An Over-Sea-Ice Seismic Reflection Survey: Offshore New Harbor, Antarctica

During the austral spring of 2008, approximately 48 km of multi-channel seismic reflection data were collected on a sea-ice platform east of New Harbor, Antarctica. The Offshore New Harbor (ONH) survey is third in a series of three successful over-sea-ice seismic reflection surveys recently conducted in McMurdo Sound, Antarctica. For rapid data acquisition, the ONH project employed a 60-channel snow streamer cable, with gimbaled geophones installed at 25 m spacing. A dual-chamber Generator-Injector air gun, used as a seismic source, mitigated problems inherent with surface and explosive seismic sources. These ONH data were collected to support the ANtarctic geological DRILLing Program (ANDRILL) which seeks to understand past tectonic and climatic regimes by recovering coevally deposited sediments. ONH data tie into the 2005 Southern McMurdo Sound (SMS) multi-channel seismic survey which successfully delineated sedimentary rock reflectors on the western margin of the Victoria Land Basin (VLB). However, changes in surveying and data processing techniques have improved ONH data quality comparative to SMS data. In order to achieve better signal response at depth than the SMS survey, the GI air gun pressure was increased from 3.4 x 106 Pa to 13.8 x 106 Pa. Unlike SMS data, static and timing errors associated with over-sea-ice surveys were discovered and corrected to improve ONH data resolution. The 2008 ONH project also resurveyed a portion of PD-90-46, a single-channel marine seismic survey collected in 1990 by the Polar Duke research vessel. Unlike Polar Duke’s single-channel data, multi-channel data from the ONH survey has allowed us to remove the sea-floor multiple which masks deeper primary reflections from sedimentary rock boundaries. The ONH data clearly show primary reflector signal beneath the sea-floor multiple where we expect to image Eocene and Oligocene sedimentary rocks. The CIROS-1 borehole was intersected by one of the ONH survey lines and recovered Eocene and Oligocene sedimentary rocks that were below an unconformity 366 m below the sea-floor. ANDRILL hopes to locate (up-dip from CIROS-1) a more complete sequence of sedimentary rocks that records the transition from the Eocene Greenhouse World to the Oligocene Icehouse World. The ONH project has generated new seismic data that could lead to the future drilling of sediment cores that will resolve paleoenvironments that controlled sedimentation during the Eocene and late Oligocene in the VLB.