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Shackleton Fracture Zone: No barrier to early circumpolar ocean circulation

¹ British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK
² Alfred Wegener Institute for Polar Research, Columbusstrasse, 27568 Bremerhaven, Germany
³ British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK
⁴ Instituto Andaluz de Ciencias de la Tierra, C.S.I.C., Universidad de Granada, Campus de Fuentenueva, s/n, 18002 Granada, Spain

The opening of Southern Ocean gateways was critical to the formation of the Antarctic Circumpolar Current and may have led to Cenozoic global cooling and Antarctic glaciation. Drake Passage was probably the final barrier to deep circumpolar ocean currents, but the timing of opening is unclear, because the Shackleton Fracture Zone could have blocked the gateway until the early Miocene. Geophysical and geochemical evidence presented here suggests that the Shackleton Fracture Zone is an oceanic transverse ridge, formed by uplift related to compression across the fracture zone since ca. 8 Ma. Hence, there was formerly (i.e., in the Miocene) no barrier to deep circulation through Drake Passage, and a deep-water connection between the Pacific and Atlantic Oceans was probably established soon after spreading began in Drake Passage during the early Oligocene.

Key Words: gateways • Southern Ocean • Antarctic Circumpolar Current • Shackleton Fracture Zone • transverse ridge

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