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J. Paul Spence, Michael Eby, and Andrew J. Weaver

1. Introduction Variation in the poleward transport of heat by the Atlantic meridional overturning circulation (AMOC) is commonly evoked as a mechanism to explain large-scale climate events found in paleorecords ( Bond et al. 1993 ; Rahmstorf 2002 ). A wide range of modeling studies have demonstrated a weakened AMOC in response to surface freshwater forcing at North Atlantic Deep Water (NADW) formation sites (e.g., Stommel 1961 ; Weaver and Hughes 1992 ; Stouffer et al. 2006 ); specifically

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Guido Vettoretti, Marc d’Orgeville, William R. Peltier, and Marek Stastna

scenarios ( Otto-Bliesner 1999 ; Federov and Philander 2000 ; Peltier and Solheim 2004 ) provides a means to assess the fidelity of these predictive models. Studies of the impact of freshwater forcing on tropical Pacific climate variability (e.g., Zhang and Delworth 2005 ; Dong and Sutton 2007 ) have discussed several of the mechanisms that could be involved in supporting an “atmospheric bridge” between the polar Atlantic and tropical Pacific Oceans. Timmermann et al. (2005) has suggested that an

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Marc d’Orgeville and W. Richard Peltier

. 2004 ) argue that North Pacific decadal variability is in fact forced by variations in the tropical Pacific through atmospheric teleconnections. Some “tropical theories” argue specifically for a tropically forced mechanism where atmospheric teleconnections from the tropics are assumed to impact North Pacific SST decadal variability, either by a direct transfer of the tropical decadal variability ( Trenberth 1990 ), or by ENSO-related interannual forcing, which is subsequently integrated or

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Marc d’Orgeville and W. Richard Peltier

SST, two further ingredients (salinity and atmospheric variability) have been invoked to refine this basic concept. The role of salinity and atmospheric forcing in sustaining such oscillatory behavior has been extensively studied in the context of uncoupled ocean-only general circulation models (see, e.g., Weaver and Sarachik 1991 ; Winton and Sarachik 1993 ). In the present paper, our focus will be on the results delivered by a fully coupled model. A sea surface salinity (SSS) anomaly in the

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Michael S. Pritchard, Andrew B. G. Bush, and Shawn J. Marshall

1. Introduction Although high-frequency climate variability on the annual to subannual scale is reasonably well understood, there is an ongoing effort to account for observed low-frequency climate variability on interdecadal to millennial scales. A recent approach that has helped to address this problem is the incorporation of higher-frequency external forcing mechanisms into models of lower-frequency processes. Several such studies have provided useful insight into the evolution of slow modes

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Garry K. C. Clarke, Andrew B. G. Bush, and John W. M. Bush

necessarily avoids the question of how freshwater that is added at the ocean margins can migrate to the mid-Atlantic ocean. For these modeling studies the maximum MOC reduction ranges from around 40% to a near-complete shutdown. In terms of a proper representation of the freshwater forcing, the minimum forcing used by Wiersma et al. (2006) and that used by LeGrande et al. (2006) represent the best efforts thus far. Recent paleochemical studies give evidence for cooling and freshening of the North

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M. Eby, K. Zickfeld, A. Montenegro, D. Archer, K. J. Meissner, and A. J. Weaver

CaCO 3 weathering flux diagnosed from the ocean sediment burial flux. The weathering flux was then held fixed while the burial flux of CaCO 3 was allowed to evolve with time for all subsequent experiments. Historical emissions were applied until the end of the year 2000. These historical CO 2 emissions include contributions from both fossil fuel burning and land use changes. All other transient forcings (insolation, orbital forcing, tropospheric and stratospheric sulfates, and non-CO 2

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Garry K. C. Clarke, Etienne Berthier, Christian G. Schoof, and Alexander H. Jarosch

has been followed by Haeberli (1985) and Haeberli and Hoelzle (1995) . Plasticity estimators require no knowledge of the mass balance forcing for the glacier but do assume, implicitly, that the glacier is healthy enough to maintain its basal stress near the yield stress. An alternative approach that requires additional assumptions is to assume that the glacier is near a steady-state configuration with respect to a known or estimated mass balance forcing. With this assumption the balance ice

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Stephen D. Griffiths and W. Richard Peltier

1. Introduction Tides occur throughout the oceans as periodic oscillations in currents and sea surface height, typically with diurnal or semidiurnal time scales. The amplitude of the surface oscillations is about 50 cm over much of the open ocean and about 1 m along many coastlines, but local resonances can lead to tides of over 5 m in special coastal locations (e.g., Garrett 1972 ; Arbic et al. 2007 ). However, tidal amplitudes are sensitive to the frequency of the lunar and solar forcing (i

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A. E. Viau and K. Gajewski

strong regional responses to orbital forcing (e.g., COHMAP Members 1988 ). Radiocarbon-dated pollen (and other) records, however, show variability on suborbital scales. Studies have shown that vegetation responds rapidly to climate change ( Webb 1986 ; Gajewski 1987 ) and that there is evidence of a synchronous vegetation response to abrupt climate changes during the late glacial period and Holocene ( Grimm et al. 1993 ; Williams et al. 2002 ; Viau et al. 2002 , 2006 ; Gajewski et al. 2006 ) as

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