Astronomical forcing of sub-Milankovitch climate oscillations during the late Quaternary

Abstract

A climate signal of ~1500-yr quasi-periodicity (e.g., Bond events) has been found from the Arctic to Antarctica, in palaeoclimatic data derived from a range of environmental proxy records. Solar and lunar forcing have individually been suggested as the cause of this millennial-scale signal, although some contend that it is little more than stochastic resonance within the climate system. Also debated is whether this climate signal is forced by the ocean-atmosphere dynamics of the North Atlantic or the tropical Pacific, as well as relevant climatic teleconnections. The cause of this cycle is elusive as no known solar cycle of this length exists, whilst forcing due to lunar gravitation has been dismissed as being too weak.The most likely cause of any periodic climate signal is an astronomical one, as demonstrated in Milankovitch cycles. This thesis explores a potential astronomical cause of millennial-and centennial-scale periodicities and variability, based on a combination of solar and lunar forcing.Conceptual and trigonometric models, physical models of insolation, solar irradiance, and gravitation, and astronomical data were used in this exploration. Identified as a possible cause of the ~1500-yr climate cycle is precession. Precession changes the timing of Earth's seasons relative to our calendar and external reference points, such as the fixed stars and the closest point in Earth's orbit to the Sun