What is the main factor contributing to ocean stratification?

The primary factor leading to ocean stratification is the variation in temperature and salinity, which together determine the density of seawater. When water temperatures change, especially between the warmer surface waters and the cooler deeper waters, it creates distinct layers within the ocean. Additionally, salinity, which can be affected by processes such as evaporation, precipitation, river inflow, and melting ice, also plays a significant role in density differences.

When warm, less dense water sits atop cooler, denser water, it establishes a stratified structure where the layers do not mix easily. This stratification is crucial for various oceanic processes, including nutrient distribution, light penetration, and the distribution of marine life, since different species may thrive in specific layers based on these conditions. Other options such as changes in ocean currents, atmospheric pressure, and marine biodiversity influence the ocean indirectly but are not the fundamental causes of stratification itself.