Cool water at the surface traps nutrients deep in the lake to provide food during the winter.
Explanation:
During winter, <u>ice forms on the surface of the lake</u> when the temperature drops below 4 degrees Celsius. However, the <u>water below remains warm</u> because the ice layer on top also acts as insulation of heat transfer in case of further temperature drops. Further, ice formation <u>retains/seals off</u> nutrients and gases flow below the ice sheet. The amount of nutrients is sufficient for phytoplankton activity during light hours (there is no complete darkness even after thick ice sheet is formed). Resultantly, the <u>photosynthesis</u> produces <u>oxygen and food</u> for aquatic organsism within the lake environment and support their <u>survival during winter season</u>.
