14c carbon 14 for dating prehistoric findings
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.
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.
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.
Even then, they were thought to represent variations in solar activity. Paul Mayewski, one of George Denton’s students, was the scientist in charge of coordinating the effort of over 200 scientists in the American Ice Core Program that in 1993 completed the Greenland Ice Sheet Project II (GISP2). A NAO negative phase is produced when the weakening of the Iceland low and the Azores high reduces the pressure gradient resulting in weaker more southern westerlies producing colder conditions over much of North America and Northern Europe while moving the storm tracks southward towards the Mediterranean. They propose solar variability as the forcing behind these oscillations. Under humid conditions trees were unable to grow on wetter bogs. Although Ireland hydrology shows a complex pattern over the increasingly wet Neoglacial trend, lows in the Bray cycle are associated with periods of increased precipitation (figure 54 d). Superimposed on this trend are millennial-scale SST variations coherent with some of the North Atlantic ice-rafting events defined by Bond et al. (2013), and shows that every Bray cycle low coincides with a significant downward departure from the general temperature trend (figure 55 c).
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.