The density of seawater is affected by both temperature and salinity. The exact relationship is pretty complicated, but fresher water can be denser than more saline water if it's considerably colder. That's why physical oceanography has a concept of spiciness. Warm and salty water is 'spicy' while cold and fresher water is 'minty.' Because density is affected by both salinity and temperature, minty and spicy water can potentially have exactly the same density.

Here are a couple of figures I pulled from Talley's Descriptive Physical Oceanography textbook. Here's a map showing the temperature and the salinity of the circumpolar deep water around Antarctica. If you compare it to the Antarctic bottom water, you can see that the Antarctic bottom water is a little fresher than the CDW, but it's considerably colder.