Late Oligocene initiation of the Antarctic Circumpolar Current: Evidence from the South Pacific

Links between CO<sub>2</sub>, glaciation and water flow: reconciling the Cenozoic history of the Antarctic Circumpolar Current

“…The variations in atmospheric CO 2 concentration, Antarctic ice sheet extent and Southern Ocean tectonics are therefore crucial to understanding the evolution of the ACC through the Cenozoic. They can also be invoked to reconcile upholders of an EO initiation of the ACC (Borrelli et al, 2014;Diekmann et al, 2004;Latimer and Filippelli, 2002) and upholders of an OM initiation (Lyle et al, 2007;Pfuhl and McCave, 2005) by providing a mechanism for an EO strengthening of the circumpolar current as well as for an OM reinforcement. To our knowledge, no study has yet analyzed material spanning both the EO and the OM transitions in search for ACC initiation.…”

“…Possible shutdown or slowdown of the ACC between approximately 29 and 22 Ma has also been suggested due to the temporary constriction of Drake Passage (Lagabrielle et al, 2009) and can be invoked to reconcile this apparent discrepancy in the timing of the ACC: after a period of shallow circulation in the middle to late Eocene (Scher and Martin, 2006), the first onset of the circumpolar current would have occurred close to the EO boundary (Borrelli et al, 2014;Katz et al, 2011;Latimer and Filippelli, 2002) following Antarctic glaciation and before a period of possible variations in its intensity under changes in pCO 2 , ice sheet size and tectonics; this development would have ended with a period of progressive slowdown (Lagabrielle et al, 2009). The Oligocene-Miocene boundary would then mark the second onset of the ACC (Lyle et al, 2007;Pfuhl and McCave, 2005), predating the evolution towards its modern features (Dalziel et al, 2013;Heinrich et al, 2011).…”

“…For example, Pfuhl and McCave (2005) analyze sediment grain size from South Tasman Rise (ODP Leg 189) and, based on the size increase around 23.9 Ma, conclude that there was an intensification of deep-water currents related to the deepening of Drake Passage and the initiation of the ACC. Lyle et al (2007) use sediments from an upper Oligocene to Holocene piston core to place the onset of the ACC between 25 and 23 Ma. These findings are not necessarily at odds with the results of this study, which favors an earlier initiation of a proto-ACC.…”

“…Consequently, the evolution of the ACC through time between the Eocene and the Miocene remains unclear. Some studies have proposed an onset in the earliest Oligocene (Florindo and Roberts, 2005;Katz et al, 2011), while other evidence tends to point to initiation in the late Oligocene or early Miocene (Lyle et al, 2007;Pfuhl and McCave, 2005;Scher and Martin, 2008). In a modeling approach, Toggweiler and Bjornsson (2000) found that the opening of Drake Passage had a cooling effect over southern high latitudes, but DeConto and Pollard (2003b) showed that possible changes in ocean heat transport due to gateways opening only had a limited impact on the Eocene-Oligocene Antarctic glaciation.…”

Early Miocene subtropical water temperatures in the southeast Pacific

“…Incipient opening of the Drake Passage occurred around 41 Ma (Scher and Martin, 2006), and its deepening allowed for initiation of the ACC. There is debate as to whether the ACC was fully established either in the Early Oligocene, between 34 and 30 Ma (Livermore et al, 2005) or in the latest Oligocene, at about 24 Ma (Pfuhl and McCave, 2005;Lyle et al, 2007). In any case, in the Early Miocene the ACC was active, in analogy to the present-day situation, and correspondingly extensive ice sheets developed over Antarctica.…”