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Author Topic: Energy NOT needed for bottom-melting in 2017 and energy transport  (Read 6307 times)

seaicesailor

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It is interesting to consider how much extra energy is required to bottom-melt MYI in the Arctic Ocean because it has strong implications in this melting season (that extra energy WON'T be needed in the Pacific half of the Arctic):
- Out of spring, water right underneath the ice is at -1.8C in thermodynamic equilibrium  with the freezing bottom.
- Let's say bottom melting starts in June/July depending on the location (year/round near Atlantic currents).

From what I am learning, by observing the buoy data and reading, what I wrote below is wrong. Being the mechanisms of melting more complicated for both FYI and MYI, brine pocket formation and brine rejection involved, what I simplistically wrote down here is simply very far from true. I would remove the thread altogether, but there are valid contributions from other people

- For MYI, after a while of bottom-melting the half a meter or so of last season bottom-freezing, the temperature of the water has to raise from -1.8C to 0C in order to continue melting. In contrast, for the more saline FYI, melting proceeds at or slightly above -1.8C.
- This raise of temperature to continue bottom-melting MYI must happen for the whole water column of the mixed layer. In other words, the mixing that happens in this layer will take care of keeping its temperature homogeneous, with a turnover time of the order of the day or a few days.
- Assume the mixing layer is 20 to 40 m depending on location. Let's take 30 m in average.
- The energy for raising 1.8 degrees 30 m of water is equivalent to that needed for bottom-melting approximately 0.75 m of ice!!!! (since raising 1C of a 80m-deep extent of water requires the same energy to melt 1m of the same extent of ice)

So what happens this summer? In parts of the pacific half of the Arctic, and, especially, along Eurasia, we find typically 25-100 cm thinner ice than any previous year.

https://forum.arctic-sea-ice.net/index.php/topic,119.msg112166.html#msg112166

 On top of that, most of it is FYI, which will require "75 cm-equivalent less energy" to start bottom-melting than MYI. The MYI is mostly accumulated in a region that is gradually melting out no matter what due to its proximity with Atlantic water.

So as in 2013 (or even more than 2013), we will have to ask ourselves, in case it is an uneventful season, why there was no record or even <1m km2 ice in September. Something must happen in the melting season to prevent so (negative feedback due to snow cover, a cold PAC to prevent insolation and WAAs,...). Otherwise I have little doubt we can get a record low in September.
« Last Edit: June 29, 2017, 05:34:40 PM by seaicesailor »

seaicesailor

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Re: Energy NOT needed for bottom-melting in 2017 and energy transport
« Reply #1 on: May 09, 2017, 11:15:58 AM »
From Sterks:
Quote
I think I am going to move this to a separate thread, but it is interesting to consider how much extra energy is required to bottom-melt MYI in the Arctic Ocean because it has strong implications in this melting season:
- Out of spring, water right underneath the ice is at -1.8C in thermodynamic equilibrium  with the freezing bottom.
- Let's say bottom melting starts in June/July depending on the location (year/round near Atlantic currents).
- For MYI, after a while of bottom-melting the half a meter or so of last season bottom-freezing, the temperature of the water has to raise from -1.8C to 0C in order to continue melting. In contrast, for the more saline FYI, melting proceeds at or slightly above -1.8C.
- This raise of temperature to continue bottom-melting MYI must happen for the whole water column of the mixed layer. In other words, the mixing that happens in this layer will take care of keeping its temperature homogeneous, with a turnover time of the order of the day or a few days.
- Assume the mixing layer is 20 to 40 m depending on location. Let's take 30 m in average.
- The energy for raising 1.8 degrees 30 m of water is equivalent to that needed for bottom-melting approximately 0.75 m of ice!!!! (since raising 1C of a 80m-deep extent of water requires the same energy to melt 1m of the same extent of ice)

So what happens this summer? In parts of the pacific half of the Arctic, and, especially, along Eurasia, we find typically 25-100 cm thinner ice than any previous year.

https://forum.arctic-sea-ice.net/index.php/topic,119.msg112166.html#msg112166

 On top of that, most of it is FYI, which will require "75 cm-equivalent less energy" to start bottom-melting than MYI. The MYI is mostly accumulated in a region that is gradually melting out no matter what due to its proximity with Atlantic water.

So as in 2013 (or even more than 2013), we will have to ask ourselves, in case it is an uneventful season, why there was no record or even <1m km2 ice in September. Something must happen in the melting season to prevent so (negative feedback due to snow cover, a cold PAC to prevent insolation and WAAs,...). Otherwise I have little doubt we can get a record low in September.

Good exercise. However, we must not forget that there are ocean currents in the Arctic that help spread that energy. And those streams end abruptly in certain areas of the Central Arctic as a result of the oceanographic topography. In other words, the ice can melt a lot from this distribution of energy, but upon reaching a certain high latitude, the flow is off. Coincidentally, the albedo feedback too. Note that we are talking about the central Arctic, which will be frozen and cold until August.

Only two mechanisms I can imagine. One is powerful export of ice toward the Atlantic Ocean during the summer, but does not seem likely at all, and very heavy storms in August as well as last summer.

« Last Edit: May 09, 2017, 11:35:45 AM by seaicesailor »

seaicesailor

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Re: Energy NOT needed for bottom-melting in 2017 and energy transport
« Reply #2 on: May 09, 2017, 11:23:49 AM »

Good exercise. However, we must not forget that there are ocean currents in the Arctic that help spread that energy. And those streams end abruptly in certain areas of the Central Arctic as a result of the oceanographic topography. In other words, the ice can melt a lot from this distribution of energy, but upon reaching a certain high latitude, the flow is off. Coincidentally, the albedo feedback too. Note that we are talking about the central Arctic, which will be frozen and cold until August.
Not so sure about how much the bathymetry plays a role, everything has a limit.

This plot an envelope-curve, a minimum of minima of September NSIDC extents. I have taken the ice edge for every year minimum and kept only the edge of each year that is closest to the Pole. I only needed from 2016 back to 2007. Before that year, all the ice edge at September fall out of the curve below.
To take into account that
 - NSIDC September extent is very conservative due to the weird algorithm they used
 - There have been regions in the past with a very low concentration of ice (for instance 2013 near the Pole) that however will never be reflected in these minimum extent ice edges.
I agree that ocean currents help the ice retreat every year, and these currents that are warmer in the continental shelves then sink, BUT you can see that some years have put the edge of the ice well over deep ocean... by hundreds (even thoushand) of kilometers

« Last Edit: May 09, 2017, 12:11:49 PM by seaicesailor »

Sterks

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Re: Energy NOT needed for bottom-melting in 2017 and energy transport
« Reply #3 on: May 09, 2017, 11:58:55 AM »

Not so sure about how much the bathymetry plays a role, everything has a limit.

This plot an envelope-curve, a minimum of minima of September NSIDC extents. I have taken the ice edge for every year minimum and kept only the edge of each year that is closest to the Pole. I only needed from 2016 back to 2007. Before that year, all the ice edge at September fall out of the curve below.


Indeed! You are supporting me in my claim that the bathymetry is likely to prevent the so-called blue ocean event for many years. That red line you have drawn so clearly follows the bathymetry of the Atlantic side. Not so much the Pacific side but taking into account ocean stratification on that side is very special, with a third layer of Pacific water which offers cooler fresher water than the Atlantic, helping the ice to survive, but also salty and warm enough, so much that it will support the albedo feedback during the summer in the seas of Beaufort, Chukchi and ES.

Indeed, I like your plot, that represents the ice edge as I imagine it at the minimum of this year or a bad year, give or take 500,000 km2. I repeat, only a strong "flushing" event during summer as it has never happened in summer except for 2007 and 2010-2012 -but stronger- or very strong storms could end with that core of ice that you show in your map. And notice that the region you are marking is approximately the same as the region of MYI as marked in the last ice-age maps, and the thickest in Cryosat 2 and PIOMAS. Likely to survive!



seaicesailor

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Re: Energy NOT needed for bottom-melting in 2017 and energy transport
« Reply #4 on: May 09, 2017, 12:18:51 PM »
Indeed! You are supporting me in my claim that the bathymetry is likely to prevent the so-called blue ocean event for many years. That red line you have drawn so clearly follows the bathymetry of the Atlantic side. ...

Indeed, I like your plot, that represents the ice edge as I imagine it at the minimum...

You did not read my comment carefully, no I don't support your claim! Ocean currents help in melting peripheral sea ice, but you can see the ice edge (as conservatively as defined by the NSIDC) has retreated thousands of kilometers above deep ocean in past seasons, and in the Atlantic side (2013; 2014 Laptev bite) and in the Pacific side.
But if you like the map as your theoretical minimum minimorum of a bad year, well all yours. But that was not my intention.
« Last Edit: May 09, 2017, 12:24:42 PM by seaicesailor »

gerontocrat

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Re: Energy NOT needed for bottom-melting in 2017 and energy transport
« Reply #5 on: May 09, 2017, 02:36:39 PM »
I thought ocean currents were not merely surface water phenomena. Indeed, that the volume of water moving in these currents made the mightiest land-based rivers appear as tiddly streams. A metre or two of surface ice not much of an obstacle, so bottom melting can continue until the heat is exhausted?

And I am sure that ASIF has the people who have the data on the warm and cold currents flowing in the Arctic together with the staggering amounts of heat and cold transported within them. Only with that and assessments of the quantity of heat absorbed by insolation into the ocean can reasoned conclusions be drawn?
« Last Edit: May 09, 2017, 02:42:13 PM by gerontocrat »
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Sterks

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Re: Energy NOT needed for bottom-melting in 2017 and energy transport
« Reply #6 on: May 09, 2017, 04:42:10 PM »
I thought ocean currents were not merely surface water phenomena. Indeed, that the volume of water moving in these currents made the mightiest land-based rivers appear as tiddly streams. A metre or two of surface ice not much of an obstacle, so bottom melting can continue until the heat is exhausted?

And I am sure that ASIF has the people who have the data on the warm and cold currents flowing in the Arctic together with the staggering amounts of heat and cold transported within them. Only with that and assessments of the quantity of heat absorbed by insolation into the ocean can reasoned conclusions be drawn?
Alright. There are many sorts of currents. Yes currents are complicated but there is an unavoidable tendency of warmer saltier water to sink in the presence of colder fresher water, and that happens at the big slopes of the Basins of the Arctic Ocean. That this colder fresher water exists on top of it all is one interesting thing, which seems to me is not going to change in one season, and therefore I don't believe in any blue ocean event anytime soon. What seaicesailor has depicted in red looks to me as a very reasonable boundary of a very bad season nowadays. Warm currents cannot melt ice over the main Arctic Basins (the Canada Basin is a special case that we can discuss at length).



DoomInTheUK

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Re: Energy NOT needed for bottom-melting in 2017 and energy transport
« Reply #7 on: May 09, 2017, 05:32:06 PM »
That colder fresher water on top will only stay there as long as we don't get a thumping great storm wandering over it and mixing it all up. The odds are that we will be getting more storms in the Arctic, so I think the fresh water layer won't persist for too long.

John_The_Elder

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Re: Energy NOT needed for bottom-melting in 2017 and energy transport
« Reply #8 on: May 09, 2017, 08:03:46 PM »
I thought ocean currents were not merely surface water phenomena. Indeed, that the volume of water moving in these currents made the mightiest land-based rivers appear as tiddly streams. A metre or two of surface ice not much of an obstacle, so bottom melting can continue until the heat is exhausted?

And I am sure that ASIF has the people who have the data on the warm and cold currents flowing in the Arctic together with the staggering amounts of heat and cold transported within them. Only with that and assessments of the quantity of heat absorbed by insolation into the ocean can reasoned conclusions be drawn?
Alright. There are many sorts of currents. Yes currents are complicated but there is an unavoidable tendency of warmer saltier water to sink in the presence of colder fresher water, and that happens at the big slopes of the Basins of the Arctic Ocean. That this colder fresher water exists on top of it all is one interesting thing, which seems to me is not going to change in one season, and therefore I don't believe in any blue ocean event anytime soon. What seaicesailor has depicted in red looks to me as a very reasonable boundary of a very bad season nowadays. Warm currents cannot melt ice over the main Arctic Basins (the Canada Basin is a special case that we can discuss at length).

I believe that you have your facts reversed above:Deep Water Masses: The deep Atlantic is relatively salty (34.9). This water is derived from the sinking of chilled saline surface water in the northern North Atlantic. The cooling makes the surface water dense, forcing it to sink, or convect into the deep ocean, and spread southward at depth. It is called North Atlantic Deep Water (NADW).
John

RoxTheGeologist

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Re: Energy NOT needed for bottom-melting in 2017 and energy transport
« Reply #9 on: May 09, 2017, 08:22:53 PM »

The NADW is a description of how the whole of the Atlantic overturns, and has very little to do with the Arctic basin. The Arctic ocean has very little deep water connectivity to the Atlantic ocean, and none to the Pacific.

Simply, the Arctic's density structure is fairly well understood. As ice forms, it expels briny water that mixes the top part of the ocean, forming the polar mixed layer. In the summer, the ice melts, and along with freshwater from rivers, forming a strongly density stratified freshwater lens over the ocean that prevents mixing. Atlantic and Pacific waters are warm and much denser. They flow into the Arctic and down the continental slope and form the  a deep, warm, and saline layer within the Arctic Basins.

There's a decent summary in this:

http://neba.arcticresponsetechnology.org/report/chapter-1/13/

in section 1.2.2


seaicesailor

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Re: Energy NOT needed for bottom-melting in 2017 and energy transport
« Reply #10 on: May 09, 2017, 09:40:03 PM »
Alright. There are many sorts of currents. Yes currents are complicated but there is an unavoidable tendency of warmer saltier water to sink in the presence of colder fresher water, and that happens at the big slopes of the Basins of the Arctic Ocean. That this colder fresher water exists on top of it all is one interesting thing, which seems to me is not going to change in one season, and therefore I don't believe in any blue ocean event anytime soon. What seaicesailor has depicted in red looks to me as a very reasonable boundary of a very bad season nowadays. Warm currents cannot melt ice over the main Arctic Basins (the Canada Basin is a special case that we can discuss at length).

May I speculate that you just recently learned about the bathymetry of the Arctic Ocean and implications on oceanic inflows and outflows... and you changed your mind about blue ocean events just as recently? See below (sorry for doing this but couldn't help after you mentioning again the curve I plotted above, that does NOT represent any minimum extent in particular:-/ ).

[...]
If we do happen to see a 2007 type summer, I could see us losing all we have there in one go. Why? I do think that the thick ice that is currently there is nothing more then contaminated salty ice that under 2007 or 2012 type summer will vanish in a flash because there is no solid structure to that ice.
Without knowing the whole story of 2007, only partial bits, a scenario like you describe seems entirely reasonable as leading to the first summer virtually without ice. This is my expectation if such weather comes

Edit. By the way I discussed about this last year mentioning an Arctic Sea Ice News article

https://forum.arctic-sea-ice.net/index.php/topic,382.msg84116.html#msg84116

You may want to read the article, as it is out of the question bathymetry has a large influence.... (but inconclusive, as I am because it is a very complicated matter... maybe we will learn something this year).

Edit edit. And even more interesting this response by Bill Fothergill
https://forum.arctic-sea-ice.net/index.php/topic,382.msg84153.html#msg84153

And this by Rob Dekker
https://forum.arctic-sea-ice.net/index.php/topic,382.msg84140.html#msg84140
« Last Edit: May 09, 2017, 10:10:53 PM by seaicesailor »

johnm33

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Re: Energy NOT needed for bottom-melting in 2017 and energy transport
« Reply #11 on: May 10, 2017, 11:07:25 AM »
Looking at the bathymetry image above I'm struck by the course agreement of the ice edge and the continental slopes on the Siberian and N.American sides. So I suspect some relation, perhaps it takes that far for any internal and gravity waves to dissipate enough not to disturb the ice?
Sorry ot.

seaicesailor

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Re: Energy NOT needed for bottom-melting in 2017 and energy transport
« Reply #12 on: May 10, 2017, 12:58:21 PM »
Looking at the bathymetry image above I'm struck by the course agreement of the ice edge and the continental slopes on the Siberian and N.American sides. So I suspect some relation, perhaps it takes that far for any internal and gravity waves to dissipate enough not to disturb the ice?
Sorry ot.
Well this went OT by me that I opened the thread and it's all fine since I like the issue.
I don't question the importance of bathymetry. Atlantic currents that enter east and west of Svalbard, and north of FJL and into Kara sea travel shallow waters, but do not stay close to the surface once over the Arctic basins. They sink as soon as they reach the shelf boundaries into the Arctic basins.
That puts a lot of heat away as we all know (or learn).
I dont know as much about gravity currents, but in any case the tendency of warmer & saltier water to sink down the continental slopes is there all around the Arctic.
Still, look at the minimum of minima extent and notice many kilometers of penetration of the ice edge away from the warm currents inside or above the basins, particularly in the Pacific side.
As I said, this could be an excellent year to test the limiting force of the bathymetry in the reach of the ice edge. My feeling is that if melting propagates early by albedo feedback, sun radiation can force the edge ahead to the north pole, and we have never seen that yet.

Sterks

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Re: Energy NOT needed for bottom-melting in 2017 and energy transport
« Reply #13 on: May 10, 2017, 01:02:09 PM »

May I speculate that you just recently learned about the bathymetry of the Arctic Ocean and implications on oceanic inflows and outflows... and you changed your mind about blue ocean events just as recently? See below (sorry for doing this but couldn't help after you mentioning again the curve I plotted above, that does NOT represent any minimum extent in particular:-/ ).

Edit. By the way I discussed about this last year mentioning an Arctic Sea Ice News article

https://forum.arctic-sea-ice.net/index.php/topic,382.msg84116.html#msg84116

You may want to read the article, as it is out of the question bathymetry has a large influence.... (but inconclusive, as I am because it is a very complicated matter... maybe we will learn something this year).

Edit edit. And even more interesting this response by Bill Fothergill
https://forum.arctic-sea-ice.net/index.php/topic,382.msg84153.html#msg84153

And this by Rob Dekker
https://forum.arctic-sea-ice.net/index.php/topic,382.msg84140.html#msg84140

seaicesailor:

1. Yes, I wrote that about this season, but I was already convinced that there is not enough energy from insolation alone to melt out all Central Arctic areas where the weather is cold, the pack is closed until August and the warm currents, whether from the Atlantic Ocean or from the Pacific Ocean, do not reach such high latitudes. In any case, when I wrote that I was also thinking on Fram Export event as occurred in 2007. During that summer, export was non-stop, in opposition to what usually happens in most summers. If this summer is warm and also the export continues, we may see a new record far exceeding the previous one. Happy?
2. The article you mention does not but confirm my positions as well as Bill Fothergill's comments and (in part) Rob Dekker.
3. The Canada Basin is a more special place. For example, thanks to the Beaufort Gyre that rotates on top of it, upwelling currents happen along the coast of Canada and Alaska and the Chukchi Sea. The upward flows can transport Atlantic water from the abyss through the layers of Atlantic and Pacific halocline and mix it up with the mixed layer. The article RoxTheGeologist links to mentions it. There are also many eddies created by instabilities of currents that always appear at the slopes of the continental shelf. Also mentioned in the article. This makes the Beaufort Sea a very dynamic sea in summer, where melting can continue at high pace, in which differences in salt content and temperature can arise from the most unexpected places. The melting is also supported by frequent warm air intrusions from the continent, and the albedo feedback mechanism. However, the Beaufort Sea ice used to survive the summer in the 20th Century. Is it not surprising that on top of the whole Canada Basin that ice was able to survive? Global warming means that the Multi Year Ice no longer survives in the Beaufort Sea.
4. In any case, I reaffirm my position. Not that this denies anything. I simply think the AGW progresses slowly and, as the Canada Basin is now free of ice when it was not the case 20 years ago, the same will happen with the other basins. But I'm not sure if I will get to see it, unless perfect conditions happen as what I implied in January and in paragraph 1 of this comment.
Apologies for the lengthy answer

DoomInTheUK

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Re: Energy NOT needed for bottom-melting in 2017 and energy transport
« Reply #14 on: May 10, 2017, 01:04:44 PM »
The minimum of minima (MoM?) will also be influenced by the trans polar drift.
That might give a clue as to why the ice edge tends to be closer to the drop off on the Atlantic side and further from the Pacific. It's a trend in the data.

Just a thought.

seaicesailor

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Re: Energy NOT needed for bottom-melting in 2017 and energy transport
« Reply #15 on: May 10, 2017, 02:48:24 PM »
The minimum of minima (MoM?) will also be influenced by the trans polar drift.
That might give a clue as to why the ice edge tends to be closer to the drop off on the Atlantic side and further from the Pacific. It's a trend in the data.

Just a thought.
Completely right. Providing that observed offset toward the Greenland sea. And the Gyre combined with the "ice slaughter" of Beaufort sea explains the void in Beaufort and Chukchi seas.
Pending the question of how far the ice edge can retreat due to heat amplification inside the core of the CAB - aside from the effect of wind drift. Ocean currents unable.

To me it all boils down to having a very early generalized surface melting and propagating melt front.

And the ace card of the summer (the GACs).

johnm33

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Re: Energy NOT needed for bottom-melting in 2017 and energy transport
« Reply #16 on: May 11, 2017, 11:15:57 AM »
DoomInThe UK, it may be that the ridge seperating the Amundsen and Nansen basins acts as a baffle reducing wave damage on the Atlantic side, just a thought.
Seaicesailor, one cause of internal waves is the arrival of deep lows or extreme highs over the arctic, the forecast you posted on the season page shows a deep low arriving on the Siberian side, if that pans out I would expect a surge of water towards that area, whether it's surface, or deeper layers that move is another question. If it's deeper water we'll see the ice forced away from the shore, if it's surface waters cracks and some thinning further out, er... I think.