Climate Dynamics

, Volume 43, Issue 11, pp 3025–3046 | Cite as

Seasonal variability of the equatorial undercurrent termination and associated salinity maximum in the Gulf of Guinea

  • Nicolas Kolodziejczyk
  • Frédéric Marin
  • Bernard Bourlès
  • Yves Gouriou
  • Henrick Berger
Article

Abstract

The termination of the Equatorial Undercurrent (EUC) in the eastern equatorial Atlantic during boreal summer and fall, and the fate of the associated saline water masses, are analyzed from in situ hydrological and currents data collected during 19 hydrographic cruises between 2000 and 2007, complemented by observations from Argo profiling floats and PIRATA moorings, and from a numerical simulation of the Tropical Atlantic Ocean for the period 1993–2007. An intense variability of the circulation and hydrological properties is evidenced from observations in the upper thermocline (24.5–26.2 isopycnal layer) between June and November. During early boreal summer, saline water masses are transported eastward in the upper thermocline to the African coast within the EUC, and recirculate westward on both sides of the EUC. In mid-boreal summer, the EUC weakens in the upper thermocline and the equatorial salinity maximum disappears due to intense mixing with the surface waters during the upwelling season. The extra-equatorial salinity maxima are also partially eroded during the boreal summer, with a slight poleward migration of the southern hemisphere maximum until late boreal summer. The upper EUC reappears in September, feeding again the eastern equatorial Atlantic with saline waters until boreal spring. During December–January, numerical results suggest a second seasonal weakening of the EUC in the Gulf of Guinea, with a partial erosion of the associated equatorial salinity maximum.

References

  1. Antonov JI, Seidov D, Boyer TP, Locarnini RA, Mishonov AV, Garcia HE, Baranova OK, Zweng MM, Johnson DR (2010) World ocean atlas 2009, volume 2: salinity. In: Levitus S (ed) NOAA atlas NESDIS 69, U.S. Government Printing Office, Washington, DC, 184 ppGoogle Scholar
  2. Arhan M, Tréguier AM, Bourlès B, Michel S (2006) Diagnosing the annual cycle of the equatorial undercurrent in the Atlantic Ocean from a general circulation model. J Phys Oceanogr 36:1502–1522CrossRefGoogle Scholar
  3. Athié G, Marin F (2008) Cross-equatorial structure and temporal modulation of intraseasonal variability at the surface of the Tropical Atlantic Ocean. J Geophys Res 113:C08020. doi:10.1029/2007JC004332 Google Scholar
  4. Barnier B, Marchesiello P, de Miranda AP, Molines JM, Coulibaly M (1998) A sigma-coordinate primitive equation model for studying the circulation in the South Atlantic. Part I: model configuration with error estimates. Deep Sea Res 45:543–572CrossRefGoogle Scholar
  5. Barnier B, Madec G, Penduff T, Molines J-M, Tréguier A-M, Le Sommer J, Beckmann A, Biastoch A, Böning C, Dengg J, Derval C, Durand E, Gulev S, Remy E, Talandier C, Theetten S, Maltrud M, McClean J, De Cuevas B (2006) Impact of partial steps and momentum advection schemes in a global ocean circulation model at eddy permitting resolution. Ocean Dyn 4. doi:10.1007/s10236-006-0082-1
  6. Berger H, Treguier A-M, Perenne N, Talandier C (2014) Dynamical contribution to sea surface salinity variations in the eastern Gulf of Guinea base on numerical modelling. Clim Dyn (submitted)Google Scholar
  7. 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
  8. Blanke B, Arhan M, Lazar A, Prévost G (2002) A Lagrangian numerical investigation of the origins and fates of the salinity maximum water in the Atlantic. J Geophys Res 107(C10):3163. doi:10.1029/2002JC001318 CrossRefGoogle Scholar
  9. Böning CW, Kröger J (2005) Seasonal variability of deep currents in the equatorial Atlantic: a model study. Deep Sea Res I 52:99–121CrossRefGoogle Scholar
  10. Bourlès B, Gouriou Y, Chuchla R (1999) On the circulation in the upper layer of the western equatorial Atlantic. J Geophys Res 104:21151–21170CrossRefGoogle Scholar
  11. Bourlès B, D’Orgeville M, Eldin G, Gouriou Y, Chuchla R, du Penhoat Y, Arnault S (2002), On the evolution of the thermocline and subthermocline eastward currents in the equatorial Atlantic. Geophys Res Lett 29. doi:10.1029/2002GL015098
  12. Bourlès B, Brandt P, Caniaux G, Dengler M, Gouriou Y, Key E, Lumpkin R, Marin F, Molinari RL, Schmid C (2007) African monsoon multidisciplinary analysis (AMMA): special measurements in the tropical Atlantic. CLIVAR Exch Lett 41(12):2Google Scholar
  13. 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
  14. Brandt P, Schott FA, Provost C, Kartavtseff A, Hormann V, Bourlès B, Fischer J (2006) Circulation in the central equatorial Atlantic: mean and intraseasonal to seasonal variability. Geophys Res Lett 33:L07609. doi:10.1029/2005GL025498 Google Scholar
  15. Brodeau L, Barnier B, Tréguier A-M, Penduff T, Gulev S (2010) An ERA-40-based atmospheric forcing for global ocean circulation models. Ocean Model 31:88–104CrossRefGoogle Scholar
  16. Cane MA, Moore DW (1981) A note on low-frequency equatorial basin modes. J Phys Oceanogr 11:1578–1584CrossRefGoogle Scholar
  17. Cane MA, Sarachik ES (1983) Equatorial oceanography. Rev Geophys 21:1137–1148CrossRefGoogle Scholar
  18. Chang P, Zhang R, Hazeleger W, Wen C, Wan X, Ji L, Haarsma RJ, Breugem W-P, Seidel H (2008) Oceanic link between abrupt changes in the north Atlantic Ocean and the African monsoon. Nature 1:444–448Google Scholar
  19. Da-Allada CY, 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 118:332–345. doi:10.1029/2012JC008357 CrossRefGoogle Scholar
  20. Da-Allada CY, du Penhoat Y, Jouanno J, Allory G, Hounkonnou NM (2014) Mixed layer salinity balance in the Gulf of Guinea: seasonal and interannual variability. Clim Dyn (submitted)Google Scholar
  21. Dai A, Trenberth KE (2002) Estimates of freshwater discharge from continents: latitudinal and seasonal variations. J Hydrometeorol 3:660–687CrossRefGoogle Scholar
  22. de Coetlogon G, Janicot S, Lazar A (2010) Intra-seasonal variability of the ocean-atmosphere coupling in the Gulf of Guinea during boreal spring and summer. Q J Roy Meteorol Soc 136:426–441CrossRefGoogle Scholar
  23. Ding H, Keenlyside NS, Latif M (2009) Seasonal cycle in the upper equatorial Atlantic Ocean. J Geophys Res 114:C09016. doi:10.1029/2009JC005418 Google Scholar
  24. Gaillard F, Autret E, Thierry V, Galaup P, Coatanoan C, Loubrieu T (2009) Quality control of large Argo data sets. J Atmos Ocean Technol 26(2):337–351CrossRefGoogle Scholar
  25. Giarolla E, Nobre P, Malagutti M, Pezzi LP (2005) The Atlantic equatorial undercurrent: PIRATA observations and simulations with GFDL modular ocean model at CPTEC. Geophys Res Let 32. doi:10.1029/2004GL022206
  26. Gouriou Y, Reverdin G (1992) Isopycnal and diapycnal circulation of the upper equatorial Atlantic Ocean in 1983–1984. J Geophys Res 97:3543–3572CrossRefGoogle Scholar
  27. Grodsky SA, Carton JA (2002) Surface drifter pathways originating in the equatorial Atlantic cold tongue. Geophys Res Lett 29:2147. doi:10.1029/2002GL015788 CrossRefGoogle Scholar
  28. Han W, Webster PJ, Lin J-L, Liu WT, Fu R, Yuan D, Hu A (2008) Dynamics of intraseasonal sea level and thermocline variability in the equatorial Atlantic during 2002–03. J Phys Oceanogr 38:945–966CrossRefGoogle Scholar
  29. Hazeleger W, de Vries P (2003) Fate of the equatorial undercurrent in the Atlantic. In Goni GJ, Malanotte-Rizzoli P (eds) Interhemispheric water exchange in the Atlantic ocean. Amsterdam, Elsevier, pp 175–191Google Scholar
  30. Hazeleger W, de Vries P, Friocourt Y (2003) Sources of the equatorial undercurrent in the Atlantic in a high-resolution ocean model. J Phys Oceanogr 33:677–693CrossRefGoogle Scholar
  31. Hisard P (1973) Variations saisonnières à l’équateur dans le Golfe de Guinée, Cah. ORSTOM Sér Océanogr XI: 349–358Google Scholar
  32. Hisard P, Morlière A (1973), La terminaison du contre-courant équatorial subsuperficiel atlantique (courant de Lomonosov) dans le Golfe de Guinée, Cah. ORSTOM, Sér Océanogr XI:455–464Google Scholar
  33. Hormann V, Brandt P (2007) Atlantic Equatorial Undercurrent and associated cold tongue variability. J Geophys Res 112:C06017. doi:10.1029/2006JC003931 Google Scholar
  34. Houghton RW (1983) Seasonal variations of the subsurface thermal structure in the Gulf of Guinea. J Phys Oceanogr 13:2070–2081CrossRefGoogle Scholar
  35. Hummels R, Dengler M, Bourlès B (2013) Seasonal and regional variability of upper ocean diapycnal heat flux in the Atlantic Cold Tongue. Prog Oceanogr 111:52–74CrossRefGoogle Scholar
  36. Johns WE, Brandt P, Bourlès B, Tantet A, Papapostolou A, Houk A (2014) Zonal structure and seasonal variability of the atlantic equatorial undercurrent. Clim Dyn (submitted)Google Scholar
  37. Jouanno J, Marin F, du Penhoat Y, Sheinbaum J, Molines JM (2011a) Seasonal heat balance in the upper 100 m of the Equatorial Atlantic Ocean. J Geophys Res 116:C09003. doi:10.1029/2010JC006912 Google Scholar
  38. Jouanno J, Marin F, du Penhoat Y, Molines JM, Sheinbaum J (2011b) Seasonal modes of surface cooling in the Gulf of Guinea. J Phys Oceanogr 41:1408–1416. doi:10.1175/JPO-D-11-031.1 CrossRefGoogle Scholar
  39. Jouanno J, Marin F, du Penhoat Y, Molines JM (2013) Intraseasonal modulation of the surface cooling in the Gulf of Guinea. J Phys Oceanogr 43:382–401. doi:10.1175/JPO-D-12-053.1 CrossRefGoogle Scholar
  40. Katz E (1984) Basin wide thermocline displacements along the equator of the Atlantic in 1983. Geophys Res Lett 11:729–732. doi:10.1029/GL011i008p00729 CrossRefGoogle Scholar
  41. Katz E, Molinari RL, Cartwright D, Hisard P, Lass H, deMesquita A (1981) The seasonal transport of the Equatorial Undercurrent in the western Atlantic (during the Global Weather Experiment). Ocean Acta 4:445–450Google Scholar
  42. Kolodziejczyk N, Bourlès B, Marin F, Grelet J, Chuchla R (2009) Seasonal variability of the equatorial undercurrent at 10 W as inferred from recent in situ observations. J Geophys Res 114:C06014. doi:10.1029/2008JC004976 Google Scholar
  43. Locarnini RA, Mishonov AV, Antonov JI, Boyer TP, Garcia HE, Baranova OK, Zweng MM, Johnson DR (2010) World Ocean Atlas 2009, Volume 1: Temperature. In: S. Levitus (ed) NOAA Atlas NESDIS 68, U.S. Government Printing Office, Washington, DC, 184 ppGoogle Scholar
  44. Lumpkin R, Speer K (2003) Large-scale vertical and horizontal circulation in the North Atlantic Ocean. J Phys Oceanogr 33:1902–1920. doi:10.1175/1520-0485(2003)033<1902:LVAHCI>2.0.CO;2 CrossRefGoogle Scholar
  45. Madec G (2008) NEMO ocean engine: version3.1, Note du Pôle de modélisation de l’IPSL n°27Google Scholar
  46. Marin F, Caniaux G, Giordani H, Bourlès B, Gouriou Y, Key E (2009) Why were sea surface temperatures so different in the eastern equatorial Atlantic in June 2005 and 2006? J Phys Oceanogr 39:1416–1431CrossRefGoogle Scholar
  47. Mercier H, Arhan M, Lutjeharms J (2003) Upper-layer circulation in the eastern equatorial and South Atlantic Ocean in January–March 1995. Deep Sea Res I 50:863–887CrossRefGoogle Scholar
  48. Molinari RL, Bauer S, Johnson GC, Bourlès B, Gouriou Y, Mercier H (2003) A comparison of kinematic evidence for tropical cells in the Atlantic and Pacific oceans. In: Goni GJ, Malanotte-Rizzoli P (eds) Interhemispheric water exchange in the Atlantic Ocean. Elsevier, AmsterdamGoogle Scholar
  49. Okumura Y, Xie S-P (2006) Some overlooked features of Tropical Atlantic climate leading to a new Niño-like Phenomenon. J Clim 19:5859–5874CrossRefGoogle Scholar
  50. Pacanowski RC, Philander SGH (1981) Parameterization of vertical mixing in numerical models of Tropicals Oceans. J Phys Oceanogr 11:1443–1451CrossRefGoogle Scholar
  51. Peter A-C, 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
  52. Philander SGH, Pacanowski R (1986) A model of the seasonal cycle of the Tropical Atlantic ocean. J Geophys Res 91:14192–14206CrossRefGoogle Scholar
  53. Redelsperger J-L, 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 87:1739–1746CrossRefGoogle Scholar
  54. Rhein M, Dengler M, Sültenfuß J, Hummels R, Hüttl-Kabus S, Bourlès B (2010) Upwelling and associated heat flux in the equatorial Atlantic inferred from helium isotope disequilibrium. J Geophys Res 115:C08021. doi:10.1029/2009JC005772 Google Scholar
  55. Richardson P, Reverdin G (1987) Seasonal cycle of velocity in the Atlantic NECC as measured by surface drifters, current meters and ship drifts. J Geophys Res 92:3691–3708CrossRefGoogle Scholar
  56. Schott FA, Fischer J, Stramma L (1998) Transports and pathways of the upper-layer circulation in the western tropical Atlantic. J Phys Oceanogr 28:1904–1928CrossRefGoogle Scholar
  57. Snowden D, Molinari RL (2003), Subtropical cells in the Atlantic ocean: an observational summary. In: Goni GJ, Malanotte-Rizzoli P (eds) Interhemispheric water exchange in the Atlantic Ocean. Elsevier Oceanography Series 68:287–312Google Scholar
  58. Stramma L, Schott F (1999) The mean flow field of the tropical Atlantic Ocean. Deep Sea Res II 46(1–2):279–303CrossRefGoogle Scholar
  59. Tréguier A-M, Barnier B, De Miranda AP, Molines JM, Grima N, Imbard N, Madec G, Messager C (2001) Eddy permitting model of the Atlantic circulation: evaluating open boundary conditions. J Geophys Res 106(C10):22115–22129. doi:10.1029/2000JC000376 CrossRefGoogle Scholar
  60. Verstraete J-M (1992) The seasonal upwellings in the Gulf of Guinea. Prog Oceanogr 29:1–60CrossRefGoogle Scholar
  61. Voituriez B (1983) Les variations saisonnières des courants équatoriaux à 4°W et l’upwelling équatorial du Golfe de Guinée, I. Le sous-courant équatorial. Oceanogr Trop 18(2): 163–183Google Scholar
  62. Wacongne S (1989) Dynamical regimes of fully nonlinear stratified model of the Atlantic Equatorial Undercurrent. J Geophys Res 94(C4):4801–4815CrossRefGoogle Scholar
  63. Wacongne S, Piton B (1992) The near-surface circulation in the northeastern corner of the South Atlantic Ocean. Deep-Sea Res 39:1273–1298CrossRefGoogle Scholar
  64. Wade M, Caniaux G, du Penhoat Y (2011) Variability of the mixed layer heat budget in the eastern equatorial Atlantic during 2005–2007 as inferred using Argo floats. J Geophys Res 116:C08006. doi:10.1029/2010JC006683 Google Scholar
  65. Wang C (2005) Subthermocline tropical cells and equatorial subsurface countercurrents. Deep-Sea Res I 52:123–135CrossRefGoogle Scholar
  66. Zhang D, McPhaden MJ, Johns WE (2003) Observational evidence for flow between the subtropical and tropical Atlantic: the Atlantic subtropical cells. J Phys Oceanogr 33:1783–1797CrossRefGoogle Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  • Nicolas Kolodziejczyk
    • 1
  • Frédéric Marin
    • 2
    • 3
  • Bernard Bourlès
    • 2
    • 4
  • Yves Gouriou
    • 5
  • Henrick Berger
    • 6
  1. 1.Sorbonne Universités (UPMC, Univ Paris 06)-CNRS-IRD-MNHN, LOCEAN LaboratoryParisFrance
  2. 2.Université de Toulouse, UPS (OMP-PCA)ToulouseFrance
  3. 3.IRD, LEGOSNouméaNew Caledonia
  4. 4.IRD, LEGOSPlouzanéFrance
  5. 5.IRD-US191PlouzanéFrance
  6. 6.IFREMER, DYNECO-PYSEDPlouzanéFrance

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