Although they flow near the bottom of the ocean, sometimes flow on top of other currents.

Although they flow near the bottom of the ocean, deep currents sometimes flow on top of other currents. while surface currents flow near the top of the ocean where they can reach depths of several meters. Some of the factors that control deep currents are salinity, density, and temperature. Deep current they occur deep in oceans which are influenced by salinity, temperature, and water. 
A good example of deep current is Antarctic bottom water.

Tbh idk dude but guess

C14 dating since carbon is present in both living and no living objects .