What phenomenon occurs during lake turnover in Spring and Fall?

During lake turnover in spring and fall, the phenomenon primarily involves the mixing of water layers due to temperature changes. In colder months, the water at the surface cools and eventually becomes denser than the warmer water below it. When this happens in the fall, the cold water sinks, which initiates the turnover process. In spring, as the ice melts and the water warms, the opposite occurs.

This turnover is crucial for aquatic ecosystems, as it allows for the mixing of nutrients and oxygen throughout the water column. It helps to prevent stagnation and promotes a healthy environment for aquatic life. The process ensures that nutrients from the bottom of the lake, which can be depleted in stagnant layers, are brought to the surface where they are accessible for consumption by various organisms.

The other options do not accurately reflect the process of turnover. The warm water remaining on the surface and cool water being less dense contradicts the principles of density related to temperature variations in water. The stratification of water layers throughout the seasons implies that there is no mixing, which contradicts the concept of turnover itself.