Dear Souad Annane.

You asked a question for which there is no correct answer.

Salinity is the total amount of all salts in grams dissolved in 1 kg of sea water. The main composition of sea water (in ions) is as follows (°/oo): Сl- (18.979); SO42- (2.6486); HCO3 (0.1397); Br- (0.0646); F-(0.0013); H2BO2 (0.0260); Na+ (10.5561); Mg2+ (1.2720); Ca2+ (0.4001); K+ (0.3800); Sr2+ (0.0133). Salinity is measured by measuring the concentration of the chloride ion, assuming a constant salt composition of sea water (Dietmar's law). This law does not apply to river mouths. I regret.

Electrical conductivity does not characterize the total weight of all salts in grams dissolved in 1 kg of sea water. Salt ions with a large weight may have a small electrical charge, and ions with a small weight may have a large electrical charge.

If you need a conversion with an unknown accuracy, use the calculator:

https://planetcalc.ru/9427/

But I guarantee the answer is false.

Hi

I dont agree with Borys Kapochkin , as you mentioned CTD devices measure Temperature and electric conductivity to calculate Salinity (what Borys missed is that in seawater the ratio between different salts is conservtive).

The answer to your question depends on the type of CTD you are using, most of the brands (actually all of the brands I know) have a software that automatically calculates salinity.

If you want a more general solution, there is a software package in many programing languages (on the TEOS-10 website https://www.teos-10.org/software.htm). TEOS 10 is the latest international standard for seawater thermodynamic calclations.

Kindly check the online calculater, which converts conductivity to salanity at specific water temperature.

note: Equations used are based on the practical salinity scale and are valid for surface waters with salinity between 2 and 42 ppt

online calculater : - http://www.fivecreeks.org/monitor/sal.shtml

for more reference about formulation : - https://slideplayer.com/slide/7640533/

Dear Yair Suari,

I wrote everything correctly. You read my answer inattentively. I voiced one definition and two theses.

Definition. Salinity is the total amount of all salts in grams dissolved in 1 kg of sea water.

Thesis one. The correct determination of salinity is made by evaporating water and weighing the solid residue. I missed a few details. In fact, the concentration of the chlorine ion is measured, and on the basis of Dietmar's law (the law of the constancy of the ratios between ion concentrations), the salinity is calculated using the Knutsen formula. Everyone understands that in this case salinity is not measured (not measured). Who can confirm the correctness of Dietmar's law and Knudsen's formula. These formulas are over 100 years old. I doubt them. For example, Dietmar's law is based on only 107 water samples from the surface of the ocean. How to treat him?

Thesis second. The conversion of electrical conductivity to salinity is possible if there is a reliable correlation between molecular weight and electric charge. There is no such correlation. I'll give you an example. The sodium ion has the same electrical charge as the chloride ion (one missing/extra electron). But the molecular weight of sodium is about half that of chlorine. Thus, 10 g of sodium will carry an electrical charge twice that of 10 g of chlorine.

Where am I wrong?

Я это делал градуировкой, но нужна соль для эталона соответствующая той, которой будете измерять. И надо обратить внимание. чтоб электроды не покрывались наслоениями.... Лучше на слабом переменном токе.

Чем больше соли (до определенного количества), тем выше ток.

It seems to me that Yair's comment that in seawater the ratio between different salts is conservative is accurate, therefor simple formulas relating conductivity to salinity may be accurate over a wide range of salinity. Exceptions:(1) concentrated brines (where some ions may precipitate out)--is this an estuary in one of the oceans, or instead in an inland briny sea?--or are there places in the estuary where significant evaporation & briney water occurs? (2) where an estuary is fed by a brackish (or briney) stream that may have different ratios of dissolved ions than does the seawater it flows into.

Dear Souad Annane

The value of Electrical Conductivity converted to salinity by the following formula

Salinity (‰) = 𝐄𝐂 (μ𝐒/𝐜𝐦) × 𝟎.𝟎𝟎𝟎𝟔𝟒

* Typically expressed in ppt (part per thousand)

Dear colleagues

Your communication regarding the transfer of electrical conductivity to salinity was transformed from a purely technical question into a scientific discussion, which cannot but please the researcher. I remember my surprise when I first learned about the law of constancy of the salt composition of the water of the World Ocean. It seemed to me at the time that such a thing could not happen and it was on the verge of fiction. What are the reasons for these surprising ratios? The ways of entry of potassium, calcium, boron, and chlorine ... into the ocean are different, but the result is always the same. What processes control this effect? There is no theory on this issue yet, although I once read one of the hypotheses of an American scientist (unfortunately, I forgot his last name). The same applies to the selectivity of absorption-transmission of solar radiation by the atmosphere, water and the optical range (human eye); functions of the Skin - layer of the Ocean. The same wonderful things are discovered when studying the phenomenon of wind waves, which absorb more than 80% of wind energy and spend it practically on idle work, scrolling water particles in one place. That is, the Ocean system has certain mechanisms of regulation and self-protection from external influences to preserve its identity. And we are somewhere not far from the beginning of understanding these processes.

Consider that this is an ode (a replica!) to those researchers who discovered the law of constancy of the salt composition in just 107 samples.

I am not an expert in oceanology, but I remember that there located an article that there was an underground ocean at a relatively large depth in the planet. And this indicates the possible connectivity of all oceans. And this forces, according to partial pressure, to maintain the same composition of dissolved substances in water.