Thermohaline: Why is cold and dense seawater salty when warm water holds more dissolved salts? I read that thermohaline circulation is caused by cold and saline water sinking, while warm and less dense water rises. link

I understand that saline water is more dense, as there is a higher mass due to dissolved salts.

However, decreasing the temperature of water decreases the solubility, so in theory, shouldn't cold water hold less salt than warm water? 

Vice-versa, shouldn't warm equatorial water increase in density as it is able to hold more salt?
Warm water does hold more salt - at saturation, but seawater isn't even close to saturation. Surface sea water gets warm, starts to evaporate (hence clouds) and therefore gets denser. So it sinks to the ocean floor, where it cools down to about 4 deg Celsius, and gets denser still. But it still is a very long way from being saturated with salt, so 'how much salt the water can hold' doesn't come into it.