Seasonal Variability of the Mauritania Current and Hydrography at 18°N

• Published in: Journal of Geophysical Research: Oceans
• Main Authors: Klenz, Thilo, Dengler, Marcus, Brandt, Peter
• Format: Article in Journal/Newspaper
• Language: English
• Published: AGU (American Geophysical Union) 2018
• Subjects: Curl; North Atlantic
• Online Access: https://oceanrep.geomar.de/id/eprint/44753/; https://oceanrep.geomar.de/id/eprint/44753/1/2018_Klenz_etal_Circ_Hydro_var_off_Mauritania.pdf; https://doi.org/10.1029/2018JC014264

Extensive field campaigns in the Mauritanian upwelling region between 2005 and 2016 provide the database for analyzing the seasonal variability of the eastern boundary circulation (EBC) and associated water mass distribution at 18°N. The data set includes shipboard upper ocean current, hydrographic, and oxygen measurements from nine research cruises conducted during upwelling (December to April) and relaxation (May to July) seasons. During the upwelling season, the EBC closely resembles a classical eastern boundary current regime, with a poleward undercurrent flowing beneath an equatorward coastal jet. In contrast, elevated poleward flow exceeding 30 cm/s and extending from the surface down to 250-m depth is observed during the relaxation season. The pronounced seasonal variability of the across-shore structure of the EBC can be related to local wind forcing and is in general agreement with Sverdrup balance. The EBC transport is correlated to the wind stress curl leading the transport by 7 days. The short lead time suggests a fast response of locally forced waves adjusting the EBC to wind forcing. The seasonal and vertical water mass distribution is presented based on hydrographic observations. The meridional oxygen distribution and corresponding water mass partitioning into South and North Atlantic Central Water masses reveal a possible northerly ventilation pathway in the deeper layers of the central water stratum. Our results suggest that the poleward surface flow and the poleward undercurrent both are a consequence of the cyclonic wind stress curl forcing and thus propose to name it the Mauritania Current.