Deep currents circulate seawater around the globe due to differences in the density of water at different locations. two factors that can alter the density of water are salinitymarine lifespecific heat and windtemperatureearth's rotation.

salinity, temperature

Explanation:

The density of almost everything in nature changes with a change in temperature because of the thermal expansion.

If the temperature of the sea water rises, then its volume will increase while its mass remains the same. So the density of sea water will decrease.

The density of sea water changes when the salinity changes. When the salinity changes the volume of the sea water remains the same but the total mass of the sea water changes.

The salinity will increase if more sediment are added to the ocean. In which in turn will increase the density. The salinity will decrease if polar ice caps melt and fresh water is added to the ocean, which in turn will decrease the density.