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Sea Level change

8 December 2016

In the journal Geology (28th July 2015) doi:10.1130/G36914.1 … there is an article that seeks to establish a synchronicity in key Holocene chronologies by extracting evidence from Irish bog pines – by Max Torbenson, et al. (a collaboration between scientists from Queens University in Belfast, Gottingen in Germany and the University of Alabama). It was described as an opportunity to test the stability of the Greenland Ice Cor chronology against IntCa (C14 calibration curve) and the idea was to see if there was any corresponding evidence of the 6200BC event. At 8160BP (8000 years ago) dendrochronological dating of trees pulled from Irish bogs reveals that pine trees were growing. The colonisation of pine trees on peatland is interpreted in terms of a drier surface, conditions quite unlike the bog environment. It represents evidence of a switch in climate accompanying the 8.2ky climate cooling event which is known from other sources (such as ice cores). The pines were growing on two separate bogs in Ireland and four trees from Ballinderry bog wee used to create a 374 year long tree ring sequence. Wiggle matching was used to create a tighter fit (than ice cores). The date for the beginning of the 'event' was 8277BP. Out of 40 oak trees collected from Irish bogs a third of them embrace the period 8160 – 8137BP (116 years after the beginning of the phase). The pine horizon represents a phase of regeneration indicating lower water levels and a drier climate. A low growth tree ring event is also recorded that was recorded over ten years – and not so severe over 20 years (8020-8000BP). Pines continued to germinate on bogs for a couple of decades and then failed to do so – presumably as conditions grew much wetter again.

The British Isles as a whole underwent a sharp drop in temperature as registered by stable isotopic records and the mollusc assemblage. A speleothem from SW Ireland also indicates colder and drier conditions – and bogs and mires in northern Scotland also became much drier.

The paper went on to show a discrepancy for the dating of the 'event' between ice cores and tree rings on the order of 65-75 years (and a similar discrepancy had been noted for the onset of the Younger Dryas 13,000 years ago. What this means is unclear for the moment. 

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