Early Oligocene record of an “iceberg alley” in the Weddell Sea from quartz sand microtextural analysis at ODP Site 696

Abstract The greenhouse to icehouse transition at the Eocene-Oligocene boundary (34 Ma) marked the appearance of continental-scale glaciation in Antarctica. The material recovered from Ocean Drilling Program Site 696 is the only record spanning this major climatic shift in the Weddell Sea region. Using scanning electron microscopy, quartz microtextures in 13 samples across the Eocene-Oligocene transition were analyzed to understand the degree of glacial modification and the transportation history of the 150 µm material. The quartz grains were visually grouped, characterized, and interpreted by grain outline, relief, and surface microtextures. Glacial textures are present throughout the entire interval (34.4–33.2 Ma), with the proportion of iceberg-rafted grains in each sample decreasing into the early Oligocene (33.6 Ma), accompanied by an increase in the frequency of eolian and sea-ice-rafted grains. Mass accumulation rates reveal that the flux of iceberg-rafted debris increased coincident with the flux of eolian and sea-ice-rafted grains following 33.6 Ma, suggesting a strong coupling between land-ice development and high-latitude atmospheric processes. When compared with other Antarctic climate proxy data sets, the intensification of ice rafting at Site 696 occurred after ice-sheet inception in East Antarctica. The prominent influx of terrigenous material after 33.6 Ma points to strengthened glacial conditions accompanied by major changes in the environment of the Weddell Sea region, supporting the idea of a high-latitude role in climate perturbations, in agreement with interpretations of other global proxies.