Bacterial concentrations are present though most of the sediment section at Site 1027 but decrease by one to two orders of magnitude in the first 20 m below the seafloor (Mather and Parkes, Chap. 13, this volume). Concentrations rise again at the base of the sediment section, where sulfate associated with partially altered seawater diffuses up from basement. Amino acids also are most abundant within shallow Leg 168 sediments but decrease in concentration rapidly with depth (Andersson et al., 2000). Within basement rocks, microbes were observed on fractured surfaces of volcanic breccia cored at Site 1026 (Fisk et al., Chap. 14, this volume). Filtered formation water from this same site had low cell abundance, suggesting that there is not a large microbial population in the formation water sampled at this site.