What are the differences and similarities between thermohaline and surface currents?

There are a number of differences between these two types of currents.

First, surface currents affect much less water than thermohaline currents do.  Surface currents can only affect about the top 400 meters of water in the ocean.  By contrast, thermohaline currents move huge amounts of water -- more than 100 times the flow of the Amazon at any given time.

Second, surface currents are caused by winds and by the Coriolis Effect (having to do with the Earth's rotation).  Thermohaline currents are caused by differences in the temperature and salinity of water in various areas of the oceans.