The oceans affect the biosphere by i) producing a substantial amount of the biosphere's oxygen ii) adding carbon dioxide to the atmosphere iii) being the source of most of earth's rainfall iv) regulating the ph of freshwater biomes and terrestrial groundwater

iii) being the source of most of earth's rainfall

Explanation:

The oceans are most responsible for the formation of rain that occurs on our planet. This is because the water of the oceans in contact with the solar heat, evaporates, and becomes water vapor. This vapor is captured by clouds that become overloaded and start the precipitation process.

Precipitation is essential for human activities, such as agriculture, in addition to contributing to the smooth functioning of the hydrological cycle.