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article, a change of 1 mm</DIV><DIV style=3D"marg There has been quite a bit of discussion about whether Nova Scotia is either sinking or rebounding relative to the our somewhat mythical "sea level". The answer of course is yes! Sea level has been rising world wide over the last 20,000 years, this has nothing to do with the efforts or sins of mankind, but the really sobering thought is that man induced changes are only making it worse and apparently changing the rate of that increase. Locally in the Bay of Fundy, the height of the sea relative to the land had been rising steadily by almost 40 centimetres every century, that may well be now increasing. Isostatic changes caused by the removal of the huge weight of the glacial ice has also had a major effect in this region. The ice was apparently thickest in the region between the New Brunswick shore and the Digby Neck area, the land here being depressed some 140 metres. The sea level at the time was about 100 metres lower than at present - this accounts for the raised beaches at about 40 metres elevation found along Digby Neck. This rebound now being largely over, most of Nova Scotia is currently sinking. Geodetic levelling has shown that the Truro region has subsided about 30 Centimetres and the rest of the region by about 20 centimetres. You can see that effect in the submerged forests near Grand Pre, Yarmouth and elsewhere. As the sea level has been increasing by about 10 cm per century, the remainder of the change is due to subsidence. Another sobering consideration is the fact that the famed Bay of Fundy tides were absolutely normal when all the deepening of the local water began after the last ice age. Magnification of the tides caused by the shape of the Bay, has itself increased over the years. I have no knowledge about whether the tidal enhancement process has reached its peak but that would seem unlikely, so a small increase in relative sea level could cause a larger increase in our already inflated tides. Yet more changes to deal with! Deeper water brings stronger waves closer to the coast and more storm damage. Parts of the Minas Basin are already eroding by about 1 metre per year - hence all the silt in the water. You can reasonably expect that to get worse. The notion of sea level is a locally determined convenient point from which to measure other things, such as depths, heights, relative elevations and the form of the terrain. It is found by measuring the rise and fall of the ocean at tide gauge stations over a period of 19 years and averaging the fluctuations recorded. It is an average figure, there is nothing absolute about it and it will vary from place to place with the shape of the Earth. It is constantly fluctuating and considerably varied. Sea level in Maine is 38 mm higher than in Florida. If you want to use a GPS for elevations you have to take and adjust for local variations otherwise your figures will not bear much resemblance to reality. When our maps say things like "elevations are based on mean sea level" we are not all using the same standard, merely a convenient approximation. Sea level has now been shown to contain hills and valleys, smaller but similar to those found on land, due to gravitational variations and other factors. Some advanced radar satellites now use the "bumpy" surface of the sea to tell us the shape of the ocean bottom hidden far below in a manner we have never seen before. Hopefully this is a little clearer than Fundy mud!
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