These highlights from ODP Leg 165 emphasize the value in addressing the aqueous geochemical aspects of deep-marine sediments within a well-constrained, integrated context. By defining the system carefully in terms of both solid and dissolved species of varying concentrations and reactivities, the downcore distributions of a wide range of interstitial components are qualitatively and perhaps at least semiquantitatively interpretable with regard to rates and styles of sequestration and release. The above results, although only highlights, document the complex interplay among reactive carbonate phases, alteration of volcanic ash occurring as discrete layers and as a dispersed fraction within the host sediment, and alteration of the crystalline basement. Biogeochemical processes overprint many of the constituents as a function of the reactivity and availability of solid organic phases and, possibly, secondary hydrocarbon enrichments controlled by the physical properties of the sediment. In general, the sediments at Sites 998, 999, 1000, and 1001 are characterized by low levels of organic carbon and, correspondingly, microbial redox pathways dominated by suboxic process and low modeled levels of sulfate reduction. However, concentration and isotope relationships for sulfur, when viewed in conjunction with trace metal distributions, suggest that basinal fluids may epigenetically overprint permeable ash layers and associated sediments in tectonically active deep-sea settings such as Site 999. Finally, a better mechanistic understanding of these diverse processes further constrains the global mass balances for a wide range of major and minor components of seawater.