Climate Dynamics

, Volume 27, Issue 6, pp 593–611 | Cite as

On the climate response of the low-latitude Pacific Ocean to changes in the global freshwater cycle

  • P. D. Williams
  • E. Guilyardi
  • R. T. Sutton
  • J. M. Gregory
  • G. Madec
Article

Abstract

Under global warming, the predicted intensification of the global freshwater cycle will modify the net freshwater flux at the ocean surface. Since the freshwater flux maintains ocean salinity structures, changes to the density-driven ocean circulation are likely. A modified ocean circulation could further alter the climate, potentially allowing rapid changes, as seen in the past. The relevant feedback mechanisms and timescales are poorly understood in detail, however, especially at low latitudes where the effects of salinity are relatively subtle. In an attempt to resolve some of these outstanding issues, we present an investigation of the climate response of the low-latitude Pacific region to changes in freshwater forcing. Initiated from the present-day thermohaline structure, a control run of a coupled ocean–atmosphere general circulation model is compared with a perturbation run in which the net freshwater flux is prescribed to be zero over the ocean. Such an extreme experiment helps to elucidate the general adjustment mechanisms and their timescales. The atmospheric greenhouse gas concentrations are held constant, and we restrict our attention to the adjustment of the upper 1,000 m of the Pacific Ocean between 40°N and 40°S, over 100 years. In the perturbation run, changes to the surface buoyancy, near-surface vertical mixing and mixed-layer depth are established within 1 year. Subsequently, relative to the control run, the surface of the low-latitude Pacific Ocean in the perturbation run warms by an average of 0.6°C, and the interior cools by up to 1.1°C, after a few decades. This vertical re-arrangement of the ocean heat content is shown to be achieved by a gradual shutdown of the heat flux due to isopycnal (i.e. along surfaces of constant density) mixing, the vertical component of which is downwards at low latitudes. This heat transfer depends crucially upon the existence of density-compensating temperature and salinity gradients on isopycnal surfaces. The timescale of the thermal changes in the perturbation run is therefore set by the timescale for the decay of isopycnal salinity gradients in response to the eliminated freshwater forcing, which we demonstrate to be around 10–20 years. Such isopycnal heat flux changes may play a role in the response of the low-latitude climate to a future accelerated freshwater cycle. Specifically, the mechanism appears to represent a weak negative sea surface temperature feedback, which we speculate might partially shield from view the anthropogenically-forced global warming signal at low latitudes. Furthermore, since the surface freshwater flux is shown to play a role in determining the ocean’s thermal structure, it follows that evaporation and/or precipitation biases in general circulation models are likely to cause sea surface temperature biases.

References

  1. Allen MR, Ingram WJ (2002) Constraints on future changes in climate and the hydrologic cycle. Nature 419:224–232CrossRefPubMedGoogle Scholar
  2. 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 16:156–166CrossRefGoogle Scholar
  3. Barsugli J, Shin S-I, Sardeshmukh PD (2005) Tropical climate regimes and global climate sensitivity in a simple setting. J Atmos Sci 62:1226–1240CrossRefGoogle Scholar
  4. Barthelet P, Terray L, Valcke S (1998) Transient CO2 experiment using the ARPEGE/OPAICE non-flux corrected coupled model. Geophys Res Lett 25:2277–2280CrossRefGoogle Scholar
  5. Bindoff NL, McDougall TJ (2000) Decadal changes along an Indian ocean section at 32°S and their interpretation. J Phys Oceanogr 30:1207–1222CrossRefGoogle Scholar
  6. Bosilovich MG, Schubert SD, Walker GK (2005) Global changes of the water cycle intensity. J Clim 18(10):1591–1608CrossRefGoogle Scholar
  7. Braconnot P, Joussaume S, Marti O, de Noblet N (1999) Synergistic feedback from ocean and vegetation on the African monsoon response to mid-holocene insolation. Geophys Res Lett 26:2481–2484CrossRefGoogle Scholar
  8. Broecker WS, Peteet DM, Rind D (1985) Does the ocean-atmosphere system have more than one stable mode of operation? Nature 315:21–26CrossRefGoogle Scholar
  9. Chahine MT (1992) The hydrological cycle and its influence on climate. Nature 359(6394):373–380CrossRefGoogle Scholar
  10. Dai A, Fung IY, Del Genio AD (1997) Surface observed global land precipitation variations during 1900–88. J Clim 10:2943–2962CrossRefGoogle Scholar
  11. Delecluse P, Madec G (1999) Ocean modelling and the role of the ocean in the climate system. In: Holland WR, Joussaume S, David F (eds) Modeling the Earth’s Climate and its Variability. NATO Advanced Study Institute, Les Houches, 1997, Elsevier Science, pp 237–313Google Scholar
  12. Deser C, Alexander MA, Timlin MS (1996) Upper-ocean thermal variations in the North Pacific during 1970–1991. J Clim 9:1840–1855CrossRefGoogle Scholar
  13. Dong BW, Sutton RT (2002) Adjustment of the coupled ocean-atmosphere system to a sudden change in the thermohaline circulation. Geophys Res Lett 29(15):1728CrossRefGoogle Scholar
  14. Dufresne J-L, Fairhead L, Le Treut H, Berthelot M, Bopp L, Ciais P, Friedlingstein P, Monfray P (2002) On the magnitude of positive feedback between future climate change and the carbon cycle. Geophys Res Lett 29(10):1405CrossRefGoogle Scholar
  15. Fedorov AV, Pacanowski RC, Philander SG, Boccaletti G (2004) The effect of salinity on the wind-driven circulation and the thermal structure of the upper ocean. J Phys Oceanogr 34:1949–1966CrossRefGoogle Scholar
  16. Gaffen DJ, Barnett TP, Elliott WP (1991) Space and time scales of global tropospheric moisture. J Clim 4:989–1008CrossRefGoogle Scholar
  17. Gualdi S, Guilyardi E, Navarra A, Masina S, Delecluse P (2003a) The interannual variability in the tropical Indian Ocean as simulated by a CGCM. Clim Dyn 20:567–582Google Scholar
  18. Gualdi S, Navarra A, Guilyardi E, Delecluse P (2003b) Assessment of the tropical Indo-Pacific climate in the SINTEX CGCM. Ann Geophys 46(1):1–26Google Scholar
  19. Guilyardi E (2006) El Niño–mean state–seasonal cycle interactions in a multi-model ensemble. Clim Dyn 26:329–348CrossRefGoogle Scholar
  20. Guilyardi E, Madec G (1997) Performance of the OPA/ARPEGE-T21 global ocean-atmosphere coupled model. Clim Dyn 13:149–165CrossRefGoogle Scholar
  21. Guilyardi E, Madec G, Terray L (2001) The role of lateral ocean physics in the upper ocean thermal balance of a coupled ocean-atmosphere GCM. Clim Dyn 17(8):589–599CrossRefGoogle Scholar
  22. Guilyardi E, Delecluse P, Gualdi S, Navarra A (2003) Mechanisms for ENSO phase change in a coupled GCM. J Clim 16:1141–1158CrossRefGoogle Scholar
  23. Guilyardi E, Gualdi S, Slingo J, Navarra A, Delecluse P, Cole J, Madec G, Roberts M, Latif M, Terray L (2004) Representing El Niño in coupled ocean-atmosphere GCMs: the dominant role of the atmosphere component. J Clim 17(24):4623–4629CrossRefGoogle Scholar
  24. Haine TWN, Hall TM (2002) A generalized transport theory: water-mass composition and age. J Phys Oceanogr 32:1932–1946CrossRefGoogle Scholar
  25. Hall A, Manabe S (1997) Can local linear stochastic theory explain sea surface temperature and salinity variability? Clim Dyn 13:167–180CrossRefGoogle Scholar
  26. IPCC (2001) Climate change 2001: the scientific basis. Cambridge University Press, CambridgeGoogle Scholar
  27. Jackett DR, McDougall TJ (1995) Minimal adjustment of hydrographic profiles to achieve static stability. J Atmos Ocean Technol 12:381–389CrossRefGoogle Scholar
  28. Levitus S (1982) Climatological atlas of the world ocean. Technical report, National Oceanic and Atmospheric Administration, 1982. NOAA Professional Paper 13Google Scholar
  29. Madec G, Imbard M (1996) A global ocean mesh to overcome the North Pole singularity. Clim Dyn 12(6):381–388CrossRefGoogle Scholar
  30. Madec G, Delecluse P, Crepon M (1991) A three-dimensional numerical study of deep-water formation in the northwestern Mediterranean Sea. J Phys Oceanogr 21(9):1349–1371CrossRefGoogle Scholar
  31. Madec G, Delecluse P, Imbard M, Levy C (1998) OPA version 8.1 Ocean General Circulation Model reference manual. LODYC/IPSL Technical Report 11Google Scholar
  32. Maes C, Picaut J, Belamari S (2002) Salinity barrier layer and onset of El Niño in a Pacific coupled model. Geophys Res Lett 29(24), 2206Google Scholar
  33. Maes C, Picaut J, Belamari S (2005) Importance of the salinity barrier layer for the buildup of El Niño. J Clim 18(1):104–118CrossRefGoogle Scholar
  34. Munk W (1981) Evolution of physical oceanography, chapter Internal waves and small-scale processes. MIT Press, Cambridge, pp 264–291Google Scholar
  35. Murray RJ (1996) Explicit generation of orthogonal grids for ocean models. J Comp Phys 126(2):251–273CrossRefGoogle Scholar
  36. Osborn TJ (1998) The vertical component of epineutral diffusion and the dianeutral component of horizontal diffusion. J Phys Oceanogr 28:485–494CrossRefGoogle Scholar
  37. Pardaens AK, Banks HT, Gregory JM, Rowntree PR (2003) Freshwater transports in HadCM3. Clim Dyn 21:177–195CrossRefGoogle Scholar
  38. Rahmstorf S (1996) On the freshwater forcing and transport of the Atlantic thermohaline circulation. Clim Dyn 12:799–811CrossRefGoogle Scholar
  39. Reynolds RW (1988) A real-time global sea surface temperature analysis. J Clim 1:75–86CrossRefGoogle Scholar
  40. Roberts MJ, Banks H, Gedney N, Gregory J, Hill R, Mullerworth S, Pardaens A, Rickard G, Thorpe R, Wood R (2004) Impact of an eddy-permitting ocean resolution on control and climate change simulations with a global coupled GCM. J Clim 17:3–20CrossRefGoogle Scholar
  41. Roeckner E et al (1996) The atmospheric general circulation model ECHAM-4: model description and simulation of present-day climate. Max-Planck-Institut für Meteorologie report number 218Google Scholar
  42. Russell GL, Miller JR, Rind D (1995) A coupled atmosphere-ocean model for transient climate change studies. Atmos Ocean 33:687–730Google Scholar
  43. Saenko OA, Gregory JM, Weaver AJ, Eby M (2002) Distinguishing the influence of heat, freshwater, and momentum fluxes on ocean circulation and climate. J Clim 15(24):3686–3697CrossRefGoogle Scholar
  44. Schmitt RW (1995) The ocean component of the global water cycle. Rev Geophys, pp 1395–1409Google Scholar
  45. Schneider N (2004) The response of tropical climate to the equatorial emergence of spiciness anomalies. J Clim 17(5):1083–1095CrossRefGoogle Scholar
  46. Schneider N, Barnett TP (1995) The competition of freshwater and radiation in forcing the ocean during El Niño. J Clim 8:980–992CrossRefGoogle Scholar
  47. Schneider EK, Bhatt US (2000) A dissipation integral with application to ocean diffusivities and structure. J Phys Oceanogr 30(6):1158–1171CrossRefGoogle Scholar
  48. Spall MA (1993) Variability of sea surface salinity in stochastically forced systems. Clim Dyn 8:151–160CrossRefGoogle Scholar
  49. Speer K, Tziperman E (1992) Rates of water mass formation in the north Atlantic ocean. J Phys Oceanogr 22:93–104CrossRefGoogle Scholar
  50. Speer K, Guilyardi E, Madec G (2000) Southern ocean transformation in a coupled model with and without eddy mass fluxes. Tellus 52:554–565CrossRefGoogle Scholar
  51. Tailleux R, Lazar A, Reason C (2005) Physics and dynamics of density compensated temperature and salinity anomalies. Part I: Theory. J Phys Oceanogr 35:849–864CrossRefGoogle Scholar
  52. Timmermann A, An S-I, Krebs U, Goosse H (2005) ENSO suppression due to weakening of the North Atlantic Thermohaline Circulation. J Clim 18:3122–3139CrossRefGoogle Scholar
  53. Uppala SM, Kallberg PW, Simmons AJ, Andrae U, da Costa Bechtold V, Fiorino M, Gibson JK, Haseler J, Hernandez A, Kelly GA, Li X, Onogi K, Saarinen S, Sokka N, Allan RP, Andersson E, Arpe K, Balmaseda MA, Beljaars ACM, van de Berg L, Bidlot J, Bormann N, Caires S, Chevallier F, Dethof A, Dragosavac M, Fisher M, Fuentes M, Hagemann S, Holm E, Hoskins BJ, Isaksen L, PA. EM. Janssen, Jenne R, McNally AP, Mahfouf J-F, Morcrette J-J, Rayner NA, Saunders RW, Simon P, Sterl A, Trenberth KE, Untch A, Vasiljevic D, Viterbo P, Woollen J (2005) The ERA-40 re-analysis. Q J Roy Meteor Soc 131:2961–3012CrossRefGoogle Scholar
  54. Valcke S, Terray L, Piacentini A (2000) The OASIS coupler user guide Version 2.4. Technical report TR/CMGC/00-10, CERFACSGoogle Scholar
  55. Vellinga M, Wood RA (2002) Global climatic impacts of a collapse of the Atlantic thermohaline circulation. Clim Change 54(3):251–267CrossRefGoogle Scholar
  56. Veronis G (1972) On properties of seawater defined by temperature, salinity and pressure. J Mar Res 30:227–255Google Scholar
  57. 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 28:1071–1088CrossRefGoogle Scholar
  58. Vialard J, Delecluse P (1998b) An OGCM study for the TOGA decade. Part II: Barrier-layer formation and variability. J Phys Oceanogr 28:1089–1106CrossRefGoogle Scholar
  59. Vialard J, Menkes C, Boulanger J-P, Guilyardi E, Delecluse P, McPhaden MJ (2001) Oceanic mechanisms driving the SST during the 1997–98 El Niño. J Phys Oceanogr 31:1649–1675CrossRefGoogle Scholar
  60. Vialard J, Delecluse P, Menkes C (2002) A modelling study of salinity variability and its effects in the tropical Pacific Ocean during the 1993–1999 period. J Geophys Res 107:8005CrossRefGoogle Scholar
  61. Wong APS, Bindoff NL, Church JA (1999) Large-scale freshening of intermediate waters in the Pacific and Indian oceans. Nature 400:440–443CrossRefGoogle Scholar
  62. Yeager SG, Large WG (2004) Late-winter generation of spiciness on subducted isopycnals. J Phys Oceanogr 34(7):1528–1547CrossRefGoogle Scholar

Copyright information

© Springer-Verlag 2006

Authors and Affiliations

  • P. D. Williams
    • 1
  • E. Guilyardi
    • 1
    • 2
  • R. T. Sutton
    • 1
  • J. M. Gregory
    • 1
    • 3
  • G. Madec
    • 4
  1. 1.Centre for Global Atmospheric Modelling, Department of MeteorologyUniversity of ReadingReadingUK
  2. 2.Laboratoire des Sciences du Climat et de l’Environnement (IPSL/LSCE)Gif-sur-YvetteFrance
  3. 3.Hadley Centre for Climate Prediction and ResearchExeterUK
  4. 4.Laboratoire d’Océanographie et de Climat par Expérimentation et Approche Numérique (IPSL/LOCEAN)Université Paris VIParisFrance

Personalised recommendations