We are constantly harangued that Global Warming and melting ice will cause the oceans to rise.
But what really controls ocean depth? Is it really ice? Or does the ocean floor vs continental mass depend on something bigger?
http://mappingignorance.org/2013/03/06/mantle-convective-flow-determines-the-depth-of-the-ocean/
Mantle convective flow determines the depth of the ocean
Mireia Altimira March 6, 2013The depth of the ocean is directly related to the behavior of the tectonic plates. Studies conducted so far have assumed that the sea floor depth depends solely on its age. However, these results do not match the experimental measurements.
The work developed by Adam and Vidal 1 shows that the convective flow of the underlying viscous mantle plays a strong role on the plates’ movement and, therefore, on the sea-floor depth.
[…]Flow lines were computed using several kinematic models, which gave very similar trajectories. Figure 3 (right) clearly shows the differences between trajectories following the age-gradient compared to the flow lines derived from mantle convection. Along the flow lines, a linear relation between the sea-floor depth and the square root of the distance from the ridge is observed, which is in turn proportional to the sinking rate. This relation holds all along the plate, so a more accurate fit to the actual sea-floor depth is obtained. Local geophysical processes such as volcanoes, swells or fracture zones explain local discrepancies observed in Figure 3 (left).
In short, the authors propose a more simple and accurate way to reproduce the sea-floor depth by relating it to the mantle convective flow. Instead of introducing new variables in the existing model, they questioned the basis of the model itself, setting a good example of Occam’s razor.
I’ve often complained that sediments flowing into the oceans will cause them to rise while both the ocean floor and continental crust are rising / falling in different places and with a whole lot of motion going on, the ocean depth is dependent on geology much more than on ice melting.
This article looks to have the same idea, but looked at data to confirm it, and modeled the process.
So tell me again why sea level rises and falls? And what role CO2 does or doesn’t play in it…
Musings from the Chiefio 
Goes back to my longstanding argument that all their sea level calculations are based on the idea that the volume of the ocean basin is fixed, and accurately known. What if it bubbles and moves like the surface of a simmering pot of thick spaghetti sauce. We know volcanos inflate and deflate as magma rises inside their magma chamber and plumbing. I see no reason to assume that basin volume is fixed and not constantly changing slowly. Continental drift, crustal rebound, subsea volcanism (lava flow volume, inflation and deflation, earthquake lifting and subsidence of plate blocks (demonstrated by the Alaska Good Friday earthquake and the Christmas tsunami of 2004 and Japanese tsunami 2011 earth quakes), as well as sedimentation at river deltas to name several likely mechanisms which could and likely do change ocean basin volume over long time spans.
An important insight.
Now, how much acidification of the ocean is involved in a pH shift from 8.2 to 8.1. If pH 7 is neutral then at 8.1 its still basic.
Interesting discussion here (http://www.reefkeeping.com/issues/2007-05/rhf/) about achieving lower pH in aquariums to enhance coral growth by addition of Soda Water or White Vinegar.
@Earl Happ:
The bottom of the ocean is covered in metal nodules and carbonate deposits from shells and “gut rocks”. The ocen can not become acidic.
Larry says, ” I see no reason to assume that basin volume is fixed and not constantly changing slowly. Continental drift, crustal rebound, subsea volcanism (lava flow volume, inflation and deflation, earthquake lifting and subsidence of plate blocks” and we can add in other non CO2 factors, ground water depletion, global flat lining of reservoir building, (a .17 mm per year deduction in SL no longer happening) space dust, (more then one may think) volcanic flux creating water expansion or contraction, etc…
But when your only tool is CO2, everything looks like your SUV caused it.
And slow rise and fall of large areas of sea floor from the activities of magma plumes, plus the gravitational changes moving water around on the globe and changing the shape of the equatorial bulge. Small changes, but over giant areas.
===|==============/ Keith DeHavelle
Thanks for the link to the website mappingignorance.org. Some interesting article there in a good range of topics including geoscience under which this article is listed.
I note that the author Mireia Altimare is a mechanical engineer who at least appears to have an understanding of fluid dynamics which most scientists lack. I also note she is at KTH where there appears to be some such as Prof Claes Johnson ( http://claesjohnson.blogspot.com.au/) who think outside the box of establishment scientists and mathematicians.
My only question is: what time scale does this work on? And for sudden events like the one that cause the Japan tsunami in 2011, do those actually appear in the sea level data as shifts?
Since we’re listing the whole laundry list…
Don’t forget those large long cycle lunar tidal changes. It isn’t just that the tide gets higher or lower in, say, the North Sea, but also that the water moves to a place with a different bottom topology. I don’t know the magnitude of the change, but when you pull back from a flat area and move into a steep sided one (or vice versa) the effective size of the ‘bowl’ changes.
@mpcraig:
I think the only reasonable answer is “it depends”. For the article, they are talking about very slow plate tectonic things that take millions of years. The spreading and sinking of plates as they cool. The larger view, though, includes very rapid changes like the Indonesia quake where a several hundred mile chunk of sea floor rose 9 feet ( 3 m~) in just a minute or two.
The short events are going to be lost in the noise of tides and wind, and then diluted over a globe sized area of ocean, so I’d be very very surprised if they show up in sea level data as events. Only a many year aggregate is likely to show up (along with the sedimentation and dust and…) For the plate tectonic data, it is just too slow. We’re talking 10,000 years as a “fast event” that might show up.
HOWEVER….
There are things in recorded history like when Heracles in Egypt sank below the sea in a great quake. That was 10s of feet ( maybe 10 meters?) of drop all of a sudden. Similarly, there are what look like structure evidence under the Caribbean Sea at something like 2000 feet down, that can’t be from post glacial sea rise, so IFF they are really structures of human cause, that chunk of the ocean bottom had to drop a long ways fairly fast. We fool ourselves that we think we know all the tricks the crust can play… It is an extremely thin thing compared to length under the oceans and well inside the range where buckling, breaking and heaving can happen. (Look at the folding of rocks of sedimentary origin all over the world and you see a lot of folding and buckling. We don’t really know how fast it happens, only “directed speculation” that it is ultra slow as the rocks are not broken. Quakes show movement can be fast, though usually that is a slip on a fault or a thrust of an entire block upward / downward But even there, if a mantle plume picks up speed, doesn’t that mean stresses change and blocks can suddenly start moving more?)
So while I’m generally in agreement with the “uniformitarian” POV in geology and rocks, there are clearly some bits that are very “punctuated” with rapid changes (supervolcano anyone?) so you can’t dismiss ‘rapid change’ wholesale. Catastrophism has evidence. (See the many feet thick volcanic tuff in Nebraska… http://www.worldcat.org/title/deposits-of-volcanic-ash-in-nebraska/oclc/28895704 for example).
Now a super volcano is not a frequent thing, nor are asteroid impacts, yet they speak to the existence of similar things of smaller scale. Nothing prevents a magma bulge under the sea floor near active sites from making a sudden “Mount Everest” of added sea floor height. It is happening now just off of The Big Island Hawaii, and Tambora is rebuilding. So we have evidence for things happening inside human historic time scales.
The implicit assumption is that these all average out to no change. There is no proof of that assumption. Just like it is assumed that sedimentation is averaged out by subduction of the deposits. We know that The Grand Canyon has eroded and filled in a trench about 9000 feet deep of the coast of Mexico and up into Southern California filling in part of the Gulf Of California. That happened fairly fast in geologic time (a few million years) and it has not yet been subducted, so a net rise of sea level so far. The Basin And Range area (Nevada, Utah, California mountains) has been uplifted, and a chunk of sea floor scraped up to make the California Coastal Range, but does that mean sea level went down? We have no clue the net-net of all the geologic movements; but just assume they are on our human time scale not relevant.
We don’t live long enough to observe on the 1000 year time scale. (Yet we have “stories” like the sinking of Atlantis that imply ‘maybe it can happen’ and stories of ‘the great flood’).
Yeah, long winded way of saying “don’t know” ;-)
Thanks for the reply E.M.
I agree that “don’t know” is usually pretty good answer to questions about large Earth systems like the climate or the oceans. I think your point is taken that when discussing mean sea level (MSL), the overall ocean floor is usually assumed to be static. Sure, there have been local adjustments for isostatic rebound or subsidence but nothing for the other 69.99% of the Earth which is under water.
Along the same lines, I have often wondered about underwater volcanic activity in the Arctic ocean (e.g. the Gakkel Ridge) and the effect on ocean temperatures and sea ice.
But then again, what do I know? I’m just and electrical engineer. ☯
I have lost the trust in the satellite measured sea level and prefer to use this:
http://www.psmsl.org/data/obtaining/
Whenever i am told that an area will be drowned in 30 or 100years i look it up to see what really has happened.
The satellite product somehow try to estimate the amount of water in the oceans, which could be interesting in itself, but has not so much to do with the level along the shores.
Interesting item about the earths spin axis and movement of water due to drought and unusually wet weather shifting mass around the glob.
http://www.cnbc.com/2016/04/09/scientists-just-figured-out-whats-causing-earth-to-wobble.html
It dawned on me as I was reading this that not only does the rotational axis change position but the equatorial bulge would also move about which would also change mean sea level as the bulge shifts location. Not to mention changes in ocean basin content as the total distribution of water shifts from the fresh water holdings on land to the sea and back.
Prior to the year 2000 the polar drift was toward the great lakes region but since 2000 that drift vector is now pointed toward spain (approximately 70 – 90 degree shift in the direction of the drift.