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Under water findings

  1. Sep 2, 2009 #1
    Underwater Expedition Delivers Key Findings In Search For Evidence Of Early Americans.

    First raises the question, what kind of years? Archeologists tend to talk in carbon dating years, which requires quite a correction to convert to calendar dates: 13,000 carbon dated years (13 ka BP) is 15,300 calendar years (15.3 ka Cal BP).

    One could also wonder about that 130 feet of water as sea level rise, if that was to be due to melting ice sheets it would be the equivalent of some 5 to 6 Greenland ice sheets, but most of the melting started well before that, maybe something like around 17,500 Calendar years ago and obviously you don't need more than a meter or two to make that area uninhabitable. So what is it?
     
  2. jcsd
  3. Oct 2, 2009 #2
    Don't know about the "carbon/calender" issue, but see:

    Underwater Exploration Seeks Evidence Of Early Americans
    ScienceDaily (July 9, 2009)
    http://www.sciencedaily.com/releases/2009/07/090709120654.htm

    "The decision to take their expedition underwater in the first place, Adovasio said, stems from the premise that early Americans probably hugged the American coastline, congregating around freshwater rivers, before heading inland. At that time, much of the world's water was confined to glaciers, causing ocean levels to be lower and exposing more of the continental shelf. As the earth warmed and water levels rose, evidence of past settlements became submerged."
     
  4. Oct 3, 2009 #3

    Borek

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    130 feet is about 40 meters and it looks like it won't differ much from the plot here:

    http://www.ncdc.noaa.gov/paleo/ctl/clisci100k.html#sea

    which gives even much lower level of water for the period in question (even shifting it +/-2kyears won't change much, we are still in a correct ballpark). I can be missing something.
     
  5. Oct 3, 2009 #4
    You're not missing anything as far as the known graphs go, like this for instance:

    barbados.gif

    which shows that 15-13 thousand years ago (Thorium-Uranium series dating) that sea level was supposed to be 100 -70 meters lower than today.

    The problem is that 40 meters (or 70 or 100) sea level rise is roughly equivalent to 8 times (or 10 times or 15 times) the current Greenland ice sheet, but if you read a few dozen studies about the dating of receding ice sheets after the glacial maximum, you will find that most ice had disappeared around 11-13 thousand years ago, the bulk around 17 thousand years.

    So my question is, where did all that water hide between something like 17,000 and 13,000 years ago.
     
    Last edited: Oct 3, 2009
  6. Oct 3, 2009 #5

    Borek

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    OK, I thought you are questioning depth.
     
  7. Oct 3, 2009 #6

    Xnn

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    There were numerous massive ice sheets during the last glacial maximum that are now long gone. In addition, Antarctica and Greenland were covered with more ice than today.

    These ice sheets did not all reach their maximum extent at the same time.
    Also, they did not all melt in unison.
    There were significant regional variations as the globe gradually warmed.
    Some ice sheets were rapidly melting, while others were gaining mass.
    On top of this are all the problems inherent in paleo dating and measurements.

    What does the most recent peer reviewed paper say?
    Any good links or pdf?
     
  8. Oct 3, 2009 #7

    sylas

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    The work of this expedition is also reported at The First Snowbirds: The Archaeology of Inundated Late Pleistocene Landscapes in the Northeastern Gulf of Mexico, at the oceanexplorer website at NOAA, the mission summary by J. M. Adovasio and A. Hemmings, July 2008. The press release that is the basis of the sciencedaily link in the first post is http://mai.mercyhurst.edu/news/article/?article_id=326 [Broken], Mercyhurst Achaeological Institute, Aug 28 2009. They are limited to 130 feet depth by their diver rankings.

    As I understand it, Adovasio is looking for evidence that North America was populated early on, while sea level was still low; but not as low as the in the last glacial maximum. The work reported in this thread appears to be looking at drowned land which was coastal sometime after the meltwater pulse 1-A.

    The work does not involve any change to dating of sea levels or known artifacts, as I understand it. The references for this report at the NOAA pages includes a relevant paper on sea levels.
    • Simms et. al. (2007) http://dx.doi.org/10.1016/j.quascirev.2007.01.001 [Broken], in Quaternary Science Reviews, Volume 26, Issues 7-8, April 2007, Pages 920-940

    This paper addresses a particular problem with sea levels in this region. You can't simply take data on past global sea level height and compare with current depths at a particular location; because at a given location, the changes in depth are a function both of sea level rise and of local change in land level where you are looking at the depths.

    In the Gulf of Mexico in particular, which is the site for the expedition described in the original post of the thread, submerged landscapes are at a smaller depth than is expected simply from global sea level change. There are several possible reasons for this.

    Here is the abstract of the paper:
    Sea-level records from the Gulf of Mexico at the Last Glacial Maximum, 20 ka, are up to 35 m higher than time-equivalent sea-level records from equatorial regions. The most popular hypothesis for explaining this disparity has been uplift due to the forebulge created by loading from Mississippi River sediments. Using over 50 new radiocarbon dates as well as existing published data obtained from shallow-marine deposits within the northern Gulf of Mexico and numerical models simulating the impact of loading due to the Mississippi Fan and glacio-hydro-isostasy, we test several possible explanations for this sea-level disparity. We find that neither a large radiocarbon reservoir, sedimentary loading due to the Mississippi Fan, nor large-scale regional uplift can explain this disparity. We do find that with an appropriate model for the Laurentide Ice Sheet, the observations from the Gulf of Mexico can be explained by the process of glacio-hydro-isostasy. Our analysis suggests that in order to explain this disparity one must consider a Laurentide Ice Sheet reconstruction with less ice from 15 ka to its disappearance 6 ka and more ice from the Last Glacial Maximum to 15 ka than some earlier models have suggested. This supports a Laurentide contribution to meltwater pulse 1-A, which could not have come entirely from its southern sector.

    The real problems here are not quite as Andre describes. At least, I have yet to see any scientific reference which describes the problems in the way that Andre does.

    Andre; I agree with you that there is a lot of uncertainty and open questions about the history of ice sheets and sea levels. What I don't see is a problem with "hiding" the water. The ice sheets of the last ice age were huge. The Laurentide sheet in particular was quite likely larger than the Antarctic sheet is now, with roughly 30 M km3 of ice at the last maximum. That’s more than ten Greenland ice sheets. But there is a lot of uncertainty in that number. We can't measure the volume of a melted ice sheet easily. There were other ice sheets as well; though this was the biggest one for the Northern Hemisphere. So the problem is not "hiding" of water. It is simply of sorting out how big the different sheets where and how they melted. The process of melting ice sheets was not uniform, either in time or in location.

    The paper by Simms et al (2007) proposes that the main reason for the discrepancy between the prehistory of depths in the Gulf of Mexico and the prehistory of global sea levels is from "Glacio-hydro-isostasy", or changes in land height from the loading of ice or water. They compare a variety of models for the Earth and for the Ice load, and the conclusion of the paper is as follows:
    ... The best fit between the glacio-hydro-isostatic models and the observational data from the Gulf of Mexico is found when using a minimum ice-sheet reconstruction for the Laurentide Ice Sheet for the time period between 15 ka to the present with a significant increase in the thickness of the ice sheet between 25 and 15 ka and a small time-dependent correction for the uplift associated with loading due to the Mississippi Fan. The data is consistent with a Laurentide Ice Sheet whose ice volume is greatly reduced at the time of MWP1-A. However, a meltwater source from the southern Laurentide Ice Sheet alone cannot reconcile the sea-level observations with the model predictions, and a reduction in ice thickness across much of the Laurentide Ice Sheet is required.

    The MWP1-A is a "meltwater pulse", or a rapid rise in sea levels, within the middle of the whole process of melting of iceage ice sheets across the globe, which occurs between 14 and 15 thousand calendar years ago, which would be about 12 to 12.7 thousand radiocarbon years. That matches with the rapid rise in sea level of about 25m mentioned in Adovasio's work. Adovasio speaks of current depths of 75m for material before this pulse and 50m depth afterwards.

    The brief report of Adovasio's expedition at the NOAA oceanexplorer page refers to radiocarbon years. They also seem to have covered quite a lot of land at varying depths, and have not as yet found the human artifacts they would like to confirm his theories. I have found some of Adovasio's conference papers at the mercyhurst site, and frustratingly they include a request that they not be cited in any context without permission; but I can confirm that Adovasio tends to speak in radiocarbon years.

    Andre's response appeared while I was preparing this post, so I'll comment briefly. I do not know the source of his graph on sea levels, but it looks okay. What is very odd indeed is this remark:
    The figures are a bit off. Total melt of the current Greenland ice sheet is generally considered to be about 7.3 meters sea level; so 40 meters would be a bit less than 6 Greenland ice sheets. Total volume of the Laurentide ice sheet at the LGM is roughly 10 Greenland ice sheets, but with a large uncertainty, allowing both larger or smaller values.

    I don't know what studies you mean, Andre. But the major source of information for ice sheet volumes is sea level history. If you read the studies, you find most ice has disappeared at the times when there is a high sea level, because sea level is the proxy par excellence for discovering total ice sheet volumes. I'll be surprised if you can find any paper that thinks there's a problem with "hiding the water" between 13 and 17 thousand years ago. You are the only person I have seen put it in such terms, but it makes no sense to me in the light of the scientific literature on ice sheets and sea levels since the last glacial maximum... and there's no shortage of genuine open questions and disagreements in that literature!

    Adovasio appears to be looking for material after meltwater pulse 1-A, from 10 to 12 thousand radiocarbon years old, or up to 14 thousand calendar years old. That was by no means the end of rising sea levels.

    There are different ideas for the sources of this pulse. Simms et al (2007) are arguing for a source in the vast Laurentide ice sheet, particularly in the light of studies in the Gulf of Mexico, where Adovasio is also conducting this research.

    Cheers -- sylas
     
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  9. Oct 3, 2009 #8
    could it be possible that the extent of the ice sheets decreased faster than the volume?
    lower portions would have less ice to melt, be at lower altitude and so would be less cold and have less snowfall.

    when the ice receded from certain areas is much more certain than how quickly the thickness decreased.
     
  10. Oct 3, 2009 #9
    Obviously there is a lot to investigate here to see if loose ends meet. Not looking good though.

    Adding to the controveries for instance, take again meltwater pulse 1a, that is codated with the Bølling-Allerød Warm Interval, about 14.7 to 12.7 ka Cal BP


    Some fragments from my writings somewhere:


    Note that these glacial readvances codate with Melt waterpulse 1A, so where did they get all that water from? Both for the readvance and for the meltwater?

    Edit update, http://www.icms.com.au/inqua2007/abstract/1391.htm is another one supporting those observations also in New Zealand:

    and Davis et al

    11,900 14C yrs. B.P is 13,770 Cal BP years and 11,800 14C yrs. B.P is 13,690 Cal years BP according to the Intcal04 conversion table placing this glacial readvance event also in the Bolling Allerod period, close to or coinciding with melt water pulse 1A.

    Refs:

    Clark, D.H, 2003. Complex Timing and Patterns of Glaciation in the American Cordillera during Termination 1, Poster presentation XVI INQUA Congress, Paper No. 88-4, July 30.

    Davis RB, Bradstreet TE, Stuckenrath R, Jr. Borns, Jr.HW (1975) Vegetation and associated environments during the past 14,000 years near Moulton Pond, Maine, Quaternary Research Volume 5, Issue 3 , September 1975, Pages 435-465

    Rinterknecht VR, Clark PU, Raisbeck GM, Yiou F, Brook EJ, Bitinas A, Marks L, Zelcs V, Lunkka JP, Pavlovskaya IE, Piotrowsk JAI, Raukas A 2006. The Last Deglaciation of the Southeastern Sector of the Scandinavian Ice Sheet. Science 311, 1449-1452.


    Edit: Sorry, Sylas, about the mix up in Greenland ice sheet equavalents for sea level rise. I had a figure of 6.5 meters in the back of my head somehow. But regardless if it is 5 or 6 or 8 equivalent ice sheets, it's still a lot to account for.
     
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  11. Oct 3, 2009 #10

    sylas

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    I would appreciate a link to scientific literature -- not your writings -- for anyone who thinks there is a problem in the same sense that you do. Your links are to material that is all part of the conventional picture with extensive ice melting before, during and after the meltwater pulse. There is no "missing water" problem.

    There are two main hypotheses. North, or South. South means that a large amount came from the WAIS in Antarctica. North means that it came mostly from the Laurentide sheet. This is an ongoing disagreement. In neither case would the pulse remove all the ice from the corresponding reservoirs, or even most of it. There's LOT of ice involved here. The major take home lesson is:
    In particular, multiple ice sheets represent multiple reservoirs, each potentially behaving independently of each other in response to regional or hemispheric climate change.
    -- http://www.pages-igbp.org/products/...on/science highlights/Clark_2009-2(64-66).pdf by Peter Clark in PAGES News, Vol.17, No 2, June 2009​

    The precise numbers are a minor mix up; no problem. The main point is that it may be a lot to account for but it is still one whole heck of a lot less than what is available. There is no problem with finding the necessary water. The problem is simply identifying which of the various enormous reservoirs of ice was the major source for this pulse.

    You are doing here what you did in the other thread on this. You give a lot of literature which shows some details of the complex history of melting ice, without ever giving anything that repeats your own personal claim about "missing water".

    In [post=2338924]msg #17[/post] of thread "A Return to Phanerozoic Average Sea Level?" I review information from a special issue of Quaternary Science Reviews on ice sheets and sea level of the Last Glacial Maximum (LGM). Here again is the data on where is the water. The source is the introduction and summary paper for the special issue.
    • Clark, P.U. and Mix, A.C. (2002) http://dx.doi.org/10.1016/S0277-3791(01)00118-4 [Broken], in Quaternary Science Reviews, Vol 21, Iss 1-3, Jan 2002, pp 1-7, doi:10.1016/S0277-3791(01)00118-4
    This data is from Table 1, giving estimates of excess ice-equivalent sea level in meters for LGM ice sheets. Columns give max and min for the CLIMAP estimates made in 1981, max and min for the revised ice sheet modeling based estimates, and one more column for estimates by Peltier. (The footnotes clarify that Peltier's 6m estimate for Greenland is known to be too high, and that he has since revised his estimates to about 3m, in a subsequent paper.) Note that for ice sheets that still exist, this is an estimate of how much they have reduced. Greenland, for instance, still has about 7 meters equivalent of sea level locked up in the modern ice cap, and Antarctica still has some 70 meters equivalent or so.
    Code (Text):

    Ice Sheet      CLIMAP Min CLIMAP Max  Ice sheet Min  Ice sheet Max  Peltier
    Antarctica      24.5        24.5        14.0           21.0          17.6
    North America   77.0        92.0        82.4           82.4          64.3
    Greenland        1.0         6.5         2.0            3.0           6.0
    Scand/Barents   20.0        34.0        13.8           18.0          25.5
    All others       5.0         6.0         6.0            6.0
    Total          127.5       163.0       118.2          130.4         113.5
    The Laurentide sheet I have mentioned is in North America. Together with the smaller Cordilleran sheet, accounts for nearly 12 modern Greenland sheets equivalent. Meltwater pulse 1-A involves about 25m sea level rise, or between 3 and 4 modern Greenland sheets equivalent. There's no problem here at all with "missing water".

    In that other thread, I also pointed out that your references don't actually support the specifics of your claims. We have had no response to that post so far... just a repeat of the similar claims now in THIS thread... again with no mention of any credible source that supports your own description of the supposed problems.

    See [post=2341474]msg #27[/post] of thread "A Return to Phanerozoic Average Sea Level?". At the end of the post, I note that there's still nothing in any of the papers you've linked that gives any support at all to your personal claims about insufficient time to form the sheet or insufficient ice to exceed what is now in Antarctica. Your own references in that thread indicate a large extent for the ice and potential for rapid changes in volume; in sharp contrast to your own claims in that thread. That was in 10 Sept; and there's no response from you to this post, as yet.

    I don't mind if you prefer to leave it with us both having expressed contrasting positions for readers to consider. I appreciate you have limited time. But I think I have shown in that thread that your own personal claims are idiosyncratic and not supported even in the references you offer on your own behalf.

    We've reached a similar point here. You speak of a "missing water problem". You give references for melting ice prior to Meltwater pulse 1-A. So what? Of course ice was melting before this pulse. Some glaciers and ice sheets were gone completely by this time. You could also look at the Barents-Kara ice cap, which was gone even earlier. None of this supports your view of missing water. There was ice melting before the pulse, and after the pulse. The history of sea level change shows that it has a number of short sharp episodes, or pulses, probably because of the complex dynamics of the ice sheets and their capacity to reach a point of instability and collapse. Here is a diagram of stepwise postglacial sea-level rise in the western Pacific. The image is a link to a full size version at North Carolina State University.
    http://lh3.ggpht.com/_WtnYwFZtgHI/SsfhQ8fAIRI/AAAAAAAAAes/qWhakvjHSQE/s400/Liu_Postglacial_Sealevel.jpg

    Felicitations -- sylas
     
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  12. Oct 3, 2009 #11

    turbo

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    Well, how much was tied up in the Laurentide ice sheet? All of Maine was covered to such a depth that our tallest mountains (about a mile high) were engulfed, and the crust was depressed so much that even though the sea level was lower at that time, salt water intruded into central Maine. We find marine clays mixed with the moraines in central Maine. At least as far north as Skowhegan, large deposits of fine blue marine clay can be found. Farther north, clay is still found, but marine silt seems to become a bit more prevalent. The sea-levels were lower during the last ice age, but areas of the state that are today about 200' above sea level were submerged in salt water.

    It's easy to make assumptions based on todays topography that may be off the mark, in part because of the plasticity of the Earth's crust.
     
  13. Oct 3, 2009 #12
    And the effect of gravitic anomalies over time.

    See:
    http://www.csr.utexas.edu/grace
     

    Attached Files:

  14. Oct 4, 2009 #13
    That's exactly the point I'm trying to make but will never succeed as you can see from Sylas response. Is there no problem?

    How natural is that a ice sheet (much) bigger and higher than Antarctica (Laurentian) disappears in a few thousand years while the adjacent lower Greenland Ice sheet just stays put, without a scratch?

    See this, but patience it's 56MB from here

    But looking at that, how can warm loving insects live where there was supposed to be an ice sheet near by?

    How can it be that during the period of the biggest melt water pulse (1A), which should indicate fasted retreat, we have evidence of glacial readvance in several parts of the world? This as well as a considerable spike in ice accumulation in Greenland?
     
    Last edited: Oct 4, 2009
  15. Oct 4, 2009 #14

    sylas

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    We obviously have differences of opinion, but I am not simply giving a sole focus on trying to discredit you for its own sake. I am attempting to discuss the issues substantively and constructively, with all people participating.

    What will it take for you to accept that? Simple agreement with you?

    Sorry, I can't do that. But I don't see any problem with continuing to engage with mutual personal respect and robust engagement on the substance. It is not true that I am focusing only in trying to discredit you. I have pointed out places where we agree, and places where we disagree. There's no animosity here. I want to keep engaging with you, and I am doing so as fairly and honestly as I can.

    ----

    The point about land rebounding is in fact one of the major points in the paper I have cited, specifically on the Gulf of Mexico, by Simms et al. (2007). The thing is... it has nothing to do with "missing water", which is what you spoke of previously. If you were trying to make a point about rebound, you should have mentioned that in the post, not "missing water". In fact, rebound means that asking about "missing water" is the wrong question.

    There are certainly plenty of problems and open questions. For example, there is the difference over the source of water in MWP-1A, which I described. That's only one of the many open questions; there are plenty more throughout the scientific literature.

    It's completely natural. It is natural for Earth to have significant regional differences.

    More to the point; it's data. No matter whether you find it peculiar or not, it happened. There was a large ice sheet there, and now there isn't; while Greenland is still there. (Not entirely "without a scratch" -- the numbers I quoted previously indicate that it has lost mass since the LGM. The numbers I quoted seem to suggest about a 30% loss.)

    Here is a picture of conventional ideas of how the ice sheets retreated in North America. In all seriousness I would like to know... do you personally have any problem with this broad picture of the retreat? Do you know of any scientific objection to this?

    LGM%20deglaciation.jpg See also a http://www.homepage.montana.edu/~esci111/111glacierlab/LGM%20deglaciation.jpg" [Broken].

    It will help if you can answer the question, please. It is an honest question. I am not aware of any scientific case for a problem with the broad details of the retreat of the Laurentide sheet. It is comparatively well known by comparison with some of the other ice sheets, at least for extent of the sheet.

    Cheers -- sylas
     
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  16. Oct 4, 2009 #15
    well you carefully ignore the problems with simultaneous readvancing glaciation and meltwater pulse 1A for one, and exactly in the period that is thought to be several degrees warmer than before.

    Isostatic rebounce is nowhere near beginning to explain that.

    And we even having looked inside the deep ocean yet, to see if anything signifant happened there, or for instance evidence of increased tectonic activity.
     
  17. Oct 4, 2009 #16
    one could quarrel about the fringes like here, but the main problem is not the lateral extend but the ice volume.

    we have discussed this before but who is convincing whom:

    The ice volume is inferred from the necessity to balance the apparant sea level rise, giving large domes of ~4 km altitude (see the models I linked to). So then the question arise how to accumulate and melt those kind of volumes in the available time span, respectively after the last interglacial, the Sangamonian (US) or Eemian (Eur), some 130-110 thousand years ago to accumulate and the mere 21,000 to 7000 years ago to melt completely.

    Mind that a 4km high plain makes it's own orographic climate like Antarctica, which is a permanently sub freezing and most arid place in the world, and that is not even 4km thick but approximately 3200 meters.

    Now see in that series that 110,000 years is on a depth of 1470 meters here, ? Of course the first 2 km can go relatively fast, with less orographic effect

    So why would the Laurentide be so much different and what would be required to have it grow to ~4km elevation. Who else thinks that things do not add up?

    But then there is that sea level variation to account for. Suppose that was in error? It would be completely different if we accepted that we may be off the mark, in part because of the plasticity of the Earth's crust and that is far beyond the usual explanation of isostatic rebounce.

    Seeing the detailed problems of finding a source for meltwater pulse 1A, on the contrary, we find simultaneously readvancing glaciation on several places, then would it be far fetched to assume that meltwater pulse 1A is not a meltwater pulse, but the result of the 'plasticity of the Earth's crust'?

    In that case it would be no problem to accept that the real eustatic sea level rise was significantly less, This would reduce the volume and altitude of the Laurentide ice sheet to acceptable values within the growing and melting time boundaries. If it was significant lower it could explain why it melted, without Greenland melting, as Greenland maintained it's own orographic climate.

    Then for balancing the sea level with ice volume, we would have to accept that the sudden melt water pulses could be something else, It would also help understanding this one for instance:

    Wuchang Wei, 2002, Beijing inundated by the sea within the past 80 k.y.: Nannofossil evidence; Geology; April 2002; v. 30; no. 4; p. 379-381

    I'm merely trying to answer to that call.
     
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  18. Oct 4, 2009 #17

    sylas

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    (A) Response to msg #15

    I don't think this is a problem. The Earth is not uniform; and as I quoted from Clark (2009) previously:
    In particular, multiple ice sheets represent multiple reservoirs, each potentially behaving independently of each other in response to regional or hemispheric climate change.
    So a meltwater pulse from North America or Antarctica, simultaneous with retreat of glaciers in Europe or New Zealand, for example, is information I am happy to take on board.

    I'm not "carefully" ignoring it. It's just not something I've posted about, or which I see as a problem. What I would really appreciate from you, if possible, is not just citations for information that you personally see as a problem, but a clear description of the purported problem itself from the scientific literature. Does anyone publish on this in the scientific literature as a serious problem? If not, then I'm really not all that interested. It doesn't strike me as a problem, and I'm content for you to disagree with that personally.

    Note that glacier advance and retreat depend on precipitation and other factors, and as well as temperature; and that temperature changes are not at all uniform across the globe anyway. The Younger Dryas cooling, for example, is much stronger in the Northern Hemisphere than in the Southern Hemisphere, and it postdates MWP-1a. I don't know the details off the top of my head, but I also know that there can be significant changes that arise simply from a change in seasons. Some climate change can be colder winters and warmer summers, for example, or changes in the lengths of seasons. Some of the Milankovitch cycles tend to have such effects. My understanding is that the pulses are not only a reflection of temperature, but are considered to indicate a shift in ice sheet dynamics.

    As far as I am concerned, the meltwater pulses are now firmly established as real. The retreat of the ice sheets from the LGM to the Holocene is firmly established as real. There are open questions about the timing of events, and sources of sea level rise; but there's no reason to doubt that sea level rise between 20 ka and 8 ka is primarily from melting ice sheets.

    Please don't take me as a representative of the entire scientific community with an obligation to take up every issue you personally have with conventional paleoclimatology. I don't always respond to everything, and I don't demand that you respond to everything either. We all have limited time.

    If you have a refutation of something in one of my posts, based on counter-claims in the scientific literature, and you would like a response in turn, please single it out. I can't possibly respond to everything, but if you don't mind singling out a definite point for special attention, I'll make it a point to give a response.

    My response on the simultaneous advance of certain glaciers with the meltwater pulse is that I don't know much about it, but I don't find it troubling or problematic. It strikes me as a matter of regional detail, which is not my primary interest. That might change if you could show a scientific paper which describes this as an actual problem.

    (B) Response to msg #16

    That last question is something I also have asked. Does anyone else think it doesn't add up? Who? This is a sincere question.

    If it is only you or a few other individuals with an amateur interest in the subject, that is your prerogative, but it doesn’t bother me. I think it adds up pretty well. I would really like to see if there is any legitimate scientific reference which describes these supposed problems in the same terms as you do. I have asked for this several times now.

    In the literature I have seen, it is accepted that ice sheets can build up quickly and retreat even faster. Here is a diagram I have given previously, of Fig 2 from Marshal et. al. (2002) North American Ice Sheet reconstructions at the Last Glacial Maximum, in QSR 21, Iss 1-3, pp 175-192; also discussed in [post=2338924]msg #17[/[post] of thread "A Return to Phanerozoic Average Sea Level?"
    [URL]http://lh4.ggpht.com/_WtnYwFZtgHI/Sqf-AMhYCHI/AAAAAAAAAdY/HPNYEGCbrJw/s800/MarshallFig2.JPG
    I don't know why you find it implausible for ice sheets to build up or melt in a geologically short period of time. It seems fine to me, and I have yet to see it given as a problem in the literature. A 4km high plain most certainly has an enormous effect on local climate, and beyond, with drastic effects on circulation in the atmosphere. That's not a problem with the idea of a 4km high plain or a reason to doubt the volume. It is an added complexity for sorting out climate impacts, as is clear in the PMIP3 references you cited previously.

    I don't think there is a problem with different sheets in different parts of the world having different behaviour and timing for their advance and retreat. This is explicit in the literature as well.

    Yes, in my opinion, it would be EXTREMELY far fetched, because the meltwater pulse 1a is shows up in sea level reconstructions all over the globe. For example, the graph I showed in [post=2376780]msg #10[/post] is from the Yellow Sea, between Korea and China. I don't think this proposal has the slightest credibility. But more importantly, it's a personal speculation with no support in the scientific literature. We have plenty to discuss here concerning the open questions within the bounds of conventional science, and that's the scope for discussion in physicsforums.

    I appreciate that you find it frustrating when your personal theories get short shrift on this basis. I don't. There are other venues where you might be able to explore your own notions like this freely. I consider this a poorly founded speculation with no reason to take it seriously, and with nothing to refute.

    As always, there's no intent to insult you personally. But I am truly not particularly interested in your personal theories. I do find you sometimes have interesting contributions from more conventional sources, and continue to find your posts worth reading.

    Cheers -- sylas
     
    Last edited by a moderator: Apr 24, 2017
  19. Oct 4, 2009 #18
    Fist of all, I don't think anything has changed in the field of evidence, since the IPCC mentioned http://www.grida.no/publications/other/ipcc_tar/?src=/CLIMATE/IPCC_TAR/WG1/index.htm [Broken] what is here alleged to be my personal theory. Perhaps only that several publications like Hubberten et al (2004) have further confined the size of the ice sheets, smaller than assumed by the IPCC in 2001 .

    Then..



    Not sure what you are talking about, because this:

    ..which is not really all over the globe, it is just the Indonesean - North Australia area. the Sunda Shelf and the Bonaparte Gulf. The other area with similar sea level behavour is around Barbados north of Venezuela, both close to the equator and that may be a clue.

    Furtermore from the TAR IPCC (see link above) fig 11.5:

    http://www.grida.no/CLIMATE/IPCC_TAR/WG1/images/fig11-5.gif [Broken]

    Caption:

    would that add up to:

    Better identify and show the geologic sources of Melt water pulse 1A, like the scientific method would like to see, until that happens, it is just a hypothesis not supported by evidence.
     
    Last edited by a moderator: May 4, 2017
  20. Oct 4, 2009 #19

    sylas

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    There is no mention there of your "missing water" problem. There's no mention of your problem with rapid formation and melt of ice sheets on geological time scales. There's no mention of your problem with a very high ice dome in the Laurentian sheet.

    You've been speaking of all kinds of alleged inconsistencies, of advancing glaciers in Europe and New Zealand occurring around the same time of the meltwater pulse. You specifically singled this out as a purported problem I supposedly ignore. There's no mention of that as a problem either. I don't think it is a problem at all, and I've seen no indication any else does either.

    Of course there are uncertainties about the volume of ice sheets. This not a "problem" in the sense of a difficulty finding hidden water, or requiring any drastic revision of how we use proxies to infer information about the past, or rejecting broad conclusions about the role of melting ice sheets in sea level rise or the meltwater pulses. It's all just the normal process in conventional Earth science of refining and improving details in our picture of the past.

    You mention the IPCC 3rd AR. In http://www.grida.no/publications/other/ipcc_tar/?src=/climate/ipcc_tar/wg1/075.htm [Broken] it says:
    Current best estimates indicate that the total LGM land-based ice volume exceeded present ice volume by 50 to 53x106 km3

    That's ample water for all the sea level rise you need. There is no missing water problem.

    There's nothing at all in Hubberten et al (2004) to give any reduction in ice volumes that I can see. I discussed this reference in [post=2338924]msg #17[/post] of thread "A Return to Phanerozoic Average Sea Level?". It is not about inferences in ice volume at all; but simply takes for granted the conventional work of Svendsen et al for the Eurasian sheets, which we already know were much smaller than the Laurentide sheet at the LGM.

    Svendsen et al represents the conventional picture for Eurasian ice sheets, as I understand it. There are alternative minority ideas in the literature for a larger sheet (Grosswald being a major name for this) but I think this is usually thought to be incorrect for the last glacial maximum, and I have not used those figures. Neither did the IPCC in its 2001 report. The picture for the LGM in the 2001 report is captured in figure 11.4:
    IPCC_3ar_Fig11_4.JPG

    The Eurasian sheets are shown here as the smallest of the large icesheets (Fennoscandian, including Barents region) contributing only about 11m or 12m to the sea level rise in total since the LGM. In the table I provided in [post=2376780]msg #10[/post], coming out after the 3rd AR, the range is given as 13.8 to 18. You are mistaken about Hubberten assuming smaller ice sheets than IPCC 3rd AR.

    True enough; not "all over the globe", but in "many different locations" around the globe. I gave this as an example, not a comprehensive list. The data does include the Bonaparte Gulf and Sunda Shelf, which are indeed near the equator. The diagram also shows more data from further north, in the East China Sea (ECS) and the Yellow Sea (YS). For more details see the reference I gave in msg #10 to Lui et al (2004). The picture is figure 18 of this reference. The evidence for the meltwater pulse shown in the diagram includes data from around the Shandong peninsula, a long way north of the tropic.

    I am not interested in "clues" or hints to your own personal theories. No authority cited so far questions the reality of the meltwater pulse.

    This figure shows local sea level changes as a combination of rebound and changes in the ocean volume. The ocean volume changes are the same in all parts of figure 11.5: this is the "esl" curve. In the caption for the figure it is "from the change in ocean volume due to the melting of all Late Pleistocene ice sheets (curve marked esl)".

    The esl curve used here in figure 11.5 corresponds to about 120m of additional sea level from melting ice since the LGM, the same as shown in the figure 11.4 I have provided. It's all consistent, and consistent with all the scientific literature, and inconsistent with your own personal view which is (correct me if I am wrong) that there was less ice to melt than anything proposed by anyone in the scientific literature.

    It is true that these sites do not allow resolution of the meltwater pulse, and so I should not have said "all over the globe" previously, but rather "in many locations around the globe".

    I've already done this, for heavens sake! Look again at Simms (2007) as cited back in [post=2376201]msg #7[/post] for a geological source of the pulse coming primarily from the North American sheet. Or at [post=2376780]msg #10[/post] which identifies the two major scientific hypotheses for the geological source of the pulse. Or at [post=2338924]msg #17[/post] of thread "A Return to Phanerozoic Average Sea Level?" where I give two primary references (Clark et al 2009 and Peltier 2005) for the evidence and arguments for the two possible sources of MWP-1A.

    This is still an open question, of course; but it is thoroughly grounded in study of empirical evidence and concrete proposals for the geological source of the pulse. It is being investigated using stock standard scientific method for open questions about geological history. Whether you prefer the Northern origin, or the Southern origin, there's no "missing water" problem. There's heaps of water available in the ice sheets at this time.

    You, on the other hand, have yet to give ANY evidence for the idea that MWP-1a is from some kind of change in the geoid, which appears to be what you are proposing as an alternative to the conventional notion of MWP-1a as a pulse of meltwater. You have yet to give any indication that any authority takes your proposal seriously, or even bothers to mention it at all.

    As I have said before, you are welcome to your own personal theories. But for my part, I'm not really interested in them. It seems to me that that they are extremely far fetched, and I am pretty sure that all the authors of all the scientific literature you have cited would think so too. I don't mind if you think your theory is credible. But until you can actually SHOW that someone proposes this idea seriously in the scientific literature, I'm just not interested; and it is not something we should be looking at in this forum.

    Cheers -- sylas
     
    Last edited by a moderator: May 4, 2017
  21. Oct 4, 2009 #20
    Where does Simms et al identify the source as in showing massive glacial retreat and other geologic events. I can only see carbon dates from sea sediments showing sea level rise, not the cause.

    What evidence value has any hypothesis?
    But nevertheless Clarke et al (2009) referenced in there states:

    Not looking good, does it?

    How about Peltier et al 2005?:

    Hence Peltiers et al actually have their considerations about a southerly source. So, Sylas, it looks that you reinforce my case. Show where exactly the water came from by identifing the locations where the ice melted and water floods passed exactly at the right moment to account for MWP1a. There is an abundance of that type of evidence in the literature. So if it supports MWP1a, where is it? But mind that Clark's et al 2009 statement implies that they could not find it.
     
    Last edited: Oct 4, 2009
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