Glacial–interglacial changes in H<sub>2</sub><sup>18</sup>O, HDO and deuterium excess – results from the fully coupled ECHAM5/MPI-OM Earth system model
In this study we present the first results of a new isotope-enabled general circulation model set-up. The model consists of the fully coupled ECHAM5/MPI-OM atmosphere–ocean model, enhanced by the JSBACH interactive land surface scheme and an explicit hydrological discharge scheme to close the global...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-02-01
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| Series: | Geoscientific Model Development |
| Online Access: | http://www.geosci-model-dev.net/9/647/2016/gmd-9-647-2016.pdf |
| Summary: | In this study we present the first results of a new
isotope-enabled general circulation model set-up. The model consists of the
fully coupled ECHAM5/MPI-OM atmosphere–ocean model, enhanced by the JSBACH
interactive land surface scheme and an explicit hydrological discharge scheme
to close the global water budget. Stable water isotopes H<sub>2</sub><sup>18</sup>O and
HDO have been incorporated into all relevant model components. Results of two
equilibrium simulations under pre-industrial and Last Glacial Maximum
conditions are analysed and compared to observational data and paleoclimate
records for evaluating the model's performance in simulating spatial and
temporal variations in the isotopic composition of the Earth's water cycle.
For the pre-industrial climate, many aspects of the simulation results of
meteoric waters are in good to very good agreement with both observations and
earlier atmosphere-only simulations. The model is capable of adequately
simulating the large spread in the isotopic composition of precipitation
between low and high latitudes. A comparison to available ocean data also
shows a good model–data agreement; however, a strong bias of overly depleted
ocean surface waters is detected for the Arctic region. Simulation results
under Last Glacial Maximum boundary conditions also fit to the wealth of
available isotope records from polar ice cores, speleothems, as well as
marine calcite data. Data–model evaluation of the isotopic composition in
precipitation reveals a good match of the model results and indicates that
the temporal glacial–interglacial isotope–temperature relation was
substantially lower than the present spatial gradient for most mid- to
high-latitudinal regions. As compared to older atmosphere-only simulations, a
remarkable improvement is achieved for the modelling of the deuterium excess
signal in Antarctic ice cores. Our simulation results indicate that cool
sub-tropical and mid-latitudinal sea surface temperatures are key for this
progress. A recently discussed revised interpretation of the deuterium excess
record of Antarctic ice cores in terms of marine relative humidity changes on
glacial–interglacial timescales is not supported by our model results. |
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| ISSN: | 1991-959X 1991-9603 |