If you want to know what the Younger Dryas is Wikipedia is always a good place to find out: If you want to know exactly how the Younger Dryas was discovered, check out Spencer Wearts excellent book The discovery of Global Warming: http://www.aip.org/history/climate/rapid.htm http://www.aip.org/history/climate/cycles.htm This stable isotope graph from a Ice core of Greenland is supposed to represent temperatures and would indicate clearly the "cold" spike of the Younger Dryas: Please Register or Log in to view the hidden image! It was the discovery of these spikes that really triggered the global warming...eh.. idea (being mild), that climate could change drastically within a few years, and yes if that was to be true, I would probably be in the scaremongering camp. But it isn't true. And the key to that is in this sentence: If you do a search of a few hundred scientific publications, as I did, specifically checking that dating problem, you're in for a big surprise. It's something completely different. Non Calor Sed Umor. Anybody interested in the rest of the story?
Another attempt. Let's see some geologic evidence. How about a pollen diagram, one of the most outstanding comes from the Meerfelder Maar, a small crater lake in Germany, from the study: Brauer et al (1999) High resolution sediment and vegetation responses to Younger Dryas climate change in varved lake sediments from Meerfelder Maar, Germany, Quaternary Science Reviews 18 (1999) 321-329 Please Register or Log in to view the hidden image! What we see is an analysis of a lake sediment core that shows annual accumulation layers (varves). Each year the spring brings blooming diatoms that form a light layer. Those layers can be counted. Known volcanic ashs layers (tephra) are used to calibrate starting and ending years for counting (how educational isn't it). By identifying the pollen families and counting the number of pollen, we can do a fairly accurate climate reconstruction. We see indeed sharp changes at the Younger Dryas borders. But what kind of changes exactly? Is it really about warm - cold? What is the tell tale evidence? Anybody?
Notice that the authors use the term "Younger Dryas climate change" and also nowhere in the study the term "cooling" is used. And the reason is obvious, the herb pollen in centre are all present day common herbs in Germany and apparantly also flourishing during the Younger Dryas. An exception could be Helianthemum, which is more common in the mediteranian and locally in southern Germany, not as far north as the Meerfelder maar. There are no typical arctic species at all. The explosion of aquatic Potamogeton (duckweed) and Pediastrum (algae) points to low water levels and perhaps more swampy conditions. Furthermore the low pollen count and the shift from trees to grass land fauna (Gramineae = grass) all point toward more arid conditions, by no means colder conditions as Helianthemum clearly indicates. It's not the heat, it's the humidity.
Now we have seen that in Germany, during the Younger Dryas, at least the pollen season was as warm if not warmer than today, but that could have been a local phenomenon. So if the ice cores at Greenland tell us about extremely cold conditions during the Younger Dryas, could we also find a pollen core at Greenland covering the Younger Dryas to confirm that? Well how about this: http://www.geol.lu.se/personal/seb/Geology.pdf.pdf Now Björck et al don't seem to want to rock the boat too much, so they hurry to explain it with Fohn effect, but given the position of the lake in southernmost Greenland, you need near constant northerly winds for that. And Northerly winds are not really renowned to be warm, despite the fohn effect. Moreover there is also the preceeding cool summers that you have to compensate for. Notice the arid-moist change, fits exactly with the meerfelder maar! It's now two pollen to one (ice core area) that says that the Younger Dryas was not that cold at all. Anybody want me to increase that score? But how is this possible if all those studies unanimously seem to point at a very cold Younger Dryas with massive glacial advances. Well of one, those glacier advances did not occur in South Greenland otherwise that pollen core would not have been available. No, again, the problem lies here:
Let's have a closer look at some glacier readvances in North America: http://gsa.confex.com/gsa/inqu/finalprogram/abstract_55882.htm Look at that, not a lot of glacier readvances in the Younger Dryas at all, when the carbon dating is calibrated to calender dating. Instead then those readvances seem to have happened in that preceeding -alleged warm- "Bolling Allerod interstadial". More inconsistencies. Are we about to discover a major flaw in the chronology of the last "termination" of the ice age? Please Register or Log in to view the hidden image! You bet. Please Register or Log in to view the hidden image!
Chronology is about dating, carbon dating being one of the earlier developments and the most popular. Carbon dating is very precise but highly inaccurate. That is, we can determine the ratio of radioactive 14Carbon to normal carbon to several digits, but that doesn't say much about the real age. Carbon dating depended on the assumption that the ratio of radiocarbon 14C in the atmospheric CO2 was to be constant and that it would remain that way during photosynthesis and biologic processed. However, both are highly variable. Check here: http://en.wikipedia.org/wiki/Carbon_dating http://www.allaboutarchaeology.org/is-carbon-dating-accurate-faq.htm The calibration of radiodating to counting methods like tree rings from fossil trees and those lake varves, mentioned earlier, took a long while to devellop. Useful calibration tables appeared only in the mid nineties. The latest one (for NH land) is INTCAL04 Reimer et al (2004); Radiocarbon 46:1029-1058 I made a excel sheet for automatic date calibration. Very convenient. If anybody wants a copy PM me. Anyway in the early ninetees, the carbon dating problem was not really identified to it's fullest extend and geologists were happy to use only carbon dating. However, the difference with calender dates is highly variable and increases sharply around and after the Younger Dryas: 10,000 BP is 11,400 Cal BP 11,000 BP is 12,910 Cal BP 12,000 BP is 13,800 Cal BP 13,000 BP is 15,320 Cal BP Notice that the YD could easily fit within the difference!! Anyway, when in the 1980's and early 1990's the ice cores were analyzed (and dated rather accurately by annual layer counting), it was well known that isotope ratios can have several meanings. Since there was the notion of ice ages, it appeared highly logical that the spikes stood for temperature changes in and out of glacial periods. Nevertheless, science requires independent proof to gain trustworthiness for such an idea and therefore it was essential to check if those isotope spikes were indeed temperature changes: Please Register or Log in to view the hidden image! and sure enough, unaware of the full extend of the dating problem, the researchers compared the geologic studies, (all in carbon dating) to the calendar dating of the ice cores. Now check Clark again in the former post: Ah, That must be the warm Bolling Allerod (NOT) Ah, That must be the cold Younger Dryas (NOT) There you are: Many of those retreats appeared to be in the warm Bolling Allerod and many of those (minor) re-advances appeared to be in the Younger Dryas when the carbon dated glacial behavior "apples" were compared to the calendar dated ice core "oranges". But those "Younger Dryas glacier re-advances" were actually in the preceding Bolling Allerod “interstadial” whereas the glacial retreats were well before the Bolling Allerod. So what is warm and what is cold? This, however, was the very root to several essential mistakes: -calling the Bolling Allerod warm and the Younger Dryas cold, which wasn't -identifying the isotope spikes of the ice cores directly with global temperatures, which isn't. -linking those spurious temperature changes with the atmospheric CO2 levels -concluding that those changing CO2 levels had any causal effect for temperature changes and thus.. -the global warming idea -Billions of research $$ wasted on a wrong base for climatology But now we have the Younger Dryas busted and we can replace it with the real story of the ice core spikes Non Calor Sed Umor.
Quick poll, what do you think sofar? - Hmm, carry on - Uninteresting BS, what was that was, who cares - Whatever you say, it's wrong, because global warming must be right.
Sure, I will, just checking if anybody was looking for a good debate as this is all toe curling -Kuhnian- counter intuitive for anybody who had to memorize the Pleistocene textbooks by heart. And sure enough there are publications that seem to tell a different story. But after some (re)calibration things may look different. Anyway for the moment we have (attempted) to tear down the spurious "Calor" -heat- part, let's rebuild it now with the "Umor" -humidity- part. It's already some time ago that I plotted the Vostok ice core stable (Deuterium) isotopes against the annual layer height (both relative to the average trend or detrended). This resulted in what must be the strongest correlation ever: R2>99%: A part of the graph, the enlargment 75-70Ky was originally intended to see if we could find the Mt Toba eruption back in climate (Not really) but it shows the stunning isotope - precipitation correlation, not a single spike is missed. Please Register or Log in to view the hidden image! Actually it's probably too good to be true. Perhaps that Petit has used the isotope values to wriggle-match the individual dating on the lenght of the core in between different dating points. Never found anybody explaining that. In that case it would be circular reasoning of course, but nevertheless it suggests that Petit had good reasons to assume that isotopes and precipitation were strongly related as can be seen for the independently measured layer heights at the Greenland ice cores around the Younger Dryas: Please Register or Log in to view the hidden image! Of course you can say, the warmer the more precipitation but the people in the Sahara are going to doubt that simplification. We see that methane is also behaving in the same way. Interesting So, what's going on here?
Andre, you are making a vey strong case (until now) for debunking the Younger Dryas. Excellent work. You have me almost convinced, but I need some time for studying your arguments and analyze the data provided. I wonder what our friend Hans Erren will think, he is so much for CO2 and shunns methane...
Now, let's do some analysing of ice cores. This one is very young and very fresh with several samples per year: Please Register or Log in to view the hidden image! See how the isotope value is cyclic with the seasons? Low in the winter, high in the summer? Let's see exactly what happens in the water cycle. First water evaporates on the ocean surface. Light isotopes (16O and 1H) evoporate more easily than the heavies: 18O and 2H or D (deuterium). The isotope ratio of the water vapour is dependent on three factors: water temperature, local weather influencing evaporation (humidity - wind), and source isotope ratio, which can also change considerably: http://www.giss.nasa.gov/~gavin/ Picture doesn't downlink so please scroll down half way. (Yes Gavin it was helpful, thanks) How about condensation? again several factors are working to change the ratio again, the heavy isotopes condensate first, depending again on mainly local temperature since RH=100. Because of that, the remaining water vapour gets "lighter" so the older the air is, the lighter the rainwater or snow water. This is called the rayleigh effect. This is especially noticable with the last water coming out like on high elevations, an far inland as well is the summit ice sheets in Central Greenland and Antarctica. Hence very low d18O signals around 36 mil. Now the winter isotopes are much lower not only because of the temperature but also due to that rayleigh effect. The main source (open ocean) is further away due to oceanic winter ice, and the absolute humidity is much lower due to the temperature, both are causing a strongly increased rayleigh effect. I probably need to elaborate more on that next time?
it seems on first sight that those isotopes values are not really representing the average Arctic temperatures very accurately: Please Register or Log in to view the hidden image!
But let's get back to this one again: Please Register or Log in to view the hidden image! Notice that the range of the annual isotope ratio change is the highest at the right, the youngest part of the ice core, some 10 mil range(promille). From a large database of the Global Network for Isotopes in Precipitation, http://isohis.iaea.org/ we see even larger annual variation for high Arctic stations like Eureka NWT for instance up to ~20 mil between summer and winter. The reason that it's progressive less in the ice core with depth, is the slow merging of the snow during compression under the weight of the overlaying snow. So the differences get less and less and after several thousand years (some ten) the typical annual wave form is no longer visible. The isotope values have regressed to the average value by then. Now we are getting to the most essential part of the thread. So I wait for everybody to catch up. The question to answer is: what average?
Most certainly they do. But in due time. Perhaps peek in advance to check ODP hole 893A (Kennett et al 2000 Science). But there is so much more. back later
Back to the ice core and the isotopes. Let's try and make a simplified model of an ice core with the annual cycle in isotope ratio but also an annual precipitation cycle. As common knowledge wants, the rate of possible precipitation is dependent on temperature. In winter time with polar temps way below -40 the snowfall is minimum whereas most snow is falling in summertime with temperatures above -20C. Now remember Bjorck et al a few posts ago, the Younger Dryas was about warm dry summers and the other periods about cool moist summers. Now for our ice core model construction let's forget about temperatures by having the cyclic amplitudes constant. But lets focus on the change - increase in summer precipitation during the rapid transition from the Younger Dryas to the Preboreal around 11,650 Cal BP. You would expect tight cycles in the YD with little snow accumulation and wider cycles with a wider top spike after the transition due to the increased summer snowfall. This would look like this: Please Register or Log in to view the hidden image! Now, look what happens when we compress that ice core like this in ten steps, with mixing of the different isotope ratios to regress to the average value. Please Register or Log in to view the hidden image! And thus we have recreated the isotope jump at the transition from the Younger Dryas to the Preboreal only with the change of the precipitation without changing temperatures. Apart from some other effects, this is what really has happened.
Now what was that with averages? Please Register or Log in to view the hidden image! it should be clear that in a assymmetric function the average value is not equal to the median value. The real weighted average value is there where the surface below and above are equal. It's not only the isotope ratio in the ice but also the volume of ice that counts. So less of more summer snow with a higher heavy isotope ratio directly affects the average ratio. The other factors that have not discussed here are changing Rayleigh effect in summertime that could or could not happen or changing isotope ratios in the source, the ocean, due to other processes. The conclusion for now can be that the observed precipitation changes at the boundary of the Younger Dryas are most likely directly related to the isotope spikes in the ice cores. There is no clear relationship of those spikes with temperature. And that would constitute quite a paradigm shift, so it's probably going to take a few decades. The thread is now about halfway. There is plenty more where this is coming from. Because answers usually generate more questions.
Shall we bring in the mammoths now or somebody wants to battle 15N and 40Ar and borehole temperatures in ice cores first?
Or perhaps introduce the oceans first when looking at the last few 100,000 years: Please Register or Log in to view the hidden image! This is a comparison of oceanic isotopes against the longest ice core on Record, EPICA Dome C. The "Benthic Stack" is a mammoth job of those two ladies, compyling the data of some 50-60 different oceanic sediment cores with the oxygen isotope of bottom dwelling (benthic) foraminifera. The usual explanation for that is polar ice sheet volume. When the ice sheets grow they accumulate water with very little heavy 18O isotopes since those stay behind in the oceans. Consequently the ocean gets enriched with 18O this is what the benthic stack appears to represent (NOT!) One simply refutation would be that the ocean signals lead the ice core signals but the ocean is a very slow -inert- system. When the isotope ratios change at the surface it takes decenniums to mileniums before the benthic water can react. We know thus from radio-active 14C behavior. Moreover, from the ice core we know now that we are looking at spikes about precipitation changes more than temperature changes. Yet the ocean goes first!! Why?
