Sunday, August 9, 2015

The Gravity of Sea Level Change

Fig. 1 Three Phases: Ice Sheet Melt & Impact
I. Background

Sea level change (SLC) is the preferred description of what takes place when ice sheets melt.

Sea level rise does not completely nor sufficiently describe the process.

Several posts have pointed this out (Peak Sea Level - 2, Why Sea Level Rise May Be The Greatest Threat To Civilization - 5, Sea Level Fall: The Forgotten Aspect of Sea Level Rise?).

II. The Process

The graphic, Fig. 1, depicts three generalized phases of ice sheet melt, as well as the resulting impact which the meltwater, or ice bergs flowing into the sea, have on sea level.
Fig. 2 Newton's Law of Gravity

The color cyan represents the ice sheet mass, the color brown represents the land mass above and below sea level, and the color blue represents the ocean.

Fig. 2 depicts gravitational force which the ice mass, m1, exerts on the sea water, m2, around it.

The distance, d, between the centers of those two masses stays the same for the purpose of this process, but in general the greater the distance between the two masses, the weaker the force of gravity is.

As the ice melts or calves into the sea, m1 (ice mass) decreases, so the gravitational force exerted on the sea water, m2, weakens to the degree that the ice sheet's mass effectively disappears into the sea.

The sea level near the continent, therefore, falls to the degree that the ice sheet melts or calves into the sea, thereby causing m1 to decrease.

A. Phase I

In Phase 1, area "C" represents the Peak Sea Level near the continent upon which the ice sheet rests (e.g. Greenland or Antarctica).

The higher sea level near the continent is caused by the gravity associated with the ice sheet's mass, which exerts a force, a pull if you will, on the ocean water.

Area "B" is at the maximum distance, d, upon which the ice mass, m1, can exert gravitational influence on the sea water.

Area "A" is: the sea level that is unaffected by the gravitational pull of the ice sheet, but nevertheless is impacted by the increased quantity of water that has ended up in the sea as the ice sheet melts or calves off the continent.

B. Phase 2

In Phase 2, area "C" represents the Lowered Sea Level near the continent upon which the ice sheet rests (Greenland or Antarctica).

The lower sea level near the continent is caused by the decreased gravity associated with the ice sheet mass, which eventually exerts no more force or pull on the ocean.

In this phase the continent is still deformed from the past ice sheet's weight that had deformed the land before the ice sheet melted (a small amount of ice and/or meltwater is still in the deformed area because it can't slide up hill over the edge). 

Area "B" is the at the maximum distance, d, upon which the ice mass, m1, once exerted gravitational influence on the sea water, m2.

Area "A" is: a) where the sea water ends up after being released from the gravitational pull of the ice sheet, as the ice sheet melts and its gravity therefore weakens; and b) where axial relocation and rotational forces of the Earth finally focus the sea level rise.

C. Phase 3

In Phase 3, area "C" represents the Lowest Sea Level near the continent upon which the ice sheet once rested (Greenland or Antarctica).

The lowest sea level near the continent is caused by the additional apparent sea level fall, now due primarily to the uplifting of the continent where the deformity had been.

Any ice or meltwater residue, which remained in the deformity, has now also been emptied into the sea.

Area "B" is where the lowered sea level now ends, and where the sea level begins to incrementally rise, because the melted ice sheet is now sea water.

Area "A" is: a) where the sea level rise ends up, after it has been released from the gravitational pull of the ice sheet;  and b) where axial relocation and rotational forces of the Earth focus the sea level rise incrementally, until it reaches its maximum level.

D. Lunar Gravity Induced SLC

Even though the gravitational power of the Moon is far greater than the gravitational power
Fig. 3 Lunar SLC
of an ice sheet, the impact on sea level is still a normal, everyday event along sea shores.

The graphic, Fig. 3, from Wikipedia, shows how the moon's gravity constantly causes mobile SLC on the oceans of the Earth.

Ice sheet gravity is the same force described by the same law of gravity (Fig. 2), but with weaker force.

The Moon causes high tide, however, the magnitude of that high tide, the high tide mark put on the beach, is altered by ice sheet gravity near the continent, and also altered away from the continent (area "A") by ice sheet melt-water that increases the water volume and level of the sea.

You might consider that several disciplines are involved, when comprehending both lunar and global warming induced SLC dynamics.

I am in reference to disciplines such as astronomy, astrophysics, oceanography, and climatology.

Climate scientists, oceanographers, and others, can benefit from interdisciplinary conferences, and the like, which can involve relevant scientific material that they might not otherwise consider (Weekend Rebel Science Excursion - 47).

III. How SLC Looks on a Map of The Earth

The video at the bottom of this post features Professor Jerry Mitrovica, Harvard University, talking about interdisciplinary perspectives, or the lack thereof, as a source of improper factor exclusion.

Fig. 4 SLC @ Greenland
For example, astronomers ordinarily consider the effect of gravity on SLC, but climate scientists ordinarily consider melting ice sheets as the cause of SLC.

When the two disciplines merge in a global warming induced climate change scenario, each discipline benefits by comparing notes on the interdisciplinary issues.

The graphic Fig. 4 was presented in one such interdisciplinary conference where the video at the bottom of this post was made.
Fig. 5 SLC @ Antarctica (see video)

The same is true for Fig. 5

They both show ice sheet gravity induced SLC.

Neither case is caused by the Moon's gravity.

Ice sheet gravity is every bit as critical to understanding global warming induced SLC, as lunar gravity is to understanding tidal SLC.

Both instances of the power of gravity are important to consider, because civilization cannot prepare for SLC without considering both sea level fall and sea level rise.

IV. Conclusion

Since international intercourse, in the form of sea based export and import trade and commerce, in all manner of goods, is a fundamental infrastructure of current civilization, we must consider the gravity of SLC on sea ports.

The links furnished in Section I of this post are good places to begin to comprehend the unexpected magnitude of the subject of endangered sea ports.

There are severe implications associated with facing the gravity of SLC.

The next post in this series is here.

Professor Jerry Mitrovica, Harvard University:


Randy said...

OMG is a new NASA program to determine the depth of Greenland's ice sheet at fjords where they meet the sea.

The deeper they are the more mass they have (link).

Anonymous said...

You know i'm with you all the way on this stuff, Dredd.

i get down about it's use though. Nobody is going to listen and give up their little "lives" (in service to their own petty self-interests). The government, the way it works now, is completely beholden to the powers that be and their campaign contributions and other legal bribes. There is no incentive to change this (TO THEM), so any change suggested/demanded by the hoi polloi just goes into the dust bin or is given the DC runaround to death.

If it's all just winding down to oblivion, what difference does it make if it's a sudden quantum level jump down or it takes a century or more. We are just playing out "survive as long as you can" no matter what the time frame. Rates are only changing gauges of decimation until no one's around to register it.

Other than that [Mrs. Lincoln, how did you like the play?] this is fascinating stuff! It seemed so counter-intuitive at first, but the physics explains it and it's clear sea level CHANGE is the proper term to indicate variability, and certainly different from what it is now. This insight and the "fingerprinting" helps figure it out for individual locations. [fat lot of good it'll do them, it's already too late to react]