Skip to main content
SpringerLink
Log in

Seasonal Variability of Sea Surface Salinity in the NW Gulf of Guinea from SMAP Satellite

  • Published:
Remote Sensing in Earth Systems Sciences Aims and scope Submit manuscript

Abstract

The advent of satellite-derived sea surface salinity (SSS) measurements has boosted scientific study in less-sampled ocean regions such as the northwestern Gulf of Guinea (NWGoG). In this study, we examine the seasonal variability of SSS in the NWGoG from the Soil Moisture Active Passive (SMAP) satellite and show that it is well-suited for such regional studies as it is able to reproduce the observed SSS features in the study region. SMAP SSS bias, relative to in-situ data comparisons, reflects the differences between skin layer measurements and bulk surface measurements that have been reported by previous studies. The study results reveal three broad anomalous SSS features: a basin-wide salinification during boreal summer, a basin-wide freshening during winter, and a meridionally oriented frontal system during other seasons. A salt budget estimation suggests that the seasonal SSS variability is dominated by changes in freshwater flux, zonal circulation, and upwelling. Freshwater flux, primarily driven by the seasonally varying Intertropical Convergence Zone, is a dominant contributor to salt budget in all seasons except during fall. Regionally, SSS is most variable off southwestern Nigeria and controlled primarily by westward extensions of the Niger River. Anomalous salty SSS off the coasts of Cote d’Ivoire and Ghana especially during summer are driven mainly by coastal upwelling and horizontal advection.

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

Similar content being viewed by others

Data availability

SMAP SSS data are available at https://smap.jpl.nasa.gov/data/. CCMP Version-2.0 vector wind analyses are produced by Remote Sensing Systems. Data are available at http://www.remss.com/measurements/ccmp/. CORA and ERA5 data are obtained from Copernicus Marine Service, https://resources.marine.copernicus.eu/?option=com_csw&task=results. OSCAR data were obtained from https://podaac-tools.jpl.nasa.gov/drive/files/allData/oscar/L4/oscar_1_deg.

Code Availability

None.

References

  1. Anderson JE, Riser SC (2014) Near-surface variability of temperature and salinity in the near-tropical ocean: observations from profiling floats. J Geophys Res Oceans 119:7433–7448

    Article  Google Scholar 

  2. Arhan M, Treguier A, Bourles B, Michel S (2006) Diagnosing the annual cycle of the Equatorial Undercurrent in the Atlantic Ocean from a general circulation model. J Phys Oceanogr 36(8):1502–1522

    Article  Google Scholar 

  3. Bakun A (1978) Guinea current upwelling. Nature 271:147–150

    Article  Google Scholar 

  4. Belhabib D, Rashid Sumaila U, Le Billon P (2019) The fisheries of Africa: exploitation, policy, and maritime security trends. Mar Policy 101:80–92

    Article  Google Scholar 

  5. Berger H, Treguier 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 43:3105–3122

    Article  Google Scholar 

  6. Bingham FM, Foltz GR, McPhaden MJ (2010) Seasonal cycles of surface layer salinity in the Pacific Ocean. Ocean Sci 6:775–787. https://doi.org/10.5194/os-6-775-2010

    Article  Google Scholar 

  7. Bonjean F, Lagerloef GSE (2002) Diagnostic model and analysis of the surface currents in the Tropical Pacific Ocean. J Phys Oceanogr 32(10):2938–2954

    Article  Google Scholar 

  8. Bourlès B, D’Orgeville M, Eldin G, Gouriou Y, Chuchla R, Penhoat YD, Arnault S (2002) On the evolution of the thermocline and subthermocline eastward currents in the Equatorial Atlantic. Geophys Res Lett 29(16):1785. https://doi.org/10.1029/2002GL015098

    Article  Google Scholar 

  9. Bourlès B, Molinari RL, Johns E, Wilson WD, Leaman KD (1999) Upper layer currents in the western tropical Atlantic (1989–1991). J Geophys Res 104(C1):1361–1375

    Article  Google Scholar 

  10. Boutin J, Chao Y, Asher WE, Delcroix T, Drucker R, Drushka K, Kolodziejczyk N, Lee T, Reul N, Reverdin G et al (2016) Satellite and in situ salinity: understanding near-surface stratification and subfootprint variability. Bull Amer Meteor Soc 97:1391–1407

    Article  Google Scholar 

  11. Cabanes C, and Coauthors (2013) The CORA dataset: Validation and diagnostics of in-situ ocean temperature and salinity measurements. Ocean Sci 9: 1–18

  12. Camara I, Kolodziejczyk N, Mignot J, Lazar A, Gaye AT (2015) On the seasonal variations of salinity of the tropical Atlantic mixed layer. J Geophys Res Oceans 120:4441–4462

    Article  Google Scholar 

  13. Caniaux G, Giordani H, Redelsperger JL, Guichard F, Key E, Wade M (2011) Coupling between the Atlantic cold tongue and the West African monsoon in boreal spring and summer. J Geophys Res Oceans. https://doi.org/10.1029/2010JC006570

    Article  Google Scholar 

  14. Chao Y, Farrara JD, Schumann G, Andreadis KM, Moller D (2015) Sea surface salinity variability in response to the Congo River discharge. Cont Shelf Res 99:35–45

    Article  Google Scholar 

  15. Da-Allada CY, Alory G, Penhoat YD, Kestenare E, Durand F, Hounkonnou N (2013) Seasonal mixed-layer salinity balance in the tropical Atlantic Ocean: mean state and seasonal cycle. J Geophys Res Oceans 118(1).https://doi.org/10.1029/2012JC008357.

  16. Da-Allada CY, du Penhoat Y, Jouanno J, Alory G, Hounkonnou N (2014) Modeled mixed-layer salinity balance in the Gulf of Guinea: seasonal and interannual variability. Ocean Dyn 64(12):1783–1802

    Article  Google Scholar 

  17. Da-Allada CY, Gaillard F, Kolodziejczyk N (2015) Mixed-layer salinity budget in the tropical Indian Ocean: seasonal cycle based only on observations. Ocean Dyn 65:845–857. https://doi.org/10.1007/s10236-015-0837-7

    Article  Google Scholar 

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

    Article  Google Scholar 

  19. de Boyer MC, 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 109:C12003. https://doi.org/10.1029/2004JC002378

    Article  Google Scholar 

  20. Delcroix T, Henin C (1991) Seasonal and Interannual variations of the sea surface salinity in the tropical Pacific Ocean. J Geophys Res 96:22135–22150

    Article  Google Scholar 

  21. 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. Part I 41:81–100

    Google Scholar 

  22. Dossa A, Da-Allada C, Herbert G, Bourlès B (2019) Seasonal cycle of the salinity barrier layer revealed in the northeastern Gulf of Guinea. Afr J Mar Sci 41(2):163–175

    Article  Google Scholar 

  23. Drushka K, Asher WE, Ward B, Walesby K (2016) Understanding the formation and evolution of rain-formed fresh lenses at the ocean surface. J Geophys Res Oceans 121:2673–2689

    Article  Google Scholar 

  24. Foltz GR, McPhaden MJ (2009) Impact of barrier layer thickness on SST in the central tropical North Atlantic. J Clim 22(2):285–299

    Article  Google Scholar 

  25. Giarolla E, Nobre P, Malagutti M, Pezzi L (2005) The Atlantic Equatorial Undercurrent: PIRATA observations and simulations with GFDL Modular Ocean model at CPTEC. Geophys Res Lett, 32(10): L10 617. http://www.agu.org/journals/ABS/2005/2004GL022206.shtml.

  26. Grist JP, Nicholson SE (2001) A study of the dynamics factors influencing the rainfall variability in the West African Sahel. J of Clim 14:1337–1359

    Article  Google Scholar 

  27. Grodsky SA, Reul N, Bentamy A, Vandemark D, Guimbard S (2019) Eastern Mediterranean salinification observed in satellite salinity from SMAP mission. J Mar Sys 198:103190. https://doi.org/10.1016/j.jmarsys.2019.103190

    Article  Google Scholar 

  28. Grodsky SA, Vandemark D, Feng H (2018) Assessing coastal SMAP surface salinity accuracy and its application to monitoring Gulf of Maine circulation dynamics. Remote Sens 10(8):1232. https://doi.org/10.3390/rs10081232

    Article  Google Scholar 

  29. Grodsky SA, Vandemark D, Feng H, Levin J (2018) Satellite detection of an unusual intrusion of salty slope water into a marginal sea: using SMAP to monitor Gulf of Maine inflows. Remote Sens Environ 217:550–561

    Article  Google Scholar 

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

    Article  Google Scholar 

  31. Hackert EC, Kovach RM, Busalacchi AJ, Ballabrera‐Poy J (2019) Impact of Aquarius and SMAP satellite sea surface salinity observations on coupled El Niño/Southern Oscillation forecasts. J Geophys Res 124https://doi.org/10.1029/2019JC015130

  32. Hall SB, Subrahmanyam B, Nyadjro ES, Samuelsen A (2021) Surface freshwater fluxes in the Arctic and Subarctic Seas during contrasting years of high and low summer sea ice extent. Remote Sens 13:1570. https://doi.org/10.3390/rs13081570

    Article  Google Scholar 

  33. Hazeleger W, de Vries P, Friocourt Y (2003) Sources of the equatorial undercurrent in the Atlantic in a high-resolution ocean model. J Phys Ocean 33(4):677–693

    Article  Google Scholar 

  34. Houndegnonto OJ, Kolodziejczyk N, Maes C, Bourlès B, Da-Allada CY, Reul N (2021) Seasonal variability of freshwater plumes in the eastern Gulf of Guinea as inferred from satellite measurements. J Geophys Res 126:e2020JC017041. https://doi.org/10.1029/2020JC017041

    Article  Google Scholar 

  35. Iqbal K, Zhang M, Piao S (2020) Symmetrical and asymmetrical rectifications employed for deeper ocean extrapolations of in situ CTD data and subsequent sound speed profiles. Symmetry 12(9):1455. https://doi.org/10.3390/sym12091455

    Article  Google Scholar 

  36. Jacox MG, Edwards CA (2012) Upwelling source depth in the presence of nearshore wind stress curl. J Geophys Res 117:C05008. https://doi.org/10.1029/2011JC007856

    Article  Google Scholar 

  37. Jang E, Kim YJ, Im J, Park Y-G (2021) Improvement of SMAP sea surface salinity in river-dominated oceans using machine learning approaches. GISci Remote Sens 58(1):138–160

    Article  Google Scholar 

  38. 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 43:3025–3046

    Article  Google Scholar 

  39. Korosov A, Counillon F, Johannessen JA (2015) Monitoring the spreading of the Amazon freshwater plume by MODIS, SMOS, Aquarius, and TOPAZ. J Geophys Res Oceans 120:268–283

    Article  Google Scholar 

  40. Lamb PJ (1978) Case studies of tropical Atlantic surface circulation pattern during recent sub-Saharan weather anomalies, 1967–1968. Mon Weather Rev 106:482–491

    Article  Google Scholar 

  41. Lee T, Lagerloef G, Gierach MM, Kao H-Y, Yueh S, Dohan K (2012) Aquarius reveals salinity structure of tropical instability waves. Geophys Res Lett 39(12):L12610-1-L12610-6

    Article  Google Scholar 

  42. Maloney E, Shaman J (2008) Intraseasonal variability of the West African monsoon and Atlantic ITCZ. J Clim 21(12):2898–2918

    Article  Google Scholar 

  43. Mears CA, Scott J, Wentz FJ, Ricciardulli L, Leidner SM, Hoffman R, Atlas R (2019) A near-real-time version of the cross-calibrated multiplatform (CCMP) ocean surface wind velocity data set. J Geophys Res Oceans 124:6997–7010

    Article  Google Scholar 

  44. Meissner T, Wentz FJ, Manaster A, Lindsley R (2019) Remote sensing systems SMAP ocean surface salinities [level 2c, level 3 running 8-day, level 3 monthly], version 4.0 validated release. Remote Sensing Systems, Santa Rosa, CA, USA. Available online at www.remss.com/missions/smap, https://doi.org/10.5067/SMP40-3SMCS

  45. Menezes VV (2020) Statistical Assessment of sea-surface salinity from SMAP: Arabian Sea, Bay of Bengal, and a promising Red Sea application. Remote Sens 12:447. https://doi.org/10.3390/rs12030447

    Article  Google Scholar 

  46. Moon J-H, Song YT (2014) Seasonal salinity stratifications in the near-surface layer from Aquarius, Argo, and an ocean model: focusing on the tropical Atlantic/Indian oceans. J Geophys Res Oceans 119:6066–6077

    Article  Google Scholar 

  47. Nichols RE, Subrahmanyam B (2019) Estimation of surface freshwater fluxes in the Arctic Ocean using satellite-derived salinity. Remote Sens Earth Syst Sci 2:247–259

    Article  Google Scholar 

  48. Nyadjro ES (2021) Impacts of the 2019 Strong IOD and monsoon events on Indian Ocean Sea surface salinity. Remote Sens Earth Syst Sci. https://doi.org/10.1007/s41976-021-00054-1

    Article  Google Scholar 

  49. Nyadjro ES, Rydbeck AV, Jensen TG, Richman JG, Shriver JF (2020) On the generation and salinity impacts of intraseasonal westward jets in the equatorial Indian Ocean. J Geophys Res 125https://doi.org/10.1029/2020JC016066

  50. Nyadjro ES, Subrahmanyam B (2014) SMOS satellite mission reveals the salinity structure of the Indian Ocean Dipole. IEEE Geosci Remote Sens Lett 11(9):1564–1568

    Article  Google Scholar 

  51. Nyadjro ES, Subrahmanyam B (2016) Spatial and temporal variability of central Indian Ocean salinity fronts observed by SMOS. Remote Sens Environ 180:146–153

    Article  Google Scholar 

  52. Rao SA, Behera SK (2005) Subsurface influence on SST in the tropical Indian Ocean: structure and interannual variability. Dyn Atmos Oceans 39:103–139

    Article  Google Scholar 

  53. Santos-Garcia A, Jacob MM, Jones WL (2016) SMOS Near-surface salinity stratification under rainy conditions. IEEE J Sel Top Appl Earth Obs Remote Sens 9(6):2493–2499

    Article  Google Scholar 

  54. Sommer A, Reverdin G, Kolodziejczyk N, Boutin J (2015) Sea surface salinity and temperature budgets in the North Atlantic Subtropical Gyre during SPURS experiment: August 2012-August 2013. Front Mar Sci 2:107. https://doi.org/10.3389/fmars.2015.00107

    Article  Google Scholar 

  55. Song YT, Lee T, Moon J-H, Qu T, Yueh S (2015) Modeling skin–layer salinity with an extended surface–salinity layer. J Geophys Res Oceans 120:1079–1095

    Article  Google Scholar 

  56. Sprintall J, Tomczak M (1992) Evidence of the barrier layer in the surface layer of the tropics. J Geophys Res 97:7305–7316

    Article  Google Scholar 

  57. Tang W, Fore A, Yueh S, Lee T, Hayashi A, Sanchez-Franks A et al (2017) Validating SMAP SSS with in situ measurements. Remote Sens Environ 200:326–340. https://doi.org/10.1016/j.rse.2017.08.021

    Article  Google Scholar 

  58. 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 

  59. Vinogradova N, Lee T, Boutin J, Drushka K, Fournier S, Sabia R, Stammer D, Bayler E, Reul N, Gordon A et al (2019) Satellite salinity observing system: recent discoveries and the way forward. Front Mar Sci 6:243

    Article  Google Scholar 

  60. Wiafe G, Nyadjro ES (2015) Satellite observations of upwelling in the Gulf of Guinea. IEEE Geosci Remote Sens Lett 12(2):1066–1070. https://doi.org/10.1109/LGRS.2014.2379474

    Article  Google Scholar 

Download references

Acknowledgements

The authors acknowledge the freely available data obtained from the NASA Jet Propulsion Laboratory, Remote Sensing Systems, and the European Union’s Copernicus Marine Service. We thank the anonymous reviewers whose comments helped improve the manuscript.

Author information

Authors and Affiliations

  1. Northern Gulf Institute, Mississippi State University, Stennis Space Center, MS, USA

    Ebenezer S. Nyadjro

  2. Department of Marine and Fisheries Sciences, University of Ghana, Legon, Ghana

    Bennet A. K. Foli, Kwame A. Agyekum & George Wiafe

  3. Global Monitoring for Environment and Security and Africa, University of Ghana, Legon, Ghana

    Bennet A. K. Foli, Kwame A. Agyekum & George Wiafe

  4. School of Ocean Science and Engineering, University of Southern Mississippi, Stennis Space Center, MS, USA

    Senam Tsei

Authors
  1. Ebenezer S. Nyadjro
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Bennet A. K. Foli
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Kwame A. Agyekum
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. George Wiafe
    View author publications

    You can also search for this author in PubMed Google Scholar

  5. Senam Tsei
    View author publications

    You can also search for this author in PubMed Google Scholar

Corresponding author

Correspondence to Ebenezer S. Nyadjro.

Ethics declarations

Conflict of Interest/Competing Interests

Authors declare no financial and competing interests.

Additional information

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Rights and permissions

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Nyadjro, E.S., Foli, B.A.K., Agyekum, K.A. et al. Seasonal Variability of Sea Surface Salinity in the NW Gulf of Guinea from SMAP Satellite. Remote Sens Earth Syst Sci 5, 83–94 (2022). https://doi.org/10.1007/s41976-021-00061-2

Download citation

  • Received:

  • Revised:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1007/s41976-021-00061-2

Keywords

Search

Navigation