Turbulente Vermischungsprozesse und Zirkulation im Auftriebsgebiet vor Nordwestafrika

Schafstall, Jens (2010) Turbulente Vermischungsprozesse und Zirkulation im Auftriebsgebiet vor Nordwestafrika (Doctoral thesis/PhD), Christian-Albrechts-Universität, Kiel, Germany, 205 pp

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Abstract

The upwelling region off Mauritania is an important region for the global ecosystem as it is one of the most productive areas of the world ocean. Additionally it is an oceanic source for several climate relevant trace gasses such as CO2 and N2O. This study determines physical and biogeochemical processes from microstructure, CTD and ADCP measurements taken on five ship surveys during the period 2005-2008. The main focus of this study is to identify turbulent mixing processes and to quantify their importance for the upwelling region off Mauritania. Therefore magnitude and spatial distribution of vertical diffusivities has been determined from energy dissipation rates. The turbulence measurements taken from these surveys show that the mixing is greatest close to the shelf break. The observed mean dissipation rates inshore of the 500\,m isobath (away from the surface) is 5 × 10-8 W kg. The resulting mean diffusion coefficient of Kρ = 12 × 10-4 m2 s-1 is more than one magnitude higher compared to the values found at greater distances from the coast. This increased mixing is responsible for an increased exchange of heat, climate relevant trace gases and nutrients between the surface layer and the deeper ocean. Many processes are responsible for the increased mixing dominated by the interaction between internal tide and topography. The presented observations also show high variabilities, both spatial and temporal, in the mixing rates of the upper ocean. Additionally, studies of the circulation show a modified surface circulation in comparison to previous studies. A southward continuation of the Canary Current on the shelf was not observed. The existence of an easterly boundary current, also known as Upwelling Undercurrent (UUC), could be confirmed with a mean transport of 1\,Sv. It describes the main supply of the nutrient rich South Atlantic Central Water for the coastal upwelling region. Generally the circulation is dominated by eddies. The observed intensified inshore northwards and offshore southwards current tendency between the African coast and the Cape Verde Islands give the confirmation for a cyclonical circulation cell.

Document Type: Thesis (Doctoral thesis/PhD)
Thesis Advisors: Dengler, Marcus and Böning, Claus W.
Keywords: Diapyknische Vermischung, turbulente Flüsse, Auftrieb, Mauretanien, interne Gezeiten diapycnal mixing, turbulent fluxes, upwelling, Mauritania, internal tides, Poseidon, POS348, POS320/1
Research affiliation: OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-TM Theory and Modeling
OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-PO Physical Oceanography
Projects: SOPRAN
Expeditions/Models:
Date Deposited: 07 Feb 2011 10:19
Last Modified: 17 Sep 2015 10:28
URI: http://eprints.uni-kiel.de/id/eprint/10956

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