Which statements correctly explain why biological productivity in the tropical ocean is so meager when compared to biological productivity on land in tropical environments?

The answer to this question would be: 
- The permanent thermocline presents a barrier that keeps nutrients in deeper water from mixing with surface waters.
- The sunlight penetrates deep into the tropical ocean, warming the surface waters and creating stratification of water masses.

In tropical lands, the area is getting sunlight all around the year. This will cause the plant to be able to do photosynthesis all around the year too. Sunlight can penetrate the ocean, but the intensity will be much lower in deeper part. The ocean also become warmer but it will become cold in the deeper part too. 

When scientist examine data such as historical documents, they are using the "scientific methods"