my answer -
when surface water becomes more dense than surrounding water it sinks to
a lower level, (this happens due to heat loss and evaporation causing
the remaining water to become more saline) when it hits the bottom of
the ocean it forces the water mass that was there to move. at the other
end of the current it is pulled up as water at the surface is moved by
winds and the current at the other end.
P.S
Happy to help have an AWESOME!!! day :)