Study the graph below. at what depth does the thermocline begin? a line graph relating ocean depth to water temperature. at 0 meters, temperature is approximately 27°c. at 100 meters, temperature is approximately 24°c. at 200 meters, temperature is approximately 11°c. at 300 meters, temperature is approximately 8°c.

The thermocline begins at 100 meters.

The thermocline in an aquatic ecosystem presents a layer of water which has a steep decline in temperature. In this layer, the temperature of the water drops much faster than in the layers above. This happens because this layer is a ''buffer'' zone between the warm water of the surface layers and the cold layers of the deep.
So, in this case, in the zone between 100 and 200  meters, there is a sharp decline from 24 degrees to 11 degrees.