Bistability of the Atlantic subpolar gyre in a coarse‐resolution climate model

[1] High resolution models indicate that the dynamics of the Nordic Seas and the subpolar gyre is crucial for deep water formation and overturning circulation in the Atlantic. During the last decades significant changes in ocean properties have been observed in this region. We show that large-scale dynamics, as captured by coarse resolution climate models, allows for a bistability of the Atlantic subpolar gyre. We suggest three positive feedbacks which yield the necessary nonlinearity for this behavior. Transitions between the two states can be triggered by small fluctuations in surface freshwater flux to the Nordic Seas, only slightly larger than natural variability presently observed in the region.

[1]  Carsten Eden,et al.  Mechanism of Interannual to Decadal Variability of the North Atlantic Circulation , 2001 .

[2]  S. Rahmstorf,et al.  The earth system model of intermediate complexity CLIMBER-3α. Part I: description and performance for present-day conditions , 2005 .

[3]  E. Maier‐Reimer,et al.  Centennial‐scale interactions between the carbon cycle and anthropogenic climate change using a dynamic Earth system model , 2005 .

[4]  A. Timmermann,et al.  ENSO suppression due to weakening of the North Atlantic thermohaline circulation , 2005 .

[5]  P. Gent,et al.  Isopycnal mixing in ocean circulation models , 1990 .

[6]  S. Østerhus,et al.  CLIMATE SCIENCE: Enhanced: Already the Day After Tomorrow? , 2004 .

[7]  J. F. Read,et al.  CONVEX-91: water masses and circulation of the Northeast Atlantic subpolar gyre , 2000 .

[8]  B. Barnier,et al.  Self-Adapting open boundaries for a sigma coordinate model of the eastern North Atlantic , 2000 .

[9]  Richard A. Wood,et al.  Global Climatic Impacts of a Collapse of the Atlantic Thermohaline Circulation , 2002 .

[10]  Stephen Dye,et al.  Rapid freshening of the deep North Atlantic Ocean over the past four decades , 2002, Nature.

[11]  A. Biastoch,et al.  Decadal variability of subpolar gyre transport and its reverberation in the North Atlantic overturning , 2006 .

[12]  Cecilie Mauritzen,et al.  Dilution of the Northern North Atlantic Ocean in Recent Decades , 2005, Science.

[13]  Richard B. Lammers,et al.  Increasing River Discharge to the Arctic Ocean , 2002, Science.

[14]  M. Spall.  Buoyancy-forced circulations in shallow marginal seas , 2005 .

[15]  D. Bailey,et al.  Formation and pathways of North Atlantic Deep Water in a coupled ice–ocean model of the Arctic–North Atlantic Oceans , 2005 .

[16]  S. Bacon.  Circulation and Fluxes in the North Atlantic between Greenland and Ireland , 1997 .

[17]  A. Weaver,et al.  JEBAR, Bottom Pressure Torque, and Gulf Stream Separation , 1996 .

[18]  Stefan Rahmstorf,et al.  Dynamic sea level changes following changes in the thermohaline circulation , 2005 .

[19]  S. Häkkinen,et al.  Decline of Subpolar North Atlantic Circulation During the 1990s , 2004, Science.

[20]  R. Curry,et al.  Oceanic transport of subpolar climate signals to mid-depth subtropical waters , 1998, Nature.

[21]  S. Levitus,et al.  A diagnosis of interpentadal circulation changes in the North Atlantic , 1991 .

[22]  Thierry Penduff,et al.  The North Atlantic Subpolar Gyre in Four High-Resolution Models , 2005 .

[23]  M. G. Morgan,et al.  Expert judgements on the response of the Atlantic meridional overturning circulation to climate change , 2007 .

[24]  F. Straneo.  Heat and Freshwater Transport through the Central Labrador Sea , 2006 .

[25]  J. Schewe,et al.  Lack of bipolar see‐saw in response to Southern Ocean wind reduction , 2007 .

[26]  H. Drange,et al.  Influence of the Atlantic Subpolar Gyre on the Thermohaline Circulation , 2005, Science.