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    Evolution of the Fundy Tides
    From: Trevor Kenchington
    Date: 2004 Jan 3, 17:25 +0000

    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
                          http://home.istar.ca/~gadus
    
    
    

       
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