User:Joan2329/sandbox/Phytoplankton Bloom - Arctic

Arctic Phytoplankton Bloom

Phytoplankton blooms occur when phytoplankton, a unicellular primary producer, reproduces at such a rapid rate a visible structure with a cloud like appearance occurs in the water column. The increase in phytoplankton may cause the water to appear green due to the absorption of the sun’s energy by the phytoplankton’s pigment during photosynthesis. Photosynthesis is the process that phytoplankton uses to convert sunlight energy and raw materials into energy and food for nourishment. Phytoplankton can live in many different aquatic ecosystems usually in the photic zone for optimal light availability. Phytoplankton blooms are very important resources as a source of food used by a variety of animals, which are either permanent under ice dwelling animals or animals that migrate to the shoreline for their food.

Arctic phytoplankton blooms can occur in many different freshwater and marine systems. Under-ice ponds cover about 5% of the Arctic. Because these ponds have low salinity, the pond allows more stability and a greater amount of solar irradiance in order to have optimal conditions to form the under-ice pond and surface-ice pond blooms.

In marine systems phytoplankton blooms can occur in coastal regions and at deeper oceanic depths. In different regions there are also different types of phytoplankton that they can consist of. The coastal or neritic species are described as a ‘resting’ species, which allows them to survive the dark Northern winters. These ‘resting’ species are formed in the last phase of the bloom cycle and then sink to the ocean floor for survival, but in the spring or late winter the thermohaline circulation extends downwards and draws the phytoplankton back towards the surface along with the warm Atlantic waters. The most common of neritic bloom species are Coccolithophore Emiliania. Phytoplankton in the open ocean are not considered to be ‘resting’ and are not able to survive all year in the high north due to the amount of ice pack limiting the amount of irradiance able to pass through the ice in the winter, unless in the water is in connection with the Atlantic water masses. The oceanic bloom is dominated by the Coccolithophore Decipiens species.

In marine systems phytoplankton blooms occur due to the presence of the growth of phytoplankton entering the Arctic by the thermohaline circulation, which draws warm algal and bacteria rich Atlantic water up and into the Barents Sea. Phytoplankton can then reside inside the sea ice, in polynyas, and in marginal zone. Inside the ice phytoplankton can take shelter in brine pockets and channels in the bottom of the ice layer, during the winter when there isn’t enough solar radiance or nutrients to sustain a phytoplankton bloom. In the late winter/early spring, a large biomass of algae develops in this section of ice and can then enter the open water column through the process of brine drainage or simply from current turbulence dislodging them from the ice. The algae have then two purposes upon exiting the brine channels; the dying phytoplankton cells will then sink to the ocean’s benthic zone, or living cells may then reproduce quickly and form phytoplankton blooms.

Phytoplankton is a fantastic food resource for many different land animals and marine animals; such as zooplankton, and therefore has the greatest impact on the Arctic foodweb. When phytoplankton from the bloom dies, or dead cells from brine channels or from within ice crystals die they become dissolved organic matter (DOM) that reduces the amount of dissolved oxygen (DO) in the benthic zone after sinking to then ocean floor. Here the dissolved organic matter can serve as nutrients to floor dwelling zooplankton and any ocean floor vegetation1, but when the phytoplankton resource begins to be depleted the Arctic food web is affected and impacts the fish diversity of the upper trophic levels in result.

For a phytoplankton bloom to occur there are many different environmental conditions that need to be met and there are also many different environmental factors that affect the ability of phytoplankton blooms survival. Different phytoplankton species have different optimal living conditions, but many share the same requirement of environmental factors; such as, temperature, salinity, and nutrient availability.

Nitrogen (N) and phosphorous (P) are two of the most important nutrients that phytoplankton, like plants, need to survive in the correct concentrations, but these nutrients can be very limited in densely ice packed areas. When these nutrients are no longer available or too abundant, or when there is increased grazing of the phytoplankton by animals these blooms will find the conditions unsuitable and may become fully depleted in this area until it becomes optimal again for growth. The salinity of water also plays a great part in the optimal conditions for a phytoplankton bloom to survive, as there is an increase in ice melt this decreases the salinity of the water and lower salinity allows for greater stability and also the decrease in ice thickness allows a greater amount of solar irradiance into the water column.

As stated, phytoplankton blooms can occur in the Arctic dependent on nutrient availability, but also dependent on sea ice coverage, location, and seasonality. The growth and production of phytoplankton blooms can be greatly affected by ice thickness and dense snow pack, as it limits the amount of solar irradiance (photosynthetically active radiation) that is able to transmit through the ice and snow and reach the phytoplankton for photosynthesis. The increasing temperature of the water is also very important to the production of phytoplankton blooms, as warmer water has shown to increase heterotrophic and bacterial activity. The influx of warmer water can be due to the thermohaline circulation (great oceanic conveyor belt) bringing up warm Atlantic water. Solar radiance also, but to a much smaller degree, contributes to the warming water temperatures.

There are many different ways that phytoplankton blooms in the Arctic can be researched and monitored; such as, by satellite imagery, ice core sampling, and water column sampling. These techniques use a wide range of invasive sampling as well as non-invasive sampling that help to determine the current and past phytoplankton bloom events, which in turn will help to predict the future outlook of ice-melt and the amount of phytoplankton blooms that will occur and how long they will persevere throughout the year.