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| Titel |
Sensitivity Simulations on the Deglacial Rise in CO2: the Last Glacial Maximum to the Present according to the UVic Model |
| VerfasserIn |
Christopher Simmons, Lawrence Mysak, H. Damon Matthews |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250077376
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| Zusammenfassung |
| The University of Victoria Earth System Climate Model of intermediate
complexity (v. 2.9) is used to investigate carbon cycle
dynamics from the Last Glacial Maximum (LGM) to the present.
Incorporating an ocean GCM (with 1.8° x 3.6° resolution and 19
levels), a simple 1D atmosphere, a representation of land surface
processes and vegetation (TRIFFID), and a comprehensive carbon cycle,
this particular model is able to perform transient simulations over
the entire glacial termination and interglacial period within an
efficient time frame. From a spin-up generated for LGM conditions, two
types of transient experiments were conducted: (1) prescribed carbon
(PC) simulations, where the carbon reservoirs in simulations beginning
from the LGM are forced to adjust to the atmospheric CO2 trends in the
Vostok and the Taylor Dome/Law Dome ice cores, and (2) free carbon
(FC) simulations, where carbon reservoirs, including atmospheric CO2,
evolve with no outside influence beyond prescribed orbital forcing and
glacial ice retreat. Within these two formats, a variety of
sensitivity studies tested a 700 PgC deglacial release of carbon
(approximating permafrost release), CO2 and CH4 radiative forcing, and
different weathering rates. A comparison of the prescribed and free
carbon simulations provides useful details about the important
processes involved in the deglacial increase in CO2 and why the
model's FC simulations failed to reproduce the ~90 ppm post-glacial
CO2 rise. In particular, the model's PC simulations accurately
revitalized the deep North Atlantic circulation following the timing
established in proxy records [Galbraith et al., Nature (449), 2007] and produced a much better-circulated ocean than the FC simulations (which only provide a modest increase of 20 ppm CO2 over the entire period and a
largely-unrecovered North Atlantic meridional circulation). It was
further determined that the warming effect of radiative forcing from
greenhouse gases (and not ice-albedo warming) is predominantly
responsible for the recovery of North Atlantic deepwater formation and
greater ocean circulation, which in turn leads to less deep-ocean
carbon storage and a carbon source to the atmosphere and terrestrial
reservoirs. Furthermore, much greater sediment storage in the FC
simulations (versus the PC simulations) implies another 200 PgC
potential source to the atmosphere. Sensitivity simulations also
reveal that weathering rates have a non-negligible effect on
atmospheric CO2 on these time scales, contributing to the order of 10
ppm the resulting CO2 in the FC simulations. Varying the extent of
Antarctic ice shelves also yields a 5-10 ppm effect on CO2 during the
Holocene in most experiments. |
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