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Dating the Warming of the Younger Dryas event

9 December 2013

This refers to a paper by a German-British team of geoscientists that say that the warming of the cold Younger Dryas period happened rapidly but at different times. In Germany's Eifel region it occurred 120 years prior to when it did in southern Norway See http://wattsupwiththat.com/2013/12/04/rapid-climate-changes-in-the-young…

The paper was published in the journal Geology 41:12 and refers to an event that happened during the YD (or Dryas 3 as they call it), namely a volcano that was then subsequently used to date the warming episode. In this paper the YD is reduced to just 1100 years – when it is normally allowed 1300 years (although I have seen some geologists date it at just 900 years in length). It is therefore a period that is somewhat flexible – and later we shall learn why that is. No matter, the time marker involves ash from a volcano, thought to be Katla on Iceland. The ash was distributed by strong winds across large parts of northern and central Europe (and turns up in lake sediments). In addition, sediment at the bottom of lakes in temperate and cool latitudes tends to form a series of seasonal bands, known as varves – now back in fashion with a vengeance. These layers have been examined under the microscope, year by year, summer and winter, and back in time. The Eifel maar lake depicts rapid warming 100 years before the volcanic ash presence but in the lake sediments from Norway the warming is seen just 20 years after the ash presence, providing the difference of 120 years (one before and the other after the volcano). The geoscientists say the difference can be explained by a shift in hemispheric wind systems. Climate changed in both regions quickly but the polar front, the atmospheric boundary layer between cold polar air and the warmer air of the mid latitudes, required more than 100 years to retreat from its glacial position at Eifel at 50 degrees N to the Norwegian position at 62 degrees N. Hence, the warming slowly moved northwards – why might this be so?

As fascinating as that might be the commenters in general were not so impressed – in fact, they were highly dubious, a legacy that climate science will have for many a long year. The idea of a 120 year time lag was subject to criticism by commenter after commenter, and several reasons why it must be wrong were aired in spite of the fact the time lag may actually be telling us something rather interesting about the Earth system. However, at 11.48am a voice of reason entered the comment list, somebody calling himself 'tty' – and came out in support of the paper. We learn that the ash is known as the Vedde ash layer which is found all the way from Switzerland, France and Germany, across Britain and Ireland as far north and east as Karelia. It was an exceptionally heavy and widespread ash fall that occurred within Dryas 3 (YD) and the date would have been determined by counting annual varves after and before the ash fall. This is a well established dating technique in northern Europe, pioneered by the Scandinavians many moons ago. The Vedde ash is unique in that time range and cannot be mixed up with other volcanoes, he assures the commenters. There is no trace of a second ash fall of such breadth – in the YD.

One commenter asks why C14 was not used to date pollen grains but 'tty' rises to the occasion once more. He explains 'there is a C14 plateau' about a thousand years long at that time (associated with Dryas 3). He continues, events within Dryas 3 (YD) cannot be reliably separated by C14 dating – and this is highly illuminating as over at http://cosmictusk.com/fair-enough-van-hoessel-breaks-down-ydb-science-in… *    .. a new paper by Annalies van Hoesel et al rejects the cosmic theory for the YD based on dating methodology. It seems tty in one sentence might have squashed their argument flat.

In a further comment, at 2.02pm, 'tty' says it is strange none of the commenters have picked up on the main point – or the weakness within the paper and its argument, and this is that the event is not at the end of Dryas 3 (YD) but represents a shift from 'very cold' temperatures in the first part of the Younger Dryas to not so cold temperatures in the second part of the Younger Dryas. In Scandinavia this was a less dramatic shift – and there are even two end moraines during Dryas 3. In other words, the warming concerned in this paper is not the rather dramatic warming at the end of the Younger Dryas/Dryas 3. See also varve chronology at http://climateaudit.org/2013/12/04/more-on-hvitarvatn-varves/

* the idea that the YD boundary event happened at different times in N America and Europe revolves around the  IntCal13 calibration curve (C14 dating) – see page 13 of 20. The whole paper can be downloaded in pdf format – or simply read online by scrolling down.

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