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Agulhas leakage dynamics affects decadal variability in Atlantic overturning circulation


Predicting the evolution of climate over decadal timescales requires a quantitative understanding of the dynamics that govern the meridional overturning circulation (MOC)1. Comprehensive ocean measurement programmes aiming to monitor MOC variations have been established in the subtropical North Atlantic2,3 (RAPID, at latitude 26.5° N, and MOVE, at latitude 16° N) and show strong variability on intraseasonal to interannual timescales. Observational evidence of longer-term changes in MOC transport remains scarce, owing to infrequent sampling of transoceanic sections over past decades4,5. Inferences based on long-term sea surface temperature records, however, supported by model simulations, suggest a variability with an amplitude of ±1.5–3 Sv (1 Sv = 106 m3 s-1) on decadal timescales in the subtropics6. Such variability has been attributed to variations of deep water formation in the sub-arctic Atlantic, particularly the renewal rate of Labrador Sea Water7. Here we present results from a model simulation that suggest an additional influence on decadal MOC variability having a Southern Hemisphere origin: dynamic signals originating in the Agulhas leakage region at the southern tip of Africa. These contribute a MOC signal in the tropical and subtropical North Atlantic that is of the same order of magnitude as the northern source. A complete rationalization of observed MOC changes therefore also requires consideration of signals arriving from the south.

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Figure 1: Strength of the interhemispheric transport in the Atlantic Ocean.
Figure 2: Mid-depth circulation in the high-resolution Agulhas nest.
Figure 3: Low-pass-filtered Agulhas-induced MOC anomalies.
Figure 4: Illustration of the wave processes conveying Agulhas-induced anomalies in the upper limb of the MOC.
Figure 5: Attribution of interannual MOC variability to different mechanisms.

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  1. Keenlyside, N. S., Latif, M., Jungclaus, J., Kornblueh, L. & Roeckner, E. Advancing decadal-scale climate prediction in the North Atlantic sector. Nature 453, 84–88 (2008)

    Article  ADS  CAS  Google Scholar 

  2. Cunningham, S. A. et al. Temporal variability of the Atlantic meridional overturning circulation at 26.5° N. Science 317, 935–938 (2007)

    Article  ADS  CAS  Google Scholar 

  3. Kanzow, T., Send, U., Zenk, W., Chave, A. D. & Rhein, M. Monitoring the integrated deep meridional flow in the tropical North Atlantic: Long-term performance of a geostrophic array. Deep-Sea Res. I 53, 528–546 (2006)

    Article  Google Scholar 

  4. Bryden, H., Longworth, H. R. & Cunningham, S. A. Slowing of the Atlantic meridional overturning circulation at 25° N. Nature 438, 655–657 (2005)

    Article  ADS  CAS  Google Scholar 

  5. Wunsch, C. Mass and volume transport variability in an eddy-filled ocean. Nature Geosci. 1, 165–168 (2008)

    Article  ADS  CAS  Google Scholar 

  6. Latif, M. et al. Is the thermohaline circulation changing? J. Clim. 19, 4631–4637 (2006)

    Article  ADS  Google Scholar 

  7. Böning, C. W., Scheinert, M., Dengg, J., Biastoch, A. & Funk, A. Decadal variability of subpolar gyre transport and its reverberation in the North Atlantic overturning. Geophys. Res. Lett. 33 doi: 10.1029/2006GL026906 (2005)

  8. Gordon, A. L. Inter-ocean exchange of thermocline water. J. Geophys. Res. 91, 5037–5046 (1986)

    Article  ADS  Google Scholar 

  9. Lutjeharms, J. R. E. The Agulhas Current (Springer, 2006)

    Google Scholar 

  10. Olson, D. B. & Evans, R. H. Rings of the Agulhas Current. Deep-Sea Res. A 33, 27–42 (1986)

    Article  ADS  Google Scholar 

  11. De Ruijter, W. P. M. et al. Dynamics, estimation and impact of South Atlantic inter-ocean exchange. J. Geophys. Res. 104, 20885–20910 (1999)

    Article  ADS  Google Scholar 

  12. Peeters, F. J. C. et al. Vigorous exchange between Indian and Atlantic Ocean at the end of the last five glacial periods. Nature 430, 661–665 (2004)

    Article  ADS  CAS  Google Scholar 

  13. Weijer, W., de Ruijter, W. P. M., Dijkstra, H. A. & van Leeuwen, P. J. Impact of interbasin exchange on the Atlantic overturning circulation. J. Phys. Oceanogr. 29, 2266–2284 (1999)

    Article  ADS  Google Scholar 

  14. Marsh, R., Hazeleger, W., Yool, A. & Rohling, E. J. Stability of the thermohaline circulation under millennial CO2 forcing and two alternative controls on Atlantic salinity. Geophys. Res. Lett. 34 doi: 10.1029/2006GL027815 (2007)

  15. Van Leeuwen, P. J., de Ruijter, W. P. M. & Lutjeharms, J. R. E. Natal pulses and the formation of Agulhas rings. J. Geophys. Res. 105, 6425–6436 (2000)

    Article  ADS  Google Scholar 

  16. Biastoch, A., Lutjeharms, J. R. E., Böning, C. W. & Scheinert, M. Mesoscale perturbations control inter-ocean exchange south of Africa. Geophys. Res. Lett. doi: 10.1029/2008GL035132 (in the press)

  17. Biastoch, A., Böning, C., Getzlaff, J., Molines, J.-M. & Madec, G. Causes of interannual - decadal variability in the meridional overturning circulation of the mid-latitude North Atlantic Ocean. J. Clim. doi: 10.1175/2008JCLI2404.1 (in the press) (2008)

  18. Debreu, L., Vouland, C. & Blayo, E. AGRIF: Adaptive grid refinement in Fortran. Computers Geosci. 34, 8–13 (2008)

    Article  ADS  Google Scholar 

  19. Maltrud, M. E. & McClean, J. An eddy resolving global 1/10° ocean simulation. Ocean Model. 8, 31–54 (2005)

    Article  ADS  Google Scholar 

  20. Johnson, H. L. & Marshall, D. P. A theory for the surface Atlantic response to thermohaline variability. J. Phys. Oceanogr. 32, 1121–1132 (2002)

    Article  ADS  Google Scholar 

  21. Getzlaff, J., Böning, C. W., Eden, C. & Biastoch, A. Signal propagation related to the North Atlantic overturning. Geophys. Res. Lett. 32 doi: 10.1029/2004GL021002 (2005)

  22. Dong, B. W. & Sutton, R. T. Adjustment of the coupled ocean-atmosphere system to a sudden change in the thermohaline circulation. Geophys. Res. Lett. 29 doi: 10.1029/2002GL015229 (2002)

  23. Garzoli, S. L. et al. Three Agulhas rings observed during the Benguela Current Experiment. J. Geophys. Res. 104, 20971–20985 (1999)

    Article  ADS  Google Scholar 

  24. Van Sebille, E. & van Leeuwen, P. J. Fast northward energy transfer in the Atlantic due to Agulhas rings. J. Phys. Oceanogr. 37, 2305–2315 (2007)

    Article  ADS  Google Scholar 

  25. Van Aken, H. M. et al. Observation of a young Agulhas ring, Astrid, during MARE, the Mixing of Agulhas Rings Experiment, in March 2000. Deep-Sea Res. II 50, 167–195 (2003)

    Article  ADS  Google Scholar 

  26. Madec, G. NEMO Ocean Engine (Note du Pôle de Modélisation, Institut Pierre-Simon Laplace, 2006)

    Google Scholar 

  27. Large, W. G. & Yeager, S. G. Diurnal to Decadal Global Forcing for Ocean and Sea-Ice Models: the Data Sets and Flux Climatologies (NCAR Technical Note NCAR/TN-460+STR, National Center for Atmospheric Research, 2004)

    Google Scholar 

  28. Gent, P. R. & McWilliams, J. C. Isopycnal mixing in ocean circulation models. J. Phys. Oceanogr. 20, 150–155 (1990)

    Article  ADS  Google Scholar 

  29. Hsieh, W. W., Davey, M. K. & Wajsowicz, R. C. The free Kelvin wave in finite-difference numerical models. J. Phys. Oceanogr. 13, 1383–1397 (1983)

    Article  ADS  Google Scholar 

  30. Rio, M. H., Schaeffer, P., Hernandez, F. & Lemoine, J.-M. in Gocina: Improving Modelling of Ocean Transport and Climate Prediction in the North Atlantic Region using GOCE Gravimetry (eds Knudsen, P., Johannessen, J., Gruber, T., Stammer, S & van Dam, T.) 6 pp. (Cahiers du Centre Européen de Géodynamique et de Séismologie 25, EGCS, 2005)

    Google Scholar 

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The integration of the experiments was performed at the Höchstleistungsrechenzentrum Stuttgart and the Computing Centre at Kiel University. We thank the NEMO and AGRIF System Teams as well as J.-M. Molines and M. Scheinert for technical support. The analysis was performed under the DFG project no. BO 907/2-2. J.R.E.L. received support from the Alexander von Humboldt-Stiftung.

Author Contributions A.B. and C.W.B. designed the experiments. A.B. implemented and conducted the experiments and carried out the analysis. All authors discussed the results and jointly wrote the manuscript.

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Correspondence to A. Biastoch.

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Biastoch, A., Böning, C. & Lutjeharms, J. Agulhas leakage dynamics affects decadal variability in Atlantic overturning circulation. Nature 456, 489–492 (2008).

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