DIFFERENTIAL LATE HOLOCENE SEA-LEVEL CHANGE AROUND NEWFOUNDLAND: SALT-MARSH AND TIDE GAUGE RECORDS

Analysis of basal salt-marsh peats and tide gauge data from several locations around Newfoundland provide data critical for constraining differential late Holocene sea-level change. Sea-level trends from the mid- to late Holocene are not well developed, but are important to determine for linking well-studied early Holocene trends to historical data indicating continuing differential sea-level change. Surficial peat samples collected at four locations (Hynes Brook, Port-au-Port Peninsula; St. Paul's Inlet; New World Island; and Placentia, Avalon Peninsula) yield different foraminiferal assemblages and zonations at each location. These modern zonations are used to determine a paleo-elevation range for each basal peat sample. Coupled with an AMS ¹⁴C date, this becomes an index point on a high-resolution sea-level change reconstruction. Surficial samples collected from the backbarrier environment Deadman's Bay did not yield any foraminifera, although a limited number of species are abundant in some basal samples at this location. Initial results indicate late Holocene sea-level trends are not always comparable to trends determined from tide gauges. Salt-marsh stratigraphy at Placentia (Avalon Peninsula) suggests a slightly slower rate of rise during the late Holocene than the trend indicated by two nearby tide gauges. At Hynes Brook, on the west coast, long-term sea-level rise interpreted from salt-marsh stratigraphy has been about half as fast as the historic trend. To the north along this coast, tide gauges indicate a rapid change from rising to falling sea level. The hinge is presently located on the Northern Peninsula, but the stratigraphy at St. Paul's Inlet may have captured a recent (~1000 yr BP) transition from falling to rising sea level as the hinge line migrated to the northwest across the island. Identification of the timing and position of this hinge and differential late Holocene sea-level trends provide important constraints on numerical models predicting crustal isostatic responses to deglaciation.