On the stability of the Atlantic meridional overturning circulation during the last deglaciation
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Using a generalized stability indicator L, we explore the stability of the Atlantic meridional overturning circulation (AMOC) during the last deglaciation based on a paleoclimate simulation. From the last glacial maximum, as forced by various external climate forcings, notably the meltwater forcing, the AMOC experiences a collapse and a subsequent rapid recovery in the early stage of deglaciation. This change of the AMOC induces an anomalous freshwater divergence and later convergence across the Atlantic and therefore leads to a positive L, suggesting a negative basin-scale salinity advection feedback and, in turn, a mono-stable deglacial AMOC. Further analyses show that most anomalous freshwater is induced by the AMOC via the southern boundary of the Atlantic at 34°S where the freshwater transport (M ovS ) is about equally controlled by the upper branch of the AMOC and the upper ocean salinity along 34°S. From 19 to 17 ka, as a result of multiple climate feedbacks associated with the AMOC change, the upper ocean at 34°S is largely salinified, which helps to induce a switch in M ovS , from import to export. Our study has important implications to the deglacial simulations by climate models. A decomposition of L shows that the AMOC stability is mostly determined by two terms, the salinity stratification at 34°S and the change of stratification with the AMOC. Both terms appear positive in model. However, the former is likely to be distorted towards positive, as associated with a common bias existing over the South Atlantic in climate models. Therefore, the AMOC is potentially biased towards mono-stability in most paleoclimate simulations.
KeywordsAMOC Stability indicator Freshwater transport Feedback The last deglaciation
Wei Liu and Zhengyu Liu are supported by NSF, DOE and NSFC 41,130,105. Jun Cheng is supported by NSFC 41206024. Haibo Hu is supported by the National Key Program for Developing Basic Science (Grant Nos. 2010CB428504, 2012CB956002).
- Dong B, Sutton RT (2002) Adjustment of the coupled ocean–atmosphere system to a sudden change in the thermohaline circulation. Geophys Res Lett 29. doi: 10.1029/2002GL015229
- Hu A, Meehl GA, Han W, Timmermann A, Otto-Bliesner BL, Liu Z, Washington W, Large W, Abe-Ouchi A, Kimoto M, Lambeck K, Wu B (2012) Role of the Bering Strait on the hysteresis of the ocean conveyor belt circulation and glacial climate stability. Proc Natl Acad Sci 109(17):6417–6422. doi: 10.1073/pnas.1116014109 CrossRefGoogle Scholar
- Liu W (2012) Insights from deglacial changes in the Southern Ocean and Atlantic meridional overturning circulation during the last deglaciation. Ph.D thesis 150 pp. Univ of Wisconsin-MadisonGoogle Scholar
- Lutjeharms JRE (2006) The agulhas current. Springer, BerlinGoogle Scholar
- Lynch-Stieglitz J, Adkins JF, Curry WB, Dokken T, Hall IR, Herguera JC, Hirschi J, Ivanova E, Kissell C, Marchal O, Marchitto TM, McCave IN, McManus JF, Mulitza S, Ninnemann US, Yu E, Zahn R (2007) Atlantic overturning circulation during the Last Glacial Maximum. Science 316:66–69CrossRefGoogle Scholar
- Schäfer-Neth C, Paul A (2003) The Atlantic Ocean at the last glacial maximum: 1. objective mapping of the GLAMAP sea-surface conditions. In: Wefer G, Mulitza S, Ratmeyer V (eds) The South Atlantic in the late quaternary: material budget and current systems. Springer, Berlin, pp 531–548CrossRefGoogle Scholar
- Sijp WP, England MH, Gregory JM (2012) Precise calculations of the existence of multiple AMOC equilibria in coupled climate models. Part I: equilibrium states. J Clim 25:282–298Google Scholar
- Stouffer RJ, Dixon KW, Spelman MJ, Hurlin WJ, Yin J, Gregory JM, Weaver AJ, Eby M, Flato GM, Robitaille DY, Hasumi H, Oka A, Hu A, Jungclaus JH, Kamenkovich IV, Levermann A, Montoya M, Murakami S, Nawrath S, Peltier WR, Vettoretti G, Sokolov AP, Weber SL (2006) Investigating the causes of the response of the thermohaline circulation to past and future climate changes. J Clim 19:1365–1387. doi: 10.1175/JCLI3689.11 CrossRefGoogle Scholar
- Xie S-P, Carton JA (2004) Tropical Atlantic variability: patterns, mechanisms, and impacts, in Earth’s climate: the ocean–atmosphere interaction. Geophys Monogr Ser, vol 147, edited by Wang C, Xie S-P, Carton JA, AGU, Washington, DC, pp 121–142Google Scholar