ANDRILL MacKay Sea Valley (MSV) Seismic Reflection Survey 2007

During the austral summer, 2007, approximately 20.5 km of high-quality seismic reflection data were collected in Granite Harbor.  The focus of this study was to find Quaternary geological successions in the hope that these records could help decipher environmental changes. The MacKay Sea Valley (MSV) is a deep trough thought to have been eroded beneath Granite Harbor by previous expansion of the MacKay Glacier. The seismic survey's intent was to image recent sediment layers that accumulated in the MSV following erosion. The MSV seismic survey incorporated and refined techniques of over-sea-ice seismic data collection that had been used previously during the ANtarctic geological DRILLing (ANDRILL) Program's Southern McMurdo Sound (SMS) seismic site survey in 2005.  A Generator-Injector (GI) air gun was used as the seismic source that was lowered into the water column through holes drilled through the sea ice. The GI air gun minimized the source bubble effects that had plagued previous over-sea-ice experiments in the Antarctic.  A 60-channel seismic snow streamer consisting of vertically oriented gimbaled geophones with 25-m takeout spacing was employed to aid rapid data collection.  The MSV seismic survey was successful in locating a thin succession of low-amplitude reflections atop the higher-amplitude granite basement reflections in the deepest parts of the valley. The low-amplitude reflections are likely caused by layers of pelagic sediment. Future coring of these recent sediments could provide a high-resolution Quaternary climate record.