RESPONSE OF NORTHERN TIDAL MARSHES TO SEA LEVEL CHANGE

The Quaternary glaciation of northern coasts has caused them to have a complex sea level history that largely has been revealed through study of tidal marsh deposits. Observations of changes in tidal marshes from Canada’s James Bay and eastern coastline, south to the Gulf of Maine give us an indication of ecological changes, rates of change and geological indicators of the change in both regressive and transgressive situations. Sea water temperatures are probably similar to those experienced by tidal marshes that occurred on more southern coasts during the last glacial maximum. Thus, study of these northern tidal marshes provides insight into wetland evolution that likely occurred during the early Holocene along paleo-coastlines now buried under bogs in northern Canada or submerged on the continental shelves along the mid-Atlantic coast of the United States. On the coast of James Bay, where isostatic rebound is still occurring, new tidal marshes can be observed forming over a human lifetime while transition of older marshes to freshwater fens can occur over the same period. The coast of the Bay of Fundy in the Gulf of Maine is transgressive but short term regressions do occur, resulting in shifts in vegetation zones. These changes can be indicated by palynological indicators in marsh deposits, but the rapidity of responses we observe suggests that to detect them in organic-rich deposits compressed over thousands of years requires fine scale sampling.