IMPACT OF THE HOLOCENE TRANSGRESSION ON THE ATLANTIC COASTLINE OF NOVA-SCOTIA

As analogs for impact of a future sea-level rise on the coast of Nova Scotia (eastern Canada), geological data and information on relative s ea-level changes are examined at three different time scales. Relative sea level rose swiftly during the early Holocene, at a maximum rate o f 11 m/ka at 7500 radiocarbon years BP. Freshwater, salt-marsh, and es tuarine sediments that formed during this period have been located on the inner shelf. After 5000 BP the rate slackened to about 2 m/ka. Des pite overall submergence and coastal retreat since that time, gravel b arriers have persisted where large amounts of sediment have been added to the littoral system by erosion of glacial deposits. The barriers o ften display evidence of early progradational phases in the form of gr avel beach ridges, partly or wholly submerged in lagoons behind contem porary storm beaches. Tide-gauge data from the post century show subme rgence rates averaging 3.5 mm/a, well in excess of the longterm trend. The response of the coastline to this rapid rise is complex. Unconsol idated cliffs (bluffs) retreat at up to 5 m/a during initial exposure to wave attack and during extreme storm events, but at lesser rates (< 0.5 m/a) as protective beaches, lag shoals or boulder frames accumulat e at the base of the cliffs. Beach retreat rates are sometimes very hi gh (>8 m/a) in some locations, but low elsewhere, in some cases showin g almost no movement over the past 10 years, and neighbouring beaches are sometimes observed to behave in completely different ways. Sedimen t released by coastal erosion finds its way into nearby estuaries, cau sing growth of flood-tidal deltas and marsh aggradation. If a global r ise in sea level occurs, the processes of erosion and sedimentation op erating along the coast of Nova Scotia during the Holocene are expecte d to continue in a similar fashion, but rates of change will increase at many locations.