TOEFL Reading: ETS-TOEFL阅读机经 - 3P7M4YGVS32DL20GL$

Thermal stratification is the phenomenon by which the different layers of water in lakes and oceans have different temperatures. A. Sunlight is rapidly absorbed by the upper layer of water, which makes it warmer and consequently less dense than the water below. B. Photosynthesizing plants, which provide the food and oxygen for most other forms of aquatic life, are limited to the levels of oceans and lakes where sunlight is available. C. The diversity of plant life in shallow water makes it attractive to zooplankton. D. As water becomes less dense and moves to the surface of the ocean or lake, it cools down and moderates the temperature of the surface. E. Because more solar energy is absorbed by bodies of water in the tropics, the topmost layer of the thermocline is widest there. F. In the tropics, permanent thermal stratification limits the amount of life supported in deep bodies of water; however, in temperate climates, seasonal thermal stratification allows vertical circulation and mixing of water, allowing the support of more life.