The instructions for demonstrating ocean turnover are provided in this resource. You could set this up for your earth science class as part of a lecture on convection currents or as an explanation of how ocean currents form. An animation...

Step-by-step instructions, with photos, of how to construct a hot-air balloon from tissue paper, to demonstrate that heated air expands, creating a convection current. This activity requires the use of a hot air gun and is labor-intensive.