Friday, March 22, 2019

The Gravity of Sea Level Change - 5

Three at a time
I. The Competing Melts

I haven't written a post in this series about the gravity of sea level change (SLC) for several years now (The Gravity of Sea Level Change, 2, 3, 4).

However, recently I did present some graphics concerning how gravity and the Earth's rotation determine several aspects of SLC (see Fig. 1, Fig. 2, and Fig. 3 at this post: Countries With Sea Level Change - 2).

Today, I thought I would mention relevant factors in the context of tidewater glaciers and their individual impacts on SLC.

Regular readers know that I do not use sea level rise (SLR) as the only event taking place as a result of melting ice sheets.
Antarctica (0 - 200 m)
Antarctica (>200 - 1000 m)
Glacier Bay (0 - 200 m)
Glacier Bay (>200 - 1000 m)
Greenland (0 - 200 m)
Greenland (>200 - 1000 m)
Patagonia (0 - 200 m)
Patagonia (>200 - 1000 m)
Svalbard (0 - 200 m)
Svalbard (>200 - 1000 m)

I also discuss SLC as well as the least known of the trio, sea level fall (SLF).

Some researchers see SLF as the trouble maker because those who see ghost water describe it as "a seawater relocation dynamic" brought to us by gravity and the planet's rotation.

If you don't already see ghost water, but now want to see it, then peruse the post NASA Busts The Ghost.

The gist of it is that SLC is composed of both SLF and SLR (Woodward, 1888, PDF).

II. The SLC Theaters
Featuring The Three Melts

The WOD in situ data used to generate today's graphs concern the following theaters or areas: Antarctica, Greenland, Glacier Bay, Svalbard, and Patagonia.

The graphs of those areas display Conservative Temperature (CT), Absolute Salinity (SA), Potential Enthalpy (hO, a.k.a. Ocean Heat Content), and Depth-Pressure (P).

They appear in that order on the graphs (upper left pane, upper right pane, lower left pane, lower right pane).

Depth is in meters and Pressure is in dbars (the numbers on the graphs showing depth and pressure values represent both, i.e. "100" means both 100 dbars of pressure and 100 meters of depth).

III. The Two Pelagic
Depth Layers

Since we are focusing on tidewater glaciers, the graphs depict the two top pelagic depths: Epipelagic (0 - 200 m) and Mesopelagic (>200 - 1000 m).

Those depths should contain the grounding line depth of most tidewater glaciers, so we look at the characteristics of seawater and glacial ice in those two top layers.

The heat content calculated by the TEOS-10 toolbox software is expressed in Joules per kilogram (J/kg) while the seawater temperature is expressed in proportional degrees Celsius (C).

Thus, the patterns on the graphs made by temperature and heat content are in proportion to one another (the patterns match even if the values are not equal).

But, Absolute Salinity, pressure, and depth are not in proportion with the heat content and temperature.

Heat content is something that is added to the seawater, like heat that is added to anything - it comes from a heat source.

The Sun heat source radiates heat then green-house gases trap some of that heat, and most of the heat is then added to the oceans.

When the heat content of seawater atoms and molecules is near or in contact with tidewater glaciers the heat flows spontaneously from the seawater into the ice, causing it to change its state from ice to melt water.

The number of photons of infrared radiation which radiate from seawater into glacial ice can be calculated (The Ghost Photons, 2, 3).

IV. The Areas

The five areas mentioned in Section II above have either ice sheets, large glacial fields, or ice caps.

These areas cause SLF near them as they loose mass and gravitational pull while melting.

Tide gauge stations within about 2,000 km of such an area show SLF over the years as the seawater is relocated by the Earth's rotation to other areas of the oceans (Proof of Concept, 2, 3, 4, 5, 6, 7, 8, 9).

At the distance of "the hinge point" (~2,000 km) SLR takes over, as SLF disappears (The Evolution and Migration of Sea Level Hinge Points, 2).

The further away from an ice sheet a tide gauge station is located, the more it will experience SLR from that ice sheet's loss of ice, and the closer a tide gauge station is to an ice sheet, the more it will experience SLF as the seawater around the ice sheet is released from that ice sheet's mass-induced gravitation (ibid).

V. The Measurement Results

The measurements taken by research scientists over the years, and used to make today's graphs, show that tidewater glaciers are increasingly impacted by seawater that contains enough heat content in it to radiate heat into tidewater glaciers.

Some large areas of Antarctica tidewaters contain glaciers that show a six-fold increase in melting over the span of time from 1979 through 2017 (Four decades of Antarctic Ice Sheet mass balance from 1979–2017).

Greenland glacial melt is also increasingly based on tidewater characteristics:
"These rates of submarine melting are two orders of magnitude larger than surface melt rates, but comparable to rates of iceberg discharge. We conclude that ocean waters melt a considerable, but highly variable, fraction of the calving fronts of glaciers before they disintegrate into icebergs, and suggest that submarine melting must have a profound influence on grounding-line stability and ice-flow dynamics ... The widespread two to threefold acceleration of the glaciers cannot be explained solely by enhanced lubrication of the bed from surface meltwater ..."
(Rignot et al. 2010, Nature Geoscience). The place where the action is happens to be the tidewaters of the areas show in today's graphs.

These are areas where ocean heat and glacial melt is generally increasing.

VI. Closing Comments

The next phase of linking ocean heat content, tidewater glaciers, and SLC together will be "Countries With Sea Level Change - 3".

It will be written in the style of Countries With Sea Level Change - 2.

The exercise in that post will be to attribute SLC values to each of the various areas detailed today.

In other words, the part each area contributes to the SLC of those countries will be quantified as percentages of SLC (SLR or SLF).

The previous post in this series is here.

Lyrics to Overkill are here.