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Thread: Greenland paleo isotope thermometer challenged

  1. #1 Greenland paleo isotope thermometer challenged 
    Forum Sophomore andre's Avatar
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    Climate discussers will generally be familiar with the Greenland paleothermometer here. showing huge temperature changes at the last glacial transition:



    It looks like we have found some real problems here. Before posting the complete article under review now let me try and describe it.

    The discovery of the North Atlantic Younger Dryas “cold” oscillation of the last glacial transition, originates from early Swedish investigation finding abundant arctic Dryas pollen in Swedish lake piston cores. Also several other geologic evidence like the Usselo horizon points towards large climate changes in short cycles several thousand years ago. Around the 1950's carbon dating appeared on the scene and these cold events were dated as at least 11,000 “14C years” ago. More strong indications of climate changes were also found roughly 10,000 “14C years” ago and this became the traditional confines of the Younger Dryas.

    But the investigation techniques progressed. Modern investigation of the carbon dating revealed large variations mostly due to strong and rapid variation in radiocarbon concentrations in the atmosphere during the last glacial cycle. Calibration of those traditional carbon dating borders would give about 12,900 and 11,500 calendar years respectively.

    Meanwhile the paleobotanic records increased and many showed that the traditional Younger Dryas was actually divided into two distinct periods; it started with the coldest and wettest period from 11,000 14C years ago roughly to 10,550 14C years ago, followed by a milder but much more arid phase.

    Then came the ice cores showing a distinct dip in isotope concentrations which looked a lot like the Younger Dryas cold spell and the Greenland GISP-2 was the first which was accurately counted all the way to the Younger Dryas with a small error margin established at 12,920 and 11,660 counted years BP, an excellent match with the paleobotanic Younger Dryas. Calculations showed that the temperature may have dropped and risen again for 10 degrees within just a decade. The flickering climate hypothesis was born.

    However more counted ice core and lake records emerged which actually found the isotope drop not at 12,900 counted calendar years but actually around 12,650 calendar years with very little variation and all in close agreement.

    Now what is 250 years between friends? It becomes a big deal though when we see that this new 12,650 counted years border closely matches the carbon date of the paleo botanic mid Younger Dryas transition of 10,550 carbon years.

    This means that the first cold and wet phase of the Younger Dryas completely precedes the isotope drop of the Greenland ice cores as well as the isotopes of the European lake records. The real isotope drop occurred actually on the transition to the second mild and arid phase of the Younger Dryas, completely at odds with the temperature interpretation of the isotopes.

    It doesn’t help to indicate the geographic mismatch of botanical records and Greenland ice cores. Not only are the lake records of south Greenland actually confirming this mismatch but also the German Lakes show highly identical isotope signatures with the Greenland ice cores while the abundant paleobotanic records close to these lake cores still suggest the coldest moist period before the isotope drop and the warm arid period after the drop during the isotope minimum, assumed to be the actual Younger Dryas.

    From this there is only one conclusion possible. The ice core and lake isotopes do show aridity, not temperature, and this can be explained by isotope behaviour in the precipitation cycle under arid conditions. The misidentification of the older Younger Dryas border with some 250 years appears to have grave consequences, putting glaciological climatology in an awkward position. Hence the sharp isotope variation is not about ten degrees within a decade but about sudden droughts. We have still a lot to learn from paleo climate.


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    Forum Isotope Bunbury's Avatar
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    Interesting. How do ocean sediment data fit in with this theory? Do they also show aridity and not temperature?


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    WYSIWYG Moderator marnixR's Avatar
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    in principle it should be possible to have some sort of measure of aridity, which usually shows up as dust spikes in submarine sediments
    not sure whether the amount of dust capture in ice caps is an equally good indicator
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
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    Quote Originally Posted by Bunbury
    Interesting. How do ocean sediment data fit in with this theory? Do they also show aridity and not temperature?
    First of all there is no theory, it's merely another test of the isotope paleo thermometer with rather weird results.

    But talking about oceans and aritiy. It is a given that the high resolution ocean sediment cores like Hole 893A in the Santa Barbara bassin or the several cores of the Cariaco basin, Venezuela mimic the isotope pattern exactly. But which caused which? The oceans were heavily agitated in that period. oceans are also source of precipitation. Could there be a slight change that we had the causality the wrong way around? And low sea surface temperatures, due to ocean overturning, do cause aridity but not necesarily low ambient temperatures, because the lack of low clouds increases the direct solar radiation.

    Suppose that climate was steering the ocean, which is rather unlikely due to the gigantic difference in heat capacity, where is the inertia of the oceans reacting to that? There is none. It seems that the idea that the ocean caused all this may be worth further testing.
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    Quote Originally Posted by marnixR
    in principle it should be possible to have some sort of measure of aridity, which usually shows up as dust spikes in submarine sediments
    not sure whether the amount of dust capture in ice caps is an equally good indicator
    The dust is there. Another measure of arid conditions at the water source is high deuterium excess, which is there too.

    See: http://www.glaciology.gfy.ku.dk/papers/pdfs/242.pdf

    Now if you scrutinze Jouzel et al 2006, you'd see that they just don't touch the subject. It appears that they know what all this is pointing to but can't accept it. Just an idea.

    Paleobotanical moisture indicators are shifts from dense forests to open grassland, lake lowstands, in America it's the remarkable shifts between pinus (pine) domination and Picea (spruce) domination. It is assumed that this is a temperature indicator but both genera cover the same temperature range. Pinus however is from the arid ground and Picea prefers a moist environment though. In North Europa the Younger dryas is indicated on many places with sterile aeolian cover sands blown from the empty sea beds.
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    Nice to see you still alive and well and thinking outside the box Andre.
    Greetings. 8)
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    Quote Originally Posted by Ophiolite
    Nice to see you still alive and well and thinking outside the box Andre.
    Greetings. 8)
    Hi Ophiolite!
    Good to see you too. And indeed the accumulated data of the Quartenary don't fit in the box anymore, for sure. Need to make it bigger and this is an attempt.
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  9. #8  
    WYSIWYG Moderator marnixR's Avatar
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    will this box do ?

    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
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    Quote Originally Posted by marnixR
    will this box do ?

    Excellent illustration how little thinking out of the box is done, even when Schrödinger put that animal in there, he kept thinking in that box, forgetting to count the lifes of a cat.

    Now where are the glacialogists pointing to the complex isotope business or the abundant late glacation evidence in the UK and Norway?

    No specialists around? Anyone interested in pre-peer review?
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    How are the cores counted? If by hand/eye it would be easy (presumably) to make an error of a few hundred years in 12,000. Is there some automated method? I suppose I could google this...
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    Quote Originally Posted by Bunbury
    How are the cores counted? If by hand/eye it would be easy (presumably) to make an error of a few hundred years in 12,000. Is there some automated method? I suppose I could google this...
    All done by hand. For ice cores, the first few hunderd layers are easy, the individual snow layers are recognisable. It gets more difficult when under compression the layers are squeezed to solid ice, however the annual dust layers from snowless seasons (winter) may help or annual cycles in conductivity of the ice. There are also comparison tricks, traces of ashes of known volcanic eruptions for instance (tephra), abeit limited in geographic spread. Around the Younger dryas there are a multitude of those tephra layers, the strongest are the Laacher See Tephra in Germany and the Vedde Ash.

    Annual stratified sedimentation of lake cores (varves) is much easier to count. However lakes dry up and show discontinuities. There are however three continuous lake cores in Europe that agree very closely on the Younger Dryas together with the GRIP and NGRIP ice cores:



    Source:
    http://www.gfz-potsdam.de/pb3/pg33/p...aar/index.html

    The annual varves of the Meerfelder maar during the Allerod to Younger Dryas transition (same source):



    Thus those uninterrupted lake sediment cores contain much more information than ice cores.
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    A Picture (although mutulated by the system) is worth a thousand words



    This graph shows the reason of the Younger Dryas controversy. On top two compilations of many paleo botanic studies dividing the Younger Dryas in two parts, a wet cold first part from about 11,000 radiocarbon (14C) years BP to about 10,550-10,500 radiocarbon years BP. Carbon years on the upper scale. This is followed by a second warmer but drier part.

    On the lower scale the counted (calendar years) showing two isotope records with high mutual correlation, the Greenland GRIP ice core and a varve counted core from the Ammersee in Southern Germany in the middle of the area of the inventarisation of Isarin and Bohncke.

    So if you let the Younger Dryas start at the red vertical line around 12900 calendar years ago, you capture the cold phase and you can argue that the YD was about a sudden return to cold glacial conditions. However the isotopes went the other way, up instead of down.

    If you start at the isotope drop around 12650 calendar years ago, the alleged start of the cold phase of Younger Dryas at the vertical bold black line, you won't find any sudden temperature drop, not even a cold Younger Dryas. So this is what caused the controversy. Not calibrating all events on the same time scale and the abbaration of the GISP-2 ice core, all precluding to see that the isotopes appear to react exactly opposite to the actual temperatures.

    References:

    Isarin R.F.B, S.J.P. Bohnke, 1999 Mean July Temperatures during the Younger Dryas in Northwestern and Central Europe as Inferred from Climate Indicator Plant Species, Quaternary Research
    Volume 51, Issue 2, March 1999, Pages 158-173


    von Grafenstein, U., H. Erlenkeuser, A. Brauer, J. Jouzel, and S.J. Johnsen, 1999, A Mid-European Decadal Isotope-Climate Record from 15,500 to 5000 Years B.P., Science, Volume 284, Number 5420, pp. 1654-1657, Jun 4 1999.

    van’t Veer R., G.A. Islebe, H. Hooghiemstra, 2000; Climate change during the Younger Dryas chron in Northern South America: a test of the evidence. Quartenary Science Review Vol 19 (2000) pp 1821 - 1835

    d18O Data here
    ftp://ftp.ncdc.noaa.gov/pub/data/pal...ersee_1999.txt

    ftp://ftp.ncdc.noaa.gov/pub/data/pal...s/gripd18o.txt
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    Hi Andre.

    What are the units of the Y-axis scale?

    Just from looking at the two graphs, the placement of the bold black line at 12650 counted years ago seems completely arbitrary, in between the peaks and troughs. What am I missing?

    Also, what is the margin of error in hand counting layers in an ice core?

    Just trying to understand.
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  15. #14  
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    Quote Originally Posted by Bunbury
    Hi Andre.

    What are the units of the Y-axis scale?
    Isotope values are depicted as ratio's in relation to a certain standard, in this case the VSMOW. The values are (dimensionless) in mils or thousands. So -10 mil means that this sample contained 10 mil or one percent less heavy 18O isotopes than the standard water sample.

    Just from looking at the two graphs, the placement of the bold black line at 12650 counted years ago seems completely arbitrary, in between the peaks and troughs. What am I missing?
    It is supposed to be the moment when the midvalue between spikes is passed. But this graph here should be identical to the one linked to in a previous post from Potzdam, also showing the Ammersee and GRIP isotope ratio as well as the same boundary between Allerod and Younger Dryas. It's only rotated 90 degrees to reflect the orientation of the cores. Therefore we are talking about an lower Younger Dryas boundary. So I did not make it up

    Also, what is the margin of error in hand counting layers in an ice core?

    Just trying to understand.
    I'm not aware of good error estimations in the ice core counting. However when the difference between GRIP and GISP-2 was discussed the difference of 200+ years was considered within the error margin.

    For the lake varve count Brauer et al estimate 1% But here the tephra layers help to correct. For instance the dominant Laacher See Tephra layer has been dated with about all techniques available to 12,900 Cal BP (coincidence?) In the Meerfelder maar he counts it on 12880 Cal BP so that's pretty good I'd say. So that gives a very hard data point for many records in the environment. But the independently counted third lake, Lake Gosziac also gets very close to the same number

    I estimated the mid value transitions as follows:

    Ammersee 12,640
    Lake Gościąż 12,650
    GRIP 12,640
    NGRIP 12,660
    Meerfelder Maar 12,680 (according to Brauer, although that picture suggest earlier)

    Note that for Lake Gościąż the distance to the Laacher See Tephra also has been verified.

    That would make GISP-II with ~12,900 years a distinct outlier while those other five would suggest 12,654 +/- 17 stdev.
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  16. #15  
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    So I did not make it up
    Nothing was further from my mind!

    I'm just trying to make sure I understand this, and having understood the facts, then to try to see how it relates to the broader issue of climate change today. I'll have to wait till I get home to spend a little more time reading the links, but this might not happen tonight as there are some interesting political happenings to focus on.
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    Before talking about the consequences for climatology why not investigate one of those records, the Younger Dryas in the Meerfelder maar a bit closer.

    The pollen record:



    Source:

    Lücke, A. Brauer A., 2004. Biogeochemical and micro-facial fingerprints of ecosystem response to rapid Late Glacial climatic changes in varved sediments of Meerfelder Maar (Germany). Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 211, Issues 1- 2, 19 August.

    Note:
    High lacustrine primary production was further favored by relatively warm YD summer temperatures.
    If you *known* (biased) that you are supposed to look at cold period, that's easily confirmed by the strong reduction in pollen count. But suppose, I was not to know the timeframe and I was to find out for myself what could be said about temperature and humidity, I would first look at temperature sensitive taxa.

    Oak, Quercus, for instance is a typically moderate warmth loving tree, you won't find them in the mountains. Yet I see a tiny amount of oak pollen throughout the whole period and most certainly not declining in the Younger Dryas.

    I also see the moderate winter hardy great burnet (Sangisorba officinalis) and Helianthemum appearing in the Younger Dryas and disappearing afterwards. But this genus is generally in arid/warm conditions. The decline of trees in favor of "graminae" grasses, the appearance of Ephedra and the decline of pollen is also consistent with aridness. Also the thriving of aquaric plants Potamogeton (pondweed), Botrychium (ferns) and Pediastrum (algae) would tell me that large parts of the lake were marshy, so there was a distinct lake low level stand not seen before and after the period: aridness.

    Of course I would also look for typical abundant cold indicating taxa and species of the north, like Dryas octopetala or Crowberry (Empetrum). But those are absent. Actually the general mix of herbs then closely resembles the mix of the present for that area.

    So my *blind* unbiased conclusion would be that the Younger Dryas was definitely arid and most certainly not colder than the periods before and after or perhaps even nowadays.

    So what does that mean for nowadays climate?

    The strong correlation between the Greenland isotopes and methane concentrations and the sudden spikes have giving fuel to the flickering climate hypothesis (Taylor et al 1993) with methane as possible driver and some strong feedbacks, causing temperature variability of over 10 degrees. While it is crystal clear that things happened, it was not the temperature but the moisture. The temperature apparantly going actually in the opposite direction. This would suggest that the methane did not do anything according it's reputation as a strong greenhouse gas. But wé'd better find out about the cause of the aridity and prepare for living in near deserts should we encounter another Younger Dryas.

    Ref:

    Taylor K.C., G. W. Lamorey, G. A. Doyle, R. B. Alley, P. M. Grootes, P. A. Mayewski, J. W. C. White, L. K. Barlow, 1993 The “flickering switch” of late Pleistocene climate change Nature 361, 432 - 436 (04 Feb 1993)
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    Waiting for the discusion. For instance a certain geological expert from Scotland would certainly challenge these allegations since there is a plethora of studies about Scottisch glaciations during the Younger Dryas. So how to explain that?

    Let's have a look at one of the latest publications (Golledge 2007) about that subject. We read:

    Complete disappearance of the Younger Dryas ice mass by 10.6–10.4 ka 14C BP is inferred from dated basal organic sediments on Rannoch Moor Golledge (Lowe, and Walker, 1976)...

    ....The timing of glaciation in the study area is bracketed by organic deposits buried beneath subglacial till at Croftamie, southeast of Loch Lomond, suggesting a maximum glacier extent at 10.560 _ 160 14Cka BP, (Evans and Rose, 2003), and inferred ice-free conditions on Rannoch Moor by 10,660 +/-240 – 10.390 +/-200 14Cka BP, (Lowe and
    Walker, 1976).
    So when again did the Younger Dryas general isotope drop started again? See the vertical boldface line again? 10560 years 14C BP:



    So, those glacial events took place roughly between the red and black line, the alleged warm last phase of the Allerod. The confusion is all in the usual but erratic older Younger Dryas carbon years boundary of 11,000 years 14C BP.

    It's just how you want to define the Younger Dryas but the cold period had nothing to do with the isotopes of the ice cores.

    References:

    Golledge, N.R. 2007 An ice cap landsystem for palaeoglaciological reconstructions: characterizing the Younger Dryas in western Scotland, Quaternary Science Reviews 26 (2007) 213–229

    Lowe, J.J., Walker, M.J.C., 1976. Radiocarbon-dates and deglaciation of
    Rannoch Moor, Scotland. Nature 264, 632–633.

    Evans, D.J.A., Rose, J. 2003. Croftamie. In: Classic Landforms of
    the Loch Lomond Area. Geographical Association, Sheffield,
    pp. 38–39.
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    Quote Originally Posted by andre
    Waiting for the discusion. For instance a certain geological expert from Scotland would certainly challenge these allegations since there is a plethora of studies about Scottisch glaciations during the Younger Dryas. So how to explain that?
    Andre the depth of your research in this area makes it practically impossible for me to challenge you without conducting a comparable amount of research. Since my current interests revolve more around planetary accretionary processes, geotectonics on terrestrial worlds, pan spermia, evolutionary mechanisms, the Drake equation, and how to make enough money to survive a year or two in retirement, I suspect I shan't get around to climatalogical issues any time soon.
    I shall continue to read your thoughts with interest, but unless I spot something blatantly inconsistent I won't be questioning anything. :wink:
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  20. #19  
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    Quote Originally Posted by Ophiolite
    Andre the depth of your research in this area makes it practically impossible for me to challenge you without conducting a comparable amount of research. Since my current interests revolve more around planetary accretionary processes, geotectonics on terrestrial worlds, pan spermia, evolutionary mechanisms, the Drake equation, and how to make enough money to survive a year or two in retirement, I suspect I shan't get around to climatalogical issues any time soon.
    I shall continue to read your thoughts with interest, but unless I spot something blatantly inconsistent I won't be questioning anything. :wink:
    Okay that's fair. :-D However the idea is indeed to come up with the highest quality to withstand peer review. Especially when overthrowing basic paradigms. That's where forums can help finding glitches. And there is one. Turned out that they overhauled the Greenland GRIP and NGRIP ice core chronology, apparantly unhappy with the difference with the GISP-II ice core. Alternately, they could have been happy with the matching European lake varve chronology. Anyway we have to deal with that.

    So here is a new chronology for the GRIP/NGRIP/Dye-3 ice cores in Greenland.

    The publication: http://www.gfy.ku.dk/~www-glac/papers/pdfs/220.pdf

    The data: http://www.gfy.ku.dk/~www-glac/data/..._27nov2006.txt

    Now I converted the "b2k" base of their GICC05 timescale (2000AD) to the traditional 1950AD to stay compatible with the rest. Then we get this for the start of the Younger Dryas:



    The graph shows 100 years smoothed data, for comparison the original GRIP data are visible showing that it's rather hard to plot an arbitrary mid point as starting point of the YD.

    Anyway we now get values around 12,780 cal Year BP, over 100 years older than previously. Why?

    Notice in the text of the data:

    In the Holocene, GRIP is dated year by year. Below 11700 b2k the NGRIP based time scale has been transferred to GRIP depths by linear interpolation between volcanic match points (markers shown on Fig. 10 in Rasmussen et al. (2006)
    However fig 10 does not show volcanic markers explicitely, merely matching of variable conductivity of the ice, which also can be attributed to volcanic events. However there are identified volcanic ash layers (tephra); and we find in table 4 their dating of the Vedde ash: 12,171 +/- 114 year b2K (or 12,121 Cal years BP). So they counted it and did not use it as a hard dating horizon. They did not even acknowledge a difference with the conventional dating of the Vedde ash (no reference), which is widely referred to as 10,310 14C years BP, calibrating to 12,085 Cal years BP. The accuracy of this dating is higher than average due to a temporary atmospheric increase of 14C, so they seemed to have over counted a bit here suggesting that a better value for the start of their YD might be 12,740 years

    It must also be noted that the previously counted Vedde ash layer in GRIP was on 11,980 cal. yr BP some 95 years too early.

    Furthermore the Saksunarvatn volcanic layer is dated at 10,347 b2K (10,297 cal BP) against the reference age of 10.180 Ka cal BP, hence also a bit high.

    So we need to go over the varves again, triple check the tephra ages and see what most recent results are. However the basic challenge still stands.
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    Waiting for the discusion.
    This is heavy, man. Be patient. 8)
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    I have to take issue with this statement:

    Oak, Quercus, for instance is a typically moderate warmth loving tree, you won't find them in the mountains.
    We have gambrel oak (scrub oak) growing abundantly at at least 8,000 ft asl in Colorado, and I'm pretty sure it can be found at higher elevations, having had to bushwhack through them occasionally. They are tolerant of quite cold winters.
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    Quote Originally Posted by Bunbury
    I have to take issue with this statement:

    Oak, Quercus, for instance is a typically moderate warmth loving tree, you won't find them in the mountains.
    We have gambrel oak (scrub oak) growing abundantly at at least 8,000 ft asl in Colorado, and I'm pretty sure it can be found at higher elevations, having had to bushwhack through them occasionally. They are tolerant of quite cold winters.
    Little doubt about that, it's quite winterhardy here too, however in Europe, quercus is seen to react clearly on climate change, see for instance:
    http://www.geog.leeds.ac.uk/people/k.roucoux/EPSL.pdf
    http://www.cosis.net/abstracts/EGU20...-J-11511-1.pdf

    while here, it did seem to appear closely before the Younger Dryas with a fairly constant relative abundance troughout the YD and into the Preboreal. Ephedra for instance is also very winter hardy but you won't find it to the north, probably the total of climate variables is important here and treelines in the mountains are still slightly different from treelines in the north, due to the annual and diurnal insolation difference.
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    Certainly it's the combination of elevation and latitude that matters - treelines are lower the further north you go. Your statement just seemed to need some qualification, that's all. You will find oaks in the mountains, at least in some areas.
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    It is well known that the isotopes (temperature) of Antarctica and Greenland differ greatly:

    http://www.agu.org/pubs/crossref/1997/97GL02658.shtml



    No Younger Dryas whatsoever, but instead an much earlier Antarctic Cold reversal. But it appears that the earlier cooling is consistent with the re-glaciation events in the Northern hemisphere like Two Creeks and Scotland. Could it be that the Antarctic ice cores isotopes are more consistent with global temperatures than the Greenland isotopes?

    Could it be then that Greenland isotopes are not about temperature but about precipitation. Perhaps we should really zoom in on the physical processes associated with the isotope fractinations in the precipitation cycle.

    Homework:
    http://wateriso.eas.purdue.edu/water...ackground.html

    http://wwwrcamnl.wr.usgs.gov/isoig/isopubs/itchch2.html

    Note Fretwell's law:

    "Warning! Stable isotope data may cause severe and contagious stomach upset if taken alone. To prevent upsetting reviewers' stomachs and your own, take stable isotope data with a healthy dose of other hydrologic, geologic, and geochemical information. Then, you will find stable isotope data very beneficial." (Marvin O. Fretwell, pers. comm. 1983).
    That's extremely true.
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    Quote Originally Posted by andre
    It is well known that the isotopes (temperature) of Antarctica and Greenland differ greatly:

    http://www.agu.org/pubs/crossref/1997/97GL02658.shtml



    No Younger Dryas whatsoever, but instead an much earlier Antarctic Cold reversal. But it appears that the earlier cooling is consistent with the re-glaciation events in the Northern hemisphere like Two Creeks and Scotland. Could it be that the Antarctic ice cores isotopes are more consistent with global temperatures than the Greenland isotopes?

    Could it be then that Greenland isotopes are not about temperature but about precipitation. Perhaps we should really zoom in on the physical processes associated with the isotope fractinations in the precipitation cycle.
    surely that's only one possible reading of the data - another one would be that the younger dryas event was a reversal restricted to the northern hemisphere and in some way related to the meltdown of the massive ice caps covering canada and north-western europe
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
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    Quote Originally Posted by marnixR
    [

    surely that's only one possible reading of the data - another one would be that the younger dryas event was a reversal restricted to the northern hemisphere and in some way related to the meltdown of the massive ice caps covering canada and north-western europe
    See that the isotopes of Antarctica start rising 18,000 years ago, I could list a couple of pages of refs and I will later (hurry now) that the deglaciation on the Northern hemisphere indeed started around that time with a strong increase 17,500 years ago, long before that sudden Greenland spike around 14,500 years ago. Therefore that period has now been termed the Mystery interval. Ref:

    Denton, G.H, W.S. Broecker, R.B. Alley 2006, “The Mystery Interval 17.5 to 14.5 kyrs ago” by in PAGES News, Vol. 14, No. 2, August 2006, pp. 14-16

    The mystery would cease to exist immediately if you could think out the box: ""what if those Greenland spikes are NOT temperature", then that early warming is consistent with Antarctica.

    We have also seen that the (world wide ) glacial readvances did not happen in the Younger Dryas but (well) before that, which would be no problem to accept if that Antarctic cold reversal was a global cold reversal starting around 14,000 years ago and if the Greenland isotopes were NOT temperature.

    Then we see a warming again during the Younger Dryas (12,7 - 11,500 years) for which is also a plethora of evidence in the Northern hemisphere, which is perfectly acceptable when comparing with the isotope warming in Antarctica and if the Greenland isotopes were NOT temperature.

    Then if we glance at isotope behavior (later much more) we see that two main features drive the isotope ratio: temperature and relative humidity. We know that the annual snowfall in Greenland corrolates extremely well with the isotope ratios. snowfall and humidity are perhaps related a bit? So is it so hard to assume that it may be the same signal, overshadowing the effect of warming.
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    Before getting the exact math, let's compare the precipitation cycle under moist and arid conditions, assuming that you all have read up on the isotope links I provided.

    So in the first step, evaporation, the fractination of the heavy isotopes is mainly a function of local tempeature and humidity. If it's colder less water molecules with heavy isotopes (heavy hydrogen - Deuterium (D) or 2H and heavy oxygen 18O) evaporate. But if the relative humidity is higher, the dynamic equilibrium between evaporation and condensation tends to decrease the fractination process (factor 1-h). So under arid conditions less heavy isotopes evaporate which looks like cold. But note that low relative humidity conditions has two options: apart from less evaporation it could also indicate higher ambient temperatures. Few if any of the textbooks and studies about isotope fractination address this.

    But we conclude that water vapor with less heavy isotopes indicate colder and/or arid conditions (implicitely with possibly warmer conditions).

    The next step is lifting (advection) of the warm air mass with our evaporated water to higher altitudes, where the air mass cools due to expansion and clouds and evaporation forms when the dew point is reached. Moist air needs little cooling for condensation to take place and clouds can form at lower, warmer altitudes than arid air, with higher and hence colder clouds.

    Again the fractination is a function of temperature and humidity but at condensation, relative humidity is almost by definition 100% or 1, so only condensation temperature or dew point is determining the fractination process. The colder, the more heavy isotopes condensate and leave the airmass. But with a more arid air mass, the dew point is automatically, intrinsically, lower, removing more heavy isotopes without ground temperatures being lower. Few if any of the textbooks and studies about isotope fractination address this.

    Now the overall important effect during the transport of the air mass from southerly sources to northerly ice sheets is the Rayleigh or rain out effect. After condensation at lower lattitudes we are interested in the isotope ratio of remaining water vapor. So in moist condition with warmer lower clouds, less heavy isotopes condesate, leaving more heavy isotopes for the remainder of the traject than the dry air mass.

    So when this precipitating air mass finally reaches the Greenland ice sheet or the lakes in Germany, the evaporation, condensation and Rayleigh effect under arid condition all have reduced the heave isotope ratio of the arriving precipitation more than under generally moist conditions, giving a false cold signal.

    But at the same time arid conditions and ground level actually means increased temperature difference between ground level evaporation and cloud dew point temperature, which means that ground level temperatures are basically higher in arid (relative humidity) conditions.

    That's why the Antarctic isotopes reflect precipitation and moisture rather than temperature.
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    How about some more suggestions that the isotope spikes are about moist-arid cycles rather than temperature,

    Calling to the stand, Jouzel et al 2006, investigating the behavior of "deuterium excess" in ice cores.

    Note:

    The deuterium-excess parameter, d= dD - 8 * d18O, defined
    by Dansgaard (1964) and hereafter called the excess, characterizes the isotopic composition of precipitation in dD/d18O space (...)

    The scaling factor of 8 is derived from the empirical
    Meteoric Water Line (MWL) dD = 8 * d18O+10, which
    describes very well present-day precipitation (Craig, 1961).

    Modern excess values in precipitation thus have an average value of 10, but vary both spatially and temporally at all timescales. Whereas the degree of moisture removal from a cloud, a process strongly controlled by temperature, is the key parameter for the distribution of either dD or d18O in precipitation (Dansgaard, 1964); excess values are largely influenced by conditions prevailing in the oceanic moisture source regions where this precipitation originates (Craig and Gordon, 1965; Merlivat and Jouzel, 1979).
    Emphasis mine. There is a very important statement.

    See fig 2 on page 5, the (f) graph is the deuterium excess. Notice the heavy spike at the left. That's the Younger Dryas showing clear extreme high values compared to the average.

    Note that Jouzel et al do their very best to unexplain that and attempt to tie the deuterium excess to the alleged temperature changes. For instance:

    A possible explanation for the progressive cooling of Greenland and the east–west migration of the polar front during the BA is a progressive decrease of the salinity of the Greenland-Norwegian Sea surface waters sustained by the surplus of fresh-water runoff from the Scandinavian Ice Sheet, which lost a considerable part of its volume during this period.
    However other sources, as I showed earlier, point to readvance of Norwegian glaciers in the same period.

    Note also in the conclusion:

    General Circulation Models (GCMs). In principle, these models allow us to account for the complexity of topographic changes, source conditions and atmospheric circulation. They have, however, up to now, shown a very poor representation of the predicted characteristics of deuterium-excess in precipitation and clearly require additional work.
    Don't blame the models, if the hypothesis is wrong, the models can't change that.

    Occams Razor: here we read the most simple explanation for high deuterium excess:

    Vapour generated under low humidity conditions has a high deuterium excess.
    Accepting that, would remove a lot of ice core deuterium excess mysteries.

    Next, saved for the last, the best part, seasonality of precipitation.
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    Seasonality of precipitation then. This is a fragment of the first comprehensive study investigating the feasibility of the ice core isotopes as paleo thermometer:



    Jouzel, J. et al 1997. Validity of the Temperature Reconstruction from Water Isotopes in Ice Cores; Journal of Geophysical Research Vol 102, No C12 pp 26,471-26,487, November 30

    See that?

    If major changes in seasonality occurs between climates, such as a shift from summer-dominated to winter-dominated precipitation, the impact on the isotope signal could be large.
    This is logical, since the eventually deep in the ice sheets the ice is compressed and smeared out, averaging out the isotope-warm summer and isotope cold winter temperatures to a volume ratio. Whatever is the is the most of will show up. After all the isotope thermometer only works when it snows. However Jouzel et al do some modeling and decide that there is no reason to assume variation of seasonality in precipation.

    Here we see how climate science can fail. Models don't proof a thing. Reality does, direct evidence like:

    Anomalously mild Younger Dryas summer conditions in southern Greenland.

    ABSTRACT
    The first late-glacial lake sediments found in Greenland were analyzed with respect to a variety of environmental variables. The analyzed sequence covers the time span between 14 400 and 10 500 calendar yr B.P., and the data imply that the conditions in southernmost Greenland during the Younger Dryas stadial, 12 800–11 550 calendar yr B.P., were characterized by an arid climate with cold winters and mild summers, preceded by humid conditions with cooler summers. Climate models imply that such an anomaly may be explained by local climatic phenomenon caused by high insolation and Fohn effects. It shows that regional and local variations of Younger Dryas summer conditions in the North Atlantic region may have been larger than previously found from proxy data and modeling experiments.
    So the authors think that they have found an anomaly and get to the models to see if they can unexplain it with all kind of constructions. And both use models to unexplain the reality, which would be over-obvious with mutually consistent evidence without models. Indeed there were large seasonality changes. It's no abnomality, it's reality, the Younger Dryas had warmers summers than normal.

    So, if you find yourself back constantly explaining anomalies with models, doesn't that mean that you don't have a theory anymore?:
    Chapter VIII

    C: In responding to these crises, scientists generally do not renounce the paradigm that has led them into crisis:

    -3: They devise numerous articulations and ad hoc modifications of their theory in order to eliminate any apparent conflict.
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    A quick wrap up,

    The intial interpretation of the isotope jumps in the Greenland ice cores pertained enormous large temperature changes with the blink of the eye. Moreover these changes seemed completely independent of the ice core isotopes of Antarctica.

    Careful study of a plethora of regional detailed climate studies, focussing on correct chronologies, reveal that reality was completely different. It is especially noted that the isotopes of the European lake sediments (Ammersee, Lake Gosciaz) mimic the Greenland ice cores but detailed climate study in the same areas find a completely different climate history with trends sometimes opposite to the isotopes.

    We have seen that seasonality of precipitation affects the weighted isotope average and the absence of warm summer precipitation gives a false impression of cooling. We also have seen that a reduced water cycle under low relative humidity conditions leads to the same isotope depletion as cooling.

    We have also seen that the records are consitent with seasonalty changes and low relative humidity conditions. We therefore conclude that the isotope variation in the Northern hemisphere records during the last Glacial termination is completely explainable by the observed changes in the precipitation cycle.

    Moreover, we contend that the actual observed temperature variation in the northern hemisphere is consistent with the isotope variation in the southern hemisphere, albeit that the temperature variation during the oscilations was in the rough order of magnitude of 1 -3 degrees, and nowhere near the claimed 10-15 degrees for the (Ant-) Arctic ice cores.

    As a consequence any model that is based on parameters derived from the glacial cycles is way off.

    Now, you all, permission to RIA* attemps.




    *RIA: rip it apart
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