Stable water isotopes in the ECHAM5 general circulation model: Toward high-resolution isotope modeling on a global scale

Abstract

[1] In this study, a first set of four present-day global experiments with the ECHAM5 atmospheric general circulation model enhanced by stable water isotope diagnostics (ECHAM5-wiso) is presented. Model resolution varies from a typical coarse horizontal grid of 3.8°× 3.8°(T31) to a fine grid of 0.75°× 0.75°(T159). Vertical resolution varies from 19 to 31 model levels. On a global scale, the ECHAM5-wiso simulation results are in good agreement with available observations of the isotopic composition of precipitation from the Global Network of Isotopes in Precipitation (GNIP), on an annual as well as a seasonal time scale. In many instances, the isotope simulation results clearly benefit from an increased horizontal and vertical model resolution. The exemplary relevance of this model resolution dependence is demonstrated for the simulation of the isotopic composition of Antarctic precipitation. Here, the simulation with the fine T159L31 model resolution not only yields a better agreement with observational data sets but also allows for a more realistic retuning of the supersaturation function leading to improved deuterium excess performance over the Antarctic continent, which is important for the interpretation of polar ice cores. Finally, the ECHAM5-wiso simulation results are compared to newly available measurements of the isotopic composition of atmospheric water vapor. Model and data agree well, with differences in the range of ±10‰ for near-surface atmospheric values at several GNIP stations. A comparison of the ECHAM5-wiso simulations with total column averaged HDO data from the Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY) instrument on board the environmental satellite Envisat shows the same latitudinal gradients but an offset between 20‰ and 50‰ of unknown origin.Citation: Werner, M., P. M. Langebroek, T. Carlsen, M. Herold, and G. Lohmann (2011), Stable water isotopes in the ECHAM5 general circulation model: Toward high-resolution isotope modeling on a global scale,

Oxygen isotope geochemistry of Laurentide ice-sheet meltwater across Termination I

“…Isotope-enabled GCMs have been used to simulate the geographic distribution of oxygen isotope values in precipitation (Carlson et al, 2008a;LeGrande et al, 2006;Pausata et al, 2011;Risi et al, 2010;Ullman et al, 2014;Werner et al, 2011;Yoshimura et al, 2008). Paleohydrologic records and modeling studies of North America from the LGM show that westerly storm tracks were shifted southward and intensified during the LGM (Oster et al, 2015, and references therein), and d 18 O records also indicate that precipitation was up to 7‰ more negative during glacial intervals .…”

“…In addition, global circulation models (GCMs) that incorporate Rayleigh-type fractionation (Carlson et al, 2008a;LeGrande et al, 2006;Pausata et al, 2011;Risi et al, 2010;Ullman et al, 2014;Werner et al, 2011;Yoshimura et al, 2008) can estimate oxygen isotope heterogeneity in precipitation. These types of models offer an alternative approach to modeling ice-sheet heterogeneity, and recent efforts have begun to link modeled d 18 O w of Pleistocene precipitation with LIS-derived groundwater measurements (Ferguson and Jasechko, 2015).…”

δ<sup>18</sup>O water isotope in the <i>i</i>LOVECLIM model (version 1.0) – Part 2: Evaluation of model results against observed δ<sup>18</sup>O in water samples

“…The pioneering implementation of water isotopes used atmospheric general circulation models (AGCMs) (Joussaume et al, 1984;Jouzel et al, 1987) and paved the way to process based understanding of H 2 18 O in climate models. Today, most IPCC class AGCMs include the possibility for water isotopes tracing (Hoffmann et al, 1998;Noone and Simmonds, 2002;Mathieu et al, 2002;Lee et al, 2007;Yoshimura et al, 2008;Risi et al, 2010;Werner et al, 2011). The subsequent development of water isotopes modules in oceanic general circulation models (OGCM) (Schmidt, 1998;Delaygue et al, 2000;Xu et al, 2012) opens the prospect for coupled simulations of present and past climates, conserving water isotopes through the hydrosphere (Schmidt et al, 2007;Zhou et al, 2008;Tindall et al, 2009).…”

Climatology of stable isotopes in Antarctic snow and ice: Current status and prospects

“…Jouzel et al [37] provides the first estimate of an annual average distribution of water isotopes over Antarctica through AGCMs. Hereafter, with the enhancement of the capability to explicitly simulate the water isotopes, a number of studies have attempted to use AGCMs and MICM to evaluate the spatial and temporal variability in Antarctic precipitation isotopes to better interpret the stable isotopic records in Antarctic ice cores [37][38][39][40][41][42][43][44]. AGCMs [37][38][39][40][41][42][43] and MICM [44] well reproduce the spatial distribution of stable isotopes in Antarctic precipitation, especially in West Antarctica and in the coastal areas.…”

“…Although development in the vertical and horizontal resolution of AGCMs largely improved their accuracy in recent years, its simulation ability remains limited for the Antarctic inland (Figure 2(a) and (b)) [42], likely due to poor representation of atmospheric boundary layer, temperature inversion, cloud microphysics, and large scale advection of water vapor [36,45]. Warm biases of AGCMs could result in the insufficient estimate of the stable isotopic depletion.…”