Calculating the Concentrations of an Icy Brinicle of Death

This article is the follow-up to the Icy Brinicle of Death: A COOL Example of Freezing Point Depression. Specifically, this short post provides a sample calculation to determine the molality, m, of an icy brinicle, or "icy finger of death".

Fresh (pure) liquid water freezes at 0 degrees Celsius (32 degrees Fahrenheit), but the freezing temperature of seawater, a complex combination of water and salts, varies on account of the varying concentrations of dissolved salts, its salinity. Salinity is a measure of the concentration of dissolved salts in water and is usually described in practical salinity units (psu), which is equivalent to parts-per-thousand (ppt), or kilograms salt per thousand kilograms water. For every 5 psu increase in salinity, the freezing point decreases by 0.28 degrees Celsius (0.5 degrees Fahrenheit)1; thus, in polar regions with an ocean salinity of about 32 psu, the water begins to freeze at -1.8 degrees Celsius (28.8 degrees Fahrenheit)1. Though the Arctic Ocean is generally fresher (less saline) than other oceans (with psu values between 30 and 34), its salinity varies by region and distance from the coast (near shore versus off shore waters)1.

For example, in January 2014 along the coast of the White Sea recorded that at an air temperature of −1 °C the brine salinity was between 30 and 35 psu while the salinity at sea was 28 psu.2 And when the air temperature was −12 °C the salinity of the brine increased to between 120 and 156 psu2. As 90% of ocean salt is composed of sodium chloride3, van Hoff’t factor is two.

156 psu x ( 0.28 °C / 5 psu ) = 8.7 ° C --> Delta Tf = Kf * i * m
8.7 °C = ( 1.86 °C / m) (2) * m

m = 2.3 mol NaCl / kg H2O = 135 g NaCl in 1 liter of sea water.



1. Cottier, F., Eicken, H., & Wadhams, P. (1999). Linkages between salinity and brine channel distribution in young sea iceJ. Geophys. Res. 104(C7), 15859–15871. doi:10.1029/1999JC900128

2. Voronova, A., Krasnova, E. & Voronov, D. (2015). A simple method to demonstrate that ice formation creates stratification in salt meromictic lakes. EARSeL eProceedings, 14(S1): 23-27. Accessed May 10, 2021,

3. salty?qt-science_center_objects=0#qt-science_center_objects; Accessed May 10, 2021