Due to less food energy because biotic are that primary source
Seawater has many different gases dissolved in it, especially nitrogen, oxygen and carbon dioxide. It exchanges these gases with the atmosphere to keep a balance between the ocean and the atmosphere. This exchange is helped by the mixing of the surface by wind and waves.
It is known as the sedimentation.. this process spreads widely (horizontally) keeping the youngest on the top and the oldest at the bottom..
hope this helps:)
what is the climate in the Serengeti like?

The average temperature in Serengeti is fairly consistent throughout the year. The region will see highs of about 27°C (80°F), and lows of about 14°C (57°F).
The climate of the Serengeti National Park is subtropical, with a dry and relatively cool season from May to August, a warmer and still quite dry season in September and October, and a rainy and quite hot season from November to April.