Dynamical contribution to sea surface salinity variations in the eastern Gulf of Guinea based on numerical modelling

Type Article
Date 2014-12
Language English
Author(s) Berger Henrick1, 2, 3, Treguier Anne-Marie1, 3, Perenne Nicolas2, Talandier Claude1, 3
Affiliation(s) 1 : CNRS Ifremer UBO IRD, Lab Phys Oceans, Plouzane, France.
2 : Actimar, Brest, France.
3 : Ifremer, France
Source Climate Dynamics (0930-7575) (Springer), 2014-12 , Vol. 43 , N. 11 , P. 3105-3122
DOI 10.1007/s00382-014-2195-4
WOS© Times Cited 15
Note This paper is a contribution to the special issue on tropical Atlantic variability and coupled model climate biases that have been the focus of the recently completed Tropical Atlantic Climate Experiment (TACE), an international CLIVAR program (http://www.clivar.org/organization/atlantic/tace). This special issue is coordinated by William Johns, Peter Brandt, and Ping Chang, representatives of the TACE Observations and TACE Modeling and Synthesis working groups.
Keyword(s) Gulf of Guinea, Salinity, Modelling, Congo, Bight of Biafra, Mixed layer budget
Abstract In this study, we analyse the seasonal variability of the sea surface salinity (SSS) for two coastal regions of the Gulf of Guinea from 1995 to 2006 using a high resolution model (1/12°) embedded in a Tropical Atlantic (1/4°) model. Compared with observations and climatologies, our model demonstrates a good capability to reproduce the seasonal and spatial variations of the SSS and mixed layer depth. Sensitivity experiments are carried out to assess the respective impacts of precipitations and river discharge on the spatial structure and seasonal variations of the SSS in the eastern part of the Gulf of Guinea. In the Bight of Biafra, both precipitations and river runoffs are necessary to observe permanent low SSS values but the river discharge has the strongest impact on the seasonal variations of the SSS. South of the equator, the Congo river discharge alone is sufficient to explain most of the SSS structure and its seasonal variability. However, mixed layer budgets for salinity reveal the necessity to take into account the horizontal and vertical dynamics to explain the seasonal evolution of the salinity in the mixed layer. Indeed evaporation, precipitations and runoffs represent a relatively small contribution to the budgets locally at intraseasonal to seasonal time scales. Horizontal advection always contribute to spread the low salinity coastal waters offshore and thus decrease the salinity in the eastern Gulf of Guinea. For the Bight of Biafra and the Congo plume region, the strong seasonal increase of the SSS observed from May/June to August/September, when the trade winds intensify, results from a decreasing offshore spread of freshwater associated with an intensification of the salt input from the subsurface. In the Congo plume region, the subsurface salt comes mainly from advection due to a strong upwelling but for the Bight of Biafra, entrainment and vertical mixing also play a role. The seasonal evolution of horizontal advection in the Bight of Biafra is mainly driven by eddy correlations between salinity and velocities, but it is not the case in the Congo plume.
Full Text
File Pages Size Access
18 6 MB Access on demand
Author's final draft 41 962 KB Open access
Top of the page