Southern Ocean sediments are a major sink for biogenic silica (50-75% of the oceanic total of 4.5 x 1014 g SiO2 y-1; DeMaster, 1981) but only a minor sink for organic carbon (<1% of the oceanic 2 x 1014 (g organic C) y-1; Romankevich, 1"984). The high rates of biogenic silica accumulation in the Southern Ocean (predominantly beneath the Polar Front) initially were thought to result from high rates of primary production; however, direct measurements of primary production made during the past two decades (e.g., El-Sayed et al., 1983; Holm-Hansen et al., 1977) typically indicate that the rates in the Southern Ocean are low to moderate. These data suggest that the preservation efficiency for biogenic silica in the Southern Ocean plays a key role in the processes contributing to the massive silica accumulation. Primary production in the waters south of the Polar Front is not controlled by major nutrient (nitrate, phosphate, or silicate) availability (see Kamykowski and Zentara, 1989, for review) but may be restricted by low levels of irradiance coupled with deep mixed layers (e.g., Mitchell et al., 1991; Nelson and Smith, 1991) or by limited amounts of micronutrients such as iron (Martin et al., 1990). Regardless of the mechanism that limits biological production, Southern Ocean phytoplankton typically have a biogenic-silica-to-organic-carbon weight ratio ranging from 1 to 3 (Nelson and Smith, 1986). Therefore, the relatively high rates of biogenic silica accumulation in Southern Ocean sediments relative to organic carbon (~60:1 on a weight basis) must result from the preferential preservation of biogenic silica in the Antarctic water column and/or seabed.