The Equatorial Undercurrent in the central Atlantic and its relation to tropical Atlantic variability

Abstract

Seasonal to interannual variations of the Equatorial Undercurrent (EUC) in the central Atlantic at 23°W are studied using shipboard observation taken during the period 1999–2011 as well as moored velocity time series covering the period May 2005–June 2011. The seasonal variations are dominated by an annual harmonic of the EUC transport and the EUC core depth (both at maximum during September), and a semiannual harmonic of the EUC core velocity (maximum during April and September). Substantial interannual variability during the period of moored observation included anomalous cold/warm equatorial Atlantic cold tongue events during 2005/2008. The easterly winds in the western equatorial Atlantic during boreal spring that represent the preconditioning of cold/warm events were strong/weak during 2005/2008 and associated with strong/weak boreal summer EUC transport. The anomalous year 2009 was instead associated with weak preconditioning and smallest EUC transport on record from January to July, but during August coldest SST anomalies in the eastern equatorial Atlantic were observed. The interannual variations of the EUC are discussed with respect to recently described variability of the tropical Atlantic Ocean.

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

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

References

  1. Arhan M, Treguier AM, 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. doi:10.1175/Jpo2929.1

    Article  Google Scholar 

  2. Athie G, Marin F (2008) Cross-equatorial structure and temporal modulation of intraseasonal variability at the surface of the Tropical Atlantic Ocean. J Geophys Res Oceans 113(C8). doi:10.1029/2007jc004332

  3. Barnett TP (1983) Interaction of the monsoon and Pacific trade-wind system at interannual time scales. Part I: the equatorial zone. Mon Weather Rev 111(4):756–773. doi:10.1175/1520-0493(1983)111<0756:Iotmap>2.0.Co;2

    Article  Google Scholar 

  4. Brandt P, Schott FA, Provost C, Kartavtseff A, Hormann V, Bourles B, Fischer J (2006) Circulation in the central equatorial Atlantic: mean and intraseasonal to seasonal variability. Geophys Res Lett 33(7). doi:10.1029/2005gl025498

  5. Brandt P, Hormann V, Bourles B, Fischer J, Schott FA, Stramma L, Dengler M (2008) Oxygen tongues and zonal currents in the equatorial Atlantic. J Geophys Res Oceans 113(C4). doi:10.1029/2007jc004435

  6. Brandt P, Caniaux G, Bourles B, Lazar A, Dengler M, Funk A, Hormann V, Giordani H, Marin F (2011a) Equatorial upper-ocean dynamics and their interaction with the West African monsoon. Atmos Sci Lett 12(1):24–30

    Article  Google Scholar 

  7. Brandt P, Funk A, Hormann V, Dengler M, Greatbatch RJ, Toole JM (2011b) Interannual atmospheric variability forced by the deep equatorial Atlantic Ocean. Nature 473(7348):497–500. doi:10.1038/Nature10013

    Article  Google Scholar 

  8. Brandt P, Greatbatch RJ, Claus M, Didwischus SH, Hormann V, Funk A, Hahn J, Krahmann G, Fischer J, Kortzinger A (2012) Ventilation of the equatorial Atlantic by the equatorial deep jets. J Geophys Res Oceans 117. doi:10.1029/2012jc008118

  9. Bunge L, Provost C, Kartavtseff A (2007) Variability in horizontal current velocities in the central and eastern equatorial Atlantic in 2002. J Geophys Res Oceans 112(C2). doi:10.1029/2006jc003704

  10. Bunge L, Provost C, Hua BL, Kartavtseff A (2008) Variability at intermediate depths at the equator in the Atlantic ocean in 2000–06: annual cycle, equatorial deep jets, and intraseasonal meridional velocity fluctuations. J Phys Oceanogr 38(8):1794–1806. doi:10.1175/2008jpo3781.1

    Article  Google Scholar 

  11. 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 116. doi:10.1029/2010jc006570

  12. Chang P, Yamagata T, Schopf P, Behera SK, Carton J, Kessler WS, Meyers G, Qu T, Schott F, Shetye S, Xie SP (2006) Climate fluctuations of tropical coupled systems—the role of ocean dynamics. J Clim 19(20):5122–5174. doi:10.1175/Jcli3903.1

    Article  Google Scholar 

  13. Cromwell T, Montgomery RB, Stroup ED (1954) Equatorial undercurrent in Pacific Ocean revealed by new methods. Science 119(3097):648–649. doi:10.1126/Science.119.3097.648

    Article  Google Scholar 

  14. Firing E, Lukas R, Sadler J, Wyrtki K (1983) Equatorial Undercurrent disappears during 1982–1983 El-Nino. Science 222(4628):1121–1123. doi:10.1126/Science.222.4628.1121

    Article  Google Scholar 

  15. Foltz GR, McPhaden MJ (2010) Abrupt equatorial wave-induced cooling of the Atlantic cold tongue in 2009. Geophys Res Lett 37. doi:10.1029/2010gl045522

  16. Foltz GR, McPhaden MJ, Lumpkin R (2012) A strong Atlantic Meridional Mode event in 2009: the role of mixed layer dynamics. J Clim 25(1):363–380. doi:10.1175/Jcli-D-11-00150.1

    Article  Google Scholar 

  17. Foltz GR, Schmid C, Lumpkin R (2013) Seasonal cycle of the mixed layer heat budget in the northeastern tropical Atlantic Ocean. J Clim 26(20):8169–8188. doi:10.1175/JCLI-D-13-00037.1

    Article  Google Scholar 

  18. Ganachaud A, Wunsch C (2000) Improved estimates of global ocean circulation, heat transport and mixing from hydrographic data. Nature 408(6811):453–457. doi:10.1038/35044048

    Article  Google Scholar 

  19. 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 Lett 32(10). doi:10.1029/2004gl022206

  20. Goes M, Wainer I (2003) Equatorial currents transport changes for extreme warm and cold events in the Atlantic Ocean. Geophys Res Lett 30(5). doi:10.1029/2002gl015707

  21. Greatbatch RJ, Brandt P, Claus M, Didwischus SH, Fu Y (2012) On the width of the equatorial deep jets. J Phys Oceanogr 42(10):1729–1740. doi:10.1175/Jpo-D-11-0238.1

    Article  Google Scholar 

  22. Han WQ, Webster PJ, Lin JL, Liu WT, Fu R, Yuan DL, Hu AX (2008) Dynamics of intraseasonal sea level and thermocline variability in the equatorial Atlantic during 2002–03. J Phys Oceanogr 38(5):945–967. doi:10.1175/2008jpo3854.1

    Article  Google Scholar 

  23. Hormann V, Brandt P (2007) Atlantic Equatorial Undercurrent and associated cold tongue variability. J Geophys Res Oceans 112(C6). doi:10.1029/2006jc003931

  24. Hormann V, Brandt P (2009) Upper equatorial Atlantic variability during 2002 and 2005 associated with equatorial Kelvin waves. J Geophys Res Oceans 114. doi:10.1029/2008jc005101

  25. 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. doi:10.1016/j.pocean.2012.11.001

    Article  Google Scholar 

  26. Johnson GC, Zhang DX (2003) Structure of the Atlantic Ocean equatorial deep jets. J Phys Oceanogr 33(3):600–609. doi:10.1175/1520-0485(2003)033<0600:Sotaoe>2.0.Co;2

    Article  Google Scholar 

  27. Johnson GC, Sloyan BM, Kessler WS, McTaggart KE (2002) Direct measurements of upper ocean currents and water properties across the tropical Pacific during the 1990s. Prog Oceanogr 52(1):31–61. doi:10.1016/S0079-6611(02)00021-6

    Article  Google Scholar 

  28. Jouanno J, Marin F, du Penhoat Y, Molines JM, Sheinbaum J (2011a) Seasonal modes of surface cooling in the Gulf of Guinea. J Phys Oceanogr 41(7):1408–1416. doi:10.1175/Jpo-D-11-031.1

    Article  Google Scholar 

  29. Jouanno J, Marin F, du Penhoat Y, Sheinbaum J, Molines JM (2011b) Seasonal heat balance in the upper 100 m of the equatorial Atlantic Ocean. J Geophys Res Oceans 116. doi:10.1029/2010jc006912

  30. Kessler WS, Johnson GC, Moore DW (2003) Sverdrup and nonlinear dynamics of the Pacific equatorial currents. J Phys Oceanogr 33(5):994–1008. doi:10.1175/1520-0485(2003)033<0994:Sandot>2.0.Co;2

    Article  Google Scholar 

  31. Kolodziejczyk N, Bourles B, Marin F, Grelet J, Chuchla R (2009) Seasonal variability of the equatorial undercurrent at 10 degrees W as inferred from recent in situ observations. J Geophys Res Oceans 114. doi:10.1029/2008JC004976

  32. Lumpkin R, Speer K (2003) Large-scale vertical and horizontal circulation in the North Atlantic Ocean. J Phys Oceanogr 33(9):1902–1920

    Article  Google Scholar 

  33. Marin F, Caniaux G, Bourles B, Giordani H, 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(6):1416–1431. doi:10.1175/2008jpo4030.1

    Article  Google Scholar 

  34. McCreary JP, Lu P (1994) Interaction between the subtropical and equatorial ocean circulations—the subtropical cell. J Phys Oceanogr 24(2):466–497

    Article  Google Scholar 

  35. Metcalf WG, Voorhis AD, Stalcup MC (1962) The Atlantic equatorial undercurrent. J Geophys Res 67(6):2156–2202. doi:10.1029/JZ067i006p02499

    Google Scholar 

  36. Okumura Y, Xie SP (2006) Some overlooked features of tropical Atlantic climate leading to a new Nino-like phenomenon. J Clim 19(22):5859–5874. doi:10.1175/Jcli3928.1

    Article  Google Scholar 

  37. Philander SGH, Pacanowski RC (1980) The generation of equatorial currents. J Geophys Res Oceans 85(Nc2):1123–1136. doi:10.1029/Jc085ic02p01123

    Article  Google Scholar 

  38. Philander SGH, Pacanowski RC (1981) The oceanic response to cross-equatorial winds (with application to coastal upwelling in low latitudes). Tellus 33(2):201–210

    Article  Google Scholar 

  39. Polo I, Lazar A, Rodriguez-Fonseca B, Arnault S (2008) Oceanic Kelvin waves and tropical Atlantic intraseasonal variability: 1. Kelvin wave characterization. J Geophys Res Oceans 113(C7). doi:10.1029/2007jc004495

  40. Provost C, Arnault S, Chouaib N, Kartavtseff A, Bunge L, Sultan E (2004) TOPEX/Poseidon and Jason equatorial sea surface slope anomaly in the Atlantic in 2002: comparison with wind and current measurements at 23 W. Mar Geod 27(1–2):31–45. doi:10.1080/01490410490465274

    Article  Google Scholar 

  41. Qiao L, Weisberg RH (1997) The zonal momentum balance of the equatorial undercurrent in the central Pacific. J Phys Oceanogr 27(6):1094–1119

    Article  Google Scholar 

  42. Richter I, Behera SK, Masumoto Y, Taguchi B, Sasaki H, Yamagata T (2013) Multiple causes of interannual sea surface temperature variability in the equatorial Atlantic Ocean. Nat Geosci 6(1):43–47. doi:10.1038/Ngeo1660

    Google Scholar 

  43. Schott FA, Fischer J, Stramma L (1998) Transports and pathways of the upper-layer circulation in the western tropical Atlantic. J Phys Oceanogr 28(10):1904–1928

    Article  Google Scholar 

  44. Schott FA, Mccreary JP, Johnson GC (2004) Shallow overturning circulations of the tropical–subtropical oceans. In: Wang C, Xie S-P, Carton JA (eds) Earth climate: The ocean–atmosphere interaction. Geophys Monogr 147. American Geophysical Union, Washington, DC, pp 261–304

  45. Sutton RT, Jewson SP, Rowell DP (2000) The elements of climate variability in the tropical Atlantic region. J Clim 13(18):3261–3284. doi:10.1175/1520-0442(2000)013<3261:Teocvi>2.0.Co;2

    Article  Google Scholar 

  46. von Schuckmann K, Brandt P, Eden C (2008) Generation of tropical instability waves in the Atlantic Ocean. J Geophys Res Oceans 113(C8). doi:10.1029/2007jc004712

  47. Weisberg RH, Hickman JH, Tang TY, Weingartner TJ (1987) Velocity and temperature observations during the seasonal response of the Equatorial Atlantic Experiment at 0°, 28°W. J Geophys Res Oceans 92(C5):5061–5075. doi:10.1029/Jc092ic05p05061

    Article  Google Scholar 

Download references

Acknowledgments

This study was funded by the Deutsche Bundesministerium für Bildung und Forschung (BMBF) as part of the projects NORDATLANTIK (03F0443B), RACE (03F0651B), MIKLIP (01LP1114A) and by the Deutsche Forschungsgemeinschaft through several research cruises with RV Meteor and RV Maria S. Merian and as part of the Sonderforschungsbereich 754 “Climate–Biogeochemistry Interactions in the Tropical Ocean”. Moored velocity observations were acquired in cooperation with the PIRATA project. We would like to thank Verena Hormann and Ingo Richter for helpful discussion and two anonymous reviewers for their comments that lead to significant improvements in the manuscript.

Author information

Affiliations

Authors

Corresponding author

Correspondence to Peter Brandt.

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

Cite this article

Brandt, P., Funk, A., Tantet, A. et al. The Equatorial Undercurrent in the central Atlantic and its relation to tropical Atlantic variability. Clim Dyn 43, 2985–2997 (2014). https://doi.org/10.1007/s00382-014-2061-4

Download citation

Keywords

  • Equatorial Atlantic circulation
  • Moored and shipboard observations
  • Cold tongue
  • Seasonal cycle
  • Interannual variability
  • African monsoon