Dendrochronology relative dating method
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.Their efforts resulted in an understanding that the Holocene climate could be subdivided into periods of different climatic conditions, like in a diagram by Rutger Sernander from 1912 (figure 50 A, upper diagram). Postglacial vegetation and climate periods as understood during the first half of the 20th century. Upper diagram, Rutger Sernander’s view of postglacial warm climate periods in southern and central Sweden, showing his proposed abrupt climate degradation at the Sub-Boreal/Sub-Atlantic transition, termed “fimbulvintern.” The dashed line indicates G. Iversen for southern and central Sweden confirming Sernander’s climatic reconstruction. These stages allow us to distinguish a 2500-year vegetation and faunal cycle.Andersson’s opposite view of continuous temperature evolution. Some botanists, like Rutger Sernander, proposed that these transitions were abrupt and not gradual. 5-year-resolution δO isotope record from Dongge Cave (southern China) stalagmite DA as a proxy for the strength of the Asian monsoon over the past 9000 years. A winter precipitation reconstruction from Norway’s coastal glaciers shows periods of increasing precipitation at the lows of the Bray cycle (Matthews et al., 2005; figure 54 b).Lower diagram, Late Glacial/Postglacial temperature evolution in southern and central Sweden based on biological evidence, after Magnus Fries, showing the temporal disposition of the nine pollen zones in Roman numbers. In particular, he proposed that the last transition between the Sub-Boreal and the Sub-Atlantic, at around 650 BC corresponded to the “Fimbulvintern” or Great Winter of the Sagas that marks the end of the Nordic Bronze Age (figure 50 A), and made the Nordic countries a colder place. The atmospheric reorganization that takes place at the lows of the Bray cycle and causes increased polar circulation is partially evident in eolian soil sediments in southern Iceland (Jackson et al., 2005; figure 52 d). Yellow bars denote the timing of Bond events 0 to 5 in the North Atlantic. Besides feeding glacier advances at these times (figure 51 a), the Norway glacier-derived winter precipitation record matches almost exactly the Norway marine-derived Atlantic warm-water inflow record (figure 53 d), supporting a causal relationship.
As Bray had done previously, Denton & Karlén (1973) correlated periods of major glacier advances to periods of high C production (low solar activity). He described this effort and its fruits in his 2002 book “The Ice Chronicles: The Quest to Understand Global Climate Change.” While other researchers took on studying gases, isotopes, or dust in the GISP2 ice core, Mayewski and colleagues studied the chemical composition of major ions brought to the ice by the wind, using them as tracers for atmospheric circulation. Mean grain size of eolian soil deposition at Hólmsá, Iceland, indicative of wind strength. A NAO negative phase usually features more frequent and longer blocking conditions when a stationary pressure pattern allows cold Arctic air to spill over mid-latitudes. Detrended (grey) and smoothed (black) /g) record as a proxy of warmer Atlantic water flow through the Iceland-Scotland strait of the Nordic Seas from a sediment core off Norway. The increased salinity of the Atlantic inflow observed at the times of reduced NADW formation identified by Oppo et al. This is in contrast with a Neoglacial drying trend in much of the rest of Europe and the world The hydrological changes caused by the 2400-year climatic cycle are not restricted to the North Atlantic region. Sea Surface Temperature reconstruction at the Davao Gulf, south of Mindanao, from Mg/Ca levels in the surface foraminifer . 2001, including the lows of the Bray cycle (blue bars). This is confirmed also by the finding in the same area (south of Magindanao) that Holocene SST display variability in the 1000, 1500, and 2500 periodicities, and the 2500 periodicity coincides very well with the Bray cycle (Khider et al., 2014; figure 55 d). measure the water surface temperature changes associated with the Bray cycle at the Indo-Pacific Warm Pool as 0.3°C, and calculate a climate sensitivity to millennial solar cycles of 9.3-16.7 °C/Wm, an order of magnitude higher than the estimated sensitivity to the 11-year solar cycle.That article summarizes the current scientific understanding of the ~ 2400-year cycle.In part A of this article, we are going to review, in detail, the evidence for the existence of the ~ 2400-year climate cycle.The thin line represents a near-millennial oscillation in humidity. The glaciological 2400-year climate cycle In the early 1950’s, researchers noticed a correlation between glacier movements in North America and sunspots for the previous 300 years. Some of the biggest grain sizes transported by the strongest winds are associated with cold periods and coincide with some of the lows of the Bray cycle (B3 & B4, figure 52 d). Two grey bars indicate two other notable weak Asian monsoon events that can be correlated to ice-rafted debris events. Spanish fluvial chronology also supports a 2400-year cycle in precipitation (Thorndycraft & Benito, 2006; figure 54 c).In the 1960’s James Roger Bray constructed a solar index starting in 527 BC by combining telescopic sunspot observations with naked-eye sunspot and auroral observations. The authors of the work underscore the wind pattern similarity to the North Atlantic drift-ice Bond record. Three of the five main flooding periods highlighted by the authors coincide with B1, B2, and B5 lows in the Bray cycle.
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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.