Friday, March 27, 2020

The Ghost Plumes - 11

Fact Finder
I. Yesterday

The fundamental quantum of an expert opinion concerning glacier/ocean interaction is scientific fact.

The fundamental quantum of scientific fact is in situ measurements.

These facts are collected then presented in the form of a hypothesis.

A valid hypothesis is one that can be either confirmed or falsified:
"Do whatever it takes ensure you do not fool yourself into thinking something is true that is actually false, or that something is false which is actually true."
(Neil deGrasse Tyson). This is an exercise that can be difficult at times, extremely difficult at other times, and virtually impossible upon occasion.

Even in very recent history we see the statement "worse than previously thought" or something similar, which illustrates the point that some science is difficult even for experts.

For example, not long ago scientists contributing to the content of textbooks were sure that East Antarctica's Ice Sheet was "stable" and its volume was increasing, that the greatest quantity of Antarctica's and Greenland's Ice Sheet melt was taking place above sea level, that Antarctica's ice melt lagged behind Greenland's ice melt, and that glacial plumes were things that originated only in basal melt.

II. Now

Now the science informs us that East Antarctica is melting, most glacial melt takes place below sea level, and that basal melt ultimately slows the process of glacial ice flow on land (see video of Dr. Rignot who was recently voted into a scientific "Academy").

In addition to that, I argue that most of that below-sea-level melt takes place in the form of plumes formed at or above the grounding line where ambient ocean water radiates infrared photons into the ice face.

That eventually causes the ice to melt which, along with other physical phenomena, generates a plume flow.

It is a continuous process conforming to the laws of thermodynamics.

See: The Ghost Plumes, 2, 3, 4, 5, 6, 7, 8, 9, 10  and The Ghost Photons, 2, 3.

III. Tomorrow

The object of this Dredd Blog series is to produce software and analyze scientific papers that can help us grasp polar ice sheet melt at the grounding lines of tidewater glaciers, and then report about it to readers.

I have made some helpful strides in that direction lately, and want to update Dredd Blog readers about what it means for the future.

Regular readers know that at this blog readers and I are aware of coming dangers like some observers were aware of the coming danger posed by the infamous Coronavirus:
"It's very hard to get one's mind around the scale of the developing [coronavirus pandemic] calamity. But it also provides an important window into a potential future of unchecked climate change. The coronavirus pandemic is a warp-speed tutorial in what will happen if we don't get our act together and slash greenhouse gas emissions.
This is what an uncontrolled, exponentially-accelerating crisis looks like on the ground: first slow, then all at once. Past procrastination and dithering means that once the seriousness of what is happening is undeniable, the worst effects can only be mitigated, not avoided.

Climate change is going to be exactly like this ..."
(Coronavirus And Climate Change). Unfortunately, the current U.S. administration is composed primarily of deniers in both the Corona-virus and climate change situations.

So, like the governors of the states, we who are concerned must "go it alone" without any help from the deniers.

IV. Recent Ice Sheet Developments

In addition to Antarctica's Thwaites and Totten glaciers, the Denman glacier is receiving a lot of attention lately:
"East Antarctica’s Denman Glacier has retreated nearly 3 miles over the past two decades, losing 268 billion tons of ice between 1979 and 2017, according to a new study published in the journal Geophysical Research Letters. If the glacier were to melt completely, it holds enough water to raise global sea levels by about 5 feet.

The 9,266-square-mile glacier currently fills Antarctica’s deepest canyon. As it melts, water is traveling from the canyon into the ocean. Scientists warn the shape of the ground under the ice makes it very susceptible to rapid climate-driven collapse. Not only would this raise sea levels globally, the unblocked canyon could also serve as a pathway for ocean water to penetrate inland and further melt ice sheets.

'The configuration of the bed of the glacier makes this one of the weakest spots in east Antarctica,' Virginia Brancato, a NASA scientist and lead author of the new study, told The Washington Post. 'If I have to look at East Antarctica as a whole, this is the most vulnerable spot in the area.'"
(A Massive Glacier in East Antarctica Has Retreated 3 Miles in 22 Years, emphasis added; accord East Antarctica's Denman Glacier has retreated almost 3 miles over last 22 years).

V. Recent Software Development

The software I mentioned above is designed to calculate the quantity of ice melt and plume volume, which includes Thwaites, Totten, Denman, and all other tidewater glaciers of Antarctica.

This is accomplished with the help of the scientists who mapped out the grounding line lengths (Bindschadler, et. al.).

That paper and the ASAID data along with it give us the lengths of the grounding lines in each WOD zone (the length of the grounding line can be larger or smaller than the zone dimensions).

That leaves us with the height and depth(a.k.a. thickness).

The depth(a.k.a. thickness) is easy, 1 meter thick (a cubic meter, m3), because the TEOS-10 software formulas deal with one meter thickness dimensions (a cubic meter, m3).

That leaves us with the plume height, which is "not an exact science."

By that I mean we must work backwards from a Dr. Rignot et. al paper which gives us the annual gigatonne loss for Antarctica:
"The total mass loss from Antarctica increased from 40 ± 9 Gt/y in the 11-y time period 1979–1990 to 50 ± 14 Gt/y in 1989–2000, 166 ± 18 Gt/y in 1999–2009, and 252 ± 26 Gt/y in 2009–2017, that is, by a factor 6 (Fig. 2, Table 1, and SI Appendix, Fig. S1). This change in mass loss reflects an acceleration of 94 Gt/y per decade in 1979–2017, increasing from 48 Gt/y per decade in 1979–2001 to 134 Gt/y per decade in 2001–2017, or 280%. Most of the 1979–2017 acceleration is from West Antarctica (48 Gt/y per decade), followed by East Antarctica (29 Gt/y per decade) and the Antarctic Peninsula (16 Gt/y per decade) (Fig. 3). In 2009–2017, West Antarctica contributed 63% of the total loss (159 ± 8 Gt/y), East Antarctica 20% (51 ± 13 Gt/y), and the Peninsula 17% (42 ± 5 Gt/y) (Table 2). The mass loss from West Antarctica is three to four times larger than that from East Antarctica and the Peninsula, respectively. We find that the Antarctic Ice Sheet has been out of balance with snowfall accumulation the entire period of study, including in East Antarctica."
(Four decades of Antarctic Ice Sheet mass balance from 1979–2017, emphasis added). That gives me something to start with.

In the video below Dr. Rignot says "most of the [ice sheet] changes are ... where the glaciers meet the ocean ... all the [major] changes [are] taking place [at the grounding line] ... calving is just a participant to that".

Calculating plume flow / ice melt using Dredd Blog software and the TEOS-10 toolbox is a matter of applying the WOD dataset of in situ measurements (temperature, salinity, depth, latitude, and longitude taken in relevant proximity) to the grounding line.

Various TEOS-10 functions can, using those measurements, calculate whether or not the ice will melt at those locations under those measured conditions.

If the calculations determine that melt will take place, then comes the calculation for the density of the melt water compared to the density of the ambient seawater.

Those, along with the gravitational force at that location, and the height of the ice that is "in contact" with the seawater, will determine the plume flow per cubic meter all along the grounding line.

So, one must (to derive the full ice-melt and resulting plume flow) also estimate the "height."

For the graphs in today's appendices I use 15 meters for the Epipelagic depth level ice height, 30 meters for the Mesopelagic depth level ice height, and 15 meters for the Bathypelagic depth level height.

In other words, a 15 meter high, 1 meter thick, gazillions of meters long (the grounding line length) strand of ice melts into a plume component (along with an additional a 30 meter high, 1 meter thick, gazillions of meters long (the grounding line length) strand of ice, along with the final  15 meter high, 1 meter thick, gazillions of meters long (the grounding line length) strand of ice.

There are only three depth components because  the Abyssopelagic and Hadopelagic depths are not included because tidewater glacier grounding lines don't go that deep at this time (the Denman glacier may do so when the melt moves the grounding line further inland).

With those values the graphs show about a 170 gigatonne ice melt generating about a 159 gigatonne plume flow for 2019.

Which brings up the other uncertainty, which is how much is "most"?

Dr. Rignot says that "most" ice loss takes place by melt under the ocean surface, not in the glacial flow of ice into the ocean.

The "most" I currently calculate is 68% plume flow/underwater melt with 32% glacial calving & surface melt.

In future posts I expect to become more exact on "most".

Which, in terms of software, will be easy because all I have to do is change the 15, 30, 15 meter values up or down and the software will automatically re-calculate and generate new graphs (in seconds).

In terms of digits I am looking for precise numbers from anyone ... hey readers jump in ... with your comments on the 15, 30, 15 parameters.

VI. Closing Comments

Today's Appendices contain graphs made from WOD data processed through the TEOS-10 C++ toolkit.

Appendix A shows plume flow quantities in gigatonnes for various areas around Antarctica, and a final combination thereof.

Appendix B shows ice melt quantities in gigatonnes for the same areas.

Note that ice melt quantities are about 1.08 times larger than plume volume quantities because ice has a lower density per cubic meter (metre) than seawater (ice takes up more space than water does).

The next post in this series is here, the previous post in this series is here.

Academy of Sciences member Dr. Eric Rignot:

No comments:

Post a Comment