How would salinity change if more pure water were added to the 1,461,000 grams of ocean water

the salinity would decrease

Explanation:

if you have a certain amount of water in the ocean, and you add more pure water with no salt, your adding more space for the salt molecules to spread out into. This lowers the salinity as the water becomes less dense. More space, less dense. less space, more dense. more dense, higher salinity. less dense, lower salinity.