They're created out of differences in water density.

它们是由于水密度的差异而产生的。

And the key to this cycle is the ocean water’s density.

这个循环的关键是海水的密度。

If we speed this up you can even see the force of the rising and falling water densities creating a current in this tank.

如果我们加快速度，你甚至可以看到水密度的上升和下降在这个水箱中产生水流。

They can be driven by winds at the surface affecting the water column below, deep water tides or differences in the water density caused by temperature and salinity, known as thermohaline currents.

它们可以由影响水下水柱的表面风、深水潮汐或由温度和盐度引起的水密度差异（称为温盐流）驱动。

This sudden change in water temperature is known as the Thermocline, and the resulting  change in water density is so pronounced that submariners will pick it up as a " false bottom"   since sonar will reflect off this layer.

这种水温的突然变化被称为温跃层，由此引起的水密度变化非常明显， 潜艇人员会将其视为“假底” ，因为声纳会从这一层反射。