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| Titel |
The role of ocean physics in setting glacial atmospheric CO2 |
| VerfasserIn |
Kevin Oliver, Simon Mueller, Neil Edwards, Gideon Henderson, Ros Rickaby |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250042837
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| Zusammenfassung |
| The impact of ocean physics on atmospheric pCO2 is examined analytically and using
ensembles experiments with the Earth system model GENIE. Results are interpreted in terms
of the “red loop” (global low-mid-latitude upper and mode waters, and the Atlantic
overturning cell), in which the efficiency of nutrient utilisation is high, and the “blue loop”
(the Antarctic overturning cell) in which the efficiency of nutrient utilisation is low. For fixed
efficiency of the red loop, atmospheric pCO2 can be lowered by decreasing ventilation of the
blue loop, increasing ventilation of the red loop, increasing mixing between the
red and blue loops, or decreasing particle flux from the red loop to the blue loop.
This is because any of these changes increase the fraction of nutrients in the global
ocean that was last at the surface in the red loop, rather than the blue loop. GENIE
experiments yield an ambiguous response to increasing red loop ventilation rates, however,
because the efficiency of this loop decreases in response to increased ventilation
rates.
These findings are used, in conjunction with geochemical proxy simulations in the
GENIE ensemble, to illuminate hypothesised mechanisms of glacial pCO2 cycles. A
variety of mechanisms can produce δ13C distributions comparable to last glacial
maximum (LGM) observations, and this is associated with a decrease in pCO2
if the cause is the formation of high salinity, high density water in the Southern
Ocean. This results in a highly stratified ocean and a contraction of the red loop.
Nevertheless, the strong LGM meridional density gradients suggested by pore water
salinity measurements are only sustained if there is plentiful energy for diapycnal
mixing. This increases mixing between the red and blue loops, and can reconcile low
atmospheric pCO2 with the absence of an exceptionally old water mass in the deep ocean. |
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