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A Last Glacial Maximum world-ocean simulation at eddy-permitting resolution – Part 1: Experimental design and basic evaluation
Stockholm University, Faculty of Science, Department of Meteorology .
Stockholm University, Faculty of Science, Department of Meteorology .ORCID iD: 0000-0001-8745-7510
Stockholm University, Faculty of Science, Department of Meteorology .
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2013 (English)In: Climate of the Past Discussions, ISSN 1814-9340, E-ISSN 1814-9359, Vol. 9, 297-328 p.Article in journal (Refereed) Published
Abstract [en]

Most state-of-the-art climate models include a coarsely resolved oceanic compo- nent, which has difficulties in capturing detailed dynamics, and therefore eddy- permitting/eddy-resolving simulations have been developed to reproduce the observed World Ocean. In this study, an eddy-permitting numerical experiment is conducted to simulate the global ocean state for a period of the Last Glacial Maximum (LGM, ∼26500 to 19000yr ago) and to investigate the improvements due to taking into account these higher spatial scales. The ocean general circulation model is forced by a 49-yr sample of LGM atmospheric fields constructed from a quasi-equilibrated climate-model simulation. The initial state and the bottom boundary condition conform to the Paleoclimate Modelling Intercomparison Project (PMIP) recommendations. Be- fore evaluating the model efficiency in representing the paleo-proxy reconstruction of the surface state, the LGM experiment is in this first part of the investigation, compared with a present-day eddy-permitting hindcast simulation as well as with the available PMIP results. It is shown that the LGM eddy-permitting simulation is consistent with the quasi-equilibrated climate-model simulation, but large discrepancies are found with the PMIP model analyses, probably due to the different equilibration states. The strongest meridional gradients of the sea-surface temperature are located near 40° N and S, this due to particularly large North-Atlantic and Southern-Ocean sea-ice covers. These also modify the locations of the convection sites (where deep-water forms) and most of the LGM Conveyor Belt circulation consequently takes place in a thinner layer than today. Despite some discrepancies with other LGM simulations, a glacial state is captured and the eddy-permitting simulation undertaken here yielded a useful set of data for comparisons with paleo-proxy reconstructions. 

Place, publisher, year, edition, pages
2013. Vol. 9, 297-328 p.
National Category
Oceanography, Hydrology, Water Resources
Research subject
Atmospheric Sciences and Oceanography
Identifiers
URN: urn:nbn:se:su:diva-88440DOI: 10.5194/cpd-9-297-2013OAI: oai:DiVA.org:su-88440DiVA: diva2:611224
Available from: 2013-03-15 Created: 2013-03-15 Last updated: 2017-12-06Bibliographically approved
In thesis
1. The thermohaline circulation during the Last Glacial Maximum and in the Present-Day climate
Open this publication in new window or tab >>The thermohaline circulation during the Last Glacial Maximum and in the Present-Day climate
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The thermohaline circulation (THC) corresponds to the large time- and spatial-scales ocean circulation associated with the transport of heat and salt, and is known to be an important factor controlling the climate variability. The large scales involved in the THC make it difficult to observe, and therefore the synergy of numerical models and climate proxy reconstructions is particularly relevant to study the characteristics of this circulation in the present and past climates.

In this doctoral thesis, the THC during the Last Glacial Maximum (LGM) and the Present-Day (PD) is explored using a state-of-the-art Ocean General Circulation Model in its high- and low-resolution regimes. By comparing the LGM model outputs with the paleo-proxy reconstructions, it is shown that the high-resolution simulation improves the representation of the sea surface tem- peratures in the regions where the current structures appear to be complex, i.e., the western boundary currents (Agulhas, Kuroshio, Gulf Stream) and the Antarctic Circumpolar Current, although statistical comparisons with paleo- proxy reconstructions are not significantly improved on a global scale.

The THC involves a superposition of processes acting at widely different spatial and temporal scales, from the geostrophic large-scale and slowly-varying flow to the mesoscale turbulent eddies and at even smaller-scale, the mixing generated by the internal wave field. Not all these processes can be properly resolved in numerical models, and thus need to be parameterized. Analyzing the THC in an eddy-permitting numerical model, it was found that the temporal scales required for diagnosing the Southern Ocean circulation should not exceed 1 month and the spatial scales needed to be taken into account must be smaller than 1°. Important changes in the nature and intensity of the THC were observed between the LGM and PD simulations. An estimation of the turnover times (i.e., the time it takes for the water parcel to make and entire loop on the Conveyor Belt) revealed that the LGM THC could be more vigorous than under the PD conditions. As a result, the ocean transports of heat and freshwater, the oceanic uptake of CO2, the ventilation of the deep ocean and the reorganization of the passive and active tracers (e.g., temperature, salinity, greenhouse gases, nutrients) can be altered in these different regimes.

Place, publisher, year, edition, pages
Stockholm: Department of Meteorology, Stockholm University, 2013. 52 p.
Keyword
ocean model, circulation, LGM
National Category
Oceanography, Hydrology, Water Resources
Research subject
Atmospheric Sciences and Oceanography
Identifiers
urn:nbn:se:su:diva-89011 (URN)978-91-7447-697-2 (ISBN)
Public defence
2013-05-24, Högbomsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 10:00 (English)
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Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 5: Manuscript. 

Available from: 2013-05-02 Created: 2013-04-08 Last updated: 2014-01-31Bibliographically approved

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