Journal of Oceanography

, Volume 68, Issue 2, pp 243–265 | Cite as

Long-term variations of surface and intermediate waters in the southern Indian Ocean along 32°S

Original Article

Abstract

Variations of water properties in surface and intermediate layers along 32°S in the southern Indian Ocean were examined using a 50-year (1960–2010) time series reproduced from historical hydrographic and Argo data by using optimum interpolation. Salinity in the 26.7–27.3σθ density layer decreased significantly over the whole section, at a maximum rate of 0.02 decade−1 at 26.8–26.9σθ, for the 50-year average. Three deoxygenating cores were identified east of 75°E, and the increasing rate of apparent oxygen utilization in the most prominent core (26.9–27.0σθ) exceeded 0.05 ml l−1 decade−1. The pycnostad core of Subantarctic Mode Water (SAMW) and the salinity minimum of Antarctic Intermediate Water shifted slightly toward the lighter layers. Comparisons with trans-Indian Ocean survey data from 1936 suggest that the tendencies found in the time series began before 1960. Interestingly, cores of many prominent trends were located just offshore of Australia at 26.7–27.0σθ, which is in the SAMW density range. Spectrum analysis revealed that two oscillation components with time scales of about 40 and 10 years were dominant in the subsurface layers. Our results are fairly consistent with, and thus support, the oceanic responses in the southern Indian Ocean to anthropogenic climate change predicted by model studies.

Keywords

Long-term trend Oscillation Climate change Southern Indian Ocean Subantarctic Mode Water Antarctic Intermediate Water 

Notes

Acknowledgments

We thank all members of the Ocean Climate Change Research Program, Japan Agency for Marine-Earth Science and Technology, for their comments, especially S. Hosoda, T. Hasegawa, and T. Ohira for their kind advice on our analysis. Two reviewers gave us valuable comments that have improved the manuscript. This study used data from the international Argo Program (http://www.argo.ucsd.edu). Argo is part of the Global Ocean/Global Climate Observing System. Data from Argo profiling floats are freely available.

References

  1. Alory G, Wijffels S, Meyers G (2007) Observed temperature trends in the Indian Ocean over 1960–1999 and associated mechanisms. Geophys Res Lett 34:L02606. doi:10.1029/2006GL028044 CrossRefGoogle Scholar
  2. Aoki S, Bindoff NL, Church JA (2005) Interdecadal water mass changes in the Southern Ocean between 30°E and 160°E. Geophys Res Lett 32:L07607. doi:10.1029/2004GL022220 CrossRefGoogle Scholar
  3. Aoki S, Hariyama M, Mitudera H, Sasaki H, Sasai Y (2007) Formation regions of Subantarctic Mode Water detected by OFES and Argo profiling floats. Geophys Res Lett 34:L10606. doi:10.1029/2007GL029828 CrossRefGoogle Scholar
  4. Argo Data Management Team (2010) Argo quality control manual version 2.6. Argo Data Management Website. http://www.argodatamgt.org/Documentation, updated on December 2010
  5. Argo Science Team (2001) Argo: the global array of profiling floats. In: Koblinsky CJ, Smith NR (eds) Observing the Oceans in the 21st century. Godae Project Office, Bureau of Meteorology, Melbourne, pp 248–258Google Scholar
  6. Banks HT, Bindoff NL (2003) Comparison of observed temperature and salinity changes in the Indo-Pacific with results from the coupled climate model HadCM3: processes and mechanisms. J Clim 16:156–166. doi:10.1175/1520-0442(2003)016<0156:COOTAS>2.0.CO;2 CrossRefGoogle Scholar
  7. Banks H, Wood R (2002) Where to look for anthropogenic climate change in the ocean. J Clim 15:879–891. doi:10.1175/1520-0442(2002)015<0879:WTLFAC>2.0.CO;2 CrossRefGoogle Scholar
  8. Banks HT, Wood RA, Gregory JM, Johns TC, Jones GS (2000) Are observed decadal changes in intermediate water masses a signature of anthropogenic climate change? Geophys Res Lett 27:2961–2964. doi:10.1029/2000GL011601 CrossRefGoogle Scholar
  9. Banks H, Wood R, Gregory J (2002) Changes to Indian Ocean Subantarctic Mode Water in a coupled climate model as CO2 forcing increase. J Phys Oceanogr 32:2816–2827. doi:10.1175/1520-0485(2002)032<2816:CTIOSM>2.0.CO;2 CrossRefGoogle Scholar
  10. Bindoff NL, McDougall TJ (1994) Diagnosing climate change and ocean ventilation using hydrographic data. J Phys Oceanogr 24:1137–1152. doi:10.1175/1520-0485(1994)024<1137:DCCAOV>2.0.CO;2 CrossRefGoogle Scholar
  11. Bindoff NL, McDougall TJ (2000) Decadal changes along an Indian Ocean section at 32°S and their interpretation. J Phys Oceanogr 30:1207–1222. doi:10.1175/1520-0485(2000)030<1207:DCAAIO>2.0.CO;2 CrossRefGoogle Scholar
  12. Bőning CW, Dispert A, Visbeck M, Rintoul SR, Schwarzkopf FU (2008) The response of the Antarctic Circumpolar Current to recent climate change. Nat Geosci 1:864–869. doi:10.1038/ngeo362 CrossRefGoogle Scholar
  13. Bryden HL (2003) RRS Charles Darwin Cruise 139, 01 MAR–15 APR 2002: trans-Indian hydrographic section across 32°S. Southampton Oceanography Centre Cruise Rep 45, Southampton, p. 122Google Scholar
  14. Bryden HL, McDonagh EL, King BA (2003) Changes in ocean water mass properties: oscillation or trend? Science 300:2086–2088. doi:10.1126/science.1083980 CrossRefGoogle Scholar
  15. Cunningham SA, Alderson S (2007) Transatlantic temperature and salinity changes at 24.5°N from 1957 to 2004. Geophys Res Lett 34:L14606. doi:10.1029/2007GL029821 CrossRefGoogle Scholar
  16. Dong S, Sprintall J, Gille ST, Talley L (2008) Southern ocean mixed-layer depth from Argo float profiles. J Geophys Res 113:C06013. doi:10.1029/2006JC004051 CrossRefGoogle Scholar
  17. Downes SM, Bindoff NL, Rintoul SR (2009) Impacts of climate change on the subduction of mode and intermediate water masses in the Southern Ocean. J Clim 22:3289–3302. doi:10.1175/2008JCLI2653.1 CrossRefGoogle Scholar
  18. Durack PJ, Wijffels SE (2010) Fifty-year trends in global ocean salinities and their relationship to board-scale warming. J Clim 23:4342–4362. doi:10.1175/2010JCLI3377.1 Google Scholar
  19. Freeland HJ, Roemmich D, Garzoli SL et al (2011) Argo—a decade of progress. In: Hall J, Harrison DE, Stammer D (eds) OceanObs′09: Sustained Ocean Observations and Information for Society, vol 2. ESA Publication WPP-306. doi:10.5270/OceanObs09.cwp.32 (in press)
  20. Gille ST (2008) Decadal-scale temperature trends in the Southern Hemisphere Ocean. J Clim 21:4749–4765. doi:10.1175/2008JCLI2131.1 CrossRefGoogle Scholar
  21. Haines K, Blower JD, Drecourt J-P, Liu C (2006) Salinity assimilation using S(T): covariance relationships. Mon Weather Rev 134:759–771. doi:10.1175/MWR3089.1 CrossRefGoogle Scholar
  22. Harrison DE, Carson M (2007) Is the world ocean warming? Upper-ocean temperature trends: 1950–2000. J Phys Oceanogr 37:174–187. doi:10.1175/JPO3005.1 CrossRefGoogle Scholar
  23. Herraiz-Borreguero L, Rintoul SR (2011) Subantarctic mode water: distribution and circulation. Ocean Dyn 61:103–126. doi:10.1007/s10236-010-0352-9 CrossRefGoogle Scholar
  24. Hosoda S, Minato S, Shikama N (2006) Seasonal temperature variation below the thermocline detected by Argo floats. Geophys Res Lett 33:L13604. doi:10.1029/2006GL026070 CrossRefGoogle Scholar
  25. Intergovernmental Panel on Climate Change (2000) Emissions scenarios. Cambridge University Press, Cambridge, p 570Google Scholar
  26. Jackett DR, McDougall TJ (1997) A neutral density variable for the world’s oceans. J Phys Oceanogr 27:237–263. doi:10.1175/1520-0485(1997)027<0237:ANDVFT>2.0.CO;2 CrossRefGoogle Scholar
  27. King BA, McDonagh EL (2005) Decadal changes in ocean properties revealed by ARGO floats. Geophys Res Lett 32:L15601. doi:10.1029/2005GL023145 CrossRefGoogle Scholar
  28. Kobayashi T (1999) Study of the formation of North Pacific Intermediate Water by a general circulation model and the particle-tracking method, 1. A pitfall of general circulation model studies. J Geophys Res 104:5423–5439. doi:10.1029/1998JC900084 CrossRefGoogle Scholar
  29. Kobayashi T, Minato S (2005) Importance of reference dataset improvements for Argo delayed-mode quality control. J Oceanogr 61:995–1009. doi:10.1007/s10872-006-0016-z CrossRefGoogle Scholar
  30. Kobayashi T, Suga T (2006) The Indian Ocean Hydrobase: a high-quality climatological dataset for the Indian Ocean. Prog Oceanogr 68:75–114. doi:10.1016/j.pocean.2005.07.001 CrossRefGoogle Scholar
  31. Koch-Larrouy A, Morrow R, Penduff T, Juza M (2010) Origin and mechanism of Subantarctic Mode Water formation and transformation in the Southern Indian Ocean. Ocean Dyn 60:563–583. doi:10.1007/s10236-010-0276-4 CrossRefGoogle Scholar
  32. Levitus S, Antonov J, Boyer T (2005) Warming of the world ocean, 1955–2003. Geophys Res Lett 32:L02604. doi:10.1029/2004GL021592 CrossRefGoogle Scholar
  33. Marshall GJ (2003) Trends in the Southern Annular Mode from observations and reanalyses. J Clim 16:4134–4143. doi:10.1175/1520-0442(2003)016<4134:TITSAM>2.0.CO;2 CrossRefGoogle Scholar
  34. McCarthy MC, Talley LD (1999) Three-dimensional isoneutral potential vorticity structure in the Indian Ocean. J Geophys Res 104:13251–13267. doi:10.1029/1999JC900028 Google Scholar
  35. McCartney MS (1977) Subantarctic Mode Water. In: Angel M (ed) A Voyage of Discovery: George Deacon 70th Anniversary Volume (Supplement to Deep-Sea Res and Oceanographic Abstracts). Pergamon Press, Oxford, pp 103–119Google Scholar
  36. McDonagh EL, Bryden HL, King BA, Sanders RJ, Cunningham SA, Marsh R (2005) Decadal changes in the south Indian Ocean thermocline. J Clim 18:1575–1590. doi:10.1175/JCLI3350.1 CrossRefGoogle Scholar
  37. Murray RJ, Bindoff NL, Reason CJC (2007) Modeling decadal changes on the Indian Ocean section I5 at 32°S. J Clim 20:3106–3130. doi:10.1175/JCLI4160.1 CrossRefGoogle Scholar
  38. Orsi AH, Whitworth T III, Norwlin WD Jr (1995) On the meridional extent and fronts of the Antarctic Circumpolar Current. Deep Sea Res I 42:641–673. doi:10.1016/0967-0637(95)00021-W CrossRefGoogle Scholar
  39. Reid JL (2003) On the total geostrophic circulation of the Indian Ocean: float patterns, tracers, and transports. Prog Oceanogr 56:137–186. doi:10.1016/S0079-6611(02)00141-6 CrossRefGoogle Scholar
  40. Rintoul SR, England MH (2002) Ekman transport dominates local air-sea fluxes in driving variability of Subantarctic Mode Water. J Phys Oceanogr 32:1308–1321. doi:10.1175/1520-0485(2002)032<1308:ETDLAS>2.0.CO;2 CrossRefGoogle Scholar
  41. Roemmich D (1983) Optimal estimation of hydrographic station data and derived fields. J Phys Oceanogr 13:1544–1549. doi:10.1175/1520-0485(1983)013<1544:OEOHSD>2.0.CO;2 CrossRefGoogle Scholar
  42. Sallée JB, Wienders N, Speer K, Morrow R (2006) Formation of Subantarctic Mode Water in the southeastern Indian Ocean. Ocean Dyn 56:525–542. doi:10.1007/s10236-005-0054-x Google Scholar
  43. Sallée JB, Speer KG, Rintoul SR (2010) Zonally asymmetric response of the Southern Ocean mixed-layer depth to the Southern Annular Mode. Nat Geosci 3:273–279. doi:10.1038/ngeo812 Google Scholar
  44. Schmidtko S, Johnson GC (2011) Multi-decadal warming and shoaling of Antarctic Intermediate Water. J Clim. doi:10.1175/JCLI-D-11-00021.1 (in press)
  45. Sen Gupta A, England MH (2006) Coupled ocean-atmosphere-ice response to variations in the Southern Annular Mode. J Clim 19:4457–4486. doi:10.1175/JCLI3843.1 CrossRefGoogle Scholar
  46. Stark S, Wood RA, Banks HT (2006) Reevaluating the causes of observed changes in Indian Ocean water masses. J Clim 19:4075–4086. doi:10.1175/JCLI3845.1 CrossRefGoogle Scholar
  47. Swift JH, Johnson GC (2009) US Global Ocean Carbon and Repeat Hydrography Program Cruise I5, 20 March–15 May 2009, Preliminary Cruise Report. Scripps Institution of Oceanography, San Diego, p 90Google Scholar
  48. Talley LD, Baringer MO (1997) Preliminary results from WOCE hydrographic sections at 80°E and 32°S in the central Indian Ocean. Geophys Res Lett 24:2789–2792. doi:10.1029/97GL02657 CrossRefGoogle Scholar
  49. Thompson DWJ, Wallace JM, Hegerl GC (2000) Annular modes in the extratropical circulation, Part II: trends. J Clim 13:1018–1036. doi:10.1175/1520-0442(2000)013<1018:AMITEC>2.0.CO;2 CrossRefGoogle Scholar
  50. Wong APS (2005) Subantarctic Mode Water and Antarctic Intermediate Water in the south Indian Ocean based on profiling float data 2000–2004. J Mar Res 63:789–812. doi:10.1357/0022240054663196 CrossRefGoogle Scholar
  51. Wong APS, Bindoff NL, Church JA (1999) Large-scale freshening of intermediate waters in the Pacific and Indian Oceans. Nature 400:440–443. doi:10.1038/22733 Google Scholar
  52. Wong APS, Johnson GC, Owens WB (2003) Delayed-mode calibration of autonomous CTD profiling float salinity data by θ-S climatology. J Atmos Ocean Technol 20:308–318. doi:10.1175/1520-0426(2003)020<0308:DMCOAC>2.0.CO;2 CrossRefGoogle Scholar
  53. Woo M, Pattiaratchi C (2008) Hydrography and water masses off the western Australian coast. Deep Sea Res I 55:1090–1104. doi:10.1016/j.dsr.2008.05.005 CrossRefGoogle Scholar

Copyright information

© The Oceanographic Society of Japan and Springer 2011

Authors and Affiliations

  1. 1.Research Institute for Global Change, Japan Agency for Marine-Earth Science and TechnologyYokosukaJapan
  2. 2.Graduate School of Science, Tohoku University SendaiJapan

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