Thread: Tidal trigger for Ice Age?

(Tidal effect on ice age worth its own discussion was Split from Sea level thread which was suffering a normal death)
Enjoy
Lynx_Fox


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This topic has been quiet for a bit. How about a different angle.

Now first, I assume we are measuring the average ocean height rather than high tide. Would that be correct? Either way, I thing we should establish what the measurement is for those of us who do not know for sure. What ever we are measuring, I think the strength of the tidal forces should receive attention too.

Now here is my thought. The earth currently has an eccentricity of 0.0167 in its orbit around the sun. Although the moon is the primary driver of the tides, the sun has an pretty good effect also. Throughout our known history, the eccentricity of the earth has been declining. Currently, the gravitational forces exerted on the earth by the sun vary about 7% between the aphelion and perihelion. In 10,000 years, the eccentricity will reduce to about 0.011. Just under 0.005 in 20,000 years, and just under 0.03 when it reaches it's lowest point in about 26,000 years.

Then there is the axial tilt (obliquity) of the earth too. As it increases, the effect of tides in the polar regions increase, and decrease around the equator. As it decreases, the tidal effect increases at the equator, and decrease around the poles. I wonder if tidal effects could one of the triggers that helps take us out of an ice age. I cannot assume it to be part of what we see today, because this effect has been declining over the last few thousand years. Right now, its effect for the equatorial area is favored. Now please don't argue the couple degrees of change will have no bearing. I know it is small, but it doesn't mean the effect may not be real. The range is 22° 38’ to 24° 21’, and we are currently about 23.44° of axial tilt. I believe that precession has no bearing on the topic.

The moon also has an eccentricity that ranges from 0.026 to 0.077. We are currently at about 0.055. Now the inclination of the moon makes a difference to. It is about 5.1°, and the moon varies between in line with he earth-sun plane, and out. Anyone who has played with vector mathematics and trigonometry can see how many variables we start to have to change the tidal forces.

from wiki: Orbital eccentricity

wiki: Axial tilt

wiki: Orbit of the Moon

Originally Posted by Wild Cobra

I wonder if tidal effects could one of the triggers that helps take us out of an ice age.

Very interesting idea. I'm gonna keep that in mind.

I've wondered about the continental shelves. They appear to be the low-water mark of ice ages. But strangely if the water rises up a bit from that mark it's suddenly rushing over huge relatively flat expanses... and further flattening them... like the Bay of Fundy only thousands of times more surface area. That tidal wash would pump the seas full of air and nutrients. Conversely just a little further freezing shrinks the ocean surface considerably, suddenly.

It's safe to assume the shelves at every latitude mark the ice-age minimum sea level, because the sea itself marked them. The shelves end at pretty consistent depth, but not precisely I'll bet. Given that, one could theoretically predict the date of future ice-age maximum by forecasting local tide-tables. Or experimentally predict earlier ice-ages, then see if you've got a winner.

Originally Posted by Pong

Originally Posted by Wild Cobra

I wonder if tidal effects could one of the triggers that helps take us out of an ice age.

Very interesting idea. I'm gonna keep that in mind.

My major thought on that point is with more inclination, the polar tidal effects are more, which would more readily break up the ice shelves. More water exposed to the sun rather than being reflected, warming the oceans more.

Originally Posted by Pong

I've wondered about the continental shelves. They appear to be the low-water mark of ice ages. But strangely if the water rises up a bit from that mark it's suddenly rushing over huge relatively flat expanses... and further flattening them... like the Bay of Fundy only thousands of times more surface area. That tidal wash would pump the seas full of air and nutrients. Conversely just a little further freezing shrinks the ocean surface considerably, suddenly.

I never really thought of that, but it seems highly probable.

Do you know if the depth matches the level of the ocean during any of the ice ages? I saw some amazing number once how much lower the sea level was during the last ice age. If I recall right, it was much more a level change then the 71 meter estimate for Antarctica and Greenland completely melting.

Originally Posted by Pong

It's safe to assume the shelves at every latitude mark the ice-age minimum sea level, because the sea itself marked them. The shelves end at pretty consistent depth, but not precisely I'll bet. Given that, one could theoretically predict the date of future ice-age maximum by forecasting local tide-tables. Or experimentally predict earlier ice-ages, then see if you've got a winner.

Good point, if my thought has validity. I still believe eccentricity is a primary driver of global temperature. I differ from what I have read about the Milankovitch Cycle, in that, I think eccentricity is primary over the other two factors. If the earth had an eccentricity of zero (perfect circle) then all seasons would be 1 AU from the sun and As it is right now, the northern hemisphere summer gets about 7% less solar radiation than the southern hemisphere summer. That's where precession and obliquity probably help in climate modification from the sun, as one pole is ocean, the other is land. I also think 65S insolation would be more important than 65N insolation since water has a higher absorbency of the solar radiation than land.

Back to eccentricity.

At zero eccentricity, each season receives the same solar radiation level, assuming of course, the sun remains constant. When we have (and always do have) an elliptical orbit (eccentricity <0 and >1), the earth spend more than half the year farther from the sun than it does closer. The greater the eccentricity, the greater the effect. Therefore, the annual solar radiation decreases as eccentricity increases.

Keeping to the tidal effects.

Does the moon's orbit follow the earth's Axial tilt (obliquity) or Axial precession? I can see the moon's orbit, with it's huge enormous rotational inertia have a pretty strong effect to dampen precession.




I see link link between tidal effects on ice age and eccentricity.

First, let me thank-you for splicing this out. I had thought about asking, but you beat me to it.

Originally Posted by Lynx_Fox

Keeping to the tidal effects.

Does the moon's orbit follow the earth's Axial tilt (obliquity) or Axial precession? I can see the moon's orbit, with it's huge enormous rotational inertia have a pretty strong effect to dampen precession.

As far as I know, it doesn't. At least it doesn't make sense for it to, to me. I never really took the time to learn much about celestial mechanics, I only know the basis. As far as I know, the moon pretty much maintains the 5 degree axis difference from the earths orbit. I would suspect that it slowly declines over the years, and doesn't increase again.

Originally Posted by Lynx_Fox

I see link link between tidal effects on ice age and eccentricity.

Cool... Sometimes I wonder if I'm imagining things, because it seems nobody will acknowledge what I see.

The solar tides would be caused by the difference between the distances to the sun during each revolution - coming toward, going away.

Tilting the axis toward/away the sun should reduce the difference, with the strongest effect at 45 degrees latitude if the start axis is perpendicular. Places of little rotational effect ever, such as near the poles, would have even less at tilt.

The actual manifestations of tides - their height, frequency, etc - depend strongly on very local topography. The influence of the particular shape of the ice front at grounding would be more likely to be significant than the small effects of revolutionary inclination.

Almost all of the ice in recent ice ages was piled up in the center of the continents involved, hundreds of feet above sea level and hundreds of miles from any coastline.

Apparently the Eurasian mass centered on the Barents Sea.

http://www.qpg.geog.cam.ac.uk/lgmextent.html

Looking at those maps keep in mind that the permanent extent of sea ice is not included. Year-round sea ice must have been humongously thick and pushing south (across land and sea) like a glacier. In that view, the offshore extent of ice sheets really means where their bottoms cease to touch land, due to combination of buoyancy and ocean depth.