How do we know that sea level has changed?
GSC researchers and their colleagues in universities and provincial geological survey departments have collected information that reveals how sea levels have changed since the end of the last ice age in Atlantic Canada. Trees and other organic remains found below modern sea level show that sea level has risen. On the other hand, beaches found at high elevations and far inland provide evidence of falling sea levels (see geographic change after 13,000 years).
Sea levels have always changed, and are changing now. Because of human intervention in the climate system, they may change more quickly in the near future.
Submerged tree stumps on Poverty Beach, Prince Edward Island. Sea level was below the modern level when they were alive.
The age of tree stumps such as these can be determined using the radiocarbon dating technique. Recently, divers found rooted trees 11 m below sea level at the mouth of Halifax Harbour. A sample of wood was dated at 4150 radiocarbon years before present. The calibrated age shows that there is a 68% probability that it grew between 2880 and 2620 BC.
A geologist from the GSC is taking samples from a cliff cut in the salt marsh at Amherst Point, NS. The mud cliff is about 8 m high and contains the layered remains of salt-marsh plants. The plant layers indicate that the high water level has risen nearly 8 metres over the past 3000 years.