Climate of the Last Glacial Maximum: sensitivity studies and model-data comparison with the LOVECLIM coupled model

Abstract

Abstract. The Last Glacial Maximum climate is one of the classical benchmarks used both to test the ability of coupled models to simulate climates different from that of the present-day and to better understand the possible range of mechanisms that could be involved in future climate change. It also bears the advantage of being one of the most well documented periods with respect to palaeoclimatic records, allowing a thorough data-model comparison. We present here an ensemble of Last Glacial Maximum climate simulations obtained with the Earth System model LOVECLIM, including coupled dynamic atmosphere, ocean and vegetation components. The climate obtained using standard parameter values is then compared to available proxy data for the surface ocean, vegetation, oceanic circulation and atmospheric conditions. Interestingly, the oceanic circulation obtained resembles that of the present-day, but with increased overturning rates. As this result is in contradiction with the current palaeoceanographic view, we ran a range of sensitivity experiments to explore the response of the model and the possibilities for other oceanic circulation states. After a critical review of our LGM state with respect to available proxy data, we conclude that the oceanic circulation obtained is not inconsistent with ocean circulation proxy data, although the water characteristics (temperature, salinity) are not in full agreement with water mass proxy data. The consistency of the simulated state is further reinforced by the fact that the mean surface climate obtained is shown to be generally in agreement with the most recent reconstructions of vegetation and sea surface temperatures, even at regional scales.

Deglacial ice sheet meltdown: orbital pacemaking and CO<sub>2</sub> effects

“…Sea level and the ocean bathymetry are not adapted to ice sheet variations. The land-sea mask in ECBilt/VECODE and the ocean bathymetry in CLIO are prescribed according to LGM sea level, based on Roche et al (2007). In particular, the Bering Strait is closed, and the parameterization of the water and sea ice transport through the Bering Strait in CLIO as described by Goosse et al (1997) is not applied.…”

“…The numerical model used in this study is based on the Ice sheet model for Integrated Earth system Studies IcIES (Saito and Abe-Ouchi, 2004;Abe-Ouchi et al, 2007), bidirectionally coupled to the atmosphere-ocean-sea ice-land components of the intermediate complexity model LOVE-CLIM (Driesschaert et al, 2007) with LGM (Last Glacial Maximum) boundary conditions (Roche et al, 2007). The coupled model is driven by orbital parameter changes (Berger, 1978), and reconstructed atmospheric concentrations of CO 2 (Lüthi et al, 2008), CH 4 (Loulergue et al, 2008), and N 2 O (Schilt et al, 2010).…”

Simulating Heinrich event 1 with interactive icebergs

“…The LGM boundary conditions are imposed as in the PMIP-2 protocol, as described in detail in Roche et al (2007). Summarising: Orbital parameters are taken from Berger and Loutre (1992) and set to 21 ka B.P.…”

“…We simulate a Heinrich event under LGM climatic conditions with a large armada of dynamic-thermodynamic icebergs to mimic the conditions of Heinrich event 1. The choice of this particular Heinrich event is based on the availability of a well-described LGM background state (Roche et al 2007) as well as the inclusion of this particular event in the third phase of the Paleoclimate Modelling Intercomparison Project (PMIP-3) that will allow further comparison with more complex models. PMIP-3 models being run with freshwater fluxes, we propose to explore the role of the spatial distribution of the iceberg melt and compare our results with the former typical homogeneous hosing approach.…”

The LGM surface climate and atmospheric circulation over East Asia and the North Pacific in the PMIP2 coupled model simulations

“…Masson-Delomtte et al, 2006;Kageyama et al, 2006;Braconnot et al , 2007;Hargreaves et al, 2007;Roche et al, 2007;Weber et al, 2007). The objective of this study is to investigate the surface climate and atmospheric field over East Asia and the North Pacific during the LGM by comparing the results obtained using the different CGCMs in the PMIP2 database and the paleoclimatic reconstructions.…”