Holocene relative sea-level rise of the Delaware Estuary, USA

Holocene relative sea level (RSL) rise of the mid-Atlantic United States is dominated by two processes: ice-equivalent sea-level changes and Glacial Isostatic Adjustment (GIA) driven vertical land motion. Interpreting Holocene RSL processes in the Delaware Estuary is limited by the availability of RSL data: just 26% of 49 published sea-level index points (SLIPs) were older than 3000 years BP. Here, we extend the RSL history of the Delaware Estuary by combining new, unpublished, and published data. We produced four new SLIPs using foraminiferal data and radiocarbon dates from offshore cores in the Delaware Estuary. We used sea-level indicators and radiocarbon dates to create 14 SLIPs from unpublished data. The Delaware sea-level database now contains 67 SLIPs, with 24 older than 3000 years BP. We quantified the magnitude and rate of RSL rise over the Holocene using an Error-In-Variables Integrated Gaussian Process (EIV-IGP) model. We show a 15 m rise over the past 7000 years with variable rates of RSL rise. The rate of rise during the 20th century is the fastest rate for the last 4000 years. We compared RSL changes of Delaware with data from New Jersey and a suite of 1D and 3D GIA models. The 1D GIA models generally fit the mid- and late-Holocene RSL data, but misfit the oldest SLIPs. The 3D GIA model provides the best fit, predicting an RSL of −21.4 ± 4.4 m at 7000 years BP, with the upper bound aligning with our oldest SLIPs. Comparisons with New Jersey EIV-IGP models reveal similar magnitudes and rates of change, but with a temporal offset of ~1000 years, likely due to local processes or artifacts of the models. The additional SLIPs for the Delaware Estuary extend and improve the RSL record and provide further data for refinement of GIA models in the mid-Atlantic region. © The Author(s) 2025