15.12.2014: FB1-Seminar

Charlotte Mielke (M. A.), Institute of Oceanography, University of Hamburg: Seasonal to decadal variability of the Atlantic Deep Western Boundary Current and its relation to the overturning circulation


11:00 h, Hörsaal, Düsternbrooker Weg 20



The Deep Western Boundary Current (DWBC) is a major part of the southward branch of the Atlantic meridional overturning circulation (MOC). Here, I will discuss the seasonal to decadal variability of the DWBC in the North Atlantic and its relation to the overturning circulation, as simulated in a high-resolution ocean general circulation model. The DWBC is defined in density classes after a comparison of temperature and salinity data from observations and the model, and the modeled DWBC’s mean, structure and type of variability are consistent with the available observations. We find that the DWBC's variability is modulated by wind stress curl variations at the western boundary on both seasonal and decadal timescales, and particularly in the subtropical gyre. On seasonal timescales, this implies that the DWBC has a prominent seasonal cycle, which is coherent throughout the subtropical gyre. The MOC cannot be directly inferred from the DWBC on either seasonal or decadal timescales. On seasonal timescales, this is due to an anticorrelation of eastern and western basin deep transports. On decadal timescales, the relation between MOC and DWBC depends on the phasing of the wind stress between western boundary and basin interior: MOC and DWBC variabiliy agree only if the wind stress curl anomalies between the basin interior and the western boundary agree. This results in a non-stationary relation between MOC and DWBC. However, it might be feasible to combine DWBC estimates, which could be inferred from the readily available wind stress, with Argo data for a better picture of the full MOC variability in the subtropical North Atlantic.



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