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| Titel |
Quantifying the ocean's role in glacial CO2 reductions |
| VerfasserIn |
M. O. Chikamoto, A. Abe-Ouchi, A. Oka, R. Ohgaito, A. Timmermann |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1814-9324
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| Digitales Dokument |
URL |
| Erschienen |
In: Climate of the Past ; 8, no. 2 ; Nr. 8, no. 2 (2012-03-16), S.545-563 |
| Datensatznummer |
250005468
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| Publikation (Nr.) |
 copernicus.org/cp-8-545-2012.pdf |
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| Zusammenfassung |
| A series of Last Glacial Maximum (LGM) marine carbon cycle
sensitivity experiments is conducted to test the effect
of different physical processes, as simulated by
two atmosphere-ocean general circulation model (AOGCM) experiments,
on atmospheric pCO2. One AOGCM solution exhibits an
increase in North Atlantic Deep Water (NADW) formation
under glacial conditions, whereas the other mimics an increase in
Antarctic Bottom Water (AABW) associated with a weaker NADW.
None of these sensitivity experiments reproduces the observed magnitude
of glacial/interglacial pCO2 changes.
However, to explain the reconstructed vertical gradient of dissolved
inorganic carbon (DIC) of 40 mmol m−3
a marked enhancement in AABW formation
is required.
Furthermore, for the enhanced AABW sensitivity experiment the simulated
stable carbon isotope ratio
(δ13C)
decreases by 0.4‰ at intermediate depths in the South Atlantic
in accordance with sedimentary evidence.
The shift of deep and bottom water formation sites
from the North Atlantic to the
Southern Ocean increases the total preformed nutrient inventory, so that
the lowered efficiency of Southern Ocean nutrient utilization in turn
increases atmospheric pCO2.
This change eventually offsets the effect of an
increased abyssal carbon pool due to stronger AABW formation.
The effects of interhemispheric glacial sea-ice changes on
atmospheric pCO2 oppose each other.
Whereas, extended sea-ice coverage in the Southern Hemisphere
reduces the air-sea gas exchange of CO2
in agreement with previous theoretical considerations,
glacial advances of sea-ice in the Northern Hemisphere
lead to a weakening of the oceanic carbon uptake
through the physical pump.
Due to enhanced gas solubility associated with lower sea surface
temperature,
both glacial experiments generate a reduction of atmospheric pCO2
by about 20–23 ppmv.
The sensitivity experiments presented here demonstrate the presence of
compensating effects of different physical processes
in the ocean on glacial CO2 and the difficulty of finding a
simple explanation of the glacial CO2 problem by invoking ocean
dynamical changes. |
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