Overview
IODP³ and the U.S. National Science Foundation (NSF) are collaborating in implementing Expedition 501: New England Shelf Hydrogeology. This call invites scientists in IODP³ Core and Associate Member nations and the US to apply to join the Expedition Science Team. Successful scientists for IODP³/NSF Expedition 501 will expand the current Expedition Science Team, which has largely been assembled through a previous Call for Scientists.

Opportunities exist for researchers in all specialties, but we are specifically seeking applications from scientists with expertise in aqueous geochemistry, hydrogeology, and physical properties. At a minimum, successful scientists will be granted access to expedition samples and data during the moratorium period, which starts during Offshore Operations (summer 2025), and ends 1 year after the conclusion of Onshore Operations (late 2026 or early 2027). Additionally, successful scientists can also be considered for participation in the Expedition’s Offshore and/or Onshore Operations. Applicants should identify the level of participation they seek.

Research proposals attached to applications will be considered if they strengthen the research plans and anticipated science output of the current Expedition Science Team. Therefore, proposals that address new objectives or use novel techniques and/or analytical methods are especially encouraged. Interested scientists should review the expedition’s background and objectives below and are strongly advised to contact the Co-Chief Scientists with an outline of their proposed research before submitting a full application.

The Co-Chief Scientists for this Expedition are Prof. Brandon Dugan (Colorado School of Mines, USA) and Prof. Karen Johannesson (University of Massachusetts Boston, USA).

The proposal upon which this expedition is based was submitted as IODP Proposal #637 “New England Shelf Hydrogeology.” The proposal describing the primary drill sites, as well as up-to-date expedition information and the published Scientific Prospectus, can be found on the Expedition 501 webpage. You may also find it useful to consult Gustafson et al. (2019) and Siegel et al. (2014).

In many coastal settings worldwide, the distribution of freshwater 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). On Nantucket Island, a 514m deep borehole penetrating the entire Cretaceous-Tertiary sedimentary package shows considerable variations in salinity with extremely fresh (<1000 mg/l) water in sand aquifers, higher salinity (30-70% of seawater) in thick clay/silt layers, and intermediate-to-low salinity in thin confining units.

IODP Expeditions 313 and 317 also showed abrupt freshwater-saltwater boundaries linked to lithology. This demonstrates the disequilibrium nature of such systems; diffusion tends to eliminate such patterns. Pore fluid within Pleistocene to upper Cretaceous sands beneath Nantucket Island is also found to be modestly overpressured, ~4m relative to the local water table.

We hypothesize that the rapid incursion of freshwater on the continental shelf in New England could have been caused by one or more of the following mechanisms:

1. 1. meteoric recharge during Pleistocene sea-level lowstands including vertical infiltration of freshwater associated with local flow cells on the shelf;
   2. sub-ice-sheet recharge during the last glacial maximum;
   3. recharge from pro-glacial lakes.

We further hypothesize that the overpressures could be due to:

1. 1. Pleistocene sediment loading;
   2. fluid density differences associated with emplacement of a thick freshwater lens over saltwater (analogous to excess pressures in the gas legs of petroleum reservoirs).

We argue these different recharge mechanisms and overpressure models can be distinguished through drilling, coring, logging, and fluid sampling. Noble gas and environmental isotope data will be necessary to completely evaluate recharge models.

This work will extend our understanding of the current and past states of fluid composition, pressure, and temperature in continental shelf environments. It will help better constrain rates, directions, and mechanisms of groundwater flow and chemical fluxes in continental shelf systems. It will contribute to the development of new tools for measuring freshwater resources in marine environments. 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. Successful drilling will test process-based models for shelf freshwater off New England. These models can then be applied to other shelf freshwater systems around the world.

U.S.-affiliated scientists interested in participating in this expedition should apply to sail through the U.S. Science Support Program – click here to review the application process and link to the USSSP Application Portal. The deadline to apply is January 31, 2025.

For questions, please email usssp@ldeo.columbia.edu.