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Surface-ocean changes in the North Atlantic are closely linked to modes of atmospheric variability, the most dominant of which is the North Atlantic Oscillation. The aims of this study were to investigate high-frequency climate variability in the North Atlantic through the use of high-resolution fossil marine diatom records spanning the last 2000 years. Core sites in the Muros Ria, in northwest Spain, and on the western Norwegian Margin were selected for their high sedimentation rates and their proximity to the NAO pressure centres. 'he diatom record's high resolution permitted comparison to nearby instrumental time series where significant relationships were found with precipitation, the NAO Index and extended NAO Index reconstructions.

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The topic of this thesis is the wave dynamics of surface quasi-geostrophic (surface QC) flows. The surface QG equation set is a simple model of large-scale atmospheric and oceanic flows near horizontal boundaries such as low-level atmospheric weather systems, upper-ocean currents and also undulations of the tropopause. Recent renewed interest in the model has been prompted by the realisation that it is consistent with several previously unexplained phenomena such as the observed energy spectra of atmospheric motions near the tropopause, as well as the dynamical structure of upper ocean eddies. The approach taken here is to study the system from a theoretical viewpoint in order to understand some of the general observed and simulated features of the dynamics. As well as this analytic study a numerical code is used to verify and illustrate the theoretical results. There are three main directions of research. One is to understand a peculiar feature of surface QC simulations - not exhibited by other simple atmospheric models - whereby small scale instabilities very readily develop on filamentary vorticity structures. This instability is in fact a common feature of satellite water vapour imagery which, in the extra-tropics, often shows high potential vorticity stratospheric intrusions (i.e., tropopause undulations) 'rolling-up' into upper-air mesoscale vortices. The linear dynamics of this instability is investigated with some remarkable results, such as the scaling behaviour of the vortices formed. Another part of the work has been to study the behaviour and stability of vortices in the surface QG system (such as those formed as a result of the filament instability). This, again, has taken the form of an analytic study backed-up by numerical results. Together with the first study, the results provide a fairly comprehensive picture of various features of surface-enhanced flows as well as abstract surface QG turbulence simulations. In the final chapter of the thesis we move away from pure surface QG dynamics to apply the theory developed for the study of surface QG vortices to a new simple analytic model of atmospheric baroclinic instability. Unlike previous similar models, this model has the advantage that the non-linear development of the instability is quite realistic and, further, appears to exhibit both major types of wave breaking commonly observed in the atmosphere. The linear theory is fully developed and the results of some numerical integrations presented.

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