around Florida have indicated that the Atlantic Conveyor weakens during cold periods, not warm. It seems counter-intuitve unless you understand thermodynamics. It actually makes sense: heat engines rev up when temperature differences are greatest and ramp down when temperatures are colder and differences less.
Charles Higley says:
May 23, 2011 at 6:37 am
Sediment studies from the Gulf around Florida have indicated that the Atlantic Conveyor weakens during cold periods, not warm.
Could it indicate less organic life depositing the sediments instead?
“The Arctic is a region with a radiation deficit. It radiates more energy into space than it receives from the Sun. This deficit is covered by the convection of heat energy from warmer regions. If that convection of heat into the Arctic were reduced then the Arctic temperature would decline and thus its radiation of energy into space would decrease until a balance is reached. On the other hand if the net inflow of energy into the Arctic is increased then the temperatures would rise, again until a new balance is reached.
If the effects of an increase in Arctic temperatures results in a reduction of the convection of heat into the Arctic then the new balance reached for a net increase in radiation energy would involve less of a change in temperature than would occur without that reduction in convection. It is a simple case of negative feedback.”
Instead of a normal negative feedback mechanism the global warming alarmists have a model producing “no feedback until the Arctic ice is melted then suddenly the the thermohaline circulation is shut down including the Gulf Stream. The convection heat inflow suddenly drops and with it the net energy inflow. The radiation outflow then has to drop to match the decreased energy inflow. Thus this scenario has the end result of a lower temperature and energy outflow than was the initial state. This is a ridiculous scenario that only true believers of a quasi-religious dogma could accept and only charlatans could promote. ”
See
http://www.sjsu.edu/faculty/watkins/thermohaline.htm
Every sailor since Columbus has known that the current in the North Atlantic Ocean flows in a clockwise direction.
tallbloke says:
May 23, 2011 at 6:32 am
“If what I’ve been looking into is correct, the Earth’s ocean circulation isn’t driven by a ‘heat engine’ after all, but by internal tides deriving their energy from the rotation of the planet, and the topography of mid ocean ridges – the Coriolis effect.”
That is far from correct. The primary oceanic circulation is wind-driven and the winds are the product of the pressure gradients created by differential heating of the planetary surface. Like so many other things in “climate science,” secondary and tertiary adjuncts such as THC and AMOC have been elevated to a position of importance that they do not physically possess. The “great conveyor belt” pictured here and elsewhere is an artist’s impression; there is no great warm surface currest flowing northward in the the tropical mid-Atlantic. Nor do cold waters rise from the abyss to the surface in the middle of any ocean. As for the Coriolis effect, it is just that–an effect of conservation of angular momentum in an inertial reference frame upon the trajectories of motion with a meridional component viewed in an earthbound reference frame. It isn’t an actual force capable of initiating any motion.
sky, as always, thanks for your sensible comments (May 23, 2011 at 11:52 am).
What the mainstream appears to have overlooked is very simple:
Solar max interrupts the semi-annual heat pump. The frequency of pump outages controls multidecadal oscillations (via hydrology). Interannual spatiotemporal chaos makes this difficult or impossible to see using linear methods.
@tallbloke, sky
Both wrong, its not the coriolis force or winds that drive the deep circulation that is being discussed here; it is downwelling.
There are more downwelling areas than shown in the above figure which is a gross simplification, e.g. In the southern ocean – but a major one is the Norwegian sea. Surface cooling and ice formation create near-freezing hypersaline water which sinks to the bottom, driving THC including AMOC.
Variation in downwelling can periodically force long term nonlinear oscillation in the THC and thus global climate, providing a route for instance for solar and other astrophysical weak nonlimear forcing over century timescales..
BTW downwelling for instance in the north east Atlantic complicates the interpretation of SSTs, as cold water is sucked down and exits the picture. Thus while N Atlantic SSTs have often looked high in recent years, N Atlantic OHC is in a nosedive.
“They confirm this using a climate model simulation”
I am sorry, but a climate model simulation is confirmation of nothing!!! Has its skill at representing ocean energy balance and currents been proven? Hell no! The hypothesis remains un-confirmed, and therefore, cannot be used to infer observational data sets!!!
It should read “this compares with climate model simulations, however, there ability to correctly replicate ocean currents is limited / poor / un-tested”
Whats with all these papers passing peer review? My peers are incredibly skeptical of ANY modelling and would never allow a model run to be used as confirmation of any hypothesis!!! Madness
@phlogiston wrote May 23, 2011 at 4:49 pm
Are you suggesting this is independent of wind?
Paul Vaughan says:
May 24, 2011 at 6:23 am
@phlogiston wrote May 23, 2011 at 4:49 pm
Are you suggesting this is independent of wind?
No – nor BTW would I exclude an effect of the Coriolis force (every movement on earth, even spitting or peeing, is moved to the right or the left by the Coriolis force).
Wind and oceanic upwelling / downwelling can interact directly and even engage in a positive feedback. Going back to the earlier post on the ENSO as a Belousov-Zhabotinsky reaction type of nonlinear oscillator, in this article I proposed a positive feedback involving Peruvian coast upwelling and the trade winds, only to be gently informed by Bob Tisdale later that this feedback was already well established and a name exists for it – the Bjerknes feedback:
http://stratus.astr.ucl.ac.be/textbook/chapter5_node4.xml
phlogiston says:
May 23, 2011 at 4:49 pm
You totally miss the fact that my remarks were directed to tallbloke’s conjectures about ocean circulation in general. Nowhere do I suggest that gravity-diven THC is non-existent. I clearly state that it is a secondary adjunct to the wind-diven global surface circulation, which is clockwise in the N. H. and counterclockwise in the S.H. due to the Coriolis effect. The sluggish, diffuse deeper circulation is oders of magnitude less important to climate than surface currents. And upwelling of cool water from depths is definitely a wind-driven process in which the Coriolis effect plays a role. These are basic oceanographic facts that everyone should get acquainted with before attempting to tackle any nonlinear complexities.
sky, please feel welcome to load us up with links to concise reading material (either now or in the days & months ahead as convenience permits). I get the sense that you are one of few WUWT commenters who might be able to straighten the community out on ocean circulation. Thank you.
Paul,
I realize that internet links and graphs are highly favored in the blogosphere. Unfortunately, as a working scientist with limited web-surfing skills, I simply cannot take the time to track down or produce such. Much of the material found on the internet is mistake-riddled pop-sci anyway. Moreover, what I say is often based on field measurements that are not in the public domain. Thus, aside from the occasional reference to monographs or well-known websites, I can offer little more than a succint statement of my professional views . BTW, there is a monograph by a Chinese author on “Wind-driven and Thermohaline Circulation” published by Cambridge UP a couple of years ago, which I haven’t seen yet, but might fit your desires better. For a less-technical introduction, there’s always an appropriate chapter in Dietrich’s “General Oceanography,” who, unlike many academic authors nowadays, has been there and done that.
sky says:
May 24, 2011 at 1:43 pm
phlogiston says:
May 23, 2011 at 4:49 pm
Of course you’re right about the role of wind in ocean currents, although I would contest your assertion that the deep THC is unimportant, its just that we dont yet understand how it exerts its effect (not the same thing). But to suggest that the movement of the vast majority of the worlds ocean water containing practically all the heat of atmosphere and ocean is unimportant to climate and global temperature is like, well – in the scientific / scholarly sense, well expressed metaphorically by a quote from Rimmer in Red Dwarf:
“Flopping your wedding tackle in a lion’s mouth then flicking its love spuds with a wet towel”
or in other words “unsafe”.
Furthermore, the point I made in an earlier post about Bjerknes feedback:
http://stratus.astr.ucl.ac.be/textbook/chapter5_node4.xml
http://www.mendeley.com/research/haushaltsforum-fr-eingeladene-interessenvertetergruppen-26-februar-statement-ob-mhlenfeld/
Wind and upwelling combine in a time-limited positive feedback. Wind causes upwelling, but upwelling also causes wind (by creating SST gradients).
phlogiston says:
May 25, 2011 at 12:26 pm
“…to suggest that the movement of the vast majority of the worlds ocean water containing practically all the heat of atmosphere and ocean is unimportant to climate and global temperature is…”
I’m suggesting nothing of the kind. Well-developed western boundary currents extend several hundred meters downward. Celsius surface temperatures are typically in the upper 20s and current speeds well in excess of 1m/sec are commonplace. At depth, say >500m, temperatures are in single digits and, after back-and-forth tidal streams are filtered away, you’re lucky to find speeds greater than a few cm/sec. Do the math in terms of rates of thermal transport to gauge the relative importance.
I think you can get a better idea of the “shape of the AMOC” by taking a polar view:
http://en.wikipedia.org/wiki/File:Conveyor_belt.svg
In that, you can see how the Antarctic Circumpolar Current is central to the whole thing (as is the sinking – [ I hate that over affected term “downwelling” ] – of the cold water there)
The “loops” out in the various other “oceans” (remember that from a south pole view it’s all just one giant ocean…) are more like eddies and side currents. Diversions in the “race around antarctica”.
http://chiefio.wordpress.com/2010/12/22/drakes-passage/
http://chiefio.wordpress.com/2010/12/09/does-antarctic-wind-dominate/
For a good chuckle while trying to figure out how the currents work, here is a list of the 10 (yes TEN) different models that try to get it right:
http://en.wikipedia.org/wiki/List_of_ocean_circulation_models
“This time for sure” comes to mind…
This picture gives a good basic idea of what is happening on the surface:
http://en.wikipedia.org/wiki/File:Corrientes-oceanicas.gif
(with hot and cold surface currents marked)
Though any time things go near an island they get a bunch of odd eddy currents in them. You can see that in the upper image of surface currents in that link posted above:
http://er.jsc.nasa.gov/SEH/Ocean_Planet/activities/ts2siac2.pdf
The “simple” fact is that to have a handle on the ocean currents takes a 3-D current model and involves ALL of solar heating, evaporative cooling, conductive cooling, radiative cooling, ice formation, salinity changes (evaporative AND fresh water dilution), corriolis, topgraphy (including surface drag and eddy induction / drag), wind drag, precipitation and cloud impacts.
And probably some more I’ve forgotten.
As they say “good luck with that”…
IMHO, we can observe it, but we sure can’t ‘splain it worth a …. penny farthing…