USE OF SEAFLOOR PALEO-TOPOGRAPHY TO DECIPHER PALEOCLIMATE HISTORY: EXAMPLES FROM THE ROSS SEA, ANTARCTICA

Determining the timing of advance of ice sheets onto continental margins of Antarctica is a critical task in assessing the linkages between cryosphere development and changes in global climate. Identification of paleo-seafloor relief in high-resolution seismic profiles is a new tool that can be used to locate yet identified, subtle glacially carved unconformities on the margin and therefore provide a means for a higher resolution correlation of ice sheet expansion and contraction to indicators of global climate change.

Opportunities to examine high-resolution variation in seafloor relief and identification of subglacial conditions on the margin were created by development of multi-beam and deep-tow side-scan and chirp sub-bottom sonars. Seafloor relief such as mega-scale lineations and drumlins, superimposed upon large-scale ridge and trough systems on the seafloor are evidence for Pleistocene subglacial conditions on the margin and are an analog used to identify subglacial deposits deeper in the section. Not all of the glacial units are characterized by large ridge and trough systems; making glacially carved unconformities much more difficult to identify in seismic profiles. However, cross-section images of the smaller-scale features, imaged in high-resolution seismic profiles, can be used to distinguish glacially carved unconformities from those produced by a lack of deposition (e.g. Maximum Flooding Surfaces). In cross-section, lineations consist of V-shaped crests and incisions (10's of meters wide and ~10 meters tall), while drumlins have a dome-shaped morphology- lacking internal reflections, with a width on the order of ~100's of meters at the base and a height of 10's of meters (~30-50 meters). Iceberg furrows are also present on the margin, but their distribution is limited to shallow areas, such as the flanks of banks and they indicate warmer intervals, when the ice sheets retreated from the shelf and glacial marine sedimentation was prevalent. They have a shallow and irregular cross-section morphology (~10 meters wide and ~5 meters deep). Iceberg furrows can be distinguished from lineations because furrows are relatively widely dispersed, are comparatively small, and have limited positive relief. They differ from drumlins by their lack of the dome-like positive relief and their narrow width.