Investigating the seasonal and interannual variability of the poleward undercurrent in the northern Benguela system

• Main Author: Yates, Sarah Elizabeth
• Other Authors: Rouault, Mathieu, Veitch, Jennifer Anne
• Format: Master Thesis
• Language: English
• Published: University of Cape Town 2012
• Subjects: Austral; Curl; Dome The; Orca
• Online Access: http://hdl.handle.net/11427/9808; https://open.uct.ac.za/bitstream/11427/9808/1/thesis_sci_2012_yates_se.pdf

Includes bibliographical references. The Benguela Current System is unique as both the equatorward and poleward boundaries are warm water current systems. Between 15° S – 37° S the surface currents are generally equatorwards, with 7 distinct upwelling cells, narrow equatorward shelf-edge jets and a poleward undercurrent along the continental slope. Model data was used to determine the seasonal and interannual variability of the poleward undercurrent (PUC) in the northern Benguela system. The PUC is the southward extension of the Angolan Current that carries low oxygen water (LOW) originating from the Angola Dome. The LOW flows from the Angolan region southwards in the Benguela system. The focus of the study is on the PUC associated with the Sverdrup relation. The model ORCA-025 was used to reproduce zonal transects from 17° S to 30° S to determine the changing characteristics of the PUC with latitude as well as seasonal and interannual variability of this current. The PUC is faster moving in the north (~17° S) and decreases in velocity moving south (~30° S). The PUC is shallower in the north increasing in depth in the south. The model data shows the velocity of the PUC has a seasonal cycle that is faster in the austral summer and autumn and weakens in the winter. The transport of the PUC is amplified during austral winter and spring, which is consistent with the increased negative wind stress curl during those seasons. The wind stress curl in the region exhibits a strong connection with the transport of the PUC via the Sverdrup relation. The PUC exhibits interannual variability when comparing to the Benguela Niño events, but does not show a correlation with El Niño Southern Oscillation.