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Continental drift and global sea-level rise

by lucasolsson
Tags: continental, drift, global, rise, sealevel
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lucasolsson
#1
Apr25-12, 05:40 AM
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What is the relationship between continental drift/sea-floor spreading and global sea-level rise?


Kind regards.

Lucas Olsson

University of Gothenburg

Earth Sciences

lucas@student.gu.se
Phys.Org News Partner Earth sciences news on Phys.org
davenn
#2
Apr25-12, 05:53 AM
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Hi there,
welcome to PF :)

I couldnt see continental drift causing sea level rising or lowering for that matter

Why would you think that there would be a correlation ?

before I give my reasoning to my answer I would like to see your reasoning for a relationship between the two

cheers
Dave
lucasolsson
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Apr25-12, 06:25 AM
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Quote Quote by davenn View Post
Hi there,
welcome to PF :)

I couldnt see continental drift causing sea level rising or lowering for that matter

Why would you think that there would be a correlation ?

before I give my reasoning to my answer I would like to see your reasoning for a relationship between the two

cheers
Dave
Thank you!

Yeah I also have problems in seeing the correlation between the two. Ocean-floor spreading I guess can cause global sea-level rise if it is spreading at a high rate, thus causing the sea-floor to be lifted up. I'm not quite sure of this however.

For the continental drift I have no clue.

The reason behind the question is that we have a list of elements we should learn in a global tectonic course I'm having. And in this list our professor states:

"Know the relationship between continental drift/sea-floor spreading and global sea-level rise"

It is in swedish though so if i'm to translate it directly it is "continental spreading" but I think that is the same as continental drift.

Therefore I can only assume there should be some kind of relationship between continental drift and sea-level rise.

Any ideas?

davenn
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Apr25-12, 06:39 AM
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Continental drift and global sea-level rise

hi

ok, thanks for your response :)

look at it this way, as I see it, any seafloor spreading at any rifting zone is counteracted by a mixture of subduction and/or thrust faulting (compression) of land masses in other areas.
lets take the Indian ocean as an example... the seafloor spreading is taking place along the Mid-Indian ridge and a couple of others. But I would suggest that any changes are being taken up by the huge subduction rates of the zones off western Indonesia -- aka all the huge subduction quakes there, even over the last decade. On top of that the country of India is still being rammed into Asia and the compression is still pushing up the avg height of the Himilayan Mts and the Tibetan Plateau as a whole.
As a result, even just from that one region I couldnt imagine any significant changes in sealevel as a result. The Pacific Plate motions would also be producing similar results.
Africa is trudging further northwards, causing a mixture of subduction and compression across southern Europe as the Mediterranean Sea gets smaller in area

cheers
Dave
davenn
#5
Apr25-12, 06:58 AM
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Yeah I also have problems in seeing the correlation between the two. Ocean-floor spreading I guess can cause global sea-level rise if it is spreading at a high rate, thus causing the sea-floor to be lifted up. I'm not quite sure of this however.
I'm not sure how a high spreading rate relates to a lifting of the seafloor ??
not something I was taught at university.
BUT the other thought that I remembered from my own studies was that the seafloor actually sinks the further you are away from the ridge. As that ridge extruded seafloor cools over the millions of years, it becomes more dense and sinks. The avg depth of the sea will increase as you move away from the ridge.
So that fact on its own would be enough to counteract any possible seafloor rising, let alone the other factors I mentioned in my previous post :)

cheers
Dave
Ophiolite
#6
Apr26-12, 03:32 AM
P: 274
Quote Quote by davenn View Post
BUT the other thought that I remembered from my own studies was that the seafloor actually sinks the further you are away from the ridge. As that ridge extruded seafloor cools over the millions of years, it becomes more dense and sinks. The avg depth of the sea will increase as you move away from the ridge.
So that fact on its own would be enough to counteract any possible seafloor rising, let alone the other factors I mentioned in my previous post :)
Dave, I think you may have missed the answer, or part of it, within your own statement. It is not distance from the ridge that determines the amount of sinking, but cooling time. If spread rates are high then time to cool is less, so average sea depth decreases and marine incursions become more likely. This is equivalent to saying that the ridges themselves increase in breadth.

The situation was first recognised, I think, for the Cretaceous:

Hays,J.D. & Pitman, W.C. "Lithospheric Plate Motion, Sea Level Changes and Climatic and Ecological Consequences" Nature 246, 18 - 22 (02 November 1973)

Abstract:
We demonstrate quantitatively that the world-wide Mid to Upper Cretaceous transgression and subsequent regression may have been caused by a contemporaneous pulse of rapid spreading at most of the mid-oceanic ridges between −110 to −85 m.y. The rapid spreading caused the ridges to expand and hence reduced the volumetric capacity of the basins. The subsequent regression was caused by a reduction in spreading rates beginning at −85 m.y.

@lucasolsson
These papers can provide further insights to the issue:
The Phanerozoic Record of Global Sea-Level Change
Tectonic Forcing of Late Cenozoic Climate
Long-Term Sea-Level Fluctuations Driven by Ocean Basin Dynamics
Dynamic topography and long-term sea-level variations: There is no such thing as a stable continental platform
davenn
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Apr26-12, 03:39 AM
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Quote Quote by Ophiolite View Post
Dave, I think you may have missed the answer, or part of it, within your own statement. It is not distance from the ridge that determines the amount of sinking, but cooling time. If spread rates are high then time to cool is less, so average sea depth decreases and marine incursions become more likely. This is equivalent to saying that the ridges themselves increase in breadth.
You are right, I hadnt though about the fact that higher spreading rates would mean that the seafloor is warmer longer.
I need to read some of those links you have posted before I ask the next question relating to my earlier comments about subduction and collision zones.

thanks

Dave
davenn
#8
Apr26-12, 04:42 AM
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some brief reading through those articles hilights some interesting things

This from your post above of an article quote....

Hays,J.D. & Pitman, W.C. "Lithospheric Plate Motion, Sea Level Changes and Climatic and Ecological Consequences" Nature 246, 18 - 22 (02 November 1973)

Abstract:
We demonstrate quantitatively that the world-wide Mid to Upper Cretaceous transgression and subsequent regression may have been caused by a contemporaneous pulse of rapid spreading at most of the mid-oceanic ridges between −110 to −85 m.y. The rapid spreading caused the ridges to expand and hence reduced the volumetric capacity of the basins. The subsequent regression was caused by a reduction in spreading rates beginning at −85 m.y.
is totally negated by a comment from that first paper link ....

Using new sea-floor age data, Rowley (25) suggested that there have been no changes in sea-floor spreading rates over the past 180 My
I liked this comment from the last paper link in the list as it backed up my comments in my second post about subduction zones compensating the sealevel variations caused by the spreading ridges .....

Second, various simulations of mantle convective flow indicate that the spreading rate-sea level connection neglects a crucial element of the plate tectonic system, namely subduction (Hager, 1980; Mitrovica et al., 1989; Gurnis, 1990). Mitrovica et al. (1989) and Gurnis (1990) have shown that viscous stresses driven by plate subduction can drive topographic (and hence apparent sea-level) variations in the overriding lithosphere.
An increase in subduction rate, or the subduction of progressively older (colder) lithosphere, will lead to a dynamic subsidence of the overriding lithosphere and the associated infill of water to this area may, at least in part, compensate for the sea-level
rise associated with an increase in the spreading rate. There may be important phase lags between the sea-level signal from spreading and subduction rate changes (Husson and Conrad, 2006); however, the link between plate subduction and tilting of continental margins (i.e., regional transgressions and regressions of sea level) is widely established (Mitrovica et al., 1989; Gurnis, 1990).
There's also other interesting factors which influence the apparent sealevel "height"
The large increases in sealevel attributed to the icesheet melting is also offset by the elastic (isostatic) rebound of the continents as they loose their load of ice.

Its going to take some time to fully read all those papers but I'm sure its going to be a
good learning process :) A very interesting topic !

Dave
lucasolsson
#9
Apr26-12, 09:09 AM
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Thank you guys so much for your replies! They've been really helpful!

Ophiolite (your nick is a very interesting subject!): I'll look into the articles you linked to. I think I will get a much better view on the subject after reading them. Thank you!

Davenn: I'm glad you also find this subject interesting and I really appreciate the time you've taken to make the subject more clear to me.

I will get back some time next week after my exam is done. At the moment I'm all stressed out reading notes and course materials
Ophiolite
#10
Apr26-12, 10:18 AM
P: 274
One of my reasons for including the first paper was because of the reference you spotted. My impression - and this is outside my area of even amateur expertise - is that this is an example where a mechanism was deduced based upon facts that are no longer considered valid, but the mechanism has gained such 'popularity' or alternative support that it continues to be used.

(I was reading a paper on seismology this week where the author noted that the data and methodology used to identify the core-mantle boundary would be considered way to flaky today to place any reliance upon the finding.)
Dkrikowa
#11
Apr26-12, 08:52 PM
P: 1
Not sure if this is applicapable but continental positioning has a huge impact on global sea level. With antartica breaking off and drifting to its current position it stores a lot of the Earths water as ice above ground. Back when the Earth only had one land mass Pangaea it was positioned around the equater, there was no ice, the sea level was high and the water content of the atmosphere was high.

Im from Australia and I know that the Australasia Pacific plate is moving northward. Im not aware of any statement on the movements of Antartica but if Australia is moving northward it would likely correspond to Antartic moving northward but in the opposite direction, away from its position at the southern pole. If this is the case regardless of global warming Antartica would warm on its own as the continent moves north, the water it stores as ice returning to the oceans causing global sea-level rise.

On a completely different direction there is also a theory that as the continents shift and the seabeds expand that the earth its self expands. Im not sure of the link at the moment but its easily googled. I think it runs on the premiss that the pressure at the point where seabed expands is weaker then the pressure required to collide continental plates so you get this back wave of pressure which further widens the seabed rifts. This forces the crust to expand at that point of contention. I haven't looked into this theory too much but its certainly an interesting idea. It connects well with the theory that the core itself is cooling, which if the crust was expanding, increasing surface area and distance from the core, would create. Anyway what this is getting at is that if the planet is slowly expanding the sea level will actually reduce as it now has a larger surface area to cover.
geo101
#12
Apr29-12, 11:36 AM
P: 53
Did your professor say "sea-level rise" specifically or was s/he more general (i.e., climate change or sea-level change). Also, do you know what sort of time scales he was referring to?

There is a theory relating long-term tectonics to climates changes called the BLAG hypothesis, I'm not too familiar with it, but have a look at this.
The basic idea is that CO2 from volcanic degassing is one of the largest natural sources of CO2. Therefore if you have faster plate tectonics you will have more CO2, a hotter global will melt the ice caps and sea level will rise.

BUT... what it does not really accounted for is continental erosion, which is a CO2 sink. If you have faster plate tectonics, mountains are built faster and the higher a mountain is.. the faster it erodes and the mode CO2 is taken in from the atmosphere. (Weathering/erosion is as much a chemical process as it is a physical one). I dare say that there are more detailed descriptions in the book I linked to, but the BLAG hypothesis is not generally accepted.


If the topic is more general, then mountain building can act as physical barrier that dramatically change climate. For example, the Asian monsoons would not exist if the Himalayas were not there... but this is reaching the limits of what I know...
Endervhar
#13
May12-12, 06:20 PM
P: 142
This from your post above of an article quote....

Hays,J.D. & Pitman, W.C. "Lithospheric Plate Motion, Sea Level Changes and Climatic and Ecological Consequences" Nature 246, 18 - 22 (02 November 1973)

Abstract:
We demonstrate quantitatively that the world-wide Mid to Upper Cretaceous transgression and subsequent regression may have been caused by a contemporaneous pulse of rapid spreading at most of the mid-oceanic ridges between −110 to −85 m.y. The rapid spreading caused the ridges to expand and hence reduced the volumetric capacity of the basins. The subsequent regression was caused by a reduction in spreading rates beginning at −85 m.y.

is totally negated by a comment from that first paper link ....

Using new sea-floor age data, Rowley (25) suggested that there have been no changes in sea-floor spreading rates over the past 180 My
Does current geological thinking favour an increase in spreading rate between −110 to −85 m.y. ?
Darwin123
#14
Jun10-12, 10:28 PM
P: 741
Quote Quote by lucasolsson View Post
Thank you!

Yeah I also have problems in seeing the correlation between the two. Ocean-floor spreading I guess can cause global sea-level rise if it is spreading at a high rate, thus causing the sea-floor to be lifted up. I'm not quite sure of this however.

For the continental drift I have no clue.
The ocean floor spreading does next to nothing. If the sea-floor were lifted up, then it would merely lift the water on top of it and the continents on top of it up with it. Hence, subduction and uplift will do very little.
Ice versus liquid water. The big effects on sea level come from the balance between water in its liquid form and water in its liquid form.
If a glacier forms on dry land, then the sea level must go down. The reason is that the ice that forms on dry land is being lifted out of the water by the dry land. The less water in the ocean, then the lower the sea level.
If ice forms that is floating in water, the sea level doesn't change. Water expands as it freezes. When ice floats the part of the ice that sticks out of the water is merely part of that expansion due to cold. However, this doesn't apply to ice that forms on land.
Continental drift can cause glaciers on land to form in several ways. If there is no continent at a pole, then the ice that forms at that pole doesn't lower the sea level. However, if a continent drifts over a pole, then glaciers that form on that continent can will lower the sea level. Large bodies of land that move toward the poles may also gain glaciers, causing the ocean level to go down.
Another way to cause glaciers is to interfere with the ocean current conveyor belt. Cold water away from the poles on the bottom of the ocean, while warm water flows to the poles on top of the ocean. This is called the oceanic conveyor belt. This melts the ice at the poles. However, a drifting continent can get in the way of these ocean currents. Then, more ice will form at the pole. This lowers the sea level.
Continental drift can cause glaciers on land to melt in several ways. If a polar continent moves away from the pole, the ice on the continent will melt. This raises the sea levels. Similarly, if a continent that is blocking the conveyor belt moves out of the way, the pole will get cold. More ice forms at the pole on top of land. The sea level goes down.
Note that the ice that floats doesn't count for very much. At the present time, the ice at the North pole is floating. Melting it won't effect sea levels too much. However, most of the worlds ice is on dry land either at the Antarctic continent or Iceland. When that ice melts, the sea level will go way up.
Note that water vapor is playing an important role in sea level indirectly. There isn't all that much water vapor in the atmosphere. However, water vapor allows water to transfer from warm areas to cold areas. Thus, it is the dynamics of the water vapor that allows liquid water to become ice and ice to become liquid water.
So the question is how continental drift has affected glaciers. The more glacier, the lower the sea level.
Studiot
#15
Jun11-12, 01:37 PM
P: 5,462
Plate Techtonics by Condie

P195 - 196 discusses the effect of techtonics (and other causes) on sea level.
billiards
#16
Jun16-12, 07:35 AM
P: 747
This is not something I have ever thought about. And was pretty much in agreement with others here that it was nonsense. That was until last night when I was rereading an old paper: ANDERSON. HOTSPOTS, POLAR WANDER, MESOZOIC CONVECTION AND THE GEOID. Nature (1982) vol. 297 (5865) pp. 391-393.

The pent-up heat causes rifts and hotspots and results in uplift, magmatism, fragmentation and dispersal of the continents and the subsequent formation of plateaus, aseismic ridges and seamount chains which cause a global rise in sea level.
Strictly, this is not plate tectonics - it is mantle plumes. But I believe the two are bound together in the plume paradigm.

I need to look a little further into what is actually happening, but I guess the dynamic topography associated with the upwelling plume has the effect of shrinking a basin locally, which forces water to pile up elsewhere.
Darwin123
#17
Jun16-12, 06:19 PM
P: 741
Quote Quote by geo101 View Post
If the topic is more general, then mountain building can act as physical barrier that dramatically change climate. For example, the Asian monsoons would not exist if the Himalayas were not there... but this is reaching the limits of what I know...
Uplift can cause glaciers. A mountain range can form when two continents collide. If a mountain range forms, then water vapor may form a glacier and the sea levels go down. If the mountain range erodes away, then glaciers may melt away. The water goes to the sea and the sea level goes up.
I have heard some lectures on this but I haven't read a lot about it. According to these lectures, the sea level in Cenozoic times is highly correlated with the ice ages. When the glaciers cover most of the continents, the sea level goes down. During the interglacial periods, when the glaciers have retreated, the sea level goes up.
As I said in another post, glaciers can form or melt because of continental drift. If a continent drifts over or near the poles, the glacier forms and the sea level goes down. If the continent drifts away from the poles, the glacier may melt and the sea level goes up.
There is also the dynamics of large basins of water, such as the Mediterranean sea. If continental drift isolates the basin from the rest of the oceans, the water in the basin may evaporate. The evaporated water eventually finds itself in the other oceans and the sea level goes up. If continental drift opens a channel to the other oceans, wave spreads into the basin. Then the sea level goes down. This doesn't directly involve ice.
If sea levels go down, it means that some water is being sequestered. It can be sequestered as land locked ice, or in large basins. Continental drift can change the amount of water that is sequestered.
billiards
#18
Aug1-12, 05:04 PM
P: 747
Another titbit I found whilst reading:

With regard to the super continent cycle

Continental collisions compress land area and thus are expected to lower sea level; fragmentations involve crustal thinning and generate young seafloor, and therefore should raise sea level (Fischer 1984; Worsley et al. 1984).
http://sp.lyellcollection.org/content/323/1/1.full.pdf


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