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Sourabh

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Changing Arctic Ocean Currents
« on: November 26, 2013, 05:57:00 AM »
Guys,

I was trying to post this link on Neven's blog, but I kept getting "Not a HASH reference" error. So, I started a new topic.

I found this video about changing ocean currents in Arctic:



I thought you might enjoy watching it if you have not already done so.

ggelsrinc

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Re: Changing Arctic Ocean Currents
« Reply #1 on: November 26, 2013, 08:09:58 AM »
Arctic currents aren't like normal currents and can change with the wind. That event last August changed the normal Beaufort Gyre. There aren't ice shelves to make icebergs like there were in the past, but sea ice will be driven by wind direction, even if the surface is smooth.

The normal to date is the gyre going clockwise, because of high pressure zones above it. Before it gives up the ghost, I think it's direction will change to counterclockwise, but what do I know? 

Freegrass

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Re: Changing Arctic Ocean Currents
« Reply #2 on: September 09, 2020, 01:43:23 PM »
What's going on with the Alaska Coastal Current? It should go against the Beaufort gyre, not with it, right? Is this why the Beaufort sea didn't melt out this year? Because the ACC wasn't bringing in hot water from the Pacific?

https://earth.nullschool.net/#2020/09/06/0000Z/ocean/surface/currents/orthographic=-45.02,91.24,2304
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Re: Changing Arctic Ocean Currents
« Reply #3 on: September 09, 2020, 10:18:27 PM »
It certainly did not help but weather over beufort wasn't especially conducive to melt. Elsewhere it was.

Freegrass

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Re: Changing Arctic Ocean Currents
« Reply #4 on: September 10, 2020, 03:15:49 AM »
Before the melting season started I had this theory that the Bering Strait current was speeding up due to the slowdown of the AMOC. I know now that the current is indeed speeding up, but it remains a question if the slowdown of the AMOC has anything to do with it.

Because I had this theory, I watched the Alaskan Coastal Current closely at the start of the melting season, and what surprised me was that the hot Pacific water wasn't reaching the Amundsen Gulf like I expected. It seemed to stop melting the coastal ice around Barrow. This came as a total surprise for me. And yesterday I saw that the ACC had completely reversed direction.

So I put one and one together, and speculated that this could be an explanation for the slow melt in the Beaufort sea.

I know the weather wasn't favorable at the start of the season, but that changed, and there is no logical explanation why we have the scorpion tail until now. The only reason I can see now is that something changed in the ACC, preventing that hot Pacific water to reach the CAA.

I have no idea if what I say is true, but I think it's worth investigating by those who know more about this stuff. Is it normal that the ACC is flowing in the opposite direction? Has there been a fundamental change in the ACC? I really don't know. I'm just trying to find an explanation for the 2020 Beaufort enigma. That arm shouldn't be there, and yet there it is...

I don't understand it...
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Freegrass

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Re: Changing Arctic Ocean Currents
« Reply #5 on: September 10, 2020, 03:29:20 AM »
The Siberian Coastal current has changed direction again as well I notice now...
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oren

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Re: Changing Arctic Ocean Currents
« Reply #6 on: September 10, 2020, 04:06:34 AM »
Quote
there is no logical explanation why we have the scorpion tail until now.

Several logical explanations:
* High Beaufort volume at start of season. Tail is composed of originally thicker ice
* Lack of Beaufort to Chukchi transport in spring
* Cloudy weather at the edge of the GAAC in July
* Circular GAAC movement skipped Beaufort but reversed currents (see ice drift image example from mid-July)

Hefaistos

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Re: Changing Arctic Ocean Currents
« Reply #7 on: September 10, 2020, 05:02:36 AM »
Before the melting season started I had this theory that the Bering Strait current was speeding up due to the slowdown of the AMOC. I know now that the current is indeed speeding up, but it remains a question if the slowdown of the AMOC has anything to do with it.

Because I had this theory, I watched the Alaskan Coastal Current closely at the start of the melting season, and what surprised me was that the hot Pacific water wasn't reaching the Amundsen Gulf like I expected. It seemed to stop melting the coastal ice around Barrow. This came as a total surprise for me. And yesterday I saw that the ACC had completely reversed direction.

So I put one and one together, and speculated that this could be an explanation for the slow melt in the Beaufort sea.

I know the weather wasn't favorable at the start of the season, but that changed, and there is no logical explanation why we have the scorpion tail until now. The only reason I can see now is that something changed in the ACC, preventing that hot Pacific water to reach the CAA.

I have no idea if what I say is true, but I think it's worth investigating by those who know more about this stuff. Is it normal that the ACC is flowing in the opposite direction? Has there been a fundamental change in the ACC? I really don't know. I'm just trying to find an explanation for the 2020 Beaufort enigma. That arm shouldn't be there, and yet there it is...

I don't understand it...

According to several recent research papers, the AMOC is currently increasing. So maybe the very starting point of your hypothesis is wrong.
Here's some references / links for you:

Desbruyères et al, 2019, Ocean Sci., 15, 809–817 clearly demonstrate that the AMOC is currently strengthening, and they even give a bold forecast for the coming years:

"An easily observed surface quantity – the rate of warm to cold transformation of water masses at high latitudes – is found to lead the observed AMOC at 45∘ N by 5–6 years and to drive its 1993–2010 decline and its ongoing recovery, with suggestive prediction of extreme intensities for the early 2020s."

AMOC is forecasted to have "extreme intensities" in the coming years, as the AMOC is 'downstream' with a lag of 5 to 6 years from the already intensified warm to cold transformation of water masses at high latitudes.

https://www.researchgate.net/publication/338658885_Pending_recovery_in_the_strength_of_the_meridional_overturning_circulation_at_26_N

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2017GL076350

https://os.copernicus.org/articles/15/809/2019/

Freegrass

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Re: Changing Arctic Ocean Currents
« Reply #8 on: September 15, 2020, 10:33:03 AM »
According to several recent research papers, the AMOC is currently increasing. So maybe the very starting point of your hypothesis is wrong.
Here's some references / links for you:

Desbruyères et al, 2019, Ocean Sci., 15, 809–817 clearly demonstrate that the AMOC is currently strengthening, and they even give a bold forecast for the coming years:

"An easily observed surface quantity – the rate of warm to cold transformation of water masses at high latitudes – is found to lead the observed AMOC at 45∘ N by 5–6 years and to drive its 1993–2010 decline and its ongoing recovery, with suggestive prediction of extreme intensities for the early 2020s."

AMOC is forecasted to have "extreme intensities" in the coming years, as the AMOC is 'downstream' with a lag of 5 to 6 years from the already intensified warm to cold transformation of water masses at high latitudes.

https://www.researchgate.net/publication/338658885_Pending_recovery_in_the_strength_of_the_meridional_overturning_circulation_at_26_N

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2017GL076350

https://os.copernicus.org/articles/15/809/2019/
That's the first I hear about that. Everything I read is about a slowing AMOC. Maybe it has recovered a little, but overall the speed is still approximately 15% lower than it used to be, no?

https://www.nature.com/articles/d41586-018-04086-4

Quote
11 APRIL 2018
North Atlantic circulation slows down
Evidence suggests that the circulation system of the North Atlantic Ocean is in a weakened state that is unprecedented in the past 1,600 years, but questions remain as to when exactly the decline commenced.
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binntho

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Re: Changing Arctic Ocean Currents
« Reply #9 on: September 15, 2020, 11:13:00 AM »
I've never really been convinced that the AMOC was slowing or weakening. The system as a whole is very variable and changes cyclically, but the waters north of the GIS gap and south of Labrador have both been unusually warm for several years, indicating that the Greenland cold spot is an unrelated phenomena and that the conveyance of oceanic heat to the far north is continuing unabated.

The much hyped putative driver behind a percieved slow-down doesn't really exist in geologically modern times: No glacier is big enough, close enough, and melting fast enough, or draining suffiiciently into the Arctic to cause a fresh-water induced slowdown - which is a popular theory to explain big swings in the AMOC in the geological past.

And a quick google on "amoc strengthening" finds plenty of evidence to support Hefaistos' post, including this one in Science Direct from 2016: There is no real evidence for a diminishing trend of the Atlantic meridional overturning circulation

here is another interesting paper, On freshwater fluxes and the Atlantic meridional overturning circulation. From the Abstract:

Quote
While the role of freshwater forcing in the AMOC has received much attention, this question remains unresolved ... Our results robustly suggest that for the equilibrium state of the modern ocean, freshwater fluxes strengthen the AMOC

Recent research is pointing to a link between the Indian Ocean and the AMOC, with a warmer
IO causing a stronger AMOC. There are plenty of papers to be found online, including this one:

PC23A-03 - The Strengthening of the Atlantic Ocean Meridional Overturning Circulation Caused by Enhanced Indian Ocean Warming, from the Abstract:

Quote
Here, we describe how a salient feature of anthropogenic climate change – enhanced warming of the tropical Indian ocean (TIO) – can strengthen the Atlantic meridional overturning circulation (AMOC) by modulating salinity distribution in the Atlantic
« Last Edit: September 15, 2020, 11:22:21 AM by binntho »
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Re: Changing Arctic Ocean Currents
« Reply #10 on: September 16, 2020, 10:42:01 AM »
thanks, i had never heard of it either. If I understood correctly, we are reinforcing the engine of the AMOC, and the power of its brake is questioned
perhaps we are strengthening the "Indian Ocean" engine so much that it compensates for the brake at Greenland (Greenlandic explanation seemed logical all the same, isn't it  ?)
Sorry, excuse my bad english

binntho

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Re: Changing Arctic Ocean Currents
« Reply #11 on: September 16, 2020, 11:09:13 AM »
thanks, i had never heard of it either. If I understood correctly, we are reinforcing the engine of the AMOC, and the power of its brake is questioned
perhaps we are strengthening the "Indian Ocean" engine so much that it compensates for the brake at Greenland (Greenlandic explanation seemed logical all the same, isn't it  ?)
There were several explanations for the "cold blob" or "warming hole" south of Greenland. One was that it was due to melt-water runoff from Greenland and a commonly stated effect was that it was somehow slowing down the AMOC in that area. This perhaps sounded logical but that doesn't make it right.

To begin with, meltwater runoff from Greenland is still nowhere near enough to cause any significant changes to the AMOC. Secondly, the "cold blob" is in an area where the water is heading down south again, and may well sink below a surface cooled by northerly winds. And the high SSTs both north and south of the blob indicates a vigorous heat transport.

A very recent article about this is Multiple drivers of the North Atlantic warming hole, from the Abstract it seems as if one of the explanation is increased heat transfer to the north of the area. Or in other words: The "cold blob" is cold because more of the heat is being transferred further north, and thus the waters returning south are colder than usual.



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Re: Changing Arctic Ocean Currents
« Reply #12 on: September 16, 2020, 11:17:10 PM »
thanks, i had never heard of it either. If I understood correctly, we are reinforcing the engine of the AMOC, and the power of its brake is questioned
perhaps we are strengthening the "Indian Ocean" engine so much that it compensates for the brake at Greenland (Greenlandic explanation seemed logical all the same, isn't it  ?)
There were several explanations for the "cold blob" or "warming hole" south of Greenland. One was that it was due to melt-water runoff from Greenland and a commonly stated effect was that it was somehow slowing down the AMOC in that area. This perhaps sounded logical but that doesn't make it right.

To begin with, meltwater runoff from Greenland is still nowhere near enough to cause any significant changes to the AMOC. Secondly, the "cold blob" is in an area where the water is heading down south again, and may well sink below a surface cooled by northerly winds. And the high SSTs both north and south of the blob indicates a vigorous heat transport.

A very recent article about this is Multiple drivers of the North Atlantic warming hole, from the Abstract it seems as if one of the explanation is increased heat transfer to the north of the area. Or in other words: The "cold blob" is cold because more of the heat is being transferred further north, and thus the waters returning south are colder than usual.
OK thank you, that makes sense
That reminds me that sometimes global warming can produce local cooling
Sorry, excuse my bad english

Glen Koehler

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Re: Changing Arctic Ocean Currents
« Reply #13 on: September 18, 2020, 11:08:44 AM »
I've never really been convinced that the AMOC was slowing or weakening.  The system as a whole is very variable and changes cyclically, but the waters north of the GIS gap and south of Labrador have both been unusually warm for several years, indicating that the Greenland cold spot is an unrelated phenomena and that the conveyance of oceanic heat to the far north is continuing unabated.

The much hyped putative driver behind a percieved slow-down doesn't really exist in geologically modern times: No glacier is big enough, close enough, and melting fast enough, or draining suffiiciently into the Arctic to cause a fresh-water induced slowdown - which is a popular theory to explain big swings in the AMOC in the geological past.

And a quick google on "amoc strengthening" finds plenty of evidence to support Hefaistos' post, including this one in Science Direct from 2016: There is no real evidence for a diminishing trend of the Atlantic meridional overturning circulation

here is another interesting paper, On freshwater fluxes and the Atlantic meridional overturning circulation. From the Abstract:

Quote
While the role of freshwater forcing in the AMOC has received much attention, this question remains unresolved ... Our results robustly suggest that for the equilibrium state of the modern ocean, freshwater fluxes strengthen the AMOC

Recent research is pointing to a link between the Indian Ocean and the AMOC, with a warmer
IO causing a stronger AMOC. There are plenty of papers to be found online, including this one:

PC23A-03 - The Strengthening of the Atlantic Ocean Meridional Overturning Circulation Caused by Enhanced Indian Ocean Warming, from the Abstract:

Quote
Here, we describe how a salient feature of anthropogenic climate change – enhanced warming of the tropical Indian ocean (TIO) – can strengthen the Atlantic meridional overturning circulation (AMOC) by modulating salinity distribution in the Atlantic
     Here is what Stefan Rahmstorf (who wrote the oft-quoted paper about a 15% AMOC slowdown, and who probably eats AMOC Sverdrup data for breakfast every morning) said about it on September 17 at http://www.realclimate.org/?comments_popup=18180#comment-626528

New studies confirm weakening of the Gulf Stream circulation (AMOC)
     "[T]here is growing evidence that another climate forecast is already coming true: the Gulf Stream system in the Atlantic is apparently weakening, with consequences for Europe too."

 "The Intergovernmental Panel on Climate Change (IPCC) stated for the first time a year ago in the Summary for Policy Makers of its Special Report on the Oceans:
   “Observations, both in situ (2004–2017) and based on sea surface temperature reconstructions, indicate that the Atlantic Meridional Overturning Circulation (AMOC) has weakened relative to 1850–1900.”  "

"Two new studies now provide further independent evidence of this weakening."

1. "The result: the Florida current has weakened significantly since 1909 and in the last twenty years has probably been as weak as never before. Piecuch’s calculations also show that the resulting reduction of heat transport is sufficient to explain the ‘cold blob’ in the northern Atlantic."

2. "Model simulations show that a weakening of the AMOC leads to an accumulation of salt in the subtropical South Atlantic." 
"This is exactly what the measured data show, in accordance with computer simulations. The authors speak of a “salinity fingerprint” of the weakening Atlantic circulation."

"In addition to these oceanographic measurements, a number of studies with sediment data indicate that the Gulf Stream circulation is now weaker than it has been for at least a millennium."

"[T]he latest generation (CMIP6) of climate models shows one thing: if we continue to heat up our planet, the AMOC will weaken further – by 34 to 45% by 2100. This could bring us dangerously close to the tipping point at which the flow becomes unstable.

This article appeared originally in German in Der Spiegel: Das Golfstromsystem macht schlapp"



Hefaistos

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Re: Changing Arctic Ocean Currents
« Reply #14 on: September 18, 2020, 11:33:14 AM »

     Here is what Stefan Rahmstorf (who wrote the oft-quoted paper about a 15% AMOC slowdown, and who probably eats AMOC Sverdrup data for breakfast every morning) said about it on September 17 at http://www.realclimate.org/?comments_popup=18180#comment-626528

New studies confirm weakening of the Gulf Stream circulation (AMOC)
     "[T]here is growing evidence that another climate forecast is already coming true: the Gulf Stream system in the Atlantic is apparently weakening, with consequences for Europe too."

 "The Intergovernmental Panel on Climate Change (IPCC) stated for the first time a year ago in the Summary for Policy Makers of its Special Report on the Oceans:
   “Observations, both in situ (2004–2017) and based on sea surface temperature reconstructions, indicate that the Atlantic Meridional Overturning Circulation (AMOC) has weakened relative to 1850–1900.”  "

"Two new studies now provide further independent evidence of this weakening."

1. "The result: the Florida current has weakened significantly since 1909 and in the last twenty years has probably been as weak as never before. Piecuch’s calculations also show that the resulting reduction of heat transport is sufficient to explain the ‘cold blob’ in the northern Atlantic."

2. "Model simulations show that a weakening of the AMOC leads to an accumulation of salt in the subtropical South Atlantic." 
"This is exactly what the measured data show, in accordance with computer simulations. The authors speak of a “salinity fingerprint” of the weakening Atlantic circulation."

"In addition to these oceanographic measurements, a number of studies with sediment data indicate that the Gulf Stream circulation is now weaker than it has been for at least a millennium."

"[T]he latest generation (CMIP6) of climate models shows one thing: if we continue to heat up our planet, the AMOC will weaken further – by 34 to 45% by 2100. This could bring us dangerously close to the tipping point at which the flow becomes unstable.

This article appeared originally in German in Der Spiegel: Das Golfstromsystem macht schlapp"

Rahmstorf  isn't providing anything new here, this is just his opinions.
What the scientific discussion is about, is that there is conflicting evidence. Some researchers find a strengthening circulation, and predict further strengthening in the coming years.
 
Regrettably, we won't get the RAPID data updated until another year, the expedition to retrieve data from the buyos was recalled while already out in the Atlantic Ocean, due to the pandemic worries in the UK.
Thus, the latest data we have is from September 2018, and the earliest time for update is in Summer 2021. This is according to direct communication with the researchers.

binntho

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Re: Changing Arctic Ocean Currents
« Reply #15 on: September 18, 2020, 03:06:05 PM »
I agree with Hefaistos - the evidence is not conclusive. And as one of the commenters on Real Climate pointed out: Rahmsdorf forgot to post the graph showing the clever tidal gauge based reconstruction of the Florida current. So here it is below.

Altough it is true that there is a slight downward trend, and that 1909 was one of the peak years, probably in second place after 1932, what is sorely missing is any correlation with other events on our fair planet.

It is possible to discern a drop after the temperature peak at the middle of the century, but other than that there is no visible correlation with recent warming - in other words, the downwards trend is not speeding up.

Rather the oppisite, the last 30 years seem to show no trend or possibly a slight upwards trend. But without clear correlation with other planetary changes, nor any clear causal connection, a clear conclusion seems a distant dream.
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Freegrass

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Re: Changing Arctic Ocean Currents
« Reply #16 on: September 18, 2020, 03:10:50 PM »
I think that both statements - of a weakening and a strengthening AMOC - can both be true at the same time. Maybe the AMOC did weaken in the last 100 years, and it could be recovering in the last few years from the weakest level.

One research is done with historical sediment data, and the other is done by measurement if I understand correctly. So I don't see why it couldn't be true that the AMOC has weakened, and is now recovering again.
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Re: Changing Arctic Ocean Currents
« Reply #17 on: Today at 10:12:45 AM »
Freegrass, I think you're spot on there.
The 'weakening AMOC' is older data, and is a more long-term evaluation.
The 'strengthening AMOC' is newer data, since e.g. the RAPID buoys were deployed.

As with everything connected with ocean currents, there is a lot of natural variability going on, as the time-scale for the overturning of the MOC is many 100's of years.