Subtropical sea surface salinity maxima in the South Indian Ocean

  • Yu Wang
  • Yuanlong Li
  • Chuanjie WeiEmail author


Subtropical sea surface salinity (SSS) maximum is formed in the subtropical South Indian Ocean (SIO) by excessive evaporation over precipitation and serves as the primary salt source of the SIO. Space-borne SSS measurements by Aquarius satellite during September 2011–May 2015 detect three disconnected SSS maximum regions (>35.6) in the eastern (105°E–115°E, 38°S–28°S), central (60°E–100°E, 35°S–25°S), and western (25°E–10°E, 38°S–20°S) parts of the subtropical SIO, respectively. Such structure is however not seen in gridded Argo data. Analysis of Argo profile data confirms the existence of the eastern maximum patch and also reveals SSS overestimations of Aquarius near the western and eastern boundaries. Although subjected to large uncertainties, a mixed-layer budget analysis is employed to explain the seasonal cycle of SSS. The eastern and central regions reach the highest salinity in February–March and lowest salinity in August–September, which can be well explained by surface freshwater forcing (SFF) term. SFF is however not controlled by evaporation (E) or precipitation (P). Instead, the large seasonal undulations of mixed layer depth (MLD) is the key factor. The shallow (deep) MLD in austral summer (winter) amplifies (attenuates) the forcing effect of local positive E–P and causes SSS rising (decreasing). Ocean dynamics also play a role. Particularly, activity of mesoscale eddies is a critical factor regulating SSS variability in the eastern and western regions.


sea surface salinity (SSS) subtropical salinity maximum Aquarius Argo float freshwater flux 


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  1. Atlas R, Ardizzone J, Hoffman R N. 2008. Application of satellite surface wind data to ocean wind analysis. In: Proceedings of SPIE 7087, Remote Sensing System Engineering. SPIE, San Diego, California, United States. 70870Bp, Scholar
  2. Beal L M, Bryden H L. 1999. The velocity and vorticity structure of the Agulhas Current at 32°S. Journal of Geophysical Research: Oceans, 104(C3): 5 151–5 176.CrossRefGoogle Scholar
  3. Beal L M, De Ruijter W P M, Biastoch A, Zahn R. 2011. On the role of the Agulhas system in ocean circulation and climate. Nature, 472(7344): 429–436.CrossRefGoogle Scholar
  4. Beal L M, Elipot S. 2016. Broadening not strengthening of the Agulhas Current since the early 1990s. Nature, 540(7634): 570–573.CrossRefGoogle Scholar
  5. Bingham F M, Busecke J, Gordon A L, Giulivi C F, Li Z J. 2014. The North Atlantic subtropical surface salinity maximum as observed by Aquarius. Journal of Geophysical Research: Oceans, 119(11): 7 741–7 755.Google Scholar
  6. Bonjean F, Lagerloef G S E. 2002. Diagnostic model and analysis of the surface currents in the tropical Pacific Ocean. Journal of Physical Oceanography, 32(10): 2 938–2 954.CrossRefGoogle Scholar
  7. Cannon G A. 1966. Tropical waters in the western Pacific Ocean, August-September 1957. Deep Sea Research and Oceanographic Abstracts, 13(6): 1 139–1 148.CrossRefGoogle Scholar
  8. De Boyer Montégut C, Madec G, Fischer A S, Lazar A, Iudicone D. 2004. Mixed layer depth over the global ocean: An examination of profile data and a profile-based climatology. Journal of Geophysical Research: Oceans, 109(C12): C12003, Scholar
  9. Du Y, Zhang Y H, Feng M, Wang T Y, Zhang N N, Wijffels S. 2015. Decadal trends of the upper ocean salinity in the tropical Indo-Pacific since mid-1990s. Scientific Reports, 5: 16050, CrossRefGoogle Scholar
  10. Ducet N, Le Traon P Y, Reverdin G. 2000. Global highresolution mapping of ocean circulation from TOPEX/Poseidon and ERS-1 and-2. Journal of Geophysical Research: Oceans, 105(C8): 19 477–19 498.CrossRefGoogle Scholar
  11. Durack P J, Wijffels S E. 2010. Fifty-year trends in global ocean salinities and their relationship to broad-scale warming. Journal of Climate, 23(16): 4 342–4 362.CrossRefGoogle Scholar
  12. Entekhabi D, Njoku E G, O’Neill P E, Kellogg K H, Crow W T, Edelstein W N, Entin J K, Goodman S D, Jackson T J, Johnson J, Kimball J, Piepmeier J R, Koster R D, Martin N, McDonald K C, Moghaddam M, Moran S, Reichle R, Shi J C, Spencer M W, Thurman S W, Tsang L, Van Zyl J. 2010. The soil moisture active passive (SMAP) mission. Proceedings of the IEEE, 98(5): 704–716.CrossRefGoogle Scholar
  13. Fang F X, Morrow R. 2003. Evolution, movement and decay of warm-core Leeuwin Current eddies. Deep Sea Research Part II: Topical Studies in Oceanography, 50(12–13): 2 245–2 261.CrossRefGoogle Scholar
  14. Feng M, Meyers G, Pearce A, Wijffels S. 2003. Annual and interannual variations of the Leeuwin Current at 32 S. Journal of Geophysical Research, 108(C11): 3355, Scholar
  15. Feng M, Wijffels S, Godfrey S, Meyers G. 2005. Do eddies play a role in the momentum balance of the leeuwin current? Journal of Physical Oceanography, 35(6): 964–975.CrossRefGoogle Scholar
  16. Guan B, Lee T, Halkides D J, Waliser D E. 2014. Aquarius surface salinity and the Madden-Julian Oscillation: The role of salinity in surface layer density and potential energy. Geophysical Research Letters, 41(8): 2 858–2 869, Scholar
  17. Huffman G J, Adler R F, Morrissey M M, Bolvin D T, Curtis S, Joyce R, McGavock B, Susskind J. 2001. Global precipitation at one-degree daily resolution from multisatellite observations. Journal of Hydrometeorology, 2(1): 36–50.CrossRefGoogle Scholar
  18. Johnson B K, Bryan F O, Grodsky S A, Carton J A. 2016. Climatological annual cycle of the salinity budgets of the subtropical maxima. Journal of Physical Oceanography, 46(10): 2 981–2 994.CrossRefGoogle Scholar
  19. Johnson E S, Bonjean F, Lagerloef G S E, Gunn J T, Mitchum G T. 2007. Validation and error analysis of OSCAR sea surface currents. Journal of Atmospheric and Oceanic Technology, 24(4): 688–701.CrossRefGoogle Scholar
  20. Katsumata K, Fukasawa M. 2011. Changes in meridional fluxes and water properties in the Southern Hemisphere subtropical oceans between 1992/1995 and 2003/2004. Progress in Oceanography, 89(1–4): 61–91.CrossRefGoogle Scholar
  21. Katsura S, Oka E, Qiu B, Schneider N. 2013. Formation and subduction of north pacific tropical water and their interannual variability. Journal of Physical Oceanography, 43(11): 2 400–2 415.CrossRefGoogle Scholar
  22. Kido S, Tozuka T. 2017. Salinity variability associated with the positive Indian Ocean dipole and its impact on the upper ocean temperature. Journal of Climate, 30(19): 7 885–7 907.CrossRefGoogle Scholar
  23. Lagerloef G, Colomb F R, Le Vine D, Wentz F, Yueh S, Ruf C, Lilly J, Gunn J, CHAO J, deCharon A, Feldman G, Swift C 2008. The Aquarius/SAC-D mission: Designed to meet the salinity remote-sensing challenge. Oceanography, 21(1): 68–81.CrossRefGoogle Scholar
  24. Lagerloef G, Wentz F, Yueh S, Kao H Y, Johnson G C, Lyman J M. 2012. Aquarius satellitemission provides new, detailed view of sea surface salinity. Bulletin of the American Meteorological Society, 93: S70–S71.Google Scholar
  25. Le Traon P, Nadal F, Ducet N. 1998. An improved mapping method of multisatellite altimeter data. Journal of Atmospheric and Oceanic Technology, 15(2): 522–534.CrossRefGoogle Scholar
  26. Lebedev K V, Yoshinari H, Maximenko N A, Hacker P W. 2007. Velocity data assessed from trajectories of Argo floats at parking level and at the sea surface. IPRC Technical Note, 4(2): 1–16.Google Scholar
  27. Lee T. 2004. Decadal weakening of the shallow overturning circulation in the South Indian Ocean. Geophysical Research Letters, 31(18): L18305, Scholar
  28. Li Y L, Han W Q, Lee T. 2015. Intraseasonal sea surface salinity variability in the equatorial Indo-Pacific Ocean induced by Madden-Julian oscillations. Journal of Geophysical Research: Oceans, 120(3): 2 233–2 258.Google Scholar
  29. Li Y L, Han W Q, Ravichandran M, Wang W Q, Shinoda T, Lee T. 2017. Bay of Bengal salinity stratification and Indian summer monsoon intraseasonal oscillation: 1. Intraseasonal variability and causes. Journal of Geophysical Research: Oceans, 122(5): 4 291–4 311.Google Scholar
  30. Li Y L, Han W Q, Wang W Q, Ravichandran M. 2016. Intraseasonal variability of SST and precipitation in the arabian sea during the Indian summer monsoon: impact of ocean mixed layer depth. Journal of Climate, 29(21): 7 889–7 910.CrossRefGoogle Scholar
  31. Li Y L, Han W Q. 2016. Causes for intraseasonal sea surface salinity variability in the western tropical Pacific Ocean and its seasonality. Journal of Geophysical Research: Oceans, 121(1): 85–103.Google Scholar
  32. Li Y L, Wang F, Han H Q. 2013. Interannual sea surface salinity variations observed in the tropical North Pacific Ocean. Geophysical Research Letters, 40(10): 2 194–2 199.CrossRefGoogle Scholar
  33. Li Y L, Wang F. 2012. Spreading and salinity change of North Pacific tropical water in the Philippine Sea. Journal of Oceanography, 68(3): 439–452.CrossRefGoogle Scholar
  34. Li Y L, Wang F. 2015. Thermocline spiciness variations in the tropical Indian Ocean observed during 2003–2014. Deep Sea Research Part I: Oceanographic Research Papers, 97: 52–66.CrossRefGoogle Scholar
  35. Matano R P, Beier E J, Strub P T, Tokmakian R 2002. Large-scale forcing of the Agulhas variability: The seasonal cycle. Journal of Physical Oceanography, 32(4): 1 228–1 241.CrossRefGoogle Scholar
  36. Menezes V V, Phillips H E, Schiller A, Bindoff N L, Domingues C M, Vianna M L. 2014b. South Indian Countercurrent and associated fronts. Journal of Geophysical Research: Oceans, 119(10): 6 763–6 791.Google Scholar
  37. Menezes V V, Vianna M L, Phillips H E. 2014a. Aquarius sea surface salinity in the South Indian Ocean: Revealing annual-period planetary waves. Journal of Geophysical Research: Oceans, 119(6): 3 883–3 908.Google Scholar
  38. O’Connor B M, Fine R A, Olson D B. 2005. A global comparison of subtropical underwater formation rate. Deep Sea Research Part I: Oceanographic Research Papers, 52(9): 1 569–1 590.CrossRefGoogle Scholar
  39. Owens W B, Wong A P S. 2009. An improved calibration method for the drift of the conductivity sensor on autonomous CTD profiling floats by θ-S climatology. Deep Sea Research Part I: Oceanographic Research Papers, 56(3): 450–457.CrossRefGoogle Scholar
  40. Qu T D, Gao S, Fine R A. 2013a. Subduction of south pacific tropical water and its equatorward pathways as shown by a simulated passive tracer. Journal of Physical Oceanography, 43(8): 1 551–1 565.CrossRefGoogle Scholar
  41. Qu T D, Gao S, Fukumori I. 2011. What governs the North Atlantic salinity maximum in a global GCM? Geophysical Research Letters, 38(7): L07602, Scholar
  42. Qu T D, Gao S, Fukumori I. 2013b. Formation of salinity maximum water and its contribution to the overturning circulation in the North Atlantic as revealed by a global general circulation model. Journal of Geophysical Research: Oceans, 118(4): 1 982–1 994, Scholar
  43. Qu T D, Meyers G. 2005. Seasonal variation of barrier layer in the southeastern tropical Indian Ocean. Journal of Geophysical Research: Oceans, 110(C11): C11003, Scholar
  44. Reul N, Tenerelli J, Chapron B, Vandemark D, Quilfen Y, Kerr Y. 2012. SMOS satellite L-band radiometer: A new capability for ocean surface remote sensing in hurricanes. Journal of Geophysical Research: Oceans, 117(C2): C02006, Scholar
  45. Roemmich D, Gilson J. 2009. The 2004–2008 mean and annual cycle of temperature, salinity, and steric height in the global ocean from the Argo Program. Progress in Oceanography, 82(2): 81–100.CrossRefGoogle Scholar
  46. Schott F A, Dengler M, Schoenefeldt R. 2002. The shallow overturning circulation of the Indian Ocean. Progress in Oceanography, 53(1): 57–103.CrossRefGoogle Scholar
  47. Siedler G, Rouault M, Lutjeharms J R E. 2006. Structure and origin of the subtropical South Indian Ocean Countercurrent. Geophysical Research Letters, 33(24): L24609, Scholar
  48. Stevenson J W, Niiler P P. 1983. Upper ocean heat budget during the Hawaii-to-Tahiti shuttle experiment. Journal of Physical Oceanography, 13(10): 1 894–1 907.CrossRefGoogle Scholar
  49. Tang W, Yueh S H, Fore A G, Hayashi A. 2014. Validation of Aquarius sea surface salinity with in situ measurements from Argo floats and moored buoys. Journal of Geophysical Research: Oceans, 119(9): 6 171–6 189.Google Scholar
  50. Tsuchiya M. 1968. Upper waters of the intertropical Pacific Oceans. In: Beal R C, DeLeonibus P S, Katz I eds. Johns Hopkins Oceanography Studies. Johns Hopkins University Press, Baltimore. 50p.Google Scholar
  51. Vargas-Hernandez J M, Wijffels S, Meyers G, Holbrook N J. 2015. Slow westward movement of salinity anomalies across the tropical South Indian Ocean. Journal of Geophysical Research: Oceans, 120(8): 5 436–5 456.Google Scholar
  52. Vinogradova N T, Ponte R M. 2013. Clarifying the link between surface salinity and freshwater fluxes on monthly to interannual time scales. Journal of Geophysical Research: Oceans, 118(6): 3 190–3 201.Google Scholar
  53. Warren B. 1981. Transindian hydrographic section at lat. 18 S: Property distributions and circulation in the south Indian Ocean. Deep Sea Research Part A. Oceanographic Research Papers, 28(8): 759–788.CrossRefGoogle Scholar
  54. Wijffels S, Sprintall J, Fieux M, Bray N. 2002. The JADE and WOCE I10/IR6 throughflow sections in the southeast Indian Ocean. Part 1: Water mass distribution and variability. Deep Sea Research Part II: Topical Studies in Oceanography, 49(7–8): 1 341–1 362.CrossRefGoogle Scholar
  55. Yu L S, Weller R A. 2007. Objectively analyzed air-sea heat fluxes for the global ice-free oceans (1981–2005). Bulletin of the American Meteorological Society, 88(4): 527–539.CrossRefGoogle Scholar
  56. Yu L S. 2011. A global relationship between the ocean water cycle and near-surface salinity. Journal of Geophysical Research: Oceans, 116(C10): C10025, Scholar
  57. Yueh S H, Tang W Q, Fore A G, Hayashi A, Song Y T, Lagerloef G S E. 2014. Aquarius geophysical model function and combined active passive algorithm for ocean surface salinity and wind retrieval. Journal of Geophysical Research: Oceans, 119(8): 5 360–5 379.Google Scholar
  58. Yueh S H, Tang W Q, Fore A G, Neumann G, Hayashi A, Freedman A, Chaubell J, Lagerloef G S E. 2013. L-band passive and active microwave geophysical model functions of ocean surface winds and applications to Aquarius retrieval. IEEE Transactions on Geoscience and Remote Sensing, 51(9): 4 619–4 632.CrossRefGoogle Scholar

Copyright information

© Chinese Society for Oceanology and Limnology, Science Press and Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  1. 1.North China Sea Offshore Engineering Survey InstituteNorth China Sea Branch of Ministry of Natural ResourcesQingdaoChina
  2. 2.Key Laboratory of Ocean Circulation and Waves, Institute of OceanologyChinese Academy of SciencesQingdaoChina
  3. 3.Center for Ocean Mega-ScienceChinese Academy of SciencesQingdaoChina
  4. 4.Engineering and Technology Department, Institute of OceanologyChinese Academy of SciencesQingdaoChina
  5. 5.University of Chinese Academy of SciencesBeijingChina

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