Climate of the Past Discussions
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10.5194/cpd-4-309-2008
http://www.clim-past-discuss.net/4/309/2008/
http://www.clim-past-discuss.net/4/309/2008/cpd-4-309-2008.html
http://www.clim-past-discuss.net/4/309/2008/cpd-4-309-2008.pdf
309
333
2008-03-18
Influence of the Atlantic thermohaline circulation on neodymium isotopic composition at the Last Glacial Maximum – a modelling sensitivity study
T. Arsouze
J.-C. Dutay
dutay@lsce.ipsl.fr
M. Kageyama
F. Lacan
R. Alkama
O. Marti
C. Jeandel
Laboratoire 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
Laboratoire d'Etudes en Géophysique et Océanographie Spatiale (LEGOS), CNES/CNRS/UPS/IRD, Observatoire Midi-Pyrénées, 14 av. E. Belin, 31400 Toulouse, France
The oceanic neodymium isotopic composition (hereafter expressed as
ε <sub>Nd</sub>) 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 <sub>Nd</sub> in
the Atlantic basin. Three different LGM freshwater forcing experiments are
performed to test the variability in ε <sub>Nd</sub> 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 <sub>Nd</sub>, particularly
in deep waters of the western part of the basin. However, mean Atlantic LGM
ε <sub>Nd</sub> 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 <sub>Nd</sub> signature of
Northern end-members (NADW or GNAIW glacial equivalent) that is sufficient
to explain the shift in mean ε <sub>Nd</sub> during our LGM
simulations. None of our three LGM circulation scenarios gives a better
agreement with the existing ε <sub>Nd</sub> 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 <sub>Nd</sub> gradient in
the three LGM scenarios is the most important (up to 3 ε <sub>Nd</sub>). This would also aid more precise conclusions concerning the north
end-member ε <sub>Nd</sub> signature evolution, and thus the potential
use of ε <sub>Nd</sub> as a tracer of past oceanic circulation.
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