New Seismic Methods to Support Sea-Ice Platform Drilling

America). By drilling, coring and analyzing stratigraphic. By drilling, coring and analyzing stratigraphic By drilling, coring and analyzing stratigraphic By drilling, coring and analyzing stratigraphic y drilling, coring and analyzing stratigraphic archives along the Antarctic continental margin, ANDRILL , ANDRILL pursues its primary goal of better understanding the role the primary goal of better understanding the role the of better understanding the role the better understanding the role the ing the role the the role the Antarctic cryosphere plays in the global climate system (Harwood et al., 200�). The ANDRILL drilling system was developed to operate on both ice shelf and sea-ice platforms Florindo et al., 2008). While thick multiyear sea ice provides stable and safe drilling platforms, identifying drilling targets in regions where these sea-ice conditions occur can be problematic due to a paucity of marine seismic re��ection data because near-constant sea ice limits ship access (Fig. 1).-constant sea ice limits ship access (Fig. 1). constant sea ice limits ship access (Fig. 1). In response to this problem ANDRILL developed new over-sea-ice seismic methods to extend seismic re��ection data coverage to regions of multiyear sea ice. Previous over-sea-ice seismic experiments had limited success due to (1) poor source coupling caused by thin sea ice, (2) source-induced ice ��exural modes that cause coherent-induced ice ��exural modes that cause coherent induced ice ��exural modes that cause coherent noise, which is difficult to remove from data, and (3) source bubble-pulse effects caused by explosive seismic sources During the austral spring-summer of 2005, approximately 28 km of over-sea-ice seismic re��ection data were recorded in McMurdo Sound, Antarctica (Fig. 2) for ANDRILL�s Southern McMurdo Sound (SMS) Project (Harwood et al., 2004). ANDRILL developed seismic survey techniques for the SMS Project that improved the quality of over-sea-ice seismic data (Betterly et al., 2007). A Generator-Injector (GI) air gun was used as the seismic source (Fig. 3A). Single airgun source marine seismic surveys typically use a GI technique, in which a secondary air pulse is injected into the primary air pulse on a short time delay. The injection of the secondary air pulse dampens the generation of the bubble pulse. The GI air gun was lowered into the water column via holes drilled through the sea ice. The GI air gun minimized the source ice. The GI air gun minimized the source ice. The GI air gun minimized the source bubble effects that plagued previous over-sea-ice …