Ocean Dynamics

, Volume 64, Issue 12, pp 1783–1802 | Cite as

Modeled mixed-layer salinity balance in the Gulf of Guinea: seasonal and interannual variability

  • Casimir Y. Da-Allada
  • Yves du Penhoat
  • Julien Jouanno
  • Gael Alory
  • Norbert Mahouton Hounkonnou


A regional numerical simulation and observations were used to investigate the various processes controlling mixed-layer salinity balance on seasonal and interannual time scales in the Gulf of Guinea. Processes were quantified using a mixed-layer salt budget. Model results correctly reproduced the mean, phase, and amplitude of observed seasonal near-surface salinity. The results indicated that on seasonal time scales, the mixed-layer salinity balance differed from one region to another. The surface salinity seasonal cycle was characterized by strong salinization during May for coastal areas north and south of the equator. Model results suggested that vertical mixing controls the mixed-layer salinity increase at the equator during May, while both vertical mixing and vertical advection contribute to the salinity increase in coastal regions. We also determined that freshening from horizontal advection and freshwater flux tended to balance the salinization effects of vertical diffusion and vertical advection during the seasonal cycle. On interannual time scales, based on the mixed-layer salinity balance and sensitivity experiments, we determined that for the northern and equatorial Gulf of Guinea, changes in near-surface salinity were largely due to changes in precipitation and winds. For the southern Gulf of Guinea, only wind changes were determined to be important for explaining near-surface salinity changes.


Sea surface salinity Gulf of guinea Model Mixed-layer budget Seasonal variability Interannual variability 



SSS observations were obtained from the French SSS observation service and are available at We thank the CICESE for supercomputing facilities. We also thank the PIRATA Project and the TAO Project Office at NOAA/PMEL for providing open access to PIRATA data. The regional configuration was established in cooperation with the DRAKKAR project ( Special thanks are due to Fabien Durand and Elodie Kestenare for interesting discussions. C.Y. D-A thanks the SCAC of the French Embassy in Cotonou, Bénin, and the IRD for support through PhD grants. The research leading to these results received funding from the EU FP7/2007–2013 under grant agreement no. 603521. The authors thank TOTAL S.A. for supporting ICMPA, where this work was completed. Finally, sincere thanks are due to reviewers, whose precious contributions helped improve and complete an earlier version of this manuscript.


  1. Adler RF et al (2003) The version 2 global precipitation climatology project (GPCP) monthly precipitation analysis (1979–present). J Hydrometeorol 4:1147–1167CrossRefGoogle Scholar
  2. Barnier B, Madec G, Penduff T, Molines JM, Tréguier AM, Beckmann A, Biastoch A, Boning C, Dengg J, Gulev S, Le Sommer J, Rémy E, Talandier C, Theetteen S, Maltrud M, Mc Lean J (2006) Impact of partial steps and momentum advection schemes in a global ocean circulation model at eddy permitting resolution. Ocean Dyn 56(5–6):543–567Google Scholar
  3. Berger H, Tréguier AM, Perenne N, Talandier C (2014) Dynamical contribution to sea surface salinity variations in the eastern Gulf of Guinea based on numerical modelling. Clim Dyn. doi:10.1007/s00382-014-2195-4Google Scholar
  4. Blanke B, Delecluse P (1993) Variability of the tropical Atlantic Ocean simulated by a general circulation model with two different mixed-layer physics. J Phys Oceanogr 23:1363–1388CrossRefGoogle Scholar
  5. Bourlès B, Lumpkin R, McPhaden MJ, Hernandez F, Nobre P, Campos E, Yu L, Planton S, Busalacchi A, Moura AD, Servain J, Trotte J (2008) The PIRATA program: history, accomplishments and future directions. Bull Am Meteorol Soc 89:1111–1125CrossRefGoogle Scholar
  6. Bretherton FP, Davis RE, Fandry CB (1976) A technique for objective mapping and design of oceanographic experiments. Deep-Sea Res 23:559–582Google Scholar
  7. Da-Allada YC, Alory G, du Penhoat Y, Kestenare E, Durand F, Hounkonnou NM (2013) Seasonal mixed-layer salinity balance in the Tropical Atlantic Ocean: mean state and seasonal cycle. J Geophys Res Oceans 118(1):332–345. doi: 10.1029/2012JC008357
  8. Da-Allada YC, Alory G, du Penhoat Y, Jouanno J, Hounkonnou NM (2014) Causes for the recent increase in sea surface salinity in the Gulf of Guinea. Afr J Mar Sci 36(2):197–205. doi:10.2989/1814232X.2014.927398Google Scholar
  9. Dai A, Trenberth K (2002) Estimates of freshwater discharge from continents: latitudinal and seasonal variations. J Hydrometeorol 3:660–687CrossRefGoogle Scholar
  10. Dai A, Qian T, Trenberth K, Milliman J (2009) Changes in continental freshwater discharge from 1948 to 2004. J Climate 22:2773–2792CrossRefGoogle Scholar
  11. de Boyer MC, Madec G, Fischer AS, Lazar A, Ludicone D (2004) Mixed-layer depth over the global ocean: an examination of profile data and a profile-based climatology. J Geophys Res Oceans 109(C12):52–71Google Scholar
  12. Dessier A, Donguy JR (1994) The sea surface salinity in the tropical Atlantic between 10°S and 30°N– seasonal and interannual variations (1977–1989). Deep-Sea Res I 41:81–100CrossRefGoogle Scholar
  13. Doi T, Tozuka T, Sasaki H, Masumoto Y, Yamagata T (2007) Seasonal and interannual variations of oceanic conditions in the Angola dome. J Phys Oceanogr. doi: 10.1175/2007JPO3552.1 Google Scholar
  14. Ferry N, Reverdin G (2004) Sea surface salinity interannual variability in the western tropical Atlantic: an ocean general circulation model study. J Geophys Res Oceans. doi: 10.1029/2003JC002122
  15. Foltz GR, McPhaden MJ (2008) Seasonal mixed layer salinity balance of the tropical North Atlantic Ocean. J Geophys Res 113:C02013. doi: 10.1029/2007JC004178 Google Scholar
  16. Foltz GR, Grodsky SA, Carton JA, McPhaden MJ (2004) Seasonal salt budget of the northwestern tropical Atlantic Ocean along 38°W. J Geophys Res 109:C03052. doi: 10.1029/2003JC002111 Google Scholar
  17. Jouanno J, Marin F, du Penhoat Y, Sheinbaum J, Molines JM (2011) Seasonal heat balance in the upper 100 m of the equatorial Atlantic Ocean. J Geophys Res 116:C09003. doi: 10.1029/2010JC006912 Google Scholar
  18. Jouanno J, Marin F, du Penhoat Y, Sheinbaum J, Molines JM (2013) Intraseasonal modulation of the surface cooling in the Gulf of Guinea. J Phys Oceanogr. doi: 10.1175/JPO-D-12-053.1 Google Scholar
  19. Large W, Yeager S (2004) Diurnal to decadal global forcing for ocean sea ice models: the data sets and flux climatologies. Rep. NCAR/TN-460+STR. Natl Cent for Atmos Res. Boulder, ColoradoGoogle Scholar
  20. Lukas R, Lindstrom E (1991) The mixed layer of the western equatorial Pacific Ocean. J Geophys Res 96:3343–3357CrossRefGoogle Scholar
  21. Lumpkin R, Garzoli SL (2005) Near-surface circulation in the tropical Atlantic. Deep-Sea Res I 52:495–518CrossRefGoogle Scholar
  22. Madec G (2008) NEMO ocean engine. Note du pole de modélisation, Institut Pierre-Simon Laplace (IPSL), ParisGoogle Scholar
  23. Materia S, Gualdi S, Navarra A, Terray L (2012) The effect of Congo River freshwater discharge on Eastern Equatorial Atlantic climate variability. Clim Dyn. doi: 10.1007/s00382-012-1514-x Google Scholar
  24. Mignot J, Frankignoul C (2003) On the interannual variability of surface salinity in the Atlantic. Clim Dyn. doi: 10.1007/s00382-002-0294-0 Google Scholar
  25. Peter AC, Le Hénaff M, du Penhoat Y, Menkes CE, Marin F, Vialard J, Caniaux G, Lazar A (2006) A model study of the seasonal mixed-layer heat budget in the equatorial Atlantic. J Geophys Res 111:C06014. doi: 10.1029/2005JC003157 Google Scholar
  26. Reverdin G, Kestenare E, Frankignoul C, Delcroix T (2007) Surface salinity in the Atlantic Ocean (30°S–50°N). Prog Oceanogr 73:311–340. doi: 10.1016/j.pocean.2006.11.004 CrossRefGoogle Scholar
  27. Schouten MW, Matanao RP, Strub TP (2005) A description of the seasonal cycle of the equatorial Atlantic from altimeter data. Deep-Sea Res I 52:477–493. doi: 10.1016/j.dsr.2004.10.007 CrossRefGoogle Scholar
  28. Sprintall J, Tomczak M (1992) Evidence of the barrier layer in the surface layer of the tropics. J Geophys Res 97:7305–7316CrossRefGoogle Scholar
  29. Tzortzi E, Josey SA, Skrokosz M, Gommenginger C (2013) Tropical Atlantic salinity variability: new insights from SMOS. Geophys Res Lett. doi: 10.1002/grl.50225, Accepted toGoogle Scholar
  30. Vialard J, Menkes C, Boulanger JP, Delecluse P, Guilyardi E (2001) A model study of oceanic mechanisms affecting equatorial pacific sea surface temperature during the 1997–1998 EL Nino. J Phys Oceanogr 31:1649–1675CrossRefGoogle Scholar
  31. Webster PJ (1994) The role of hydrological processes in ocean atmosphere interactions. Rev Geophys 32:427–476CrossRefGoogle Scholar
  32. Yu L (2011) A global relationship between the ocean water cycle and near surface salinity. J Geophys Res 116:C10025. doi: 10.1029/2010JC006937 CrossRefGoogle Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  • Casimir Y. Da-Allada
    • 1
    • 2
    • 3
    • 4
    • 7
  • Yves du Penhoat
    • 1
    • 3
    • 4
  • Julien Jouanno
    • 3
    • 6
  • Gael Alory
    • 1
    • 2
    • 3
    • 4
    • 5
  • Norbert Mahouton Hounkonnou
    • 1
  1. 1.International Chair in Mathematical Physics and Applications (ICMPA-UNESCO Chair)Université d’Abomey-CalaviCotonouBénin
  2. 2.Université de Toulouse; UPS (OMP)LEGOSToulouseFrance
  3. 3.IRDLEGOSToulouseFrance
  4. 4.IRHOBCotonouBénin
  5. 5.CNAPLEGOSToulouseFrance
  6. 6.Departamento de Oceanografía FísicaCICESEEnsenadaMexico
  7. 7.IfremerLPO UMR 6523, CNRS/Ifremer/IRD/UBOPlouzanéFrance

Personalised recommendations