Sedimentation of two contrasting continental shelf environments have been investigated. Numerical ocean models were used to assess the oceanic processes which dominate Torres Strait and the Gulf of Papua, Northern Australia, and then the ocean cavity beneath the Amery Ice Shelf, East Antarctica. A three-dimensional, numerical ocean model (MECO) was applied to the Torres Strait/Gulf of Papua region at 0:05 degree resolution. Validation of the model was carried out against current meter and sea-level observational data. Dispersal pathways of sediments, derived from the Fly River, Papua New Guinea, and from a resuspension event on the Northern Great Barrier Reef, into Torres Strait were investigated via the introduction of passive tracers into the model. Sediment input into Torres Strait is found to be greater during the Trade season by approximately 10%. Wave data was also obtained, and together with hydrodynamic model output, sediment mobility due to currents, waves and wave-current interactions was considered for both the Trade and Monsoon seasons. Sediment mobility in the Gulf of Papua is dominated by wave motion, whereas Torres Strait is a mixed environment of waves and tidal currents. Two numerical ocean models were applied to the Amery Ice Shelf/Prydz Bay region to determine the oceanic processes responsible for the distribution of marine sediments beneath the ice shelf. The MECO model was used to determine the sub-ice-shelf tidal environment. A modified version of the Princeton Ocean Model was applied to determine the baroclinic circulation beneath the ice shelf. Validation of the tides within each model was carried out against available current meter data and sea-level records. Spring tidal currents (up to 10-15 cm/sec) are approximately two to three times the magnitude of the maximum density-driven flows (5-6 cm/sec). However, the influence of tides on the mean sub-ice-shelf melt-rates, and the mean density-driven currents, was shown to be insignificant. Thermohaline flows dominate the predicted mean sub-ice-shelf circulation and indicate a depth-integrated mass transport of 0.2 Sv, of the same order of magnitude as the overturning circulation. Combined tidal and density-driven maximum bottom currents are too small (up to 16 cm/sec)to remobilise sediments. Sediments were collected from beneath, and directly in front of, the Amery Ice Shelf. The observed sub-ice-shelf surface sediment distribution supports the dispersal pathways of diatoms beneath the ice shelf, predicted using the baroclinic model. The sediment core collected from beneath the eastern side of the Amery Ice Shelf in a region of predicted inflow (site AM02) contains a Holocene-age, siliceous mud and ooze layer, providing evidence that landward transport of hemipelagic sediments occurs beneath the Amery Ice Shelf. An imposed increase in the ocean temperature in the baroclinic model predicts increased melt rates at the ice-ocean interface, and a strengthened sub-ice-shelf circulation. An increase in sea-ice associated diatom deposition during the mid-Holocene is interpreted from AM02 down-core changes in the diatom assemblage. Results of the hydrodynamic model suggest the diatom signal may be a response to increased temperatures which may have occurred during the mid-Holocene climatic optimum. The dominant processes acting in the two continental shelf environments are able to be distinguished from each other allowing separate classification; the Torres Strait/Gulf of Papua environment is classified as a wave- and tide-dominated shelf, and the Prydz Bay/sub-Amery Ice Shelf environment is classified as a density-driven current-dominated continental shelf, and is probably typical of Antarctic shelf environments.

Coupled atmosphere-ocean general circulation models are the simplest models which are capable of simulating both the variability which occurs within each component of the climate system, and the variability which arises from the interactions between them. Only recently has it become computationally feasible to use coupled general circulation models to study climate variability and change on timescales of O(104) years and longer. Flux adjustments are often employed to maintain a control climate that is both stable and realistic; however, the magnitude of the adjustments represents a source of concern. This study employs the CSIRO Mk3L climate system model, a low-resolution coupled atmosphere-sea ice-ocean general circulation model. The atmospheric and oceanic components are spun up independently; the resulting atmospheric simulation is realistic, while the deep ocean is too cold, too fresh and too buoyant. The spin-up runs provide the initial conditions for the coupled model, which is used to conduct a 1400-year control simulation for pre-industrial conditions. After some initial adjustment, the simulated climate experiences minimal drift. The dominant mode of internal variability is found to exhibit the same spatial structure and correlations as the observed El Ni˜no-Southern Oscillation phenomenon. The ability of Mk3L to simulate the climate of the mid-Holocene is evaluated. It correctly simulates increased summer temperatures at northern mid-latitudes, and cooling in the tropics. However, it is unable to capture some of the regional-scale features of the mid-Holocene climate, with the precipitation over northern Africa being deficient. The model simulates a 13% reduction in the strength of El Ni˜no, a much smaller decrease than that implied by the palaeoclimate record. A 1400-year transient simulation is then conducted, in which the atmospheric CO2 concentration is stabilised at three times the pre-industrial value. The transient simulation exhibits a reduction in the rate of North Atlantic Deep Water formation, followed by its gradual recovery, and a cessation of Antarctic Bottom Water formation. The global-mean surface air temperature warms 2.7◦C upon a trebling of CO2, and 5.3◦C by the end of the simulation. A number of modifications to the spin-up procedure for the ocean model are evaluated. A phase shift in the prescribed sea surface temperatures and salinities is found to reduce the phase lag between the model and observations, and to lead to a reduction in the magnitude of the diagnosed flux adjustments. When this spin-up run is used to initialise the coupled model, the reduced flux adjustments are found to have negligible impact upon the nature of the internal variability. While the flux adjustments are not found to have any direct influence upon the response of the model to external forcing, they are found to have an indirect influence via their effect upon the rate of drift within the control simulation. An iterative spin-up technique is also developed, whereby the response of the ocean model is used to derive a set of effective surface tracers. These result in a much more realistic vertical density profile within the ocean. The coupled model exhibits slightly increased internal variability, with reduced convection within the ocean. There is a slightly greater surface warming in response to an increase in the atmospheric CO2 concentration, with the reduced convection resulting in slower penetration of the surface warming to depth.