Clim. Past Discuss., 4, 309-333, 2008
www.clim-past-discuss.net/4/309/2008/
doi:10.5194/cpd-4-309-2008
© Author(s) 2008. This work is distributed
under the Creative Commons Attribution 3.0 License.
Review Status
This discussion paper has been under review for the journal Climate of the Past (CP). Please refer to the corresponding final paper in CP.
Influence of the Atlantic thermohaline circulation on neodymium isotopic composition at the Last Glacial Maximum – a modelling sensitivity study
T. Arsouze1,2, J.-C. Dutay1, M. Kageyama1, F. Lacan2, R. Alkama1, O. Marti1, and C. Jeandel2
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.

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, doi:10.5194/cpd-4-309-2008, 2008.
 
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