Comparing transient, accelerated, and equilibrium simulations of the last 30 000 years with the GENIE-1 model

DJ Lunt, MS Williamson, PJ Valdes, TM Lenton, R Marsh

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We examine several aspects of the ocean-atmosphere system over the last 30 000 years, by carrying out simulations with prescribed ice sheets, atmospheric CO2 concentration, and orbital parameters. We use the GENIE-1 model with a frictional geostrophic ocean, dynamic sea ice, an energy balance atmosphere, and a land-surface scheme with fixed vegetation. A transient simulation, with boundary conditions derived from ice-core records and ice sheet reconstructions, is compared with equilibrium snapshot simulations, including the Last Glacial Maximum (21 000 years before present; 21 kyrBP), mid-Holocene (6 kyrBP) and pre-industrial. The equilibrium snapshot simulations are all very similar to their corresponding time period in the transient simulation, indicating that over the last 30 000 years, the model's ocean-atmosphere system is close to equilibrium with its boundary conditions. However, our simulations neglect the transfer of fresh water from and to the ocean, resulting from the growth and decay of ice sheets, which would, in reality, lead to greater disequilibrium. Additionally, the GENIE-1 model exhibits a rather limited response in terms of its Atlantic Meridional Overturning Circulation (AMOC) over the 30 000 years; a more sensitive AMOC would also be likely to lead to greater disequilibrium. We investigate the method of accelerating the boundary conditions of a transient simulation and find that the Southern Ocean is the region most affected by the acceleration. The Northern Hemisphere, even with a factor of 10 acceleration, is relatively unaffected. The results are robust to changes to several tunable parameters in the model. They also hold when a higher vertical resolution is used in the ocean
Translated title of the contributionComparing transient, accelerated, and equilibrium simulations of the last 30 000 years with the GENIE-1 model
Original languageEnglish
Pages (from-to)221 - 235
Number of pages15
JournalClimate of the Past
Issue number2
Publication statusPublished - 28 Nov 2006

Bibliographical note

Publisher: Copernicus GmbH on behalf of the European Geosciences Union (EGU)
Rose publication type: Journal article

Sponsorship: This work was funded by the NERC e-Science program through the Grid ENabled Integrated Earth system model (GENIE) project NER/T/S/2002/00217. We thank the NERC RAPID program NER/T/S/2002/00462 for providing
the computer resources on which these simulations were carried out

Terms of use: © Author(s) 2006. This work is licensed
under a Creative Commons License


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