What is causing the annual variations in sea level in the Florida Keys?

In summary, the author is offering a theoretical possibility that tides may be affected by a variety of factors other than global warming, and provides a list of possible contributing factors.
  • #1
anorlunda
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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.
 
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  • #2
Tides are complicated interactions between the oceans and the moon and the sun. Less predictable are the effect of sustained wind on water levels.
 
  • #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.
 
  • #4
rocket7777 said:
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.

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]
 
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  • #5
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.
 
  • #6
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.”

http://www.usgs.gov/newsroom/article.asp?ID=3256&from=rss_home
 
  • #7
SW VandeCarr said:
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]


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.
 
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  • #8
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.
 
  • #9
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.
 
  • #10
anorlunda said:
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.

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://www.annualreviews.org/doi/abs/10.1146/annurev-marine-120308-081105

http://www.epa.gov/climatechange/science/indicators/oceans/sea-level.html

http://tidesandcurrents.noaa.gov/sltrends/sltrends.shtml

http://tidesandcurrents.noaa.gov/sltrends/

http://www.cnn.com/2012/10/02/tech/satellites-sea-level-rise/

http://wattsupwiththat.com/2013/07/...levels-rising-less-than-7-inches-per-century/

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

http://fl.usharbors.com/florida-tide-charts

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
 

1. What is the main cause of prolonged sea level changes?

Prolonged sea level changes are primarily caused by changes in the Earth's climate. This can be due to natural factors such as fluctuations in solar radiation or volcanic activity, or human-induced factors like greenhouse gas emissions.

2. How do scientists measure prolonged sea level changes?

Scientists use a variety of methods to measure prolonged sea level changes, including satellite altimetry, tide gauges, and sediment core analysis. These methods provide data on changes in sea level over time, allowing scientists to track long-term trends and patterns.

3. What are the potential impacts of prolonged sea level changes?

Prolonged sea level changes can have significant impacts on coastal communities, including increased flooding and erosion, loss of biodiversity, and displacement of populations. They can also affect global ocean circulation and climate patterns.

4. Are prolonged sea level changes reversible?

While some sea level changes are reversible, prolonged sea level changes can have long-lasting effects that are difficult to reverse. For example, melting of ice sheets can contribute to sea level rise for centuries, even if emissions are reduced and temperatures are stabilized.

5. How do scientists predict future sea level changes?

Scientists use computer models and climate projections to predict future sea level changes. These models take into account factors such as melting of ice sheets, thermal expansion of seawater, and changes in ocean currents to provide estimates of how sea levels may change in the future.

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