Saturday, September 11, 2021

Quantum Oceanography - 13

Fig. 1 Antarctic Areas

I. Review

This series has been focused on the heat content of seawater, in terms of the potential to emit that heat in the form of infrared photons (Quantum Oceanography, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12; The Ghost Photons; The Photon Current).

In some of the recent posts the issue of the location of infrared photons in seawater was focused on, in terms of whether those photons were primarily located in the water molecules or in the 'salt' molecules, or maybe both.

This is an important issue for successfully understanding the dynamics of how seawater freezes, as well as for grasping the dynamics of how seawater melts glacial ice in and around Antarctica in the Southern Ocean (Fig. 1, Fig. 2).

II. Seawater Temperatures Near Tidewater Glaciers

Today's set of graphs (Fig. 3 - Fig. 8) show the seawater temperature impacting the 'grounding line' ice of Antarctic 'ice sheets'.

An 'ice sheet' is where the ice flows along the ground of the continent down to the coastal area of the Southern Ocean where they become 'tidewater glaciers'.

Fig. 2 WOD Zones within Antarctic Areas

The 'grounding line' is the point where 'tidewater glaciers' leave the ground or seabed to float.

The area of the tidewater glacier that is floating on the ocean is not called an 'ice sheet', rather, it is called an 'ice shelf'.

Most of the melting of the glacial ice takes place at the face of tidewater glaciers at or above their 'grounding line' .

As you can see from the graphs (Fig. 3 - Fig. 8), the seawater along the grounding line and above it along the face of the tidewater glaciers is warm enough to melt the ice.

The graph lines at the bottom of the graphs indicate the melting point of the glacial ice, while the lines at the upper portion of the graphs indicate the 'CT' of the seawater ('CT' means Conservative Temperature).

III. Ice Sheets Are Not Frozen Seawater

Fig. 3 Western Pacific Area B

The ice sheet is frozen fresh water, and the ice shelf is close to the same.

During Antarctic winters the temperature is cold enough to freeze the surface of the Southern Ocean surrounding it.

When that seawater freezes, what happens is basically a separation of the water from the salt.

In other words, the water goes in one 'direction', but the minerals ('salinity') go in another 'direction': "Ocean water freezes just like freshwater, but at lower temperatures. Fresh water freezes at 32 degrees Fahrenheit but seawater freezes at about 28.4 degrees Fahrenheit, because of the salt in it. When seawater freezes, however, the ice contains very little salt because only the water part freezes. It can be melted down to use as drinking water" (Can the ocean freeze?).

The 'direction' I mentioned is that upon freezing the water portion of seawater goes upward because it is less dense than the brackish brine that goes downward.

Fig. 4 Weddell Sea Area F

What this means is that the upward moving now-fresh water can refreeze to become the lower portion of the ice shelf, but the now very salty brine won't refreeze.

IV. The 'Warm' Water

As you can see from the graphs, the temperature of the seawater is warmer as the depth increases (at least up to a point).

The surface to 200 meters down is the Epipelagic, below that to 1,000 meters is the Mesopelagic, and below that down to 4,000m is the Bathypelagic (Pelagic zone).

These warmer depths (see graphs) cover most of any tidewater glacier grounding line depths, and above, so a lot of melt is taking place along the ~58,000 kilometers of Antarctica's Tidewater Glaciers.

V. The Infrared Photons

I found a research paper that probably answers the question "does the water absorb, harbor, and radiate the infrared photons (a.k.a. "potential enthalpy" or "ocean heat") or does the 'salinity' part of seawater do it?":

Fig. 5 Ross Sea Area C

"The analysis by infrared spectroscopy of aqueous solutions of the binary inorganic salts NaI and NaCl and the ternary salts CaCl2 and BaCl2 at concentrations from 1000 to 2mM was carried out to complement a previous study done at higher concentrations on nine binary salts (alkali halides) and one ternary salt (MgCl2) [J.-J. Max and C. Chapados, J. Chem. Phys. 115, 2664 (2001)]. These salts are completely ionized in aqueous solutions, forming monoatomic species that do not absorb IR [infrared]"

(Scitation Org, emphasis added). That is a reasonable conclusion in the sense that the pure water is about 96.5% and the salinity is about 3.5% of seawater:

Fig. 6 Indian Ocean Area A

"The infrared spectrum of liquid water is dominated by the intense absorption due to the fundamental O-H stretching vibrations. Because of the high intensity, very short path lengths, usually less than 50 μm,are needed to record the spectra of aqueous solutions. There is no rotational fine structure, but the absorption bands are broader than might be expected, because of hydrogen bonding.​ Peak maxima for liquid water are observed at 3450 cm−1 (2.898 μm), 3615 cm−1 (2.766 μm) and 1640 cm −1 (6.097 μm). Direct measurement of the infrared spectra of aqueous solutions requires that the cuvette windows be made of substances such as calcium fluoride which are water-insoluble. This difficulty can alternatively be overcome by using an attenuated total reflectance (ATR) device rather than transmission."

Fig.7 Bellingshausen Sea Area E

"In the near-infrared range liquid water has absorption bands around 1950 nm (5128 cm−1), 1450 nm (6896 cm−1), 1200 nm (8333 cm−1) and 970 nm, (10300 cm−1). The regions between these bands can be used in near-infrared spectroscopy to measure the spectra of aqueous solutions, with the advantage that glass is transparent in this region, so glass cuvettes can be used. The absorption intensity is weaker than for the fundamental vibrations, but this is not important as longer path-length cuvettes can be used. The absorption band at 698 nm (14300 cm−1) is a 3rd overtone (n=4). It tails off onto the visible region and is responsible for the intrinsic blue color of water. This can be observed with a standard UV/vis spectrophotometer, using a 10 cm path-length. The colour can be seen by eye by looking through a column of water about 10 m in length; the water must be passed through an ultrafilter to eliminate color due to Rayleigh scattering which also can make water appear blue."

Fig. 8 Amundsen Sea Area D

"The spectrum of ice is similar to that of liquid water, with peak maxima at 3400 cm−1 (2.941 μm), 3220 cm−1 (3.105 μm) and 1620 cm−1 (6.17 μm) ... In both liquid water and ice clusters, low-frequency vibrations occur, which involve the stretching (TS) or bending (TB) of intermolecular hydrogen bonds (O–H•••O). Bands at wavelengths λ = 50-55 μm or 182-200 cm−1 (44 μm, 227 cm−1 in ice) have been attributed to TS, intermolecular stretch, and 200 μm or 50 cm−1 (166 μm, 60 cm−1 in ice), to TB, intermolecular bend"

...

"The extra bonding between water molecules also gives liquid water a large specific heat capacity. This high heat capacity makes water a good heat storage medium (coolant) and heat shield." 

...

"Water is relatively transparent to visible light, near ultraviolet light, and far-red light, but it absorbs most ultraviolet light, infrared light [infrared photons], and microwaves."

(Wikipedia, Electromagnetic absorption by water, emphasis added). The H2O portion of seawater at ~96.5% carries the "potential enthalpy" in the form of infrared photons much more so than does the ~3.5% salinity portion.

VI. Closing Comments

This research in this series has been useful at informing us of the reality of what is taking place at Tidewater Glaciers in Antarctica. (cf. On the interpretation of the steric and mass components of sea level variability: The case of the Mediterranean basin; Steric sea level variations during 1957–1994: Importance of salinity).

Quantum Oceanography matters (see video below).

The previous post in this series is here.



1 comment:

  1. It is amazing that the commentariat (link) is not aware that 'ocean heat' is 'potential enthalpy' (link).

    Got TEOS-10 (link)?

    ReplyDelete