Composite Velocity Profile of Shelf Site 1103 (ODP Leg 178, Western Antarctic Peninsula)

Direct constraints on Antarctic Peninsula Ice Sheet grounding events between 5.12 and 7.94 Ma

“…To project the seismic reflectors to ground truth at sites 1097 and 1103, the TWTT elevations of seismic reflectors were measured and converted to depth. The Moerz et al [2002] TWTT-depth chart for Site 1097 was not used because the electric log velocity measurements were unreliable. Instead, we created a TWTT-depth conversion table using the 42 measurements of P wave velocity from a Hamilton-Frame sensor pair [Shipboard Scientific Party, 1999].…”

“…[15] According to our TWTT-depth conversions (Table 3), ODP Site 1103 penetrates only 2 of the 14 package 3 reflectors in the north segment of the study area (Figures 3 and 7). Table 3 shows TWTT-depth conversions derived from the Moerz et al [2002] velocity model. For the reasons mentioned in section 3, this section focuses on depth conversions obtained from the Tinivella et al [2002] velocity data (i.e., Table 3).…”

“…In this scenario, the ice sheet retreated from the shelf edge, but the grounding zone did not migrate landward of Site 1097 before grounded ice readvanced to the shelf edge. Indeed, the subglacial sediments from both the base and top of units 3.12 and 3.11 suggest that there was no Tinivella et al [2002] velocity model and the TWTT converted to depth using the Moerz et al [2002] velocity model are given. For each scheme, the elevation of the seismic reflectors are reported in milliseconds below the sea surface (ms bss), milliseconds below the seafloor (ms bsf), and meters below the seafloor (m bsf).…”