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Prolonged Sea Level Changes

  1. Nov 10, 2013 #1


    Staff: Mentor

    In southern Florida, and especially in the Florida Keys, there are some very shallow areas that make it very obvious how low low-tide is. I'm stumped to notice that there seems to be significant variations from year to year.

    For example, an area we call the flats is normalls under six inches of water at low tide. A few years back, it was high and dry at nearly every low tide for seven months. This year is the opposite, and everyone in Southern Florida is talking about unusually high tides.

    I understand spring tides and neap tides. I understand how large weather patterns out to sea can push water one way or the other for weeks at a time.

    But I find it hard to imagine anything that would change average high/low tides over periods as long as six months to a year, or that we should have high water years or low water years. No I do not believe it is due to global warming; the changes are much too fast for that.

    I'm talking about local changes on the scale of perhaps 500 miles in diameter, and I'm talking about annual variations in the average high/low of perhaps 15 cm.

    El niño like effects on sea level???

    The wikipedia article on sea level talks about several reasons for variations but only The Chandler wobble (astronomical) with a 14 month period fits the time scale. No clues in the article about the magnitude of the Chandler wobble's effect on sea level.

    I'm stumped for an explanation.
  2. jcsd
  3. Nov 10, 2013 #2


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    Tides are complicated interactions between the oceans and the moon and the sun. Less predictable are the effect of sustained wind on water levels.
  4. Nov 15, 2013 #3
    Since you did not specify accurate dates I assume you did not take sun's tidal affect.
    "El niño like effects on sea level??? " might have some sort of thermal expansion of water; different current; or winds.
    One other thing is moisture in air and where it rains might have some impact. For example if east have drought vs heavy flood that year, it probably have some impact too.
  5. Nov 15, 2013 #4
    Heavy rains and floods or drought are not likely to have impacts on tide levels. However, barometric pressure and prolonged winds from one direction can have significant short term effects on local tides. As already discussed, there are also significant monthly and seasonal effects on tides.

    http://www.bom.gov.au/oceanography/tides/met_effects.shtml [Broken]
    Last edited by a moderator: May 6, 2017
  6. Nov 15, 2013 #5


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    Throw in lunar precession, seiches in the Caribbean, Gulf, and Atlantic basins, and you can throw sea level around by tens of centimeters with very little difficulty; you want a tide table that includes effects beyond lunar precessions, it probably doesn't exist.
  7. Nov 16, 2013 #6


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    Although this report does not mention the Keys, it seems plausible that your local tidal extremes may indeed be affected by a variety of effects.

    "Sea Level Rise Accelerating in U.S. Atlantic Coast"
    Released: 6/24/2012
    Excerpt: "Many people mistakenly think that the rate of sea level rise is the same everywhere as glaciers and ice caps melt, increasing the volume of ocean water, but other effects can be as large or larger than the so-called 'eustatic' rise," said USGS Director Marcia McNutt. "As demonstrated in this study, regional oceanographic contributions must be taken into account in planning for what happens to coastal property."
    Though global sea level has been projected to rise roughly two-to-three feet or more by the end of the 21st century, it will not climb at the same rate at every location. Differences in land movements, strength of ocean currents, water temperatures, and salinity can cause regional and local highs and lows in sea level.”

  8. Nov 20, 2013 #7

    First, australia is not really good location to start generalization about local tidal information in florida.
    For example, rain trap pattern, snow, somewhat trapped gulf of mexico.

    Second, I am offering THEORETICAL possibility without regard to actual magnitude of contribution.
    Mississippi river had high(hurricane katrina) and low(drought) with in few years. Also, it take time for water to completely mix with average ocean water. Also water is lighter than ocean water, so like tip of iceburg it can be higher level. So both volume and density will be contributing factor.
    I would suspect water is cooler than average florida coastal ocean water plus extra cloud probably have impact on temperature.

    So unless I see regional simulation with all the factors included, I do not see much reason to not believe theoretical possibility of relevant (even 1cm) contribution.
    Last edited by a moderator: May 6, 2017
  9. Dec 11, 2013 #8


    Staff: Mentor

    I sould like to rephrase the question. Is there a source of data for sea levels in various ocean regions covering several years?

    If I had that data I could calculate means and deviations myself.
  10. Dec 11, 2013 #9


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    There are tide gauges with records going back centuries, at places such as the Netherlands where that really mattered.
    NASA and NOAA as well as the US Navy have active sea level monitoring programs, check their web sites.
    Do note the topic is quite contentious, as the sea levels fluctuate around the globe and it is difficult to distinguish that from possible permanent changes. However, there seems to be a consensus that sea levels are rising by a couple of millimeters per year, with no big change in that rate over the past century.
  11. Dec 11, 2013 #10


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    You may visit the below sites for source data for sea levels in various ocean regions covering several years: (I added in some specifics for the Florida Keys: Boca Raton)

    “We first present sea level observations from tide gauges over the twentieth century and from satellite altimetry since the early 1990s.”






    http://fl.usharbors.com/monthly-tides/Florida-Lower Keys/Boca Chica Marina/2012-05


    Boca Chica Marina Tides - May/2012 24°35'N 81°42'W - See more at: http://fl.usharbors.com/monthly-tid...oca Chica Marina/2012-05#sthash.SWckEwX9.dpuf
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