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anthropocene

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Relative height of North Pacific and Atlantic
« on: June 04, 2015, 11:58:29 PM »
In an interview (http://www.ecoshock.info/2015/05/crashing-climate-change.html?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+EcoshockNews+%28Ecoshock+News%29) Paul Beckwith states that in normal conditions the Pacific is higher than the Atlantic. There is therefore a gradual flow from Bering Strait to Barents. He also states that this differential was increased in 2010 and the influx of warm water this caused was a major factor in the collapse of ice volume in that year. He also implies that this differential is larger in El Nino years. Everything would therefore point to a large differential in 2015. I know this was discussed many years ago on this blog but I can't find the thread. Anybody know of a resource for near real time sea-level differences between Pacific and Atlantic and/or a near real time measure of flow through Bering Strait? With the "North Pacific warm blob" if this flow is large I suspect this year will be close to minimum low no matter what the weather does.

plinius

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Re: Relative height of North Pacific and Atlantic
« Reply #1 on: June 05, 2015, 12:24:27 AM »

Bruce Steele

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Re: Relative height of North Pacific and Atlantic
« Reply #2 on: June 05, 2015, 12:56:57 AM »
Plinius, Maybe it's bad form but I am going to copy a post I made on another page.

I have been wondering about the transfer of warm water from the Pacific through the Aleutians  and via the Alaskan Coastal current into the Beaufort and Chukchi Seas. Wood et 2015

http://www.sciencedirect.com/science/article/pii/S0079661115001020

From the article



"Steele et al 2010 showed that 80% of the ocean heating in the Pacific Arctic north of Alaska is from ocean heat flux, and only 20% due to ocean lateral heat flux( e.g. Bering Sea inflow), which mostly occurs within a few hundred kilometers from the coast. Moreover, the movement of Pacific Water from the Aleutian Passes to BeringStrait takes more than one year, with the exception of the small
portion that enters the shelf through the Zemchug Canyon, which takes 8 months.
Hence , most of the water of Pacific origin entering the Bering Strait has gone through a seasonal cycle on the journey and thus cooled to near freezing ( -1.8 *C )
( Stabeno et al, in press ) as reflected in the low temperatures recorded at the mooring array in the Strait."
" This would imply that most of the warm water advected into into the Bering Strait ( and available to melt sea ice ) must be heated in transit from the atmosphere ( insolation and downward long wave radiation ) in the Northern Bering  Sea ( Woodward et al 2010 ) "

   It seems to me there will be much more advection of Pacific heat via the Alaskan Coastal Current when the Bering Sea warms to the point that Bristol Bay and Norton Sound stay mostly ice free year round. Then summer insolation and long wave radiation will work on coastal waters for longer periods and that heat can then move into the Beaufort and Chukchi earlier.  I am not going to speculate on when this may happen but when the ACC starts with water above -1.8 C  each spring the extra heat moved North will add substantially to current heat transfer from the Pacific.
 Neven speculated on the effects of the Pacific warm water "blob" over on the Sea Ice Blog last post before vacation .   

One of the contributing factors to the sea height differential Atlantic / Pacific is evaporation of Atlantic
moisture moving across Central America and precipitating in the Pacific. El Nino may play some roll in the amount of moisture moved across the Istmus but there would be some time lag between that sea level change and it's arrival at the Bering Strait. 

plinius

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Re: Relative height of North Pacific and Atlantic
« Reply #3 on: June 05, 2015, 02:35:46 AM »
Bruce, I am a bit surprised. How does that work?
One of the contributing factors to the sea height differential Atlantic / Pacific is evaporation of Atlantic
moisture moving across Central America and precipitating in the Pacific.


You mean there is a salinity effect?

Bruce Steele

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Re: Relative height of North Pacific and Atlantic
« Reply #4 on: June 05, 2015, 05:06:33 AM »
Plinius, Yes the moisture transport changes salinity also but "pressure head " differences are what I was referring to. Here is a Q&A with Rebecca Woodgate.

Question from Sam: Why does the water flow from the Chukchi Sea into the Deep Basin?
Answer: I asked Chief Scientist Rebecca Woodgate to answer this question. She has been studying the physical oceanography of the Arctic for over a decade.

"We have some ideas of why water flows north through the Chukchi into the Arctic, and it's to do with the ocean and atmosphere circulation of the whole world. Basically, water evaporates from the Atlantic ocean, is carried over to the Pacific ocean by air currents, and rains back down on the Pacific. So now we have "too much" water in the Pacific and it has to get back somehow, so it flows back through the Chukchi Sea and the Arctic. That's part of it. The ocean currents could be doing the same sort of thing - pushing too much water into the Pacific, so it leaks out at the top into the Arctic. We call these effects "pressure head" effects, because there is more water on one side (the Pacific) than on the other (the Arctic) and so that drives a flow. It's the same effect as causes your toilet to flush - kinda. The winds drive the water in the Chukchi Sea too, but the average wind is actually towards the south, and tries to drive the water back south against this pressure head. The effect of the wind is however less than the pressure head effect, so on average the water still goes north.

anthropocene

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Re: Relative height of North Pacific and Atlantic
« Reply #5 on: June 05, 2015, 12:25:57 PM »
Thanks for the link. Hard to spot differences at that scale but the major change seems to be height reduction south of Greenland. With fresh cold outflow of glacier melt this makes sense. Interesting to see if Bering to Greenland flow has speeded up since that 2010 paper.

Vergent

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Re: Relative height of North Pacific and Atlantic
« Reply #6 on: June 05, 2015, 02:56:17 PM »
http://www7320.nrlssc.navy.mil/hycomARC/navo/arcticssh_nowcast_anim30d.gif

Verg

Edit: The static parts are due to gravity anomaly. The dynamic parts are due to tides, weather, and thermohaline circulation.
« Last Edit: June 05, 2015, 03:10:25 PM by Vergent »