CPD Climate of the Past Discussions CPD 1814-9359 Copernicus GmbH Göttingen, Germany 10.5194/cpd-7-1567-2011 Heinrich event 1: an example of dynamical ice-sheet reaction to oceanic changes Álvarez-Solas J. 1 2 Montoya M. 1 3 Ritz C. 4 Ramstein G. 2 Charbit S. 2 Dumas C. 2 Nisancioglu K. 5 Dokken T. 5 Ganopolski A. 6 Dpto. Astrofísica y Ciencias de la Atmósfera, Universidad Complutense, Madrid, Spain LSCE, CEA-CNRS-UVSQ, UMR8212, CNRS – CEA Saclay, Gif-sur-Yvette, France Instituto de Geociencias (UCM-CSIC), Facultad de Ciencias Físicas, Madrid, Spain Laboratoire de Glaciologie et de Géophysique de l'Environnement, CNRS, Saint Martin d'Hères, France Bjerknes Centre for Climate Research, Bergen, Norway Potsdam Institute for Climate Impact Research, Potsdam, Germany 12 05 2011 7 3 1567 1583 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.clim-past-discuss.net/7/1567/2011/cpd-7-1567-2011.html The full text article is available as a PDF file from http://www.clim-past-discuss.net/7/1567/2011/cpd-7-1567-2011.pdf

Heinrich events, identified as enhanced ice-rafted detritus (IRD) in North Atlantic deep sea sediments (Heinrich, 1988; Hemming, 2004) have classically been attributed to Laurentide ice-sheet (LIS) instabilities (MacAyeal, 1993; Calov et al., 2002; Hulbe et al., 2004) and assumed to lead to important disruptions of the Atlantic meridional overturning circulation (AMOC) and North Atlantic deep water (NADW) formation. However, recent paleoclimate data have revealed that most of these events probably occurred after the AMOC had already slowed down or/and NADW largely collapsed, within about a thousand years (Hall et al., 2006; Hemming, 2004; Jonkers et al., 2010; Roche et al., 2004), implying that the initial AMOC reduction could not have been caused by the Heinrich events themselves. Here we propose an alternative driving mechanism, specifically for Heinrich event 1 (H1), by which North Atlantic ocean circulation changes are found to have strong impacts on LIS dynamics. By combining simulations with a coupled climate model and a three-dimensional ice sheet model, our study illustrates how reduced NADW and AMOC weakening lead to a subsurface warming in the Nordic and Labrador Seas resulting in rapid melting of the Hudson Strait and Labrador ice shelves. Lack of buttressing by the ice shelves implies a substantial ice-stream acceleration, enhanced ice-discharge and sea level rise, with peak values 500–1500 yr after the initial AMOC reduction. Our scenario modifies the previous paradigm of H1 by solving the paradox of its occurrence during a cold surface period, and highlights the importance of taking into account the effects of oceanic circulation on ice-sheets dynamics in order to elucidate the triggering mechanism of Heinrich events.

 References Alvarez-Solas, J., Charbit, S., Ramstein, G., Paillard, D., Dumas, C., Ritz, C., and Roche, D.: Millennial-scale oscillations in the Southern Ocean in response to atmospheric CO2 increase, Global Planet. Change, 128–136, doi:10.1016/j.gloplacha.2010.12.004, 2010a. Global and Planetary Change 76, Alvarez-Solas, J., Charbit, S., Ritz, C., Paillard, D., Ramstein, G., and Dumas, C.: Links between ocean temperature and iceberg discharge during Heinrich events, Nat. Geosci., 3, 122–126, 2010b. Arbic, B., MacAyeal, D., Mitrovica, J., and Milne, G.: PalaeoclimateOcean tides and Heinrich events, Nature, 432, 460–460, 2004. Bond, G. and Lotti, R.: Iceberg Discharges into the North Atlantic on Millennial Time Scales During the Last Glaciation, Science, 267, 1005–1010, 1995. Bond, G., Heinrich, H., Broecker, W., Labeyrie, L., McManus, J., Andrews, J., Huon, S., Jantschik, R., Clasen, S., Simet, C., Tedesco, K., Klas, M., Bonani, G., and Ivy, S.: Evidence for massive discharge of icebergs into the North Atlantic Ocean during the last glacial, Nature, 360, 245–249, 1992. Calov, R., Ganopolski, A., Petoukhov, V., Claussen, M., and Greve, R.: Large-scale instabilities of the Laurentide ice sheet simulated in a fully coupled climate-system model, Geophys. Res. Lett., 29, 691–694, 2002. Charbit, S., Ritz, C., Philippon, G., Peyaud, V., and Kageyama, M.: Numerical reconstructions of the Northern Hemisphere ice sheets through the last glacial-interglacial cycle, Clim. Past, 3, 15–37, http://dx.doi.org/10.5194/cp-3-15-2007doi:10.5194/cp-3-15-2007, 2007. Clark, P., Hostetler, S., Pisias, N., Schmittner, A., and Meissner, K.: Mechanisms for an~ 7-kyr Climate and Sea-Level Oscillation During Marine Isotope Stage 3, Geophysical Monograph-American Geophysical Union, 173, 209, 2007. CLIMAP: Climate: Long-Range Investigation, Mapping, and Prediction (CLIMAP) Project Members, The surface of the ice-age, Science, 191, 1131–1137, 1976. Dansgaard, W., Johnsen, S., Clausen, H., Dahl-Jensen, D., Gundestrup, N., Hammer, C., Hvidberg, C., Steffensen, J., Sveinbjornsdottir, A., Jouzel, J., et~al.: Evidence for general instability of past climate from a 250-kyr ice-core record, Nature, 364, 218–220, 1993. De~Vernal, A., Rosell-Melé, A., Kucera, M., Hillaire-Marcel, C., Eynaud, F., Weinelt, M., Dokken, T., and Kageyama, M.: Comparing proxies for the reconstruction of LGM sea-surface conditions in the northern North Atlantic, Quaternary Sci. Rev., 25, 2820–2834, 2006. Dokken, T. and Jansen, E.: Rapid changes in the mechanism of ocean convection during the last glacial period, Nature, 401, 458–461, 1999. Flückiger, J., Knutti, R., and White, J.: Oceanic processes as potential trigger and amplifying mechanisms for Heinrich events, Paleoceanography, 21, PA2014, doi:10.1029/2005PA001204, 2006. Grootes, P M., Stuiver, M., White, J. W C., Johnsen, S., and Jouzel, J.: Comparison of oxygen isotope records from the GISP2 and GRIP Greenland ice cores, Nature, 366, 552–554, 1993. Grousset, F., Pujol, C., Labeyrie, L., Auffret, G., and Boelaert, A.: Were the North Atlantic Heinrich events triggered by the behavior of the European ice sheets?, Geology, 28, 123–126, 2000. Hall, I R., Moran, S B., Zahn, R., Knutz, P C., Shen, C C., and Edwards, R L.: Accelerated drawdown of meridional overturning in the late-glacial Atlantic triggered by transient pre-H event freshwater perturbation, Geophys. Res. Lett., 33, L16616, doi:10.1029/2006GL026239, 2006. Hebbeln, D., Dokken, T., Andersen, E., Hald, M., and Elverhøi, A.: Moisture supply for northern ice-sheet growth during the Last Glacial Maximum, Nature, 309, 357–360, 1994. Heinrich, H.: Origin and consequences of cyclic ice rafting in the northeast Atlantic Ocean during the past 130,000 years, Quaternary Res., 29, 142–152, 1988. Hemming, S R.: Heinrich events: Massive late Pleistocene detritus layers of the North Atlantic and their global climate imprint, Rev. Geophys, 42, RG1005, doi:10.1029/2003RG000128, 2004. Hulbe, C.: Palaeoclimate: Extreme iceberg generation exposed, Nature Geoscience, 3, 80–81, 2010. Hulbe, C., MacAyeal, D., Denton, G., Kleman, J., and Lowell, T.: Catastrophic ice shelf breakup as the source of Heinrich event icebergs, Paleoceanography, 19, 1004–1029, 2004. Hutter, K.: Theoretical glaciology: material science of ice and the mechanics of glaciers and ice sheets, Springer, 1983. Jonkers, L., Moros, M., Prins, M., Dokken, T., Dahl, C., Dijkstra, N., Perner, K., and Brummer, G.: A reconstruction of sea surface warming in the northern North Atlantic during MIS 3 ice-rafting events, Quaternary Sci. Rev., 29, 1791–1800, 2010. Levermann, A., Griesel, A., Hofmann, M., Montoya, M., and Rahmstorf, S.: Dynamic sea level changes following changes in the thermohaline circulation, Clim. Dyn., 24, 347–354, 2005. MacAyeal, D.: Large-scale ice flow over a viscous basal sediment- Theory and application to ice stream B, Antarctica, J. Geophys. Res., 94, 4071–4087, 1989. MacAyeal, D.: Binge/purge oscillations of the Laurentide ice sheet as a cause of the North Atlantic's Heinrich events, Paleoceanography, 8, 775–784, 1993. Mignot, J., Ganopolski, A., and Levermann, A.: Atlantic subsurface temperatures: response to a shut-down of the overturning circulation and consequences for its recovery, J. Clim., 20, 4884–4898, 2007. Montoya, M. and Levermann, A.: Surface wind-stress threshold for glacial Atlantic overturning, Geophys. Res. Lett., 35, L03608, http://dx.doi.org/10.1029/2007GL032560doi:10.1029/2007GL032560, 560, 2008. Montoya, M., Griesel, A., Levermann, A., Mignot, J., Hofmann, M., Ganopolski, A., and Rahmstorf, S.: The Earth System Model of Intermediate Complexity CLIM\it BER-3α. Part I: description and performance for present day conditions, Clim. Dyn., 25, 237–263, 2005. Morland, L.: Thermomechanical balances of ice sheet flows, Geophys. Astro. Fluid, 29, 237–266, 1984. Peltier, W.: Global glacial isostasy and the surface of the ice-age Earth- The ICE-5 G(VM 2) model and GRACE, Ann. Rev. Earth and Plan. Sci., 32, 111–149, 2004. Peyaud, V., Ritz, C., and Krinner, G.: Modelling the Early Weichselian Eurasian Ice Sheets: role of ice shelves and influence of ice-dammed lakes, Clim. Past, 3, 375–386, http://dx.doi.org/10.5194/cp-3-375-2007doi:10.5194/cp-3-375-2007, 2007. Philippon, G., Ramstein, G., Charbit, S., Kageyama, M., Ritz, C., and Dumas, C.: Evolution of the Antarctic ice sheet throughout the last deglaciation: A study with a new coupled climate-north and south hemisphere ice sheet model, Earth Planet. Sci. Lett., 248, 750–758, 2006. Rignot, E., Casassa, G., Gogineni, P., Krabill, W., Rivera, A., and Thomas, R.: Accelerated ice discharge from the Antarctic Peninsula following the collapse of Larsen B ice shelf, Geophys. Res. Lett, 31, L18401, doi:10.1029/2004GL020697, 2004. Ritz, C., Rommelaere, V., and Dumas, C.: Modeling the evolution of Antarctic ice sheet over the last 420,000 years: Implications for altitude changes in the Vostok region, J. Geophys. Res.-Atmos., 106, 31943–31964, 2001. Roche, D., Paillard, D., and Cortijo, E.: Constraints on the duration and freshwater release of Heinrich event 4 through isotope modelling, Nature, 432, 379–382, 2004. Sarnthein, M., Winn, K., Jung, S., Duplessy, J., 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, 209–209, 1994. Scambos, T., Bohlander, J., Shuman, C., and Skvarca, P.: Glacier acceleration and thinning after ice shelf collapse in the Larsen B embayment, Antarctica, Geophys. Res. Lett, 31, L18402, doi:10.1029/2004GL020670, 2004. Shaffer, G., Olsen, S., and Bjerrum, C.: Ocean subsurface warming as a mechanism for coupling Dansgaard-Oeschger climate cycles and ice-rafting events, Geophys. Res. Lett., 31, L24202, doi:10.1029/2004GL020968, 2004. Trenberth, K., Olson, J., and Large, W.: A Global Ocean Wind Stress Climatology based on ECMWF Analyses, Tech. Rep. NCAR/TN-338+STR, National Center for Atmospheric Research, Boulder, Colorado, USA, 1989. Winsborrow, M., Clark, C., and Stokes, C.: Ice streams of the Laurentide ice sheet, Géographie Physique et Quaternaire, 58, 269–280, 2004.