DIFFERENTIAL LATE HOLOCENE SEA-LEVEL CHANGE ON THE WEST COAST OF NEWFOUNDLAND?

Records of sea-level change from two sites on the west coast of Newfoundland indicate different trends for the late Holocene period. This differential sea-level change reflects, in part, the long-term glacioisostatic adjustment of the island. Previously published numerical models predict that sea-level histories will vary around the island due to glacioisostatic adjustment and the migration of collapsing marginal forebulge from southeast to northwest (Quinlan and Beaumont, 1981). Along the west coast, sea-level at the southern end has risen since the early Holocene, and at the northern end has fallen to present. To determine the detailed variation of late Holocene sea-level change in this region, we analyzed salt-marsh deposits at two locations. Cores and surface samples were collected along transects at a site on the Port-au-Port peninsula (southern west coast) and at St. Paul's Inlet (central west coast). We analyzed vegetation and foraminiferal assemblages of salt-marsh deposits. Detrital grass fragments from basal samples were submitted for AMS ¹⁴C dating. These fragments are associated with foraminiferal assemblages that indicate the range of paleo-elevation of the sample with respect to sea level. A series of data points based on these basal samples are used to construct sea-level histories for each location. At Hynes Brook, on the Port-au-Port peninsula, our data agree with previously published data indicating sea-level rise of during the late Holocene. At St. Paul's Inlet, the trend of recent sea-level change is different. We interpret preliminary data to constrain the transition from falling to rising sea level to between 1910 ± 100 to 1190 ± 120 ¹⁴C years. Both index points are close to each other in elevation (approximately 0.5 m apart), suggesting that sea level has been close to present for an extended period. These data support the hypothesis of differential sea-level change resulting from migration of a collapsing marginal forebulge. The differences in these sea-level histories will help constrain the magnitude of sea-level change associated with long-term glacioisostatic adjustment.