<p>Because of post glacial rebound. The asthenosphere was pressed down under <a href="http://en.wikipedia.org/wiki/Laurentide_ice_sheet" rel="noreferrer">Laurentide ice sheet</a> during last ice age and is now finding a new balance, without the weight of the ice. </p>

<p>Note that around the ice sheet, the land is actually sinking today, like when ones partner gets up from a waterbed mattress. </p>

<p><img src="https://i.sstatic.net/xvigt.jpg" alt="&quot;PGR Paulson2007 Rate of Lithospheric Uplift due to PGR&quot; by Erik Ivins, JPL. -  Licensed under Public Domain via Wikimedia Commons"></p>

CC BY-SA 3.0
2015-04-22T20:04:57.283Z
and here is a better map of the uplift in Canada: http://www.nrcan.gc.ca/earth-sciences/geomatics/geodetic-reference-systems/tools-applications/3d-networks/9082
user2821
CC BY-SA 3.0
2015-04-22T19:42:35.057Z
2015-04-22T19:47:43.393Z
2015-04-22T19:47:43.393Z
user2821
<p><a href="https://i.sstatic.net/3tMxR.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/3tMxR.png" alt="enter image description here"></a></p>

<p>The graph shows sea level fall (SLF) at the Churchill tide gauge station.</p>

<p>It is on the west side of Hudson Bay.</p>

<p>These jagged edge ups and downs, and severe drop in a short time, indicate this is not the result of rising land mass. </p>

<p>Greenland ice mass loss is the source of SLF in a wide area.</p>

CC BY-SA 3.0
2016-08-23T03:40:14.303Z
Sea level has been declining in New Jersey for many years now...which says to me global warming is leading to greater evaporation...especially in areas where fresh water sits on top of salt water while the current takes the salt water away (western Hudson Bay, New Jersey to Nova Scotia, the Outer Banks of North Carolina, North Florida) If continuing entire Gulf of Mexico might see a huge drop because of Mississippi "boring" and Eastward Flow. Tide go out...not come back for fifty years...
Doctor Zhivago
CC BY-SA 4.0
2022-01-28T01:02:53.140Z
Yes, local sea levels are falling around Greenland because the loss of ice mass reduces gravitational pull on surrounding ocean water. This NASA vid shows global sea level changes between 2002 and 2015 (adjusted for isostatic changes iiuc) and shows sea level FALL around Greenland - https://www.youtube.com/watch?v=VY_SeZiBcM4
Ken Fabian
CC BY-SA 3.0
2015-10-10T15:12:07.140Z
2015-10-10T15:12:07.140Z
Dredd
<p>Gravitational dynamics of the Greenland Ice sheet have an impact, sea level fall, not often mentioned (e.g. on Europe: <a href="http://blogdredd.blogspot.com/2015/10/proof-of-concept-5.html" rel="nofollow">Proof of Concept - 5</a>).</p>

<p>It causes sea level fall and sea level rise, depending on distance from the ice sheet (<a href="http://ecocosmology.blogspot.com/2015/08/the-gravity-of-sea-level-change.html" rel="nofollow">The Gravity of Sea Level Change</a>).</p>

CC BY-SA 3.0
2015-10-10T13:30:35.687Z
2015-10-10T13:30:35.687Z
Dredd Blog
<p><strong>The area is experiencing <a href="https://en.wikipedia.org/wiki/Post-glacial_rebound" rel="nofollow noreferrer">post-glacial isostatic rebound</a>.</strong></p>
<p>Much of Canada was covered in an extensive ice sheet in the <a href="https://en.wikipedia.org/wiki/Last_glacial_period" rel="nofollow noreferrer">last glacial period</a> (the 'Ice Age'), from about 110 ka until 12 ka. The ice in the Hudson Bay area was among the last to melt:</p>
<p><img src="https://i.sstatic.net/FEFew.png" alt="Ice retreat in North America" /></p>
<p>A thick ice sheet depresses the crust (the lithosphere), making a small dent in the uppermost mantle (the <a href="https://en.wikipedia.org/wiki/Asthenosphere" rel="nofollow noreferrer">asthenosphere</a>) in the process. Well, not that small: p 375 in <a href="https://books.google.ca/books?id=yRMgYc-8mTIC" rel="nofollow noreferrer">Gornitz</a> (2009, <em>Encyclopedia of Paleoclimatology and Ancient Environments</em>) says it could be 800 m for a 3000 metre-thick ice sheet!</p>
<p>Since the asthenosphere is highly viscous, it takes a long time time for the depression to 'bounce' back up. This map from Natural Resources Canada shows the current rate:</p>
<p><img src="https://i.sstatic.net/kd0gN.jpg" alt="Isostatic rebound rate in Canada" /></p>
<p>Since <em>global</em> sea-level is <a href="https://en.wikipedia.org/wiki/Current_sea_level_rise" rel="nofollow noreferrer">currently rising</a> at about 3 mm/a, a <em>local</em> uplift at this rate will break even. Anything more will result in relative sea-level fall, as we see in Hudson Bay (as well as in Scandinavia, the UK, Alaska, and elsewhere — <a href="https://tidesandcurrents.noaa.gov/sltrends/sltrends.html" rel="nofollow noreferrer">this map is wonderful</a>).</p>
<p>Interesting, for geologists anyway, is the sedimentological record this leaves. I love this example of raised beaches and a small delta experiencing <a href="https://www.sepmstrata.org/Terminology.aspx?id=forced%20regression" rel="nofollow noreferrer">forced regression</a> on the shores of Hudson Bay:</p>
<p><img src="https://i.sstatic.net/5ugZd.jpg" alt="Forced regression of small delta" /></p>
<p>Last thing — you asked:</p>
<blockquote>
<p>Would it make sense for it to recede at the level that it is
receding with sources of freshwater relatively close?</p>
</blockquote>
<p>Since Hudson Bay is connected to the world's ocean, mainly through Hudson Strait, the runoff into the Bay has no measurable effect on the water level.</p>
<p><strong>Credit</strong>
<a href="https://commons.wikimedia.org/wiki/File:Retrait_des_glaces_en_Am%C3%A9rique.svg" rel="nofollow noreferrer">Ice retreat map</a> by TKostolany, licensed CC-BY-SA. Rebound map by NRCan, free of copyright. Google Maps image contains own credit.</p>

CC BY-SA 4.0
2022-01-26T08:22:09.710Z
Is the "this map is wonderful" link down? I cannot access it.
Eric Duminil
CC BY-SA 4.0
2022-01-27T18:38:53.537Z
@EricDuminil They finally got SSL! I fixed the link.
Matt Hall
CC BY-SA 4.0
2022-01-28T00:48:04.607Z
[After 10,000 years, Hudson Bay is only half way through its “spring back” and may have another 100 meters to rise. When uplift is complete, Hudson Bay will mostly or entirely disappear."](https://wawataynews.ca/home/walk-hudson-bay-coast-longer-i-remember) But maybe AGW sea level rise will save it.
Keith McClary
CC BY-SA 3.0
2015-04-23T10:48:41.850Z
Great answer - but did you mean "Anything more will result in relative sea-level *fall*" near the middle?
Semidiurnal Simon
CC BY-SA 4.0
2015-04-22T23:23:29.887Z
2022-01-27T18:38:30.897Z
2022-01-27T18:38:30.897Z
Matt Hall
<p><img src="https://i.sstatic.net/SY7gr.png" alt="Relative sea-level data for Hudson Bay"></p>

<p>Why is the sea level in Hudson Bay decreasing so much? Hudson Bay is pretty far up north, much closer to glaciers. Would it make sense for it to recede at this level with sources of fresh water relatively close? </p>

<geology><oceanography><sea-level><ice-sheets><glaciation>
Why is relative sea-level falling in Hudson Bay?
Lucian09474
# Why is relative sea-level falling in Hudson Bay?

(Asked by: username_0 on 2015-04-22)

![Relative sea-level data for Hudson Bay](https://i.sstatic.net/SY7gr.png)

Why is the sea level in Hudson Bay decreasing so much? Hudson Bay is pretty far up north, much closer to glaciers. Would it make sense for it to recede at this level with sources of fresh water relatively close?

**Tags:** geology, oceanography, sea-level, ice-sheets, glaciation


---

## 4 answers

### Answer by username_6 on 2015-04-22. Score: 35 | Accepted answer

**The area is experiencing [post-glacial isostatic rebound](https://en.wikipedia.org/wiki/Post-glacial_rebound).**

Much of Canada was covered in an extensive ice sheet in the [last glacial period](https://en.wikipedia.org/wiki/Last_glacial_period) (the 'Ice Age'), from about 110 ka until 12 ka. The ice in the Hudson Bay area was among the last to melt:

![Ice retreat in North America](https://i.sstatic.net/FEFew.png)

A thick ice sheet depresses the crust (the lithosphere), making a small dent in the uppermost mantle (the [asthenosphere](https://en.wikipedia.org/wiki/Asthenosphere)) in the process. Well, not that small: p 375 in [Gornitz](https://books.google.ca/books?id=yRMgYc-8mTIC) (2009, *Encyclopedia of Paleoclimatology and Ancient Environments*) says it could be 800 m for a 3000 metre-thick ice sheet!

Since the asthenosphere is highly viscous, it takes a long time time for the depression to 'bounce' back up. This map from Natural Resources Canada shows the current rate:

![Isostatic rebound rate in Canada](https://i.sstatic.net/kd0gN.jpg)

Since *global* sea-level is [currently rising](https://en.wikipedia.org/wiki/Current_sea_level_rise) at about 3 mm/a, a *local* uplift at this rate will break even. Anything more will result in relative sea-level fall, as we see in Hudson Bay (as well as in Scandinavia, the UK, Alaska, and elsewhere — [this map is wonderful](https://tidesandcurrents.noaa.gov/sltrends/sltrends.html)).

Interesting, for geologists anyway, is the sedimentological record this leaves. I love this example of raised beaches and a small delta experiencing [forced regression](https://www.sepmstrata.org/Terminology.aspx?id=forced%20regression) on the shores of Hudson Bay:

![Forced regression of small delta](https://i.sstatic.net/5ugZd.jpg)

Last thing — you asked:

> Would it make sense for it to recede at the level that it is
> receding with sources of freshwater relatively close?

Since Hudson Bay is connected to the world's ocean, mainly through Hudson Strait, the runoff into the Bay has no measurable effect on the water level.

**Credit**
[Ice retreat map](https://commons.wikimedia.org/wiki/File:Retrait_des_glaces_en_Am%C3%A9rique.svg) by TKostolany, licensed CC-BY-SA. Rebound map by NRCan, free of copyright. Google Maps image contains own credit.

> **Comments:**
> **username_9**: Great answer - but did you mean "Anything more will result in relative sea-level *fall*" near the middle?  
> **username_7**: Is the "this map is wonderful" link down? I cannot access it.  
> **username_6**: @username_7 They finally got SSL! I fixed the link.  
> **username_8**: [After 10,000 years, Hudson Bay is only half way through its “spring back” and may have another 100 meters to rise. When uplift is complete, Hudson Bay will mostly or entirely disappear."](https://wawataynews.ca/home/walk-hudson-bay-coast-longer-i-remember) But maybe AGW sea level rise will save it.  

---

### Answer by username_1 on 2015-04-22. Score: 14

Because of post glacial rebound. The asthenosphere was pressed down under [Laurentide ice sheet](http://en.wikipedia.org/wiki/Laurentide_ice_sheet) during last ice age and is now finding a new balance, without the weight of the ice.

Note that around the ice sheet, the land is actually sinking today, like when ones partner gets up from a waterbed mattress.

!["PGR Paulson2007 Rate of Lithospheric Uplift due to PGR" by Erik Ivins, JPL. -  Licensed under Public Domain via Wikimedia Commons](https://i.sstatic.net/xvigt.jpg)

> **Comments:**
> **username_1**: and here is a better map of the uplift in Canada: http://www.nrcan.gc.ca/earth-sciences/geomatics/geodetic-reference-systems/tools-applications/3d-networks/9082  

---

### Answer by username_2 on 2015-10-10. Score: 3

[![enter image description here](https://i.sstatic.net/3tMxR.png)](https://i.sstatic.net/3tMxR.png)

The graph shows sea level fall (SLF) at the Churchill tide gauge station.

It is on the west side of Hudson Bay.

These jagged edge ups and downs, and severe drop in a short time, indicate this is not the result of rising land mass.

Greenland ice mass loss is the source of SLF in a wide area.

> **Comments:**
> **username_3**: Sea level has been declining in New Jersey for many years now...which says to me global warming is leading to greater evaporation...especially in areas where fresh water sits on top of salt water while the current takes the salt water away (western Hudson Bay, New Jersey to Nova Scotia, the Outer Banks of North Carolina, North Florida) If continuing entire Gulf of Mexico might see a huge drop because of Mississippi "boring" and Eastward Flow. Tide go out...not come back for fifty years...  
> **username_4**: Yes, local sea levels are falling around Greenland because the loss of ice mass reduces gravitational pull on surrounding ocean water. This NASA vid shows global sea level changes between 2002 and 2015 (adjusted for isostatic changes iiuc) and shows sea level FALL around Greenland - https://www.youtube.com/watch?v=VY_SeZiBcM4  

---

### Answer by username_5 on 2015-10-10. Score: 1

Gravitational dynamics of the Greenland Ice sheet have an impact, sea level fall, not often mentioned (e.g. on Europe: [Proof of Concept - 5](http://blogdredd.blogspot.com/2015/10/proof-of-concept-5.html)).

It causes sea level fall and sea level rise, depending on distance from the ice sheet ([The Gravity of Sea Level Change](http://ecocosmology.blogspot.com/2015/08/the-gravity-of-sea-level-change.html)).


---

