They noticed a good correlation between the atmospheric maxima and clusters of three grand solar minima (GSM) of the Maunder- and Spörer-type patterns, with the most recent one taking place during the LIA (O’Brien et al., 1995; figure 52 c). Holocene North Atlantic and Arctic atmospheric changes. GISP2 polar circulation index, a time series of the dominant empirical orthogonal function, EOF1, of the major ions in the ice core, that provides a relative measure of the average size and intensity of polar atmospheric circulation. The oceanic 2400-year climate cycle Given the strong coupling between atmospheric and oceanic variability, it is not surprising that the ~ 2400-year climate cycle is prominently displayed by some oceanic current proxies, particularly in the North Atlantic. (2003) used an established deepwater proxy, the carbon-isotope composition of benthic foraminifera, to evaluate Holocene deepwater variability at a sediment core in the NE subpolar Atlantic. As is the case with the Bond series, there is variability in drift ice records, since some cold events do not belong to the Bray cycle. Most of the centennial and millennial variability in the Asian and Indian monsoons has traditionally been linked by multiple authors to solar variability (Wang et al., 2005; Neff et al., 2001). Global average temperature reconstruction from Marcott et al., 2013, using proxy published dates, and differencing average, with temperature anomaly rescaled as discussed here. The main disagreement is with B4 due to the 8.2 kyr event, that affected SST in the North Atlantic as early as 8.4 kyr BP, but seems to have had a delayed effect in the tropics around 8.1 kyr BP, possibly preempting the effect of B4 a few centuries later. The Bond record also reflects the 2400-year Bray cycle as the lows in the Bray cycle coincide with Bond events 0 (LIA), 2a, 4a, 5a, and 7 (figure 55 f).
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.
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.
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.