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Ice algae are any of the various types of Algae communities found in annual and Multi-year ice sea, and terrestrial lake ice or glacier ice.
On sea ice in the polar oceans, ice algae communities play an important role in primary production. The timing of Algal bloom of the algae is especially important for supporting higher at times of the year when light is low and ice cover still exists. Sea ice algal communities are mostly concentrated in the bottom layer of the ice, but can also occur in Brine rejection within the ice, in melt ponds, and on the surface.
Because terrestrial ice algae occur in freshwater systems, the species composition differs greatly from that of sea ice algae. In particular, terrestrial glacier ice algae communities are significant in that they change the color of glaciers and ice sheets, impacting the Albedo of the ice itself.
While sea ice algae communities are found throughout the column of sea ice, abundance and community composition depends on the time of year. There are many microhabitats available to algae on and within sea ice, and different algal groups have different preferences. For example, in late winter/early spring, motile diatoms like N. frigida have been found to dominate the uppermost layers of the ice, as far as briny channels reach, and their abundance is greater in multi-year ice (MYI) than in first year ice (FYI). Additionally, dinoflagellates have also been found to dominant in the early austral spring in Antarctic sea ice.
Sea ice algal communities can also thrive at the surface of the ice, in surface , and in layers where rafting has occurred. In melt ponds, dominant algal types can vary with pond salinity, with higher concentrations of diatoms being found in melt ponds with higher salinity. Because of their adaption to low light conditions, the presence of ice algae (in particular, vertical position in the ice pack) is primarily limited by nutrient availability. The highest concentrations are found at the base of the ice because the porosity of that ice enables nutrient infiltration from seawater.
To survive in the harsh sea ice environment, organisms must be able to endure extreme variations in salinity, temperature, and solar radiation. Algae living in brine channels can secrete , such as dimethylsulfoniopropionate (DMSP), which allows them to survive the high salinities in the channels after ice formation in the winter, as well as low salinities when the relatively fresh meltwater flushes the channels in the spring and summer. Some sea ice algae species secrete ice-binding proteins (IBP) as a gelatinous extracellular polymeric substance (EPS) to protect cell membranes from damage from ice crystal growth and freeze thaw cycles. EPS alters the microstructure of the ice and creates further habitat for future blooms. Ice algae survive in environments with little to no light for several months of the year, such as within ice brine pockets. Such algae have specialized adaptations to be able to maintain growth and reproduction during periods of darkness. Some sea ice diatoms have been found to utilize mixotrophy when light levels are low. For example, some Antarctic diatoms downregulate glycolysis in environments with low to no irradiance, while upregulating other mitochondrial metabolic pathways, including the Entner−Doudoroff pathway which provides the TCA cycle (an important component in cellular respiration) with pyruvate when pyruvate cannot be obtained via photosynthesis. Surface-dwelling algae produce special pigments to prevent damage from harsh Ultraviolet. Higher concentrations of xanthophyll pigments act as a sunscreen that protects ice algae from photodamage when they are exposed to damaging levels of ultraviolet radiation upon transition from ice to the water column during the spring. Algae under thick ice have been reported to show some of the most extreme low light adaptations ever observed. They are able to perform photosynthesis in an environment with just 0.02% of the light at the surface. Climate change boosts algae growth in the Arctic Extreme efficiency in light utilization allows sea ice algae to build up biomass rapidly when light conditions improve at the onset of spring.
Because sea ice algae are often the base of the food web, these alterations have implications for species of higher trophic levels. The reproduction and migration cycles of many polar primary consumers are timed with the bloom of sea ice algae, meaning that a change in the timing or location of primary production could shift the distribution of prey populations necessary for significant keystone species. Production timing may also be altered by the melting through of surface melt ponds to the seawater below, which can alter sea ice algal habitat late in the growing season in such a way as to impact grazing communities as they approach winter.
The production of DMSP by sea ice algae also plays an important role in the carbon cycle. DMSP is oxidized by other plankton to dimethylsulfide (DMS), a compound which is linked to cloud formation. Because clouds impact precipitation and the amount of solar radiation reflected back to space (albedo), this process could create a positive feedback loop. Cloud cover would increase the Solar irradiance reflected back to space by the atmosphere, potentially helping to cool the planet and support more polar habitats for sea ice algae. As of 1987, research has suggested that a doubling of cloud-condensation nuclei, of which DMS is one type, would be required to counteract warming due to increased atmospheric CO2 concentrations.
Organisms dwelling on the sea ice eventually detach from the ice and fall through the water column, particularly when the sea ice melts. A portion of the material that reaches the seafloor is buried before it is consumed and is thus preserved in the Core sample.
There are a number of organisms whose value as proxies for the presence of sea ice has been investigated, including particular species of diatoms, dinoflagellate cysts, , and Foraminifera. Variation in carbon and oxygen isotopes in a sediment core can also be used to make inferences about sea ice extent. Each proxy has advantages and disadvantages; for example, some diatom species that are unique to sea ice are very abundant in the sediment record, however, preservation efficiency can vary.
Snow and glacier Ice algae Algae also thrive on snow fields, glaciers and ice sheets. The species found in these habitats are distinct from those associated with sea ice because the system is freshwater and the algae are pigmented. Even within these habitats, there is a wide diversity of habitat types and algal assemblages that colonize snow and ice surfaces during melt. For example, cryosestic communities are specifically found on the surface of glaciers where the snow periodically melts during the day. Research has been done on glaciers and ice sheets across the world and several species have been identified. However, although there seems to be a wide array of species they have not been found in equal amounts. The most abundant species identified on different glaciers are the glacier ice algae Ancylonema nordenskioldii and the snow algae Chlamydomonas nivalis.
Table 1. Algae Species Composition Across Studies on Glaciers and Ice Sheets
On enduring ice sheets and snow pack, terrestrial ice algae often color the ice due to accessory pigments, popularly known as "watermelon snow". The dark pigments within the structure of algae increases sunlight absorption, leading to an increase in the melting rate. Algae blooms have been shown to appear on glaciers and ice sheets once the snow had begun to melt, which occurs when the air temperature is above the freezing point for a few days. The abundance of algae changes with the seasons and also spatially on glaciers. Their abundance is highest during the melting season of glaciers which occurs in the summer months. Climate change is affecting both the start of the melting season and also the length of this period, which will lead to an increase in the amount of algae growth.
The Black and Bloom project is conducting research to determine the amount algae are contributing to the darkening of the Greenland Ice Sheet, as well as algae's impact on the melting rates of the ice sheets. It is important to understand the extent to which algae is changing the albedo on glaciers and ice sheets. Once this is known, it should be incorporated into global climate models and then used to predict sea level rise.
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