AMOC slowdown

[bbr2314]

Yesterdays article by Ramstorf.
http://www.realclimate.org/index.php/archives/2018/05/if-you-doubt-that-the-amoc-has-weakened-read-this/

In the comments Ramsdorf seems to dismiss Greenland melt's impacts.... I would say that is quite incorrect...

[sidd]

In the response he indicated that melt has impact on surface salinity but not on largescale temperature.

"[Response: You mean by cold meltwater from Greenland flowing in? You can work that out from a simple heat budget calculation. The amount is far too small to matter for the large-scale sea surface temperature, but enough to matter for sea surface salinity. -Stefan] "

I did a simple heat calculation, and i agree with him.

sidd

[bbr2314]

In the response he indicated that melt has impact on surface salinity but not on largescale temperature.

"[Response: You mean by cold meltwater from Greenland flowing in? You can work that out from a simple heat budget calculation. The amount is far too small to matter for the large-scale sea surface temperature, but enough to matter for sea surface salinity. -Stefan] "

I did a simple heat calculation, and i agree with him.

sidd

What about snowmelt from adjacent areas in North America as well? I think a look at recent evolving SSTAs shows this is indeed a major factor...

I would also add that contrary to his research, you can see the pulse of high heights begin to rise off the East Coast of North America in July / August / September rather than in wintertime (each and every year, most recently). Again, this supports a greater relationship with melt (IMO).

[bbr2314]

See attached -- I would be extremely surprised if the residual albedo anomalies due to extra extant land-snowcover and the melt from that extra SWE/Greenland are unrelated to the worsening NATL anomalies we have seen this month. The currents may be the driver, but the situation ^^^ has, IMO, been a major aggravator to the current appearance.

[sidd]

The graf in the post above is air temperature. SST is more appropriate in AMOC/Rahmstorf context.

sidd

[Richard Rathbone]

In the response he indicated that melt has impact on surface salinity but not on largescale temperature.

"[Response: You mean by cold meltwater from Greenland flowing in? You can work that out from a simple heat budget calculation. The amount is far too small to matter for the large-scale sea surface temperature, but enough to matter for sea surface salinity. -Stefan] "

I did a simple heat calculation, and i agree with him.

sidd

Stefan's being a little disingenuous here. It makes a big difference to the cooling whether the ice melts on shore and meltwater enters the sea, or whether icebergs fall off Greenland and the ice melts at sea. Hansen reckoned that cooling was important enough to hose with a berg/meltwater mix rather than the traditional meltwater only, and I'm inclined to accept his judgement on it.

[bbr2314]

In the response he indicated that melt has impact on surface salinity but not on largescale temperature.

"[Response: You mean by cold meltwater from Greenland flowing in? You can work that out from a simple heat budget calculation. The amount is far too small to matter for the large-scale sea surface temperature, but enough to matter for sea surface salinity. -Stefan] "

I did a simple heat calculation, and i agree with him.

sidd

Stefan's being a little disingenuous here. It makes a big difference to the cooling whether the ice melts on shore and meltwater enters the sea, or whether icebergs fall off Greenland and the ice melts at sea. Hansen reckoned that cooling was important enough to hose with a berg/meltwater mix rather than the traditional meltwater only, and I'm inclined to accept his judgement on it.

And I would argue it makes an even bigger difference if hosing effects in Quebec begin prior to other regions, amplifying albedo / extent beyond normal bounds, and allowing (relatively) cold continental winds to blow across the anomalous region, further compounding the cold blob...!

[bbr2314]

Welp.

The change over the past 30 days has been extremely severe. I would say this is probably the worst disruption or occurrence of melt we have witnessed in the satellite era, at least in my recollection.

It looks like the second melt pulse of SWE in early June was the causative factor.



If this occurs with current departures vs. normal, I hate to think about what happens if we accumulate enough volume to result in a July melt pulse. It seems evident that the +++volume and April melt pulse was sufficient to stall May melt momentum substantially.

This begs the question of whether we need crazy departures for snow to make it through summer. If we have another 1000KM^3 of volume in 10-15 years, that could suffice for allowing enough melt pulsage that, by July/August, the remaining extant volume (now occupying a much greater area) is substantially more protected by the larger extant continental crysophere (further aided by decaying sea ice up north causing it to be "stuck" between oceanic ridging derived from continually accumulating heat). So summer quickly goes from abbreviated (2018) to non-existent (2035).

https://weather.gc.ca/saisons/animation_e.html?id=month&bc=sea

[Alexander555]

A July melt puls ? If the information is correct there is less snow in the Americas below Canada. So how would that extra volume preventing the summer to kick in ? Would it not be possible that the area with snow cover gets smaller or the periodes shorter if the temperature keeps going up ? Anyway , you keep the debat going 

[bbr2314]

A July melt puls ? If the information is correct there is less snow in the Americas below Canada. So how would that extra volume preventing the summer to kick in ? Would it not be possible that the area with snow cover gets smaller or the periodes shorter if the temperature keeps going up ? Anyway , you keep the debat going 

I am talking about future years. If we have another 1000KM^3 of volume vs 2018 by 2035, there will be enough mass that the spring melt pulses / ensuing protective freshwater runoff will allow the pack to last into July. You can see how the melting of the SWE follows distinctive pulses and doesn't run off all at once.

Also here is June 2018 vs. 2012. Some regions are now 20F+ colder (on monthlies!) than they were only six years ago.

[AbruptSLR]

Consensus scientist's like to gamble with public safety that a slow-down of the AMOC it doesn't increase the rate of global warming, but that does not make it so:

Title: "Does a slow AMOC increase the rate of global warming?"

http://www.realclimate.org/index.php/archives/2018/07/does-a-slow-amoc-increase-the-rate-of-global-warming/

[FishOutofWater]

That cool area south of Greenland was not caused by melting of Canadian snow. The fresh water from Canadian snowmelt stays close to the coastline and moves south with the Labrador current.



The Greenland vortex pattern that has been dominating the weather since spring is the cause of that pattern. Storms and persistent NW winds down the Labrador sea has increased mixing in the Labrador and Greenland seas and cooled the surface layer.



The AMOC slowdown may be a problem for the Arctic sea ice because heat not transported northwards into the Labrador sea may be transported northeastwards wards into the Arctic ocean.

[AbruptSLR]

The linked research provides more evidence that a slowing of the AMOC will lead to increased warming at high latitudes due to abrupt warming during the summer months (which increases Arctic Amplification):

G. Bromley et al. (06 April 2018), "Interstadial Rise and Younger Dryas Demise of Scotland's Last Ice Fields", Paleoceanography and Paleoclimatology, Vol. 33, Issue 4, https://doi.org/10.1002/2018PA003341

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2018PA003341

Abstract
Establishing the atmospheric expression of abrupt climate change during the last glacial termination is key to understanding driving mechanisms. In this paper, we present a new 14C chronology of glacier behavior during late‐glacial time from the Scottish Highlands, located close to the overturning region of the North Atlantic Ocean. Our results indicate that the last pulse of glaciation culminated between ~12.8 and ~12.6 ka, during the earliest part of the Younger Dryas stadial and as much as a millennium earlier than several recent estimates. Comparison of our results with existing minimum‐limiting 14C data also suggests that the subsequent deglaciation of Scotland was rapid and occurred during full stadial conditions in the North Atlantic. We attribute this pattern of ice recession to enhanced summertime melting, despite severely cool winters, and propose that relatively warm summers are a fundamental characteristic of North Atlantic stadials.

Plain Language Summary
Geologic data reveal that Earth is capable of abrupt, high‐magnitude changes in both temperature and precipitation that can occur well within a human lifespan. Exactly what causes these potentially catastrophic climate‐change events, however, and their likelihood in the near future, remains frustratingly unclear due to uncertainty about how they are manifested on land and in the oceans. Our study sheds new light on the terrestrial impact of so‐called “stadial” events in the North Atlantic region, a key area in abrupt climate change. We reconstructed the behavior of Scotland's last glaciers, which served as natural thermometers, to explore past changes in summertime temperature. Stadials have long been associated with extreme cooling of the North Atlantic and adjacent Europe and the most recent, the Younger Dryas stadial, is commonly invoked as an example of what might happen due to anthropogenic global warming. In contrast, our new glacial chronology suggests that the Younger Dryas was instead characterized by glacier retreat, which is indicative of climate warming. This finding is important because, rather than being defined by severe year‐round cooling, it indicates that abrupt climate change is instead characterized by extreme seasonality in the North Atlantic region, with cold winters yet anomalously warm summers.

[sidd]

How does that paper indicate that " a slowing of the AMOC will lead to increased warming at high latitudes due to abrupt warming during the summer months "

All i see is increased summer temperatures shortly after 12.8 to 12.6 Kyr BP.

sidd

[bbr2314]

How does that paper indicate that " a slowing of the AMOC will lead to increased warming at high latitudes due to abrupt warming during the summer months "

All i see is increased summer temperatures shortly after 12.8 to 12.6 Kyr BP.

sidd

I would think it is because the "bubble" of super-warm ATL SSTs reaches the high Arctic, turns it ice-free, and forces progressively colder continents. This may be a self-reinforcing mechanism until the cold continents sufficiently overwhelm the SSTs to cause the Arctic to refreeze entirely. Thus, you end up with an "interlude" of extremely warm temps / summers in certain regions as the domino effect kicks in, which first occurs adjacent to extant ice sheets (i.e., Greenland), before spreading across the rest of the NHEM and resolving the warm oceanic anomalies.

[AbruptSLR]

How does that paper indicate that " a slowing of the AMOC will lead to increased warming at high latitudes due to abrupt warming during the summer months "

All i see is increased summer temperatures shortly after 12.8 to 12.6 Kyr BP.

sidd

In addition to bbr2314's points, the fact that the Scottish glacier melted with a slowing AMOC is physical evidence of at least local Artic Amplification .

[johnm33]

It looks like the AMOC is changing in a more complex way than just slowing. Open the ssh/t/s gifs on these two pages to look at the vortices and the various streams. https://www7320.nrlssc.navy.mil/GLBhycomcice1-12/glfstr.html
https://www7320.nrlssc.navy.mil/GLBhycomcice1-12/natspg.html
The way i see this is you have water coming out of the arctic moving more or less orthogonally away from the axis of rotation that has to gain 15mph/24kph every deg. it moves south to be at equilibrium. It's energetic state is indicated by the low ssh and the fact that it holds fast to the east coast as it moves south, both on Greenland and America. From the south there's water that has shifted about 11⁰ and 1/8 closer [not much] in relation to the axis since it rose from the depths off equatorial Africa where it was already moving slower than the planets rotational speed which remains the case untill it gets to 35N . Then these two bodies meet and begin to exchange qualities, heat, inertia, salinity and spin one slows the other accelerates.
 There's a gif here that helps to visualise the tidal rotation around the amphidromic point in the N.ATL. also shown. Looking at the ssh gif in the second link above it appears that there are vortices of polar water moving south and east feeding a growing area of cooler water going south from Spain as far as the Cape Verde islands. The amphidromic point seems to coincide with a relatively quiet [vortice wise] area of the N.ATL. on Nullschool . It appears that this fraction of water is being drawn south away from there as the tides rotate, whether this is permanent or just one of the random fluctuations we can expect ?
hope that makes sense.
 

[AbruptSLR]

The linked reference evaluates various factors influencing the AMO including the AMOC.  It does note that a slowdown of the AMOC results in a warming of the Tropical Atlantic waters:

ROBERT C. J. WILLS et a;. (2018), "Ocean-atmosphere dynamical coupling fundamental to the Atlantic Multidecadal Oscillation", Journal of Climate,

https://atmos.washington.edu/~rcwills/papers/2018_Wills_etal_AMO_JClim.pdf

Abstract: "The North Atlantic has shown large multidecadal temperature shifts during the 20th century. There is ongoing debate about whether this variability arises primarily through the influence of atmospheric internal variability, through changes in ocean circulation, or as a response to anthropogenic forcing. This study isolates the mechanisms driving Atlantic temperature variability on multidecadal timescales by using low-frequency component analysis (LFCA) to separate the influences of high-frequency variability, multidecadal variability, and long-term global warming. This analysis objectively identifies the North Atlantic subpolar gyre as the dominant region of Atlantic multidecadal variability. In unforced control runs of coupled climate models, warm subpolar temperatures are associated with a strengthened Atlantic Meridional Overturning Circulation (AMOC) and anomalous local heat fluxes from the ocean into the atmosphere. Atmospheric variability plays a role in the intensification and subsequent weakening of ocean overturning and helps to communicate warming into the tropical Atlantic. These findings suggest that dynamical coupling between atmospheric and oceanic circulations is fundamental to the Atlantic Multidecadal Oscillation (AMO) and motivate approaching decadal prediction with a focus on ocean circulations."

[Niall Dollard]

2018 International AMOC Science Meeting Agenda

There is a wealth of information available here on the current state of the AMOC, with many of the presentations freely available to download :

https://usclivar.org/meetings/2018-amoc-rapid-meeting-agenda

[bluesky]

A new paper makes the dot between drop in oxygen content in St Laurent estuary, weakening of the Labrador current and a correlation with weakening AMOC

"Rapid coastal deoxygenation due to ocean circulation shift in the northwest Atlantic"
Mariona Claret et al. Sept 2018

Abstract
"Global observations show that the ocean lost approximately 2% of its oxygen inventory over the past five decades1,2,3, with important implications for marine ecosystems4,5. The rate of change varies regionally, with northwest Atlantic coastal waters showing a long-term drop6,7 that vastly outpaces the global and North Atlantic basin mean deoxygenation rates5,8. However, past work has been unable to differentiate the role of large-scale climate forcing from that of local processes. Here, we use hydrographic evidence to show that a Labrador Current retreat is playing a key role in the deoxygenation on the northwest Atlantic shelf. A high-resolution global coupled climate–biogeochemistry model9 reproduces the observed decline of saturation oxygen concentrations in the region, driven by a retreat of the equatorward-flowing Labrador Current and an associated shift towards more oxygen-poor subtropical waters on the shelf. The dynamical changes underlying the shift in shelf water properties are correlated with a slowdown in the simulated Atlantic Meridional Overturning Circulation (AMOC)10. Our results provide strong evidence that a major, centennial-scale change of the Labrador Current is underway, and highlight the potential for ocean dynamics to impact coastal deoxygenation over the coming century."

under paywall, but I think it can be requested on research gate so should be accessible:
https://www.researchgate.net/publication/327702404_Rapid_coastal_deoxygenation_due_to_ocean_circulation_shift_in_the_northwest_Atlantic

[sidd]

Here is an interesting paper in GRL on a global climate model that has a bistablity between glaciated and nonglaciated states. It is a crude model, but rather nice in that it explicitly shows the origin of the bistability.

"Two stable equilibria of climate are supported, one "Cold" and one "Warm" for the same external forcing and parameters, thus demonstrating that multiple equilibria are possible in a coupled GCM comprising a myriad of degrees of freedom. The difference in the climate of the two states is of planetary scale. Global average sea surface temperature and surface air temperature differ by 8.2 and 13.5 ∘ C, respectively (patterns are shown in Figure S1). In the southern hemisphere (SH), the sea ice edge (as measured by the 15% annual mean concentration) expands by about 15 ∘ of latitude in the Cold state (Figure 1). The northern hemisphere, which is nearly ice free in the Warm state, exhibits a large ice cap extending over the subpolar gyre (45 N) in the Cold state, with a similar expansion of snow cover over land (Figure 1, top left)."

Why do i post the paper in this thread: Because the bistability is not driven by AMOC collapse:

"The multiple states described here differ fundamentally from AMOC bistability and are supported by coupled ocean-atmosphere-sea ice dynamics. Although the MOC does change between states in our simulations (Figure 3), this change does not correspond to a collapse and is in fact a symptom rather than a driver of the bistability (Ferreira et al., 2011)."


I attach fig 1

sidd

[bbr2314]

I don't know where to ask this question so perhaps this is the right place. While shelf temps along the NE seaboard are dropping, the EURO is showing what I believe to be an unprecedented surge of heat developing and arriving very close offshore (GIF is 11/23/2017 vs 2018). This starts around D4 and the end result appears to follow the continental shelf fairly closely. So what is causing this / could it be the freshwater input from whatever happened with Beaufort Gyre this summer (maybe it intensified the GS response?) or also albedo / SST interaction due to Quebec's snowy autumn?

This may portend significant disturbances down the line as well.

[oren]

Interesting but I think the best time to ask that question is after this event will have happened, in 10 days from now. Then the comparison will be fully valid.

[bbr2314]

Interesting but I think the best time to ask that question is after this event will have happened, in 10 days from now. Then the comparison will be fully valid.

So after your rebuke I went back and compared EURO forecasts for the same region in recent weeks with reality upon verification. And you are correct to be wary, because it appears the EURO has a systemic bias of GREATLY overwarming the NATL adjacent to the NE seaboard. This is actually very good to know and it partially explains why it is always too progressive with ejecting airmasses from Northeast North America (fake oceanic warmth -> more ridging, verification of less warmth -> more troughing vs forecast).

[aperson]

The ECMWF wasn't even atmosphere-ocean coupled until this year. It's definitely got a long way to go before it can be used as any sort of useful indicator for D10 SSTs. A lot of the other global models aren't even coupled altogether.

[Sleepy]

https://www.ecmwf.int/en/newsletter/156/meteorology/ifs-upgrade-brings-more-seamless-coupled-forecasts

On 5 June 2018, ECMWF implemented a substantial upgrade of its Integrated Forecasting System (IFS). IFS Cycle 45r1 brings coupling to all ECMWF forecasts, from forecast day 1 to one year, by including the three-dimensional ocean and sea-ice model in the single high-resolution forecast (HRES). This is a further step towards the implementation of the 2016–2025 Strategy, whose goals include a more complete and seamless description of the Earth system across all ECMWF configurations.

[Pmt111500]

https://www.ecmwf.int/en/newsletter/156/meteorology/ifs-upgrade-brings-more-seamless-coupled-forecasts

On 5 June 2018, ECMWF implemented a substantial upgrade of its Integrated Forecasting System (IFS). IFS Cycle 45r1 brings coupling to all ECMWF forecasts, from forecast day 1 to one year, by including the three-dimensional ocean and sea-ice model in the single high-resolution forecast (HRES). This is a further step towards the implementation of the 2016–2025 Strategy, whose goals include a more complete and seamless description of the Earth system across all ECMWF configurations.

Browser crashed, not going to write the longer response again. Looks like the tropical forecasts get an improvement in ecmwf. Does someone know if they incorporate weekends, holidays and similar cultural effects on their model? Simple yes or no will do. I mean, have they checked if forecasts made on Monday data are more accurate than those done on Fridays' data? This might be one way to improve on longer forecasts, but would require some predictability of human behavior... Not something many endorse, it's entirely possible humans stop emissions on their freetime instead of rushing to the shores of plastic seas.

[Sleepy]

Pmt, I haven't thought about that but it seems like they will hit the roof soon (with todays tech) even without incorporating human behaviour.
https://www.ecmwf.int/en/about/what-we-do/scalability

[gerontocrat]

Pmt, I haven't thought about that but it seems like they will hit the roof soon (with todays tech) even without incorporating human behaviour.
/quote]
I wonder if a similar sort of scary graph is where mankind is going on power use by computer /communications gear in general as world-wide systems and data storage expand exponentially . Chuck in AI, which apparently requires a quantum jump in data and processing power, and ......

ps: My doubts on AI have always been that the brain must work fundamentally differently from computers. The brain has ridiculously low processing speeds and pathetically low amounts of data storage but.....

pps: But should I be reminding sleepy of his less than wonderful experiences of the IT industry.

[Sleepy]

Oh, they were wonderful gerontocrat, I had everything except a life. Now it's the other way around. And you?

[gerontocrat]

Oh, they were wonderful gerontocrat, I had everything except a life. Now it's the other way around. And you?

It was good for a long time in some of the poorest parts of the world. I even did stuff for the Swedish International Development Association - they sent me to Vasteras to learn Portuguese..

But socialism died, the demand was to support privatisation and the Anglo-Saxon Capitalist model. Once I was sent a project proposal to tax famine ( I kid you not). So in the end I chucked it. I have a CV that says to prospective employers - you did too much, you know too much. Over-qualified people are unemployable.

So nowt to do now but be a witness to the coming shit-storm and try to persuade my daughter to prepare her defences. People tell me to write the book - it seems we all have one book inside us. Too much like hard work?

AMOC slowdown ? whoops.

[Pmt111500]

Oh, they were wonderful gerontocrat, I had everything except a life. Now it's the other way around. And you?

I have a CV that says to prospective employers - you did too much, you know too much. Over-qualified people are unemployable.
AMOC slowdown ? whoops.

AMOC slowdown.
It could be the increased heat absorption by the AGW in the North Atlantic is responsible for the continued decrease of ice in the Arctic Atlantic sector. Rather than trying to directly measure the heat transport from Tropics we might do better relying on satellite/ship measurements over the whole North Atlantic. It's been clear that East Greenland and Baffin current systems have brought an almost steady feed of cold water southwards.
Nowadays, probably for 3 years now the Nares transport has been diminishing (well way longer, just throwing a number here) and the eastern parts of north Atlantic currents have on occasion backtracked (not sure this is how it happens) along the edge of the ice all the way over the northern tip of Greenland. Thus the heat transport via the North Atlantic eastern coasts might be seen to be a factor in the melt of NE Greenland, a place at least I once thought to be among the last to start melting.
This heat absorbed by the Eastern North Atlantic might neatly connect to the bbr hypothesis of Quebec and Labrador harshness. Cutting out a conduit (the East Greenland Current and Nares Transport) for cold waters might increase transport elsewhere (CAA channels), unless the ice melts in place.
Anyway, the 'cold patch' South of Greenland, occasionally can manifest itself on a much wider area in CAA, Labrador and Quebec giving the residents (and bbr) much to talk about. Personally I do not think part of Greenland ice should melt and be transported by warped airflows to the mainland Canada. What the cold patch (along with its other counterpart (the other one in the Southern hemisphere might be a figment of  my imagination) warmch in North Pacific) does do is to help create the Ridiculously Resilient Ridge and the associated high amplitude waves over the whole hemisphere. Thus we might see bbrs' hypothesis as an extreme case of standing waves directing only cold rains (yea, it's snow) towards Canadian eastern seaboard.

That is about my current understanding of what's happening in Overturning, I know salinity plays a role in the Ocean, but I left it out since I don't get it well enouhj.

[Sleepy]

Another by Wei Liu, paywalled and not (yet) available to cheap non paying customers.

The mechanisms of the Atlantic Meridional Overturning Circulation slowdown induced by Arctic sea ice decline
https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-18-0231.1

We explore the mechanisms by which Arctic sea ice decline affects the Atlantic Meridional Overturning Circulation (AMOC) in a suite of numerical experiments perturbing Arctic sea ice radiative budget within a fully coupled climate model. The imposed perturbations act to increase the amount of heat available to melt ice, leading to a rapid Arctic sea ice retreat within 5 years after the perturbations are activated. In response, the AMOC gradually weakens over the next ∼100 years. The AMOC changes can be explained by the accumulation in the Arctic and subsequent downstream propagation to the North Atlantic of buoyancy anomalies controlled by temperature and salinity. Initially, during the first decade or so, the Arctic sea ice loss results in anomalous positive heat and salinity fluxes in the subpolar North Atlantic, inducing positive temperature and salinity anomalies over the regions of oceanic deep convection. At first, these anomalies largely compensate one another, leading to a minimal change in upper ocean density and deep convection in the North Atlantic. Over the following years, however, more anomalous warm water accumulates in the Arctic and spreads to the North Atlantic. At the same time, freshwater that accumulates from seasonal sea ice melting over most of the upper Arctic Ocean also spreads southward, reaching as far as south of Iceland. These warm and fresh anomalies reduce upper ocean density and suppress oceanic deep convection. The thermal and haline contributions to these bouyancy anomalies, and therefore to the AMOC slowdown during this period, are found to have similar magnitudes. We also find that the related changes in horizontal wind-driven circulation could potentially push freshwater away from the deep convection areas and hence strengthen the AMOC, but this effect is overwhelmed by mean advection.

Edit; that didn't take long...

[vox_mundi]

Century-Scale Deep-Water Circulation Dynamics in the North Atlantic Ocean
https://phys.org/news/2019-05-century-scale-deep-water-circulation-dynamics-north.html

... AMOC is a process whereby cold and salty surface water sinks into deep ocean in the high-latitude North Atlantic, the lower level deep water (known as North Atlantic Deep Water: NADW) flows southward (Image 1), and eventually rises to the surface in the North Pacific Ocean. The force of this circulation is known to affect global heat flow and regional climates. To study these circulation dynamics, the North Atlantic Ocean is especially important, because it is the place that deep water is formed through cooling surface water in the high latitudes.

The lower (deeper) part of NADW below 2,500 meters is well studied, but upper NADW (intermediate water) behavior is poorly understood since the last deglaciation—that is, the transitional period from the last ice age to the warmer contemporary interglacial climate state. Furthermore, NADW dynamics for the past ~11,700 years (known as the Holocene) remain equivocal. Dr. Yasuhara and his collaborators showed that subtropical North Atlantic intermediate-water temperature varied significantly during both of these time periods, based on trace element geochemistry of calcified shells of deep-sea microcrustacean Ostracoda in a sediment core. Their reconstructions reveal a series of multi-century-scale abrupt deep-water warming events likely caused by the reduction deep-water circulation. The authors also discovered that many of these weakening events of deep-water circulation can be widely recognized in the western North Atlantic.

Lead author of the study Dr. Yasuhara said "Holocene deep-water circulation was more dynamic than previously thought. There is increasing evidence that this circulation change in the North Atlantic affects climates of remote places including East Asia and also marine and terrestrial ecosystems. As recently discovered by scientists including my HKU colleagues Drs Benoit Thibodeau and Christelle Not, this global deep-water circulation has substantially weakened during the last century. If further weakening happens in the future, there may be unexpectedly broad implications not only on our atomospheric and ocean systems, but also on Earth's ecological systems and our society.


Deepwater circulation around Svalbard & Greenland

Moriaki Yasuhara et al. North Atlantic intermediate water variability over the past 20,000 years, Geology (2019)

Benoit Thibodeau et al. Last Century Warming Over the Canadian Atlantic Shelves Linked to Weak Atlantic Meridional Overturning Circulation, Geophysical Research Letters (2018)

[johnm33]

Looking at this https://phys.org/news/2019-06-link-north-atlantic-currents-sea.html it seems a no brainer to me that if you have increased Arctic waters flowing down the coast lets say with the inherent inertia of 75⁰N then it'll have two main effects. The first is that it will force itself into the coast, and continue to do that further south. The second is that once it is forced by Gulf stream waters away from the coast those waters will mix until equilibrium is reached slowing down the gulf stream/north atlantic drift.
What does this model show if not that?

If you open nullschool and select O from projections you'll see from 90-60⁰N is about half of the distance of the equator from the axis of rotation and 30⁰N about an eighth of the distance. Thus the inertia of tropical waters is too low to separate from the coast until the distance to the axis [surface speed] begins to decrease, so I would expect the highest effects of slr to be where both streams detatch and all points north, until the water reaches equilibrium with rotational speed, which may vary but just now appears to be about 52N, so peaking around 41N. Why am I wrong?

[bbr2314]

Looking at this https://phys.org/news/2019-06-link-north-atlantic-currents-sea.html it seems a no brainer to me that if you have increased Arctic waters flowing down the coast lets say with the inherent inertia of 75⁰N then it'll have two main effects. The first is that it will force itself into the coast, and continue to do that further south. The second is that once it is forced by Gulf stream waters away from the coast those waters will mix until equilibrium is reached slowing down the gulf stream/north atlantic drift.
What does this model show if not that?

If you open nullschool and select O from projections you'll see from 90-60⁰N is about half of the distance of the equator from the axis of rotation and 30⁰N about an eighth of the distance. Thus the inertia of tropical waters is too low to separate from the coast until the distance to the axis [surface speed] begins to decrease, so I would expect the highest effects of slr to be where both streams detatch and all points north, until the water reaches equilibrium with rotational speed, which may vary but just now appears to be about 52N, so peaking around 41N. Why am I wrong?

I wonder if we are seeing amplified seasonal flux moreso than other factors. I.E. during the winter and springtime snow melts, the stream is pushed south more than it used to be (especially so by spring). And then, as snowmelt ceases, the Stream is more prone to drifting farther north than normal due to the tropical thermal inertia and slackening of freshwater supply.

Long-term, as Greenland contributes more and more to summer melt, I guess the end result would be a more permanent pattern matching late springtime that persists through most of the year.

[bbr2314]

Spring is already failing in many recent years (2013, 2014, 2015, 2018, 2019).



What happens next? If 2019 is any reasonable guide, it is going to start snowing in much of the populated Midwest into June by the 2020s, and into June in the unpopulated innermost regions of the continent (with proximity to the Great Lakes and Hudson Bay). We are seeing record-worst corn harvests this year due to the conditions that have prevailed. And it is almost certainly only a preview of what's to come within another decade.

[johnm33]

bbr.
I intend to have another look for numbers on the export of arctic waters through Davis strait, they may indicate when the amoc slows, or not? I think we agree that Hudson will grow colder as a result of increased flow and Quebec will cool as a consequence, and i've said elsewhere that cooling and increased precipitation falling on Alberta/Montana is to be expected but thats another topic.
 Looking at the increased flow through Nares and potentially the whole NWP if my present opinion has any merit then we should see +anomalous slowing of amoc later this year. 
Nice suite btw
john

[Tom_Mazanec]

https://www.yaleclimateconnections.org/2019/08/video-the-north-atlantic-ocean-current-may-be-slowing/
A region of the North Atlantic south of Greenland has experienced some of its coldest temperatures on record in recent years, a cooling unprecedented in the past thousand years. What explains that anomaly?
Climatologist Michael Mann of Penn State University, in this month’s “This is Not Cool” video, explains that this phenomenon may be an indication that the North Atlantic current, part of a larger global ocean circulation, is slowing down.

[kassy]

Atlantic Ocean may get a jump-start from the other side of the world

Summary:
A key question for climate scientists in recent years has been whether the Atlantic Ocean's main circulation system is slowing down, a development that could have dramatic consequences for Europe and other parts of the Atlantic rim. But a new study suggests help may be on the way from an unexpected source -- the Indian Ocean.

...

For the new study, they looked at warming in the Indian Ocean.

"The Indian Ocean is one of the fingerprints of global warming," said Hu, who is first author of the new work. "Warming of the Indian Ocean is considered one of the most robust aspects of global warming."

The researchers said their modeling indicates a series of cascading effects that stretch from the Indian Ocean all way over to the Atlantic: As the Indian Ocean warms faster and faster, it generates additional precipitation. This, in turn, draws more air from other parts of the world, including the Atlantic, to the Indian Ocean.

With so much precipitation in the Indian Ocean, there will be less precipitation in the Atlantic Ocean, the researchers said. Less precipitation will lead to higher salinity in the waters of the tropical portion of the Atlantic -- because there won't be as much rainwater to dilute it. This saltier water in the Atlantic, as it comes north via AMOC, will get cold much quicker than usual and sink faster.

"This would act as a jump-start for AMOC, intensifying the circulation," Fedorov said. "On the other hand, we don't know how long this enhanced Indian Ocean warming will continue. If other tropical oceans' warming, especially the Pacific, catches up with the Indian Ocean, the advantage for AMOC will stop."

https://www.sciencedaily.com/releases/2019/09/190916114032.htm

[be cause]

So it's not so much 'world climate runs amok' , more , 'AMOK runs the world's climate' ?   b.c.

[Hefaistos]

Atlantic Ocean may get a jump-start from the other side of the world

Maybe this 'jump start' already started.

Seems that the AMOC slowdown has reversed, but has incredibly large variability.
Measured and reported in research paper "Atlantic Meridional Overturning Circulation: Observed Transport and Variability"
Eleanor Frajka-Williams, et al. 2019

"...the AMOC ranged from 4 to 35 Sv over a single year, had a seasonal cycle
with amplitude over 5 Sv, and that the dip in 2009/10 of 30%
exceeded the range of interannual variability found in climate
models.  ... 
striking differences between the AMOC mean state and variability amongst models."

Figure caption: FIGURE 6 | A time series of AMOC transport (MOCρ ) at the OVIDE section (eastern subpolar gyre: Portugal to Cape Farewell) for 1993–2017, constructed from
altimetry and hydrography. The gray line is from altimetry combined with a time-mean of Argo velocities; the green curve is low-pass filtered using a 2-year running
mean. The black curve is from altimetry and Argo. Red circles are estimates from OVIDE hydrography with associated errors given by the red lines. The mean of the
gray curve is given by the black dashed line (Updated from Mercier et al., 2015).

[Hefaistos]

"Stronger evidence for a weaker Atlantic overturning"

AMOC "...is weaker today than any time before in more than 1000 years. Sea surface temperature data analysis provides new evidence that this major ocean circulation has slowed down by roughly 15 percent since the middle of the 20th century"

https://phys.org/news/2018-04-stronger-evidence-weaker-atlantic-overturning.html

Conflicting evidence.

Seems to me that these researchers, using Sea surface temperature data,  have a weaker case than Frajka-Williams, et al. 2019 in my previous post, who found the exact opposite result, and the AMOC slowdown has been reversed as measured by buyous down in the AMOC itself.

It seems implausible that you would be able to dispute the fact that a certain amount of Sverdrups of water are passing by the dedicated measuring arrays they used for their analysis.

Need to change a lot of conclusions on climate change if this research holds up:
"As the currents slow down increase, they bring less more heat toward the north"
etc.etc.

[blumenkraft]

North Atlantic Current may cease temporarily in the next century
Total collaps in the next 1,000 years unlikely

Link >> https://www.eurekalert.org/pub_releases/2019-12/uog-nac122719.php

[pleun]

different article about the same research :

https://www.nature.com/articles/s41598-019-56435-6

[johnm33]

I read through this linked by uniquorn on the freezing thread, about the cooling of Barents, I wonder if there's any assessment of volume. That is I would assume that the current that rises off the west coast of Africa to become the ocean stream into the Caribean and then the Gulf stream continues to deliver about the same amount of source water. Then the gulf stream meets and mixes with arctic waters coming through Fram/Nares/CAA and meltwater off Greenland, and it's the relative inertia of this arctic water that slows down the current, so I'm thinking that the volume of water passing through the Norwegian sea would increase, be cooler, cool less due to a smaller temperature gradient, then pass on into the Arctic carrying more heat further and accelerating this process.[?]

[kassy]

Seafloor Discovery Shows The Ocean's Undergoing a Change Not Seen in 10,000 Years

Changes in ocean circulation may have caused a shift in Atlantic Ocean ecosystems not seen for the past 10,000 years, new analysis of deep-sea fossils has revealed.

...

The climate has been quite stable over the 12,000 years or so since the end of the last Ice Age, a period known as the Holocene. It is thought that this stability is what allowed human civilisation to really get going.

In the ocean, the major currents are also thought to have been relatively stable during the Holocene. These currents have natural cycles, which affect where marine organisms can be found, including plankton, fish, seabirds and whales. ... But there still seems to be a prevailing view that not much has happened in the ocean so far – in our minds the really big impacts are confined to the future.

Looking into the past

To challenge this point of view, we had to look for places where seabed fossils not only covered the industrial era in detail, but also stretched back many thousands of years. And we found the right patch of seabed just south of Iceland, where a major deep sea current causes sediment to pile up in huge quantities.

...

A recent global study showed that modern foraminifera distributions are different to the start of the industrial era. Climate change is clearly already having an impact.

Similarly, the view that modern ocean currents are like those of the past couple of thousand years was challenged by our work in 2018, which showed that the overturning "conveyor belt" circulation was at its weakest for 1,500 years.

Our new work builds on this picture and suggests that modern North Atlantic surface circulation is different to anything seen in the past 10,000 years – almost the whole Holocene.

The effects of the unusual circulation can be found across the North Atlantic. Just south of Iceland, a reduction in the numbers of cold-water plankton species and an increase in the numbers of warm-water species shows that warm waters have replaced cold, nutrient-rich waters.

...

Melting following the peak of the Little Ice Age in the mid 1700s may have triggered an input of freshwater, causing some of the earliest changes that we found, with modern climate change helping to propel those changes beyond the natural variability of the Holocene.

We still don't know what has ultimately caused these changes in ocean circulation. But it does seem that the ocean is more sensitive to modern climate changes than previously thought, and we will have to adapt.

https://www.sciencealert.com/fossils-reveal-our-ocean-is-changing-in-a-ways-it-hasn-t-for-10-000-years

Paper:
https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020GL087577