Continental rises – Criteria for identification of continental rises include the occurrence of a smooth sloping seabed as indicated by evenly-spaced, slope-parallel contours (eg. Curray et al., 2002; Dowdeswell et al., 2008; Covault et al., 2011). In this study, the term “Rise” was restricted to features that abut continental margins and does not include the mid-ocean ridge (or “rise”), which was mapped as a separate feature. The GEBCO Gazetteer of geographic names of undersea features (IHO-IOC, 2012) was used to ensure all named features were included. There is considerable variability in the mean thickness of sediment characterising rises in the different ocean regions, ranging from around 450 m in the South Pacific to over 3,100 m in the Indian Ocean.
Most continental rises occur adjacent to passive continental margins; the continental rise covers more than 27.1 million km2 adjacent to passive margins and less than 2.3 million km2 adjacent to active margins. The continental rise completely surrounds Antarctica covering 39.4% of the Southern Ocean (see Table), forming a halo of sediment surrounding the Antarctic continent.