Antarctic Ice Sheet history and Scotia Sea evolution: re-evaluation of the paradigm that ocean circulation changes controlled development of the Antarctic cryosphere
The fact that circum-Antarctic ocean circulation and the Antarctic cryosphere developed in parallel during the Cenozoic era was revealed by results from Antarctic and Southern Ocean Deep Sea Drilling Project (DSDP) legs in the 1970s. This association provided the basis for the paradigm that developm...
| Main Authors: | , , |
|---|---|
| Format: | Conference Object |
| Language: | unknown |
| Published: |
2013
|
| Subjects: | |
| Online Access: | https://epic.awi.de/id/eprint/33235/ https://hdl.handle.net/10013/epic.41724 |
| Summary: | The fact that circum-Antarctic ocean circulation and the Antarctic cryosphere developed in parallel during the Cenozoic era was revealed by results from Antarctic and Southern Ocean Deep Sea Drilling Project (DSDP) legs in the 1970s. This association provided the basis for the paradigm that development of the Antarctic Circumpolar Current (ACC) reduced meridional heat transport, isolated the continent within an annulus of cold water, and was thus the main cause of intensifying glaciation (e.g. Kennett, 1977). From 1970s DSDP results it was already clear that the main glacial-climatic thresholds had been crossed near the Eocene-Oligocene boundary, during the Middle Miocene and during the Late Pliocene. Subsequent more detailed studies and increasingly refined timescales have narrowed down the times of these steps in environmental evolution to 34.0–33.6, 14.2–13.8 and 3.3–2.5 Ma. A challenge to the paradigm emerged ten years ago from a coupled climate-ice sheet modelling study (DeConto and Pollard, 2003). The modelling results suggested that ice sheet feedbacks associated with declining atmospheric pCO2 may have been sufficient to cause rapid growth of the Antarctic Ice Sheet at around the time of the Eocene-Oligocene boundary in the absence of any changes in ocean circulation. Remarkably, these results also suggested ice sheet growth in two steps within 0.5 Myr, which was subsequently confirmed by detailed palaeoceanographic data (Coxall et al., 2005). DeConto & Pollard (2003) did, however, also attempt to model the effect of ACC onset by using a parameterized 20% increase in southward ocean heat transport to simulate ice sheet growth with Drake Passage closed. The results suggested that ACC onset resulting from opening of Drake Passage could have been the critical factor controlling the timing of ice sheet inception, but only if atmospheric pCO2 was between 2.5 and 3 times pre-industrial level (i.e. in the range 700–840 ppmv). A recent estimate of past atmospheric pCO2 levels derived from alkenones in marine ... |
|---|