Answer
See answers.
Work Step by Step
a. Calculate the Carnot efficiency for an engine operated between those hot and cold temperatures.
$$e_{Carnot}=1-\frac{T_L}{T_H}=1-\frac{273+4}{273+27}=0.077$$
b. The efficiency of 7.7 percent is low, but the volume of hot fuel (warm ocean water) is essentially unlimited.
c. Exchanging water between very different depths would transport tiny creatures from their natural habitats, exposing them to new environmental conditions and predators, reducing their population. This effect would propagate up the food chain. It might be feasible to filter out animals that small, but the pump’s efficiency would suffer.
Stirring up the water might also affect the climate, in at least that area, and perhaps on a larger scale.
