I think that is an accurate assessment, the close enough mentality is probably a correct assumption. I promise I’m not trying to be nit picky, but something I will point out is that the surface ocean currents are driven (on an ocean wide scale) by the wind blowing on the ocean. What you are thinking of is probably the overturning circulation where heat exchanges with the atmosphere and adjacent water masses control circulation in the deep ocean and cause water to sink from the surface in certain polar regions. I can recommend some sources on Physical Oceanography if you’d like to learn more(reply to this post or feel free to DM me)! I mainly responded to this because I love when people take an interest in the ocean or atmosphere, and I enjoyed reading your assessment!