CONCLUSIONS

1. Clay mineral assemblages in surficial continental margin sediments west of the Antarctic Peninsula consist of smectite, chlorite, and illite, with kaolinite occurring only in trace amounts. High smectite concentrations typify the shelf sediments off northern Graham Land, whereas chlorite and illite dominate shelf deposits offshore from the southern Antarctic Peninsula. At the continental rise, a bottom current transports smectite supplied from the northern Antarctic Peninsula to the southwest.
2. An upper Quaternary sediment sequence from site PS1565 comprises an interglacial clay mineral assemblage with high smectite amounts and a glacial assemblage characterized by enhanced chlorite concentrations. During glacial periods, chlorite-enriched detritus was supplied to the continental rise by gravitational downslope processes triggered by the advance of grounded ice streams to the shelf break.
3. Upper Miocene to Quaternary sediments recovered at continental rise Sites 1095 and 1096 exhibit clay mineral fluctuations alternating between two end-member assemblages. One assemblage is characterized by <20% smectite and >40% chlorite. The other assemblage has >20% smectite and <40% chlorite. The clay mineral fluctuations are similar to those observed at site PS1565. We ascribe the short-term changes in clay mineral composition at Sites 1095 and 1096 to repeated ice advances and retreats across the shelf west of the Antarctic Peninsula, reflecting glacial-interglacial cyclicity. We conclude that oscillations in Antarctic ice volume may have influenced the global climate already during the late Miocene.
4. Only slight long-term changes are observed in the clay mineral assemblages deposited at ODP Sites 1095 and 1096. A slight enhancement of smectite contents between ~7.0 and ~5.4 Ma at Site 1095 may be a consequence of a higher smectite supply caused by an intensification of volcanism in the northern Antarctic Peninsula region and by a strengthening of glacial erosion in northern Graham Land in response to local uplift associated with ridge crest-trench collision. An increase of illite at Site 1096 between ~1.5 and ~0.2 Ma is probably caused by changes in the supply of glacial debris from different source areas on the southern Antarctic Peninsula. The clay mineral assemblages deposited at Drift 7 point to an onset of vast glaciation in the Antarctic Peninsula region before 9 Ma but give no evidence for major deglaciation events since then.