<p>The geoid <a href="https://web.archive.org/web/20230606041313/https://oceanservice.noaa.gov/facts/geoid.html" rel="nofollow noreferrer">is a model of global mean sea level</a>:</p>
<blockquote>
<p>If one were to remove the tides and currents from the ocean, it would
settle onto a smoothly undulating shape (rising where gravity is high,
sinking where gravity is low).</p>
</blockquote>
<p>On one hand, if gravity were to be constant, then the geoid would have no ondulations.</p>
<p>On the other hand, gravity depends on crustal material densities, and oceanic crust is much denser than continental crust:</p>
<ul>
<li>high densities ---&gt; high gravity above oceanic crust</li>
</ul>
<p>The geoid represents the equipotential height of the sea surface.
If a molecule is subject to the earth’s gravitational field, it has a potential energy associated, derived from being pulled toward the Earth.</p>
<p>If in a certain place A there is a higher gravity than in B, a molecule of water in A must be at a higher level than in B to feel the same attractive gravitational force (i.e. at a bigger distance from the mass center of the earth, for visualization purposes assume that all the mass is centered in a point in the core of the Earth, but gravity can vary azimutally).</p>
<p>See also <a href="https://www.esri.com/news/arcuser/0703/graphics/geoid2_lg.gif" rel="nofollow noreferrer">this image</a> from a company providing geogrpahical services.</p>

CC BY-SA 4.0
2023-06-14T08:52:28.377Z
This answer doesn't address the question being asked, "why is there a correlation between sea level and gravity values?".
Fred
CC BY-SA 4.0
2023-06-20T10:23:46.187Z
@Fred this answer tries now to bring some background to the question.
EarlGrey
CC BY-SA 4.0
2023-06-20T14:28:36.547Z
The answer is better now but still, it just repeats the initial observation that high gravity = higher sealevels. Maybe the answer is somehow really obvious and I'm just missing it. I think what I'm maybe looking for is some diagram that illustrates how the water would behaved in non-uniform gravity or something like that.
Jason C
CC BY-SA 4.0
2023-06-20T14:50:53.037Z
maybe it is even clearer now. Regarding *" how the water would behaved in non-uniform gravity"* you are describing the geoid :D !
EarlGrey
CC BY-SA 4.0
2023-06-21T01:59:39.263Z
"If in a certain place..." -- I think I see; so if I modelled the Earth as a sort of non-uniform blob of multiple smaller balls with varying gravity, I should expect the "balls" with higher gravity to have more water around them. Imagining all the balls together overlapping eachother, that'd translate to higher sealevels on the surface of the Earth "blob". Something like that?
Jason C
CC BY-SA 4.0
2023-06-21T07:44:14.233Z
@JasonC not more water, but higher sea level with respect to the distance from the center of the Earth.
EarlGrey
CC BY-SA 4.0
2023-06-21T07:53:46.820Z
@JasonC see this map comparing bathymetry and free-air gravity anomaly: 
https://www.researchgate.net/profile/Ross-Parnell-turner/publication/283940969/figure/fig1/AS:299709466988545@1448467713153/Bathymetry-and-gravity-of-north-Atlantic-Ocean-showing-location-of-JC50-seismic.png
the sea bottom is just at -1000m depth wher the gravity is higher, while it is at -2000m where the gravity is "regular" ... the sea level is higher, but the water column is shorter.
EarlGrey
CC BY-SA 4.0
2023-06-14T07:02:24.603Z
2023-06-20T14:50:04.753Z
2023-06-20T14:50:04.753Z
EarlGrey
<p>The EGM96 geoid map depicts hypothetical sealevel due to gravitational variations on the Earth's surface:</p>
<p><a href="https://i.sstatic.net/C9IIA.png" rel="noreferrer"><img src="https://i.sstatic.net/C9IIA.png" alt="enter image description here" /></a></p>
<p><sup><a href="https://en.wikipedia.org/wiki/Geoid#/media/File:Earth_Gravitational_Model_1996.png" rel="noreferrer">image source</a></sup></p>
<p>It places one of the highest areas in the northern part of the Atlantic ocean.</p>
<p>The gravitational map from the GRACE mission depicts gravitational acceleration due to the same variations on the Earth's surface:</p>
<p><a href="https://i.sstatic.net/MJNKd.png" rel="noreferrer"><img src="https://i.sstatic.net/MJNKd.png" alt="enter image description here" /></a></p>
<p><sup><a href="https://en.wikipedia.org/wiki/Gravity_of_Earth#/media/File:Gravity_anomalies_on_Earth.jpg" rel="noreferrer">image source</a></sup></p>
<p>It places an area of high acceleration in the northern part of the Atlantic ocean.</p>
<p>In fact, all of the high sealevel areas correspond to areas of high gravitational acceleration.</p>
<p>I would have expected the opposite.</p>
<p>Why is this so? I am assuming the images are correct. Why would higher gravitational acceleration lead to higher sealevels instead of pulling the water closer to Earth's center and leading to lower sealevels? Or am I misreading the images?</p>

CC BY-SA 4.0
2023-06-19T21:23:08.320Z
Interesting. Perhaps higher *g* attracts more water causing sea levels to be higher? Water is mostly incompressible, so the level must be higher.
BMF
CC BY-SA 4.0
2023-06-20T10:19:11.090Z
@BMF the geoid is a model of global mean sea level: it does not mean that there is more water, it means that the water level would be higher ...
EarlGrey
CC BY-SA 4.0
2023-06-20T17:13:55.950Z
@EarlGrey I think you missed my point. More water may be collected around higher sources of gravitation than around lower ones, causing the level to be higher. I didn't suggest the geoid was a model of where there's "more water", only a possible correlation between the two models.
BMF
CC BY-SA 4.0
2023-06-20T17:32:53.997Z
This is a map of the north Atlantiic Ocena bathymetry: https://www.researchgate.net/profile/Jean-Claude-Sibuet-2/publication/249551899/figure/fig1/AS:298314076573699@1448135026217/North-Atlantic-bathymetric-map-Smith-Sandwell-1997-showing-features-of-the-conjugate.png
There is actually less water around higher source of gravitation. But that less water is pulled higher (see my answer and its extension)
EarlGrey
<oceanography><gravity>
Why is sealevel higher where gravity is higher?
Jason C
# Why is sealevel higher where gravity is higher?

(Asked by: username_0 on 2023-06-08)

The EGM96 geoid map depicts hypothetical sealevel due to gravitational variations on the Earth's surface:

[![enter image description here](https://i.sstatic.net/C9IIA.png)](https://i.sstatic.net/C9IIA.png)

[image source](https://en.wikipedia.org/wiki/Geoid#/media/File:Earth_Gravitational_Model_1996.png)

It places one of the highest areas in the northern part of the Atlantic ocean.

The gravitational map from the GRACE mission depicts gravitational acceleration due to the same variations on the Earth's surface:

[![enter image description here](https://i.sstatic.net/MJNKd.png)](https://i.sstatic.net/MJNKd.png)

[image source](https://en.wikipedia.org/wiki/Gravity_of_Earth#/media/File:Gravity_anomalies_on_Earth.jpg)

It places an area of high acceleration in the northern part of the Atlantic ocean.

In fact, all of the high sealevel areas correspond to areas of high gravitational acceleration.

I would have expected the opposite.

Why is this so? I am assuming the images are correct. Why would higher gravitational acceleration lead to higher sealevels instead of pulling the water closer to Earth's center and leading to lower sealevels? Or am I misreading the images?

**Tags:** oceanography, gravity

> **Comments:**
> **username_1**: Interesting. Perhaps higher *g* attracts more water causing sea levels to be higher? Water is mostly incompressible, so the level must be higher.  
> **username_2**: @username_1 the geoid is a model of global mean sea level: it does not mean that there is more water, it means that the water level would be higher ...  
> **username_1**: @username_2 I think you missed my point. More water may be collected around higher sources of gravitation than around lower ones, causing the level to be higher. I didn't suggest the geoid was a model of where there's "more water", only a possible correlation between the two models.  
> **username_2**: This is a map of the north Atlantiic Ocena bathymetry: https://www.researchgate.net/profile/Jean-Claude-Sibuet-2/publication/249551899/figure/fig1/AS:298314076573699@1448135026217/North-Atlantic-bathymetric-map-Smith-Sandwell-1997-showing-features-of-the-conjugate.png There is actually less water around higher source of gravitation. But that less water is pulled higher (see my answer and its extension)  

---

## 1 answers

### Answer by username_2 on 2023-06-14. Score: -5

The geoid [is a model of global mean sea level](https://web.archive.org/web/20230606041313/https://oceanservice.noaa.gov/facts/geoid.html):

> If one were to remove the tides and currents from the ocean, it would
> settle onto a smoothly undulating shape (rising where gravity is high,
> sinking where gravity is low).

On one hand, if gravity were to be constant, then the geoid would have no ondulations.

On the other hand, gravity depends on crustal material densities, and oceanic crust is much denser than continental crust:

* high densities ---> high gravity above oceanic crust

The geoid represents the equipotential height of the sea surface.
If a molecule is subject to the earth’s gravitational field, it has a potential energy associated, derived from being pulled toward the Earth.

If in a certain place A there is a higher gravity than in B, a molecule of water in A must be at a higher level than in B to feel the same attractive gravitational force (i.e. at a bigger distance from the mass center of the earth, for visualization purposes assume that all the mass is centered in a point in the core of the Earth, but gravity can vary azimutally).

See also [this image](https://www.esri.com/news/arcuser/0703/graphics/geoid2_lg.gif) from a company providing geogrpahical services.

> **Comments:**
> **username_3**: This answer doesn't address the question being asked, "why is there a correlation between sea level and gravity values?".  
> **username_2**: @username_3 this answer tries now to bring some background to the question.  
> **username_0**: The answer is better now but still, it just repeats the initial observation that high gravity = higher sealevels. Maybe the answer is somehow really obvious and I'm just missing it. I think what I'm maybe looking for is some diagram that illustrates how the water would behaved in non-uniform gravity or something like that.  
> **username_2**: maybe it is even clearer now. Regarding *" how the water would behaved in non-uniform gravity"* you are describing the geoid :D !  
> **username_0**: "If in a certain place..." -- I think I see; so if I modelled the Earth as a sort of non-uniform blob of multiple smaller balls with varying gravity, I should expect the "balls" with higher gravity to have more water around them. Imagining all the balls together overlapping eachother, that'd translate to higher sealevels on the surface of the Earth "blob". Something like that?  
> **username_2**: @username_0 not more water, but higher sea level with respect to the distance from the center of the Earth.  
> **username_2**: @username_0 see this map comparing bathymetry and free-air gravity anomaly:  https://www.researchgate.net/profile/Ross-Parnell-turner/publication/283940969/figure/fig1/AS:299709466988545@1448467713153/Bathymetry-and-gravity-of-north-Atlantic-Ocean-showing-location-of-JC50-seismic.png the sea bottom is just at -1000m depth wher the gravity is higher, while it is at -2000m where the gravity is "regular" ... the sea level is higher, but the water column is shorter.  

---

