A Preindustrial Sea‐Level Rise Hotspot Along the Atlantic Coast of North America

The Atlantic coast of North America north of Cape Hatteras has been proposed as a “hotspot” of late 20th century sea‐level rise. Here we test, using salt‐marsh proxy sea‐level records, if this coast experienced enhanced sea‐level rise over earlier multidecadal‐centennial periods. While we find in agreement with previous studies that 20th century rates of sea‐level change were higher compared to rates during preceding centuries, rates of 18th century sea‐level rise were only slightly lower, suggesting that the “hotspot” is a reoccurring feature for at least three centuries. Proxy sea‐level records from North America (Iceland) are negatively (positively) correlated with centennial changes in the North Atlantic Oscillation. They are consistent with sea‐level “fingerprints” of Arctic ice melt, and we therefore hypothesize that sea‐level fluctuations are related to changes in Arctic land‐ice mass. Predictions of future sea‐level rise should take into account these long‐term fluctuating rates of natural sea‐level change. Plain Language Summary Measurements of sea‐level change have shown that during the 20th century sea‐level rise along the Atlantic coast of North America between Cape Hatteras and Nova Scotia has been faster than the global average. We investigated whether this anomaly also occurred earlier by reconstructing historical sea‐level changes from salt‐marsh sediments and microscopic salt‐marsh fossils (foraminifera). We found evidence in three locations (Nova Scotia, Maine, and Connecticut) for rapid sea‐level rise in the 18th century, which was almost as rapid as the 20th century sea‐level rise. Using additional sea‐level reconstructions from across the North Atlantic, we propose an explanation for the periods of enhanced sea‐level rise. We hypothesize that they occur during distinct phases of the North Atlantic Oscillation and during periods of enhanced ice melt in the Arctic. The fluctuations are a reoccurring feature and should be considered in planning for future sea‐level rise and coastal hazards. Key Points An episode of rapid sea‐level rise occurred in the 18th century along the Atlantic coast of North America (Nova Scotia to Cape Hatteras) The 18th century and previously identified 20th century hotspots occur in similar geographic regions We hypothesize that these centennial sea‐level changes are related to variations in Arctic land‐ice mass