Holocene bond cycles: Real or imaginary?

Abstract

During the Holocene (last 12,000 years) nine cold relapses were observed mainly in the North Atlantic Ocean area and its surroundings. Based on the pioneering studies by Bond et al. (1997, 2001) these events are called Bond Cycles and thought to be the Holocene equivalents of the Pleistocene Dansgaard-Oeschger cycles. The first event was the Younger Dryas (~12,000 BP; Broecker 2006), the last one was the Little Ice Age (AD 1350-1860; Grove 1988). A number of trigger mechanisms is discussed (see Table 1), but a theory for the Bond Cycles does not exist. Based on spectral analyses of both, forcing factors and climatological time series, we argue that one single process did likely not cause the Holocene cooling events. It is conceivable that the early Holocene coolings were triggered by meltwater pulses. However, the late Holocene events (e.g., the Little Ice Age) were rather caused by a combination of different trigger mechanisms. In every case it has to be taken in mind that natural variability was also playing a decisive role.