Arctic Ocean salinity, temperature and waves

[johnm33]

Looking at Mercator salinity 30m it seems the Atl. waters are short circuiting and returning along Lomonosov from Laptev, they appear to be mixing with returns from ESS creating turbulence immediately beneath the openings in the ice north of Greenland.  I also suspect overflow from the Canadian side, by Belov trough, is forcing internal waves and actual movement in the basal layers towards Fram.
Strange that it [Atl.] doesn't get mixed maybe there's a wall of inert water holding station along the American side?
 

[uniquorn]

mercator current 92m, mar21-aug17

mercator salinity and current for this day from 2017-2020 or nearest where available (salinity useful for showing up/downwelling)

[vox_mundi]

Arctic Ocean Moorings Shed Light On Winter Sea Ice Loss
https://phys.org/news/2020-08-arctic-ocean-winter-sea-ice.html

The eastern Arctic Ocean's winter ice grew less than half as much as normal during the past decade, due to the growing influence of heat from the ocean's interior, researchers have found.



The finding came from an international study led by the University of Alaska Fairbanks and Finnish Meteorological Institute. The study, published in the Journal of Climate, used data collected by ocean moorings in the Eurasian Basin of the Arctic Ocean from 2003-2018.

The moorings measured the heat released from the ocean interior to the upper ocean and sea ice during winter. In 2016-2018, the estimated heat flux was about 10 watts per square meter, which is enough to prevent 80-90 centimeters (almost 3 feet) of sea ice from forming each year. Previous heat flux measurements were about half of that much.

"In the past, when weighing the contribution of atmosphere and ocean to melting sea ice in the Eurasian Basin, the atmosphere led," said Igor Polyakov, an oceanographer at UAF's International Arctic Research Center and FMI. "Now for the first time, ocean leads. That's a big change."

Typically, across much of the Arctic a thick layer of cold fresher water, known as a halocline, isolates the heat associated with the intruding Atlantic water from the sea surface and from sea ice.

This new study shows that an abnormal influx of salty warm water from the Atlantic Ocean is weakening and thinning the halocline, allowing more mixing. According to the new study, warm water of Atlantic origin is now moving much closer to the surface.

"The normal position of the upper boundary of this water in this region was about 150 meters. Now this water is at 80 meters," explained Polyakov.



A natural winter process increases this mixing. As sea water freezes, the salt is expelled from ice into the water. This brine-enriched water is heavier and sinks. In the absence of a strong halocline, the cold salty water mixes much more efficiently with the shallower, warm Atlantic water. This heat is then transferred upward to the bottom of sea ice, limiting the amount of ice that can form during winter.

Polyakov and his team hypothesize that the ocean's ability to control winter ice growth creates feedback that speeds overall sea ice loss in the Arctic. In this feedback, both declining sea ice and the weakening halocline barrier cause the ocean's interior to release heat to the surface, resulting in further sea ice loss. The mechanism augments the well-known ice-albedo feedback—which occurs when the atmosphere melts sea ice, causing open water, which in turn absorbs more heat, melting more sea ice.

When these two feedback mechanisms combine, they accelerate sea ice decline. The ocean heat feedback limits sea ice growth in winter, while the ice-albedo feedback more easily melts the thinner ice in summer.

"As they start working together, the coupling between the atmosphere, ice and ocean becomes very strong, much stronger than it was before," said Polyakov. "Together they can maintain a very fast rate of ice melt in the Arctic."

Polyakov and Rippeth collaborated on a second, associated study showing how this new coupling between the ocean, ice and atmosphere is responsible for stronger currents in the eastern Arctic Ocean.

According to that research, between 2004-2018 the currents in the upper 164 feet of the ocean doubled in strength. Loss of sea ice, making surface waters more susceptible to the effects of wind, appears to be one of the factors contributing to the increase.

The stronger currents create more turbulence, which increases the amount of mixing, known as shear, that occurs between surface waters and the deeper ocean. As described earlier, ocean mixing contributes to a feedback mechanism that further accelerates sea ice decline.



Igor V. Polyakov et al, Weakening of Cold Halocline Layer Exposes Sea Ice to Oceanic Heat in the Eastern Arctic Ocean, Journal of Climate (2020)
https://journals.ametsoc.org/jcli/article/33/18/8107/353233/Weakening-of-Cold-Halocline-Layer-Exposes-Sea-Ice

Igor V. Polyakov et al. Intensification of Near‐Surface Currents and Shear in the Eastern Arctic Ocean, Geophysical Research Letters (2020).
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2020GL089469

[johnm33]

I was looking at movement along the CAA coast, there was an interesting feature further out so I wondered what caused it and fitted it to the bathymetry.

[uniquorn]

Igor V. Polyakov et al, Weakening of Cold Halocline Layer Exposes Sea Ice to Oceanic Heat in the Eastern Arctic Ocean, Journal of Climate (2020)
https://journals.ametsoc.org/jcli/article/33/18/8107/353233/Weakening-of-Cold-Halocline-Layer-Exposes-Sea-Ice

Thanks vox.

Heat associated with oceanic currents originating from lower latitudes provides an important, and year-round, source of heat to the Arctic Ocean (e.g., Carmack et al. 2015). The dominant external source of oceanic heat is the warm (temperature > 0°C) and salty water of Atlantic origin [Atlantic Water (AW)], which is distributed throughout the deep basins at intermediate depths (~150–900 m; Fig. 1) and holds sufficient heat to melt the Arctic sea ice 3–4 times over (Carmack et al. 2015). Across much of the eastern (>70°E) Eurasian Basin (EB) this heat is isolated from the surface, and hence the sea ice, by large vertical density gradients associated with the Arctic halocline (60–150 m; Fig. 1). The presence of the halocline impedes the transport of AW heat upward toward the surface across much of the Arctic Ocean (e.g., Fer 2009). The exception to this is the western (<70°E) Nansen Basin where substantial turbulent mixing linked to the tides (Fer et al. 2010; Padman and Dillon 1991; Rippeth et al. 2015; Renner et al. 2018) and wind events (e.g., Provost et al. 2017; Graham et al. 2019) supports heat fluxes in excess of 50 W m−2.

edit: my bold

Maybe has something to do with this

[uniquorn]

Position of moorings and potential temperature chart 2013-2017 for the paper above.

Depth–time diagram of potential temperature θ (°C) from the M13 mooring. Black lines show the depth of the halocline base and lower Atlantic Water boundary, both defined by 0°C isotherms.

https://en.wikipedia.org/wiki/Potential_temperature

The potential temperature of a parcel of fluid at pressure P is the temperature that the parcel would attain if adiabatically brought to a standard reference pressure P 0, usually 1,000 hPa (1,000 mb).

Now, how long does it take for laptev water to reach the yermak plateau/north of Greenland?

[binntho]

The paper vox linked to is indeed very interesting. I missed the highligted (by you, Uniqorn?) mention of tides. And it makes me wonder - if there is "substantial" turbulent mixing due to tides and wind in the Nansen Basin west of Franz Josef Land, where are the visible effects of this?

And what is meant by "substantial" - and how come that you highlighted parts of the sentence without saying so, and forgot the latter half of the sentence, i.e. the wind mention? Saying "in excess of" 50 W/m2 is not really good enough, is this a continuous heat flux or something that happens occasionally? As in "substantial" once a month for three hours?

[uniquorn]

If it makes you wonder binntho, we must be getting somewhere. I've edited the post to show my bold and I'm pleased that it made you notice it. There's no need to be suspicious. I'm just looking for evidence to support my ideas, as you should do.

[binntho]

If it makes you wonder binntho, we must be getting somewhere. I've edited the post to show my bold and I'm pleased that it made you notice it. There's no need to be suspicious. I'm just looking for evidence to support my ideas, as you should do.

It does make me wonder - it seems dishonest to make changes in other people's text without making it clear that you are doing so. And it seems dishonest to seperate the two halves of the sentence, to make it look as if it is only about tides.

In fact, the article does not count as evidence of any substantial tidal effect, and here I mean substantial as in making a discernible difference to the overall state of the ice.

[uniquorn]

So we disagree again. It's quite common on this forum to bold parts of text to highlight them.
I'll give you the chance to retract the slur on my integrity before reporting you to the moderator.

[binntho]

So we disagree again. It's quite common on this forum to bold parts of text to highlight them.
I'll give you the chance to retract the slur on my integrity before reporting you to the moderator.

Please report me. It is dishonest if you don't mention it, if you do mention it it is perfectly normal. In the first post I asked if you had done it and you answered snidely, so you are obviously not aware that this is not how things are done.

Whether or not is dishonest to only highligt only part of the sentence, I'll happily retract that, it could have been a simple error.

[uniquorn]

I've edited the post to include the whole sentence.

[uniquorn]

A longer look at the low concentration north of the yermak plateau, western end of the Nansen basin. Note how the low concentration stays in the same area despite ice drifting over it. In my view this low concentration can't be due to wind and there is good evidence of turbulence, possibly caused by tides

[uniquorn]

Also reposting some stuff from west of FJL in january (already on this thread)

[uniquorn]

buoys over the yermak plateau



a wider view of more buoys



evidence of turbulence. Thanks to JayW

[uniquorn]

Today's worldview terra of the yermak plateau area. Too cloudy again for rammb I think.

[uniquorn]

Tidal forcing, energetics, and mixing near the Yermak Plateau
I.Fer1,3, M. Müller2, and A. K. Peterson1,
Published: 27 March 2015

Abstract
The Yermak Plateau (YP), located northwest of Svalbard in Fram Strait, is the final passage for the inflow of warm Atlantic Water into the Arctic Ocean. The region is characterized by the largest barotropic tidal velocities in the Arctic Ocean. Internal response to the tidal flow over this topographic feature locally contributes to mixing that removes heat from the Atlantic Water. Here, we investigate the tidal forcing, barotropic-to-baroclinic energy conversion rates, and dissipation rates in the region using observations of oceanic currents, hydrography, and microstructure collected on the southern flanks of the plateau in summer 2007, together with results from a global high-resolution ocean circulation and tide model simulation. The energetics (depth-integrated conversion rates, baroclinic energy fluxes and dissipation rates) show large spatial variability over the plateau and are dominated by the luni-solar diurnal (K1) and the principal lunar semidiurnal (M2) constituents. The volume-integrated conversion rate over the region enclosing the topographic feature is approximately 1 GW and accounts for about 50% of the M2 and approximately all of the K1 conversion in a larger domain covering the entire Fram Strait extended to the North Pole. Despite the substantial energy conversion, internal tides are trapped along the topography, implying large local dissipation rates. An approximate local conversion–dissipation balance is found over shallows and also in the deep part of the sloping flanks. The baroclinic energy radiated away from the upper slope is dissipated over the deeper isobaths. From the microstructure observations, we inferred lower and upper bounds on the total dissipation rate of about 0.5 and 1.1 GW, respectively, where about 0.4–0.6 GW can be attributed to the contribution of hot spots of energetic turbulence. The domain-integrated dissipation from the model is close to the upper bound of the observed dissipation, and implies that almost the entire dissipation in the region can be attributed to the dissipation of baroclinic tidal energy.

My bold

It's possible that this contributes to the lower concentration ice in this area very recently.
A short extract that may also be relevant.

Baroclinic  disturbances in response to tidal flow over topography above the critical latitude are thus topographically trapped near the generation site (a continental slope, a ridge, or a seamount). The energy propagation of topographically trapped waves is possible  along  the  slope,  around  the  topographic  feature  with negligible radiation away in the cross-slope direction. This is analogous to the sub-inertial baroclinic trapped waves propagating  around  isolated  seamounts  (Brink,  1989).  Trapped tides  dissipate  their  energy  locally,  or  elsewhere  along  the topography, leading to substantial vertical mixing

[binntho]

It's possible that this contributes to the lower concentration ice in this area very recently.

Entirely possible. Although I must admit that I find it difficult to get a grip on the scale and understand the energy involved.

For example, what is meant by

From the microstructure observations, we inferred lower and upper bounds on the total dissipation rate of about 0.5 and 1.1 GW, respectively, where about 0.4–0.6 GW can be attributed to the contribution of hot spots of energetic turbulence. The domain-integrated dissipation from the model is close to the upper bound of the observed dissipation, and implies that almost the entire dissipation in the region can be attributed to the dissipation of baroclinic tidal energy.

They express something called "dissipation rate" in the region of 1GW - is this a measure of water flow or heat flow? I suspect the former, since they attribute it to "tidal energy", which is definitely not heat.

And if this is a measure of water flow then we should be able to compare it to a terrestrial hydropower station. Just down the road from me they are building a massive dam (the Grand Reneissance Dam or GERD) with a max planned installed capacity of 6.45GW from the flow of the Blue Nile, from an average flow of some 1500 m3/second which equates to 0.0015 Sverdrup.

Compare this with the West Spitzbergen Current which flows in over the Yearmak Plateau, it is not easy to find exact numbers but according to Wikipedia it swings between 5 and 20 sverdrups,

So my conclusion from this, given that I am not totally misunderstanding the 1GW in the article, is that the tidal effect over the Yearmak Plateau is smaller than the West Spitzbergen Current by a factor of  at least 10.000.

[uniquorn]

Turbulence dissipation is the rate at which turbulence kinetic energy is converted into thermal internal energy.

What is Turbulence Energy Dissipation Rate?
The dissipation of the kinetic energy of turbulence(the energy associated with turbulent eddies in a fluid flow) is the rate at which the turbulence energy is absorbed by breaking the eddies down into smaller and smaller eddies until it is ultimately converted into heat by viscous forces.

But this is more likely to be the larger contributor

Trapped tides  dissipate  their  energy  locally,  or  elsewhere  along  the topography, leading to substantial vertical mixing

My bold

[uniquorn]

Some background reading on trapped diurnal internal tides from studies done off the California coast, citing other possibly relevant papers.

Trapped D₁ internal tides are often more energetic than D₂ internal tides in the SCB. These waves may have considerable impact on mixing as noted earlier (Section 1) because there are likely numerous sites of generation and dissipation in close proximity at rough topography (Tanaka et al., 2013). Elsewhere,at a sea mount in the North Pacific near 321N, dissipation is strong enough to dissipate the trapped D₁ motions within 3 days, which makes for a strongly forced and damped system (Kunze and Toole,1997). In the SCB, surface drifters in this area show diurnal/inertial oscillations with decay scales of 10 days (Poulain, 1990).There are numerous sources of D₂ internal tides along the continental slope and over the rough topography of the SCB(Beckenbach and Terrill, 2008; Buijsman et al., 2012). Internal tidal generation may produce local mixing (Johnston et al., 2011a;Klymak et al., 2006). Propagating internal tides may encounter topography, scatter to smaller scales, and break (Johnston and Merrifield, 2003; Johnston et al., 2003; Kelly et al., 2012; Martini et al., 2011; Nash et al., 2004)

[uniquorn]

At last....

arctic tidal current atlas
Till M. Baumann, Igor V. Polyakov, Laurie Padman, Seth Danielson, Ilker Fer, Markus Janout, William Williams & Andrey V. Pnyushkov
Received: 17 January 2020; Accepted: 24 June 2020;Published online: 21 August 2020

Background & Summary
Tidal currents are often the dominant source of current variability and play an important role in shaping the Arctic Ocean hydrography and sea ice cover. Tidal currents are also a key element shaping the marine ecosystem with impacts ranging from creating the habitat of the intertidal zone to mixing of nutrients. Furthermore, information about tidal currents is used for many practical applications, such as navigation, fisheries and marine structures and operations.

Barotropic tidal models based on the depth-integrated momentum and continuity equations provide ocean surface height and depth-averaged currents for major tidal constituents throughout the Arctic. These comparatively simple models show very little tidal activity (<0.5 cm/s) in the central Arctic deep basins, but strong amplitudes (>10 cm/s) over portions of the continental shelves and slopes. Where barotropic tidal currents flow across steep slopes or rough topography in the presence of stratification, energy can be converted from barotropic to baroclinic (internal) tides whose energy finally dissipates in mixing processes. The importance of baroclinic tidal processes was highlighted, for example, by Luneva et al, who found that the addition of tidal currents to an atmospherically forced three-dimensional simulation reduced pan-Arctic sea ice volume by ~15%. The authors attributed this sea ice reduction to the entrainment of warm subsurface Atlantic Water into the cold near-surface waters by mixing caused by increased surface stresses and by upper-ocean shear instabilities from the combination of baroclinic tides and the atmospherically forced three-dimensional circulation. In contrast to barotropic tides, the generation, propagation and dissipation of baroclinic tidal waves are sensitive to stratification, mean flow, and energy losses through friction and mixing within the water column. They may, therefore, change substantially with variations in the background ocean state associated with weather-band and seasonal changes in forcing, ocean mesoscale variability (e.g., eddies) and as the Arctic Ocean changes on longer time scales. Despite the importance of tides for the Arctic Ocean and its sea ice, most ocean general circulation models used for climate projections do not currently include tides.

Concluding remarks.
Tidal currents play a vital role in the Arctic climate and ecosystems, but our understanding of their spatio-temporal variability is limited. The goal of our atlas of tidal currents described herein is to provide a tool that enables investigations into regional high-frequency dynamics in a changing Arctic Ocean. As a ground-truth for the modelling community, this may contribute to more reliable projections of future Arctic Ocean states.

[uniquorn]

Internal Tides and Abyssal Mixing

M.C. Gregg, in Reference Module in Earth Systems and Environmental Sciences, 2013
Internal Tides   

The horizontal currents produced by surface tides are constant with depth. Called barotropic flows, they are driven by horizontal pressure gradients induced by the sea surface slopes accompanying the tides. When these currents cross sloping bottoms, the oscillations produced by disrupting the ambient stratification propagate away as internal tides, shown schematically in Figure 2. Internal tidal currents vary with depth (unlike barotropic tidal currents) and are associated with vertical displacements of 10 m or more in the thermocline. Their surface displacements, however, are reduced about 1000-fold, the ratio of the density of water and that of air.

Existence of internal tides has long been known from fluctuations of temperature observed in the thermocline with moorings. Their spatial structure and importance, however, were not generally suspected until discovered by an acoustic array north of Hawaii (Dushaw et al., 1995). This and weak signatures in records of surface displacements led Ray and Mitchum (1996) to search for large-scale patterns in sea surface heights measured with radar altimeters on Topex/Poseidon satellites. Against expectations, they were able to remove meter-scale surface tides to reveal the centimeter-scale displacements of internal tides. Ray and Mitchum discovered coherent displacements between rather widely spaced satellite tracks indicating internal tides radiating northward from the Hawaiian Ridge. Peaks in along-track spectra indicated horizontal wavelengths of 150–160 km for mode-one M2 (lunar) and S2 (solar) tides. Mode-two peaks were also detectable with wavelengths about half as long. These results led in turn to the Hawaiian Ocean Mixing Experiment (HOME) early in the twenty-first century.

This perhaps explains the eddy just east of the Lomonosov ridge posted by blumenkraft on aug13.

[uniquorn]

worldview terra modis, yermak plateau area, aug26, heavy contrast.
click to compare with a very light contrast version

a peek through the clouds with rammb. Some eddy motion by the large floes can just be made out.

[oren]

Uniquorn big thanks for your great contributions on this thread.

[binntho]

Uniquorn big thanks for your great contributions on this thread.

+1

[binntho]

At last....

Indeed, a very good find. I've snipped two interesting parts of the text from your post:

[quote author = https://www.nature.com/articles/s41597-020-00578-z.pdf]
These comparatively simple models show very little tidal activity (<0.5 cm/s) in the central Arctic deep basins, but strong amplitudes (>10 cm/s) over portions of the continental shelves and slopes.

and further :
[quote author = https://www.nature.com/articles/s41597-020-00578-z.pdf]
The importance of baroclinic tidal processes was highlighted, for example, by Luneva et al, who found that the addition of tidal currents to an atmospherically forced three-dimensional simulation reduced pan-Arctic sea ice volume by ~15%. The authors attributed this sea ice reduction to the entrainment of warm subsurface Atlantic Water into the cold near-surface waters by mixing ...

So finally a number that allows for comparison with other processes active in the Arctic. And I'll admit it is bigger than I expected. The localized upward mixing caused by tidal movement has a pan-Arctic effect of keeping volume 15% lower than would otherwise be the case.

Since this mixing is localized, I wonder if there is a strong variability at surface, i.e. whether these ongoing upwards mixing processes have the potential to "punch through" the ice at some time in the future, making them suddenly visible.

[uniquorn]

A quick look at the persistent low concentration area north of NSI/ESS, 80.7N 154.5

amsr2-uhh, aug17-26
today's worldview overlaid onto noaa bathymetry

[uniquorn]

https://go.nasa.gov/34DrtAq, nth greenland for ref (clahe 1.7)

[uniquorn]

mercator sst with amsr2-uhh, aug1-27

[uniquorn]

Intriguing description of motion in the fram strait here

By Matthew Shupe

7/25/20 Round and Round
We are just spinning in circles around here. Around and around. Our floe just keeps on turning. Over the many days that we’ve been here the orientation of our floe didn’t change much, the ship having a robust SW heading. But in the last two days we have spun in two full circles, including about 410 degrees in just the last day! This is really remarkable, and I have no idea how it happens. Is it somehow drag on the floe due to the ship, or just dynamics in the ocean? There have not really been many winds to speak of. No one else understands this either. But it has a fascinating effect on our perspective. Standing out on the short of the floe, you look out and so many other floes go drifting by, seemingly moving quickly. While some of these floes are likely moving in reality, our spinning floe gives the impression that everything else is moving very fast. We are not used to that, as typically our floe just drifts along with everything else. Another one of those Arctic mysteries.

On jul25 they were just crossing 80N, a little east of the large rotating eddy. (weather was only clear on jul22)

  79.9   -1.0 20-07-25 15:00    6   30     -0.1  7  1  97  4042 89/9/ 1017.8
  79.9   -0.9 20-07-25 14:00    6   30      0.0  /  /  //  //// ///// 1018.2
  80.0   -0.7 20-07-25 11:00    6   10      0.0  /  /  //  //// ///// 1018.2
  80.0   -0.7 20-07-25 10:00    5   10      0.3  /  /  //  //// ///// 1018.4



A rather messy buoys eye view of the movement. It didn't occur to me before that the floes might be spinning independently of each other. Different keels, smaller eddies...

[binntho]

It didn't occur to me before that the floes might be spinning independently of each other. Different keels, smaller eddies...

Or perhaps the larger floe that they are on is only partially entering a larger movement (eddies or currents). This would cause it to rotate and from the point of view of someone standing at the edge of the floe, smaller floes would seem to be moving away (i.e. staying in place as the observer moves past) as long as the observer is facing away from the current. So observing the smaller floes for a full 360 degrees turn of the larger would tell you more about what was going on.

[uniquorn]

Could be.
Southerlies from the Laptev opening up some weaker areas in the CAB. The oval low concentration area persists.

added rammb of the oval area. Stationary frames left in (no cheating )

[uniquorn]

A very close look at axib buoy 91790, ~86.1N -45 (north of Greenland)

Somewhere near the middle of the clear worldview image from aug28 

I think arctic ocean 'waking up' might not have been too far off the mark

rammb nth greenland

[binntho]

Fantastic swirling - but scale is not obvious. Based on the latitudes and longitudes at start and finish it seems that the swirling is taking place in a very small area, perhaps 1 or 2 km from side to side.

[uniquorn]

Worldview terra modis of the low concentration area north of ESS, jul24-30

[binntho]

At first sight the area of open water seems persistent, but I am not convinced that it is caused by underlying processes and not vagaries of wind. For one, scale is missing making it impossble to estimate the forces involved, and secondly, the other smaller bits of low concentration seem to move at the same rate and in the same general direction.

[uniquorn]

https://go.nasa.gov/32F4bYr, it takes a couple of minutes. Once an area has been selected, using the measuring tools bottom right, it stays overlayed while scrolling through the dates. The low concentration does drift somewhat, but remains north of the shelf break.

'vagaries of the wind' does not address why it is low concentration in the first place.

[uniquorn]

The ice edge is getting very close to the Yermak plateau low concentration area.
P222 at ~82.3N 3E is just north of the ice edge. (orientation is different with 0deg down)

[uniquorn]

gmrt bathymetry with amsr2-uhh overlay at 75% transparency. 0% concentration, normally dark blue, has been set to fully transparent. sep1-7

[uniquorn]

https://www.nature.com/articles/ngeo2350

Tide-mediated warming of Arctic halocline by Atlantic heat fluxes over rough topography
Tom P. Rippeth, Ben J. Lincoln, Yueng-Djern Lenn, J. A. Mattias Green, Arild Sundfjord & Sheldon Bacon

Abstract

The largest oceanic heat input to the Arctic Ocean results from inflowing Atlantic water. This inflowing water is warmer than it has been in the past 2,000 years. Yet the fate of this heat remains uncertain, partly because the water is relatively saline, and thus dense: it therefore enters the Arctic Ocean at intermediate depths and is separated from surface waters by stratification. Vertical mixing is generally weak within the Arctic Ocean basins, with very modest heat fluxes (0.05–0.3 W m−2) arising largely from double diffusion. However, geographically limited observations have indicated substantially enhanced turbulent mixing rates over rough topography. Here we present pan-Arctic microstructure measurements of turbulent kinetic energy dissipation. Our measurements further demonstrate that the enhanced continental slope dissipation rate, and by implication vertical mixing, varies significantly with both topographic steepness and longitude. Furthermore, our observations show that dissipation is insensitive to sea-ice conditions. We identify tides as the main energy source that supports the enhanced dissipation, which generates vertical heat fluxes of more than 50 W m−2. We suggest that the increased transfer of momentum from the atmosphere to the ocean as Arctic sea ice declines is likely to lead to an expansion of mixing hotspots in the future Arctic Ocean.

[colding]

gmrt bathymetry with amsr2-uhh overlay at 75% transparency. 0% concentration, normally dark blue, has been set to fully transparent. sep1-7

Apologies for what might be a stupid question, but it is accepted lore that the stratification of the arctic ocean over the deep water, prevents the relatively hot and salty waters of the deep from reaching the surface. This makes it comparatively easy to refreeze the surface each vinter.

Now, however, we see two large regions of deep water, which has been ice free for some time.

How long does it takes to destroy the halocline over those areas and have a well-mixed ocean?

[uniquorn]

How long does it takes to destroy the halocline over those areas and have a well-mixed ocean?

Quick answer. I don't know. I try to analyse what is happening now, presently attempting to link low concentration areas with possible turbulence.
whoi itp114 and other active itp's give us an idea of what is happening in the middle of the Beaufort today. Thermocline/halocline are still there. Temperature at 5m is ~-1C. Temperature at 50m looks to be on the high side but I haven't done a thorough yearly comparison. You could go back through the years and document the beaufort buoys. A few members would be very grateful and the data might give you a trend to work from.
Hopefully mosaic will deploy another itp near the pole to give us something to compare regarding atlantification.

[uniquorn]

Now, how long does it take for laptev water to reach the yermak plateau/north of Greenland?

my bolds

Cross-correlation analysis of time series of AW temperature measured at 250 m from 1997–2018 in Fram Strait, the entry point of AW into the Arctic, and from 2002–18 in the eastern EB (red time series in Fig. 5a) shows the strongest correlation, R = 0.67, for a lag of 682 days (Fram Strait series leads; Fig. 5b). The fit between the two time series is better over the last 7–8 years than it is over the earlier period. The ~2-yr lag suggests that warm pulses of AW that entered the Arctic Ocean through Fram Strait are traveling toward the eastern EB at a speed 2–2.5 times faster than that estimated for a warm AW pulse that entered the eastern EB in 2004 (Polyakov et al. 2005). This implies that the rate of advection has increased over time. However, noisy data due to gaps in the EB record preclude meaningful statistical analysis using just the early part of the time series. Assuming that the lagged correlation between the two time series will persist in the near future, the latest part of the Fram Strait series (not shown) implies that the AW temperature in the eastern EB reached its peak in late 2018 (these data are not yet available) and will slowly decrease over the next 1–2 years.

Does it take 2 years to get back to the north of Greenland?

Composite 2002–18 time series of (a) monthly mean potential water temperature θ and (c) daily depth of the lower halocline boundary Hbase defined by the 0°C isotherm at the M14 mooring location (for location, see Fig. 2). (b) Comparison of deseasonalized monthly mean time series of normalized θ anomalies from 250 m of the M14 mooring of the eastern EB (EEB) relative to F2–F3 moorings of Fram Strait lagged by 678 days (as obtained from correlation analysis); time series are normalized by their standard deviations.

[Tor Bejnar]

https://www.nature.com/articles/ngeo2350

Tide-mediated warming of Arctic halocline by Atlantic heat fluxes over rough topography
Tom P. Rippeth, Ben J. Lincoln, Yueng-Djern Lenn, J. A. Mattias Green, Arild Sundfjord & Sheldon Bacon
...

Is it reasonable to connect what this paper (well, abstract) says (Atlantic water heat and vertical mixing associated with tides and topography) with the partly melted out CAA-Greenland mega crack? 

[uniquorn]

I think there's a good case for the low concentration area north of the Yermak plateau. North of Ellesmere Island looks like coastal upwelling which is the ultimate rough topography. North of Greenland? Surprising there is not more discussion. It's rough topography but with returning AW. Hardly any recent data. It's a shame that itp116 profiler failed before it passed right over that area. (failed at 88.3N on new years day). Mosaic was all further east.
So it's a reasonable connection but some may not be convinced 

[binntho]

It seems that this whole tidal turbulence and upwelling aspect of Arctic waters is a ripe field for investigation. I agree with uniqorn, and I think I mentioned this before, but these turbulences (wherever they may be found) could be on the brink of "punching through" the overlying ice in summer in various locations, possibly starting a cascading breakdown of the halocline and "oceanification" in the middle of the pack?

[FishOutofWater]

On the north coast of south America, flow is dominated by large eddies. Easterly and ENE winds howl through the southern Caribbean sea causing upwelling in some areas on the shelf margin and driving what would be a warm current towards the west and WNW. The Coriolis effect makes normal current flow impossible so large eddies form transporting water westwards and somewhat northwards across the Caribbean and into the Gulf of Mexico.

This doesn't happen north of Greenland but if persistent high pressure existed at the north pole eddies might spin from the Fram into the waters north of Greenland carrying warm salty water into the region dominated by cold fresh water. Could that have happened this summer?

As I wrote over at the MOSAiC thread, I wish they had deployed a grid full of buoys to study what's happening between Greenland and the pole.

[binntho]

... I wish they had deployed a grid full of buoys to study what's happening between Greenland and the pole.

Second that!

[FishOutofWater]

Tor there are papers about how Atlantic water has been getting under glaciers on the east coast of Greenland in recent years. After the shelf ice is gone, tides and eddies cause more mixing. This may be happening on the N coast of Greenland. There are multiple topographic highs under water where they could induce increased mixing after ice shelves melted and rates of flow increased.

[uniquorn]

mercator 0m salinity(SSS), jun1-sep11