14c carbon 14 for dating prehistoric findings
By Javier The existence of a ~ 2400-year climate cycle, discovered in 1968 by Roger Bray, is supported by abundant evidence from vegetation changes, glacier re-advances, atmospheric changes reflected in alterations in wind patterns, oceanic temperature and salinity changes, drift ice abundance, and changes in precipitation and temperature.This is established with proxy records from many parts of the world.Introduction In our attempt to better understand the nature of our planet’s abrupt climate changes I have already reviewed the glacial-interglacial cycle, and the Dansgaard-Oeschger cycle’s that take place during glacial periods.I now start reviewing the millennial climate cycles that abruptly impact the slowly changing Holocene climate.They could distinguish the sediment layers into wet/dry, cold/warm, periods, and developed crude dating methods. Analytical pollen zones defined by Knud Jenssen and Johs. Figure 50 summarizes decades of work by botanists to establish vegetation stages in the Northern Hemisphere Holocene.
In part C, we will discuss what it is considered the most likely mechanism by which solar variability could affect climate, as proposed by the authors researching the subject. The development of palynology (pollen studies) by Lenart von Post in the 1930’s allowed Knud Jenssen and Johs.His research shows very clearly the impact of Holocene climatic change. Winter precipitation is more important than summer temperature for glacier expansion episodes. 2) This climate cycle is clearly evident in numerous proxies from the North Atlantic region and other places in the world that reflect ~ 2400 year-periodic changes in wind patterns, oceanic currents strength and salinity, drift ice, precipitation, and temperatures.There is a general trend to increasing dryness during the Neoglacial, after a wetter HCO. Holocene mid-European lake-level reconstruction from a data set of 180 radiocarbon, tree-ring and archaeological dates of higher and lower lake-level events based on multiple lines of evidence, obtained from sediment sequences of 26 lakes in the Jura mountains, the northern French Pre-Alps and the Swiss Plateau. Acknowledgements I thank Andy May for reading the manuscript and improving its English.He observed in the data a possible 2300-2700-year cycle, that he projected into the past from the Little Ice Age, finding that a 2600-year period closely matched both vegetation transitions like the Atlantic/Sub-Boreal, or the Sub-Boreal/Sub-Atlantic transitions, and significant glacier re-advances from the past after the Younger Dryas (Bray, 1968). In this and following figures, blue bars mark the position of the lows of the ~ 2400-year Bray cycle. By the mid-70’s the scientific community was aware of the existence of a 2500-year climatic cycle that caused glacier advances and recessions, and that separated significantly different vegetation stages and cultural phases (figure 51B). In the negative phase, the polar low-pressure system (also known as the polar vortex) over the Arctic is weaker, which results in weaker upper level winds (the westerlies). Data is missing around the 8.2 kyr event when the basin entered a bioturbated non-varved interval similar to glacial stadials. The last 1300 years register a large increase in the frequency of floods in Spanish rivers.Since he was the first to correctly identify and describe the ~ 2400 year climatic and solar cycles they should carry his name as this is the tradition. Due to its coincidence with C fluctuations, it was inferred that its cause was solar variability. Therefore, cold Arctic air and storm tracks move farther south, causing a drop in northern hemisphere temperatures and changes in precipitation patterns. Temperature and salinity analysis of the Atlantic Meridional Overturning Circulation (AMOC) using a sediment core south of Iceland, where the Faroe and Irmingen currents branch out of the North Atlantic current, shows that episodes of warm saline sub-thermocline conditions are centered at 0.3 (B1), 1.0, 2.7 (B2) and 5.0 (B3) kyr ago, coinciding with known climatic perturbations in the North Atlantic region (Thornalley et al., 2009; figure 53 b). The authors propose an increased preservation potential and/or increased human impact on the landscape as likely cause. That the global temperature reconstruction truly reflects global temperature changes and is not dominated by northern hemisphere records is confirmed by the Rosenthal et al.