here is why because think about it most oceans are measured by how much goes in it every day by the thousands of gallons of sea water so i hope this helps you understand your question
Explanation: How much salt in a sea is measured in parts. So, meaning by that, it is measured by 35 parts per thousand. It's use as the grams of salt in the water, which is 1,000 grams of salt in water. 35 grams of salty water is equal to 1 kilogram of seawater.
