Cretaceous sea levels

Discussion in 'Earth Science' started by sculptor, Apr 5, 2020.

  1. sculptor Valued Senior Member

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    7,221
    ok
    so
    tell me
    What does adding the prefix bwa to hahahahahaha signify?
    ................
    Is that some sort of pop-culture thing?
     
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  3. origin Heading towards oblivion Valued Senior Member

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    It's an attempt to write out the sound of explosive laughter.
     
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  5. billvon Valued Senior Member

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    Sculptor's favorite trick is whataboutism. "Yeah, the temperatures are rising with CO2 concentrations. And yeah, we're emitting the CO2. But whatabout this anomalous data from the MIS 11 data set? And whatabout the depth of the ocean? And whatabout ice ages? And whatabout the K-T boundary climate changes? Can you explain all of that? No? I thought so - you can't explain AGW."
     
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  7. sculptor Valued Senior Member

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    7,221
    ok
    so
    Instead of hahahahahaha, or bwahahahahahaha:
    What would you use to indicate a bemused chuckle?
     
  8. exchemist Valued Senior Member

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    10,082
    Ah yes, whataboutery (as we call it on this side of the pond) is a rhetorical tactic of creationists, too.

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  9. sculptor Valued Senior Member

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    It may have escaped your notice, however:
    I did not start this thread so that it could be used as a platform for agw mountebanks.
    (sigh)
     
  10. iceaura Valued Senior Member

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    30,802
    Just one agw mountebank.

    The others are embarrassing to agree with, no? Let's see what kind of thread one can launch without making any definite assertions or asking any clear questions or specifying any particular topic at all.

    Apparently during the Cretaceous there were sea levels - probably a consequence of having continents or something - and people are having a hard time figuring out what they were, all those millions of years ago. So far so good?
     
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  11. sculptor Valued Senior Member

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    OK
    Perhaps, in an attempt to gain other's open minded perspectives, I do leave questions too open ended.
    Researchers have found evidence of "milankovitch" cycles dating back many millions of years.
    Researchers coring the earth in the desert south west have found evidence of strong 400 kyr cyclicity.
    Then we see changes in sea level within the cretaceous ---outside of this ice age.
    so
    if the volume of water on earth has remained relatively constant for billions of years.
    and the volume of water in the ocean basins had been changing before this ice age, by commonly 20 meters, and occasionally by up to 100 meters(almost approximating the changes within this ice age)
    Then the trees/plants/soils/lakes/rivers/atmosphere/etc... must have held that water.
    ok so far?
    Then, as the temperate zones march poleward
    Can we approximate the volume of water that will be sequestered in the trees/plants/soils/lakes/rivers/atmosphere/etc... and withheld from the ocean basins?

    give it a try?
     
  12. billvon Valued Senior Member

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    18,992
    Most of it is held in ice.
     
  13. sculptor Valued Senior Member

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    7,221
    Yes for today.(most----not quantified?)
    However:
    That is why I went without this ice age to look at sea level fluctuation, and to look for where the rest of the water was during cretaceous sea level lowstands.

    None of the sequestered water was held in ice during the cretaceous!
    Meanwhile we have at least 20 meter sea level fluctuations.

    .........................
    do you not find this interesting?
     
  14. billvon Valued Senior Member

    Messages:
    18,992
    Why do you think the water went anywhere? A 10C change in ocean temperature (on average) would result in a change in sea level of 21 meters due to thermal expansion/contraction. (assuming an average depth of 3600 meters.) That doesn't seem that fascinating.

    No doubt there were other small effects (atmosphere holds more water, more lakes when there's more rain etc) but thermal expansion was the biggest effect back then (and even today.)
     
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  15. exchemist Valued Senior Member

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    10,082
    There is also the issue of water held in the rocks of the crust and mantle. Volcanoes emit water, while subduction at plate margins entrains it. I can imagine that variations in intensity of tectonic processes could also alter the amount of water in liquid form at the surface, over geological timescales.
     
  16. iceaura Valued Senior Member

    Messages:
    30,802
    Of course.
    So have all the climate researchers for decades now.
    Ocean basin configuration, continent configuration, also apply - probably: significantly.

    They were quite a bit different then - notice that he appears to be trying to measure "sea level" not from the center of gravity but with reference to shorelines.

    It is called "sea level rise/fall" rather than "shore level fall/rise" because reasons.
     
    Last edited: Apr 21, 2020
  17. iceaura Valued Senior Member

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    30,802
    You ask the questions you ask as a method of posting innuendo and bullshit on this forum without being responsible for it.

    A typical question:
    A typical justification:
    and so forth.

    By the fourth or fifth post of that nature, the meaning of the term "sea level" itself has been obscured - is it mean distance from the gravitational center? Median? Is it instead measured as a shoreline isocline, with some complications regarding tides necessary? Is floating ice part of the sea or the shore? Does it vary from place to place? Are we to include such concepts as a virtual sea level in analyzing the Cretaceous, as we do when analyzing the Holocene? and so forth - - -

    None of this matters. The poster has not defined "sea level" in the first place, and the absence of any solid notion of what the thread is about is clearly irrelevant.
     
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  18. Hipparchia Registered Senior Member

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    As suggested by other members you seem to have over-simplified your question to the point it is meaningless. This is my attempt to raise the background to a level where fruitful discussion can follow.

    First, lets note, as simply as possible, what can alter sea level. There are only two things:
    • A change in the volume of water
    • A change in the volume of the oceans and seas that contain those volumes
    What can change these volumes? First, the volume of water:
    • Thermal expansion or contraction
    • Changes in the amount of water in lakes, rivers, vegetation and sub-surface reservoirs (including groundwater)
    • Evaporation from, or influx into, marginal seas
    • Subduction of water bearing sediments and (often associated with this) the eruption of H2O bearing magma
    • Changes in the amount of ice tied up in continental ice bodies.
    (The latter is the major contributor to changes.)

    What changes the volume of the oceans and seas?
    • Sea floor spreading rates
    • Mid-ocean ridge length variation
    • Continental collision
    • Fluctuations in sedimentation rates
    • Mantle convection (including super plumes)
    • Eruption of submarine LIPs (Large Igneous Provinces)
    I think most of these points have been raised previously, either directly or implied, but laying them out here may provide a better framework for discussion. Now my first question to you, in two parts is, do you agree with all of these; do you think any are missing?

    You speak of confusion, implying ambiguity and contradiction in the data, but you are not specific. All scientific data contains ambiguity and contradiction. (If you think otherwise you probably aren’t looking closely enough.) Hence my second question, what specifically do you find ambiguous, or contradictory, or confusing in the Cretaceous sea level data?

    In a related (and final) question are you disputing the methodology or the results of backstripping in determining Cretaceous sea levels? If so, why and on what basis?

    I also note what has been remarked on by others: you seem to lack an awareness of the different time frames over which these various controls on sea level operate (and the magnitude of changes they may cause). Thus variations in continental ice produce large changes, rapidly - 200m within several thousand years. In contrast sedimentation rate changes produce much smaller changes over 10 My or more, while sea floor spreading may generate changes at a similar rate (10m/My), but of much greater magnitude, equal to or exceeding that occasioned by ice fluctuation. You seem indifferent to, or ignorant of these contrasts. You may want to comment. (Even if you don’t, I think you should.)
     
  19. iceaura Valued Senior Member

    Messages:
    30,802
    Detail factor: large slow changes can hit tipping points after which catastrophes (in the Thom sense) occur suddenly and very rapidly. We also know that aspects of earth's climate, especially in local manifestation, are both close to such tipping points and moving toward them. Different thread.

    So: very rapid changes in the past do not conflict with, instead are predicted effects of, a combination of large slow changes that has been stable for a very long time. Also, directly: as with some earthquake classes, in many systems (especially chaotic ones) the longer the time of stability the quicker and larger the change (the farther from the new equilibrium range the change began the larger the difference likely to be covered in one of the jumps, stochastically. With exceptions, of course).

    Pertinently: homeostatic mechanisms for stabilizing a dynamic but bounded system, especially a nested one (climate of Australia, say) are likely to maintain it on one side of the equilibrium, fairly close to the tip in one direction only. That's where the minimum {per quantum of benefit} cost of a given "amount" of stability shows up - it's a hidden or cryptic factor, difficult to quantify or even locate. Information becomes key, and who has what information significant.

    Enter politics - in or out of its extraordinary euphemism camo.

    By subtle (to the unfamiliar) control of deceptive rhetoric the media pro on the vulnerable political side acts to rail the public discussion away from that tipping point (the immediate danger, the too likely catastrophe) and toward some other destination (however unlikely, long in the future, or even impossible) that covers up their past blunders and crimes. In doing that they trash ('in communication'* so to speak) enough hard data and past record to prevent consensus formation outside the firsthand circles of discovery rumors and raw data processing.

    Unfortunately, they are unable to rearrange physical reality for their convenience in that way - and agw is not that slow or smooth a train this close to so many tips (even over a couple).

    So the physical realities of Cretaceous sea levels would be meaningful often, regardless of or even specifically motivating the particular choice of definition. Knowing them by way of several definitions or measurements of "sea level" would be useful in many situations. They might even enlighten us about agw's likely future effects - just not as much as they would about other matters, such as socially imposed gene flow or the ecological effects of indigenous people's fire regimes, that at least a bit share their timeline scale.
    There is immediately a third - configuration of those basins and seas. The absolute change and difference in surface area, if any, largely determines the absolute level rise from a given increase in water volume).

    Several more factors emerge as one specifies the thing to be measured and requires greater precision as well as accuracy - in absolute as well as relative variance, in locality as well as both relative and absolute quantity, and so forth
    - partly depending on one's intended employment of "sea level", which will remain mysterious here (my prediction) this time as in the past.
    The gravitational attraction of nearby high-density and high-volume land-ice masses, for example, (which is especially significant around Greenland, Iceland, et al) the arctic region coastlines in general, as included in a plurality of Sculptor's agw aimed innuendo settings here.

    * Unable to find a term pair belonging to the taxon {in vitro / in vivo}. 'Incommunicado'and such suspend the mud in the river.
     

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