| Summary: | Tides propagate through the oceans as shallow water waves and are therefore sensitive to changes in water depth and areal extent of the ocean. In this thesis the impacts of climatologically driven sea-level changes and the resulting changes in ocean extent on the global tidal dynamics are investigated. The large global sea-level adjustments between the Last Glacial Maximum (LGM, 18,000-21,000 years BP) and the present are considered; the present day tidal changes are analysed and the impact of future collapses of the West Antarctic and Greenland Ice Sheets on the tides are investigated using a global tidal model. The 130 m glacio-eustatic sea-level drop during the LGM had a profound impact on the principal semi-diurnal tide, doubling global dissipation rates and resulting in 'megatides' in the North Atlantic region. It is shown that the magnitude of the Atlantic tides is sensitive to the grounding line location of the Antarctic Ice Sheet. Next, the impacts of the altered dissipation for LGM ocean mixing and the meridional overturning circulation (MOC) in the glacial ocean are explored using an intermediate complexity climate model. The importance of tidal mixing for the global ocean circulation is highlighted. Strong LGM tidal mixing could have provided a mechanism for sustaining a vigorous LGM MOC. During the deglacial period glacioeustatic sea-level rose rapidly and large adjustments of the global tides occurred into the early Holocene. In the late Holocene sea-level adjustments were small and tidal dynamics remained fairly constant over this period. Tide-gauge records covering the past decades show global changes in tidal amplitudes occurring in parallel with largescale sea-level changes which have been attributed to global warming. Using simulations forced with observed sea-level trends an attempt is made to reproduce the large-scale change patterns. For M2 the patterns agree well, but for K1 the model is unable to reproduce the trends, possibly due to the small magnitude of the K1 trends. A number of recent studies have highlighted an accelerated ice loss from the ice streams draining the West Antarctic and Greenland Ice Sheet together with widespread grounding line retreats in West Antarctica. It has been suggested that both ice sheets could undergo collapses under certain climate warming scenarios leading to increases in global mean sea-level of 5 m and 7 m, respectively. It is shown that the collapse of a polar ice sheet would lead to large changes in tidal dynamics and thus changes in sea-level variability. These changes have further reaching consequences for shelf-sea dynamics, ecosystems, and open ocean tidal mixing.
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