Polar

In polar open oceans, primary production is wildly fluctuating.

There is little to no sunlight, which means that for most of the year, there is no primary production taking place.

During spring, when sunlight becomes ample and day lengths increase, a huge burst in production occurs. This is also caused by the fact that there is typically no thermocline layer in polar regions. Thus, both nutrients and sunlight are abundant and non-limiting.

This spike in productivity lasts 3–4 months before returning to a dormant phase the rest of the year.

Temperate

In temperate regions, the productivity is generally more moderate.

During the winter, the thermocline layer is fully broken down, which allows for nutrient-rich water to mix with the surface water. However, light levels are low throughout winter, which constricts the productivity to relatively low levels.

In spring, productivity increases as sunlight becomes stronger. This creates a brief period of productivity increase (similar to polar regions, but not as dramatic).

When summer rolls around, light becomes plentiful again. However, the temporary thermocline becomes re-established, which limits production to very low levels.

In autumn, there is another small spike in production that occurs when the thermocline starts to breaks down again, creating a small period of time where sunlight and nutrients are both plentiful.

Tropical

The primary productivity of tropical ocean regions is so low throughout the year that they are commonly referred to as ‘marine deserts’. This is because the thermocline layer is a permanent feature in the tropics, which limits the deeper nutrient-rich water from mixing with surface water.