 |
| Titel |
Antarctic ice-sheet response to atmospheric CO2 and insolation in the Middle Miocene |
| VerfasserIn |
P. M. Langebroek, A. Paul, M. Schulz |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1814-9324
|
| Digitales Dokument |
URL |
| Erschienen |
In: Climate of the Past ; 5, no. 4 ; Nr. 5, no. 4 (2009-10-22), S.633-646 |
| Datensatznummer |
250002693
|
| Publikation (Nr.) |
 copernicus.org/cp-5-633-2009.pdf |
|
|
|
|
|
| Zusammenfassung |
| Foraminiferal oxygen isotopes from deep-sea sediment cores suggest that a
rapid expansion of the Antarctic ice sheet took place in the Middle Miocene
around 13.9 million years ago. The origin for this transition is still not
understood satisfactorily. One possible cause is a drop in the partial
pressure of atmospheric carbon dioxide (pCO2) in combination with
orbital forcing. A complication is the large uncertainty in the magnitude and
timing of the reconstructed pCO2 variability and additionally the low
temporal resolution of the available pCO2 records in the Middle
Miocene. We used an ice sheet-climate model of reduced complexity to assess
variations in Antarctic ice sheet volume induced by pCO2 and
insolation forcing in the Middle Miocene. The ice-sheet sensitivity to
atmospheric CO2 was tested for several scenarios with constant
pCO2 forcing or a regular decrease in pCO2. This showed that
small, ephemeral ice sheets existed under relatively high atmospheric
CO2 conditions (between 640–900 ppm), whereas more stable, large ice
sheets occurred when pCO2 was less than ~600 ppm. The main
result of this study is that the pCO2-level must have declined just
before or during the period of oxygen-isotope increase, thereby crossing a
pCO2 glaciation threshold of around 615 ppm. After the decline, the
exact timing of the Antarctic ice-sheet expansion depends also on the
relative minimum in summer insolation at approximately 13.89 million years
ago. Although the mechanisms described appear to be robust, the exact values
of the pCO2 thresholds are likely to be model-dependent. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|