From Eurekalert: Earth’s climate change 20,000 years ago reversed the circulation of the Atlantic Ocean
Global warming today could have similar effects on ocean currents and could accelerate climate change
The Atlantic Ocean circulation (termed meridional overturning circulation, MOC) is an important component of the climate system. Warm currents, such as the Gulf Stream, transport energy from the tropics to the subpolar North Atlantic and influence regional weather and climate patterns. Once they arrive in the North the currents cool, their waters sink and with them they transfer carbon from the atmosphere to the abyss. These processes are important for climate but the way the Atlantic MOC responds to climate change is not well known yet.
An international team of investigators under the leadership of two researchers from the UAB now demonstrates the response of the Atlantic MOC to climate change in the past. The new research results will be published on 4 November 2010 in the international front-line journal NATURE. The research project was led by Rainer Zahn (ICREA researcher) and Pere Masque, both of the UAB at the Institut de Ciència i Tecnologia Ambientals (ICTA) and Department of Physics. With collaborators at the universities of Seville, Oxford and Cardiff (UK) they investigated the distribution of isotopes in the Atlantic Ocean that are generated from the natural decay of uranium in seawater and are distributed with the flow of deep waters across the Atlantic basin. The young investigator Cesar Negre studied the natural abundance of these isotopes in the seafloor sediments 2.5 km deep in the South Atlantic and achieved a PhD degree in the Environmental Science and Technology doctoral programme at ICTA.
The study shows that the ocean circulation was very different in the past and that there was a period when the flow of deep waters in the Atlantic was reversed. This happened when the climate of the North Atlantic region was substantially colder and deep convection was weakened. At that time the balance of seawater density between the North and South Atlantic was shifted in such a way that deep water convection was stronger in the South Polar Ocean. Recent computer models simulate a reversal of the deep Atlantic circulation under such conditions while it is only now with the new data generated by UAB scientists and their colleagues from Seville and the UK that the details of the circulation reversal become apparent. This situation occurred during the ice age 20,000 years ago.
Although this was far back in time the results are relevant for our climate today and in the near future. The new study shows that the Atlantic MOC in the past was very sensitive to changes in the salt balance of Atlantic Ocean currents. Similar changes in seawater salt concentration are expected to occur in the North Atlantic in the course of climate warming over the next 100 years. Therefore the data to be published in Nature offer the climate modelling community the opportunity to calibrate their models and improve their capacity to predict reliably future ocean and climate changes.
The research has been funded by the Spanish Ministry for Science and Innovation (MICINN).
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This is just the usual press release with no link to the paper and no real scientific details to go with it, allowing compliant media minds to reprint it without questioning it. I’ll be interested to find out how they determined this reversal. If anybody locates a copy of the paper, please leave a note in comments.
I also think this headline could be true:
Atlantic Ocean ocean current reversal 20,000 years ago changed the Earth’s climate.
– Anthony
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M White says:
November 4, 2010 at 11:42 am
If the atmosphere was cooled and liquified then added to the worlds oceans, I’d be interested to know what fraction of the combined volume the atmosphere would be?
I can’t see it being much. This is why I would say it is the Oceans that have the biggest effect on our climate.
This statement just seems stupid “Global warming today could have similar effects on ocean currents and could accelerate climate change”
========
Stability of the Atlantic meridional overturning circulation in a zonally-averaged ocean model: the effects of freshwater flux, wind stress, and diapycnal diffusivity
Draft, 17 January 2010
http://earth.geology.yale.edu/~avf5/publications_pdf/SevellecFedorov.AMOC.2D.2010.pdf
“78 Although these results are typically reproduced by other models, the details of the simulations such as the amount of freshwater needed for the collapse of the AMOC, the magnitude of climatic impacts, or the role of the winds over the Southern Ocean vary from one model to the next. As a result, the 21st century projections for AMOC changes summarized in the IPCC AR4 reveal a strong discrepancy between coupled models. These issues bring about several important questions: How do we test the models? Which factors determine the sensitivity of the AMOC to the freshwater and other forcings in a given model? What is the relative importance of different processes in bringing deep water from depths back to the surface? To answer these questions we need to look at what determines ocean thermal structure and the properties of ocean meridional overturning.”
“120 The stability of the overturning circulation subject to a steady freshwater forcing has been a subject of numerous studies, starting with a box model by Stommel (1961) who showed the existence of multiple-equilibria in the system with a bistable regime. That is, a regime with two types of stable steady-state solutions – a strong circulation corresponding to the active AMOC (the on-state) and a weak circulation with the collapsed AMOC (the off-state). These results have been confirmed by direct integrations of zonally-averaged models (Stocker and Mysak, 1992; Schmittner and Weaver, 2001; Ganopolski and Rahmstorf, 2001), ocean GCMs (Rahmstorf, 2000; Hofmann and Rahmstorf, 2009; Prange et al., 2003; Nof et al., 2007), and intermediate complexity coupled models (Rahmstorf et al., 2005). Similarly, the so-called continuation techniques find AMOC steady-states in ocean GCMs without the need to use time integrations (e.g. Weijer et al., 2003; Dijkstra and Weijer, 2003).”
A prediction of what will happen in the future requires an understand of what caused the past paleo climatic changes.
Or, to know how it works the world. It was always known, as traditional symbols show, until some chose to forget and others said it was for us impossible to know (Agnosticism, a movement to govern upon people thanks to people’s ignorance). See
http://www.scribd.com/doc/40514613/Unified-Field-Explained-8
I forgot to cite William says:
November 4, 2010 at 11:47 am
Re: M White says:
November 4, 2010 at 11:42 am
“If the atmosphere was cooled and liquified then added to the worlds oceans, I’d be interested to know what fraction of the combined volume the atmosphere would be?”
The troposphere averages ~18 mm/M^2 of precipitable water relative to the surface. If this water was instantly condensed and added to the ocean only, it would add 23.4 mm of depth to the ocean. The average depth of the ocean is 3790 M (although estimates vary widely and it is actually unknown). The water from the troposphere would equal ~6.2 millionths of the combined volume.
“the way the Atlantic MOC responds to climate change is not well known yet.”
That’s as far as I need to read this article.
OT — Its official, this is going to end badly (Ice Age):
Counteracting Global Warming: A Good Idea?
November 4, 2010 by doncorrigan
http://into-nature.com/2010/11/04/counteracting-global-warming-a-good-idea/
Some climates scientists and geo-engineers say America’s political system is too dysfunctional to ever address long-term problems like global warming.”
Therefore, technologists in other countries are exploring ways to lower the earth’s temperatures. One plan involves aerosoling tiny, reflective particles into our skies to deflect the sun’s heat. Another has robotic ships shooting salt water into ocean clouds to deflect sun heat and to stabilize planet temperatures.”
These technologies are now being developed in the European Union, China and Canada. Lest you think this is all a sci-fi pipe dream, David Keith of an environmental systems group in Calgary said plans are well along for the new technology, and a major investor is Bill Gates.”
This can be explained with one word.
No, not plastics
I'm surprised it hasn't come up before. Prior comments have alluded to it, but nothing quite has the impact. Nothing quite explains just how significantly mankind's emissions have altered or will alter the earth's climate.
What is that one word?
Chronoconnections
😉
Peter Taylor:
The science daily article predicted that the reversal would happen again within 100 years, but it was not convincing to me.
Any insight?
The article indicated a reversal that occurred 20,000 years ago is expected to occur again in the next 100 years, but the explanation of why was not convincing. The abstract did not say anything about a change over the next 100 years. The change is predicted in a model due to sea water salt concentrations, but the reversal 20,000 years ago occurred when the climate of the North Atlantic region was substantially colder and deep convection was weakened. It is not clear that current conditions over the next 100 years will be the same as they were 20,000 years ago
The Science Daily article claimed the study was relevant because:
“The study shows that there was a period when the flow of deep waters in the Atlantic was reversed. The results are relevant for the near future since similar changes are expected to occur in the course of climate warming over the next 100 years.”
Later in the article:
“The study shows that the ocean circulation was very different in the past and that there was a period when the flow of deep waters in the Atlantic was reversed. This happened when the climate of the North Atlantic region was substantially colder and deep convection was weakened. At that time the balance of seawater density between the North and South Atlantic was shifted in such a way that deep water convection was stronger in the South Polar Ocean. Recent computer models simulate a reversal of the deep Atlantic circulation under such conditions while it is only now with the new data generated by UAB scientists and their colleagues from Seville and the UK that the details of the circulation reversal become apparent.
This situation occurred during the ice age 20,000 years ago. Although this was far back in time the results are relevant for our climate today and in the near future. The new study shows that the Atlantic MOC in the past was very sensitive to changes in the salt balance of Atlantic Ocean currents. Similar changes in seawater salt concentration are expected to occur in the North Atlantic in the course of climate warming over the next 100 years. Therefore the data to be published in Nature offer the climate modelling community the opportunity to calibrate their models and improve their capacity to predict reliably future ocean and climate changes.”
This is all computer modeling you need to take with a grain of salt. I have never heard anything good about climate models and expect this to be more of the same. They apparently had some studies of reaction products of uranium disintegration from the ocean floor and decided to model how they got there. What we need to know is not what happened during the ice age but what happened at the turn of the twentieth century. That is the time when the reorganization of the North Atlantic current system started bringing warm water to the north and melting the Arctic. That, and not some greenhouse effect is why sea ice is diminishing.
William
November 4, 2010 at 11:47 am
Interglacials have in the past lasted roughly 12,000 years, not 20,000 years as stated above. The past interglacials have ended abruptly.
##
That means the next ice age starts the day before, the day after tomorrow!
Darn, I was kinda hope’n that it might get a little bit warmer ‘fore the next big freeze. Seems like we never quite made it out of the last one.
More info on the study:
http://www.nature.com/nature/journal/v468/n7320/abs/nature09508.html
Looks like “everything but the main text.” Abstract, Author info (Affiliations, Contributions), and, most important:
Note: File is labeled PDF, downloads fine, my non-Adobe viewer identifies the actual file within the PDF as a Microsoft Word document. Looks nice and informative.
Wow, peer-reviewed published climate science literature with freely-available data and equations, provided up front. Who didn’t get the memo? 😉
William says:
November 4, 2010 at 11:47 am
Interglacials have in the past lasted roughly 12,000 years, not 20,000 years as stated above. The past interglacials have ended abruptly.
The span of an interglacial (the warm period) may deviate from the factors and events which create and end them. In other words; a change which starts the warming toward the interglacial will begin long before the warmth of an interglacial is reached.
During the depths of the last glacial period several relatively minor warming events occurred. The last one, the one that warmed all the way into the holocene began about 18,000 years ago. The possibility the warming was due, to some extent, by a major change in oceanic circulation which started changing 20,000 years ago (2,000 years prior to evident warming) is quite real.
Allow me to go back to the 18,000 year figure for a moment, a reason why I refer to it. Interglacials are periods of non-exact time span just like the glacial cycles. “Average” periods of durations are what is generally cited. I view the calibration, sequencing, a bit different. Present day temperatures are pretty much at the lower end of interglacial temps. Using the temps of the LIA as the ‘crossover’ point; with each interglacial the span from when the final warming during the depths of glaciation started to the time when the following interglacial ended is consistently roughly 18,000 years. The period it takes to warm up into an interglacial will vary, the period from the interglacial maximum to the re-entry into glacial may vary. However, the total time span of 18,000 years is quite constant.
Why it that important (to me anyway)? Since the duration of the interglacials vary considerably, and the duration from interglacial maximum to re-entry into glacial varies considerably one cannot, by standard sequencing, determine at what point in the holocene we are at. When will it end?
The Milankovitch cycles certainly play a large role, but, are not enough to explain the glaciation periods in full. Entry into glaciation is very difficult to correlate with the cycles. The numbers just don’t add up to establish a proper accounting. Hence, other factors must be involved. Oceanic circulation is a likely candidate for at least one of, if not one of the major, factors. Those are events which will occur with or without any influence by man.
The holocene has been an interglacial with a relatively stable climate in comparison to others. This may be, to my interpretation, due to the Younger-Dryas. Despite the obvious impacts it seems, again to me, that the Younger-Dryas mitigated / retarded some of the interglacial warming which would have otherwise occurred. With the Holocene climatic optimum being relatively cool the climate, rather than dropping right off, dropped slightly and then essentially stabilized. Man has been spoiled by the graces of nature…. for now. The true general climate of earth is not as gracious a host to man as we have become accustomed to.
I did an article on that quite some time ago. It was poorly done I must admit. Perhaps it is time to revisit the topic and generate one of better quality.
Earle Williams says: “Chronoconnections”
Enlighten us Earle. Google is no help. What’s up with Chronoconnections?
““The study shows that the ocean circulation was very different in the past and that there was a period when the flow of deep waters in the Atlantic was reversed. This happened when the climate of the North Atlantic region was substantially colder and deep convection was weakened.”
Talk about a statement of the blindingly obvious. 20,000bp was in the middle of the last ice age. So yes – the climate of the North Atlantic Region was substantially colder. Indeed it was cold to the level that the polar ice sheet extended South to New York and covered UK. An Arctic ice sheet of this extent might just alter almost all the prevailing winds, the North Atlantic Drift and the MOC – is this a surprise to anyone?
How can this be?
There is no mention of CO2 in connection to research about climate change. These guys must have it wrong. Antony I think you’re right to suggest an alternative title. It’s generally the speculation that goes beyond the data that angers me most.
It certainly looks like system variability as a driver of climate could be an option. I’d be interested how AGW theory explained climate change 20,000 years ago.
To partly answer my own question here’s something from the Geological Society’s recent document on the subject.
“How did levels of CO2 in the atmosphere change during the ice age?
The atmosphere of the past 800,000 years can be sampled from air bubbles trapped in Antarctic ice cores. The concentrations of CO2 and other gases in these bubbles follow closely the pattern of rising and falling temperature between glacial and interglacial periods. For example CO2 levels varied from an average of 180 ppm (parts per million) in glacial maxima to around 280 ppm during interglacials. During warmings from glacial to interglacial, temperature and CO2 rose together for several thousand years, although the best estimate from the end of the last glacial is that the temperature probably started to rise a few centuries before the CO2 showed any reaction. Palaeoclimatologists think that initial warming driven by changes in the Earth’s orbit and axial tilt eventually caused CO2 to be released from the warming ocean and thus, via positive feedback, to reinforce the temperature rise already in train28. Additional positive feedback reinforcing the temperature rise
5
would have come from increased water vapour evaporated from the warmer ocean, water being another greenhouse gas, along with a decrease in sea ice, and eventually in the size of the northern hemisphere ice sheets, resulting in less reflection of solar energy back into space.”
Louis Hooffstetter says:
November 4, 2010 at 4:47 pm
Earle Williams says: “Chronoconnections”
Enlighten us Earle. Google is no help. What’s up with Chronoconnections?
Louis,
You may be aware of the concept of teleconnections, where a cause and effect are seperated by distance. This distance is sufficient that absent the presumed teleconnection the two would appear to be unrelated.
Now you are ready to understand the concept of chronconnections. Cause and effect that are seperated by time. Chronoconnections, being a post-normal creation of climate science, are not constrained by the quaint notion that time flows in but one direction. Such notions are relics of the fossilized “empricial” science hegemony.
So it is now crystal clear how the unprecedented man-made CO2 pollution of the last two centuries is chronoconnected to the Atlantic reversal circa 20,000 years BCE in a causal fashion.
Bah, try to be clever and you mispell “empirical”!
😉
Espen says:
November 4, 2010 at 8:58 am
20000 years ago the last glaciation was still going strong, so the climate was very different and less stable: Climate during a glaciation is unstable climate. Climate during an interglacial is stable climate. Still these scare stories – that AGW may cause similar “disruptions” – pop up again and again.
I must disagree, in part. 20,000 years ago was just a tic in geologic time (about 2,000 years) prior to the warming event which resulted in warming into the holocene. In essence, the last glacial period was ending.
Stable vs non-stable climate as related to glacial and interglacial periods. I would tend to say that one (interglacial) is warmer and one (glacial) is colder. Though storm tracks and events may differ the climate during the two is ever changing and at about the same or similar rates.
The Holocene, our interglacial, has indeed been one of relatively consistent climate when compared to other interglacials. Man has been fortunate. The stability of the Holocene may be due to the Younger-Dryas interrupting the warming toward the interglacial (Holocene) maximum. With the climate not attaining the warmth it otherwise would have, dynamics changed, and the climate of the Holocene stabilized. Had it not been for the Younger-Dryas the temperature trend for the Holocene may have been more of an up and down spike.
Had the Holocene climatic maximum been 1.5 to 3 C warmer than it was the climate today could very well have been quite different. It is ‘possible’ that the only reason we are not clearly dropping into the next glacial period presently is due to the low temperatures of the maximum.
That said, the transition from interglacial to glacial has been stated by some to be a period of great variability, turbulence, and unpredictability of climate. That does, in a way, make sense due to the fact that numerous elements of climate dynamics would be changing. When I look at a marked difference in how the Arctic and Antarctic are behaving in contrast to other geologically recent times of similar global temperatures, and I note various changes in temperature trend patterns, it is evident (to me) that the nature of our climate is changing. Climate is always changing, the nature of it, how it is behaving now appears to be undergoing a change. A change that many may be misinterpreting.
Why would they be misinterpreting? Because they are trying to make a seven layer cake with only 2 ingredients.
Now I wait for a supporter of CAGW to state that increased warming at the time of the Holocene Climatic Optimum could not result in cooling or more rapid cooling.
To add to the discussion: Changes in oceanic currents, as well as changes in the temperature of those currents (and I am talking about the overturning currents) can be impacted by sudden influx of fresh water. This occurs when climate warms. The paradox is the abruptness of fossil evidence of this change. While the climate may warm slowly, the sudden change in currents happens because of sudden breaks in continental ice jams (think state-sized and bigger). We aren’t talking about an ice jam that suddenly breaks and releases river-sized flows. We are talking about huge ice jams that have kept great-lakes sized and bigger ponds at bay. Till that is, the ice jam breaks. It doesn’t take forever for that fresh, low-salt water to reach the ocean. And the breaks tend to occur fairly close to each other even though the ice jams may be on different continents. That’s a lot of fresh water suddenly flowing into the ocean.
If continents weren’t in the same positions 20,000 years ago so why would we expect the ocean currents to flow the way they do today? Heck tomorrow a massive upheaval under the ocean might change the currents. Seems a whole lot more likely a cause to me then a painfully slow infusion of fresh water in salt water. Nature does slow very well, its catastrophic that it changes for.
They do not understand the process but they can model it? Haven’t we already travelled down this cul-de-sac?
RE:
pkatt says:
November 4, 2010 at 10:31 pm
Certainly geographic changes affect both ocean and atmospheric currents. Even our cities with their tall buildings, change in thermals, etc. most likely have some (albeit minor) influence. Continental drift, for the most part, however is a slow (very slow) process. Australia is moving north at what?….. 1/4 inch per year or about 418 feet over 20,000 years. Would that alter currents slightly? Yes. Enough to generate noticeable and attributable change?
There is another influence over time. Sea level and coastlines. It is cited that the sea level around Australia was more than 350 feet lower 20,000 years ago. Sydney, rather than being a coastal port, would have been about 15 miles inland. Most, if not all of the present Australian coast would be far inland. Hence the change in currents due to geographics between then and now would be much more significant due to sea level rather than 418 feet of drift. Lower sea levels would also mean that subsurface geographic features could / would have greater influence on currents and climate.
At least, those are my thoughts on the matter.
Having looked into this more, they are talking about the deep, deep ocean circulation, not the surface currents.
In the Atlantic, Antarctica produces the densest, coldest water and this dominates the flow at the very bottom of the Atlantic. It doesn’t really flow too far though and kind-of just reaches an equilbium point at about 30N, two-thirds up the Atlantic.
The North Atlantic deep water is next in density and dominates the mid-deep ocean flow. Because this flow can continue on and enter other deep ocean flows thoughout the planet (and mix in with other mid-depth deep water around Antarctica), it can flow by Africa etc.
http://web.me.com/uriarte/Earths_Climate/Appendix_4._Ocean_currents_files/p237.jpg
http://www.clivar.org/organization/southern/images/lumpkin.jpg
I think this study is just saying the Antarctic deep water also dominated the mid-depth flow. It wouldn’t make much difference anyway – it is not going anywhere. Wally Broeker outlined how this circulation would probably change decades ago already although this chart is not quite what this study says occurred.
http://oceanworld.tamu.edu/resources/oceanography-book/Images/nao-en_33957.jpg
Will Crump – you ask for any insights on the current reversal –
There are two factors that ‘warming’ might induce: warmer surface waters in the North Atlantic zone of downwelling; and freshening of the North Atlantic due to either glacial melt or increased river flows in the Arctic Basin.
As far as I can tell, the warm surface waters get entrained in the downwelling of the much colder Arctic bottom water, and do not constitute a major part of the larger conveyor system – rather, the North Atlantic gyre accumulates warm water to about 200m depth, and I think this warm water pool is periodically diminished/enhanced by differential heat transfer to the atmosphere (something I put forward in the ‘Ocean Cycles’ chapter in ‘Chill’.).
With regard to freshening – this was reported by Dickson et al in 2002:
Dickson B. et.al. (2002) Rapid Freshening of the Deep North Atlantic Ocean Over the Past Four Decades Nature 416, April 25, 2002.
but this trend appears to have reversed:
Hátún H. et al (2005) Influence of the Atlantic Subpolar Gyre on the Thermohaline Circulation Science 309: 1841-1844
Likewise, the slowing down of the THC reported by:
Bryden H.L. et al.,( 2005). Slowing of the Atlantic meridional overturning circulation at 25ºN. Nature 438, 655-657.
is not regarded as consistent:
Knight J.R., et al., (2005). A signature of persistent natural thermohaline circulation cycles in observed climate. Geophysical Research Letters 32, doi:10.1029/2005GL024233.
And so, despite the warming and freshening of the North Atlantic in recent decades, the THC has both slowed down and speeded up. The expectation from sediment data is that the bottom deepwater circulation speeds up during warm periods, yet the recent major warm period in the North Atlantic coincided with a slowing down.
We should note that it takes the bottom water about 30 years to move 1000km. So measurements taken at different parts of the Atlantic – such as Norwegian data on the downwelling zone, and Bryden’s data further south, are not rally going to inform us of the true dynamic.
Thanks Peter Taylor