Ocean Dynamics

, Volume 63, Issue 2–3, pp 179–194 | Cite as

An assessment of the mixed layer salinity budget in the tropical Pacific Ocean. Observations and modelling (1990–2009)

  • Audrey E. A. Hasson
  • Thierry Delcroix
  • Raphaël Dussin


This paper investigates mechanisms controlling the mixed-layer salinity (MLS) in the tropical Pacific during 1990–2009. We use monthly 1° × 1° gridded observations of salinity, horizontal current and fresh water flux, and a validated ocean general circulation model with no direct MLS relaxation in both its full resolution (0.25° and 5 days) and re-sampled as the observation time/space grid resolution. The present study shows that the mean spatial distribution of MLS results from a subtle balance between surface forcing (E − P, evaporation minus precipitation), horizontal advection (at low and high frequencies) and subsurface forcing (entrainment and mixing), all terms being of analogous importance. Large-scale seasonal MLS variability is found mainly in the Intertropical and South Pacific Convergence Zones due to changes in their meridional location (and related heavy P), in the North Equatorial Counter Currents, and partly in the subsurface forcing. Maximum interannual variability is found in the western Pacific warm pool and in both convergence zones, in relation to El Niño Southern Oscillation (ENSO) events. In the equatorial band, this later variability is due chiefly to the horizontal advection of low salinity waters from the western to the central-eastern basin during El Niño (and vice versa during La Niña), with contrasted evolution for the Eastern and Central Pacific ENSO types. Our findings reveal that all terms of the MLS equation, including high-frequency (<1 month) salinity advection, have to be considered to close the salinity budget, ruling out the use of MLS (or sea surface salinity) only to directly infer the mean, seasonal and/or interannual fresh water fluxes.


Sea surface salinity Mixed-layer budget Seasonal variability Interannual variability 


  1. Adler RF et al (2003) The version-2 global precipitation climatology project (GPCP) monthly precipitation analysis (1979–present). J Hydrometeorol 4(6):1147–1167. doi:10.1175/1525-7541(2003)004<1147:tvgpcp>2.0.co;2
  2. Alory G, Maes C, Delcroix T, Reul N, Illig S (2012) Seasonal dynamics of sea surface salinity off Panama: the far Eastern Pacific Fresh Pool. J Geophys Res Oceans 117. doi:10.1029/2011jc007802
  3. Ando K, McPhaden MJ (1997) Variability of surface layer hydrography in the tropical Pacific Ocean. J Geophys Res Oceans 102(C10):23063–23078CrossRefGoogle Scholar
  4. Ashok K, Behera SK, Rao SA, Weng H, Yamagata T (2007) El Niño Modoki and its possible teleconnection. J Geophys Res Oceans 112(C11). doi:10.1029/2006jc003798
  5. Ballabrera-Poy J, Murtugudde R, Busalacchi AJ (2002) On the potential impact of sea surface salinity observations on ENSO predictions. J Geophys Res Oceans 107(C12). doi:10.1029/2001jc000834
  6. Barnier B 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. doi:10.1007/s10236-006-0082-1 Google Scholar
  7. Barnier B, Dussin R, Molines JM (2011) Scientific Validation Report (ScVR) for V1 Reprocessed Analysis and Reanalysis: GLORYS2V1. MyOcean FP7-SPACE-2007-1 project, report MYO-WP04-ScCV-rea-CNRSRep Google Scholar
  8. Bingham FM, Foltz GR, McPhaden MJ (2010) Seasonal cycles of surface layer salinity in the Pacific Ocean. Ocean Science 6(3):775–787. doi:10.5194/os-6-775-2010 CrossRefGoogle Scholar
  9. Blanke B, Delecluse P (1993) Variability of the tropical Atlantic Ocean simulated by a General Circulation Model with 2 different mixed-layer physics. J Phys Oceanogr 23(7):1363–1388CrossRefGoogle Scholar
  10. Bonjean F, Lagerloef GSE (2002) Diagnostic model and analysis of the surface currents in the tropical Pacific Ocean. J Phys Oceanogr 32(10):2938–2954CrossRefGoogle Scholar
  11. Bosc C, Delcroix T (2008) Observed equatorial Rossby waves and ENSO-related warm water volume changes in the equatorial Pacific Ocean. J Geophys Res Oceans 113(C6). doi:10.1029/2007jc004613
  12. Bosc C, Delcroix T, Maes C (2009) Barrier layer variability in the western Pacific warm pool from 2000 to 2007. J Geophys Res-Oceans 114(C6). doi:10.1029/2008JC005187
  13. Boulanger JP, Menkes C (1999) Long equatorial wave reflection in the Pacific Ocean from TOPEX/POSEIDON data during the 1992–1998 period. Clim Dyn 15(3):205–225. doi:10.1007/s003820050277 CrossRefGoogle Scholar
  14. Cooper NS (1988) The effect of salinity on tropical ocean models. J Phys Oceanogr 18(5):697–707. doi:10.1175/1520-0485(1988)018<0697:teosot>2.0.co;2 Google Scholar
  15. Cravatte S, Delcroix T, Zhang D, McPhaden M, Leloup J (2009) Observed freshening and warming of the western Pacific Warm Pool. Clim Dyn 33(4):565–589. doi:10.1007/s00382-009-0526-7 CrossRefGoogle Scholar
  16. de Boyer Montégut C, Madec G, Fischer A, 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:C12003CrossRefGoogle Scholar
  17. Delcroix T (1998) Observed surface oceanic and atmospheric variability in the Tropical Pacific at seasonal and ENSO time scales: a tentative overview. J Geophys Res 103:18611–18633CrossRefGoogle Scholar
  18. Delcroix T, Henin C (1991) Seasonal and interannual variations of sea surface salinity in the tropical Pacific Ocean. J Geophys Res Oceans 96(C12):22135–22150CrossRefGoogle Scholar
  19. Delcroix T, Picaut J (1998) Zonal displacement of the western equatorial Pacific "fresh pool". J Geophys Res Oceans 103(C1):1087–1098. doi:10.1029/97jc01912 CrossRefGoogle Scholar
  20. Delcroix T, Dewitte B, duPenhoat Y, Masia F, Picaut J (2000) Equatorial waves and warm pool displacements during the 1992–1998 El Niño Southern Oscillation events: observation and modeling. J Geophys Res Oceans 105(C11):26045–26062. doi:10.1029/2000jc900113 CrossRefGoogle Scholar
  21. Delcroix T, McPhaden MJ, Dessier A, Gouriou Y (2005) Time and space scales for sea surface salinity in the tropical oceans. Deep-Sea Res I Oceanogr Res Pap 52(5):787–813. doi:10.1016/j.dsr.2004.11.012 CrossRefGoogle Scholar
  22. Delcroix T, Cravatte S, McPhaden MJ (2007) Decadal variations and trends in tropical Pacific sea surface salinity since 1970. J Geophys Res Oceans 112(C3):C03012. doi:10.1029/2006jc003801 CrossRefGoogle Scholar
  23. Delcroix T, Alory G, Cravatte S, Correge T, McPhaden MJ (2011) A gridded sea surface salinity data set for the tropical Pacific with sample applications (1950–2008). Deep-Sea Res I Oceanogr Res Pap 58(1):38–48. doi:10.1016/j.dsr.2010.11.002 CrossRefGoogle Scholar
  24. Dessier A, Donguy JR (1994) The sea surface salinity in the tropical Atlantic between 10 degS and 30 degN seasonal and interannual variations (1997–1989). Deep-Sea Res I Oceanogr Res Pap 41(1):81–100. doi:10.1016/0967-0637(94)90027-2 CrossRefGoogle Scholar
  25. Dewitte B, Choi J, An SI, Thual S (2012) Vertical structure variability and equatorial waves during central Pacific and eastern Pacific El Nios in a coupled general circulation model. Clim Dyn 38(11–12):2275–2289. doi:10.1007/s00382-011-1215-x CrossRefGoogle Scholar
  26. Donguy JR, Henin C (1980) Surface conditions in the Eastern Equatorial pacific related to the intertropical convergence zone of winds. Deep Sea Res Oceanogr Res Paper 27(9):693–714. doi:10.1016/0198-0149(80)90023-0 CrossRefGoogle Scholar
  27. Donguy JR, Meyers G (1996) Seasonal variations of sea-surface salinity and temperature in the tropical Indian Ocean. Deep-Sea Res I Oceanogr Res Pap 43(2):117–138. doi:10.1016/0967-0637(96)00009-x CrossRefGoogle Scholar
  28. Durack PJ, Wijffels SE (2010) Fifty-year trends in global ocean salinities and their relationship to broad-scale warming. J Clim 23(16):4342–4362. doi:10.1175/2010jcli3377.1 CrossRefGoogle Scholar
  29. Emery W, Thomson R (1998) Data analysis methods in physical oceanography. Pergamon, Elsevier Science Ltd, New York, p 634Google Scholar
  30. Ferry N, Parent L, Garric G, Drevillon M, Desportes C, Bricaut C, Hernandez F (2011) Scientific validation report (ScVR) for V1 reprocessed analysis and reanalysis: GLORYS2V1. MyOcean FP7-SPACE-2007-1 project, report MYO-WP04-ScCV-rea-MERCATOR_V1Rep Google Scholar
  31. Gill AE (1982) Atmosphere-ocean dynamics, pp. 1–662. Academic Press, doi:10.1016/S0074-6142(08)60026-1
  32. Gouriou Y, Delcroix T (2002) Seasonal and ENSO variations of sea surface salinity and temperature in the South Pacific Convergence Zone during 1976–2000. J Geophys Res Oceans 107(C12):8011. doi:10.1029/2001jc000830 CrossRefGoogle Scholar
  33. Grodsky SA, Carton JA, Bingham FM (2006) Low frequency variation of sea surface salinity in the tropical Atlantic. Geophys Res Lett 33(14). doi:10.1029/2006gl026426
  34. Halpern D, Knox RA, Luther DS (1988) Observations of 20-day period meridional current oscillations in the upper ocean along the pacific equator. J Phys Oceanogr 18(11):1514–1534. doi:10.1175/1520-0485(1988)018<1514:OODPMC>2.0.CO;2 Google Scholar
  35. Johnson ES, Lagerloef GSE, Gunn JT, Bonjean F (2002) Surface salinity advection in the tropical oceans compared with atmospheric freshwater forcing: a trial balance. J Geophys Res Oceans 107(C12). doi:10.1029/2001jc001122
  36. Kerr YH, Waldteufel P, Wigneron JP, Martinuzzi JM, Font J, Berger M (2001) Soil moisture retrieval from space: the soil moisture and ocean salinity (SMOS) mission. IEEE Trans Geosci Remote Sens 39(8):1729–1735. doi:10.1109/36.942551 CrossRefGoogle Scholar
  37. Kessler WS (2006) The circulation of the eastern tropical Pacific: a review. Prog Oceanogr 69(2–4):181–217. doi:10.1016/j.pocean.2006.03.009 CrossRefGoogle Scholar
  38. Lagerloef GSE, Mitchum GT, Lukas RB, Niiler PP (1999) Tropical Pacific near-surface currents estimated from altimeter, wind, and drifter data. J Geophys Res Oceans 104(C10):23313–23326. doi:10.1029/1999jc900197 CrossRefGoogle Scholar
  39. Lagerloef G et al (2008) The AQUARIUS/SAC-D mission: designed to meet the salinity remote-sensing challenge. Oceanography 21(1):68–81CrossRefGoogle Scholar
  40. Lagerloef G, Schmitt R, Schanze J, Kao H-Y (2010) The ocean and the global water cycle. Oceanography 23(4):82–93CrossRefGoogle 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). doi:10.1029/2012GL052232
  42. Legeckis R (1977) Long waves in eastern equatorial Pacific Ocean—view from a geostationary satellite. Science 197(4309):1179–1181. doi:10.1126/science.197.4309.1179 CrossRefGoogle Scholar
  43. Lukas R, Lindstrom E (1991) The mixed layer of the western equatorial Pacific Ocean. J Geophys Res Oceans 96:3343–3357CrossRefGoogle Scholar
  44. Lyman JM, Johnson GC, Kessler WS (2007) Distinct 17-and 33-day tropical instability waves in subsurface observations. J Phys Oceanogr 37(4):855–872. doi:10.1175/jpo3023.1 CrossRefGoogle Scholar
  45. Madec G (2008) NEMO ocean engine, edited, p. 300, France, Institut Pierre-Simon Laplace (IPSL)Google Scholar
  46. Maes C, Ando K, Delcroix T, Kessler WS, McPhaden MJ, Roemmich D (2006) Observed correlation of surface salinity, temperature and barrier layer at the eastern edge of the western Pacific warm pool. Geophys Res Lett 33(6):L06601. doi:10.1029/2005gl024772 CrossRefGoogle Scholar
  47. McPhaden MJ, Yu X (1999) Equatorial waves and the 1997–98 El Niño. Geophys Res Lett 26(19):2961–2964. doi:10.1029/1999gl004901 CrossRefGoogle Scholar
  48. Miller JR (1976) Salinity effect in a mixed layer ocean model. J Phys Oceanogr 6(1):29–35. doi:10.1175/1520-0485(1976)006<0029:tseiam>2.0.co;2 Google Scholar
  49. Penduff T, Juza M, Brodeau L, Smith GC, Barnier B, Molines JM, Treguier AM, Madec G (2010) Impact of global ocean model resolution on sea-level variability with emphasis on interannual time scales. Ocean Sci 6(1):269–284CrossRefGoogle Scholar
  50. Picaut J, Ioualalen M, Menkes C, Delcroix T, McPhaden MJ (1996) Mechanism of the zonal displacements of the Pacific warm pool: implications for ENSO. Science 274(5292):1486–1489. doi:10.1126/science.274.5292.1486 CrossRefGoogle Scholar
  51. Picaut J, Ioualalen M, Delcroix T, Masia F, Murtugudde R, Vialard J (2001) The oceanic zone of convergence on the eastern edge of the Pacific warm pool: a synthesis of results and implications for El Niño-Southern Oscillation and biogeochemical phenomena. J Geophys Res Oceans 106(C2):2363–2386CrossRefGoogle Scholar
  52. Qiu B, Scott RB, Chen S (2008) Length scales of eddy generation and nonlinear evolution of the seasonally modulated South Pacific Subtropical Countercurrent. J Phys Oceanogr 38(7):1515–1528. doi:10.1175/2007jpo3856.1 CrossRefGoogle Scholar
  53. Qu T, Gao S, Fukumori I (2011) What governs the North Atlantic salinity maximum in a global GCM? Geophys Res Lett 38. doi:10.1029/2011gl046757
  54. Roemmich D, Boebel O, Desaubies Y, Freeland H, King B, LeTraon P.-Y, Molinari R, Owens B, Riser S, Send U, Takeuchi K, Wijffels S (1999) ARGO: the global array of profiling floats. CLIVAR Exchanges 13Google Scholar
  55. Singh A, Delcroix T, Cravatte S (2011) Contrasting the flavors of El Niño-Southern Oscillation using sea surface salinity observations. J Geophys Res Oceans 116. doi:10.1029/2010jc006862
  56. Sverdrup HU (1943) On the ratio between heat conduction from the sea surface and heat used for evaporation. Ann N Y Acad Sci 44(1):81–88CrossRefGoogle Scholar
  57. Terray L, Corre L, Cravatte S, Delcroix T, Reverdin G, Ribes A (2012) Near-surface salinity as nature's rain gauge to detect human influence on the tropical water cycle. J Clim 25(3):958–977. doi:10.1175/jcli-d-10-05025.1 CrossRefGoogle Scholar
  58. Vialard J, Delecluse P (1998a) An OGCM study for the TOGA decade. Part I: role of salinity in the physics of the western Pacific fresh pool. J Phys Oceanogr 28(6):1071–1088. doi:10.1175/1520-0485(1998)028<1071:aosftt>2.0.co;2
  59. Vialard J, Delecluse P (1998b) An OGCM study for the TOGA decade. Part II: barrier-layer formation and variability. J Phys Oceanogr 28(6):1089–1106. doi:10.1175/1520-0485(1998)028<1089:aosftt>2.0.co;2
  60. 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 Niño. J Phys Oceanogr 31(7):1649–1675. doi:10.1175/1520-0485(2001)031<1649:amsoom>2.0.co;2 Google Scholar
  61. Vialard JM, Delecluse P, Menkes C (2002) A modeling study of salinity variability and its effects in the tropical Pacific Ocean during the 1993–1999 period. J Geophys Res Oceans 107(C12). doi:10.1029/2000jc000758
  62. Vialard J, Jayakumar A, Gnanaseelan C, Lengaigne M, Sengupta D, Goswami BN (2011) Processes of 30–90 days sea surface temperature variability in the Northern Indian Ocean during boreal summer. Clim Dyn. doi:10.1007/s00382-011-1015-3
  63. Vinayachandran PN, Nanjundiah RS (2009) Indian Ocean sea surface salinity variations in a coupled model. Clim Dyn 33(2–3):245–263. doi:10.1007/s00382-008-0511-6 CrossRefGoogle Scholar
  64. Yim BY, Yeh SW, Noh Y, Moon BK, Park YG (2008) Sea surface salinity variability and its relation to El Niño in a CGCM. Asia-Pac J Atmos Sci 44(2):173–189Google Scholar
  65. Yu L (2011) A global relationship between the ocean water cycle and near-surface salinity. J Geophys Res Oceans 116. doi:10.1029/2010jc006937
  66. Yu L, Jin X, Weller RA (2008) Multidecade global flux datasets from the objectively analyzed air-sea fluxes (OAFlux) project: latent and sensible heat fluxes, ocean evaporation, and related surface meteorological variables. Rep., 64pp., Woods Hole Oceanographic Institution, Woods Hole MassachusettsGoogle Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 2013

Authors and Affiliations

  • Audrey E. A. Hasson
    • 1
  • Thierry Delcroix
    • 1
  • Raphaël Dussin
    • 2
  1. 1.Université de Toulouse 3, LEGOS, UMR 5566 CNRS-CNES-IRD-UPSToulouse Cedex 09France
  2. 2.LEGIDomaine UniversitaireGrenoble Cedex 09France

Personalised recommendations