Salt-marsh aggradation in response to late-Holocene sea-level rise at Amherst Point, Nova Scotia, Canada

Abstract

A radiocarbon 14C chronology determined for plant macrofossils in exposed salt-marsh sediments at Amherst Point, Nova Scotia, Canada, shows that the edge of the high salt marsh aggraded 7.5 m since 900 BC, equivalent to a mean rate of 25.9 cm 100 yr-1. Four phases of rapid aggradation (900–600 BC, 100 bc– AD 200, AD 700–1100, and AD 1600 to present) were interspersed with three phases of slower aggradation (600– 100 BC, AD 200–700, and (tentatively) AD 1100–1600). The stepped pattern of marsh aggradation probably resulted from eustatic sea-level fluctuations superimposed on background signals of crustal subsidence and tidal-range expansion. Because the rate of high salt-marsh aggradation lagged or exceeded the rate of higher high water (HHW) increase at various times, the high salt-marsh aggradation trend only approximates the trend of HHW increase. The eustatic sea-level fluctuations are estimated to have a range of at least 0.8 m.