Melting land-based ice raises sea levels globally but can produce
lowered levels locally

Date:
April 21, 2022
Source:
American Institute of Physics
Summary:
When a large ice sheet begins to melt, global-mean sea level
rises, but local sea level near the ice sheet may in fact
drop. A researcher illustrates this effect through a series of
calculations, beginning with a simple, analytically tractable
model and progressing through more sophisticated mathematical
estimations of ice distributions and gravitation of displaced
seawater mass. The paper includes numerical results for sea level
change resulting from a 1,000-gigatonne loss of ice, with parameter
values appropriate to the Greenland and Antarctic ice sheets.



FULL STORY ==========================================================================
It is well known that global warming is causing sea levels to rise via two processes: thermal expansion, when water expands because of its increased temperature, and melting of land-based ice, when meltwater flows into
the ocean. Less known, regarding the latter, is the nuanced phenomenon
of gravitational pull. When a large ice sheet begins to melt, global-mean
sea level rises, but local sea level near the ice sheet may in fact drop.


==========================================================================
In American Journal of Physics, by AIP Publishing, a researcher from
Saint Joseph's University illustrates this effect through a series of calculations, beginning with a simple, analytically tractable model
and progressing through more sophisticated mathematical estimations
of ice distributions and gravitation of displaced seawater mass. The
paper includes numerical results for sea level change resulting from a 1,000-gigatonne loss of ice, with parameter values appropriate to the
Greenland and Antarctic ice sheets.

"If the meltwater comes from Greenland, then sea level far from Greenland
rises by more than average, but sea level at the Greenland shore actually drops," said author Douglas Kurtze. "This is at least partially because
of how the loss of that ice changes the gravitational pull of the ice
sheet." A massive ice sheet attracts seawater, raising a mound in sea
level around the land on which the ice rests. When the ice melts into
the ocean, the global-mean sea level rises.

But the removal of ice mass weakens the gravity of the sheet, thus
lowering the mound. In some cases, the lowering of the mound height may
be greater than the rise in global-mean sea level, causing local sea
level near the ice sheet to drop.

While this cause for nonuniformity in sea level change was recognized
and systematically investigated as early as the 1880s, contemporary
scientists created sophisticated, detailed models including other
important considerations, such as changes to the earth's rotation and alterations in the shape of the solid earth, when mass, like water and
ice, is rearranged on the surface.

"My contribution here is to go in the opposite direction, making a model
that is so drastically simplified that it can be used as an example in undergraduate courses," said Kurtze. The gravitational pull phenomenon
"is a fascinating consequence of basic physics, and a great example of
just how complex the earth system is -- and how well geophysicists can
make sense of that complexity." Kurtze said he was inspired to develop
his model after hearing a radio interview with Jerry Mitrovica, a Harvard professor of geophysics and an expert in glacial isostatic adjustment.


========================================================================== Story Source: Materials provided by American_Institute_of_Physics. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Douglas A. Kurtze. Gravitational effects of ice sheets on sea level.

American Journal of Physics, 2022; 90 (5): 351 DOI:
10.1119/5.0067924 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/04/220421130951.htm

--- up 7 weeks, 3 days, 10 hours, 51 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)