Tides

[Tom_Mazanec]

Here you are, oren.
Do tides affect currents and sea ice?

[blumenkraft]

Interested people on the topic might find comprehensive GIFs in the RAMMB-SLIDER thread.

This one for example >> https://forum.arctic-sea-ice.net/index.php/topic,2649.msg244558.html#msg244558

[uniquorn]

When the tide goes up, where does the water at the bottom come from?

[kassy]

The effects of tides on the water mass mixing and sea ice in the Arctic Ocean

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.

...

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. These processes are generally not accounted for in either global or regional Arctic models, which do not have sufficiently fine horizontal meshes to resolve the required physical scales and sufficiently high vertical resolution to accurately simulate surface and benthic boundary layers. At present, none of the coupled ocean‐atmosphere general circulation models (OA‐GCMs) used in IPCC AR5 and only a few of the global or pan‐Arctic models participating in the Forum for Arctic Ocean Modeling and Observational Synthesis (FAMOS; http://www.whoi.edu/projects/famos/overview) have sufficient resolution to account for shelf‐sea physical processes.

...

Astronomical tides are strong on the Arctic shelf with M2 amplitudes reaching 4.4 m in the Hudson Strait, 2–3 m in the White Sea and >1 m in the Canadian Archipelago (for geographical names see Figure 1). Holloway and Proshutinsky [2007] reviewed the observational and modeling evidence for the role of tides in the Arctic and presented arguments on why the “omission of tides from climate modeling can be particularly troubling.” They hypothesized that tidal‐induced mixing in the AO plays an important role in the global conveyer belt. Holloway and Proshutinsky [2007] included a parameterization of tidal mixing near‐bottom topography and tidal‐induced divergence‐convergence of ice in a coarse resolution (55 km) coupled ocean‐ice general circulation model, and compared the results with and without tides on decadal time scales. Tidal currents in their study were derived from a barotropic ocean‐ice coupled model with a grid spacing of 14 km [Kowalik and Proshutinsky, 1993, 1994]. The authors showed that the regions of strongest tidal dissipation are located along the western opening to the Barents Sea, above Yermak Plateau and over Eurasian continental shelf slopes in the Barents, Kara and Laptev Seas, thus mapping well onto the pathway of the Atlantic Water (AW) inflow in the AO. They suggested that tides can result in AW ventilation and modification via the mixing of this water mass with overlying polar waters, affecting the Arctic extension of the conveyer belt and potentially changing the Arctic and global climate.

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2014JC010310

Open access , have not looked into linked articles.
Note that AO here is just short for Arctic Ocean.

[blumenkraft]

The impact of ocean bottom morphology on the modelling of the long gravity waves, from tides and tsunami to climate

Abstract

Ocean basin morphology is a major controlling parameter of the ocean dynamics. We address here its impact on long gravity waves: tsunamis, storm surges and tides. The deterministic character of the tides allows one to easily illustrate how modelling of long gravity wave in the ocean is dependant upon the knowledge of the shape and depth of the ocean basins, and on the slope of seamounts, mid ocean ridges and continental shelf breaks. A few examples are given. The first one is the impact of inaccuracies in the bathymetry on wave propagation at basin scale (the North Atlantic). The second one shows the global dependency of the solutions (the remote effect of the resolution of the tides under the Weddel Sea permanent ice shelf). The third one illustrates the trapping of energy by the continental slopes above the critical latitudes (the diurnal tides over the Yermak plateau). Particular focus is given on the importance of the energy transfer from barotropic tides to baroclinic internal waves. This transfer is taking place over seamounts, mid ocean ridges and at the shelf breaks, closely dependent upon the slope of the bathymetry. This energy transfer to internal wave could play a role on the deep ocean mixing, contributing to the maintenance of the thermohaline circulation, and hence impacting the climate of the earth.

Link >> https://www.gebco.net/about_us/presentations_and_publications/documents/cen_conf_abstract_le_provost.pdf

[blumenkraft]

In the Arctic sea-ice pack, ice motion is largely a response to local winds and ocean currents (including tides)

Link >> https://www.cambridge.org/core/journals/journal-of-glaciology/article/meso-and-microscale-seaice-motion-in-the-east-siberian-sea-as-determined-from-ers1-sar-data/E0A7D4458296C2D4D0F6A331436EC69D/core-reader

[tybeedave]

ty kassy,

 for backing up, with real evidence, my feeling that tides could influence the melting of Arctic ice in the Nares and throughout the Arctic.

to those who say ' show me where it says', consider yourself as having been shown....

great work, kassy !!!

td

[kassy]

Actually i know very little about it but it piqued my interest. Next step then is a bit googling to find out what the science says. 

[Tor Bejnar]

...
Abstract
...
simulations also differs: −2.09 x 103 km3/decade without tides and −2.49 × 103 km3/decade
...

I hope you all know that "x 103 km3" means "x 10³ km³".

[blumenkraft]

The forum even has a button for that. People should use it!

[binntho]

When the tide goes up, where does the water at the bottom come from?

Yes, uniqorn. You are here expressing one of the fundamental misunderstandings of how tidal waves (and pressure waves for that matter also) actually function.

The tide goes up because the water column expands due to changes in pressure, with the change in pressure being caused by gravitational changes.

Same happens when changes in atmospheric pressure cause corresponding changes in sea surface (appr. 1 cm per millibar, see here). Whithin the Northern Atlantic and the Arctic, differences in atmospheric pressure from one place to another can easily exceed 50 mbar, leading to a difference in sea level of half a metre. Again, this is due to expansion and contraction of the water column.

Sea level rise due to the tidal effect is usally at the same or smaller scale as this, with localized exceptions (e.g. south of Iceland and along the European Atlantic seabord, where in excess of 1 metre can be seen).

But  most of the world's oceans only see a tidal fluctuation of less than 50 cm, see here.

EDIT: Expanded slightly.

[binntho]

ty kassy,

 for backing up, with real evidence, my feeling that tides could influence the melting of Arctic ice in the Nares and throughout the Arctic.

to those who say ' show me where it says', consider yourself as having been shown....

great work, kassy !!!

td

Yes, thanks Kassy. I've read several similar papers. Not one of them supports claims such as the one that set off the current debate: That changes in Fram export that we have seen over the last months are somehow linked to phases of the moon.

[binntho]

In the Arctic sea-ice pack, ice motion is largely a response to local winds and ocean currents (including tides)

Link >> https://www.cambridge.org/core/journals/journal-of-glaciology/article/meso-and-microscale-seaice-motion-in-the-east-siberian-sea-as-determined-from-ers1-sar-data/E0A7D4458296C2D4D0F6A331436EC69D/core-reader

Yes blumenkraft. I've read similar papers online. None of them supports claims such that Fram export can change in accordance to the phases of the mooon.

I'd like to point out what I wrote yesterday:

HOWEVER!!!!!

Long-term movements of ocean currents ARE effected by the tidal pull of the moon. So the effect is not non-existent in the open ocean, but it is NOT a fluctuating effect. In other words, no research i've found indicates that changes in tidal movement on a daily or monthly basis has any discernible effect.

The existence of tides has a constant effect, not a fluctuating effect, changes in the tides on a daily or monthly  basis does not effect the large scale state of the ice in the Arctic Ocean.

[binntho]

Moving on from my last post: Of course, as any pedant can point out, the long-term tidal effects are due to the fluctuating nature of the tides.

But in the large scale of things, these fluctuations have almost no impact per se. It is the cumulative impact that is real, but the impact of indivual tidal movement is purely local and temporal, with any movement being almost exclusively up-and-down and back-and-forth, so the net effect is usually zero.

Some people have the pet ideas that they can somehow predict (or explain) daily, weekly or monthly changes in the large scale behaviour of Arctic sea ice by referring to the phases of the moon. Every such claim is unsubtantiated by both basic science and current scientific research.

[binntho]

blumenkraft has sent me a private message taking umbrage at my lack of acceptance of silly claims such that changes in Fram export can be caused by changes in the phases of the moon. Well bless him, but I guess our tempers collective and individual are not what they should be now, these corona virus times!

[blumenkraft]

Full disclosure, this is what i wrote:

You might try reading what people post!

You wasted too much of my time for you already. I googled those papers for you clearly stating that tidal forces have a crucial role to play here. I linked the GIF for you so that you can see what tidal forces do to the ice by smashing them into small pieces.

It all went down the drain.

And now you have the nerve telling me i should read your wall of text? A wall of text that says absolutely nothing?

How dare you?

Please, stop derailing the melting thread any further with this bogus.

[binntho]

Full disclosure, this is what i wrote:

Thank you. First I'd like to say that I am not the best at reading what other people write! So cricising you for that was somewhat hypocritical.

I'd like to refer you to uniqorn's "where does the water come from" comment above. Even the best and most valuable of members, that have been providing the rest of us with a constant and positive input (such as yourself) can be totally off when it comes to such basic scientific facts as what a pressure wave actually is.

That is why I dare! Because none of us knows all, but some of us have a better basic understanding of physics than others. This basic understanding can of course lead you into the briar patch, but when something jars against it, I not only dare to respond, but I do.

So silly claims, such as that the phases of the moon can effect Fram export, will be bashed by me now and in the future.

[SteveMDFP]

The tide goes up because the water column expands due to changes in pressure, with the change in pressure being caused by gravitational changes.

I don't think this makes sense.  Water is an almost totally incomprehensible substance. Subject a column of water in a laboratory to immense pressure, and the change in volume is negligible.

[interstitial]

waves on the ocean are not pressure waves.
Pressure waves travel through the medium not on top of it. Sound is a pressure wave.
The wave motion on a body of water is not a tide. The motion of water on the surface is a displacement wave. The displacement wave moves water up and down but does not move water towards the shore or away from the shore.


waves are a transference of energy not matter. Yes the move the matter locally but not very far and the net affect is not motion.


Tides flow in increasing the local water depth. This is not a wave it is a large increase in the amount of water in a region. It is caused by gravity but it is the moons gravity that causes a bulge in the ocean on the side closest to the moon and a deficit elsewhere.


This disagreement can be summed up as


1.wave does not equal tide


2.wave is movement of energy


3.tide is movement of water.

[interstitial]

My point is still valid but for clarity i didn't use the correct terms.


A pressure wave is a longitudinal wave. In a longitudinal wave displacement of particles is parallel to direction of wave travel. Net motion of particles averages to zero. longitudinal waves travel through a medium. Example a sound wave.


A transverse wave has particle displacement perpendicular to the direction of travel. Net motion of particles also averages to zero. Transverse waves travel on the surface of the medium. Example a ripple on water

[uniquorn]

When the tide goes up, where does the water at the bottom come from?

Yes, uniqorn. You are here expressing one of the fundamental misunderstandings of how tidal waves (and pressure waves for that matter also) actually function.
The tide goes up because the water column expands due to changes in pressure, with the change in pressure being caused by gravitational changes.

Sea level rise due to the tidal effect is usally at the same or smaller scale as this, with localized exceptions (e.g. south of Iceland and along the European Atlantic seabord, where in excess of 1 metre can be seen).
But  most of the world's oceans only see a tidal fluctuation of less than 50 cm, see here.
EDIT: Expanded slightly.

That is certainly not the answer I was expecting and your link doesn't provide any scientific evidence for the proposition.

I propose that tidal induced lateral movement can be caused over areas where there is a change in ocean depth. The coast being a special, easily observable, case where depth tends to zero.  Consider an area where ocean depth increases rapidly from 200m to 3000m. Does the water simply go up and down in a straight line with the tides? It is more likely to cause turbulence in the form of eddies or internal standing waves, mixing the water and, if there is sea ice on the surface, causing some of it to melt. 

https://gyre.umeoce.maine.edu/physicalocean/Tomczak/ShelfCoast/notes/chapter05.html

Tides in shallow seas
This very brief summary of tidal dynamics in deep water is still quite incomplete, but it is sufficient to understand the action of the tides on shelves and in estuaries. The first and fundamental observation with respect to tides in shallow water is that the tide-generating force is of global scale. Only the largest water bodies such as the major oceans can therefore experience tidal forcing in the way described by Laplace. Smaller water bodies such as marginal seas or estuaries cannot produce a response to astronomical tidal forcing. If there is tidal movement in these regions, it is forced by the tidal currents of the deep ocean which enter and leave the region periodically at the connection to the ocean. Tides generated in this way are known as co-oscillation tides. Marginal seas have their own resonance frequencies, determined again by their dimensions. As a consequence, the amplitudes and phases of co-oscillation tides depend on the closeness of a resonance frequency to one of the tidal frequencies and on the amplitude of the tidal currents in the deep ocean at the connecting line with the marginal sea. This explains, for example, why mediterranean seas are virtually tide-free; their connection with the open ocean is so restricted that the oceanic tides cannot produce co-oscillation.

Because co-oscillation tides are a resonance phenomenon they usually display the largest tidal range near the coast of the marginal sea or at the inner end of a bay. (You can see this demonstrated in an animation.) This can give rise to extreme tidal ranges if the co-oscillation occurs at resonance. The largest tidal range occurs in the Bay of Funday on the Canadian Atlantic coast. This bay is 151 km long and 31 km wide and at spring tide experiences a tidal range of 21 m. The North West Shelf of Australia is another region with large tidal resonance; the tidal range on the North West Shelf reaches 8 m and more.

A large tidal range is of course always associated with strong tidal currents, and tidal currents on the shelf are always larger than tidal currents in the open ocean. In some locations tidal currents can become unusually strong even under a moderate or small tidal range. This occurs where constrictions prevent the free flow of the tidal wave and force it to rush through narrow openings.

The most spectacular tidal current of this type is the famous "maelstrom" in the Saltfjord of northern Norway. This 500 m deep fjord is connected with the North Atlantic Ocean by a 3 km long channel of only 150 m width and 31 m depth. The channel is much too small to allow the fjord to follow the oceanic tide, and the difference in water level between the two ends of the channel can reach up to 1 m. This produces a periodic current through the channel of speeds in excess of 20 knots (up to 40 km/h) which produces intense whirlpools (maelstroms) of 10 - 15 m diameter. Calm conditions every 6 hours allow ships to pass through the channel, before the current starts again. For centuries it has been said that the Saltstraumen, as the current is known, runs strongest on Good Friday (the Friday before Easter). This is easily understood from tidal theory if we recall that the Christian church sets the date of Easter as the first Sunday after the full moon following the vernal equinox: By definition the tide generating potential of the sun and moon act in concert at that time.

A coastal inlet in the Kimberleys of Western Australia shows even stronger tidal currents. Its connection to the North West Shelf is only a few hundred meters long and barely 50 m wide. The difference in water level on either side of the connection is clearly visible from the top of the cliff, as a tidal waterfall rushes through the gap, changing direction every six hours.

Shallow seas which are close to resonance with one of the tidal periods are of great importance for the world's fishing industry. The flow of strong tidal currents over a shallow ocean floor produces turbulence of sufficient intensity to keep the entire water column well mixed throughout most of the year. Nutrients which usually accumulate in the sediment and are no longer available to support marine life, are continuously kept in suspension under such conditions. These coastal seas are therefore among the most productive fishing regions of the world ocean, rivalling the great coastal upwelling regions and the fertile Southern Ocean. The North Sea or the Newfoundland Banks are two examples of regions where tidal mixing keeps nutrient concentrations in the water column at a high level.

Tides in shallow water are generally a mixture of propagating waves and standing waves. One major difference between these two types of waves is the phase relationship between elevation and tidal current. As could be seen from the example of the water bowl or tank, currents and water level are 90° (or a quarter period) out of phase: Currents are strongest when the water surface is flat and vanish when the water level is at its highest and lowest (high and low tide). In propagating waves, on the other hand, currents are strongest at high and low tide, ie they are in phase with the elevation. For a given coastal location the time of strongest tidal current relative to high tide therefore depends on the type of tidal wave in the region.

Sudden changes in water depth can lead to a change of the tide from a standing wave to a propagating wave. This occurs because the propagation speed of shallow water waves depends on the water depth. If such a wave encounters a sudden change of depth, its propagation speed is slower over the shallower region than over the deeper region; its propagation speed on either side of the sudden depth change is mismatched, and the wave cannot continue unchanged across the changing topography. This leads to partial reflection of the wave. If a wave approaches a steep rise of the sea floor (Fig. 5.4), part of the wave continues as a propagating wave in the shallow water, while part of it is reflected back into the deeper water and combines with the incoming wave to form a partially standing wave. Tidal currents and elevation are thus in phase in the shallow part but out of phase, by a degree determined by the wave's reflection coefficient (Fig. 5.4), in the deeper part. This explains the wide range of observed phase relationships between tidal currents and high or low tide in the world ocean's shelf seas.

This looks interesting but sci-hub is blocked for me.
 https://doi.org/10.1029/JC083iC09p04607

Abstract

A well‐defined class of fronts occurring in the shelf seas around the United Kingdom during the summer months marks the boundary between stratified and vertically mixed regimes. The occurrence of these fronts may be interpreted in terms of the distribution of available turbulent kinetic energy from the tidal currents and wind stress and the buoyancy flux input at the surface. The principal parameter controlling stratification is the ratio of the water depth to a Monin‐Obhukov length determined by the tidal velocity. A corresponding parameter based on the wind stress is also found to contribute significantly in a combined model of tide and wind mixing. Vertical sections perpendicular to the front by undulating CTD indicate a strongly baroclinic region with horizontal temperature gradients of ∼1°C/km, which imply strong flows parallel to the front. Drogue observations show that nontidal velocities of ∼10 cm/s occur in the vicinity of the fronts but the flow regime is apparently complicated by large‐scale (∼25 km) instabilities which are clearly manifest in satellite infrared imagery and airborne radiation thermometer surveys. There is also indirect evidence for vertical motions suggesting that both upwelling and down‐welling occur in the frontal zone.

[uniquorn]

I'd like to refer you to uniqorn's "where does the water come from" comment above. Even the best and most valuable of members, that have been providing the rest of us with a constant and positive input (such as yourself) can be totally off when it comes to such basic scientific facts as what a pressure wave actually is.

That is why I dare! Because none of us knows all, but some of us have a better basic understanding of physics than others. This basic understanding can of course lead you into the briar patch, but when something jars against it, I not only dare to respond, but I do.

So silly claims, such as that the phases of the moon can effect Fram export, will be bashed by me now and in the future.

When the tide goes up, where does the water at the bottom come from?

Same happens when changes in atmospheric pressure cause corresponding changes in sea surface (appr. 1 cm per millibar, see here). Whithin the Northern Atlantic and the Arctic, differences in atmospheric pressure from one place to another can easily exceed 50 mbar, leading to a difference in sea level of half a metre. Again, this is due to expansion and contraction of the water column.

Please explain how this is relevant.

Relation between sea level and barometric pressure determined from altimeter data and model simulations
Philippe Gaspar Space Oceanography Division, Collecte Localisation Satellites, Toulouse, France Rui M. Ponte Atmospheric and Environmental Research, Inc., Cambridge, Massachusetts
Abstract.
The relation between sea level and barometric pressure and, specially, the validity of the inverted barometer (IB) approximation is examined over the global oceans, using nearly 2 years of TOPEX-POSEIDON altimeter measurements. Both crossover differences and collinear differences between consecutive cycles are utilized in this study. Linear regressions between barometric pressure and sea level time series yield coefficients between 0.8 and 1 cm/mbar poleward of 20 ø and as low as 0.5 cm/mbar in the equatorial regions. Such deviations from the IB value of 1 cm/mbar can be due to the presence of data errors or to correlations between pressure and adjusted sea level (i.e., sea level corrected for IB effect). A simple error model for the pressure fields and a number of sensitivity tests are used to evaluate the changes in the regression coefficient possibly induced by data errors (pressure errors, altimeter measurements errors, and radial orbit errors). The combined (root-mean-square) effect of the different errors amounts to 0.8 mm/mbar poleward of 20 ø and 1.8 mm/mbar within 20 ø of the equator, in general smaller than the observed deviations from the IB value. Regression coefficients thus imply a correlation between adjusted sea level and pressure. Results from a shallow-water, global ocean model forced by realistic wind and pressure fields corroborate this finding. The model is able to explain the observed coefficients, within measurement errors, with wind- driven effects being most important in accounting for differences from the simple IB model. Pressure-forced dynamical signals cause maximum deviations of only 1 mm/mbar. The analyses point to the general validity of the IB approximation over the deep oceans but also highlight the complex relation between sea level and barometric pressure resulting from correlations between various sea level signals.

This might have been a better riposte

[Andreas Muenchow]

Tides can be tricky and much confusion exists. There is tidal forcing involving gravity and rotations of planetary objects (earth, sun, moon), there are tidal sea level oscillations, and there are tidal currents. All are related and governed by conservation of mass and momentum.

The tidal motions can always be thought of as waves that propagate around ocean basins in deep water like the Atlantic or Pacific Ocean. The phase speed of the wave is usually sqrt(g*H) where H is the water depth and g=9.8 m/s^2 the constant of gravity, so in the deep ocean (2000 m) the speed is 140 m/s or 510 km per hour which is pretty fast. As this wave propagates into coastal areas the water depth changes and so do wave properties and dynamics. The coastal oceans are forced by the deep water waves as a boundary condition, because the shallow areas have little mass and are not much impacted by the gravitation of the planetary objects. This boundary condition moves water on and off the shallow areas which then respond much like a bath tub response to us trying to make waves with moving water back and forth with our legs. Sometimes resonance results and the wave in shallow are large. This happens in Nares Strait (or the North Sea in Europe), because Kane Basin is somewhat close to a resonating basin whose natural frequency (due to geometry) matches that of the tidal forcing.

Furthermore, the tides in straits or channels such as Nares Strait are forced by the Atlantic tidal wave that propagates both through the Arctic Ocean to force the northern entrance and through Baffin Bay to force the southern entrance. These two "forcing waves" have different amplitudes and phases, so strong oscillating pressure gradients from north-to-south exist that drive tidal currents. If these currents converge, sea level moves up, if currents diverge, sealevel moves down. Think of it like you think of a bathtub where water is added from the faucet and removed by the sink. Sealevel goes up when more water is added than goes out the drain, it goes down when more water leaves via the sink than is added by the faucet.

There is more.

So, does this perhaps answer the question of the original post? 

[uniquorn]

The coastal oceans are forced by the deep water waves as a boundary condition, because the shallow areas have little mass and are not much impacted by the gravitation of the planetary objects. This boundary condition moves water on and off the shallow areas

Thank you Andreas. The tidal discussion was prompted by comments relating to the Fram Strait but I'm curious whether tidal forces affect sea ice in the area north of FJL and Svalbard where the depth rapidly increases from ~200m to over 3000m into the Nansen basin. I expect that 200m isn't considered shallow, but can your explanation be extrapolated to apply to that depth?
I'm aware that the ice drift is wind driven but the low concentration area doesn't move with the ice.
uni-hamburg amsr2uhh, Svalbard and FJL, mar27-apr2
rammb animation of the same area here

[Hopen Times]

The ongoing Mosaic expedition would be a prime example - have they ever mentioned tidal effects on the movement of ice around their vessel? Not that I've seen.

MOSAiC writes about tides affecting their floe on 27. March. https://follow.mosaic-expedition.org

Ohboiohboi! All scrambles...

Even after two weeks, the dynamics of our floe do not calm down. Our ice floe with initially a diameter of several kilometers is getting smaller and smaller as a consequence of natural forces. Tides in the ocean and strong winds in the atmosphere are pushing the floe. At the same time and due to the same forces, the leads around us give space when the ice is relaxing again. These ongoing dynamics keep our personal tensions up: How will the floe look like tomorrow morning? Can we work on the ice? Which installations on the ice might need to be rescued? Can we use the powerline between the ship and the ice floe? Over the last days, the latter was not always the case as the ship was simply moving too much. Also, small "island states" that are not accessible by foot have formed. However, using the helicopters on board, allows to continue our measurements in these outposts with limitations. The expedition name "MOSAiC" says it all!

[Glen Koehler]

  FWIW - It seems that the two sides in this debate are focused on different questions. 
     
     One side documents that tides affect the Arctic Ocean waters, ice, mixing, temperature gradients etc., and thus condition of the ASI. The other is focusing only on Fram Strait export, and saying the because tidal movement alternates, the movement of water south on an outgoing tide is matched by tidal movement north on the incoming tide, so in terms of Fram Export it has zero net effect.

     Maybe it's time for a real expert to address the original question directly:  Do changes in tidal forces across the lunar cycle influence the net amount of ASI export through the Fram Strait? 

     At least I think that is the question.  I don't know enough to have an opinion, just trying to clarify the discussion.  All I do know is that my friend retired from 30+ year career at National Weather Service said that tidal mathematics is really complicated!

[blumenkraft]

This is the original post:

Tides have no effect on Fram export. Tidal effects (other than a smooth up-and-down motion) are strictly limited to the narrow coastal strip, perhaps 10 meters max into open ocean. Swells and surges can happen in enclosed waters, but only on a scale of a few hundreds of meters.

If you think differently, you can start your own thread and explain your reasoning there.

So let's sort it out bit by bit.

Tides have no effect on Fram export.

Since tidal forces are prevalent in all of the Arctic ocean (or any ocean for that matter), and also at the Fram strait, this is inherently wrong.

For example, we have the Yermak plateau, which causes lateral surface movement when tides come in and out. This is a pretty strong effect sometimes. Ice floes in this area will be smashed into small pieces. Wind can move small ice floes more easily than if it was, say, a homogenous ice surface.

A GIF, making this effect pretty obvious, can be seen here >> https://forum.arctic-sea-ice.net/index.php/topic,2649.msg244558.html#msg244558

Or here >> https://forum.arctic-sea-ice.net/index.php/topic,2649.msg218362.html#msg218362

Binntho commented on that one BTW:

Great work! Some sort of tidal effect seems the best explanation. But the circular movement indicates (to me at least) something rising from below. How can that be caused by tides?

Next,

Tidal effects (other than a smooth up-and-down motion) are strictly limited to the narrow coastal strip, perhaps 10 meters max into open ocean.

I think he meant to say 10 Km here, not meters? Anyway, as seen in the linked GIF above, which is halfway between Greenland and Svalbard (meaning nowhere near a coastal stip) this statement is obviously wrong.

Swells and surges can happen in enclosed waters, but only on a scale of a few hundreds of meters.

I mean, what does that even mean?

If you think differently, you can start your own thread and explain your reasoning there.

We did. A lot of reasoning, proof, and expert knowledge in this thread.


BTW, last year we had a lengthy discussion where Binntho vehemently stated that lateral movement due to tidal waves was not a thing at all. He was (maybe still is) convinced tides can move ice only up and down. No paper, no expert opinion, no illustrative GIF was able to convince him otherwise.

Let's see if he comes around this time.

Experts reading this, please point out if i made any wrong statements above. I, for one, am willing to learn.

[johnm33]

This is my take on tidal effects on the Arctic, i'm no expert this is just what i think i'm looking at on the various models and images available to us all. I'll start at the ridge between Scotland and Iceland. For about 13hrs. a day tides lift water over the Faroes ridge into the Norwegian/Greenland seas, the sea height rises by 40-60cm depending on the tidal cycle, so I'm guessing that at the lower end that amounts to a volume of about 20cm over the whole area and nearer 30cm at peaks and this volume delivered twice[almost] a day. Once the tidal forcing stops the residual current continues, this makes it difficult for the same body of water to recycle south. In fact this water coming from the south has inherent energy/inertia exceeding the Earths surface rotational speed here and it is thus pressed against the west coast of Norway, so a different source is needed for the water flowing south, this comes from both energetically depleted water that has circled N/G seas and from an induced flow out through Fram. The inducement is the steady flow through Denmark strait where the biggest waterfall in the world drops basal waters into the N. Atlantic.
From 60^oN the northbound flows own movement adds to it's relative inertia, since from here it more or less approaches the axis of rotation directly and the planets tangential surface speed diminishes rapidly. This gives it the momentum to scale the Barentz shelf or to penetrate Fram and deliver Atlantic water as deep into the Arctic as energy permits. Since the loss of sea ice in Barentz, which acted like a baffle in a silencer, or leaves on traffic noise, and caused a chaos of churning which inhibited flow, the tidal surge penetrates further, followed at a more sedate pace by actual A.W. which melts more ice rinse repeat. Then on the coat tails of the tidal surge slowly a residual current builds and becomes established. Note that the tidal surge is going the 'wrong' way due to it's inherent inertia so at some point as Chukchi/ESS and Laptev shed ice there'll be a counter surge building up on the Pacific side which cause a turbulent halt, some melt, then at equilibrium these waters will move gently towards the pole/Fram, as they are replaced.
For me the 'tidal' movement of the ice is a consequence of this penetration which in turn depends on both tidal cycle forcings and atmospheric pressure in that if the mslp is low in both the Norwegian sea and Barentz south of Svalbard then the effect is maximised but even then depends on pressures over the basins. Clearly the more water that enters from these forcings the more has to flow out through Fram, and to a lesser degree Nares, both of which act in some way as flywheels in the system, evening out flows, naturally as the 'flywheels' speed up they will create deficits enhancing inflows from both the Atlantic and Pacific sides.

There's an illustration of tidal forcings on page 12 of this, https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2008JC004941
This animation suggests a rotating wave around the amphidromic point south of Greenland, i'm thinking that beyond and past Iceland different bodies of water are on the move.

[kassy]

That is some cool stuff, always more to look into.

Lets note that there are 2 things.

The narrow claim form post 11:
That changes in Fram export that we have seen over the last months are somehow linked to phases of the moon. (And its effects on tides, K)


And 2 basically how it all works for us less versed in this stuff and interested in finding out more.

I wonder if anyone with more knowledge of the physics could chime in on 1.

Everything more on 2 is great too.

[binntho]

I must begin my post by apologizing for my silence - I am currently isolated in a three-house compound within spitting distance of the source of the Blue Nile, along with 3 "adopted" young men. Internet connectivity here is limited and fluctuating (albeit not with the phases of the moon as far as I can see). My work is heavily dependent on Internet access so most of the available bits have to be utilized for work rather than play.

On other personal notes (since somebody saw reason to wonder), I am an Icelandic national and well acquinted with tidal forces in coastal areas around Iceland that see some of the biggests tidal fluctuations in the world (although nowhere near as impressive as on the Canadan Pacific coast, or so I hear). My experience does include being severely seasick in small vessels during storms,  but the shipboard episodes of my life are thankfully few and far between.

Having lived on the east coast of Sicily for many years has also acquainted me with the strong coastal current that arises every now and then and some say are linked to the tides. But tidal movement in the Mediterranean are mostly very small and complicated, with the Messina current being well established as a tidal current, resulting from the (small but still existant) out-of-phase tidal movements oft he Ionic and the Tyrrhenian seas.

[binntho]

uniqorn - my apologies if I have misconstrued your comments. I have read your posts, and commented on some of them for some time, and you have on occasion commented on mine. But your contributions to this forum outweigh mine by a long shot, it is I who benefit from reading your posts and most likely not the other way around!

Seeing as how you have dregged up some of my earlier contributions, I would like to clarify:

I have "always" (let's say, for the last few decades), been of the opinion that tidal movement is primarily an up-and-down movement caused by changes in gravity.

Ghanges in gravity cause changes in pressure, which causes the water column to expand and contract. Changes in atmospheric pressure also cause changes in pressure within the water column, causing the water column to expand and contract. Hence the two phenomena are linked, and they are also of a similar magnitude.

If we were to put a number on the magnitude of the tidal force on the oceans of the world, then by far the largest number would be put on vertical movement in deep, open water. This does not exclude lateral movement in shallow coastal areas.

Tidal currents in the North Sea, tidal swirls over shallows and in and out of fjords along the Greenland coast, all of these are real and natural and should not surprise anybody. The existence of these does NOT imply that similar forces are at play in the open oceans.

And this is where I think that most of the current misunderstanding of tidal movement stems from: Very many people are aware of, and even have direct experience of, strong tidal movements close to shore. They extrapolate this and think that the 450 km wide Fram strait must have similar tidal currents. Well it doesn't.

[binntho]

Most ocean waves are not pressure waves. Tsunamies are the only large-scale example I can think of.  The tidal "wave" is therefore definitely not a pressure wave as such.

The two daily waves that seem to propagate from west to east every day are caused by the tidal effect being (relatively) static while the Earth rotates underneath (picture 1)

Density of water changes with pressure (see picture 2), and even if the effect is small, the oceans are very deep. So the biggest effect happens over the deep oceans.

But where is the biggest tidal effect felt? This is much more complicated. There is an west-to-east component and even a slight south-to-north (e.g. around Iceland, the tide hits the south-west first, and the north-east last). But the shapes of the oceans, their bathymetry, and the relentlessness of the tidal cycle, results in the tidal effect being very strangely distributed (see picture 3)

[blumenkraft]

Let's see if he comes around this time.

Nope. Just keeps spamming.

[binntho]

In the prevous post, the tidal component in the Arctic could not really be seen. But a very quick Internet search found the following, which I must say surprised me very much.

There hardly seem to be any tides in the Arctic at all! So I think we can lay to rest once and for all any discussion of whether and how the tides can affect sea ice in the Arctic ocean.

The image is from here.

[binntho]

Let's see if he comes around this time.

Nope. Just keeps spamming.

I'm saddened, blumenkraft. I truly expected better of you. Do you think that honest disagreement, dissemination of information and willingness to debate are "spamming"?

[binntho]

This whole tidal debate has in my mind always been about coastal vs. total.

The total effect of tides on water movement are totally different from localized, and coastal, effects. Lateral movement is obvious in the latter, negligible in the former.

The most recent example of lack of understanding of how tides work was the claim that the phases of the moon could somehow visibly affect Fram export.

The one before that was when someone talked about a "tidal surge" entering the Arctic Ocean.

What perhaps surprises me most is not that a few simple souls can make such claims, but that the rest of this forum does not understand why those claims are so wrong.

And unfortunately, blumenkraft and other very valuable members of this forum continue to refuse to understand why silly claims about the tides simply cannot be right. There is no tidal surge in the Arctic ocean (nor can there be), and the phases of the moon do not visibly affect Fram export.

[P-maker]

Binntho, nice to know that you are safely up into the mountains in Africaåq and away from the frigid ocean. Also, nice to know of your Icelandic origin, which bothers for an illiterate mind and a couragious world-view.

If you take a closer look at the tidal map you presented, you will see that the Fram Strait is exactly the place, where a tidal "front" exists. North of it, there is hardly any tidal waves. South of the line between NE  Greenland and Svalbard the tidal amplitude suddenly rises to 0.5 m.

Please reconsider, whether such a twice-daily "pull" of low water tide in the Greenland Sea would have have any noticable effect on the export of polar sea ice.

[binntho]

Please reconsider, whether such a twice-daily "pull" of low water tide in the Greenland Sea would have have any noticable effect on the export of polar sea ice.

What "pull" do you mean. What is pulling on what, and how?

And if a twice-daily "pull" then there must be an equal and opposite twice daily "push"? Leaving us with no net effect at all.

[binntho]

Binntho, nice to know that you are safely up into the mountains in Africaåq and away from the frigid ocean.

Thanks. It's a little bit strange thinking of this as being "up in the mountains" since I'm sitting next to a huge lake in an extensive flatland surrounded by mountains. But on the other hand, I am at an altitude of almost 2000 meters.

The nearest ocean is not "frigid", in fact, you would have difficulty swimming in the 40+C surface waters due to heat. And in Iceland, we don't usually consider the ocean "frigid" since it is more often than not warmer than the air!

[P-maker]

Binntho,

If your DTU Space-derived map is nearly correct, the sea level in the Greenland Sea will be half a meter lower twice a day than sea level North of the 80 degrees parallel in the Fram Strait.

This means that there is an immediate "pull" southwards twice a day, which may contribute to the "fracking" or "cracking" seen these days north of 80N.

It is the "pull" that does it, not the "push" at high tide in the Greenland Sea.

[binntho]

If your DTU Space-derived map is nearly correct, the sea level in the Greenland Sea will be half a meter lower twice a day than sea level North of the 80 degrees parallel in the Fram Strait.

This means that there is an immediate "pull" southwards twice a day, which may contribute to the "fracking" or "cracking" seen these days north of 80N.

It is the "pull" that does it, not the "push" at high tide in the Greenland Sea.

You imagine that because the surface is lower in one place than it is in another, then there should be a gravity-induced pull from one to the other. This is intuitive, but wrong when it comes to tides.

Just to be clear: We are talking about deep ocean, hundreds of km from the nearest shore. So there is no coastal effect.

The tides move up and down due to changes in gravity. So the surface is always at the same "level" of gravity, whether it is one meter higher or lower.

For there to be a gravitational pull (e.g.. down a slope) there has to be a difference in the gravitational pull at the surface at the top of the slope and at the bottom - there has to be a difference in what is often termed "potential energy" of any object on the upper and the lower parts of the slope. But since the graviational pull at the surface is the same (because the surface responds to changes in gravity by going up and down), no potential energy difference exists.

There is therefore no "pull" from the tide-lowered South Greenland sea, just as there is no "push" from the tide-raised South-Greenland sea, when compared to the Fram Strait boundary.

[oren]

Binntho you keep ignoring the huge difference in depths between bodies of water, even away from your beloved coast . You keep repeating the mantra of the "deep ocean", well if all the oceans were uniform some of the effects being thrown around here would not exist. And yet you ignore this and therefore keep being surprised that people claim there is an effect.
Until you acknowledge this no progress will be made.
To all other posters, well done on digging up so much useful information. Once a separate thread is created this can be done at leisure without disrupting the original thread.

[binntho]

Binntho you keep ignoring the huge difference in depths between bodies of water, even away from your beloved coast

I don't think I do. There is a difference between continental shelves and the deep ocean, of course there is. But the tidal effect is almost all to be found in the deep ocean - both when it comes to area and when it comes to volume and when it comes to sheer energy.

Besides, with the tidal effect being cyclical, expecting any effect to be more than an up-and-down and back-and-forth movement, and therefore essentially zero over any given day  would require a lot of explaining. The tides do cause currents in certain coastal areas, and these currents are able to move ice in one direction in the morning and the other direction in the evening. So what? This is such a collection of basic facts that they should hardly need to be mentioned.

. You keep repeating the mantra of the "deep ocean", well if all the oceans were uniform some of the effects being thrown around here would not exist. And yet you ignore this and therefore keep being surprised that people claim there is an effect.

I'm not surprised when people claim real effects, effects that all can see and many of us (me included) have experienced directly.

What surprises me is that most of the members of this forum are unable to see that wild claims about "tidal surges" in the deep Arctic, and that Fram export can be linked to the phases of the moon, are so very very wrong.

Until you acknowledge this no progress will be made.

But I do acknowlege it! I acknowledge all knowledge. I acknowledge all facts. I do not acknowledge wild theories without basis in reality.

The various scientific papers, I acknowledge them all. The gifs that blumenkraft and others have shonw me I acknowledge them all. I have never claimed otherwise.

But I will never acknowledge wild theorizing without any basis in reality. And I am not at all happy with the seeming lack of understanding of basic physics amongst the majority of posters in this forum.

Otherwise, my refusal to admit a moon-phase effect on Fram export would never have lead to this discussion!

[Hopen Times]

binntho, what are your thoughts on MOSAiC´s experiences with the tide? As mentioned in post #24.
 

[johnm33]

Interesting post here suggesting tidal forces may lift water over the mid atlantic ridge, https://forum.arctic-sea-ice.net/index.php/topic,2022.msg123120.html#msg123120
and another here which may explain some of the 'pull' mentioned above[the vid]. https://forum.arctic-sea-ice.net/index.php/topic,1755.msg199444.html#msg199444

[oren]

Besides, with the tidal effect being cyclical, expecting any effect to be more than an up-and-down and back-and-forth movement, and therefore essentially zero over any given day  would require a lot of explaining.

Ratcheting. Not such a long explanation I think, a cyclical motion converted to movement by way of something preventing some or all of the return movement. Not happening in the ideal uniform deep ocean but happening in areas with sharp differences in depth, especially where shallower sills, or underwater waterfalls, are involved.

[Glen Koehler]

     If the question is "Does Fram export vary with tidal forces", then getting the daily values used to create the Wipneus Fram export chart and checking for correlation with the lunar cycle would provide evidence to address the question.
https://forum.arctic-sea-ice.net/index.php/topic,119.msg258236.html#msg258236

[HapHazard]

One person here reminded me of the backfire effect.

The Misconception: When your beliefs are challenged with facts, you alter your opinions and incorporate the new information into your thinking.

The Truth: When your deepest convictions are challenged by contradictory evidence, your beliefs get stronger.

[tybeedave]

good afternoon,

Among the many forces at play in the Arctic, the gravitational flattening of the CAB and its recurving twice/day imparts oodles of energy, (scientists measure it in zillions of joules) every day, sun or no sun, wind or no.  Tides impart a significant amount of heat to and have a significant effect on, the system, even though reduced, at the pole proper.  To ignore this is folly.

It is not also obvious to those whose sunglasses block more than the glare.

I might add that by simple geometry, one can illustrate how a higher tide allows more volume to pass through the Fram.  Though true that generally tide has a to and fro character, that is not currently true in the Fram and into the Greenland Sea. The wind has blown strongly for the last 45 frigging (excuse my english) days in a southeastern direction!!!

The transport has been incredible, and yes, learned friends, high tide, twice a day, every damn day is indeed a real factor, and whether one is blinded or not to reality, waves of ice in a tide-exacerbated flow of an extreme amount, may have mortally wounded the CAB.

That this event has not appeared very robustly in extent and volume stats is interesting.   There is a simple explanation for why observation doesn't agree with measurements.  The older ice floes are separating and a thin layer of new ice forms.  The air is still cold now, but it only freezes a thin layer in all of the newly created areas still categorized as ice.  Created extent evens out the extent stats with mostly newly formed, thin ice, replacing older, thicker floes in droves.

I have no direct reason to explain the stable volume figures other than the time frames disguise it or lack of data.  I just don't know why such a large melt doesn't show up better.  Maybe it didn't happen and I'm the boy crying wolf, but I see the blood of the CAB in this area, and I don't think it's an illusion.

But, I would estimate that possibly 10 % of the CAB has been converted from the solid to the liquid via export through the Fram into the Greenland Sea and into the Barents Sea during this 45-day event.

Hopefully, weather patterns will change soon.  If they don't, and accelerated export continues through the summer (unlikely), the pole may be in open water at some point this year.


The pettiness of ignorance may be cured by the recognition that an important event is going on now and the learning that the more one learns, the more one becomes sure they don't know near as much as they think they do.

Tides are important, imho.

The tide and wind having a coordinated seiche effect on an enclosed basin (CAB) could also qualify as a heat generator as well. Once again, measured in zillions of joules lol

peace

td

[uniquorn]

<>Ghanges in gravity cause changes in pressure, which causes the water column to expand and contract. Changes in atmospheric pressure also cause changes in pressure within the water column, causing the water column to expand and contract. Hence the two phenomena are linked, and they are also of a similar magnitude.<>

A bold claim which should be easy to verify with a volume vs time chart or a scientific paper. A quick search didn't find one. Nevertheless, that search did lead me to the video attached, which is similarly challenging. Thank you.

Although each drop of water on Earth is indeed pulled by the moon's gravity, the effect isn't noticeable on a molecular level since the Earth's inward pull is overpowering.

The key, however, is that ocean water covers about 71% of Earth's surface and is connected as one liquid body. This allows the small force on each water molecule to collectively add up to "a pretty decent increase in water pressure," Perez-Giz says.

Molecules of water near Earth's poles are pulled mostly straight down toward the planet's center of gravity (near its core), and the molecules closest to the moon (at Earth's equator) experience the strongest pull toward the moon. Water molecules that are farthest from the moon, meanwhile, feel the weakest gravitational acceleration.

Since water molecules can easily move and bump into one another, these countless tiny nudges add up and "squeeze" seawater away from the poles. This global water pressure works against Earth's gravity to form two bulges: the high tides.

"The ocean isn't being lifted or stretched," Perez-Giz says. "The ocean is bulging along the Earth-moon line in the same way that a blister or pimple will bulge up if you start to squeeze it from the side."

https://www.nsf.gov/od/oia/activities/aaasfellows/bios/perez-giz.pdf