The Earth’s system has witnessed abrupt climate changes throughout its history. It is widely understood that the pacing of the large-scale glacial-interglacial cycles (tens to hundreds of thousands of years) of the Pleistocene Epoch (~2 million years) are not simply the result of changes in the incoming solar insolation (orbital forcing) alone and as such, this large-scale variability calls upon feedback mechanisms in order to explain the magnitude of such changes. This thesis investigates the shorter millennial scale events (thousands of years) and their role in determining the magnitude of glacial-interglacial cyclicity. In order to investigate this, in this thesis three sediment cores will be used, ODP Site 1063 and ODP Site 983 in the North Atlantic and ODP Site 1089 in the South Atlantic. Datasets from these core locations provide insights in to the magnitude and duration of millennial scale variability across terminations 1, 2 and 5. The two regions studied here (North and South Atlantic) are important regions for recording changes in ocean circulation, specifically the Atlantic Meridional Overturning Circulation. Upper water column reconstructions from the North and South Atlantic based on both planktonic foraminiferal faunal assemblage reconstructions and paired δ18O and Mg/Ca analysis provide insight into the abrupt changes in ocean dynamics across glacial cycles. Additionally with the use of neodymium isotope analysis, changes in the deep North Atlantic, likely the result of changes in the Meridional Overturning Circulation, have also been identified. Importantly, this data provides evidence that the timing of the resumption of the Atlantic Meridional Overturning Circulation following glacial conditions is integral in determining the extent of deglacial CO2 release. The work presented here suggests that rather than it being the magnitude of millennial scale events determining the magnitude of glacial-interglacial climate variability, instead, it is the relative timing of the millennial scale events that plays a role in controlling the magnitude of glacial-interglacial cyclicity.