 |
| Titel |
Interaction between ocean circulation and sea-ice coverage controlling marine carbon cycle |
| VerfasserIn |
Megumi O. Chikamoto, Ayako Abe-Ouchi, Akira Oka, Rumi Ohgaito |
| Konferenz |
EGU General Assembly 2010
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250034792
|
|
|
|
|
|
| Zusammenfassung |
| During the late Pleistocene, the global temperature and atmospheric carbon dioxide partial
pressure (pCO2) has varied with 100 kyr glacial-interglacial cycles. Despite of the prominent
relationship between climate and the carbon cycle, the mechanisms controlling the
glacial-interglacial pCO2 variations are still under debated. Factorial experiments are
conducted with an offline biogeochemical model and an Atmosphere-Ocean General
Circulation Model (AOGCM) to investigate the atmospheric pCO2 sensitivity to glacial
climate dynamics. The prescribed climate field is obtained from runs of an AOGCM, Model
for Interdisciplinary Research on Climate (MIROC), following the Paleoclimate Modeling
Intercomparison Project 2 protocol. This is a new approach to evaluate glacial climate effect
on marine carbon cycle using a fully coupled AOGCM. Moreover, the factorial
experiments switching on and off each climate factor enable us to recognize the
characteristics of ocean circulation and sea-ice coverage that control marine carbon
cycle and consequently atmospheric pCO2. In our simulation, atmospheric pCO2 is
lowered when Atlantic meridional overturning circulation is weakened in conjunction
with increased Southern Ocean sea-ice coverage. However, neither process alone
decreases atmospheric CO2. This is because the redistribution of oceanic dissolved
inorganic carbon (DIC) is obviously influenced by the background states of Antarctic
Intermediate Water (AAIW) and sea ice extent in the Southern Ocean. The factorial
experiment switching only on the glacial condition of sea ice in the southern hemisphere
shows that the upwelled carbon rich AAIW is transported northward. This response
increases surface DIC over the North Atlantic and consequently contributes to the
atmospheric pCO2 buildup. On the other hand, the factorial experiment switching on the
glacial conditions of sea-ice in the Southern Ocean and ocean circulation shows
that the deep-water carbon increase induced by ocean stratification is furthermore
enhanced by the sea-ice expansion in the Southern Ocean. The sea-ice extent in the two
hemispheres plays a different role in modulating atmospheric pCO2. The sea-ice
coverage in the Southern Ocean decreases atmospheric pCO2 by inhibiting the
degassing of DIC-rich deep water. However, the coverage in the northern hemisphere
increases the pCO2 through less soluble CO2 in cold water. It is the interaction
between ocean circulation and sea-ice coverage that is a key factor accounting for the
observed glacial pCO2 drawdown. We have also found that atmospheric pCO2 is
relatively insensitive to glacial ocean circulation. Since ocean circulation drives
surface DIC and alkalinity simultaneously, these responses allow the relative small
reduction in surface CO2 concentration as an influenced by seawater chemistry. The
climate-induced biogeochemical process would amplify further atmospheric pCO2. |
|
|
|
|
|
|