Peak Sea Level - 6

Retreating Glaciers (click to enlarge)

I. Background

In the third and fifth posts of this series, I discussed a hypothesis of Mitrovica and Gomez concerning the impact of sea level fall (SLF) around Antarctica.

Their hypothesis is that SLF will stop or slow down the flow of ice streams into the sea.

I countered that hypothesis (Peak Sea Level - 3, Peak Sea Level - 5).

II. The Concept

Yesterday, I discussed Zachariae Isstrom, a glacier at the terminus of the NEGIS, an ice stream in Greenland.

The discussion was in the context of a scientific paper published this week (Weekend Rebel Science Excursion - 53).

Today, I want to fuse that paper with the issue of the impact SLF is now having, and will continue to have on ice streams.

I want to also examine their hypothesis in the context of the loss of the Zachariae Isstrom ice shelf.

Generally, ice shelves slow down the flow of ice streams, that is, until the ice shelf collapses.

So, when the Zachariae Isstrom ice shelf collapsed, did the velocity of the glacial flow to the sea increase or decrease?

III. The Proof of the Concept

There are historical observations of previous ice shelf collapses:

Over the past two decades, the massive platforms of floating ice [ice shelves] that dot the coast of Antarctica have been thinning and doing so at an increasing rate, likely at least in part because of global warming. Scientists are worried about its implications for significant sea level rise.

The ice shelves—some of which are larger than California and tens to hundreds of yards thick—are the linchpins of the Antarctic ice sheet system, holding back the millions of cubic miles of ice contained in the glaciers that flow into them, like doorstops. As the ice sheets thin, the massive rivers of ice behind them can surge forward into the sea.

(Peak Sea Level - 5, quoting Scientific American). An example is the 8-fold increase in velocity of some well known Antarctic glaciers when their ice shelf collapsed:

A discussion about ice shelves vs. ice sheets:

15:29 when the ice shelf "Larsen A" collapsed the entire glacier's flow speed toward the sea increased ...
18:50 "Larsen B" ice shelf collapse caused the same thing ... the entire glacier's flow accelerated toward the sea ...
19:30 when the ice shelf goes away so does the restraint on the glacier, and they then move faster, 8 times faster, toward the sea
27:15 the East Antarctica Totten Glacier basin contains about as much ice as all of Western Antarctica, and it is destabilizing
30:30 the condition of the ice shelf controls what happens to the ice sheet

(ibid, paraphrasing Dr. Rignot video, shown below). Ok, so what does the Zachariae Isstrom paper have to say about it?

We will analyze that shortly.

IV. All Glaciers Conform To The Law of Gravity

In the first video below Professor Rignot mentions tidal fracturing of ice shelves caused by everyday tidal ups and downs.

In the second video Professor Mitrovica talks about an SLF of many meters (10m, 20m - 100m+ near ice sheet coast lines) as ice sheet mass is lost.

That would impact ice shelves near the coast by generating far greater stress on those ice shelves than daily tides do.

Even when the supporting water underneath the ice shelf falls only 5 or 10 feet at low tide, that stresses and fractures the shelf to some lesser degree.

But, when the ocean under the ice shelf falls 10, 20 - 100 meters, due to loss of ice sheet mass / gravity which induces SLF, that ice shelf is toast.

V. SLF Is An Ice Shelf Destroyer

What happened to Zachariae Isstrom, when its ice shelf collapsed, is detailed in the paper:

After 8 years of decay of its ice shelf ... The acceleration rate of its ice velocity tripled, melting of its residual ice shelf and thinning of its grounded portion doubled, and calving is now occurring at its grounding line.

(Fast retreat of Zachariæ Isstrøm, northeast Greenland). Ice streams and glaciers do not slow down when their ice shelf disintegrates, as SLF sets in.

VI. Conclusion

There is still a lot of ignorance about SLF.

Especially SLF generated at or near the coasts of land that the ice sheets rest upon.

It is not generally known that as the ice sheets lose mass they consequently lose gravitational power.

Which means that they can no longer keep a perpetual high sea level at or near their coastline.

The video by Professor Mitrovica is very worthy to use to educate yourself on the general aspects of ice sheet gravity and its impact on sea level change (SLC).

The video has previously been discussed in the sense of ways to prove the concepts it sets forth (e.g. Proof of Concept - 3).

Just because I disagree with Mitrovica and Gomez (on the issue of what happens to ice shelves and ice sheets when SLF takes place near the coast), does not mean that I disagree with the other 99% of their work (I agree with it and respect them and appreciate their work very much).

The previous post in this series is here.

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A discussion about ice shelves vs. ice sheets by Eric Rignot:

15:29 when the ice shelf "Larsen A" collapsed the entire glacier's flow speed toward the sea increased ...
18:50 "Larsen B" ice shelf collapse caused the same thing ... the entire glacier's flow accelerated toward the sea ...
19:30 when the ice shelf goes away so does the restraint on the glacier, and they then move faster, 8 times faster, toward the sea
27:15 the East Antarctica Totten Glacier basin contains about as much ice as all of Western Antarctica, and it is destabilizing
30:30 the condition of the ice shelf controls what happens to the ice sheet

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A discussion of, among other things, SLC as impacted by ice sheet mass and gravity:

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