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| Titel |
Simulation of glacial ocean biogeochemical tracer and isotope distributions based on the PMIP3 suite of climate models |
| VerfasserIn |
Samar Khatiwala, Juan Muglia, Karin Kvale, Andreas Schmittner |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250128663
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| Publikation (Nr.) |
 EGU/EGU2016-8670.pdf |
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| Zusammenfassung |
| In the present climate system, buoyancy forced convection at high-latitudes together with
internal mixing results in a vigorous overturning circulation whose major component is North
Atlantic Deep Water. One of the key questions of climate science is whether this
“mode” of circulation persisted during glacial periods, and in particular at the Last
Glacial Maximum (LGM; 21000 years before present). Resolving this question is
both important for advancing our understanding of the climate system, as well as a
critical test of numerical models’ ability to reliably simulate different climates. The
observational evidence, based on interpreting geochemical tracers archived in sediments,
is conflicting, as are simulations carried out with state-of-the-art climate models
(e.g., as part of the PMIP3 suite), which, due to the computational cost involved, do
not by and large include biogeochemical and isotope tracers that can be directly
compared with proxy data. Here, we apply geochemical observations to evaluate the
ability of several realisations of an ocean model driven by atmospheric forcing from
the PMIP3 suite of climate models to simulate global ocean circulation during the
LGM. This results in a wide range of circulation states that are then used to simulate
biogeochemical tracer and isotope (13C, 14C and Pa/Th) distributions using an
efficient, “offline” computational scheme known as the transport matrix method
(TMM). One of the key advantages of this approach is the use of a uniform set of
biogeochemical and isotope parameterizations across all the different circulations
based on the PMIP3 models. We compare these simulated distributions to both
modern observations and data from LGM ocean sediments to identify similarities and
discrepancies between model and data. We find, for example, that when the ocean
model is forced with wind stress from the PMIP3 models the radiocarbon age of the
deep ocean is systematically younger compared with reconstructions. Changes in
glacial circulation, characterized using ventilation tracers, are then analyzed in
terms of forcing factors such as wind stress, surface heat and freshwater budgets,
and sea ice to improve our understanding of the physical reasons for the changes. |
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