A physical mechanism for the Atlantic–Pacific flow reversal in the early Miocene

Barotropic wind-driven steady ocean circulation patterns have been calculated for several different continental geometries during the Tertiary. Using a shallow-water model, flows are computed at 5-Ma intervals within the 60–20 Ma period, while keeping a fixed pattern of the wind-stress forcing. The most interesting changes in ocean circulation occur between 35 and 20 Ma, in which (i) the Antarctic Circumpolar Current appears because of the widening of Drake Passage, (ii) the Tethys Current disappears because of the closure of the Tethys Seaway and (iii) the transport through Panama Straits (between North and South America) reverses. The results are qualitatively in agreement with interpretations of changes in ocean surface currents drawn on the basis of proxy studies. A physical mechanism of the flow reversal through the Panama Straits is proposed based on a detailed analysis of the changes in wind-driven transport of both the Tethys Current and the Antarctic Circumpolar Current.