July 25, 2008 Due to the impact of global warming, it has become essential to understand the causes and processes involved in past climate changes. One of the most prominent events in Earth's climatic evolution was the transition from the global warmth of the Eocene "greenhouse" to the Oligocene "icehouse" glacial conditions.
It is widely believed that the separation of South America from Antarctica and the subsequent formation of Drake Passage have influenced Cenozoic global cooling because these events enabled the development of the Antarctic Circumpolar Current.
This wind-driven current facilitates inter-ocean exchange of seawater and is speculated to have reduced heat transport to Antarctica, triggering the Oligocene global cooling. Alternatively, it has been proposed that the opening of the Drake Passage influenced circulation-induced productivity increases that may have sequestered atmospheric CO2, contributing to global cooling and Antarctic glaciation.
While the former theory is based on the presumption that the marine connection was coeval with initiation of Antarctic glaciation at the Eocene-Oligocene boundary, the latter requires an earlier (middle Eocene) ocean water exchange. Unfortunately, age estimates for the onset of a seaway through the Drake Passage range from middle Eocene to early Miocene, complicating interpretations of the relationship between ocean circulation and global cooling.
Studying the southeast tip of Tierra del Fuego, a region that was once attached to the Antarctic Peninsula, Ghiglione et al. discovered evidence for the opening of widespread early Eocene extensional depocenters. The succession of events described in their study show that the opening of a seaway through the Drake Passage was early enough to contribute to global cooling through lowering levels of atmospheric CO2.
Their data bolster interpretations of an early (Eocene) marine gateway by confirming the prediction of a continental extensional regime in the region during the period prior to the opening of small basins ca. 42 million years ago. Ghiglione et al.'s findings will have a broad impact, adding key pieces to the puzzle of the opening of the Drake Passage, and allowing a new field of investigation to continue unveiling its effects on global circulation and climate.
Journal reference: Matias Ghiglione et al., Geology. August 2008. Pages 643-646.
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