In many coastal settings worldwide, the distribution of freshened water within continental shelf sediments is far out of equilibrium with modern sea level. One of the most remarkable examples is found on the Atlantic continental shelf off New England, where groundwater within shallow Pliocene–Pleistocene sand aquifers over 100 km offshore has low salinity (3000 mg/L or less). Analyses of samples and data from IODP³–NSF Expedition 501 drill sites on the Atlantic continental shelf off Martha’s Vineyard (Massachusetts, USA) will provide information and constraints necessary to extend our understanding of the current and past states of fluid composition, pressure, and temperature in continental shelf environments. The analyses will also help better constrain rates, directions, and mechanisms of groundwater flow and chemical fluxes in continental shelf systems. In addition, the apparent transient nature of continental shelf salinity patterns could have important implications for microbial processes and long-term fluxes of carbon, nitrogen, and other nutrients to the ocean.

This volume of the Proceedings of the International Ocean Drilling Programme includes the Scientific Prospectus and scientific and engineering results of IODP³–NSF Expedition 501, as well as post-expedition scientific outcomes after completion of the operations.