Seawater refers to water from the sea or ocean. It is also called sea water. On average, the salinity of seawater around the world is about 3.5%.
Although the overall salinity of seawater is between 3.1% (based on 100ml) and 3.8%, this does not mean that the salinity of seawater around the world is uniform. Where it mixes with fresh water from river mouths or near melting glaciers, seawater can be substantially salinized.
I will refer to your explanation and supplement it when the next book is published. Thank you for your comments.