Tides

[binntho]

JayW, a couple of interesting papers, which don't really have a bearing on what I've been saying. Both of them are about effects outside of the Arctic Ocean proper, one being in the CAA and the other in the Kara between Yamal peninsula and Novaya Zemlya.

Both places have complex coastal contour and bathymetry, and both experience a tidal effect that is larger than in the Arctic Ocean. And neither paper claims a large effect from the tidal movements.

But of course, both of them are interesting and add to the general picture of the effects of tides in the Oceans in general and the Arctic in particular: Small and localized.

[oren]

There is no "transported water" in the open ocean. That's the whole point. The "bulge" attracts water to itself laterally (as I have conceded). But the bulge does not move any water as it itself moves, as you have yourself just agreed.

Binntho you again continue along this illogical path.
The bulge attracts water laterally, yet there is no transported water in the open ocean. How can this be I wonder?
Imagine a region in the Arctic ocean, north of Svalbard. At one time the water is lower by one meter or half meter compared to 6 hours later. Where did all this large volume of water come from? You bet, it came from elsewhere. Was it transported? What else would you call it? There is a net volume inflow into that region, and 6 hours later there is net volume outflow. No way around it I'm afraid,

[uniquorn]

Regarding the Yermak plateau
https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/92JC01097

Thank you JayW. A very interesting paper about a plateau north of Svalbard



In my humble opinion, ~7E to ~13E is significant. Then there is the shelf break all along the Nansen basin

[blumenkraft]

Regarding the Yermak plateau

... We review simple models of tidal current amplification in this region and find that the previous assumption of near‐resonant, barotropic shelf waves propagating around the plateau's entire perimeter is inconsistent with the true topography.

I remember overlaying the bathymetry on that movement some time ago. I thought i must have done it wrongly since the Plateau and the waves didn't match. The movement occurred a little further north. So this quoted part is especially interesting to me. Looks like this finding confirmes my overlay was correct after all. 

Also, check the upper right in the GIF above there seems to be a similar movement where the ice edge is at the moment. This is a little north to the southern elevation of the Yermak Plateau.

Binntho, if your 'in/out just the same thing' argument was true, you would see the same feature in the south of both points asynchronously. But there is no such movement there.

[uniquorn]

The turbulence appears north of the shelf. Depth rises from ~4000m to ~800m. We could do with a few more rammb's of that area to attempt to verify a daily event. Maybe in their own thread. There are currents here too, so tide will only be a contributary factor.



There aslo eddies west of the plateau and the molloy hole, of course.

[johnm33]

Bit of housekeeping, Gero. posted a link to this on the season page. https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2020GL089469
"Measurements of currents from a 15-year duration mooring record in the eastern Eurasian
Basin of the Arctic Ocean demonstrate that the previously identified weakening of
stratification in the halocline (e.g., Polyakov et al., 2017, 2018) has been accompanied by
increased upper-ocean current speeds and associated current shear. Most of this increased
energy and shear is in the semidiurnal band, which includes baroclinic tides and wind-driven
inertial oscillations, with little change of mean along-slope water transport (Pnyushkov et al.,
2018). "

[blumenkraft]

Here is a tidal swirl in the CAB. Somewhere a little east of the Lomonosov Ridge. The ocean is very deep here and the shores are far away!

[uniquorn]

Another couple of references

Baroclinic Tides: Theoretical Modeling and Observational Evidence
Vasiliy Vlasenko, Nataliya Stashchuk, Kolumban Hutter

This book was first published in 2005. When an oceanic tidal wave that is primarily active on the water surface passes an ocean shelf or a region with a seamount, it is split into a less energetic surface wave and other internal modes with different wavelengths and propagation speeds. This cascading process, from the barotropic tides to the baroclinic components, leads to the transformation of tidal energy into turbulence and heat, an important process for the dynamics of the lower ocean. Baroclinic Tides demonstrates the analytical and numerical methods used to study the generation and evolution of baroclinic tides and, by comparison with experiments and observational data, shows how to distinguish and interpret internal waves.

https://www.sciencedirect.com/science/article/abs/pii/S0079661197000281

Abstract

An approximate estimate of the energy in the first mode M2 baroclinic tide has been made from satellite observations. Results based on TOPEX/POSEIDON (T/P) precision altimetry indicate that the internal tide patterns are similar to those expected from mid-ocean topographic features in the global oceans. Both the orthotide and harmonic analyses indicate that the total energy in global M2 baroclinic tide is approximately 50 PJ. For a variety of reasons, M2 is the only component that can be obtained reliably from altimetric measurements. Even then, the energy value may be an underestimate and the energy flux, the dissipation rate, cannot be deduced from altimetry. Since it is the tidal currents flowing over mid-ocean topographic features that are responsible for generating internal tides, a model calibrated by M2 observations is a plausible alternative. Currents from a high resolution (
) barotropic tidal model have therefore been used to obtain an estimate of both the energy and the dissipation rate in M2, S2 and K1 baroclinic tides. A simple model of baroclinic tide generation has been used, and the unknown constant in this model has been selected to yield a total energy of 50 PJ in the first mode M2 baroclinic tide. Based on this calibration, the total energy is 8 PJ in S2 first mode baroclinic tide and 15 PJ in K1. The total in all first mode baroclinic tides is 90 PJ, about 16% of the total energy (580 PJ) in barotropic tides. The model results also suggest that about 360 GW of tidal energy are dissipated in M2 baroclinic tides alone, and 520 GW are dissipated in all first mode baroclinic tides. The latter value is approximately 15% of the power input into barotropic ocean tides (3490 GW) by the lunisolar tidal forces. We have preferred to be conservative and hence these are likely to be underestimates, especially since the altimetric tracks do not often intersect mid-ocean topographic features at optimum angles. While these values are very much within the range of earlier estimates in literature, they should be regarded as still uncertain to perhaps a factor of two (the dissipation rate could be anywhere from 400 GW to 800 GW, the most likely value being about 600 GW). The small signal to noise ratio involved in altimetric measurements of the surface manifestation of internal tides, and potential contamination by mesoscale signals are serious problems. In situ measurements at least a few locations underneath altimetric tracks are essential for confirmation and/or refinement of these preliminary estimates. Hopefully, these very first estimates of the energy and dissipation rate in global baroclinic tides, though rather crude, will serve as a catalyst for a better estimation in the future, since internal tides are likely to be a prominent source of mixing in the deep oceans and important to thermocline maintenance.

Quick bathy overlay using worldview, aug11   https://go.nasa.gov/30W1WR0
85.2N 157.4E  1100m drops to 3800m
(then back up to 2400m at 172.2E under the furthest east low conc area. Not sure if that is relevant)

[uniquorn]

https://twitter.com/seaice_de/status/1293073783830478848
Some interesting short videos on the thread, near FJL on the way to Polarstern

[uniquorn]

October 2, 2015
https://tos.org/oceanography/assets/docs/24-3_rainville.pdf

The Arctic Ocean traditionally has been described as an ocean with low variability and weak turbulence levels. Many years of observations from ice camps and ice-based instruments have shown that the sea ice cover effectively isolates the water column from direct wind forcing and damps existing motions, resulting in relatively small upper-ocean variability and an internal wave field that is much weaker than at lower latitudes. Under the ice, direct and indirect estimates across the Arctic basins suggest that turbulent mixing does not play a significant role in the general distribution of oceanic properties and the evolution of Arctic water masses. However, during ice-free periods, the wind generates inertial motions and internal waves, and contributes to deepening of the mixed layer both on the shelves and over the deep basins—as at lower latitudes. Through their associated vertical mixing, these motions can alter the distribution of properties in the water column. With an increasing fraction of the Arctic Ocean becoming ice-free in summer and in fall, there is a crucial need for a better understanding of the impact of direct wind forcing on the Arctic Ocean.

[johnm33]

Looking at the 'Lomonosov eddy' it's difficult  to see what else could be causing that apart from basal movement. The simplest would be Atl.W. displacing water from the Wrangel abyssal plain, moving it towards the pole through perhaps both the narrower part of the Makarov basin and also Nemilov valley and since in both cases the water is moving directly towards the pole it has to shed angular momentum. I would expect such phenomenon to be short lived [if anything] simply because of the layers they have to penetrate but there are signs of them being there or thereabouts for days which may mean whatever real forcings are occuring they are in the first[?] stages of establishing a current, it is a natural path for a current to follow and probably the hardest part of overcoming the inertia of such a massive volume of water is creating the initial movement.
More widely the build up of the next tidal cycle has begun and I would expect an acceleration of Atl. waters moving north of Greenland to continue the damage being done there, we may also see waters forcing there way through to Baffin the morning of the ^18th being the soonest and potentially the most game changing, especially if a surface current becomes established.

[uniquorn]

Lomonosov eddy - I see it as a more local volume event where 3800km³ tries to fit into 1100km³ twice a day (and back)

[johnm33]

Something occured to me probably as a result of a comment by Oren, i know [something at least] about declination and perigee but somehow had never associated them with lateral movement. Thus I've persisted in an erroneus view[i think] about movement onto/into Barentz, that was that it was simply inertia [right/east] from movement north that forced the flow along to Kara but once lateral forces are taken into account the waters are delivered to the shelf just in time for the draw of the following tide to pull them eastwards, which may explain why mslp at the shelf is so important a factor. Nullschool  click on 'projection' O added mp4 for the 18^th best viewed slow.

[blumenkraft]

John, please drop me some thoughts of yours about a thing i think about these days.

From my observations, when the Lincoln Sea (and the CAA for that matter) is solidly frozen, you see a rather constent current down the Nares into the Baffin Bay. Sometimes so strong it breaks pieces from the arch (you can tell it's a current driven by water movement i e. more or less independent from wind direction). But when the Lincoln Sea ice is broken up and weak, there is no constant current. Ice movement is usually driven by wind and tides.

Why that difference? Is the solidly frozen sea ice in the north producing a pumping of sorts below it when the tides come in from the Atlantic? But that makes no sense since the ice is flexible, or is it?

[blumenkraft]

There is no need to drag your tidal fixation into it,

On the contrary, you cannot ever leave the tides out of sight, Binntho.

[blumenkraft]

No need to hesitate! Tidal motion is real, of course, and it's actually very interesting to see it in action. And the small back-and-forth fluctuation obviously has nothing to do with John's musings.

Binntho, do you think every tide is always the same? If not, what are the variables changing them?

[johnm33]

"Why the difference?" The current varies a little with tidal pressure from the north but flows continuously at depth, because it's Atl. water it holds fast to the Greenland side and generates eddies wherever it 'snags' on that shore. In the winter without much to and fro above it those eddies reach the surface, once there's surface motion they get disrupted/masked by the more energetic turbulence of that. I think.

[blumenkraft]

flows continuously at depth

Oh, right. Thanks a lot, helps.

[Tor Bejnar]

because it's Atl. water it holds fast to the Greenland side

Within Nares Strait, the south-flowing water is on the Canadian side of the strait (and in the middle).  a small north-flowing current hugs the Greenland side.  (from the Icy Seas blog, a few years ago, I recall)

[johnm33]

If you look on the same blog you'll find a post which describes a deep Atl. current turning left at Petermann and flowing upstream to cause melt at it's grounding line, iirc.
 Surface and near surface waters being 'native' to the Arctic do hug the Canadian side.
thought i'd check, not the post i recall but similar graphic https://icyseas.org/2017/06/16/is-petermann-gletscher-breaking-apart-this-summer/

[uniquorn]

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017GL075310

Plain Language Summary

The decline in aerial extent of sea ice covering the Arctic Ocean in the recent years is perhaps one of the leading indications of climate change. Warm water enters the Arctic Ocean at depths of 100–200 m; however, it is isolated from melting the ice by the lack of mixing in the Arctic Ocean. This lack of mixing has been attributed to the ocean being isolated from the wind by ice, and the fact that much of the Arctic Ocean is north of the critical latitude, beyond which the type of internal tide that is believed to drive mixing across other major oceans on the planet cannot occur. However, new evidence has been found that suggests that the tide might be important in driving mixing in certain areas of the Arctic Ocean. Here we combine state‐of‐the‐art numerical modeling with new turbulence measurements to identify the mechanism by which the tide can drive mixing at these high latitudes.

A map of the Arctic Ocean showing the position of the observations (yellow triangle). The critical latitude at which the local inertial period matches the period of the principle semidiurnal tidal constituent (M2) is shown as a red dashed line. Lighter blue areas indicate shallower regions including continental shelf seas and ridges, while the darker blue areas indicate abyssal depths. (b) The area of interest (the box outlined by a yellow dotted line in Figure 1a) showing contours of the rate of conversion of tidal energy (W m−2), in the M2 band, from the barotropic mode. (c) The Froude number distribution in the area of interest with bottom topography overlaid (black contours representing the 100, 200 and 300 m isobaths). (d) Mean profiles of buoyancy frequency (N2) and vertical shear in the current speed (S2) at the location of the observations. The mean is calculated for the 12 h period of the observations. The variability is shown by envelopes that represent the 95% confidence limits estimated by bootstrapping. These profiles indicate that the Gradient Richardson number over the thermocline region is close to one, and so the thermocline is of marginal stability.

[gerontocrat]

Rachel Carson, in her book "The Sea Around Us" - written in the late 1940's, spent some time discussing the work of Otto PETTERSON, who in 1913 published Climatic variations in historic and prehistoric time. in the UR Svenska Hydrografisk-Biologiska Kommisionens Skrifter.

Petterson incidentally was a colleague of one F. L. Ekman, the father of Vagn Walfrid Ekman, who gave his name to upwelling (Ekman suction) and downwelling (Ekman pumping).

Petterson researched for many years the phenomenon of submarine waves and the infuence of tides on them. He believed that variations in the strength of tides over long time periods has caused large changes in the climates of Greenland and Iceland and the extent of Arctic Sea Ice in the last 1,000 years or so, and that those variations are associated with variations in the orbits of the planets.

The field work he did over such a long period makes anything that the MOSAIC project has done look like peanuts. One might not accept his conclusions but cannot should not ignore the fieldwork and trawling through historical records that he did.

His paper is still accessible at http://www.mitosyfraudes.org/calen12/petterson_1.html

I wrote aboout it on "unsorted" in Dec 2018 and ended with..

Is it not possible that this science is still valid as a force that can enhance or reduce the effects of AGW? That mixing between that cold freshwater surface layer and deeper warmer, saltier water can be increased during periods of higher tidal action and reduced during periods of lower tidal action (by submarine waves)? And that in turn depends on variations in the orbits of the planets that are easily calculated using the mathematics of Newton?

https://forum.arctic-sea-ice.net/index.php/topic,2346.msg184103.html#msg184103

____________________________________________________
ps: The Severn Bore will be a 4 star event on 18th & 19th Sept just after the 17 Sept New Moon.

[longwalks1]

Her book is available at Fadedpage.com

https://www.fadedpage.com/showbook.php?pid=20161022

Rachel Carson, author of Silent Spring, writes this book focusing on the plants and invertebrates surviving in the Atlantic zones between the lowest and the highest tides, between Newfoundland and the Florida keys. It's Appendix and Index make it a great reference tool for those interested in plant and animal life around tidepools

[uniquorn]

Some buoys near the pole

[uniquorn]

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

Internal tide
Internal tides are generated as the surface tides move stratified water up and down sloping topography, which produces a wave in the ocean interior. So internal tides are internal waves at a tidal frequency. The other major source of internal waves is the wind which produces internal waves near the inertial frequency. When a small water parcel is displaced from its equilibrium position, it will return either downwards due to gravity or upwards due to buoyancy. The water parcel will overshoot its original equilibrium position and this disturbance will set off an internal gravity wave. Munk (1981) notes, "Gravity waves in the ocean's interior are as common as waves at the sea surface-perhaps even more so, for no one has ever reported an interior calm." [1]

Figure 1: Water parcels in the whole water column move together with the surface tide (top), while shallow and deep waters move in opposite directions in an internal tide (bottom). The surface displacement and interface displacement are the same for a surface wave (top), while for an internal wave the surface displacements are very small, while the interface displacements are large (bottom). This figure is a modified version of one appearing in Gill (1982). [2]

Simple explanation
The surface tide propagates as a wave in which water parcels in the whole water column oscillate in the same direction at a given phase (i.e., in the trough or at the crest, Fig. 1, top). This means that while the form of the surface wave itself may propagate across the surface of the water, the fluid particles themselves are restricted to a relatively small neighborhood. Fluid moves upwards as the crest of the surface wave is passing and downwards as the trough passes. Lateral motion only serves to make up for the height difference in the water column between the crest and trough of the wave: as the surface rises at the top of the water column, water moves laterally inward from adjacent downwards-moving water columns to make up for the change in volume of the water column. While this explanation focuses on the motion of the ocean water, the phenomenon being described is in nature an interfacial wave, with mirroring processes happening on either side of the interface between two fluids: ocean water and air. At the simplest level, an internal wave can be thought of as an interfacial wave (Fig. 1, bottom) at the interface of two layers of the oceans differentiated by a change in the water's properties, such as a warm surface layer and cold deep layer separated by a thermocline. As the surface tide propagates between these two fluid layers at the ocean surface, a homologous internal wave mimics it below, forming the internal tide. The interfacial movement between two layers of ocean is large compared to surface movement because although as with surface waves, the restoring force for internal waves and tides is still gravity, its effect is reduced because the densities of the two layers are relatively similar compared to the large density difference at the air-sea interface. Thus larger displacements are possible inside the ocean than are possible at the sea surface.

Tides occur mainly at diurnal and semidiurnal periods. The principal lunar semidiurnal constituent is known as M2 and generally has the largest amplitudes. (See external links for more information.)

Location
The largest internal tides are generated at steep, midocean topography such as the Hawaiian Ridge, Tahiti, the Macquarie Ridge, and submarine ridges in the Luzon Strait. [3] Continental slopes such as the Australian North West Shelf also generate large internal tides. [4] These internal tide may propagate onshore and dissipate much like surface waves. Or internal tides may propagate away from the topography into the open ocean. For tall, steep, midocean topography, such as the Hawaiian Ridge, it is estimated that about 85% of the energy in the internal tide propagates away into the deep ocean with about 15% of its energy being lost within about 50 km of the generation site. The lost energy contributes to turbulence and mixing near the generation sites. [5] [6] It is not clear where the energy that leaves the generation site is dissipated, but there are 3 possible processes: 1) the internal tides scatter and/or break at distant midocean topography, 2) interactions with other internal waves remove energy from the internal tide, or 3) the internal tides shoal and break on continental shelves.

My bolds.

[johnm33]

^ Interesting and thought provoking, thanks.
Made a gif of ice cover centered on the recent new moon 11+/-4

[johnm33]

The image more or less explains itself, what I'm suggesting is that with increased momentum through Fram and consequently through Denmark strait the Nordic seas achieve a lower low so when that part of the tidal cycle hits there's an almighty amount of suction takes place in the Arctic beyond Fram. Compare the blue hue to the ice on the move. Also note that it coincides with pressure on the Pacific side.

Same image but larger where it's easier to see eddies off the Norwegian coast.
If anyone wants a closer look at the tides go here click the + top right for a polar view, select your variable[sea surface height] and adjust the numbers in the colour scale to give best contrast, bottom left is animations, there're 97 images per day so not practical here.

[kassy]

Melting Arctic Sea Ice Strengthens Tides

If climate change throws off the seasonal freeze-thaw cycle of sea ice, it could trigger a reinforcing cycle of sea ice melt in parts of the Canadian Arctic.

In the Canadian Arctic Archipelago (CAA), the strength of tides in the Kitikmeot Sea is more connected to sea ice cover than what has previously been thought and what has been observed in neighboring regions. This new understanding of the sea ice–tide connection, which came about from a year’s worth of ocean monitoring and state-of-the-art tidal modeling, suggests that as climate change lengthens the ice-free season in this region of the Arctic, the strong-tide season will lengthen, too, and could trigger a feedback loop of sea ice melt.

“In the Kitikmeot, the tidal height and currents are reduced by around 50% due to the seasonal sea ice,” explained Lina M. Rotermund, an oceanographer at Dalhousie University in Halifax, N.S., and lead researcher on the project. “The ice-free periods are becoming longer, so we will see longer periods of the stronger tides and shorter periods of the reduced tides.”

Melted Ice Leads to Stronger Tides

In the Arctic winter, the seas freeze over with ice, and in the Arctic summer the seas thaw. This cycle, as straightforward as it may seem, is just one component of the seasonal changes in the cryosphere. “Every winter the tides are reduced by the sea ice,” Rotermund said. In the Arctic and elsewhere, tides can bring both nutrients and heat from the seafloor to the surface and therefore play an important role in ocean dynamics and ecosystems. Too, they regulate the production of sea ice.

...

most computer models of sea ice growth don’t account for the role that tides play in regulating the location, thickness, concentration, and movement of Arctic ice.

To better understand the sea ice–tide relationship, the researchers collected a year’s worth of tidal data from Dease Strait in the Kitikmeot Sea (just west of Iqaluktuuttiaq, also known as Cambridge Bay), which they used to determine tidal height and currents for the year. From those data they found that the wintertime tides were 50%–60% shallower and 65% slower than the summertime tides. They used these data to help build a high-resolution tidal model of the entire Kitikmeot region, including its many narrow and shallow straits. They examined whether the tide dampening is widespread in winter and what it is about sea ice that dampens those tides.

...

Could Climate Change Trigger the Feedback Loop?

The dual seasonal cycles of sea ice and tides could be knocked out of balance by the additional melting of sea ice caused by human-driven climate change. “Less sea ice will lead to longer seasons of strong tides,” Rotermund said; “however, it is not the high tidal level but the strong tidal currents that could complete the feedback loop. Strong tidal currents lead to more [vertical] tidal mixing, particularly in shallower waters. In Arctic winters, the ocean surface is colder than the bottom water layers. So tidal mixing can bring subsurface heat to the surface and contribute to melting of ice.” Thus, the reduction in sea ice leads to stronger tides, which in turn can lead to a further reduction in sea ice.

“In the eastern Arctic Ocean, the recent strengthening of tidal currents has already brought more heat than usual from the interior of the ocean to the surface, causing more sea ice to melt—setting up a reinforcing cycle,” University of Alaska Fairbanks oceanographer Igor Polyakov told Hakai Magazine in September. “Studies like this are very important and useful because the effects of tides on Arctic waters and the ecosystem are often understated.” Polyakov was not involved with this research.

The feedback loop between sea ice and tides could play a much larger role than expected in some regions. “In the Kitikmeot region the tides are reduced by about 50% from summer to winter,” Rotermund said, “while in the western Canadian Arctic Archipelago [the reduction] is about 25% and in the eastern Canadian Arctic Archipelago it is about 5%–10%.”

https://eos.org/articles/melting-arctic-sea-ice-strengthens-tides

[johnm33]

Two 6day gifs from august 6-11 20-25 so peak tide differential on third day, looking for connection between Bering - Fram. What I have been watching is the area on the 135w side of the pole.

[johnm33]

two more sept 5-10 19-24

[johnm33]

and July 8-13 22-27 plus between the two 15 -20

[oren]

I believe the fast changes through the ice pack you are looking at in these animations are weather artifacts affecting the satellite sensor and algorithm, rather than a physical effect of tides or some other phenomenon.

[johnm33]

This is just an exploration of the possibility, not a very good one so far, it really needs to tie in to atmospherics too since these enhance or dampen the effects, and there's no telling what the time scale of any resonant connection would be anyhow. That said on all but two occasions this past season comments about odd/unexplained accelerated loss or slowed gains have occured just after peak tidal pressures, again that doesn't mean any connection across the ocean and yet there are persistent hints at an inverse s curve that enters/begins towards Bering/Wrangel passes on the 135w side of the pole and ends towards Fram, and this is the first year those hints have appeared. So in a way I'm merely looking to see if that invese s curve can overcome weather artifacts, clouds make drawing conclusions difficult for me.

[uniquorn]

I think rammb with a 51m time step would be better starting point for analysing tidal movement than daily. Documenting in near real time the effects along the inverse S might show if the conjecture is worth pursuing.  https://col.st/KXFec

rammb animations can be downloaded as a gif animation. In my experience, when downloading, left click on the ani works more reliably than right click. Large file sizes may crash the browser, possibly depending on available memory, so either concatenate shorter time series or download individual png (takes longer but more rewarding).

[uniquorn]

Tidally Forced Lee Waves Drive Turbulent Mixing Along the Arctic Ocean Margins
Ilker Fer, Zoé Koenig, Igor E. Kozlov, Marek Ostrowski, Tom P. Rippeth, Laurie Padman, Anthony Bosse, Eivind Kolås
First published: 06 August 2020
https://doi.org/10.1029/2020GL088083      Citations: 8

Abstract

In the Arctic Ocean, limited measurements indicate that the strongest mixing below the atmospherically forced surface mixed layer occurs where tidal currents are strong. However, mechanisms of energy conversion from tides to turbulence and the overall contribution of tidally driven mixing to Arctic Ocean state are poorly understood. We present measurements from the shelf north of Svalbard that show abrupt isopycnal vertical displacements of 10–50 m and intense dissipation associated with cross-isobath diurnal tidal currents of ∼0.15 m s−1. Energy from the barotropic tide accumulated in a trapped baroclinic lee wave during maximum downslope flow and was released around slack water. During a 6-hr turbulent event, high-frequency internal waves were present, the full 300-m depth water column became turbulent, dissipation rates increased by a factor of 100, and turbulent heat flux averaged 15 W m−2 compared with the background rate of 1 W m−2.

Plain Language Summary
Turbulent mixing in the Arctic Ocean water column affects sea ice variability through transport of subsurface heat toward the surface. This turbulent mixing is concentrated along the margins, mainly driven by tidal flow over sloping topography. However, processes of energy transfer from tides to turbulence in the Arctic are poorly understood, and the magnitudes and locations of mixing are poorly constrained. Here we present detailed measurements from the shelf north of Svalbard, showing a turbulent event driven by moderate tidal currents. The energy is trapped and accumulated at the time of maximum downslope flow and is released at the turn of the tide when the entire water column becomes highly turbulent. Our observations imply that this process is an important source of mixing in the Arctic Ocean.

diapycnal: At right angles to the local isopycnal surface.
isopycnal: (especially of an imaginary line or surface on a map or chart) connecting points in the ocean where the water has the same density.
nonlinear internal waves (NLIWs)

Discussion

Our observations are from a site north of Svalbard, where diurnal tides dominate cross-isobath barotropic currents. The region experiences strong, tide-modulated production of NLIWs and turbulence which increases the time-averaged heat flux four times above the background values of 1 W m−2.

Conversion of barotropic tides to baroclinic waves will be strongest when the cross-isobath component of barotropic tidal currents is largest. Energetic cross-isobath tidal currents are common along the Arctic Ocean margins (Figure 1). Near-critical or supercritical Froude numbers in these regions (Figure 1, inset) will allow trapping and unsteady evolution of lee waves and NLIWs. These calculations from the climatology likely underestimate the critical conditions (e.g., Fr inferred from the August climatology at the measurement location is 30% less than the value from observations). SAR images indeed show a widespread occurrence of NLIWs in the eastern Arctic Basin (Kozlov et al., 2017).

[johnm33]

Couple of interesting reads, which I'm trying to digest.
https://geoenergymath.com/2021/12/15/the-harmonics-generator-of-the-ocean/
https://repository.oceanbestpractices.org/bitstream/handle/11329/632/Tidal_Analysis_and_Predictions.pdf?sequence=1&isAllowed=y

[uniquorn]

Some old stuff.

Encyclopedia Arctica
15-volume unpublished reference work (1947-51)

Arctic Tides
Encyclopedia Arctica 7: Meteorology and Oceanography
https://collections.dartmouth.edu/arctica-beta/html/EA07-14.html

Semidiurnal Tides in the North Polar Sea

        The semidiurnal tide-producing potential vanishes at the Pole and obtains

only small values in the whole Polar Basin, for which reason the tides orig–

inating in the Arctic Sea will be small and almost negligible. The observed

semidiurnal tides, therefore, must be due to waves propagated from adjacent

waters. Since Bering Strait is too narrow to be of importance, the tides

from the North Pacific will not be perceptible except in the vicinity of Bering

Strait and the semidiurnal tides in the Polar Sea must be closely related to

the tides of the North Atlantic.

        The North Atlantic and the Polar Sea are in communication through Baffin

Bay, through the wide opening between Greenland and Spitsbergen, and through

the Barents Sea. The tidal wave which propagates through Baffin Bay will

possibly control the tides in the Canadian Arctic Archipelago, but is not likely

to be of much importance in the Polar Sea itself. The Barents Sea is shallow

and almost cut off from the Polar Basin by the shallow banks which extend from

Spitsbergen to Franz Josef Land and on to Novaya Zemlya. Furthermore the de–

flecting force of the earth’s rotation tends to concentrate the tidal wave

along the northern coast of Russia. The wave that passes between Novaya Zemlya

and Franz Josef Land will, therefore, be unimportant, as is seen by comparing

the tides at Cape Flora and Teplitz Bay. The tidal hours are 5.97 h. and 2.06 h.,

respectively. The tidal hour at Cape Flora indicates that the tide at this

place is connected with the branch of the tidal wave which passes across the

Bar e nts Sea. This is seen if we compare the tidal hour at Cape Flora with the

tidal hours at places in Novaya Zemlya, where at Byellushya Bay we find 5.74 h.

and at Krestovaya Bay 5.53 h.

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

Cape Flora, located in an unglacierized area in the Southwest of Northbrook Island (79°57′N 50°05′E) camp is historically significant. Benjamin Leigh Smith was shipwrecked at Cape Flora in 1881. A chance encounter between explorers Fridtjof Nansen and Frederick George Jackson took place here in 1896. Jackson was leading the Jackson–Harmsworth expedition, based at Cape Flora, when this meeting occurred, on 17 June 1896.[2]

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

Sheltered Teplitz Bay has been used as a stopping point for northbound ships. During 1899–1900, an expedition led by Prince Luigi Amedeo, Duke of the Abruzzi stopped in the area. The Ziegler Polar Expedition of 1903–1905, led by Anthony Fiala left a large hut here.[3]

Owing to the steep terrain in Rudolf Island, the only airfield access is a small snow strip 300 m (1,000 ft) up a glacier. It was constructed in 1936 as a staging area for the world's first drift ice station, North Pole-1.[2]

[binntho]

A good find Uniqorn. Not to be snobbish, but Rudol Island is actually Prince Rudolf Island, or even Crown Prince Rudolf Island, though thankfully not Archduke Rudolf Island - he was still Crown Prince when the Austro-Hungarian expedition named the island in the 1870s. Funny to think that landlocked Astro-Hungary had a polar expedition, but then again in The Sound of Music, Von Trapp is a ships captain in the Austro-Hungarian navy!

[uniquorn]

Do, a deer....

Tidal hours perhaps one of the easiest things to measure around the arctic basin pre satellite era. I wonder if they have changed since that data was collected.

This is intriguing

In the last part of the table we follow the increasing values of the tidal

hour from Bennett Island to the northern coast of Alaska and across the

Siberian shelf to Aion Island and Four Pillar Island. We see that the wave

is propagated very rapidly across the deep Polar Basin from Spitsbergen to

Cape Chelyuskin so that the time interval between high water at Port Virgo

and Maud Harbor is 3.2 hours. The distance between the two places is 1,965 km.,

giving an average velocity of propagation of 165 meters per sec. If we

compare this with the simple formula c = √(gh) we find that the velocity cor–

responds to a mean depth of 2,770 m. In reality the depths must exceed 3,000 m.

Such depths were also found by Nansen.

my emphasis

So you can work out mean ocean depth from tidal propagation.

also from

http://www.coastalwiki.org/wiki/Ocean_and_shelf_tides

Tidal energy dissipation

The total power available from moon and sun on the global ocean is estimated at 3.7 TW (1012 Watts); after allowing for a comparatively small dissipation in the atmosphere and the solid Earth, 3.5 TW remain to be dissipated in the ocean (Munk and Wunsch, 1998)[7]. For comparison, the geothermal heat loss is 30 TW, and the equator-to-pole ocean heat-flow is 2,000 TW. Solar radiation input (175,000 TW) is five orders of magnitude greater than the tidal power.

[johnm33]

I made this gif to demonstrate the coincidence of high tidal pressure at Bering and the Faroes gap, and the low at Fram. The highs moving up Norway and down Greenland, to me, indicate a persistent forcing of currents, on Norways coast the water has excess inertia due to it's southern origin, On Greenlands coast a lack of inertia, it coming from the arctic. They're obviously pulsed which indicates constant change through Fram, and although this may be typical every tide will be impacted by mslp but more especially so where the highs and lows coincide with tidal forcing. This affects where any current penetrates into the Arctic or where it originates to leave.
Do a deer and doh a deer have different implications.

[uniquorn]

difficult to know what is happening without dates, labels or a link

[SteveMDFP]

Also, tidal changes imply nothing about bulk flow of ocean water.  Areas of high tidal variation mean that the area experiences diurnal variations both ABOVE and BELOW mean sea level.  There may be some transient "pushing" when above, but this is balanced by equal "pulling" when below mean sea level. 

I don't think there's anything presented which supports any bulk flow in particular.

[uniquorn]

The effects of tides on the water mass mixing and sea ice in the Arctic Ocean
Maria V. Luneva, Yevgeny Aksenov, James D. Harle, Jason T. Holt
First published: 31 August 2015
https://doi.org/10.1002/2014JC010310

Abstract

In this study, we use a novel pan-Arctic sea ice-ocean coupled model to examine the effects of tides on sea ice and the mixing of water masses. Two 30 year simulations were performed: one with explicitly resolved tides and the other without any tidal dynamics. We find that the tides are responsible for a ∼15% reduction in the volume of sea ice during the last decade and a redistribution of salinity, with surface salinity in the case with tides being on average ∼1.0–1.8 practical salinity units (PSU) higher than without tides. The ice volume trend in the two simulations also differs: −2.09 × 103 km3/decade without tides and −2.49 × 103 km3/decade with tides, the latter being closer to the trend of −2.58 × 103 km3/decade in the PIOMAS model, which assimilates SST and ice concentration. The three following mechanisms of tidal interaction appear to be significant: (a) strong shear stresses generated by the baroclinic clockwise rotating component of tidal currents in the interior waters; (b) thicker subsurface ice-ocean and bottom boundary layers; and (c) intensification of quasi-steady vertical motions of isopycnals (by ∼50%) through enhanced bottom Ekman pumping and stretching of relative vorticity over rough bottom topography. The combination of these effects leads to entrainment of warm Atlantic Waters into the colder and fresher surface waters, supporting the melting of the overlying ice.
Key Points:

    Tides have an important role in mixing in the Arctic
    This leads to a stronger reduction in sea ice
    A new pan-Arctic NEMO model is used to explore this

extract:

Since continental shelves make up approximately 50% of the AO area, shelf-sea processes (such as ocean tides, land-fast ice-ocean interactions, coastal currents, downslope cascading, up/downwelling, and eddies) [Nurser and Bacon, 2014] have a substantial influence on the entire AO.

[uniquorn]

The generation of linear and nonlinear internal waves forced by sub-inertial tides over the Yermak Plateau, Arctic Ocean
Gabin H. Urbancic1, Kevin G. Lamb2, Ilker Fer3, and Laurie Padman4
Published-online:    02 Jun 2022
DOI:    https://doi.org/10.1175/JPO-D-21-0264.1

Abstract

The propagation of internal waves (IWs) of tidal frequency is inhibited poleward of the critical latitude, where the tidal frequency is equal to the Coriolis frequency (f). These sub-inertial IWs may propagate in the presence of background vorticity which can reduce rotational effects. Additionally, for strong tidal currents, the isopycnal displacements may evolve into internal solitary waves (ISWs). In this study, wave generation by the sub-inertial K1 and M2 tides over the Yermak Plateau (YP) is modelled to understand the linear response and the conditions necessary for the generation of ISWs. The YP stretches out into Fram Strait, a gateway into the Arctic Ocean for warm Atlantic-origin waters. We consider the K1 tide for a wide range of tidal amplitudes to understand the IW generation for different forcing. For weak tidal currents, the baroclinic response is predominantly at the second harmonic due to critical slopes. For sufficiently strong diurnal currents, ISWs are generated and their generation is not sensitive to the range of f and stratifications considered. The M2 tide is sub-inertial yet the response shows propagating IW beams with frequency just over f. We discuss the propagation of these waves and the influence of variations of f, as a proxy for variations in the background vorticity, on the energy conversion to IWs. An improved understanding of tidal dynamics and IW generation at high latitudes is needed to quantify the magnitude and distribution of turbulent mixing, and its consequences for the changes in ocean circulation, heat content, and sea ice cover in the Arctic Ocean.

paywalled

[uniquorn]

Diurnal tides on the Barents Sea continental slope
Jofrid Skarðhamar a,n, Øystein Skagseth a,b, Jon Albretsen a
a Institute of Marine Research (IMR), Postbox 1870 Nordnes, N-5870 Bergen, Norway
b Bjerknes Centre for Climate Research, Bergen, Norway
Available online 10 December 2014
https://doi.org/10.1016/j.dsr.2014.11.008

Abstract

Measurements of diurnal tides over the continental slope between the Norwegian Sea and the Barents Sea shelf are presented. Numerical 3D simulations, in agreement with field data, show strong cross-slope velocities and large vertical displacements of the interface between Atlantic Water and intermediate water over the slope. The striking correspondence between the prominent observed and modeled diurnal oscillations gives confidence that this is well represented by the model. This variability, interpreted as tidally induced diurnal period topographic waves, is confined to the diverging topography of the continental slope west of Tromsøflaket. The model results reveal highly variable magnitudes of the oscillations and the cross shelf currents in time, related to variable strength of the background flow, the Norwegian Atlantic Current. We suggest that the diurnal topographic wave can be an effective mechanism for cross slope exchange between the Norwegian Sea and the Barents Sea shelf, and important for benthic and pelagic biological processes on the shelf and slope.

5. Conclusions

Observations from March to April 2012 that quantify the diurnal tide at the continental slope connecting the Barents Sea and the Norwegian Sea are presented. The current ellipse for the diurnal tidal harmonic K1 is almost linear, with a cross-slope component of ~16 cm/s. Extending these results using a high resolution ocean model, we interpret this variability as continental shelf waves. Our results suggest that there is a location along the continental slope where the combined effects of topography, stratification and mean flow lead to conditions favourable to excitation of diurnal continental shelf waves by the large-scale background tide. Also based on the model we find a marked low-frequency variability in the amplitude of the diurnal variability connected to the strength of the background flow, the Norwegian Atlantic Current. Both the measurements and the model results show daily oscillations in temperature, salinity and cross-slope current velocities, coinciding with modeled diurnal displacements of the pycnocline, between Atlantic Water and Intermediate Water, from approximately 800 m on the slope to the shelf break at 400 m depth. In general this cross-slope diurnal variability may be of importance for cross-slope fluxes of physical and biological properties, and this exchange could be the strongest during summer.

[johnm33]

I'm thinking the persistent flow through Fram is ice being carried by an establishing residual current generated by tidal forcings. There's an mp4 at 162 above which illustrates the forces at work to some degree, there's a near co-incidence of tidal highs at the Faroes gap and Bering strait, about 180 apart so no surprise, also coincident is the low at Fram.
It seems that as more surface waters flow out through Fram more deep Atl.waters flow in, some increasing the deep southbound current through Nares the rest penetrating more easily east along Barents shelf slope. Given the right atmospherics, lows over the Faroes gap and Nordic seas more Atl. waters are also meeting less resistance flowing through Barents towards Laptev. So I suspect there are three streams flowing in the general direction of Fram, one begins by the NSI/Lomonosov gap a lightweight body of water that I suspect settles beneath the uppermost layer. Then the incoming Pacific stream which flows east in tidal pulses emerging on the Atlantic side between Greenland and Lomonosov where it flows out mixed in with the surface layer of water. Lastly the very uppermost part of the surface layer entrained with the ice which moves from the general direction of Wrangel/ Chukchi, a more 'natural' flow for this layer would be for it to gain ground/move east as it moves north, or be forced south as more ice is formed between floes and to lose ground/move west, as it once did. Once the ice passes ice central 85-87N it should expand northwards and tend to move east a little til' it passes the pole then the opposite, it barely does either. Which means very little build up of crushing ice against the N. Greenland coast or Ellesmere.
If this is happening there should be some tangible build in sea levels on the U.S. east coast, another effect may be to occupy some of the space through which the N.A.drift flowed forcing it to pass through more southerly latitudes more slowly and gain energy creating more lows which will drift through to the Nordic seas enhancing tidal forcing.

[uniquorn]

A map with some arrows would help to visualise that concept.

[johnm33]

This illustrates the impediment at the Faroes gap, best to switch depths and to salinity to get a better feel for it and the routes of Atl. ingress. Is it possible that salt retains it's inertia far longer than the water it's dissolved in?
This image illustrates the 'natural' eastward drift, due to it's relative inertia, as a body moves north, yellow. Then the vagaries of movement as a body moves south, Framward, from the pole, until it is caught by the various streams which in unison are headin for the Nordic seas, red.

This image illustrates the currents, which drive the outflow. First the Atl. waters too saline to pass beyond the NSI/Lomonosov gap, easing the resident water out[?] and pushing towards Greenland. Then the incoming from the Pacific and the lighter fraction of Atl.waters which did pass Lomonosov, enhanced by surface water and ice forced there by the Amundsen gulf tides, constantly replenished has to find the path of least resistance. Finally the most energetic fraction of Pacific waters which head east and mix a little as they pass the CAA. It has two minor flaws in that it doesn't illustrate the Atl. waters blocked and turning south by Iceland,as Mercador does, nor does it show the residual tide driven current of Atl. waters which flow south through Nares

This last image shows how little of surface Atl. waters pass north through Fram, and suggest that the entrained air, saponins or whatever keeping the micro-plastics bouyant dissipates across Barents and that water sinks such that it cannot pass between NSI and Lomonosov. I'm guessing the residual angular momentum in the saline waters across Barents shelf slope lead to deep waters constantly being recycled to the surface in the eddies and thus dominate the slope side of Gakel/Nansen basin, and this keeps the return currents at some distance.

[johnm33]

Stills of the tidal lenses relative positions deep red = .5m deep blue = -.5m from
[https://data.marine.copernicus.eu/-/chquy5f162] remove brackets

[uniquorn]

Thanks johnm33, quite a lot to think about there. 30m mercator current models strong pulses from Bering to CAA, not so notable along the trans polar drift though. Likely there is an inertial contribution along with the currents and wind, the ratios probably unknown.
Interesting overview of the Faroes gap.