A more comprehensive understanding of the Antarctic Circumpolar Current - The emergence and development of the ACC described with the help of knowledge obtained by studies using several scientific techniques

Abstract

The Antarctic Circumpolar Current is nowadays an important ocean current with the highest volume transport of all ocean currents and relatively many of its characteristics are known. However, the estimates on the onset time of the ACC vary widely. The aim of this thesis is therefore to establish a more comprehensive understanding of the onset and development of the ACC. A scientific literature search on the ACC was performed to research if the difference in the defined ages of the ACC is due to a difference in the definition of the ACC within earth scientific subdisciplines, due to a fundamental difference in definitions and descriptions used for the ACC per individual research or due to the fact that the ACC had multiple onsets. Interpretations of the results were later addressed in the discussion section and new hypotheses were established. The outcome of this thesis is that the difference in the estimated age of the ACC is due to a fundamental difference in definitions and descriptions that are used for it. The development of oceanic gateways that led to the current ACC has become generally clear. First, a westbound Antarctic Counter Current was in place at approximately 50-49 Ma. This current did not completely encircle Antarctica, as the Drake Passage was still closed. Between 49 and 41 Ma, but probably after 45 Ma, the first shallow eastward current encircled Antarctica. The first analogue of the modern ACC was established between 37 and 30 Ma. This current was of intermediate to deep depth and it had gained strength since the appearance of the first eastward current. The state of the ACC between 30 and 15 Ma is uncertain, although it is hypothesized that it weakened between 30 and 22 Ma, after which its strength remained approximately the same until about 15 Ma. The ACC gained strength in the period between 15 and 10 Ma, in which a full developed, strong and coherent ACC is reported. Lastly, the modern ACC exists of jet streams that each correspond to fronts which are predominantly steered by bathymetry.