Depositional patterns at Drift 7, Antarctic Peninsula: Along-slope versus down-slope sediment transport as indicators for oceanic currents and climatic conditions

Abstract

Understanding the processes and phases of deep-sea sediment drift formation is essential for a reconstruction of their evolution. This leads to a better understanding of the properties of oceanographic currents active during drift formation and in turn to information on the climatic conditions. A system of sediment drifts at the Antarctic Peninsula Pacific rise has been chosen to learn more about the Neogene evolution of both current systems and palaeo-climate in that area. Drift 7 was extensively surveyed (seismic and sampling), and two ODP Leg 178 sites were drilled there. Using this information, maps of reflectors depth and seismic unit thickness were compiled and interpreted regarding the controlling depositional processes. The depositional model shows an initially major along-slope sediment transport by a SW-setting bottom current (25-15 Ma), which deflected sediment supplied from the continental shelf. Between 15 Ma and 9.5 Ma down-slope transport took over as a result of the growth of the Antarctic Peninsula ice sheet. The SW setting bottom current appears to have broken down. Down-slope transport has decreased since 9.5 Ma, but a re-onset of the bottom current can only be observed since 5.3 Ma. The analysis has further shown that the nucleus of the drift is connected to a basement ridge. It is hence inferred that basement topography played a major role in the formation of this sediment drift.

Deep-sea pre-glacial to glacial sedimentation in the Weddell Sea and southern Scotia Sea from a cross-basin seismic transect

“…Maldonado et al, 2005;Uenzelmann-Neben, 2006). Although typical contourite drift structures are not clearly observed in the WS-SS transect seismic data, the seismic profiles are too sparse to exclude their existence in the pre-glacial central Weddell deep-sea units.…”

“…10) across the Weddell Sea, allow the interpretation that the southern part of the APIS probably already grounded in the early Miocene or even Oligocene, and the WAIS in the Oligocene. Sampling, drilling and multichannel seismic reflection data analyses of Drift 7 on the Pacific margin of the Peninsula, suggest down-slope transport as a result of the growth of the Antarctic Peninsula ice sheet in the Early Miocene (~15 Ma and 9.5 Ma; Uenzelmann-Neben, 2006). This early Miocene/ Oligocene APIS and Oligocene WAIS expansion is not adequately reproduced by palaeoclimate models that suggested a late Mioceneearly Pliocene APIS grounding (7.94-5.12 Ma, Bart et al, 2005;Pollard and DeConto, 2009; Table 1), but consistent with the SHALDRIL findings .…”

Early glaciation already during the Early Miocene in the Amundsen Sea, Southern Pacific: Indications from the distribution of sedimentary sequences

“…There is widespread evidence for bottom current activity since~9.6 Ma in this area and in the Bellingshausen Sea further to the west (e.g. Nitsche et al, 2000;Rebesco et al, 2002;HernandezMolina et al, 2004;Hillenbrand and Ehrmann, 2005;Scheuer et al, 2006b;Uenzelmann-Neben, 2006). Uenzelmann-Neben and Gohl (2012) inferred bottom current activity as early as the Paleogene and the onset of major glaciations in West Antarctica at 14.1 Ma from seismic reflection profiles on the continental rise in the Amundsen Sea, but chronological control was poor.…”

“…On the basis of seismic reflection profiles from the western Antarctic Peninsula margin that were correlated with drill cores, Rebesco et al (2002) and Uenzelmann-Neben (2006) identified a close interaction of contouritic and turbiditic sediment transport with indications for a major advance of the local ice sheet shortly after 15 Ma. There is widespread evidence for bottom current activity since~9.6 Ma in this area and in the Bellingshausen Sea further to the west (e.g.…”

Variability in Cenozoic sedimentation and paleo-water depths of the Weddell Sea basin related to pre-glacial and glacial conditions of Antarctica

“…5, 9C). These drift bodies developed during the transport of sediments by a combination of contour currents and/or turbidity flows (Michels et al, 2001;Uenzelmann-Neben, 2006), fed by an abundance of glacial sediments brought to the basin margin cycles of ice sheet advanced and retreat.…”