ABRUPT SEA-LEVEL CHANGE AND POSSIBLE LINKS TO CLIMATE VARIABILITY AROUND 2,900 YEARS AGO

We cored Holocene deposits on Cedar Island (southern Pamlico Sound) and in Jarrett Bay (Core Sound) North Carolina in an effort to augment the regional sea level record. The continuous Late Holocene saltmarsh peat at these sites rarely extends deeper than 2.5 m below present mean sea level, and calibrated age ranges for basal saltmarsh radiocarbon dates tend to be younger than 2,800 cal years BP. The basal stratigraphy of many cores suggests that an interval of rapid transgression, followed by minor regression, occurred shortly before the marshes became established. The establishment of marshes in response to slowing sea-level rise around 3 ka is well known (cf. Rampino & Sanders, 1981, Geology 9:63-67), but to explore the stratigraphic oscillation, we analyzed the East Coast sea-level database published by Engelhart et al. (2011, Geology 39:754-751).

Sea-level index points from the interval 3.8 to 2.4 cal ka were vertically adjusted using the local subsidence rates to remove the effects of glacial isostasy. The adjusted sea level elevations imply that global ice volume was near that of the present by around 3.6 cal ka. Notwithstanding the elevation and age errors, the regionally adjusted data hint at a minor sea-level oscillation along the East Coast, rising until 3 cal ka, followed by a slight sea-level fall until 2.7 cal ka. The hypothesized oscillation in sea-level also is supported by the temporal distribution of sea-level index points in the database. Saltmarsh index points are nearly twice as abundant from 3.5 to 3.0 cal ka (n = 29) compared with the interval from 3.0 to 2.5 cal ka (n = 15). A reduction in accumulation and preservation of marsh peat deposits in the latter interval could explain the uneven distribution; the radiocarbon plateau around this time cannot fully explain the pattern. The hypothesized sea-level oscillation spans an interval during which proxy records show abrupt northern hemisphere cooling and a reduction in meridional overturning circulation in the North Atlantic. The regional sea level changes ~2.9 cal ka likely resulted from dynamic and steric effects, as well as minor ice volume changes. The coastal response to this climate event provides insight for adapting to the sea-level changes that will accompany future climate change.