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Author Topic: Can ice mass change rotational axis of earth  (Read 602 times)

mustangchef

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Can ice mass change rotational axis of earth
« on: July 16, 2017, 08:05:50 PM »
Can a massive drifting ice shelf change the axis the Earth rotates on?
sometimes

sidd

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Re: Can ice mass change rotational axis of earth
« Reply #1 on: July 16, 2017, 09:00:55 PM »
It would have to be very massive. Say approximately the total ice melt from greenland, around 300 gigaton or so. For a paper see

DOI: 10.1126/sciadv.1501693

http://advances.sciencemag.org/content/2/4/e1501693

open access. read all about it.

sidd

RoxTheGeologist

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Re: Can ice mass change rotational axis of earth
« Reply #2 on: July 16, 2017, 09:08:07 PM »
The earths axis of rotation processes, it's not stable. You would expect small changes in rotational speed and axis as land ice on Greenland and Antartica melt.

However, sea ice is in isostatic equilibrium, and can effectively be treated as water.

The Earth weighs 6x10exp24 Kg, The Hydrosphere has 1.3x10exp18 Kg of water in it in total. That's only 0.001% of the total mass of the earth. Ice is about 1.7% of the total amount of water.  It does make a difference how the ice is distributed.. but a very very small difference.

magnamentis

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Re: Can ice mass change rotational axis of earth
« Reply #3 on: July 16, 2017, 09:52:31 PM »
Can a massive drifting ice shelf change the axis the Earth rotates on?

the way you ask the answer would be yes while there are a few less probable conditions that would have to be met.

- mass of that shelf would have to be huge for a measurable (significant) impact, even more so that it would start to melt once heading south, hence the original mass would have to be even bigger.

- speed of the drift to make sure enough of the orginal mass would reach where it has to in time to have an effect

- the necessary kind of shelf does currently not exist

- it would have be stay within certain boundaries of longitude. as long as it would for example float with the westwind drift in the souther ocean and travel around the axis the effect would be neutralized, keyword "moon" one cans extract some of the answer from the well studied impact of mass shifts, the moon is nothing else than a mass with an impact that changes it's location, while if it would stay in one place at all times many many things would be entirely different, including rotation speed of the earth, water distribution etc etc.
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sidd

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Re: Can ice mass change rotational axis of earth
« Reply #4 on: July 16, 2017, 11:50:04 PM »
Mr. Rox was kind enuf to correct my error, in that an iceberg moving about would have little effect, since the ocean is in hydrostatic equilibrium with timescales of equlibration a few hours, essentially the circumference of the earth divided by the speed of sound in water.

So more precisely: Loss of grounded ice does cause an effect, as the cited paper shows. As does loss of volume above flotation in marine based ice sheets. The effect on the direction of the rotation axis is quite small, a few tens of milliarcseconds.  And loss of floating ice shelves into icebergs has very little effect.

sidd
« Last Edit: July 17, 2017, 01:47:47 AM by sidd »

oren

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Re: Can ice mass change rotational axis of earth
« Reply #5 on: July 18, 2017, 12:36:49 AM »
Just a little note, the hydrosphere may be 0.001% of the mass, but is not 0.001% of the angular momentum (as it is all on the surface), which I would guess should the deciding factor regarding rotation.

AbruptSLR

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Re: Can ice mass change rotational axis of earth
« Reply #6 on: July 18, 2017, 12:52:41 AM »
The following internet summary is related to an old article in Nature entitled:
Rapid ice melting drives Earth’s pole to the east, by Chen et al 2013:

"The North Pole has shifted east because of ice sheet loss caused by rising temperatures, a new study published in Geophysical Research Letters has found, according to the scientific journal Nature.
The pole drifted southeast toward northern Labrador, Canada, at a rate of about 6 centimeters per year between 1982 and 2005. But since 2005, the direction and speed of the pole's journey changed. It started moving rapidly east towards Greenland at a rate of more than 21 centimeters per year.
There has been huge ice sheet loss in the polar regions due to global warming.
The study was carried out by scientists from the University of Texas, Austin, using data collected by NASA's Gravity Recovery and Climate Experiment (GRACE).
Earth's two geographic poles do not have a fixed location. As the distribution of snow, rain and humidity changes every year, the poles too wobble around, usually in a circular manner. Besides this seasonal drift, there is a long range movement which scientists believe is driven by continental drift - the movement of land plates relative to each other.
GRACE's twin probes measure changes in the Earth's gravity field, which can be used to track shifts in the distribution of water and ice, Nature said. The researchers led by Jianli Chen, a geophysicist, used GRACE data to model how melting icecaps affect Earth's mass distribution. They found that more than 90% of the post-2005 polar shift was because of increasing ice loss and sea-level rise.
The explanation for this is that when mass is lost in one part of a spinning sphere, its spin axis will tilt directly toward the position of the loss, according to Erik Ivins, a geophysicist at NASA's Jet Propulsion Laboratory in Pasadena, California quoted by Nature. This is exactly what was observed in the case of the North Pole.
These findings have opened the way to estimate long term ice loss by studying polar drift. Scientists can locate the north and south poles to within about 0.9 millimeters by using Global Positioning System measurements to determine the angle of the Earth's spin. Since polar shifts have been recorded for almost a century, Nature says, it is possible to study ice losses for that period. Direct records of ice loss in Polar regions do not go back that much in time."

In the attached images from the article, 1 mas = ~3 cm of polar motion.

The following link is to the prime author's website at the University of Texas, where you can download a preprint (made available by the author):

http://www.csr.utexas.edu/personal/chen/publication.html

and here is a link directly to the preprint pdf:

ftp://ftp.csr.utexas.edu/pub/ggfc/papers/2013GL056164_preprint.pdf

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