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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.
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.
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.
I now start reviewing the millennial climate cycles that abruptly impact the slowly changing Holocene climate.
He also constructed an index for postglacial major ice re-advances from glaciers all over the world. Holocene subdivisions and glacier fluctuations in the European Alps showing the complex pattern of advances and retreats that do not always correspond between Austrian and Swiss Alps. Since then glaciologists have reconstructed Holocene glacier movements from hundreds of glaciers all over the planet, and glacier variability has become more complex (figure 51 B). Light grey trace, inferred NAO circulation pattern from the principal component analysis of redox parameters (Ca/Ti and Mn/Fe ratios) from a Greenland lake sediment record. The changes in polar circulation and wind strength are suggestive of the Arctic Oscillation/North Atlantic Oscillation (AO/NAO). 25-year average sedimentary varve thickness record at a marine core in the Santa Barbara Basin as a proxy for annual rainfall in the area. In addition, B3 and B4 lows are also characterized by significant episodes of slackwater floods or paleofloods, that record periods of increased flood frequency related to Holocene climatic variability (Thorndycraft & Benito, 2006; figure 54 c).
He compared these two observations and found a high degree of correlation, and good agreement with Icelandic sea-ice, and C production variations. The uncalibrated radiocarbon dates scale is shown together with the corresponding calibrated scale in calendar years BP. Today we still recognize the major global advances that define the 2400-year cycle (Mayewski et al., 2004; figure 47), but there is hardly a century, especially during the Neoglacial, when glaciers were not advancing somewhere. The AO reflects the state of the atmospheric circulation over the Arctic, through a positive phase, featuring below average geopotential heights, and a negative phase in which the opposite is true. Thin line represents lowpass filter to emphasize millennial scale fluctuations. They are fine-grained sediments produced by large magnitude floods, preserved in valley side rock shelters in bedrock gorge reaches.
Such periods might see a reduction in the northward flux of warm near surface waters in the North Atlantic to maintain mass balance (that could be the cause of the NADW reduction), and would result also in the cooling of North Atlantic high latitudes. Holocene North Atlantic and Arctic oceanic currents changes. Benthic C-rich North Atlantic deepwater (NADW) contribution. Warm saline sub-thermocline conditions took place at 0.3, 1.0, 2.7 and 5.0 kyr ago, coinciding with known climatic perturbations in the North Atlantic region. It is clear however that the atmospheric reorganizations that have accompanied the 2400-year Bray climate cycle are reflected in precipitation changes in several locations. Winter precipitation reconstruction at Bjørnbreen glacier in Jotunheimen, southern Norway. This has had the result that whatever is not prominently displayed in polar ice cores is considered unreal.
The lows in the Bray cycle (blue bars), correspond to periods of reduced NADW contribution. For decades Michael Magny has been studying Holocene mid-European lake level fluctuations and their impact on prehistoric human settlements (Magny et al., 2004). Precipitation is reconstructed from the known relation between variations in the equilibrium line altitude (ELA, the boundary between the ablation and accumulation areas) and mean July temperature variations reconstructed from palynological data. Another complicating factor is that the Bray cycle is not the only cause of climate change during the Holocene and thus proxies are full of signals whose origin is often difficult to ascertain, creating much confusion among researchers that results in contradictory reports. Conclusions 1) A 2600-year climate cycle was first proposed in the late 1960s by Roger Bray based on vegetation transitions and major glacier re-advances, and linked to solar activity.