Underwater Expedition Delivers Key Findings on Early Americans

[Andre]

Underwater Expedition Delivers Key Findings In Search For Evidence Of Early Americans.

ScienceDaily (Sep. 1, 2009) — In one of the more dramatic moments of an underwater archaeological survey co-led by Mercyhurst College archaeologist James Adovasio along Florida’s Gulf Coast this summer, Andy Hemmings stood on an inundated river’s edge where man hasn't set foot in more than 13,000 years...cont'd

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?

 

[tyroman]

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."

 

[Borek]

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.

 

[Andre]

You're not missing anything as far as the known graphs go, like this for instance:

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.

 

[Borek]

OK, I thought you are questioning depth.

 

[Xnn]

So my question is, where did all that water hide between something like 17,000 and 13,000 years ago.

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?

 

[sylas]

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.

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 , 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 , 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 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.

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

 

[willem2]

you will find that most ice had disappeared around 11-13 thousand years ago, the bulk around 17 thousand years.
.

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.

 

[Andre]

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, http://www.sciencemag.org/cgi/content/abstract/299/5613/1709, about 14.7 to 12.7 ka Cal BP


Some fragments from my writings somewhere:

Rinterknecht et al (2006) show that the glacial retreat of the Weichselian Ice Sheet maximum extent around the southern Baltic area must have started 19 ka Cal years BP and that the ice had retreated from Poland before 16,760 Cal years BP. However a readvance was noted, dated around 14,600 Cal BP. We observe that this behavior directly opposes the interpretation of the Bølling Allerød events.

Clark (2003) examines evidence from alpine glacial deposits in the American Cordillera and observes glacial retreats In the Sierra Nevada, between 17,000 and ~15,000 14C yr BP(~20,100-18,500 cal yr B.P. and in the North Cascades by ~17,000 36Cl yr BP; in southern Idaho at 13ka BP (15,3 ka Cal BP) He observes limited Glacier readvance respectively after 12,200 14C yr BP (14,000) cal yr. BP and ~14,000 and 13,000 36Cl yr BP and for southern Idaho ~12,800 – 11,000 14C yr BP (~14,100-12.900 cal yr BP); . After that The Sierra Nevada remained largely or entirely free of glacier ice, including during the Younger Dryas (YD) chronozone.

Davis et al (1975) investigates a pollen core from Moulton Pond, Maine, which deglaciated about 14,000 years (14C) ago (16,7 ka Cal BP) and notes evidence of glacial readvance about 12,700 years ago or about 15,0 ka Cal BP hence around the onset of the Bølling Allerød.

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:

...Evidence for a glacial re-advance during the YD chron has been proposed based on radiocarbon dating of the Waiho Loop moraine (Denton and Hendy, 1994) and more recenty from exposure ages on a subset of the Misery moraine Group at Arthur’s Pass (~950 masl), Southern Alps, NZ (Ivy-Ochs et al 1999). This Group comprises a set of discontinuous latero-terminal moraines and elevated kame terraces (McGrath moraines) on the eastern flanks of the Pass and the proximal Misery moraine set 3 kilometres upvalley to the north within the Otira Gorge. The mean 10-Be exposure age (Ivy –Ochs, 1999) from 4 of 5 samples on two moraines at the latter site is 11.7 ± 0.3 ka, suggestive of a weak but distinct SH glacial readvance coeval with the YD-chronozone. However, our full recalculation of this data set, based on updated and revised 10-Be production rates (Stone, 2000) with re-measured site shielding factors (Arthurs’ Pass is bounded by mountains at ~1600 m) put the mean age at 14.1 ± 0.7 ka ...

and Davis et al

...Based on recent work on the glacial lake Hitchcock varve sequence in the Connecticut Vallley, Ridge et al (1999) determined an age of 11,900 - 11,800 ¹⁴C yrs. B.P. for the Littleton_Bethlehem readvance...

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.

 

[sylas]

Some fragments from my writings somewhere:

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.

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?

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​

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.

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 , 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.

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.

• Liu, J.P., et. al. (2004) Holocene development of the Yellow River's subaqueous delta, North Yellow Sea, in Marine Geology, 209(1-4): 45-67.

http://lh3.ggpht.com/_WtnYwFZtgHI/SsfhQ8fAIRI/AAAAAAAAAes/qWhakvjHSQE/s400/Liu_Postglacial_Sealevel.jpg

Felicitations -- sylas

 

[turbo]

So my question is, where did all that water hide between something like 17,000 and 13,000 years ago.

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.

 

[tyroman]

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.

And the effect of gravitic anomalies over time.

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

 

[Andre]

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.

And the effect of gravitic anomalies over time.

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

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?

 

[sylas]

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?

[...]

But no, the sole focus is on trying to discredit whatever I say.

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.

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?

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?

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

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

 

[Andre]

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.

 

[Andre]

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?

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

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 apparent 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 ftp://ftp.ncdc.noaa.gov/pub/data/paleo/icecore/antarctica/epica_domec/edc3-timescale.txt.

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:

http://geology.geoscienceworld.org/cgi/content/abstract/30/4/379

ABSTRACT

Examination of published data reveals that a marine bed in Beijing can be dated as 80 ka or younger on the basis of abundant nannofossils. This age is 30 times younger than that published previously on the basis of magnetostratigraphic and biostratigraphic interpretations. The abundant nannofossils and foraminifers suggest that Beijing was inundated by the sea within the past 80 k.y. The very recent nature of this marine transgression has profound societal and geological implications and thus calls for new studies and thorough evaluation of all relevant data sets.

I'm merely trying to answer to that call.

 

[sylas]

(A) Response to msg #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.

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

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 apparent 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 ftp://ftp.ncdc.noaa.gov/pub/data/paleo/icecore/antarctica/epica_domec/edc3-timescale.txt.

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?

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) http://www.sciencedirect.com/science/article/B6VBC-44MX5WF-C/2/ef131e9f7d417b54915e36f5dba7ac59, 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.

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'?

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

 

[Andre]

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 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..

(A) Response to msg #15

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.

Not sure what you are talking about, because this:

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.

• Liu, J.P., et. al. (2004) Holocene development of the Yellow River's subaqueous delta, North Yellow Sea, in Marine Geology, 209(1-4): 45-67.

http://lh3.ggpht.com/_WtnYwFZtgHI/SsfhQ8fAIRI/AAAAAAAAAes/qWhakvjHSQE/s400/Liu_Postglacial_Sealevel.jpg

..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

Caption:

Figure 11.5: Examples of observed relative sea level change (with error bars, right-hand side) and model predictions for four different locations. The model predictions (left-hand side) are for the glacio-hydro-eustatic contributions to the total change (solid line, right hand side). (a) Angermann River, Sweden, near the centre of the former ice sheet over Scandinavia. The principal contribution to the sea level change is the crustal rebound from the ice unloading (curve marked ice, left-hand side) and from the change in ocean volume due to the melting of all Late Pleistocene ice sheets (curve marked esl). .. cont'd

would that add up to:

would be EXTREMELY far fetched, because the meltwater pulse 1a is shows up in sea level reconstructions all over the globe.

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.

 

[sylas]

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 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.

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 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:

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.

(A) Response to msg #15

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.

Not sure what you are talking about because this:
[... snipped the diagram from [post=2376780]msg #10[/post] ...]
..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.

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.

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

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".

would be EXTREMELY far fetched, because the meltwater pulse 1a is shows up in sea level reconstructions all over the globe.

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.

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

 

[Andre]

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.

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.

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.

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

Possible sources of mwp-1A have been widely discussed (e.g., Bassett et al., 2005; Clark et al., 1996; 2002; Peltier, 2005). There are several key reasons why a significant contribution from the Northern Hemisphere is unlikely:... cont'd

Not looking good, does it?

How about Peltier et al 2005?:

..Although it has usually been assumed that this episode of rapid RSL rise was derivative of a partial collapse of the northern hemisphere ice sheets, it has recently been suggested that this pulse could have originated in a dramatic melt-back of the Antarctic Ice Sheet. In this paper the arguments presented in favour of the southern hemisphere source are revisited in order to assess the plausibility of this alternative scenario...

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.

 

[sylas]

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.

Simms et al identifies the source as primarily from melting of the Laurentide ice sheet. The geological event of isostatic uplift in the Gulf of Mexico is used to argue for this source. (p 937) The conclusion of the paper is:

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.​

Within the paper there is mention also of the evidence for some additional contribution from the Antarctic.

None of this evidence is a direct measure of changing ice volumes, of course; and as I have said the final resolution of the source is still an open question. The paper is long, and there is more considered than only the radiocarbon data. I'm not going to list out the whole argument. I'm satisfied that we've refuted the notion this is a "hypothesis not supported by evidence".

The paper is not a final proof of the Northern source hypothesis, but it does demonstrate that this is a genuine scientific investigation using empirical evidence to weigh competing hypotheses. The same applies also for the alternative hypothesis, of a source in the Antarctic sheet.

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?

This kind of "all or nothing" dichotomy is the sort of thing I'd expect from a creationist, wanting to know precisely when a common ancestor lived and exactly how every fossil fits into the evolutionary tree.

And with that, I expect I have said something unforgivable. Ah well.

The time has come, it seems, to say plainly the remarks above show very poor comprehension of how Earth science works. I know you have looked at these things a lot, and have all kinds of strong ideas, and have read widely on the subject. This makes your remarks above all the stranger.

If you can't tell the difference between a speculative proposal without evidence, a credible hypothesis tested in the light of incomplete evidence, and a confirmed result established beyond serious question by overwhelming evidence, then further discussion is not likely to help.

The evidence does not allow you to recreate every detail of the past. The melting of ice sheets for the meltwater pulse 1a is thought to have occurred over a period of about 500 years or so and there's no reason to insist you must be able to find out exactly where water flowed in this period. The ice itself is gone. Much of the land since then is now underwater. The land beneath the ice has been worked and reworked by all kinds of events in the past, and it is not always possible to give a plain chronology of all the events of the past from the traces that remain.

Where we stand at present is that the evidence shows water levels have risen since the last glacial maximum by something around 120 to 130 meters. The evidence for this is strong and in my opinion the inference is not in any credible doubt. It is not, however, formally proven. Like any genuine scientific hypothesis, it is always open in principle to revision or falsification in the light of new evidence. But until you can find other some other ideas that are actually considered within the normal channels of modern science, I'm not particularly interested.

The evidence also indicates that this sea level rise was not continuous, but had a number of sharp "pulses", or periods of accelerated rise in sea level. This also is not a formal proof; but as far as I can see it is by now pretty much universally recognized as a discovery about the world. Some proposals for smaller pulses are less strongly confirmed, but the largest pulse, MWP-1a, is on very solid empirical ground. If you disagree with that, then you seem to be a tad isolated on the point. That's not my problem.

The evidence does not indicate plainly where the water came from. That's still an open question, with two major competing hypotheses that are consistent with available evidence. That doesn't mean there's a "missing water" problem. We have ample evidence more than enough to persuade scientifically literate individuals that before, during and after the pulse there were vast reservoirs of available water in the ice sheets of that time.

I have given the proper citations to the scientific literature for the possible sources of the meltwater pulse.

I do not accept that scientists must be able to prove exactly where the water flowed at exactly the right moment. In fact, it strikes me as complete nonsense and a striking failure to understand Earth science. I do not accept that the proposed geological sources for the meltwater pulse 1a are being given as hypotheses without evidence.

I reiterate that I don't have any interest in speculations that do not appear anywhere within the scientific literature.

Cheers -- sylas

 

[Andre]

Again, there is very detailed evidence of the dating of glacial advance and retreat as I have shown before. So, it must be very easy to find evidence of glacial retreat at the right period. Simple as that. Especially if we are talking about of some 20 meters of sea level rise, the equivalent of some 2.5 Greenland ice sheets, in just a few hunderd years, that must have been a truly major event by all means. But all I can find is evidence of glacial readvance.

In that light, I'm happy to leave it up to the readers, what to think of the post above. Since the scientific method is still about verifying claims with logical evidence.

 

[turbo]

One comment. Regardless of the plasticity of the Earth's crust, it is incontrovertible that Maine's tallest mountains were subject to glaciation. The Laurentide sheet might have been much deeper, but present-day evidence points to a minimum depth of over a mile. It's pretty impressive to climb Mt. Katahdin and realize that 20Kya the whole thing was covered in ice.

When I was a kid, my friend's father would take us both to Enchanted, and we'd stay at the hunting camp for the weekend. Ronnie and I would take a day and climb Granny's Cap - a plateau-like mountain ringed by cliffs on the south side. The top of that mountain was pretty free of vegetation, and it was loaded with rounded stones consisting of sedimentary rocks containing fossils. We'd load our sacks and packs with rocks, lower them down the cliffs with ropes and then climb down ourselves. It's under 3000', but still, it was evidently much larger before it got scoured.

I don't have any idea how thick the Laurentide sheet was through any of the rest of its extent, but it was thick enough (at least in New England) to grind down one of the largest and oldest mountain ranges in North America.

 

[NileQueen]

sylas:

I reiterate that I don't have any interest in speculations that do not appear anywhere within the scientific literature.

I agree we need to refer to scientific literature to support what we are discussing, but
I am afraid the literature is lacking all the answers in Earth science. We need to think outside of the box to resolve these complex issues, and speculating, with what we do know about Earth science is a good thing.

 

[NileQueen]

sylas:

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.

Regarding the Laurentide Ice Sheet (LIS) there were many advances and retreats, with the Wisconsinan, the most recent, being the better understood. The evidence
for older glaciations has in many places been eradicated or jumbled due to subsequent glacial activity. The penultimate (next to last) glaciation was the Illinoian but there were others
http://www.dnr.state.oh.us/portals/10/pdf/glacial.pdf
see page 2.

It is interesting that the Greenland ice sheet remains while the LIS melted. One factor could be topography and ice streams feeding the ice to the oceans which transported it southwards.

 

[Andre]

Thanks Nilequeen, and congratulations for achieving your masters in geology, well done.

Anyway, considering the assumptions in geology, especially about the more abstract ones, like isotope ratios of various proxies, once more, these are inherently affirming the consequent fallacies. meaning that there could be other explanations for observations as well. Therefore they just require independent proof, which has nothing to do with creationism, just with meticulously applying of scientific methods, for instance:

1: Observation: a steep region below sea level of about 20 meters where the carbon dates all read the same value both in the Australian/Indonesion region as in the area around Barbados, and the East Chinese Sea.

2: Hypothesis: it's a sudden sea level rise due to fast melting ice sheets

3: Prediction: concurrent evidence of glacial retreat in volumes comparable to the sea level rise.

4: Result: The bulk of evidence of glacial retreat in sufficient volumes is dated well beyond error range of MWP1A. None is found at that time; some evidence suggest the opposite.

Conclusion: revision is needed, any revision, including revisiting of the methodology, until a better match is found.

I wonder what is so creationistic with that.

 

[Andre]

One comment. Regardless of the plasticity of the Earth's crust, it is incontrovertible that Maine's tallest mountains were subject to glaciation. The Laurentide sheet might have been much deeper, but present-day evidence points to a minimum depth of over a mile. It's pretty impressive to climb Mt. Katahdin and realize that 20Kya the whole thing was covered in ice.

Turbo, presently some mountains are virtually completely covered in icefields, like in BC for instance, and considering your winter pictures, there is nothing counter intuitive seeing Mt Katahdin covered with ice like that.

So what would be the evidence of the thickness of the laurentide ice sheet? Not sure which you are referring to, but I can think of modelling with assumptions based on local isostacy and sea level balancing as discussed in this thread, and related to that, isotope balancing of the deep ocean oxygen isotope ratios of foraminifera shells to estimate ice volume, although it may seem that all add up (or not - expect a thread), it's still assumptions based on assumptions. If it's true, it's true, simple as that and all future evidence will point into that direction. However things turn nasty when evidence is getting obnoxious.

I wonder why much of the geologic surface of North America is consisting of very old sediments. What to think of Ohio for instance? http://www.uwgb.edu/DutchS/StateGeolMaps/OhWVaGMap.HTM. If the Earth was more rigid, you'd expect those layers deep below the surface. Would it be an idea to include this in the rethink of the whereabouts of the laurentide ice sheet?

 

[turbo]

Turbo, presently some mountains are virtually completely covered in icefields, like in BC for instance, and considering your winter pictures, there is nothing counter intuitive seeing Mt Katahdin covered with ice like that.

There is a difference is having ice-fields on mountainsides, and having a huge glacier over-riding entire mountain ranges and grinding them down. To accomplish the latter, you need the ice sheet to move and transport abrasive materials and the ice must be deep enough to provide the weight required for the abrasive scouring to actually re-form the mountains. If you climb the Appalachians in Maine and New Hampshire you will find ample evidence of glaciation. Our mountains are not craggy, like the Rockies - they are softened and rounded over, with gently-sloped flanks. To have accomplished this, it's not enough just to accumulate snow and form a sheet of ice that simply grows and then melts. There had to be differentials in pressure that drove bulk movements in the sheet, for these mountains to have been scoured like they were.

Note: I'm not claiming that the latest ice-sheet (Laurentide) caused all this weathering - it was simply the last episode of many.

 

[Andre]

Absolutely there have been some four- five major glaciations identified in the Pleistocene originally, like the Nebraskan, Kansan, Illinioan and Wisconsin. However it has been determined that the glaciation was much more complicated. Especially the dating of advance and retreat. From the second ref for instance it can be seen a difference in maximum advances in several areas during the last glacial maximum, which of course places question marks at the assumption that the Laurentide Ice Sheet was holding that immense ice volume at its maximum extent all at the same time. And again, the major question for balancing sea levels and foraminifera isotopes is if the ice sheet retreated completely in between the major advances or not.


some refs
http://www.emporia.edu/Earth'sci/gage/pre-wisc/pre-wisc.htm

http://books.google.nl/books?id=ys2...skan, Kansan, Illinioan and Wisconsin&f=false

 

[turbo]

Also, our understanding of large glaciation events in Maine is complicated by the fact that the last one wiped out evidence of previous ones. We have deep striations in rock (yes, even on mountaintops) to show us in which directions the ice sheet advanced when it was at its thickest, and we have eskers to show us where water flowed under the ice, kettle-holes to show us where huge chunks of ice calved off and were later re-covered with till and ice, only to melt and leave steep-sided round(ish) depressions after the ice sheet receded for the last time. We also have moraines to show us how the last ice-sheet receded and dropped its material in stages. Unfortunately, evidence of previous glaciation events was scrubbed out, so we can't compare the relative strengths of the various events.

 

[sylas]

I reiterate that I don't have any interest in speculations that do not appear anywhere within the scientific literature.

I agree we need to refer to scientific literature to support what we are discussing, but I am afraid the literature is lacking all the answers in Earth science. We need to think outside of the box to resolve these complex issues, and speculating, with what we do know about Earth science is a good thing.

The literature is full of questions, proposals, and refutations of proposals. If science had all the answers, science would stop. The literature is focused on open questions, and is a great place to look for out of the box thinking that may sometime become part of the solutions. Textbooks are better for getting straightforward answers, where they exist.

My lack of interest in speculations that have failed to appear in the scientific literature is a useful filter for avoiding wasting time with ideas based on poor understanding of the problems, or what is required for a solution. There's a lot of that around. We are not going to resolve the complex issues here at physicsforums, in the sense of coming up with radical new ideas that have not occurred to working scientists, to solve significant outstanding scientific problems.

There are some people here at physicsforums who will solve significant scientific problems, or have already done so. If the problem is of general relevance, then they are usually going to be able to show us their work towards a solution with reference to their own formal publications.

What we all can realistically do here is learn. That includes learning what is unknown as well as what is known. I don't have any illusions about being able to give all the answers -- either by reference to literature or by clever outside the box thinking of my own. We can ask questions about what is described in the literature, and get answers about the problems, the evidence, and what is known, and what is so far unknown. We can get answers about what hypotheses are being explored. I'm learning a lot right now, just from reading up on all the details behind the questions.

I personally have no interest in speculations that have not appeared in the literature. That's not quite true, but it's close. There's more than enough interesting and alternative ideas in the literature to keep me reading for a lifetime; and they are almost always more worthwhile exploring.

Furthermore, there is a specific requirement in the Earth science forum especially that we stick to claims made in the scientific literature. That is because the forum is primarily for learning about conventional science, as practiced by working scientists. It is not for working out new solutions ourselves that have not been considered by scientists.

In the PF guidelines there is a provision for "outside the box" thinking of ideas that have not yet made it into the scientific literature, in a separate forum; as long as they have sufficient scholarship in their presentation. You can learn a lot by working through ideas of your own in this way. I personally don't have much interest in it, because (a) I still have far too much to learn myself before my ideas have any prospect of becoming solutions, and (b) in my experience these ideas never come to anything. The people who are going to give the real solutions are already publishing their ideas in normal scientific channels; not in web forums.

Meltwater pulse 1-A

Here is a concrete example: meltwater pulse 1-a. This is a sudden increase in sea level of about 20m, occurring around 14 to 15 thousand years ago. It is often pinned down further to 14.2 to 14.7 thousand years ago.

There are two major hypotheses for how this comes about. There is the northern source and the southern source; and each of those also has further alternative refinements. Neither is of these is known to be a true "answer". They are both hypotheses. They both involve a large "pulse" of water from accelerated melting of ice sheets; the difference is the location of the sheets involved. We can learn a lot by looking at the evidence for and against these proposals, and we get that from the ongoing scientific debate in the literature.

It has been suggested that there might be other reasons for the data. In principle, that is true, of course; but I'd like to see if anything else has actually been proposed in the literature. I've asked this, many times; and the question has always been ignored. I am pretty sure this is because the answer is no; and that working scientists now accept that the data reflects a sharp rise in sea level -- a meltwater pulse.

It has been suggested that data usually taken as indicating rising sea levels might actually be caused largely by changes in the height of land mass. I don't think this is remotely plausible, and I've suggested some reasons why. But we shouldn't be debating that here. Until it has been seriously proposed in the scientific literature as a credible solution, it belongs in the forum for new independent proposals; not in the Earth science forum.

Objections raised to the idea of a meltwater pulse

There have also been objections raised to the idea of a real pulse of meltwater. IMO it is fine to consider difficulties with solutions that are being proposed. But none of the difficulties mentioned so far in the thread actually give any reason to doubt the hypothesis.

First, a "missing water" problem was mentioned. There is no such difficulty. The amount of water bound up in the ice sheets was enormous, both before and after the meltwater pulse 1-a; much greater than what was needed to account for the pulse.

Objections have been made to the enormous volumes conventionally proposed for the Laurentide ice sheet, which suggest an ice dome of as much as 3 or 4 kilometers in height at its highest point in the last glacial maximum; and the time this would require has been raised as a difficulty. It isn't. Ice sheets can grow comparatively quickly, on the time scales being considered. For example, to get 3 kilometers of ice in ten thousand years, you need about 30cm of build up per year. In conditions where precipitation freezes and builds up the sheet, that's not lot of precipitation. There is good evidence that massive ice sheets did indeed build up and retreat, many times over the Quaternary period. Nothing in the build time required makes this particularly implausible; and the idea of massive ice sheets is now solidly established.

Andre has objected that there should be evidence of glacial retreat at this time. But if you read the papers I have cited (like Simms et al, 2007) the major cause being proposed is THINNING of the ice sheet. So it doesn't actually follow that there has to be a sudden retreat of the margins at this precise time. The main proposal as I understand it involves collapse of the parts of the ice dome, rather than retreat at the margins. We can't prove all this in detail of course; the ice is gone. But as a refutation of the hypothesis, this fails.

Also important is that we don't actually know the chronology of the retreat of the ice margins with the precision required. Others have noted that this region is worked over by many glaciations. Sorting out the margins at a specific time is not easy at all. The evidence for retreat of the margins is there, and I previously asked Andre directly if he had a problem with the reconstructions of the retreat illustrated as follows:

Note the retreat of the margins apparent here between 16.5 and 13.75 thousand years ago -- contradicting the notion that all we have over this time is a "readvance" of glaciers. My understanding is that the fine details of the chronology for this retreat are nowhere near good enough make it "simple" to test the idea of a retreat at the precise time of the meltwater pulse. It's good enough to confirm a significant retreat of the Laurentide sheet between times before the pulse and after the pulse; but not good enough to confirm or to refute an acceleration of retreat at the margins precisely at the same time as the pulse.

Regarding the Laurentide Ice Sheet (LIS) there were many advances and retreats, with the Wisconsinan, the most recent, being the better understood. The evidence for older glaciations has in many places been eradicated or jumbled due to subsequent glacial activity. The penultimate (next to last) glaciation was the Illinoian but there were others

Exactly. Also, the evidence for more recent glaciations can sometimes be confused as well, as it is not always clear which glaciations to associate with different features. The last is the easiest to sort out, but we don't actually have such a precise chronology that we can clearly identify accelerations of the margin retreat on small time scales. If you agree with this, and if Andre can agree as well, then this would be progress.

Note please that I am not the one arguing that it is simple to sort these things out! My position is that there are different ideas being proposed for the sizes of ice sheets and the timing of their retreat since the LGM, and for the source of the meltwater pulse; and that the literature does NOT give definite answers on these; neither a firm confirmation nor a strong refutation. These are open questions. They are not merely speculations without evidence; they are being considered using empirical evidence. But it is unfinished business, and the evidence is currently not sufficient to definitely confirm or reject either hypothesis.

Andre has suggested that the timing of the retreat is so well known that it should be simply to test whether or not a meltwater pulse was associated with an accelerated retreat at the margins of the LIS.

Again, there is very detailed evidence of the dating of glacial advance and retreat as I have shown before. So, it must be very easy to find evidence of glacial retreat at the right period. Simple as that. Especially if we are talking about of some 20 meters of sea level rise, the equivalent of some 2.5 Greenland ice sheets, in just a few hunderd years, that must have been a truly major event by all means. But all I can find is evidence of glacial readvance.

Andre, I have not seen you or anyone show that "very detailed evidence of the glacial retreat and advance" is available at such a great resolution that it would be "very easy" to show evidence of glacial retreat at the "right period" -- being between 14.2 and 14.7 thousand years ago. I don't think this is simple at all! The special issue of the Quaternary Science Reviews that I cited previously (Vol 21, Iss 1-3, 2002) suggests all kinds of unknowns about ice sheet margins during their retreat after the LGM.

Note that the retreat or advance of mountain glaciers is in general not synchronized with the retreat of the large ice sheets; and that the meltwater pulse source is proposed to be the ice sheets.

I don't think that there actually has to be an accelerated retreat at the margins, given that the proposal I have cited as an example (Simms et al 2007) is primarily about thinning of the sheet.

Be that as it may, the diagram I asked you about previously, of the LIS retreat, does show a large retreat of the LIS between 16.5 and 13.75 ka. I don't see any reason whatever to think it would be easy to test the idea of an accelerated margin retreat precisely at the time of the meltwater pulse, and I do not see this being raised as an objection by scientists who publish in support of the Southern source hypothesis. I think this is because the data cannot constrain the margins at anything like the resolution you require.

In summary, the source of the meltwater pulse is not definitely known. There are different proposals considered in the literature, and it remains an open question. I do think that the only credible proposal is an actual pulse of meltwater, and I don't think you've given any good reason at all to reject that idea.

There's nothing wrong with coming up with radical new ideas for the data. I remain genuinely interested to know if there are other proposals considered in the literature. So far -- apparently not. My understanding is that you can still use the "independent ideas" forum for ideas you are proposing on your own behalf. I'm not personally interested, but that shouldn't stop you.

Reasoned criticism of existing ideas here in Earth science is fine, of course. I have provided rebuttals, which is also fine.

Cheers -- sylas

 

[Andre]

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Meltwater pulse 1-A

Here is a concrete example: meltwater pulse 1-a. This is a sudden increase in sea level of about 20m, occurring around 14 to 15 thousand years ago. It is often pinned down further to 14.2 to 14.7 thousand years ago.

Now here is the problem, this is a conclusion based on data, data comprising of roughtly the same carbon dates in a vertical plane of about 20 meters. That is the fact, not the sea level rise, that's a conclusion.

I hinted already the possibility of the equator changing dynamically, not a personal theory, just one of the several nodes that could explain things.

What, for instance, if the real reason was to be that the near surface region of the ocean became unfavorable for these organisms that they died simultaneously, Not a personal theory just one of the several nodes that could explain things

What for instance if the real reason was to be that the areas rose up for a geologic short while, before sinking again, exposing these mechanisms above the sea so they died near simultanoeusly. Not a personal theory just one of the several nodes that could explain things

What for instance if the real reason was to be that some yet unknown mechanism changed the ratio of normal carbon and radioactive 14C carbon in the ocean? This would be changing the apparent dating of the death of the measured organisms. Not a personal theory just one of the several nodes that could explain things


Perhaps far fetched? But did we look at all the evidence? How about what happened below the ocean surface, just one little peak:

http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VBC-4FTS349-3&_user=10&_coverDate=11%2F30%2F2005&_rdoc=5&_fmt=high&_orig=browse&_srch=doc-info(%23toc%235923%232005%23999759979%23606496%23FLA%23display%23Volume)&_cdi=5923&_sort=d&_docanchor=&view=c&_ct=13&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=adece7344f4d7017ac4d298b38ed018d

Abstract
The general Pleistocene architecture of the Amazon Fan has been reconstructed using sediment recovered by Ocean Drilling Program Leg 155. Huge regional mass-transport deposits (MTDs) make up a significant component of the Amazon Fan. These deposits each cover an area over 15,000 km2 (approximately the size of Jamaica), reach a maximum thickness of 200 m, and consist of 5000 Gt of sediment. Benthic foraminiferal fauna analysis and sedimentology indicate that the MTDs originated on the continental slope, which is at least 200 km laterally and 1500 m above their present position. Each mass-failure event was formed by the catastrophic failure of the continental slope and has been dated and correlated with climate-induced changes in sea level. Studies of the benthic foraminiferal assemblages in the Amazon Fan has been essential to our reconstruction of the origin and cause of these failures. The MTDs contain rare shelf (Quinqueloculina cf. stalkeri, Brizalina aenariensis, Q. lamarckiana, and Pseudononion atlanticum) and dominant upper-middle bathyal species (cassidulinids and buliminids). We conclude that the MTD originated between 200 and 600 m water depth, approximately the same zone in which gas hydrates occur. We suggest that the glacial MTDs referred to as Deep Eastern MTD (35–37 ka) and Unit R MTD (41–45 ka) correlate with rapid drops in sea level which destabilized continental slope gas-hydrate reservoirs causing catastrophic slope failure. An alternative explanation is required for the deglacial MTDs referred to as Western and Eastern Debris Flows (13–14 ka) which occurred as sea level rose rapidly during the Bølling-Allerød period. We suggest that the deglaciation of the Andes and the consequent enhanced sediment supply coupled with a shift of the depo-centre to the continental shelf, caused over-burdening and thus slope failure. Evidence for a 2‰ negative δ13C shift in both planktonic foraminifera and organic matter coeval with these failures suggest that whatever the cause, there was a large release of methane hydrate associated with each failure.

We see that the piles of river debris in the ocean in front of the Amazon river contain a lot of unstable methane hydrate. If the temperature rises too much or the pressure drops it destabilizes. That happened in the same period as MWP1A and the Bolling Allerod. But Maslin et al had to assume the sea level rise and find a unlogical puzzle, which would be perfectly unpuzzled if there had not been a rapid sea level rise.

I'll fetch a dozen or so refences for glacial readvances during the B-A / MWP1A in a bit, but I have more to do.