The North Atlantic Ocean plays a critical role in regulating regional and global climate by influencing the transport of heat and salt through the ocean system. This region has undergone dramatic climate shifts, including abrupt warming and cooling events linked to ice sheet growth and changes in deep ocean circulation. Such variations have altered the movement and storage of heat, salt, and carbon in the deep ocean, affecting Earth’s climate over both short and long timescales.

IODP³ Expedition 506S seeks to integrate sediment core data from key legacy sites recovered by deep-sea drilling expeditions across the North Atlantic. Since no single location can fully capture the complexity of past climate change, a major goal of IODP³ Expedition 506S is to align data from multiple drill sites to develop a comprehensive regional record. The Expedition 506S Science Team will create and apply advanced computational tools for signal alignment and image analysis, enabling more precise and higher-resolution correlations of climatic signals than previously possible.

This volume of the Proceedings of the International Ocean Drilling Programme includes the Scientific Prospectus and scientific results of IODP³ Expedition 506S.

Ontong Java Plateau (OJP) is the largest oceanic plateau on Earth. Collision of OJP with the Solomon Islands arc halted subduction north of the arc, transferring the arc to the Pacific plate and initiating subduction on the southern side of the arc. The OJP–Solomons collision is regarded as the textbook example of subduction reversal. However, competing hypotheses for the collision invoke major differences in the timing and nature of events, with significant implications for modelling of the subduction reversal process.

Previous scientific drilling recovered cores at multiple sites on OJP. The Eocene to Miocene sequence in these cores hosts multiple volcanic ash layers, as well as numerous cryptotephras, disseminated ash, and aeolian sediments. The occurrence of these ashes has been interpreted to reflect proximity of OJP to the arc, but this has not been tested geochemically, and the ashes may represent arc, hot-spot, or mixed sources. International Ocean Drilling Programme (IODP³) Expedition 504S will analyse the ashes, cryptotephras, and aeolian materials. Determination of the provenance of the ashes will allow a test of competing subduction-reversal scenarios. Knowledge of the ash sources will also provide new constraints on wind strength and direction in the equatorial Pacific during the late Eocene to early Miocene, spanning the strengthening of the East Asian Monsoon. Cryptotephras and aeolian sediments will contribute supporting evidence of wind system reorganisation over this time.

This volume of the Proceedings of the International Ocean Drilling Programme includes the Scientific Prospectus and scientific results of IODP³ Expedition 504S.

Hadal oceanic trenches, such as the Japan Trench, are the deepest places on our planet. They form due to downward bending of subducting ocean crust along subduction zones; act as terminal sinks for sediment, particulate, and dissolved organic carbon; and form high-resolution archives to unravel the history of subduction zone processes including subduction megathrust earthquakes and tsunamis.

The International Ocean Drilling Programme (IODP³) Expedition 503 drill site recovers the whole trench-fill sequence in the central Japan Trench to date and establishes event stratigraphy for paleoseismologic interpretations and further investigations of earthquake-related element cycles in hadal trench environments. Unravelling the complete trench-fill sedimentary record and pore water profile will significantly advance our understanding of the nature and recurrence of hadal trench tsunamigenic slip and the underlying megathrust earthquakes and related geohazards, as well as the effects on enhancing carbon accumulation in the hadal trench that may stimulate carbon transformation and eventual export into the subduction zone.

This volume of the Proceedings of the International Ocean Drilling Programme includes the Scientific Prospectus and scientific and engineering results of IODP³ Expedition 503, as well as post-expedition scientific outcomes after completion of the operations.

International Ocean Drilling Programme (IODP³) Expedition 502 explores the nature of the acoustic basement in the outer-rise area of the northwest Pacific subduction system, where the sediment layer above it is unusually thin. The acoustically thin sediment cover is thought to be attributed to basalt sill intrusions or sheet lava extrusions in and on the pelagic sediment package by basalts fed by petit-spot magmatism. Petit spots are a recently discovered volcanic system characterized by highly alkalic and CO₂-rich basalt that is generated by a low degree of partial melting of the asthenosphere.

The goal of IODP³ Expedition 502 is to determine if this volcanic activity is more widespread than previously thought. If confirmed, it could significantly influence how subduction zones work, including earthquake processes, volcanic activity, and global chemical cycles. Moreover, it will help understand the role of petit-spot magmatism and its impact on the Earth's systems.

This present volume of the Proceedings of the International Ocean Drilling Programme includes the Scientific Prospectus and scientific and engineering results of IODP³ Expedition 502, as well as post-expedition scientific outcomes after completion of the operations.

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.