Watch The Ice Shelves - 3

Fig. 1 Ice Shelf loss

In previous posts of this series I focused on research that implicates Antarctica's ice shelves as harbingers of things to come (Watch The Ice Shelves, 2).

Since they hold back or resist the flow of the ice streams on the land mass, when those ice shelves go, the ice streams go faster.

I mean, more ice from the ice streams on land can flow faster and reach the ocean more easily.

Which will cause sea level change (SLC) in the form of both sea level rise (SLR) and sea level fall (SLF).

So, today let's do three things:

1) review some new research regarding ice shelf integrity,

2) further discuss ice sheet gravity as it relates to ice shelves,

3) engage in a hypothesis concerning ice shelf gravity.

I. New Research

Here is the abstract at the journal Nature concerning new research:

The floating ice shelves along the seaboard of the Antarctic ice sheet restrain the outflow of upstream grounded ice. Removal of these ice shelves, as shown by past ice-shelf recession and break-up, accelerates the outflow, which adds to sea-level rise. A key question in predicting future outflow is to quantify the extent of calving that might precondition other dynamic consequences and lead to loss of ice-shelf restraint. Here we delineate frontal areas that we label as ‘passive shelf ice’ and that can be removed without major dynamic implications, with contrasting results across the continent. The ice shelves in the Amundsen and Bellingshausen seas have limited or almost no ‘passive’ portion, which implies that further retreat of current ice-shelf fronts will yield important dynamic consequences. This region is particularly vulnerable as ice shelves have been thinning at high rates for two decades and as upstream grounded ice rests on a backward sloping bed, a precondition to marine ice-sheet instability. In contrast to these ice shelves, Larsen C Ice Shelf, in the Weddell Sea, exhibits a large ‘passive’ frontal area, suggesting that the imminent calving of a vast tabular iceberg will be unlikely to instantly produce much dynamic change.

(The Safety Band of Antarctic Ice Shelves). This paper attempts to describe some of the characteristics of the shelves and identify weak and strong parts.

A member of the scientific commentariat at ESA explains it this way:

It transpires that about 13% of the total ice-shelf area contains what is called ‘passive shelf ice’. This is the part of the floating ice body that provides no additional buttressing – so if lost there wouldn’t be an instant increase in glacial velocity.

However, behind this – there is an area of ice called the ‘safety band’, which is the most critical portion of the ice shelf restraining the ice flow.

Dr Johannes Fürst, from the University of Erlangen-Nuremberg’s Institute of Geography explained, “For some decades now satellite remote-sensing has allowed us to track changes and movement of Antarctic ice fronts. In some regions we have seen continuous ice-shelf recession.

“Once ice loss through the calving of icebergs goes beyond the passive shelf ice and cuts into the safety band, ice flow towards the ocean will accelerate, which might well entail an elevated contribution to sea-level rise for decades and centuries to come.”

However, there are some contrasting results across the continent as not all ice shelves have this passive ice.

Dr Fürst added, “The Amundsen and Bellingshausen seas have limited or almost no passive ice shelf, which implies that further retreat of current ice-shelf fronts will have serious dynamic consequences.

(Antarctic Safety Band At Risk). I guess this is at least a code yellow or perhaps even a code red for some locations there  (Proxymetry³ - 3).

II. Ice Sheet Gravity vs. Ice Shelf Gravity

The ice sheets have gravitational pull that pulls sea water toward the coastline and holds it there (The Ghost-Water Constant - 4).

Additionally, this ice sheet mass created gravitational pull must have an impact on the ice shelf.

It would be in the form of pressure put on the ice as the ocean water is pulled toward the landmass coastline.

Lunar and solar gravity caused tides do the same, except much more intensely I would think (Tidal Impact On Glaciers).

The ice shelves must also have that same effect on the sea water near them, a pull.

When the ice shelf breaks away, sea water is going to have an easier time getting to the shoreline.

III. Ice Shelf Gravity

Some of the ice shelves around Antarctica are massive, larger than some states or countries.

Fig. 2 Ice shelf impediments

They must add resistance to the ice sheet mass gravity pull on sea water (Fig. 2).

That is a pull that would bring sea water up against the coastline like a high tide or a storm surge.

But the ice shelf on top of the water would resist that.

So, when the ice shelf breaks away, a contradictory thing takes place.

Water will flow to the coast, the ice shelf now ice berg will float away and melt, then the resulting melt water will flow towards the bulge at the equator.

Back at the shore, the ice stream will speed up and dump ice into the sea, thereby losing mass and gravity.

Then, finally that will cut loose some ghost-water too.

In other words, ultimately near shore there will be SLF.

The bottom line, then, is an increase in both SLF and SLR, depending on location (latitude, longitude).

IV. Conclusion

While it may be true that SLC is not complicated, it is also true that it has a lot of moving parts.

And it is all happening at once .... I mean Greenland is losing ice at the same time Antarctica and Glacier Bay are.

And doing it on their own schedule.

So, predicting the intensity of catastrophes that SLC is bringing and will continue to bring for a long time, is not an exact science in terms of exactly predicting precise future time frames.

But it can determine what is coming, and give useful warnings.

Then it is up to those who should do something about it to do that something.

The previous post in this series is here.