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Author Topic: Halo[de]cline. The expansion of the Surface mixed zone, loss of Fresher Lens.  (Read 3384 times)

Hyperion

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This is known to be of utmost importance. If the lower salinity lens on the surface is mixed away or exported, then there is much too much thermal energy in the Atlantic and Pacific warmer, saltier layers beneath for the central Arctic Basin to refreeze in winter. Data is scarce due to only one drift buoy still active this year.

Woods ITP97 has for nearly 500 days been transiting from near Bering towards the CAA across some of the deepest parts of the basin.



The Temperature and Salinity plots show some interesting incontinuities that seem to suggest to me areas of surface/depth mixing, where the Halocline has ruptured.



Perhaps even better illustrated by the Dissolved Oxygen plot.



The Copernicus salinity models are obviously not as fine a resolution as what the Buoys are measuring. The 5m Salinity fronts actually do not appear to have changed much 2012-2017. But the Thickness of the surface mixed zone appears to be increasing throughout the basin.
hope these animate if you click them. 1 colour bar is 25m on the Thickness plot so we have the CAB gone from less than 25m surface mixed layer to up around 75m in five years it seems:


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Bruce Steele

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Hyperion, I would say it is a bit of luck that the one remaining ITP buoy is located in the same region that your mixed layer chart shows deepening in the Beaufort. I will link a paper on the Arctic Mixed Layer that says it's depth stayed between 16 meters in the summer down to rarely over 40 meters in the winter for an aggregated set of ITP buoy runs. Current depth has reached 50 meters for the mixed layer on ITP 97.
 In reading through the paper below it says , at the end of sec.3.1 that the mixed layer was down to 50 meters back in 1975. So I don't know why it appears the mixed layer in central Beaufort has deepened but maybe looking back at 1975 would help .

https://www.whoi.edu/fileserver.do?id=84144&pt=10&p=25592

Here is a completed mission for ITP 65 back in 2013 that traveled through the central Beaufort and shows the shallower mixed layer depths for that year.

http://www.whoi.edu/page.do?pid=132596

BTW The 500 days on ITP97 doesn't mean it's been around that long. Still less than a year old deployed Oct. 2016, but that's good because if we're lucky it will continue to run for awhile more. Hopefully some new buoys get set out this year.
« Last Edit: May 07, 2017, 06:28:33 AM by Bruce Steele »

Andreas T

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ITP 95 has been deployed together with IMB2017B at Barneo (10.4.2017?). http://www.whoi.edu/page.do?pid=158516
 I guess it will go out of Fram strait probably before the end of the year so its data won't just show changes over time but changing location.
last year did not have buoy data from the ice camp but previous years should be around.
ITP75 from 2013 shows how a trip across the pole to Fram looks:
http://www.whoi.edu/page.do?pid=126416
There was no NPEO buoy deployment at barneo in 2016 but 2015 deployed an ITP but I can't find its number does anybody remember?

Bruce Steele

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Andreas, maybe ITP 83 is what you're looking for ?
Thanks for pointing out ITP 95, should be something to watch and it looks like it is working well.

http://www.whoi.edu/page.do?pid=143156

Interesting that the temp/ salinity profile for ITP 83 doesn't show the shoaling of the temperatures and salinity like buoys that approach the Fram on the eastern side like ITP 74 or ITP 93. The Eastern side of the Fram has Atlantic water moving north but the western side is Arctic water exiting, I assume.
« Last Edit: May 07, 2017, 05:34:29 PM by Bruce Steele »

Andreas T

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Thanks, Bruce, April 2015 deployment near the pole, that must be the one colocated with IMB2015D.

Looking at the file of locations it crossed the 80N parallel on day 337 of 2015 which is also when the contour plot ends (unless I am overlooking something)
This matches the locations Jim shows on his site for IMB2015D.

So the absence of shoaling might be a combination of its track over the deep western side of Fram strait and lack of data further south into the Greenland sea.

Those sudden jumps in salinity around day 180 and 220 look very odd with no corresponding change in temperature. Are those data glitches? Fouling of conductivity sensor maybe?

edit: remembered something I posted a while back, profiles measured by the sabvabaa crew https://sabvabaa.nersc.no/
« Last Edit: May 07, 2017, 06:36:14 PM by Andreas T »