A flow of warm, salty water evaporates faster than nearby cold water, decreasing its temperature and increasing its salinity. This appears to be an explanation for the eventual sinkage of the Gulf Stream as it flows north. Don’t make me defend this. read more
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. read more
Cold, salty water is dense and sinks to the bottom of the ocean while warm water is less dense and remains on the surface. Cold water has a higher density than warm water. Water gets colder with depth because cold, salty ocean water sinks to the bottom of the ocean basins below the less dense warmer water near the surface. read more