Drake Passage: a major crossroads in the Earth System
Abstract
The oceanographic importance of Drake Passage is undisputed: without the development of a deep-water pathway between the Pacific and Atlantic oceans since the Eocene, circumpolar circulation as we know it could not have developed, and the Earth would now be experiencing a very different climate regime. The opening of Drake Passage provided a direct link between marine organisms of the Pacific and Atlantic oceans, but also isolated terrestrial organisms in Antarctica from South American populations. In this way, plate movements have exerted a direct influence on biological evolution and speciation. The opening may also have provided a pathway for the flow of upper mantle rocks from the shrinking Pacific basin, into the expanding Atlantic. Motion between the plates on either side of the SFZ (the Antarctic plate to the SW, the Scotia plate to the NE) is slow (a few mm/yr) and transpressional today. There is no evidence in or around Drake Passage for major subduction (convergence) in the past (e.g. volcanic arcs, deformed sediments, ophiolites), so that almost all the crust formed or pre-existing in the Drake region must still exist. Thus, in principle, it is possible to reconstruct the geography, including paleodepths and paleocoastlines, in the embryonic Drake Passage, and so establish where and when deep-water and land connections were made and broken. A major constraint on the present-day ACC pathway is the steep-sided ridge which blocks the southern Drake Passage. We have been mapping this feature recently in an effort to understand its tectonics. Specifically, is it an original feature formed during continental separation (a continental sliver), or is it (as we suspect) a tectonic feature formed by compression on the Shackleton FZ? If the former, then, as the older models suggest, deep-water connection between the Pacific and Atlantic would have been delayed until the Miocene (after 20 Ma). If the latter, then a deep-water connection could have been established soon after separation in the Oligocene (30 Ma or even earlier).
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA.....2129L