Radiocarbon dating paleoclimatology
Afterwards we recommend that the interested reader read the post “Impact of the ~ 2400 yr solar cycle on climate and human societies.” The post explores, in detail, the climatic effects and their impact on human civilization in each of the Bray cycle lows during the Holocene. Iversen to improve the postglacial period zonation (figure 50 B), and develop a summer vegetation-based temperature scale for the Scandinavian Holocene by the 1940’s.The biological 2400-year climate cycle Over a century ago Scandinavian botanists started to reconstruct the climate of the Holocene from peat bog stratigraphy. This temperature scale allowed reconstructions of the Holocene climate very similar to our current understanding by 1950 (figure 50 A, lower diagram).
Recently, the Bray (Hallstatt) Cycle was reviewed by analyzing the main findings of some of the most significant articles by researchers who have studied it.Bray’s glaciological and solar studies were reproduced in 1973 by Denton and Karlén who did a more detailed study of world glacial advances and came up with essentially the same periodicity, 2500 years (figure 51 A). Throughout this work both the climatic and solar cycle are referred to as the Bray cycle, and the lows of the cycle, associated with enhanced C production, and climatic changes manifested by cooling, glacier advances, increased drift ice in the North Atlantic, and atmospheric, oceanic, and precipitation changes, are numbered from more recent backwards as B1, B2, …, with B1 the Little Ice Age. Dark grey trace, reconstruction of time coefficient by singular spectrum analysis of detrended and normalized alkenone based SST variance, from a NW Africa marine sediment core, as a proxy for AO/NAO oscillation. The AO often shares phase with the NAO, that reflects differences in the strength of two pressure centers in the North Atlantic: the low pressure near Iceland, and the high pressure over the Azores. The authors show evidence that the increased salinity, temperature, and water stratification, at times of abrupt climate change, are due to an increase in the Atlantic inflow of warmer saline subtropical gyre waters at the expense of the fresher and colder subpolar gyre waters. Holocene Ireland hydrology has been reconstructed from oaks and pines collected from bogs. Holocene variations in subtropical Atlantic SST from marine sediment core 658C. Ice-rafted debris stack (inverted) from four North Atlantic sediment cores. (2013) reconstruction of intermediate water temperatures at the equatorial Indo-Pacific Warm Pool, the warmest oceanic region in the world.By then Hans Suess had determined the short-term fluctuations in C levels for the past 7000 years from tree rings. Synthesis of Holocene worldwide glacier fluctuations showing three broad intervals of glacier expansion within the last 6000 years and a fourth one recognized in Scandinavia. The atmospheric 2400-year climate cycle The next great advance in the characterization of the 2400-year climatic cycle came from the study of ice cores. Fluctuations in the strength of these pressure centers alter the alignment of the jet stream affecting temperature and precipitation distribution. They interpret it as a negative feedback from the subpolar gyre, that stabilized the AMOC, at times of freshwater inputs, particularly during the early Holocene when the ice sheets were still melting rapidly, and at the 8.2 kyr event when the outbreak of proglacial Lake Agassiz took place (Thornalley et al., 2009; figure 53 b). Irish bog-grown oaks (Quercus spp.) and pines (Pinus sylvestris L.) frequency (inverted scale) during the Holocene as evidence of changes in moisture delivery to Ireland. These trees, accurately dated through dendrochronology (oaks) and carbon-dating (pines), provide a record of dry conditions when the decreased water table levels allowed the colonization of these marginal environments by trees (Turney et al., 2005). The record documents a well-known shift in African monsoonal climate at 5.5 kyr, when changes in the earth’s orbit displaced the African monsoon southward, bringing much drier and warmer conditions to subtropical Africa and ending the African Humid Period. It is proposed that the increase in iceberg activity in the North Atlantic is tied to the increase in cold water advection from the Arctic and Nordic seas. Their reconstruction displays a very similar profile to the global reconstruction of Marcott et al.This is when the north polar vortex expands and meridional circulation increases, and thus represents an increase in cold and windy conditions. The evidence indicates a 2400-year periodic variation in SST and upwelling intensity off NW Africa that is associated with a climatic cycle in oceanic circulation that reflects periodic NAO conditions. While drift ice has been increasing in the past 6,000 years of Neoglacial conditions off Northern Iceland, the detrended data supports the existence of a 2400-year climatic periodicity. A high-resolution record of the strength of the Asian monsoon was obtained from oxygen isotopic analysis of stalagmite “DA” in Dongge Cave (China; Wang et al., 2005). Earth’s axis obliquity is shown to display a similar trend to Holocene temperatures. Holocene reconstruction of intermediate-water temperatures at 500 m depth from a suite of sediment cores in the Makassar Strait and Flores Sea in Indonesia, at the Indo-Pacific Warm Pool. A more complete analysis of SST temperatures in the tropical oceans and the North Atlantic region, the Mediterranean, and Red Sea, was performed by Rimbu et al. The principal mode of variability reflects Milankovitch forcing, delayed in the case of the North Atlantic by the melting of the ice sheets. The Bond record of drift-ice petrological deposition in the North Atlantic is also generally considered to correlate to colder conditions in the North Atlantic region that favor more frequent southward moving icebergs (Bond et al., 2001).The periodicity found by Mayewski and colleagues (O’Brien et al., 1995) in GISP2 salts is close to 2600 years (figure 52 b). The lows of this NAO cycle are characterized by NAO negative dominant conditions that produce northern hemisphere cooling and precipitation changes. (2004), have argued that during the Holocene, the AO/NAO atmospheric circulation was the dominant climate mode at millennial time scales. Periods of high drift ice coincide with the lows of the Bray cycle (Andrews, 2009; figure 53 c). The record supports episodes of monsoon weakness (dryness) at every one of the Bray lows, most of them highlighted by the authors of the work (figure 54 f). Temperatures expressed as anomaly relative to the temperature at 1850-1880 CE. The secondary mode of variability (principal temporal component from the second empirical orthogonal function) shows in both regions as a ~ 2300-year cycle that agrees well with the Bray cycle (Rimbu et al., 2004; figure 56). Most, if not all, Bond events have been linked to cooling and abrupt climate change outside the North Atlantic area.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.
In part B, we will go over the arguments that the ~2400-year cycle of the production of cosmogenic isotopes Be represents a cycle in solar activity.
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.
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.
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).