Friday, December 28, 2018

A Tale of Two Glaciers

Fig. 1 Where The Money Melt Is
I. Background

There was a conversation between a lawman and a lawless man.

It went something like this: "Why do you rob banks?" asked the lawman, to which the lawless man replied "That is where the money is!"

Readers of Dredd Blog may wonder why I care about a minority class of glaciers (tidewater glaciers) and a minor section of those glaciers (their terminus) which are found in tidewaters along the coasts of Greenland and Antarctica (e.g. The Ghost Plumes, 2, 3, 4; In Pursuit of Plume Theory, 2, 3).

The answer to that wonder is illustrated in Fig. 1, which shows two glaciers in Greenland.

One of those glaciers is melting rapidly, the other one which is next to it, is melting very slowly by comparison.

II. What Is And What Is Not Questioned

The melt-rate difference between the two side-by-side glaciers is not questioned:
"Tracy and Heilprin, marine-terminating glaciers that drain into the eastern end of Inglefield Gulf in northwest Greenland, exhibit remarkably different behaviors despite being adjacent systems. Losing mass since 1892, Tracy Glacier has dramatically accelerated, thinned, and retreated. Heilprin has retreated only slightly during the last century and has remained almost stationary in the most recent decade. Previous studies suggest that Tracy’s base is deeper than Heilprin’s at the calving front (over 600 m, as opposed to the 350 m depth at Heilprin), which exposes it to warmer subsurface waters, resulting in more rapid retreat. We investigate the local oceanographic conditions in Inglefield Gulf and their interactions with Tracy and Heilprin using data collected in 2016 and 2017 as part of NASA’s Oceans Melting Greenland mission. Based on improved estimates of the fjord geometry and 20 temperature and salinity profiles near the fronts of these two glaciers, we find clear evidence that fjord waters are modified by ocean-ice interactions with Tracy Glacier. We find that Tracy thinned by 9.9 m near its terminus between 2016 and 2017, while Heilprin thinned by only 1.8 m."
(Willis et al. 2018, Oceanography, Volume 31, No. 2, emphasis added). But the explanation for the contrast in melt-rate between the two glaciers is questioned.

The authors of that paper adopt basal melt plume theory (BPT) to try to explain the phenomenon.

They do so even when the basal melt water volume of Heilprin is much larger than that of Tracy:
"Heilprin Glacier has a much larger runoff catchment [than Tracy], resulting in higher peak subglacial discharge [but less ice melt and grounding line retreat]"
(ibid). Furthermore, the BPT theory is not robust.

Nevertheless, it is currently in practically universal use when researchers try to explain tidewater basal glacial melt.

Using BPT alone, they are evidently unaware of the hypothesis of thermodynamic forcing (ghost plumes).

They also resort to BPT even though the following statement is found in the literature:
"However, without direct observations of subglacial channels/outlets or their upwelling plumes, the geometries used in these [BPT] plume models are unvalidated ... Although [BPT] plume theory is idealized, it is currently the primary (almost exclusive) tool for tuning or parameterizing plumes in numerical models."
(Surveying subglacial discharge plumes, emphasis added). There is no consideration that I am aware of for the thermodynamic forces I have set forth in previous Dredd Blog posts outlining the hypothesis of the ghost plumes, or Ghost Plume Theory (GPT).

III. Look For The Ocean Heat

The essence of general "ocean heat" or specific "tidewater heat" and its impact on tidewater glaciers is not properly addressed by analyzing atmospheric-temperature-caused glacial surface melt, mixed with basal friction melt, as is typically done in current research papers (In Pursuit of Plume Theory, 2, 3; The Ghost Plumes, 2, 3, 4).

Those basal melt dynamics produce fresh basal melt water that exits at the glacier's grounding line, but IMO that is not sufficient to explain the contrast between Tracy and Heilprin.

When we search for "ocean heat" the place to look and analyze is ocean water instead of basal melt water (In Search Of Ocean Heat, 2, 3).

The specific thermodynamic property to look for in ocean water is potential enthalpy (Patterns: Conservative Temperature & Potential Enthalpy, 2).

The specific quantity of potential enthalpy to look for in seawater that comes in contact with tidewater glaciers is the amount of potential enthalpy required to melt the glacial ice.

IV. Conclusion

The proper tool to use in order to determine the potential enthalpy amount (the heat content) is the Thermodynamic Equation Of Seawater - 2010 (TEOS-10).

When basal melt, calving, and the thermodynamic melt of the ghost plumes are added together, then we are where we need to be.

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