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| Titel |
Presentation, calibration and validation of the low-order, DCESS Earth System Model (Version 1) |
| VerfasserIn |
G. Shaffer, S. Malskær Olsen, J. O. Pepke Pedersen |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1991-959X
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| Digitales Dokument |
URL |
| Erschienen |
In: Geoscientific Model Development ; 1, no. 1 ; Nr. 1, no. 1 (2008-11-06), S.17-51 |
| Datensatznummer |
250000111
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| Publikation (Nr.) |
 copernicus.org/gmd-1-17-2008.pdf |
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| Zusammenfassung |
A new, low-order Earth System Model is described, calibrated and tested
against Earth system data. The model features modules for the atmosphere,
ocean, ocean sediment, land biosphere and lithosphere and has been designed
to simulate global change on time scales of years to millions of years. The
atmosphere module considers radiation balance, meridional transport of heat
and water vapor between low-mid latitude and high latitude zones, heat and
gas exchange with the ocean and sea ice and snow cover. Gases considered are
carbon dioxide and methane for all three carbon isotopes, nitrous oxide and
oxygen. The ocean module has 100 m vertical resolution, carbonate chemistry
and prescribed circulation and mixing. Ocean biogeochemical tracers are
phosphate, dissolved oxygen, dissolved inorganic carbon for all three carbon
isotopes and alkalinity. Biogenic production of particulate organic matter
in the ocean surface layer depends on phosphate availability but with lower
efficiency in the high latitude zone, as determined by model fit to ocean
data. The calcite to organic carbon rain ratio depends on surface layer
temperature. The semi-analytical, ocean sediment module considers calcium
carbonate dissolution and oxic and anoxic organic matter remineralisation.
The sediment is composed of calcite, non-calcite mineral and reactive
organic matter. Sediment porosity profiles are related to sediment
composition and a bioturbated layer of 0.1 m thickness is assumed. A
sediment segment is ascribed to each ocean layer and segment area stems from
observed ocean depth distributions. Sediment burial is calculated from
sedimentation velocities at the base of the bioturbated layer. Bioturbation
rates and oxic and anoxic remineralisation rates depend on organic carbon
rain rates and dissolved oxygen concentrations. The land biosphere module
considers leaves, wood, litter and soil. Net primary production depends on
atmospheric carbon dioxide concentration and remineralization rates in the
litter and soil are related to mean atmospheric temperatures. Methane
production is a small fraction of the soil remineralization. The lithosphere
module considers outgassing, weathering of carbonate and silicate rocks and
weathering of rocks containing old organic carbon and phosphorus. Weathering
rates are related to mean atmospheric temperatures.
A pre-industrial, steady state calibration to Earth system data is carried
out. Ocean observations of temperature, carbon 14, phosphate, dissolved
oxygen, dissolved inorganic carbon and alkalinity constrain air-sea exchange
and ocean circulation, mixing and biogeochemical parameters. Observed
calcite and organic carbon distributions and inventories in the ocean
sediment help constrain sediment module parameters. Carbon isotopic data and
carbonate vs. silicate weathering fractions are used to estimate initial
lithosphere outgassing and rock weathering rates. Model performance is
tested by simulating atmospheric greenhouse gas increases, global warming
and model tracer evolution for the period 1765 to 2000, as forced by
prescribed anthropogenic greenhouse gas inputs and other anthropogenic and
natural forcing. Long term, transient model behavior is studied with a set
of 100 000 year simulations, forced by a slow, 5000 Gt C input of CO2 to
the atmosphere, and with a 1.5 million year simulation, forced by a doubling
of lithosphere CO2 outgassing. |
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