D.
Cold and high salinity
Step-by-step explanation:
Warmer waters are less dense than cooler/ cold waters. This is why surface ocean currents are made of warmer waters while deeper currents are cooler. The deep currents also have a higher salinity. This is because cooler water gets more concentrated faster by dissolving the same amount of solutes (in this case ocean mineral salts) compared to warm waters. This also makes deepwater currents them denser.