Internal structure of a contourite drift generated by the Antarctic Circumpolar Current

• Published in: Geochemistry, Geophysics, Geosystems
• Main Authors: Koenitz, D., White, N. J., McCave, I. N., Hobbs, R. W.
• Format: Article in Journal/Newspaper
• Language: English
• Published: AGU and the Geochemical Society 2008
• Subjects: 01 - Climate Change and Earth-Ocean Atmosphere Systems; Antarctic; Drake Passage; East Antarctic Ice Sheet; Falkland Trough; Southern Ocean; The Antarctic; Antarc*; Ice Sheet
• Online Access: http://eprints.esc.cam.ac.uk/457/; http://eprints.esc.cam.ac.uk/457/1/McCave_3G_9_6_2008.pdf; https://doi.org/10.1029/2007GC001799

We describe the internal structure and stratigraphy of a well-imaged contourite drift from the Southern Ocean. This drift, which we have named the South Falkland Slope Drift, lies on the northern flank of the Falkland Trough due south of the Falkland Islands. Drifts which occur directly in the path of the Antarctic Circumpolar Current (ACC), downstream of the Drake Passage gateway, are of considerable paleoceanographic significance since their detailed stratigraphic record will help to constrain the history of the ACC. We have reprocessed a grid of seismic reflection profiles generously provided by WesternGeco Ltd. in order to enhance imaging of the South Falkland Slope Drift and of drift deposits within the trough. The resultant high-quality images enable us to map the internal architecture of these drifts in unprecedented detail. By combining seismic stratigraphic mapping with measured sedimentation rates from nearby boreholes, we have inferred ages of the principal mappable horizons. With minor adjustments to sedimentation rates through time, we can show that these ages correspond to significant Southern Ocean events. We propose that the South Falkland Slope Drift initiated at 24.5–20.5 Ma, in accordance with some, but not all, published estimates of ACC establishment. A highly reflective horizon with an estimated age of 14.5 Ma corresponds to growth of the East Antarctic Ice Sheet, which led to a period of significant global cooling. A similarly bright reflective horizon with an estimated age of 9 Ma is thought to be related to a reorganization of bottom current flow which just predated establishment of grounded ice sheets on the Antarctic Peninsular shelf. Finally, a prominent early Pliocene unconformity at 4.5 Ma may be linked with the onset of major Northern Hemisphere glaciation or with Antarctic ice sheet expansion. We conclude that this well-imaged drift is an important, and largely continuous, stratigraphic record of ACC activity and suggest that it would be an excellent drilling target.