| Summary: | Glaciation/deglaciation is one of the most extreme and fundamental climatic events in Earth's history. The origin of the glacial-interglacial cycles has been explored for more than a century and the astronomical theory is now well established. However, the mechanism that links the astronomical forcing to the geological record in the Earth's climate system is poorly understood. In this thesis, aspects of the last glacial termination and the last glacial inception, are studied. First, the response of ocean's thermohaline circulation to changes in orbital geometry and atmospheric CO2 concentration in the last glacial termination is investigated using a coupled climate (atmosphere-ocean-sea ice) model. It is shown that the thermohaline circulation is affected by both orbital and CO2 forcing and the details of the mechanisms involved are explored. The climatic impact of changes in the thermohaline circulation is then investigated. It is revealed that the influence of changes in the thermohaline circulation on surface air temperature is concentrated in the North Atlantic and adjacent continents. It is also shown that this influence has its peak in winter rather than in summer. A dynamic ice sheet model is then globally and asynchronously coupled to the climate model. The relative importance of orbital and CO2 forcing in the mass balance of ice sheets is investigated using the coupled climate-ice sheet model. It is shown that CO2 forcing is of secondary importance to orbital forcing as the warming in eastern North America and Scandinavia due to CO2 forcing has its peak in winter, whereas that due to orbital forcing has its peak in summer. It is, nevertheless, concluded that the last glacial termination was initiated through increasing summer insolation and accelerated by a subsequent increase in atmospheric CO2 concentration. Second, the importance of subgrid topography in simulating the last glacial inception is investigated using the coupled climate model. The effects of subgrid elevation and subgrid ice-flow are ...
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