Skip to main content
SpringerLink
Log in

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

  • Published:
Climate Dynamics Aims and scope Submit manuscript

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.

This is a preview of subscription content, log in via an institution to check access.

Access this article

Log in via an institution

Price excludes VAT (USA)
Tax calculation will be finalised during checkout.

Instant access to the full article PDF.

Institutional subscriptions

Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5
Fig. 6
Fig. 7
Fig. 8
Fig. 9
Fig. 10
Fig. 11
Fig. 12
Fig. 13
Fig. 14
Fig. 15
Fig. 16

Similar content being viewed by others

References

  • Barnier B, Madec G, Penduff T, Molines JM, Treguier AM, Le Sommer J, Beckmann A, Biastoch A, Böning C, Dengg J et al (2006) Impact of partial steps and momentum advection schemes in a global ocean circulation model at eddy-permitting resolution. Ocean Dyn 56(5–6):543–567

    Google Scholar 

  • Berger H (2012) Origine des variations de la salinité de surface dans le Golfe de Guinée: analyse saisonnière et interannuelle à partir d’un modèle numérique. PhD thesis, Universite de Bretagne Occidentale, Ecole Doctorale des Sciences de la Mer

  • 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(7):1363–1388

    Article  Google Scholar 

  • Blanke B, Arhan M, Lazar A (2002) A lagrangian numerical investigation of the origins and fates of the salinity maximum water in the atlantic. J Geophys Res Oceans (1978–2012) 107(C10):1–27

    Google Scholar 

  • Bourlès B, Lumpkin R, McPhaden MJ, Hernandez F, Nobre P, Campos E, Yu L, Planton S, Busalacchi AJ, Moura AD et al (2008) The pirata program: history, accomplishments, and future directions. Bull Am Meteorol Soc 89:1111–1125

    Article  Google Scholar 

  • Brodeau L, Barnier B, Treguier AM, Penduff T, Gulev S (2010) An era40-based atmospheric forcing for global ocean circulation models. Ocean Model 31(3):88–104

    Article  Google Scholar 

  • Da-Allada CY, Alory G, Penhoat Yd, Kestenare E, Durand F, Hounkonnou N (2013a) Seasonal mixed-layer salinity balance in the tropical atlantic ocean: Mean state and seasonal cycle. J Geophys Res Oceans 118(1). doi:10.1029/2012JC008357

  • Da-Allada CY, Penhoat Yd, Alory G, Jouanno J, Hounkonnou N (2013b) Modeled mixed layer balance in the gulf of guinea; seasonal and inter annual variability. Submitted to Ocean dynamic

  • Dai A, Trenberth KE (2002) Estimates of freshwater discharge from continents: latitudinal and seasonal variations. J Hydrometeorol 3(6):660–687

    Article  Google Scholar 

  • Dai A, Qian T, Trenberth KE, Milliman JD (2009) Changes in continental freshwater discharge from 1948 to 2004. J Clim 22(10):2773–2792

    Article  Google Scholar 

  • de Boyer Montegut, C, Madec G, Fischer AS, Lazar A, Iudicone D (2004) Mixed layer depth over the global ocean: an examination of profile data and a profile-based climatology. J Geophys Res Oceans (1978–2012) 109(C12). doi:10.1029/2004JC002378

  • Debreu L, Blayo E (2008) Two-way embedding algorithms: a review. Ocean Dyn 58(5–6):415–428

    Article  Google Scholar 

  • Delcroix T, McPhaden MJ, Dessier A, Gouriou Y (2005) Time and space scales for sea surface salinity in the tropical oceans. Deep Sea Res Part I Oceanogr Res Pap 52(5):787–813

    Article  Google Scholar 

  • Dessier A, Donguy JR (1994) The sea surface salinity in the tropical atlantic between 10 s and 30 seasonal and interannual variations (1977–1989). Deep Sea Res Part I Oceanogr Res Pap 41(1):81–100

    Article  Google Scholar 

  • Eisma D, Van Bennekom A (1978) The zaire river and estuary and the zaire outflow in the atlantic ocean. Neth J Sea Res 12(3):255–272

    Article  Google Scholar 

  • 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 (1978–2012) 109(C5). doi:10.1029/2003JC002122

  • Gaillard F, Autret E, Thierry V, Galaup P, Coatanoan C, Loubrieu T (2009) Quality control of large argo datasets. J Atmos Oceanic Technol 26(2):337–351

    Article  Google Scholar 

  • Giordani H, Caniaux G (2011) Diagnosing vertical motion in the equatorial atlantic. Ocean Dyn 61(12):1995–2018

    Article  Google Scholar 

  • Giordani H, Caniaux G, Voldoire A (2013) Intraseasonal mixed-layer heat budget in the equatorial atlantic during the cold tongue development in 2006. J Geophys Res Oceans 118(2):650–671

    Article  Google Scholar 

  • Gu G, Adler RF (2004) Seasonal evolution and variability associated with the west african monsoon system. J Clim 17(17):3364–3377

    Article  Google Scholar 

  • Guiavarc’h C, Treguier AM, Vangriesheim A (2009) Deep currents in the gulf of guinea: along slope propagation of intraseasonal waves. Ocean Sci 5(2):141–153

    Article  Google Scholar 

  • Guiavarc’h C, Treguier AM, Vangriesheim A (2008) Remotely forced biweekly deep oscillations on the continental slope of the gulf of guinea. Journal of Geophysical Research: Oceans (1978–2012) 113(C6). doi:10.1029/2007JC004471

  • Hetland RD (2005) Relating river plume structure to vertical mixing. J Phys Oceanogr 35(9):1667–1688

    Article  Google Scholar 

  • Hummels R, Dengler M, Bourlès B (2013) Seasonal and regional variability of upper ocean diapycnal heat flux in the atlantic cold tongue. Prog Oceanogr 111:52–74

    Article  Google Scholar 

  • 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 Oceans (1978–2012) 116(C9). doi:10.1029/2010JC006912

  • Kolodziejczyk N, Marin F, Bourlès B, Gouriou Y, Berger H (2014) Seasonal variability of the equatorial undercurrent termination and associated salinity maximum in the Gulf of Guinea. Clim Dyn. doi:10.1007/s00382-014-2107-7 (this issue)

  • Laraque A, Mahé G, Orange D, Marieu B (2001) Spatiotemporal variations in hydrological regimes within central africa during the xxth century. J Hydrol 245(1):104–117

    Article  Google Scholar 

  • Large WG, Yeager SG (2004) Diurnal to decadal global forcing for ocean and sea-ice models: the data sets and flux climatologies. National Center for Atmospheric Research

  • Large W, Yeager S (2009) The global climatology of an interannually varying air-sea flux data set. Clim Dyn 33(2–3):341–364

    Article  Google Scholar 

  • Levitus S (1986) Annual cycle of salinity and salt storage in the world ocean. J Phys Oceanogr 16(2):322–343

    Article  Google Scholar 

  • Madec G (2008) Nemo ocean engine. Note du pôle de modelisation, Institut Pierre Simon Laplace (Paris)

  • Mahé G, Olivry JC (1999) Assessment of freshwater yields to the ocean along the intertropical atlantic coast of africa (1951–1989). Comptes Rendus de l’Académie des Sci Ser IIA-Earth Planet Sci 328(9):621–626

    Google Scholar 

  • Penduff T, Le Sommer J, Barnier B, Tréguier AM, Molines JM, Madec G et al (2007) Influence of numerical schemes on current-topography interactions in 1/4 global ocean simulations. Ocean Sci Discuss 4(3):491–528

    Article  Google Scholar 

  • 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 Oceans (1978–2012) 111(C6). doi:10.1029/2005JC003157

  • Philander S, Gu D, Lambert G, Li T, Halpern D, Lau N, Pacanowski R (1996) Why the itcz is mostly north of the equator. J Clim 9(12):2958–2972

    Article  Google Scholar 

  • Redelsperger JL, Thorncroft CD, Diedhiou A, Lebel T, Parker DJ, Polcher J (2006) African monsoon multidisciplinary analysis: an international research project and field campaign. Bull Am Meteorol Soc 87(12):1739–1746

    Article  Google Scholar 

  • Reverdin G, Kestenare E, Frankignoul C, Delcroix T (2007) Surface salinity in the atlantic ocean (30 s-50 n). Prog Oceanogr 73(3):311–340

    Article  Google Scholar 

  • Stramma L, Schott F (1999) The mean flow field of the tropical atlantic ocean. Deep Sea Res Part II Topical Stud Oceanogr 46(1):279–303

    Article  Google Scholar 

  • Treguier AM, Barnier B, De Miranda A, Molines J, Grima N, Imbard M, Madec G, Messager C, Reynaud T, Michel S (2001) An eddy-permitting model of the atlantic circulation: evaluating open boundary conditions. J Geophys Res 106(C10):22115–22129

    Article  Google Scholar 

  • Tzortzi E, Josey S, Srokosz M (2013) Tropical atlantic salinity variability: new insights from smos. Geophys Res Lett 40(10):2143–2147

    Article  Google Scholar 

  • Verstraete JM (1992) The seasonal upwellings in the gulf of guinea. Prog Oceanogr 29(1):1–60

    Article  Google Scholar 

  • Vialard J, Menkes C, Boulanger JP, Delecluse P, Guilyardi E, McPhaden MJ, Madec G (2001) A model study of oceanic mechanisms affecting equatorial pacific sea surface temperature during the 1997–98 el nino. J Phys Oceanog 31(7):1649–1675

    Article  Google Scholar 

  • Vialard J, Drushka K, Bellenger H, Lengaigne M, Pous S, Duvel JP (2012) Understanding madden-julian-induced sea surface temperature variations in the north western australian basin. Clim Dyn 41:3203–3218

  • Yoo JM, Carton JA (1990) Annual and interannual variation of the freshwater budget in the tropical atlantic ocean and the caribbean sea. J Phys Oceanogr 20(6):831–845

    Article  Google Scholar 

Download references

Acknowledgments

We thank the editor Dr. Ben Kirtman and two anonymous reviewers for their constructive comments and suggestions. This work has been supported by grants from TOTAL, from INSU/LEFE and Mercator-Ocean. H. Berger was supported by Actimar, TOTAL and the CNRS; N. Perenne is supported by Actimar and A.M. Treguier by CNRS. Computations were done on the CAPARMOR computer at Ifremer as well as on the IDRIS center of GENCI in Orsay. We thank Jean Marc Molines and Raphael Dussin, the modelling team at LGGE, for their help to set up the NEMO-AGRIF model and providing the forcing conditions. We thank Fabienne Gaillard for providing her ARV09 climatology, Clement De Boyer Montegut for the climatology of mixed layer depth, Aiguo Dai for providing his runoff dataset and Bernard Bourles for providing us the PIRATA data. We particularly thank Jerome Vialard for his helpful suggestions about this work.

Author information

Authors and Affiliations

  1. Laboratoire de Physique des Oceans, CNRS-Ifremer-UBO-IRD, BP70 , Plouzane, France

    Henrick Berger, Anne Marie Treguier & Claude Talandier

  2. Actimar, 36 quai de la douane, Brest, France

    Henrick Berger & Nicolas Perenne

Authors
  1. Henrick Berger
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Anne Marie Treguier
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Nicolas Perenne
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. Claude Talandier
    View author publications

    You can also search for this author in PubMed Google Scholar

Corresponding author

Correspondence to Henrick Berger.

Additional information

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.

Rights and permissions

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Berger, H., Treguier, A.M., Perenne, N. et al. Dynamical contribution to sea surface salinity variations in the eastern Gulf of Guinea based on numerical modelling. Clim Dyn 43, 3105–3122 (2014). https://doi.org/10.1007/s00382-014-2195-4

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1007/s00382-014-2195-4

Keywords

Search

Navigation