Within-region replication of late Holocene relative sea-level change: An example from southern New England, United States

Tide-gauge measurements in the western North Atlantic Ocean show coherent, multi-decadal relative sea-level (RSL) trends across multiple spatial scales. Proxy reconstructions developed from salt-marsh sediment can extend this instrumental record. However, the degree of coherence in proxy reconstructions is underexamined through within-region replication. To explore within-region replication, we developed a new RSL reconstruction from Fox Hill Marsh, Rhode Island to complement similar records at nearby sites. We established the elevation of former sea level from assemblages of foraminifera and bulk-sediment δ13C values using a Bayesian transfer function. We employed radiocarbon dating and recognition of pollution horizons to construct a core chronology. Since ∼1200 BCE, RSL rose by ∼3.7 m at Fox Hill Marsh. After correction for glacial isostatic adjustment, application of a statistical model intended to quantify (multi-) century-scale trends showed that the fastest rate of rise in at least the past 3000 years was 1.71 ± 0.84 mm/yr (95% credible interval) in 2020 CE. This result replicates regional tide-gauge measurements and other proxy reconstructions. Using an alternative statistical model constructed to identify sub-centennial sea-level changes, we examined if there was a hotspot of 18th century rise in the northeastern United States and found no spatially-coherent trend (i.e., occurring at all or most sites). This lack of replication indicates that accelerated rise during the 18th century is likely local (site-specific) in scale, or an artifact of individual reconstructions. Continued efforts to replicate RSL reconstructions will increase confidence in the accuracy of records and their subsequent interpretation. •Proxy reconstructions are used to investigate late Holocene relative sea-level changes in southern New England.•A new relative sea-level record from Fox Hill Marsh, Rhode Island, documents ∼3.7 m of rise since ∼1200 BCE.•The fastest century-scale rate of sea-level rise in at least the past 3000 years was 1.71 ± 0.84 mm/yr in 2020 CE•We find no spatially-coherent trend supportive of an 18th century hotspot of sea-level rise in the northeastern United States.•Accelerated 18th century sea-level rise at some sites is likely local in scale, or an artifact of individual reconstructions.