Talk:Sea level

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Untitled[edit]

The first sentence (the part in brackets) is very difficult to parse - what is it trying to say by 'especially that halfway between...'?

Here's the sentence:

"Mean sea level (MSL) is the average (mean) height of the ocean's surface (especially that halfway between mean high and low tide); used as a standard in reckoning land elevation"

I guess it should read something like '(specifically the halfway point mean mean-high and mean-low tide') or something ? I am not a technical expert on this, but was trying to find out what is meant by 'sea-level' - so the first sentence threw me... —Preceding unsigned comment added by Monowiki (talkcontribs) 21:07, 19 November 2009 (UTC)

The relevance is that the tidal patterns will tend to be repeated over the course of these cycles, and that should give a better calculation of the mean. Eclecticology

I don't think the article should assert that global warming will cause further rises in sea level. That is only a theory, and a recent one at that. There is also a theory that rising atmosphere temperature will LOWER the sea level: hotter air => more evaporation => more snow at north and south pole => net movement of sea water into polar ice.

Let's leave the issue of causes to sea level rise. --Uncle Ed

See the talk of that page why the causes should be here. In short, causes of rise are related to causes for falling sea levels. --mav 23:28 Feb 7, 2003 (UTC)
I absolutely agree. Sea Level Rise is too politicized, representing a not very NPOV. Besides, it does not make sense to make people go to another entry to find out what effects sea level. GregBenson

I does not make sense to me that sea levels would be at their lowest in earth history if we are currently in an interglacial period, according to the exxon graph (or maybe I'm reading it wrong). It could be that plate tectonics pushing up mountains has created the effect of lowering sea levels. Time will tell. --Spyder Krabb

Conflicting/Bad information[edit]

Two things. 1) the first two paragraphs of the "Changes through geologic time" conflict. The first one says that we are quite close to the lowest level of all time. The next says that during the most recent ice age the sea level was 130 m lower than today. One of these is wrong.

2) the graph looks nice, but it is ambiguous. If it is charting the level then the right side should not read "change." As it is, however, the graph seems to _chart_ the "change" (for instance, if it is showing that in 2000 the change in sea level was 10% more than the change in sea level in 1999)

I was just wandering if sea level was: a. the average height of all HIGH tides for the last 19 years b. the average height of all LOW tides for the last 19 years c. the average height of all spring high tides d. the average height of all neap tides e. the same on all coasts of the U.S. please help if you know!!! ~student with help needed~


_______________________________________

If I understand the figure on eustatic sea level change properly, it's badly mixing units of time. The units of the x-axis are said to be in millions of years, yet the most recent glacial / interglacial transition is set to "20". Either the units are in millions of years and the black bar needs to be deleted, or the units are in thousands of years and the x-axis units need to be re-labeled. The most recent glacial / interglacial transition was not 20 million years ago. (Perid (talk) 23:26, 10 June 2008 (UTC))

The bar is there to indicate the scale of the last glacial change only, not the timing. As noted in the image description, rapid changes (even those of very large scales) are not easily captured in the geologic record. Dragons flight (talk) 23:38, 10 June 2008 (UTC)

Misleading Graphs[edit]

Portraying accurately the changes in sea level is confusing enough as it is without using graphs which mislead. The problem with the graphs shown is that the one entitled "Recent Sea Level Rise" displays a right-hand axis calibrated in Centimeters, whereas the graph entitled 'Post-Glacial Sea Level Rise" displays a right-hand axis calibrated in Meters. This makes it appear as though recent changes in sea level (over the past 100 years) are much more extreme than in fact they really are.

The data portrayed in both graphs actually appears to argue just the opposite, though. Using the periodic highs and lows expressed in METERS in the 'Post-Glacial' graph, it appears that the 19 CENTIMETER rise of the past 100 years (shown in the Recent Sea Level graph) is squarely within the highs and lows of the past six-thousand years (displayed in the Post-Glacial graph).

Since change over time in mean sea level is one of the prima facie pieces of evidence used by scientists when arguing for or against the popular theory of 'global warming' and whether or not the Earth is presently in an abnormal warming trend, wouldn't it be less confusing if the graphs compared 'apples to apples' rather than 'apples to oranges'? --Fungible 08:20, 5 January 2007 (UTC).

The lead graph shows a rise of 20 cm since 1880. That is 200 mm / 120 years, which is considerably lower than the 3 mm/year given by William Connolley. 200/120 = 1.7 which rounds to 2 (not 3).
Or we can calculate 19 cm since 1905, which is 190 mm / 100 years. That also rounds to 2 (not 3). Cheers. --Uncle Ed 14:35, 24 January 2007 (UTC)
3 mm/yr *from the satellites* few of which were around in 1880... I don't like adding a specific rate to the fig caption, since this obscures the changes William M. Connolley 15:47, 24 January 2007 (UTC)

Sea level rise[edit]

This article doesn't seem to say much about sea level rise. There is another article about it (much longer too), but shouldn't it at least be summarized here? At the moment they are treated as completely separate subjects. Richard001 23:20, 14 September 2007 (UTC)

Gravity or Gravitational[edit]

This article talks about a Gravitational anomaly when I think the author probably meant a Gravity anomaly. I hope someone who is watching this article with a little more knowledge than I have can correct it if neccesary and then create a Wikilink --Matt 07:06, 22 September 2007 (UTC)

I agree with your statement, Matt. I don't know if a gravity anomaly is implied in there, but for sure there's no intended reference to a gravitational anomaly. I have edited that piece in the article. But comments from experts are still welcome. --Pallida Mors 76 21:55, 8 November 2007 (UTC)

"Last Glacial Episode"[edit]

In the Global Sea Level Fluctuations figure there seems to be a significant error in the location of the black bar to show where the "last glacial episode" occurred. In the text it stated it occurred at 20,000 years, but on the graph it is positioned closer to 20 million years. Obviously an error in reading the x-axis.

Apart from the fact that the last glacial maximum ended around 12,000 years ago. Rolf Schmidt (talk) 05:07, 19 January 2009 (UTC)

MSL for aviators[edit]

As a pilot I don't think the discussion about airport height in the "Utilization section" is correct. On an instrument approach you can us a radar altimeter or an anaeroid altimeter set to the local barometric pressure at the airport (QNH). This information is transmitted either by the tower when you ask for clearance or from ATIS. Can this be corrected by someone or do I do it?MarkC (talk) —Preceding undated comment added 10:54, 15 April 2009 (UTC). "Go, ahead and add this information, but only if you have a source such as a manual that you can cite.  Andreas  (T) 12:50, 15 April 2009 (UTC)

Sorry, I can't see how to add it when the para is completely wrong and contrary to FAR 91.121. See http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgFar.nsf/3276afbe72d00920852566c700670189/da37f1d83828491d852566cf00615210!OpenDocument.

Height is set by local barometric pressure or when in the flight levels by setting ISA barometric pressure 29.92 inHg. I've therefore deleted it, the Wiki page on Altimeters has some useful info. Cheers MarkC (talk) 12:08, 16 April 2009 (UTC)

I've written a para with links about aviation that I think is useful to replace the one I deleted, but I'm not sure it really belongs in that section -I don't see the definition of MSL as a problem for pilots :) If another ed. wants to move it elsewhere that's fine by me.MarkC (talk) 13:04, 16 April 2009 (UTC)

Question on sea level[edit]

Hey...any sea level people out there know whether sea level is a given throughout the world and all land masses are measured relative to that, or is sea level marked differently on each coast...or does my second suggestion not even make any sense? DRosenbach (Talk | Contribs) 18:10, 21 April 2009 (UTC)

Both. The level of the sea determines where sea level is. If there is some gravitational anomaly in a region, nothing is done to compensate for it for many reasons, the biggest being that no one cares if the water is a little higher or lower than it would be without it. —EncMstr (talk) 22:20, 21 April 2009 (UTC)
Sealevel (measured e.g. to the ellipsoid that best approximates the shape of the Earth) can vary noticably from one part of the world to another, due to gravity, currents, weather, etc. For the purpose of mapping or surveying the land, each country will use a particular ordnance datum to define "sea level" - this would typically be defined by measuring the mean sea level at a particular point on their coast. For the purpose of hydrographic surveying and nautical charts, tide ranges and sea levels are measured at the location being charted, and water depths are (usually) measured relative to the lowest tide level rather than mean sea level. (This is because a mariner needs to know the minimum depth below the vessel). 62.172.108.23 (talk) 09:17, 24 April 2009 (UTC)

Sea Level (novel)[edit]

'Sea Level', is a not so very original title of a Novel by 'Roger King' about a young man coming to terms with the death of his Father, and susbsequent personal crises related to these changes...

It is also, merely by coincidence, the title of another fictional work by 'Earl Stanley Bradford' of Halifax, Nova Scotia, about young American and Western Canadian student emigres reciding in Eastern Canada between 1998 and 2007 - their experiences, coming of age, and coping with a string of strange natural and political catastrophes occuring around the advent of our new Millenium. A work in progress: 'Sea Level' by Earl Stanley Bradford. —Preceding unsigned comment added by 24.224.219.156 (talk) 16:50, 11 July 2009 (UTC)

WHy don't you start two articles about these novels?  Andreas  (T) 21:22, 11 July 2009 (UTC)

A Return to Phanerozoic Average Sea Level?[edit]

Might we be near the end of a large cyclical regression; not so different from Permian end regression? Statistically might it not seem more likely that we are due to revert at least towards an average of sea level for overall Phanerozoic, or even a further transgression? Might this be a natural underlying trend, independent of any superimposed anthropomorphic effect? Might we be headed for an Eocene/Paleocene world?

30 million years hence, what might our 'present' stratum (pl: strata) of say 10 million years look like? Might there be any evidence of mankind? For example, if we occupy the middle of such strata, then plus or minus 5 million years. For the past 5 million years, there was no effect. For the future 5 million years, transgression and Yellowstone's Western and Midwest repeated ash fallout would seem to reveal nature's dominant hand. For 200 meter elevation of sea level to less than Cretaceous peak, most of southern U.S. would be inundated, and likewise for eastern coast. The Seaway would flood and enlarge Great Lakes into an inland sea. All coastal cities, and inland lake ports would become reefs initially, and then dissolution. Humanity would would once again be on the move. Therefore, might there be no evidence of mankind's handiwork in such strata (stratum); not even hard plastic cherts? So from a geological perspective, mankind's impact on the environment might be quite negligible, in comparison to nature's broader, deeper, more sustainable ways. Does our myopia greatly underestimate nature's scope and impact, in comparison to that of mankind's? —Preceding unsigned comment added by 12.72.148.104 (talk) 06:15, 6 September 2009 (UTC)

The highest sea level[edit]

It would be interesting to present here the supposed map of the Earth during the highest sea level (having in mind continental shifts as well). —Preceding unsigned comment added by 89.216.31.46 (talk) 20:36, 24 August 2010 (UTC)

In 'Sea level and dry land' the sentence "Areas like volcanic islands are experiencing relative sea level rise as a result of isostatic cooling of the rock which causes the land to sink." does not make sense. It could read "Areas like volcanic islands can experience isostatic sea level rise after a lava flow as a result of cooling of the rock causing the land to sink." —Preceding unsigned comment added by John Bruyn (talkcontribs) 12:37, 9 September 2010 (UTC)

Holocene Rising or Falling?[edit]

When you look at the two graphs: http://en.wikipedia.org/wiki/File:Post-Glacial_Sea_Level.png http://en.wikipedia.org/wiki/File:Sea_level_temp_140ky.gif

The first graph (only Holocene Period) indicates a gradual rise of sea levels from the beginning of the Holocene. The second graph (last million years) seems to indicate an early peak in the sea levels in the early Holocene, followed by a drop to current levels.

Which is the more accurate picture?Keelec (talk) 22:47, 23 January 2011 (UTC)

New Section... Local vs Global Sea Levels[edit]

One thing I noticed recently is that the sea levels fluctuations are not homogeneous. http://tidesandcurrents.noaa.gov/sltrends/sltrends.shtml http://climate.nasa.gov/blogs/index.cfm?FuseAction=ShowBlog&NewsID=239

For example, the West Coast of the USA is either stable, or falling at a slower rate than the East Coast. River Deltas such as around New Orleans, or Venice are being hit the hardest. Seismic Activity can cause either local rises, or falls of the sea level.Keelec (talk) 23:03, 23 January 2011 (UTC)

Unsourced "bouncing" paragraph removed[edit]

I've removed the following paragraph from the article:

A more recent theory as to why sea levels have varied so dramatically throughout geologic history is, in part, due to isostatic rebound. Part of this theory states that as a denser oceanic plate is subducted under a less dense continental plate at a convergence plate boundary with a subduction zone, some of the continental plate is pulled downward briefly (geologically speaking) as the oceanic plate sinks into the Earth's mantle. The continental crust then bounces back up, restoring its previous position at equilibrium. Recent studies have suggested this was the case with the continent of Australia.

It was added in on 6 October by User:Geol310LB as that user's only edit. The paragraph is unsourced and contains problematic wording - Australia has "bounced back up"? If references are avaiiable to support the content, then it can be re-added after rewording to the "Geological influences" section where it would fit. Vsmith (talk) 13:19, 29 January 2012 (UTC)

The geoid[edit]

Why no mention of the geoid?

Merger proposal[edit]

I propose that the article Height above mean sea level be merged into this article (Sea level). Both articles basically cover the same concept, Mean sea level (which at the moment redirects here to Sea level). The term 'Height above' is self-explanatory and unnecessary to warrant separate articles (i.e. we do not have, or have need of a Depth below mean sea level article).

I think that the content in the article (Height above mean sea level) can easily be incorporated in to Sea Level, and the Sea Level article is of a reasonable size that the merging of Height above mean sea level will not cause any problems as far as article size or undue weight is concerned. -- Marek.69 talk 06:42, 16 May 2013 (UTC)

  • Merge: the Height above msl article is approximately a stub for the concept and introduces only a handful of concepts. It can easily be merged here and that would greatly improve the material's lack of citations. —EncMstr (talk) 09:15, 16 May 2013 (UTC)
  • Merge as per EncMstr and because the concept is generally being replaced with that of the Geoid. Martin Hogbin (talk) 09:34, 19 May 2013 (UTC)
  • No Merge. The Zero-level elevation of Heights above mean sea level is often derived at one point in time from an ever changing main Sea level, but normally not equal to it. --Rknbg (talk) 10:41, 5 October 2013 (UTC)
  • Merge and I've merged it. Still needs a bit longer overview in the introduction, and organization (progres from the general to the particular instead of details too soon). --Wtshymanski (talk) 15:54, 9 October 2013 (UTC)