Tuesday, May 15, 2018

On Thermal Expansion & Thermal Contraction - 35

Fig. 1
I. Got Pure Water?

One thing that is never missing in the text containing the proclamation that "thermal expansion is the major cause of sea level rise" is the dogmatic statement that "water expands when heat is added to it."

Likewise, in the similar proclamation that "thermal expansion is a major cause of sea level rise" is the dogmatic statement (or mantra?) that "water expands when heat is added to it."

The only problem with that is the scientific fact that water does not always expand when heat is added to it.

The full truth is that water expands (increases in volume) OR contracts (decreases in volume) when heat is added to it.

Fig. 2
So, what controls whether water expands or contracts when heat is added to it?

The answer is that it depends on the temperature of the water at the time the heat is added (Fig. 1).

Why is that?

That is because when the water is below its maximum density temperature (4 deg. C) the addition of heat to that water will cause it to become more dense (contraction, less volume).

Fig. 3
But, when the water is above its maximum density temperature (4 deg. C) the addition of heat to that water will cause it to become less dense (expansion, more volume).

II. Got Sea Water?

Sea water, being water and all that, holds to the same principle (Fig. 2), except that, unlike pure water, its temperature of maximum density depends on its degree of "impurity" and the pressure upon it caused by its depth (i.e. unlike pure water which always has a maximum density temperature of 4 deg. C, sea water has a sliding scale of various temperatures at maximum density).

"Impurity," then, in this case means that there is more in sea water than just "water."

Yes, the characteristic of salinity ("saltiness"), alters the temperature of sea water's maximum density, depending on the degree of that salinity.

Sea water has a complicated "personality," because depth can also play a part in altering its temperature of maximum density.

Meanwhile, science done since the early models miscalculated thermal expansion is now downplaying it:
"Research over the last few years suggests most of the rise is a result of ‘thermal expansion’ of seawater. But a new study in the journal Nature Geoscience suggests that in recent years melting ice may have been the main cause of sea level rise.

The study finds that between 2005 and 2011 melting ice sheets and glaciers were responsible for about 75 per cent of sea level rise, while the effect of water warming and expanding played a much smaller role. So does the research suggest melting ice is a bigger problem than scientists previously thought?"
(Carbon Brief Org, emphasis added). Perhaps using the old EOS-80 methods to determine the thermodynamics of sea water was the reason the old models were exaggerating thermal factors (like the early satellite data did).

The scientists were unequivocal in their paper published in Nature GeoScience:
"Our reassessment suggests an ocean mass contribution of 1.80±0.47 mm yr−1, for a total sea level rise of 2.40±0.54 mm yr−1, in agreement with the altimeter-based estimates. On the basis of the GRACE data, we conclude that most of the change in ocean mass is caused by the melting of polar ice sheets and mountain glaciers. This contribution of ice melt is larger than previous estimates, but agrees with reports of accelerated ice melt in recent years."
(Nature Geoscience, emphasis added). This is in accord with the current Dredd Blog calculations concerning the contributing factors to both sea level rise and fall.

III. Got TEOS-10?

Modern scientists need to begin to use the latest technology and formulas to determine the thermodynamics of sea water:
"The EOS-80 seawater properties are obsolete; They have been superseded by the International Thermodynamic Equation Of Seawater - 2010, (TEOS-10). The official site for the thermodynamic properties of seawater is www.TEOS-10.org.


Replacement of EOS-80 with
the International Thermodynamic Equation of Seawater – 2010 (TEOS-10)

The Intergovernmental Oceanographic Commission (IOC), with the endorsement of the Scientific Committee on Oceanic Research (SCOR) and the International Association for the Physical Sciences of the Oceans (IAPSO), has adopted the International Thermodynamic Equation Of Seawater - 2010 (TEOS-10) as the official description of seawater and ice properties in marine science. All oceanographers are now urged to use the new TEOS-10 algorithms and variables to report their work. The TEOS-10 computer software, the TEOS-10 Manual and other documents may be obtained from www.TEOS-10.org."
(TEOS-10 Org, emphasis added). "Ground control to Major Tom" comes to mind.

As regular readers know, I downloaded and now use the TEOS-10 toolkit for Dredd Blog computations (see TEOS-10 software).

I have finally developed software modules (which use that software library) to calculate (among many other things) the maximum density temperature of sea water at various depths and at various degrees of impurity.

Fig. 4 Greenland waters
As it turns out, the maximum density temperature is so low that it does not impact upon thermal expansion and contraction in the most significant geographical areas.

What I mean is that when heat is added to sea water in Greenland or Antarctica, that sea water will only expand, not contract, as a result of the added heat.

The only way the sea water in those ocean areas will contract (lose volume) is if cold water from melting glaciers flows into sea water to cool it further.

That is happening at the 0-2000 meter depth levels in those areas (Fig. 4, Fig. 5).

Compare the graph at Fig. 3 (a hypothetical maximum density of sea water at 4 deg. C), and the graph at Fig. 2 (a hypothetical maximum density of sea water at about 2 deg. C), with the graph at Fig. 4 (the actual TEOS-10 calculated temperatures and maximum densities at three depth levels).

IV. Antarctica

Fig. 5 Antarctic waters
I completed the Antarctica module that focuses on the WOD zones there.

The same maximum density conditions exist there as they do in Greenland (Fig. 5).

That is, the only thermal expansion and contraction that takes place there is also at densities above the maximum density of that sea water.

The reason I have ventured into the sea water density issue is because of what is written in the TEOS-10 manual:
"Since the density of seawater is rarely measured, we recommend the approach illustrated in Figure 1 as a practical method to include the effects of composition anomalies on estimates of Absolute Salinity and density. When composition anomalies are not known, the algorithm of McDougall et al. (2012) may be used to estimate Absolute Salinity in terms of Practical Salinity and the spatial location of the measurement in the world oceans."
(TEOS-10 Manual, p. 14, p. 24 PDF). The TEOS-10 toolkit points out (in notations) its C library function which calculates the maximum density temperature of sea water:
!elemental function gsw_ct_maxdensity (sa, p)
! Calculates the Conservative Temperature of maximum density of seawater.
! This function returns the Conservative temperature at which the density
! of seawater is a maximum, at given Absolute Salinity, SA, and sea
! pressure, p (in dbar).
! SA = Absolute Salinity [ g/kg ]
! p = sea pressure [ dbar ]
! ( i.e. absolute pressure - 10.1325 dbar )
! CT_maxdensity = Conservative Temperature at which [ deg C ]
! the density of seawater is a maximum for
! given Absolute Salinity and pressure.
(Notes in the TEOS-10 "C programming library" module). Thus, the benefit we derive from having developed those modules is to simplify the calculations necessary to compute thermal expansion and contraction (On Thermal Expansion & Thermal Contraction, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34).

Tidewater glacier ice melt by sea water takes place at very cold temperatures, so very little warming at great depths will cause abundant sub-surface melting  (Hot, Warm, & Cold Thermal Facts: Tidewater-Glaciers, 2, 3, 4).

That is why hundreds of them are melting in Antarctica (Antarctica 2.0, 2, 3, 4, 5, 6 [& supplements A, B, C, D, E, F]) and in Greenland (Greenland 2.0, 2).

V. Conclusion

Imagine the difficulty in calculating actual thermal expansion and contraction if the maximum density was at 4 deg C or at 2 deg C (as shown in Fig. 2 and Fig. 3).

As we now know, the only thermal expansion which needs to be calculated is based on an increase in the Conservative Temperature (CT), while the only thermal contraction to be calculated is based on a decrease in the CT of the sea water (because the "Conservative Temperature of maximum density of seawater" is not generally crossed over according to in situ measurements).

That simplifies things, but changes nothing concerning the Dredd Blog hypothesis that, all things considered, thermal expansion is a minor factor in sea level change.

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

No comments:

Post a Comment