Continental drift and global sea-level rise

billiards

Another titbit I found whilst reading:

With regard to the super continent cycle

http://sp.lyellcollection.org/content/323/1/1.full.pdf

geo101

The argument for this is not just lifting everything up. As new oceanic crust forms it’s hot, less dense and takes up more volume. As this crust most away from the spreading ridge it cools and contracts. If plate tectonics is fast, lots of new hot crust is generated. Fast spreading rates means that the average temperature of oceanic crust is higher, hence it takes up more volume, which displaces the oceans and raises sea level. Ocean basins are big, so we talking about a lot of material The continental crust may be locally uplifted and mountain building will speed up (so will mountain destruction), but the average continental displacement will be minimal.

You’re right that Cenozoic sea-level variations are correlated with ice-volume shifts, but this is on a different time scale. Ice-volume changes generally affect sea level on times scales of thousands to tens-of-thousand years. The influence sea-floor spreading is on the ten-million year scale. The first link given by Ophiolite (post #6) explains this well. Ice-volume changes are superimposed on the larger scale effects of seafloor spreading.

Bobbywhy

Here is recent report on sea level rise along the East Coast of the USA, and is not related to seafloor spreading: From Science News, July 28th, 2012; Vol.182 #2

East Coast Faces Faster Sea Level Rise
“We have direct evidence of a hot spot stretching from Cape Hatteras in North Carolina to just above Boston,” says Asbury Sallenger Jr., an oceanographer at the U.S. Geological Survey’s St. Petersburg Coastal and Marine Science Center in Florida. “The area has an unusual sea level rise acceleration compared to the rest of the United States.”

There is no clear explanation yet of what is causing this accelerated sea level rise.
http://www.sciencenews.org/view/gene...sea_level_rise

Bill Illis

Continental Drift and sea-floor spreading does, in fact, affect global sea level. When new oceans are forming as a rift valley becomes flooded and then spreads out widening the new ocean basin, it actually forms at a very shallow depth - maybe 300 metres. Over the following 10 million years or so, it might deepen to 1000 metres.

It takes between 50 million years to 100 millions for a new ocean to sink in the mantle and reach its mature depth of 5500 metres. The central sea floor spreading region will still be at a shallower depth as the mid-Atlantic Ocean ridge is today.

The best example of this is 95 Mya when the Atlantic Ocean got to about one-quarter the size it is now. It was shallower than its average depth now and the overall global average depth of the oceans was less than today.

Sea level rose to about 265 metres higher than today. One could think of it as the same ocean water had to fit into a global ocean basin which was 265 metres less deep than it is today.

The Ocean had nowhere to go but up onto the land. All of Europe was flooded, all of the Middle East, and the middle of North America from Texas to Inuvik was a shallow sea.

About 35% of the continental shelves were under water at this time (lots of our oil comes from this period.)

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When continents pile up together as in Pangea, the land gets squeezed together and creates more overall ocean area. Sea level will fall in these situations and it was actually 75 metres lower than today during Pangea even though there was no glacial ice.

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These different sea levels can affect the climate as well. The shallow seas of the Cretaceous would have been very warm. It is even easy to imagine a warm ocean current flowing through Texas right to the Arctic ocean at this time.




Chart of most of the sea level data which is available.

Andre

So could the Paleocene Eocene Thermal Maximum also be about ocean basin changes?

Bill Illis

It might have but there is nothing specifically we can point to.

Sea level was still very high by the PETM, although it is thought the inland sea in North America had already receded back. The north Atlantic just started opening at this time and there were very significant volcanoes when Greenland and England separated but that is all we can point to.

Andre

Exactly!

Would that have anything to do with the subtropical Arctic Ocean?, I wonder.