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Influence of the Atlantic thermohaline circulation on neodymium isotopic composition at the Last Glacial Maximum – a modelling sensitivity study
1Laboratoire des Sciences du Climat et de l'Environnement (LSCE), CEA/CNRS/UVSQ/IPSL, Orme des Merisiers, Gif-Sur-Yvette, Bat 712, 91191 Gif sur Yvette cedex, France
2Laboratoire d'Etudes en Géophysique et Océanographie Spatiale (LEGOS), CNES/CNRS/UPS/IRD, Observatoire Midi-Pyrénées, 14 av. E. Belin, 31400 Toulouse, France
Abstract. The oceanic neodymium isotopic composition (hereafter expressed as ε Nd) is modeled for the Last Glacial Maximum (LGM) using the coarse resolution Ocean Global Circulation Model NEMO–ORCA2°. This study focuses on the impact of changes in the overturning cell and circulation patterns between LGM and Holocene on ε Nd in the Atlantic basin. Three different LGM freshwater forcing experiments are performed to test the variability in ε Nd oceanic distribution as a function of ocean circulation. Highly distinct representations of ocean circulation are generated in the three simulations, which drive significant differences in ε Nd, particularly in deep waters of the western part of the basin. However, mean Atlantic LGM ε Nd values are remain half a unit more radiogenic than for the modern control run. A fourth experiment shows that changes in Nd sources and bathymetry drive a shift in the ε Nd signature of Northern end-members (NADW or GNAIW glacial equivalent) that is sufficient to explain the shift in mean ε Nd during our LGM simulations. None of our three LGM circulation scenarios gives a better agreement with the existing ε Nd paleo-data, as the model fails in reproducing the dynamical features of the area. Therefore, this study cannot indicate the likelihood of a given LGM oceanic circulation scenario. Rather, our modeling results highlight the need for data from western Atlantic deep waters, where the ε Nd gradient in the three LGM scenarios is the most important (up to 3 ε Nd). This would also aid more precise conclusions concerning the north end-member ε Nd signature evolution, and thus the potential use of ε Nd as a tracer of past oceanic circulation.
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Citation: Arsouze, T., Dutay, J.-C., Kageyama, M., Lacan, F., Alkama, R., Marti, O., and Jeandel, C.: Influence of the Atlantic thermohaline circulation on neodymium isotopic composition at the Last Glacial Maximum – a modelling sensitivity study, Clim. Past Discuss., 4, 309-333, 2008. Bibtex EndNote Reference Manager
