Abstract
We investigate the model sensitivity of the Atlantic meridional overturning circulation (AMOC) to anomalous freshwater flux in the tropical and northern Atlantic. Forcing in both locations leads to the same qualitative response: a positive freshwater anomaly induces a weakening of the AMOC and a negative freshwater anomaly strengthens the AMOC. Strong differences arise in the temporal characteristics and amplitude of the response. The advection of the tropical anomaly up to the deep water formation area leads to a time delayed response compared to a northern forcing. Thus, in its transient response, the AMOC is less sensitive to a constant anomalous freshwater flux in the tropics than in the north. This difference decreases with time and practically vanishes in equilibrium with constant freshwater forcing. The equilibrium response of the AMOC shows a non-linear dependence on freshwater forcing in both locations, with a stronger sensitivity to positive freshwater forcing. As a consequence, competitive forcing in both regions is balanced when the negative forcing is about 1.5 times larger than the positive forcing. The relaxation time of the AMOC after termination of a freshwater perturbation depends significantly on the AMOC strength itself. A strong overturning exhibits a faster relaxation to its unperturbed state. By means of a set of complementary experiments (pulse-perturbations, constant and stochastic forcing) we quantify these effects and discuss the corresponding time scales and physical processes.
Similar content being viewed by others
References
Church JA et al (2001) Change in sea level. In: Houghton JT et al (eds) Climate Change 2001: the scientific basis. Contribution of working group I to the 3rd Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, pp 640–693
Collins M, the CMIP Modelling Groups (2005) El Niño- or La Niña-like climate change? Clim Dyn 24:89–104
Curry R, McCartney MS, Joyce TM (1998) Oceanic transport of subpolar climate signals to mid-depth subtropical waters. Nature 391:575–577
Curry R, Dickson B, Yashayaev I (2003) A change in the freshwater balance of the Atlantic Ocean over the past four decades. Nature 426:826–829
Dahl K, Broccoli A, Stouffer R (2005) Assessing the role of North Atlantic freshwater forcing in millennial scale climate variability: a tropical Atlantic perspective. Clim Dyn 24:325–346
Deshayes J, Frankignoul C (2005) Spectral characteristics of the response of the meridional overturning circulation to deep water formation. J Phys Oceanogr 35(10):1813–1825
Doherty R, Hulme M (2002) The relationship between the SOI and extended tropical precipitation in simulations of future climate change. Geophys Res Lett 29(10):1475
Dong B-W, Sutton R (2002) Adjustment of the coupled ocean–atmosphere system to a sudden change in the thermohaline circulation. Geophys Res Lett 26(15):178
Fichefet T, Maqueda M (1997) Sensitivity of a global sea ice model to the treatment of ice thermodynamics and dynamics. J Geophys Res 102:12609
Frankignoul C (1985) Sea surface temperature anomalies, planetary waves and air–sea feedback in the middle latitudes. Rev Geophys 23:357–390
Furevik T, Bentsen M, Drange H, Kindem I, Kvamstø N, Sorteberg A (2003) Description and evaluation of the Bergen Climate Model: ARPEGE coupled with MICOM. Clim Dyn 21:25–51
Ganachaud A, Wunsch C (2000) Improved estimates of global ocean circulation, heat transport and mixing from hydrographic data. Nature 408:453–456
Ganachaud A, Wunsch C (2003) Large-scale ocean heat and freshwater transports during the world ocean circulation experiment. J Clim 16:696
Gregory J, Dixon K, Stouffer R, Weaver A, Driesschaert E, Eby M, Fichefet T, Hasumi H, Hu A, Jungclaus J, Kamenkovich I, Levermann A, Montoya M, Murakami S, Nawrath S, Oka A, Sokolov A, Thorpe R (2005) A model intercomparison of changes in the Atlantic thermohaline circulation in response to increasing atmospheric CO2 concentration. Geophys Res Lett 32:L12703
Griesel A, Morales-Maqueda M (2006) The relation of meridional pressure gradients to North Atlantic Deep Water volume transport in an OGCM. Clim Dyn 26:781–799
Hastenrath S (1976) Variations in the low-latitude circulation and extreme climatic events in the tropical Americas. J Atmos Sci 33:202–215
Huybrechts P, de Wolde J (1999) The dynamic response of the Greenland and Antarctic ice sheets to multiple-century climatic warming. J Clim 12(8):2169–2188
Johannessen OM, Miles M, Bjørgo E (2002) The arctic’s shrinking sea ice. Nature 376:126–127
Johnson HL, Marshall DP (2002) A theory for the surface Atlantic response to thermohaline variability. J Phys Oceanogr 32:1121–1132
Johnson HL, Marshall DP (2004) Global teleconnections of meridional overturning circulation anomalies. J Phys Oceanogr 34:1702–1722
Kousky V, Kagano M, Cavalcanti I (1984) A review of the Southern Oscillation: oceanic–atmospheric circulation changes and related rainfall anomalies. Tellus Series A 36:490–504
Latif M, Roeckner E, Mikolajewicz U, Voss R (2000) Tropical stabilisation of the thermohaline cirulation in a greenhouse warming simulation. J Clim 13:1809–1813
Levermann A, Griesel A (2004) Solution of a model for the oceanic pycnocline depth: Scaling of overturning strength and meridional pressure difference. Geophys Res Lett 31:L17302
Levermann A, Griesel A, Hofmann M, Montoya M, Rahmstorf S (2005) Dynamic sea level changes following changes in the thermohaline circulation. Clim Dyn 24:347
Manabe S, Stouffer R (1997) Coupled ocean–atmosphere model response to freshwater input: comparison to Younger Dryas event. Paleoceanography 12:321–336
Mignot J, Frankignoul C (2005) On the variability of the Atlantic meridional overturning circulation, the NAO and the ENSO in the Bergen Climate Model. J Clim 18:2361–2375
Mignot J, Ganopolski A, Levermann A (2006) Atlantic subsurface temperatures: response to a shut-down of the overturning circulation and consequences for its recovery. J Clim (Submitted)
Montoya M, Griesel A, Levermann A, Mignot J, Hofmann M, Ganopolski A, Rahmstorf S (2005) The earth system model of intermediate complexity CLIMBER-3α. Part I: description and performance for present day conditions. Clim Dyn 25:237–263
Peterson BJ, Holmes RM, McClelland JW, Vörösmarty CJ, Lammers RB, Shiklomanov AI, Shiklomanov IA, Rahmstorf S (2002) Increasing river discharge to the Arctic Ocean. Science 298:2172–2173
Petoukhov V, Ganopolski A, Brovkin V, Claussen M, Eliseev A, Kubatzki C, Rahmstorf S (2000) CLIMBER-2: a climate system model of intermediate complexity. Part I: model description and performance for present climate. Clim Dyn 16:1
Philander SGH (1990) El Niño, La Niña, and the Southern Oscillation. Academic, New York, 293 pp
Rahmstorf S (1995) Bifurcations of the Atlantic thermohaline circulation in response to changes in the hydrological cycle. Nature 378:145–149
Rahmstorf S (2002) Ocean circulation and climate during the past 120,000 years. Nature 419:207–214
Rahmstorf S, Ganopolski A (1999) Long-term global warming scenarios computed with an efficient coupled climate model. Clim Change 43:353
Rahmstorf S (1996) On the freshwater forcing and transport of the Atlantic thermohaline circulation. Clim Dyn 12:799–811
Rignot E, Kanagaratnam P (2006) Changes in the velocity structure of the Greenland ice sheet. Science 311:986–990
Schmittner A, Appenzeller C, Stocker T (2000) Enhanced Atlantic freshwater export during El Niño. Geophys Res Lett 27(8):1163–1166
Stommel HM (1961) Thermohaline convection with two stable regimes of flow. Tellus 13:224–230
Stouffer R, Yin J, Gregory J, Dixon K, Spelman M, Hurlin W, Weaver A, Eby M, Flato G, Hasumi H, Hu A, Jungclaus J, Kamenkovich I, Levermann A, Montoya M, Murakami S, Nawrath S, Oka A, Peltier W, Robitaille D, Sokolov A, Vettoretti G, Weber N (2006) Investigating the causes of the response of the thermohaline circulation to past and future climate changes. J Clim 19:1365–1387
Talley L, Reid J, Robbins P (2003) Data-based meridional overturning streamfunctions for the global oceans. J Clim 16:3213–3226
Thorpe RB, Gregory JM, Johns TC, Wood RA, Mitchell JFB (2001) Mechanisms determining the Atlantic thermohaline circulation response to greenhouse gas forcing in a non-adjusted coupled climate model. J Clim 14:3102–3116
Vellinga M, Wood R (2002) Global climatic impacts of a collapse of the Atlantic thermohaline circulation. Clim Change 54:251–267
Vellinga M, Wu P (2004) Low latitude freshwater influence on centennial variability of the Atlantic Thermohaline Circulation. J Clim 17(23):4498–4511
Vellinga M, Wood R, Gregory J (2002) Processes governing the recovery of a perturbed thermohaline circulation in HadCM3. J Clim 15(7):764–780
Winguth A, Mikolajewicz U, Gröger M, Maier-Reimer E, Schurgers G, Vizcaíno M (2005) Centennial-scale interactions between the carbon cycle and anthropogenic climate change using a dynamic Earth system model. Geophys Res Lett 32:L23714
Yang J (1999) A linkage between decadal climate variations in the Labrador Sea and the tropical Atlantic Ocean. Geophys Res Lett 26(8):1023–1026
Zhang R, Delworth T (2005) Simulated tropical response to a substantial weakening of the Atlantic thermohaline circulation. J Clim 18:1853–1860
Acknowledgments
A.L. and J.M. were funded by the Comer foundation. We are indebted to two anonymous reviewers for their comments that greatly helped to improved the manuscript.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Goelzer, H., Mignot, J., Levermann, A. et al. Tropical versus high latitude freshwater influence on the Atlantic circulation. Clim Dyn 27, 715–725 (2006). https://doi.org/10.1007/s00382-006-0161-5
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s00382-006-0161-5