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Reconciling Glacial Antarctic Water Stable Reconciling glacial Antarctic water stable isotopes with ice sheet topography and the isotopic paleothermometer Martin Werner, Jean Jouzel, Valérie Masson-Delmotte, Gerrit Lohmann To cite this version: Martin Werner, Jean Jouzel, Valérie Masson-Delmotte, Gerrit Lohmann. Reconciling glacial Antarctic water stable isotopes with ice sheet topography and the isotopic paleothermometer. Nature Commu- nications, Nature Publishing Group, 2018, 9 (1), 10.1038/s41467-018-05430-y. hal-02975848 HAL Id: hal-02975848 https://hal.archives-ouvertes.fr/hal-02975848 Submitted on 26 Oct 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. ARTICLE DOI: 10.1038/s41467-018-05430-y OPEN Reconciling glacial Antarctic water stable isotopes with ice sheet topography and the isotopic paleothermometer Martin Werner 1, Jean Jouzel2, Valérie Masson-Delmotte2 & Gerrit Lohmann1 Stable water isotope records from Antarctica are key for our understanding of Quaternary climate variations. However, the exact quantitative interpretation of these important climate 1234567890():,; proxy records in terms of surface temperature, ice sheet height and other climatic changes is still a matter of debate. Here we report results obtained with an atmospheric general circulation model equipped with water isotopes, run at a high-spatial horizontal resolution of one-by-one degree. Comparing different glacial maximum ice sheet reconstructions, a best model data match is achieved for the PMIP3 reconstruction. Reduced West Antarctic elevation changes between 400 and 800 m lead to further improved agreement with ice core data. Our modern and glacial climate simulations support the validity of the isotopic paleothermometer approach based on the use of present-day observations and reveal that a glacial ocean state as displayed in the GLAMAP reconstruction is suitable for capturing the observed glacial isotope changes in Antarctic ice cores. 1 Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Sciences, Bussestr. 24, 27570 Bremerhaven, Germany. 2 Laboratoire des Sciences du Climat et l’Environnement (LSCE), Institut Pierre Simon Laplace, CEA-CNRS-UVSQ, UMR 8212, UniversitéParis Saclay, 91191 Gif-sur-Yvette, France. Correspondence and requests for materials should be addressed to M.W. (email: [email protected]) NATURE COMMUNICATIONS | (2018) 9:3537 | DOI: 10.1038/s41467-018-05430-y | www.nature.com/naturecommunications 1 ARTICLE NATURE COMMUNICATIONS | DOI: 10.1038/s41467-018-05430-y ntarctic ice cores provide a wealth of information on For such isoGCM simulations of the climate of the last glacial past atmospheric composition and climate1–4. For these maximum (LGM), major uncertainties in required boundary A 18 polar ice cores, stable water isotopes (H2 O, HDO) conditions are the prescribed sea surface temperature, sea ice belong to the key set of analysed climate proxy variables. Such extent and ice sheet topography, while orbital parameters stable water isotope records from the various Antarctic ice and GHG are well known for the LGM period. Large uncer- cores provide high-resolution information on climate variability tainties remain associated with the knowledge of glacial West at decadal to glacial–interglacial time scales5,6. Antarctic ice sheet topography, evidenced by the large spread Since the 1960s, the relationships between Antarctic stable of existing reconstructions35–39. Here, results of isoGCM simu- water isotopes and temperature have been explored using lations with prescribed different ice sheet reconstructions surface measurements7 as well as Rayleigh distillation models8 are compared with ice core data from West and East Antarctica. and atmospheric general circulation models equipped with The deviation between simulated water stable isotopes and ice stable water isotopes diagnostics9–11. The strong linear spatial core records provides a constraint on the realism of LGM relationship between annual mean surface air temperature and ice sheet reconstructions. δ18O today7,12 with a slope of 0.8‰/°C between the δ18O and local temperatures is fully consistent with theoretical Rayleigh Results distillation13 and is well captured by atmospheric general Present-day climate. As a reference simulation, the isoGCM circulation models equipped with stable water isotopes (isoGCM), ECHAM5-wiso has been run under present-day (PD) model despite model biases for temperature or precipitation in boundary conditions with an observational-based distribution of Antarctica14,15. This relationship has therefore been commonly ocean surface δ18O values (see Methods for details). This PD applied to estimate past changes in temperature from Antarctic – climate simulation shows a good agreement between observed ice cores2,5,16 18. and simulated Antarctic surface temperatures (T ) with a cor- However, the consistency between present-day observations, surf relation coefficient of 0.94 despite an overall warm bias, which distillation theory and isoGCM simulations is no proof that grows from 0 to 5 °C in the temperature range of −20 to −35 °C past temperature changes should scale to past precipitation (Fig. 1a, b). Such a warm bias over Antarctica is frequent in GCM δ18O changes with the same quantitative relationship. Indeed, simulations40,41. There is also a remarkable agreement between several processes may affect the temporal isotope–temperature observed accumulation and simulated values, with a general wet relationship, such as changes in evaporation conditions, atmo- model bias consistent with the warm bias (Fig. 1e, f). Simulated spheric transport pathways, changes in condensation vs. surface δ18O values in surface snow range between −18 and −55‰, and temperature associated with polar boundary layer processes, or their distribution mimics that of the simulated temperature changes in precipitation intermittency or seasonality. In Green- (Fig. 1c). Consistent with the model warm bias, δ18O simulated land, where alternative paleothermometry methods are available values are, on average, 5‰ less depleted that the measured iso- from ice cores, temporal slopes vary from 0.3 to 0.6‰/°C19,20, tope values, with modelled and measured δ18O values as strongly much lower than the local present-day spatial slope of about correlated as for temperature (r = 0.92; Fig. 1d). These compar- 0.7‰/°C21, an up to a factor 2 difference attributed to changes isons illustrate that the ECHAM5-wiso model, despite its warm in precipitation seasonality as well as moisture sources and bias at very low temperatures, is able to capture the present-day transport paths20,22,23. Antarctic spatial isotope distribution in good agreement with In Antarctica, the importance of several processes that could available observations (see Supplementary Note 1 for details). distort the δ18O-temperature relationship has been explored – This model skill for present-day is key to our confidence in the using deuterium excess measurements24 26 as well as low- quality of the LGM simulations that we now examine. resolution isoGCMs using simulations performed for colder than present-day climate14,27, including water tagging27,28, or warmer than present day climate projections29. The con- LGM climate. We have performed six different LGM simulations fl clusions from these studies were that under high CO2 and to evaluate the in uence of different boundary conditions on the warmer than present conditions, there may be changes simulated temperature and isotope changes in Antarctica. The in temperature-precipitation covariance accounting for a smaller main focus has been put on recent glacial Antarctic ice sheet isotope–temperature slope and for varying isotope–temperature reconstructions. Furthermore, the influence of different pre- relationships for different ice core sites on the East Antarctic scribed sea surface temperatures as well as different patterns of plateau30. Glacial isotope–temperature relationships appear the isotopic composition of the surface ocean has been investi- rather homogeneous in the East Antarctic plateau and moisture- gated (see Methods). source effects had limited impacts on glacial–interglacial In order to evaluate the quality of the different isotopic temperature reconstructions. However, these isoGCM studies simulations, we have compiled δ18O data from the following 11 were performed with low-resolution atmospheric models ice cores: Vostok, Dome F, Dome B, EDC, EDML, Taylor Dome, and were not based on the latest reconstructions of ice Talos Dome, Byrd, Siple Dome, Law Dome and WDC (Table 1 sheet, sea ice and ocean sea surface temperature changes. gives an overview about all ice core locations and isotope data). Processes associated with moisture transport may not be For this purpose, we expanded the comprehensive compilation properly resolved using atmospheric models with a resolution recently provided by the WAIS Divide Project Members32 with of 200 × 200 km15,31. Moreover, recent ice core data from data from Dome B42 and Taylor Dome43. We also investigate West Antarctica have expanded the documentation of model results
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