4SEAS

You will often read that the saltiest sea on earth is the Dead Sea, but this is really an inland lake, not a true sea. The scientific term for saltiness is, “salinity” and the world oceans have an average salinity of about 35 ‰, but this does vary across the planet. For example, the Mediterranean Sea, the Red Sea and the Arabian Sea all have relatively high salinity, while the Black Sea and Baltic Sea both have relatively low salinity. Across the oceans, the northern and southern oceans generally have slightly lower salinity than the tropical oceans.

When marine scientists talk about salinity, they often use the term “ppt”, which means ,”parts per thousand” and is also indicated by the ‘‰’ symbol. This is because it is quite easy to think of one litre of seawater containing 35 grams of salt. But, if you want to be completely accurate, then salinity is actually measured according to the ability of seawater to conduct electricity - known as its conductivity. For this reason, salinity is now measured on what is known as the Practical Salinity Scale (PSU) which has no units. So, we can say that the average salinity of seawater is 35.