Occurrence of microtextures recorded from quartz sand grains of ODP Hole 178-1101A (Table 1)

Sediment drifts on the continental rise are located proximal to the western side of the Antarctic Peninsula and recorded changes in glacial volume and thermal regime over the last ca. 15 m.y. At Ocean Drilling Program (ODP) Site 1101 (Leg 178), which recovered sediments back to 3.1 Ma, glacial-interglacial cyclicity was identified based on the biogenic component and sedimentary structures observed in X-radiographs, magnetic susceptibility and lithofacies descriptions. Glacial intervals are dominated by fine-grained laminated mud and interglacial units consist of bioturbated muds enriched in biogenic components. From 2.2 to 0.76 Ma, planktonic foraminifera and calcareous nannofossils dominate in the interglacials suggesting a shift of the Antarctic Polar Front (APF) to the south near the drifts. Prior to 2.2 Ma, cyclicity cannot be identified and diatoms dominate the biogenic component and high percent opal suggests warmer conditions south of the APF and reduced sea ice over the drifts. Analyses of the coarse-grained terrigenous fraction (pebbles and coarse sand) from Sites 1096 and 1101 record glaciers at sea-level releasing iceberg-rafted debris (IRD) throughout the last 3.1 m.y. Analyses of quartz sand grains in IRD with the scanning electron microscope (SEM) show an abrupt change in the frequency of occurrence of microtextures at ~1.35 Ma. During the Late Pliocene to Early Pleistocene, the population of quartz grains included completely weathered grains and a low frequency of crushing and abrasion, suggesting that glaciers were small and did not inundate the topography. Debris shed from mountain peaks was transported supraglacially or englacially allowing weathered grains to pass through the glacier unmodified. During glacial periods from 1.35-0.76 Ma, glaciers expanded in size. The IRD flux was very high and dropstones have diverse lithologies. Conditions resembling those at the Last Glacial Maximum (LGM) have been episodically present on the Antarctic Peninsula since ~0.76 Ma. Quartz sand grains show high relief, fracture and abrasion common under thick ice and the IRD flux is low with a more restricted range of dropstone lithologies.

(Table 2) U-channel paleomagnetic record of ODP Site 178-1098

Thick Holocene sedimentary sections (>45 m) cored in the Palmer Deep by the United States Antarctic Program (USAP) and during Ocean Drilling Program (ODP) Leg 178 provide the first opportunity to examine past geomagnetic field behavior at high southern latitudes. After removal of a low-coercivity drilling overprint the sediments display a stable, single-component remanent magnetization. Two short cores that recovered the uppermost 2.6 m of sediment have inclinations that fluctuate about the present day inclination (-57°) measured at Faraday Station, and several features with wavelengths of 10 to 20 cm appear to be correlative. However, shipboard measurements of inclination fluctuations on split-core samples from three holes drilled at ODP Site 1098 do not correlate well with each other, even though the intensity and susceptibility data correlate very well and the overall mean inclination for cores from each hole is consistent with the expected geocentric axial dipole (GAD) inclination. The correlation is improved dramatically by using inclinations measured on u-channels taken from the pristine center of a split core. Consequently, the anomalous directions and the resulting poor between-hole correlation of inclinations obtained from shipboard data can be attributed to coring-induced deformation, which is common on the outer edge of ODP piston cores, and/or measurement artifacts in the split-core data. Our preferred inclination record is thus derived from u-channel results. The upper ~25 m represents continuous sedimentation over the past 9000 yr, with an average sedimentation rate exceeding 250 cm/kyr (0.25 cm/yr). Given that remanence measurements on u-channels average over an interval <7 cm long, we obtained independent measurements of the paleo-geomagnetic field that average over only ~30 yr. This high-resolution record is characterized by an inclination that fluctuates within +/-15° of the current GAD inclination.