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Andre
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Some earlier threads have been dedicated to the Younger Dryas and a possible connection to an impacter. Here is the full paper about it.
http://www.pnas.org/cgi/reprint/104/41/16016, Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling, PNAS Vol 104, no 41, 9 Oct, pp16016–16021
Firstly I'm interested in the dating ~12,9 ka:
That's pretty clear. Open and shut case? Let's have a look http://www.gfz-potsdam.de/pb3/pg33/projects/eifelmaar/index.html.
http://www.gfz-potsdam.de/pb3/pg33/projects/eifelmaar/bilder/MFM clearly shows this transition. Consequently:
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, 211, 1-2, 139-155 p.
So what is it? 12,9 ~ 0.1 Ka or 12,690-12,670 counted years BP and what are those relatively warm YD summer temperatures doing there?
http://www.pnas.org/cgi/reprint/104/41/16016, Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling, PNAS Vol 104, no 41, 9 Oct, pp16016–16021
A carbon-rich black layer, dating to ~12.9 ka, has been previously identified at ~50 Clovis-age sites across North America and appears contemporaneous with the abrupt onset of Younger Dryas (YD) cooling. The in situ bones of extinct Pleistocene megafauna, along with Clovis tool assemblages, occur below this black layer but not within or above it. Causes for the extinctions, YD cooling, and termination of Clovis culture have long been controversial. In this paper, we provide evidence for an extraterrestrial (ET) impact event at ~12.9 ka, which we hypothesize caused abrupt environmental changes that contributed to YD cooling, major ecological reorganization, broad-scale extinctions, and rapid human behavioral shifts at the end of the Clovis Period...
Firstly I'm interested in the dating ~12,9 ka:
example, the end-Clovis stratum (theYDB)is well dated at Murray Springs,AZ, (eight dates averaging 10,890 14Cyr or calendar 12.92 ka) and the nearby Lehner site (12 dates averaging 10,940 14C yr or 12.93 calendar ka). Haynes (2) correlated the base of the black mat (the YDB) with the onset of YD cooling, dated to 12.9 ka in the GISP2 ice core, Greenland (see GISP2 chronology in SI Fig. 6) (18). Therefore, we have adopted a calendar age of 12.9 ~ 0.1 ka for the YD event.
That's pretty clear. Open and shut case? Let's have a look http://www.gfz-potsdam.de/pb3/pg33/projects/eifelmaar/index.html.
http://www.gfz-potsdam.de/pb3/pg33/projects/eifelmaar/bilder/MFM clearly shows this transition. Consequently:
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, 211, 1-2, 139-155 p.
Abstract
The response of a lacustrine ecosystem to climatic changes from 13,500 to 10,800 BP was studied in a varve dated sediment profile of Lake Meerfelder Maar, western Germany. Bulk biogeochemical parameters, stable carbon and nitrogen isotopes of sedimentary organic matter and micro-facies analysis are used for a detailed investigation of the lake's development from the Allerød interstadial (AL) to the Younger Dryas stadial (YD) and into the early Holocene (Preboreal). Varve micro-facies reveal rapid changes in composition and seasonal structure of the depositional environment mainly in temporal accordance with changes of terrestrial biozones. The respective responses of bulk proxy parameters (bi-decadal resolution) indicate different sensitivities to diverse climatic changes. A prominent transition took place within two decades at the AL/YD boundary (12,690–12,670 BP). Increased flux of nutrients released from redeposited littoral sediments and shorter YD summer seasons led to an acceleration and concentration of lacustrine primary production with reduced discrimination against 13C. High lacustrine primary production was further favored by relatively warm YD summer temperatures...
So what is it? 12,9 ~ 0.1 Ka or 12,690-12,670 counted years BP and what are those relatively warm YD summer temperatures doing there?