The origin of the 1500-year climate cycles in Holocene North-Atlantic records

Abstract

Abstract. Since the first suggestion of 1500-year cycles in the advance and retreat of glaciers (Denton and Karlen, 1973), many studies have uncovered evidence of repeated climate oscillations of 2500, 1500, and 1000 years. During last glacial period, natural climate cycles of 1500 years appear to be persistent (Bond and Lotti, 1995) and remarkably regular (Mayewski et al., 1997; Rahmstorf, 2003), yet the origin of this pacing during the Holocene remains a mystery (Rahmstorf, 2003), making it one of the outstanding puzzles of climate variability. Solar variability is often considered likely to be responsible for such cyclicities, but the evidence for solar forcing is difficult to evaluate within available data series due to the shortcomings of conventional time-series analyses. However, the wavelets analysis method is appropriate when considering non-stationary variability. Here we show by the use of wavelets analysis that it is possible to distinguish solar forcing of 1000- and 2500- year oscillations from oceanic forcing of 1500-year cycles. Using this method, the relative contribution of solar-related and ocean-related climate influences can be distinguished throughout the 10 000 yr Holocene intervals since the last ice age. These results reveal that the 1500-year climate cycles are linked with the oceanic circulation and not with variations in solar output as previously argued (Bond et al., 2001). In this light, previously studied marine sediment (Bianchi and McCave, 1999; Chapman and Shackleton, 2000; Giraudeau et al., 2000), ice core (O'Brien et al., 1995; Vonmoos et al., 2006) and dust records (Jackson et al., 2005) can be seen to contain the evidence of combined forcing mechanisms, whose relative influences varied during the course of the Holocene. Circum-Atlantic climate records cannot be explained exclusively by solar forcing, but require changes in ocean circulation, as suggested previously (Broecker et al., 2001; McManus et al., 1999).

South Atlantic island record reveals a South Atlantic response to the 8.2 kyr event

“…In the South Atlantic, however, only the effect of the weaker circulation is registered. There may also have been more general climatic effects of the 8.2 ka event and its assumed massive fresh-water discharge: the MOC may have been influenced by different processes such as dynamics in the amount of fresh-water and sea-ice/ice bergs, atmospheric circulation variability and also internal oceanic forcing (Debret et al, 2007), although the end product in the South Atlantic was the same as during later perturbations. Another or complementary explanation may be that the 8.2 kyr event was an anomaly with a different triggering mechanism, as compared to most of the other Holocene perturbations, for which solar forcing and related feedbacks have been invoked as major players (Bond et al, 2001).…”

Conceptual model for millennial climate variability: a possible combined solar-thermohaline circulation origin for the ~1,500-year cycle

“…2f) of a reconstruction based on these four components (Fig.2e) shows that they have periods of ~6500-yr, ~2500-yr, ~950-yr and ~550-yr. Previous studies associated the last three periodicities with solar forcing (O'Brien et al 1995, Stuiver et al 1995, Mayewski et al 1997, Debret 2007.…”

“…Let assume that the solar forcing is transferred through the atmosphere without any significant change of his form and then reaches the ocean surface, where is rectified by the THC. For example, in For the ocean however, both, the fundamental and derived modes can be identified in the spectrum (Debret et al 2007). Consequently, coherent ocean atmosphere variations could only be associated with the fundamental modes, as only these are present in the spectra of both climate components.…”

South Tropical Atlantic anti-phase response to Holocene Bond Events

“…Significant correlations obtained between the stacked marine records and cosmogenic radionuclides, whose activity concentrations are thought to be modulated by the solar-terrestrial geomagnetic activity, suggested originally that changes in solar activity could be the major forcing agent of these events (Bond et al, 2001). A later study conducted on the cyclicity pattern of the time series using spectral wavelet analysis was able to distinguish between the solar forcing and the oceanic forcing to show that the 1500-year cycle was basically an ocean-related climate phenomenon (Debret et al, 2007).…”