EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Sensitivity of isotopes in the hydrological cycle to simulated vs. reconstructed Last Glacial Maximum surface conditions

André Paul1, Martin Werner2, Alexandre Cauquoin2,3, Javier García-Pintado1, Ute Merkel1, and Thejna Tharammal4
André Paul et al.
  • 1MARUM – Center for Marine Environmental Sciences and Department of Geosciences, University of Bremen, Bremen, Germany
  • 2Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), Bremerhaven, Germany
  • 3Institute of Industrial Science, The University of Tokyo, Kashiwa, Chiba, Japan
  • 4Center for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bangalore, India

The evaluation of a specific component of a comprehensive climate model is often hindered by biases in the coupled system, in simulations of the present as well as of past climate conditions. To assess different implementations of water isotopes as part of the hydrological cycle, we carried out atmosphere-only runs using different atmospheric general circulation models (AGCMs, here: CAM and ECHAM) but the same pre-industrial and Last Glacial Maximum (LGM, ~19,000 to ~23,000 a before present) boundary conditions, especially with respect to the monthly sea-surface temperature (SST) and sea-ice fraction fields. For the LGM, we used a new global climatology of the ocean surface during the Last Glacial Maximum mapped on a regular grid (GLOMAP), which is an extension of the Glacial Atlantic Ocean Mapping (GLAMAP) reconstruction of the Atlantic SST based on the results of the Multiproxy Approach for the Reconstruction of the Glacial Ocean Surface (MARGO) project and several recent estimates of the LGM sea-ice extent. This way, we can, on the one hand, avoid the propagation of the SST bias in coupled climate models. On the other hand, by comparing to fully-coupled simulations, we can isolate the impact of the ocean feedback on the simulated distributions of water isotopes over land, ice and ocean. To analyze the results, we calculated the anomalies between the LGM and pre-industrial climate states and compared them between the different models and to data. It turned out that the model response was affected by the amount of global cooling as well as the structure of the SST anomalies. The patterns in the simulated isotopic composition of precipitation for the LGM tended to follow the patterns in the SST boundary condition; a more zonal structure in the SST led to a more zonal response. Our results show the advantage of using water isotopes as a diagnostic tool for an AGCM through direct model-data comparison.

How to cite: Paul, A., Werner, M., Cauquoin, A., García-Pintado, J., Merkel, U., and Tharammal, T.: Sensitivity of isotopes in the hydrological cycle to simulated vs. reconstructed Last Glacial Maximum surface conditions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10622,, 2020

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Display material version 3 – uploaded on 06 May 2020, no comments
Added a "Method" slide and slide numbers
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Version description: Added further results (surface air temperature, total precipitation) on the response to the two different[...]
  • CC1: Comment on EGU2020-10622, Sandra Gomes, 06 May 2020

    Dear André,

    Thank you for sharing your presentation. I work in the Iberian Peninsula/Iberian margin and I try to understand the palaeoclimatology using a direct land-sea correlation and my knowledge of simulations is quite limited.  

    Looking to your reconstruction if I understood it well there is a positive anomaly for the LGM surrounding the Iberian peninsula, which is more evident during the JJA. Although, the simulated conditions show a slightly negative anomaly.

    Can I say that according to your reconstructed results the IP was wetter than the pre-industrial climate state? and that is a different interpretation than the one obtained by simulations!

    Thank you for your availability


    Sandra Gomes



    • AC1: Precipitation anomaly for the LGM surrounding the Iberian peninsula, André Paul, 06 May 2020

      Dear Sandra,

      Thank you for your question, just correct me if I did not get it right!

      For clarification: All results for surface air temperature, precipitaion and the oxygen isotope ratio of precipitation derive from simulations with two Atmospheric General Circulation Models (AGCMs), namely the NCAR iCAM3 and the MPI ECHAM6-wiso. The crucial difference is in the lower, that is, sea-surface boundary conditions.

      In the simulation on the left the sea-surface temperature and sea-ice concentration was also simulated, in this case by a coupled Atmosphere-Ocean General Circulation Model (AOGCM), namely the NCAR CCSM3.

      In the two other simulations the sea-surface temperature and sea-ice concentration was estimated from paleo-reconstructions, mainly the MARGO reconstructions plus some more recent data for the sea-ice extent.

      However, regarding the precipitation anomaly for the LGM surrounding the Iberian peninsula both models and all three simulations yield similar results: Wetter conditions for winter (DJF) and similar-to-drier conditions for summer (JJA).

      Let me point out that the two models that we used are of rather coarse horizontal resolution: about 4° ("T31") in case of iCAM3 and about 2° in cse of ECHAM6-wiso ("T63"). This may compromise the quality of the results especially in regions that are influenced by local topographic features. One may find other models in the literature, either global or regional, with higher resolution, to check our results.

      If you have further questions or comments, just let me know!

      With kind regards,


      • CC1: Reply to AC1, Sandra Gomes, 06 May 2020

        Dear Andre,

        Thank you for your answer, I looked at your first presentation, but with the new one and your explanation, it is clarified. I know that RCM can give supposedly better insights but unfortunately, they are scarce. 




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