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With apologies for straying very far off topic:

A few days ago, Frank Reed queried a statement of mine about the
changing sea levels in Atlantic Canada and I warned that my reply should
not be considered as fully reliable. I have now checked the latest
published research  and discovered that things are a whole lot more
complicated than either Frank or I had suggested (no surprise there!).

Shaw et al. (2002, Quaternary Science Reviews vol. 21, pages 1861-1878)
have summarized the (limited and scattered) available data, with a large
dose of interpolation added in, to produce maps of both the shorelines
and the height of contemporary sea levels (relative to modern sea level)
  for most 1,000-year intervals between 13,000 and 6,000 years ago.
[Trends from 6,000 to now seem to have been fairly steady.] Their maps
cover southern Labrador to Cape Cod.

{There is a very brief, semi-popular account of the same research on the
Web at:
http://www.mar.dfo-mpo.gc.ca/science/review/e/html/2001/BIO-English.html
That account is also available in hard copy in the Bedford Institute of
Oceanography's "2001 In Review".}

In the past 13 millennia, most coastal and offshore areas in this region
have first moved up and then down, though some have dipped consistently.
The zero line, where contemporary sea level was the same as modern sea
level, has moved over time and is by no means straight. Hence, this is
_not_ a matter of the continent tilting around a simple hinge line.

In overly-brief summary: The Atlantic coast of Nova Scotia has been
dipping downwards continuously for about 11,000 years. However, New
Brunswick and the New England coast rose quite considerably at first --
the current shoreline rising out of the water. (That included my
half-remembered case of southern New Brunswick rising, though I
mistakenly supposed that the uplift was continuing.) What is now Georges
Bank rose out of the sea, forming a large peninsular attached to Cape
Cod, before dipping again.

Through the last 10,000 years or so, the zero line (contemporary sea
level equal to modern sea level) has roughly followed the coast of Maine
and extended southwest across Massachusetts. Nova Scotia, southeastern
Massachusetts and the offshore areas have been dipping. Inland parts of
New England have been rising. However, somewhere in New Brunswick, the
zero line turns northwest to near the St.Lawrence river, then loops
round eastwards to Newfoundland, before running north up the Labrador
Sea. Thus, much of New Brunswick, most of the Gulf of St.Lawrence and
southern Newfoundland are all dipping, whereas most of Quebec, Labrador
and northern-most Newfoundland are rising. (Where I am typing this has
dived some 40 metres into the sea in the past 10,000 or so years -- or
very roughly 5mm per year on average. The rate may have slowed somewhat
over the millennia but it is still fast enough for the effects to be
seen along the shore.)

The Bay of Fundy reached something like its present surface shape by
12,000 years ago. However, it is continuing to deepen, particularly on
its Nova Scotian side -- getting perhaps 10 metres deeper in the past
10,000 years. Perhaps more to the point, Georges Bank reached its
maximum emergence some 11,000 years ago. It then began to dip but did
not reach anything close to its present state until around 8,000.

Now that Shaw et al. have illustrated the change in basin shape and now
that numerical modelling of the Fundy tides is quite advanced, it would
be interesting to see how the resonant amplification of the semi-diurnal
lunar tide has developed over time. This really isn't a topic for
guesswork but I would not be surprised if there were no exaggerated
tides in the Bay until something in the bracket of 5,000 to 10,000 years
ago. Nor would I be surprised if the continued slow deepening is
gradually bringing the Bay closer to perfect resonance -- thus
accounting for the erosional features mentioned in earlier e-mails.



Hopefully, this is food for thought, even though not information of
practical value for navigators.



Trevor Kenchington


--
Trevor J. Kenchington PhD                         Gadus@iStar.ca
Gadus Associates,                                 Office(902) 889-9250
R.R.#1, Musquodoboit Harbour,                     Fax   (902) 889-9251
Nova Scotia  B0J 2L0, CANADA                      Home  (902) 889-3555

                     Science Serving the Fisheries
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