Since nutrients are not in infinite supply, the least common ones required for life processes are called the limiting nutrients. The most common limiting nutrients are phosphate and nitrate. Most nutrient cycles are similar and so reviewing one cycle will be representative of the pathways followed by others. The Nitrate Cycle 1. Some nitrates are released by volcanoes and soil processes.
Diatoms are 'phytoplankton' or the 'grass of the oceans'.
They live in the sunlit surface oceans and are part of the base of the food chains of the ocean biological system. Sinking dead organic matter is attacked by bacteria which decompose the organic matter using oxygen and regenerate the nitrates. Some organic matter passes though the water column and is deposited in bottom sediments. Part of this is reworked by bottom life and returned to bottom water as nitrates. Bottom water nitrates get back to the Earth's surface as part of upwelling where the process starts again.