Question

Although the open ocean is among the least productive ecosystems, it contributes greatly to the overall productivity of the biosphere. How can this situation be explained?

Answer 1

The open ocean contributes greatly to the biosphere's productivity due to the massive scale of ocean ecosystems and the vital role of phytoplankton in oxygen production through photosynthesis. The ocean upwelling also redistributes nutrients, enhancing productivity.

Step-by-step explanation:

Although the open ocean is among the least productive ecosystems, it plays a significant role in global productivity, largely due to the extent of ocean ecosystems which encompass over 70% of the Earth's surface. The ocean's vastness houses numerous species, ranging from large marine mammals to the tiniest of organisms, such as phytoplankton.

Phytoplankton are crucial for the biosphere as they release over 50% of the oxygen produced on Earth through photosynthesis. This process not only contributes to the oxygen we breathe but also forms the foundation of the marine food web. The neritic zone, with its high biodiversity and productivity, plays a significant role in supporting marine life and fisheries. However, it's the sheer scale of the open ocean that allows its contribution to overall biosphere productivity.

Moreover, phenomena such as ocean upwelling help redistribute nutrients from the ocean floor back to surface waters, aiding in the productivity of these ecosystems. Therefore, the open ocean's significant contribution to Earth's productivity can be explained by the large area it covers, the oxygen production by phytoplankton, and the mechanisms that redistribute nutrients within these aquatic systems.

Answer 2

Primary production within the open ocean is mainly through diatoms which are single-celled photosynthesising organisms. Although the concentration of productivity in the open ocean is relatively low, the vast area of the ocean means that this form of productivity contributes greatly to overall primary production on Earth. There are also regions of relatively high production from diatoms in certain parts of the ocean. This is because the productivity of diatoms is limited by a lack of certain essential nutrients in the ocean, such as iron and silica, which tend to sink to greater depths in the ocean than the surface layers that the diatoms inhabit. In these regions, upwelling occurs, bringing nutrients from the deep ocean to the surface, and resulting in diatom blooms. This occurs typically on the west coasts of continents, because upwelling occurs here due to something called the Bernoulli Effect, which relates the the way the Earth spins. This is why very productive fishery areas are usually found on the west coasts of continents, at least in the Southern Hemisphere, and why the seawater is cold in these regions.