Give a brief (and illustrative) synopsis of the tectonic events that led to the establishment of the modern Antarctic Circumpolar Current (ACC) (20 marks, max. 200 words).
The Antarctic Circumpolar Current (ACC) was established during the Eocene-Oligocene transition into a modern day east flowing, wind driven current, which connects all of the three major oceans (Barker & Thomas. 2004). Research suggests the development of the ACC was dependent upon the tectonic isolation of the Antarctic continent, through the divergence of the Indian-Australian Plate and South American Plate from Antarctica (Figure 1) (Exon et al., 2002; Seton et al., 2012). This tectonic shift led to the opening of the Tasman Gateway (TG) at the Southern end of Australia,…show more content… The role of the ACC in triggering Antarctic glaciation during the Oligocene remains hotly debated. Using the literature as a guide, discuss this controversy. What was the conventional view surrounding the mechanisms that initiated Antarctic glaciation, and how/why did a paradigm shift occur in recent years? (30 marks, max. 300 words)
For many years, the ACC onset ensuing the opening of the Tasman Gateway and the Drake Passage has been proposed as the principle driver of the Antarctic continental glaciation (Barker et al., 2007). Although, modern studies that use computer models have suggested that atmospheric CO2 lowering during the Eocene/Oligocene may be the main catalyzer for Antarctic glaciation (Lefebvre et al., 2012; Pfuhl & McCave. 2005; Stocker. 2014). These studies found that the opening of the Tasman Gateway and Drake Passage did not trigger the ACC onset. A lower temporal climate, which was dominant throughout the end of the Oligocene, is prerequisite to develop the ACC we have today (Lefebvre et al., 2012). In this colder climate, the strengthened sea-ice covering the continent of Antarctica, which resulted in a brine salinity controlling a robust latitudinal density distribution. This gradient in the southern ocean supports Ekman transport, and subsequently supporting the Antarctic Circumpolar Current (Lefebvre et al., 2012). The controversy associated with these results is that it relies heavily on computer modeling and is supported by fully coupled ocean- atmosphere model (FOAM) with an Oligocene geography, whilst not being able to be fully ‘ground truthed’. However, there is physical supporting evidence such as from core samples taken from critical zones like Site 1172 East Tasman Plateau (Barker & Thomas. 2004; Lefebvre et al.,
