Figure 2. Cross-section of subsurface water masses in a transect through the drilling sites, characterized by (a) dissolved oxygen (b) phosphate, and (c) salinity concentrations (Levitus et al., 1993). Bathymetry map is schematic. Southward-spreading middepth waters (labeled pcw for Pacific Central Water) are characterized by relatively low oxygen and salinity and high phosphate. Northward-spreading bottom waters, below ~3 km depth starts as relatively oxygen-rich Antarctic Circumpolar Deep Water (cpdw). Northward-spreading Antarctic Intermediate Water (aaiw), above 1 km depth, his high in oxygen but is low in both phosphate and salinity. Proposed ODP drilling sites (circles) span the water masses. White circles are primary sites. White circles with diagonal slashes are the highest priority optional sites to be drilled on a time-available basis. Open circles are alternate or optional sites. gu = Gunther Undercurrent, npiw = North Pacific Intermediate Water.