Can we determine what controls the spatio-temporal distribution of d-excess and 17O-excess in precipitation using the LMDZ general circulation model? 1Laboratoire de Météorologie Dynamique UMR8539, IPSL/CNRS/UPMC, 4, place Jussieu, 75252 Paris Cedex 05, France
16 Sep 2013
2Institut Pierre Simon Laplace (IPSL), Laboratoire des Sciences de Climat et de l'Environnement (LSCE), UMR8212 (CEA-CNRS-UVSQ), CE Saclay, Orme des Merisiers, Bât. 701, 91191 Gif-sur-Yvette, Cedex, France.
3Institut de Recherche pour le Développement (IRD), Laboratoire HydroSciences Montpellier (HSM), UMR5569 (CNRS-IRD-UM1-UM2), Montpellier, France
Received: 17 Sep 2012 – Published in Clim. Past Discuss.: 08 Nov 2012Abstract. Combined measurements of the H218O and
HDO isotopic ratios in precipitation, leading to second-order parameter
D-excess, have provided additional constraints on past climates compared
to the H218O isotopic ratio alone.
More recently, measurements of H217O
have led to another second-order parameter: 17O-excess.
Recent studies suggest that 17O-excess
in polar ice may provide information on evaporative conditions at
the moisture source. However, the processes controlling the spatio-temporal
distribution of 17O-excess are still far
from being fully understood.
We use the isotopic general circulation model (GCM) LMDZ to better understand what
controls d-excess and 17O-excess in precipitation at present-day (PD)
and during the last glacial maximum (LGM). The simulation of D-excess and
17O-excess is evaluated against measurements in meteoric water, water
vapor and polar ice cores. A set of sensitivity tests and diagnostics are
used to quantify the relative effects of evaporative conditions (sea surface
temperature and relative humidity), Rayleigh distillation, mixing between
vapors from different origins, precipitation re-evaporation and
supersaturation during condensation at low temperature.
In LMDZ, simulations suggest that in the tropics convective processes and
rain re-evaporation are important controls on precipitation D-excess and
17O-excess. In higher latitudes, the effect of distillation, mixing
between vapors from different origins and supersaturation are the most
important controls. For example, the lower d-excess and 17O-excess at
LGM simulated at LGM are mainly due to the supersaturation effect. The effect
of supersaturation is however very sensitive to a parameter whose tuning
would require more measurements and laboratory experiments. Evaporative
conditions had previously been suggested to be key controlling factors of
d-excess and 17O-excess, but LMDZ underestimates their role. More
generally, some shortcomings in the simulation of 17O-excess by LMDZ
suggest that general circulation models are not yet the perfect tool to
quantify with confidence all processes controlling 17O-excess.
Revised: 12 Jul 2013 – Accepted: 07 Aug 2013 – Published: 16 Sep 2013
Citation: Risi, C., Landais, A., Winkler, R., and Vimeux, F.: Can we determine what controls the spatio-temporal distribution of d-excess and 17O-excess in precipitation using the LMDZ general circulation model?, Clim. Past, 9, 2173-2193, doi:10.5194/cp-9-2173-2013, 2013.