Eisbrenner, Ezra (2017) On the influence of bottom topography on the large scale ocean circulation. (Master thesis), Christian-Albrechts-Universität Kiel, Kiel, Germany, 86 pp.

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Abstract

The effects of variable bottom topography are investigated on the basis of idealised model simulations. The simulations feature idealised bottom topographies with increasing complexity, starting with a single hemisphere flatbottomed basin and evolving to a full idealised Atlantic Ocean with continental margins, a mid oceanic ridge, a Drake Passage opening to create an Antarctic Circumpolar Current and two Nordic Seas openings to allow for dense overflows into the North Atlantic basin. The goal of the study is to expand the work of Holland (1973) concerning the impact of sloping bottom topography along the western boundary on the orizontal transport streamfunction in order to show the effects of other bottom topography features and the response of the transport streamfunction when multiple bottom topography features are combined. The diagnostics focus on the calculation of the horizontal streamfunction and the meridional overturning. The results highlight the role of variable bottom topography for the horizontal streamfunction and the crucial role of the meridional overturning. It is shown that the depth of the meridional overturning dictates whether the horizontal streamfunction is amplified or weakened by the underlying bottom topography. Furthermore, it is shown that for increasingly complex bottom topographies the horizontal streamfunction converges towards the classical gyre system, represented by the flat-bottomed Sverdrup transport. However, the variable bottom topography tends to amplify the gyres with respect to the afore mentioned Sverdrup transport, i.e. leading to a desirable increase of the transport of the subtropical western boundary current. This study provides new visualisations of the effects of varying bottom topography and provides an introduction to the necessary components of the bottom topography to realistically represent the Atlantic Ocean circulation.

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