[laviesal]

All I really understand is that it is driven by wind and waves but I don't understand the role of water density which is determined by temperature and salinity and the how salinity could alter the circulation. Can anyone explain?

[enahs]

The salinity alters the density.

Here is a nice chart that shows water density as a function of salinity and temperature:
http://www.saltinstitute.org/density.html

Now, that was just a first google result, no guarantee on how accurate the numbers are.

Now, as the density of the water changes, what happens?