Answer: -
Cold and High salinity
Explanation: -
When the temperature of the water increases, the solubility of substances like salt in water increases. Thus warmer water has more dissolved salt and thus are consequently more dense.
A heavier water then sinks, setting up something called a convection current.
Again more the temperature more the volume of the water and consequently density is less. So cold water is more dense and sinks below.
Combining them Cold and High salinity composition of water sinks down forming a deep water current.