Porewater chemical data from seafloor, Deep Sea Drilling Program, and Ocean Drilling Program cores provide information about diagenetic processes, ocean chemistry, and climatic history. In environments away from plate or continental margins, it is generally assumed that diffusion is the primary process controlling chemical profiles in sediment. In this study, we test that assumption by modelling of preservation of bottom water salinity changes from the last glacial maximum. A coupled fluid flow and transport finite-element code (SUTRA) was used to examine how the processes of diffusion, convection, sedimentation, and loading due to sea-level change impact the porewater salinity profile. In the model, the bottom water salinity was increased from 0.0035 to 0.0036 for 100 ka, as sea-level declined 120 m during glaciation. During the subsequent, 20 ka of deglaciation, the salinity was assigned to return to 0.0035. Diffusion of the changing bottom water salinity creates a peak of salinity within the sediment. However, high rates of sedimentation can significantly modify the porewater salinity profile. Sedimentation shifts the diffusive boundary condition, causing the modeled salinity peak to be slightly deeper in the sediment column and greater in magnitude. In general, the effect caused by the moving boundary condition is more significant than the fluid flow driven by convection, loading due to sedimentation, or loading due to sea-level changes.