Spring bloom
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The spring bloom is a sudden and strong bloom of phytoplankton such as diatoms or dinoflagellates in the spring in temperate and sub-polar bodies of water. In winter, the waters are well mixed, i.e., water is circulated from the bottom to the top of the water column because the water is relatively colder and therefore maintains a more uniform density). In the early spring, the upper water layers have enough nutrients circulated up from bottom waters to maintain phytoplankton growth but the phytoplankton are unable to grow as there is frequent mixing from wind and light levels are not yet strong enough. However, as the ocean warms in the later spring, the warm water will stay at the top of the water column as it is less dense. This will create a layer of stratification called the epilimnion in fresh water. At this time, the phytoplankton are maintained in waters with enough light and abundant nutrients, allowing their population numbers grow exponentially. In most cases the phytoplankton will use up the available nutrients in a matter of weeks or months, eventually dwindling their numbers in summer. Many species of diatom will sink to the bottom and create resting cysts when nutrient concentrations run low. Also, it is not uncommon to see a succession of phytoplankton species reach their growth peaks at different times through the course of the bloom as different species will have optimal nutrient uptake at different concentrations.
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