This project was performed to investigate the evolution of Western ice sheet (WIS) in the Eastern Basin (Ross Sea), Antarctica. The Ross Sea is part of the West Antarctic Rift System that has three main depocenters as the Eastern Basin, the Central Basin and the Victoria Land Basin. The Eastern Basin contains a thick sedimentary sequence that tells about the WIS advance and retreat. DSDP cores were drilled in this area (Hayes and Frakes, 1975) gives knowledge about the stratigraphy and the depositional environment of the area from Upper Miocene to Pleistocene (Hayes and Frakes, 1975). Large erosional hiatuses and poor interpretations of DSDP cores, do not let to construct of the Eastern Basin depositional history and the evolution of the WIS (Hayes and Frakes, 1975; Denton et al., 1991). On the other hand, multichannel seismic studies in the Ross Sea gives more knowledge about the sedimentary sequences and unconformities (ANTOSTRAT, 1995). These studies show that Lower Pliocene is identified by a marked erosion surface, called RSU2 (De Santis et al., 1995; Brancolini et al., 1997), and is correlated with a large hiatus in DSDP 273 which is dated from 10.5 to 4 ma (Savage and Ciesielski, 1983). Horizon RSU2 corresponds to a sharp change in the structure and lithology of sediments, which may be interpreted as a major increase of the glacial influence. Thus, it is clear that RSU2 identifies a major, unique event in the depositional history at the Ross Sea. The explanation of this event is today largely hypothetical, based on progressive climatic cooling occurred during Pliocene and the consequent grow of the Antarctic ice sheet. For setting up reliable paleo-climatic models, however, we have to define precisely the extension and features of the ice sheet: thus, we proposed to carry out a detailed geophysical study in a specific area of the Ross Sea, for reconstructing dimensions and dynamics of the Eastern ice sheet during Pliocene, a period of large changes at a global level, anda also the most debated one for the history of the Antarctic ice sheet.

During austral summer1989-90 the National Institute of Oceanography and Applied Geophysics - OGS conducted marine geological and geophysical surveys off Wilkes Land, and around the Balleny Islands. During this cruise 1284 km of 30-fold multichannel seismic reflection (MCS) data were collected between longitude 165 and 176 degrees East, and latitude 61 and 66 degrees South. The surveys were carried out by the research vessel OGS Explora. The 14 second, 4 ms sample rate, digital MCS data were recorded on a SERCEL SN 358 DMX system. The source consisted of an airgun array with a total volume of 22.5 litres fired every 50 meters into a 3000 m cable consisting of 120 hydrophone groups towed at an average depth of 12 m. A GPS + TRANSIT satellite receiver system was used for navigation. Processing of the data generally followed a conventional sequence: Reformat, Quality control, Amplitude recovery, Deconvolution, Velocity analysis, NMO corrections, Mute, Trace weighting, Stack, Mixing, Filter, Dynamic trace equalisation.

During Austral Summer1990-91 the National Institute of Oceanography and Applied Geophysics - OGS conducted marine geological and geophysical surveys in the Ross Sea, over Weddel Sea and in the Balleny Zone of the MacQuarie Triple Junction. This cruise collected approximately 6036 km of multichannel seismic reflection (MCS) data. The surveys extended, in different areas, between longitudes 37 and 56 degrees west, and between latitudes 59 and 62 degrees south (Weddel Sea), between longitudes 171 east and 178 degrees west, and between latitudes 71 and 73 degrees south (Ross Sea), between longitudes 150 and 158 degrees east , and between latitudes 51 and 62 degrees south (Balleny). The surveys were carried out by the research vessel OGS Explora. The digital MCS data were recorded on a SERCEL SN 358 DMX system. The source consisted of an airgun array with variable configuration from a total volume of 45.16 litres fired approximately every 50 meters. A GPS + TRANSIT satellite receiver system was used for navigation. Processing of the data generally followed a conventional sequence: Reformat, Trace-sum with differential NMO, Quality control, Amplitude recovery, Deconvolution, Velocity analysis, NMO corrections, Mute, Trace weighting, Stack, Mixing, Filter, Balance.

During the Antarctic summer 1988-89, a geophysical survey (seismic, gravity and magnetics) was carried out by the National Institute of Oceanography and Applied Geophysics - OGS of Trieste, Italy, in the Ross Sea with the Research Vessel O.G.S. Explora. 23 lines of total length 4113.1 Km were collected. The cruise began on December 10,1988 from the harbor of Hobart (Australia) and ended on January 15, 1989, with its arrival in Dunedin (New Zealand). Gravimetric and geomagnetic data were continuously acquired during the cruise, with minor interruptions due to adverse sea conditions. The multichannel seismic survey was run in the Ross Sea from December 18 to January 8. The project has been financially supported by the Italian Antarctic Program (PNRA).

During Austral Summer 1991-92 the National Institute of Oceanography and Applied Geophysics - OGS conducted marine geological and geophysical surveys over the Ross Sea, cruise IT91AR. During this cruise 581 km of 30-fold multichannel seismic reflection (MCS) data were collected in the Ross Sea, off the Cape Hallett, between longitudes 171 degrees East and 178 degrees West, and latitudes 71 and 73 degrees South. In 1993-94 the OGS completed the cruise IT94AR, with 852 km of 30-fold and 673 km of 3-fold multichannel seismic reflection data collected in the Ross Sea, off the coast of the McMurdo Island, between longitudes 168 degrees East and 181 degrees West, and latitudes 73 and 77 degrees South. The surveys were carried out by the research vessel OGS Explora. The digital MCS data were recorded on a SERCEL SN 358 DMX system. The source consisted of an airgun array with a total volume of 71.5 litres fired approximately every 50 meters into a 3000 m cable consisting of 120 hydrophone groups for the 30-fold profiles and every 250 meters into a 1500 m streamer for the 3-fold profiles. A GPS + TRANSIT satellite receiver system was used for the navigation. Processing of the data generally followed a conventional sequence: Reformat, Trace-sum with differential NMO, Quality control, Amplitude recovery, Deconvolution, Velocity analysis, NMO corrections, Mute, Trace weighting, Stack, Mixing, Filter, Balance.

During austral summer 1988/89, the National Institute of Oceanography and Applied Geophysics - OGS conducted marine geological and geophysical surveys off Wilkes Land, and around the Balleny Islands. During this cruise 3045 km of 30-fold multichannel seismic reflection (MCS) data were collected between longitude 152 and 169 degrees East, and latitude 60 and 68 degrees South. The surveys were carried out by the research vessel OGS Explora. The 12 second, 4 ms sample rate, digital MCS data were recorded on a SERCEL SN 358 DMX system. The source consisted of an airgun array with a total volume of 45.16 litres fired every 50 meters into a 3000 m cable consisting of 120 hydrophone groups towed at an average depth of 12 m. A GPS + TRANSIT satellite receiver system was used for navigation. Processing of the data generally followed a conventional sequence: Reformat, Trace-sum with differential NMO, Resample to 8 ms, Quality control, Amplitude recovery, Deconvolution, Velocity analysis, NMO corrections, Mute, Trace weighting, Stack, Mixing, Filter, Dynamic trace equalisation.

This project was performed to investigate the evolution of Western ice sheet (WIS) in the Eastern Basin (Ross Sea), Antarctica. The Ross Sea is part of the West Antarctic Rift System that has three main depocenters as the Eastern Basin, the Central Basin and the Victoria Land Basin. The Eastern Basin contains a thick sedimentary sequence that tells about the WIS advance and retreat. DSDP cores were drilled in this area (Hayes and Frakes, 1975) gives knowledge about the stratigraphy and the depositional environment of the area from Upper Miocene to Pleistocene (Hayes and Frakes, 1975). Large erosional hiatuses and poor interpretations of DSDP cores, do not let to construct of the Eastern Basin depositional history and the evolution of the WIS (Hayes and Frakes, 1975; Denton et al., 1991). On the other hand, multichannel seismic studies in the Ross Sea gives more knowledge about the sedimentary sequences and unconformities (ANTOSTRAT, 1995). These studies show that Lower Pliocene is identified by a marked erosion surface, called RSU2 (De Santis et al., 1995; Brancolini et al., 1997), and is correlated with a large hiatus in DSDP 273 which is dated from 10.5 to 4 ma (Savage and Ciesielski, 1983). Horizon RSU2 corresponds to a sharp change in the structure and lithology of sediments, which may be interpreted as a major increase of the glacial influence. Thus, it is clear that RSU2 identifies a major, unique event in the depositional history at the Ross Sea. The explanation of this event is today largely hypothetical, based on progressive climatic cooling occurred during Pliocene and the consequent grow of the Antarctic ice sheet. For setting up reliable paleo-climatic models, however, we have to define precisely the extension and features of the ice sheet: thus, we proposed to carry out a detailed geophysical study in a specific area of the Ross Sea, for reconstructing dimensions and dynamics of the Eastern ice sheet during Pliocene, a period of large changes at a global level, anda also the most debated one for the history of the Antarctic ice sheet.

During the Antarctic summer 1987-88, a geophysical survey (seismic, gravity and magnetics) was carried out by the National Institute of Oceanography and Applied Geophysics - OGS, in the Ross Sea with the Research Vessel Explora. Six lines of total length 2,323 km were collected. The first survey by O.G.S. in Antarctica started on January 2, 1988, when the O.G.S. Explora sailed from the harbour of Ushuaid (Tierra del Fuego, Argentina) and ended on March 8, 1988, with its arrival in Wellington Harbour (New Zealand). Gravimetric and geomagnetic data were continuously acquired during the cruise, with minor interruptions due to adverse sea conditions. The multichannel seismic survey was run in the Ross Sea from February 10 to February 24.

During Austral Summer 1993-94 the National Institute of Oceanography and Applied Geophysics - OGS conducted marine geological and geophysical surveys over the Ross Sea, cruise IT91AR. During this cruise 581 km of 30-fold multichannel seismic reflection (MCS) data were collected in the Ross Sea, off the Cape Hallett, between longitudes 171 degrees East and 178 degrees West, and latitudes 71 and 73 degrees South. In 1993-94 the OGS completed the cruise IT94AR, with 852 km of 30-fold and 673 km of 3-fold multichannel seismic reflection data collected in the Ross Sea, off the coast of the McMurdo Island, between longitudes 168 degrees East and 181 degrees West, and latitudes 73 and 77 degrees South. The surveys were carried out by the research vessel OGS Explora. The digital MCS data were recorded on a SERCEL SN 358 DMX system. The source consisted of an airgun array with a total volume of 71.5 litres fired approximately every 50 meters into a 3000 m cable consisting of 120 hydrophone groups for the 30-fold profiles and every 250 meters into a 1500 m streamer for the 3-fold profiles. A GPS + TRANSIT satellite receiver system was used for the navigation. Processing of the data generally followed a conventional sequence: Reformat, Trace-sum with differential NMO, Quality control, Amplitude recovery, Deconvolution, Velocity analysis, NMO corrections, Mute, Trace weighting, Stack, Mixing, Filter, Balance.

During Austral Summer 1989-90, the National Institute of Oceanography and Applied Geophysics - OGS, conducted marine geological and geophysical surveys off South Pacific ocean, in the Weddell Sea over Bellingshausen Sea, in the Ross Sea and over Admundsen Sea. This cruise collected approximately 8763 km of multichannel seismic reflection (MCS) data. The surveys extended, in diferent area, between longitudes 34 and 172 degrees west , and between latitudes 59 and 76 degrees south. The surveys were carried out by the research vessel OGS Explora. The digital MCS data were recorded on a SERCEL SN 358 DMX system. The source consisted of an airgun array with variable configuration from a total volume of 45.16 litres fired approximately every 50 meters. A GPS + TRANSIT satellite receiver system was used for navigation. Processing of the data generally followed a conventional sequence: Reformat, Trace-sum with differential NMO, Quality control, Amplitude recovery, Deconvolution, Velocity analysis, NMO corrections, Mute, Trace weighting, Stack, Mixing, Filter, Balance.