PACROFI VI - Electronic Program


CalcicBrine: a Microsoft Excel 5.0 Add-in for calculating salinities from microthermometric data in the system NaCl-CaCl2-H2O

Jon Naden

The British Geological Survey
Sir Kingsley Dunham Centre
Keyworth
Notts.
NG12 5GG, UK
e-mail: j.naden@bgs.ac.uk


Experimental data (Yanatieva, 1946; Vanko et al., 1988; Oakes et al., 1989) in the system NaCl-CaCl2-H2O have been regressed, using a stepwise procedure, to give the following equations:
W = co + aoT + a1R + a2T2 + a3R2 + a4RT2 + a5T3 + a6T4 + a7T5 + a8T5R	ice field
W = co + aoT + a1R + a2R2 + a3R3 + a4TR					hydrohalite field
W = co + aoT + a1R + a2T2 + a3R2 + a4R2T + a5R3 + a6TR			halite field
R = co + aoT + a1T2 + a2T3 + a3T4					ice and halite cotectics
Where:
W = bulk salinity (weight percent)
R = NaCl/(NaCl+CaCl2) weight ratio
T = Tm ice/100, T m hyd/100 or T m halite/100
The coefficients for above equations are as follows:
ice fieldhydrohalite fieldhalite fieldice cotectichalite cotectic
c00.466850 38.66684238.3510909.1263721.008221
a0-205.081250 8.9679078.25242175.2720011.341051
a1-1.138304 -62.595465-65.222188236.734329-182.932290
a2-899.749300 118.8868661.808600331.685986-1541.129700
a30.269882 -68.657555121.296429173.312094-3515.971800
a468.878422 4.595326.097604
a5-2546.864100 -68.266584
a6-3731.983700 -16.692281
a7-2147.886100
a8137.774293

An algorithm, written in Visual Basic for Applications, has been developed to calculate weight percent equivalent NaCl + CaCl2 and the NaCl/(NaCl+CaCl2) weight ratio from microthermometric data (Tm ice, Tm hydrohalite, Tm halite). The algorithm uses similar principles to those described in Bodnar et al. (1989) to solve the above equations for T, using paired input data of Tice-Thyd for compositions in the ice and hydrohalite fields or Tice-Thalite for compositions in the halite field.

Experimental bulk-salinity data are generally reproduced to within 3 percent for finalmelting in the icefield, 10 percent for bulk compositions in the hydrohalite-field and 6 percent for compositions in the halite-field. The regression equations tend to model the data of Oakes et al. (1990) and Vanko et al. (1989) better than the data Yanatieva (1946).

Limitations to the applicability algorithm are as follows:

  1. Final-ice melting (Tm ice)must be between -52 and 0.0oC
  2. Hydrohalite melting (Tm hydrohalite) must be between -52 and 0.1oC
  3. Final ice-melting and hydrohalite melting must not be above -21.2oC
  4. Halite (Tm halite) dissolution should be between 0.1 and 500oC
  5. For final-melting/dissolution in the halite field, ice-melting must be in the presence of hydrohalite
The function will not calculate salinity data where input data do not meet criteria 1 to 4 or where microthermometric data indicate compositions in the antarcticite field. However, the function will calculate salinities where ice melts metastably in the presence of halite. This is due to the construction of the algorithm; it uses ice-melting temperatures to calculate Na to Ca ratios for final melting in all three fields of the system. Thus, to preserve flexibility, it does not discriminate between stable and metastable ice melting. The algorithm is currently being modified to include a metastable ice-hydrohalite cotectic (see discussion in Vanko et al. 1988 p. 2455).

Copies of the Excel Add-in are available, by e-mail, from the author (j.naden@bgs.ac.uk).

Apple Macintosh System 7.0, 16MB RAMMicrosoft Excel 5.0
IBM PC or compatibleWindows 3.1 or `95, 16MB RAMMicrosoft Excel 5.0


References