Climate of the Past www.clim-past.net 1814-9324 1814-9332 3 1 2007 10.5194/cp-3-51-2007 http://www.clim-past.net/3/51/2007/ http://www.clim-past.net/3/51/2007/cp-3-51-2007.html http://www.clim-past.net/3/51/2007/cp-3-51-2007.pdf 51 64 2007-02-01 The modern and glacial overturning circulation in the Atlantic ocean in PMIP coupled model simulations S. L. Weber weber@knmi.nl S. S. Drijfhout A. Abe-Ouchi M. Crucifix M. Eby A. Ganopolski S. Murakami B. Otto-Bliesner W. R. Peltier Royal Netherlands Meteorological Institute (KNMI), De Bilt, The Netherlands Center for Climate System Research, The University of Tokyo Kashiwa, Japan Hadley Center for Climate Prediction and Research, Met Office, Exeter, UK School of Earth and Ocean Sciences, University of Victoria, Victoria, Canada Potsdam Institute for Climate Impact Research, Potsdam, Germany Meteorological Research Institute, Tsukuba, and Frontier Research Center for Global Change, JAMSTEC, Yokohama, Japan National Center for Atmospheric Research, Boulder, USA Department of Physics, University of Toronto, Toronto, Canada This study analyses the response of the Atlantic meridional overturning circulation (AMOC) to LGM forcings and boundary conditions in nine PMIP coupled model simulations, including both GCMs and Earth system Models of Intermediate Complexity. Model results differ widely. The AMOC slows down considerably (by 20–40%) during the LGM as compared to the modern climate in four models, there is a slight reduction in one model and four models show a substantial increase in AMOC strength (by 10–40%). It is found that a major controlling factor for the AMOC response is the density contrast between Antarctic Bottom Water (AABW) and North Atlantic Deep Water (NADW) at their source regions. Changes in the density contrast are determined by the opposing effects of changes in temperature and salinity, with more saline AABW as compared to NADW consistently found in all models and less cooling of AABW in all models but one. In only two models is the AMOC response during the LGM directly related to the response in net evaporation over the Atlantic basin. Most models show large changes in the ocean freshwater transports into the basin, but this does not seem to affect the AMOC response. Finally, there is some dependence on the accuracy of the control state. Adkins, J. F., McIntyre, K., and Schrag, D. P.: The salinity, temperature and $\delta^18$O of the glacial deep ocean, Science, 298, 1769–1773, 2002. Curry, W. B. and Oppo, D. W.: Glacial water mass geometry and the distribution of $\delta^13$C of $§igma$CO₂ in the western Atlantic ocean, Paleoceanography, 20, 1017–1028, 2005. Dickson, R. R. and Brown, J.: The production of North Atlantic Deep Water: Sources, rates and pathways, J. Geophys. Res., 99(C6), 12 319–12 341, 1994. Duplessy, J. C., Shackleton, N. J., Fairbanks, R. G., Labeyrie, L., Oppo, D. W., and Kallel, N.: Deep water source variations during the last climatic cycle and their impact on the global deep water circulation, Paleoceanography, 3, 343–360, 1988. Ganopolski, A. and Rahmstorf, S.: Rapid changes of glacial climate simulated in a coupled model, Nature, 409, 153–158, 2001. Ganopolski, A., Rahmstorf, S., Petoukhov, V., and Claussen, M.: Simulation of modern and glacial climates wih a coupled global model of intermediate complexity, Nature, 391, 351–356, 1998. Gordon, C., Cooper, C., Senior, C. A., Banks, H., Gregory, J. M., Johns, T. C., Mitchell, J. F. B., and Wood, R. A.: The simulation of SST, sea-ice extents and ocean heat transports in a version of the Hadley Centre coupled model without flux adjustments, Clim. Dyn., 16, 147–168, 2000. Gregory, J., Dixon, K. W., Stouffer, R. J., Weaver, A. J., Driesschaert, E., Eby, M., Fichefet, T., Hasumi, H., Hu, A., Jungclaus, J. H., Kamenkovich, I. V., Levermann, A., Montoya, M., Murakami, S., Nawrath, S., Oka, A., Solokov, A. P., and Thorpe, R. B.: A model intercomparison of changes in the Atlantic thermohaline circulation in response to increasing atmospheric $CO_2$ concentration, Geophys. Res. Lett., 32, L12703, doi:10.1029/2005GL023209, 2005. Hargreaves, J. C., Abe-Ouchi, A., and Annan, J. D.: Linking glacial and future climates through an ensemble of GCM simulations, Clim. Past Discuss., 2, 951–977, 2006. Hasumi, H. and Emori, S.: K-1 coupled model (MIROC) description, K-1 technical report 1, Center for Climate System Research, University of Tokyo, 2004. Hewitt, C. D., Broccoli, A. J., Mitchell, J. F., and Stouffer, R. J.: A coupled model study of the last glacial maximum: was part of the North Atlantic relatively warm?, Geophys. Res. Lett., 28, 1571–1574, 2001. Hughes, T. M. C. and Weaver, A. J.: Multiple equilibria of an asymmetric two-basin ocean model, J. Phys. Oceanogr., 24, 619–637, 1994. Kageyama, M., Laine, A., Abe-Ouchi, A., Braconnot, P., Cortijo, E., M. Crucifix, M., de Vernal, A., Guiot, J., Hewitt, C. D., Kitoh, A., Marti, O., Ohgaito, R., Otto-Bliesner, B., Peltier, W. R., Rosell-Mele, A., Vettoretti, G., Weber, S. L., and MARGO Project Members: Last Glacial Maximum temperatures over the North Atlantic, Europe and western Siberia: a comparison between PMIP models, MARGO sea-surface temperatures and pollen-based reconstructions, Quatern. Sci. Rev., 25(17–18), 2082–2102, 2006. Kamenkovich, I. V. and Goodman, P. J.: The dependence of AABW transport in the Atlantic on vertical diffusivity, Geophys. Res. Lett., 27, 3739–3742, 2000. Kitoh, A., Murakami, S., and Koide, H.: A simulation of the Last Glacial Maximum with a coupled atmosphere-ocean GCM, Geophys. Res. Lett., 28, 2221–2224, 2001. Labeyrie, L. D., Duplessy, J.-C., Duprat, J., Juillet-Leclerc, A., Moyes, J., Michel, E., Kallel, N., and Shackleton, N. J.: Changes in the vertical structure of the North Atlantic ocean between glacial and modern times, Quatern. Sci. Rev., 11, 401–413, 1992. LeGrand, P. and Wunsch, C.: Constraints from paleotracer data on the North Atlantic circulation during the last glacial maximum, Paleoceanography, 6, 1011–1045, 1995. Levitus, S. and Boyer, T. P.: World Ocean Atlas 1994 Volume 4: Temperature. NOAA ATLAS NESDIS 4. U.S. Government Printing Office, 1994. Levitus, S., Burgett, R., and Boyer, T. P.: World Ocean Atlas 1994 Volume 3: Salinity. NOAA ATLAS NESDIS 3. U.S. Government Printing Office, 1994. Marsh, R., Hazeleger, W., Yool, A., and Rohling, E. J.: Stability of the Thermohaline Circulation under millennial CO₂ forcing and two alternative controls on Atlantic salinity, Geophys. Res. Lett., in press, 2007. Masson-Delmotte, V., Kageyama, M., Braconnot, P., Charbit, S., Krinner, G., Ritz, C., Guilyardi, E., Jouzel, J., Abe-Ouchi, A., Crucifix, M., Gladstone, R. M., Hewitt, C.D., Kitoh, A., Legrande, A.N., Marti, O., Merkel, U., Motoi, T., Ohgaito, R., Otto-Bliesner, B., Peltier, W. R., Ross, I., Valdes, P.J., Vettoretti, G., Weber, S. L., Wolk, F., and Yu, Y.: Past and future polar amplification of climate change: climate model intercomparison and ice-core constraints, Clim. Dyn., 26(5), 513–529, doi:10.1007/s00382-005-0081-9, 2005. McManus, J., Francois, R., Gherardi, J., Keigwin, L., and Brown-Leger, S.: Collapse and rapid resumption of Atlantic meridional circulation linked to deglacial climate changes, Nature, 428, 834–837, 2004. Otto-Bliesner, B., Brady, E. C., Clauzet, G., Tomas, R., Levis, S., and Kothalava, Z.: Last Glacial Maximum and Holocene climate in CCSM3, J. Clim., 19, 2526–2544, 2006. Pardaens, A. K., Banks, H. T., Gregory, J. M., and Rowntree, P. R.: Freshwater transports in HadCM3, Clim. Dyn., 21, 177–195, 2003. Paul, A. and Schaefer-Neth, C.: Modeling the water masses of the Atlantic Ocean at the Last Glacial Maximum, Paleoceanography, 18(3), 1058, doi:10.1029/2002PA000783, 2003. Peltier, W. R.: Ice age paleotopography, Science, 265, 195–201, 1994. Peltier, W. R.: Global glacial isostasy and the surface of the ice-age Earth: the ICE-5G (VM2) model and GRACE, Ann. Rev. Earth Plan. Sci., 32, 111–149, 2004. Peltier, W. R. and Solheim, L. P.: The climate of the Earth at Last Glacial Maximum: statistical equilibrium state and a mode of internal variability, Quatern. Sci. Rev., 23, 335–357, 2004. Prange, M., Romanova, V., and Lohmann, G.: The glacial thermohaline circulation: stable of unstable?, Geophys. Res. Lett., 29, 2028–2031, 2002. Rahmstorf, S.: On the freshwater forcing and transport of the Atlantic thermohaline circulation, Clim. Dyn., 12, 799–811, 1996. Roche, D. M., Dokken, T. M., Goosse, H., Renssen, H., and Weber, S. L.: Climate of the last glacial maximum: sensitivity studies and model-data comparison with the LOVECLIM coupled model, Clim. Past Discuss., 2, 1105–1153, 2006. Rutberg, R. L. and Peacock, S. L.: High-latitude forcing of interior ocean $\delta^13C$, Paleoceanography, 21, PA2012, doi:10.1029/2005PA001226, 2006. Sarnthein, M., Winn, K., Jung, S. J. A., Duplessy, J.-C., Labeyrie, L., Erlenkeuser, H., and Ganssen, G.: Changes in east Atlantic deepwater circulation over the last 30,000 years: Eight time slice reconstructions, Paleoceanography, 9, 209–267, 1994. Schmittner, A., Meissner, K. J., Eby, M., and Weaver, A. J.: Forcing of the deep ocean circulation in simulations of the Last Glacial Maximum, Paleoceanography, 17, 26–35, doi:10.1029/2001PA000633, 2002. Shin, S., Liu, Z., Otto-Bliesner, B., Kutzbach, J. E., and Vavrus, S. J.: Southern ocean sea-ice control of the glacial North Atlantic thermohaline circulation, Geophys. Res. Lett., 30, 1096, doi:10.1029/2002GL015513, 2003. Thorpe, R. B., Gregory, J. M., Johns, T. C., Wood, R. A., and Mitchell, J. F. B.: Mechanisms determining the Atlantic Thermohaline circulation response to Greenhouse Gas forcing in a non-flux-adjusted coupled climate model, J. Clim., 14, 3102–3116, 2001. Vries, P. de and Weber, S. L.: The Atlantic freshwater budget as a diagnostic for the existence of a stable shut-down of the meridional overturning circulation, Geophys. Res. Lett., 32, L09606, doi:10.1029/2004GL021450, 2005. Weaver, A. J., Eby, M., Wiebe, E. C., Bitz, C. M., Duffy, P. B., Ewen, T. L., Fanning, A. F., Holland, M. M., MacFadyen, A., Matthews, H. D., Meissner, K. J., Saenko, O., Schmittner, A., Wang, H., and Yoshimori, M.: The UVic Earth System Climate Model: Model description, climatology and application to past, present and future climates, Atmosphere-Ocean, 39, 361–428, 2001. Weijer, W., de Ruijter, W. P. M., Dijkstra, H. A., and van Leeuwen, P. J.: Impact of interbasin exchange on the Atlantic overturning circulation, J. Phys. Oceanogr., 29, 2266–2284, 1999. Wunsch, C.: Abrupt climate change: an alternative view, Quatern. Res., 65, 191–203, 2006. Zahn, R. and Mix, A. C.: Benthic foraminiferal $\delta^18O$ in the ocean's temperature-salinity-density field: constraints on the ice age thermohaline circulation, Paleoceanography, 6, 1–20, 1991.