1. The problem statement, all variables and given/known data In the tropics, the water near the surface is warmer than the deep water. Would an engine operates between these two surfaces violates the second law? Why? 2. Relevant equations Clausius statement: Heat generally cannot flow spontaneously from a material at lower temperature to a material at higher temperature. 3. The attempt at a solution I only knoe that the water near the surface is a high temperature reservoir and the deep water is a low temperature reservoir. Any engine only absorb heat at high temperature reservoir and do work and rejects heat at low temperature reservoir. I don't know what is the relationship of this with the second law. Thank you.