No one has mentioned it but maths is short for mathematics. Also, your judgment of a very common figure of speech comes off as provincial.
Fair, I was being trite. The idea that the ocean is a closed system that doesn’t include all the solar energy, currents, mixing and everything else added to it plus an osmotic membrane would represent a perpetual motion machine just sounded so laughably stupid I was just trying to be equally annoying and dumb.
"Math" sounds funny as a brit - it's just what you're used to, although I will admit "math" is probably more technically correct.