| Summary: | This thesis revolves about the timing of precession-related variations in the boreal summer monsoon and the impact of North Atlantic cold events and the El Nino Southern Oscillation on this timing. Transient climate modelling experiments indicate that the intensity of the Northern Hemisphere summer monsoon varies in-phase with peak summer insolation on orbital timescales. In contrast, marine proxy records suggest a lagged response of the monsoon maximum of a few thousand years behind the insolation forcing. This phase lag is particularly large in records from the Arabian Sea. In this thesis it is shown that a ~3,000 year lag of the African monsoon, which is derived from the Mediterranean sapropel record, is consistent not only with the marine isotope chronology but also with radiometrically dated speleothem records from the Mediterranean region and China, and with the atmospheric methane record from Antarctica. It is suggested that North Atlantic cold events systematically delay the onset of strong monsoon intensity. This explanation implies a distinct precession forcing of North Atlantic ice rafting and could also explain a non-stationary behaviour of the African Monsoon over the past 3 million years. An orbital-tuning independent chronology for a North Atlantic foraminiferal benthic oxygen isotope stacked record over the last two glacial cycles supports this theory and suggests that North Atlantic ice surge events respond to an external, climatic triggering mechanism, which is distinct from the process that causes the waxing and waning of the large ice sheets. A comparison with a climate modelling study of the El Nino Southern Oscillation on orbital time scales shows that the ice surge events coincide with periods of frequent El Nino events. Warming of northern North America during El Nino events could have led to rapid disintegrations of fringing ice shelves induced by meltwater infilling of surface crevasses, thereby triggering large-scale ice surge events. It is moreover suggested, that the long phase-lag ...
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