More and more shades of green and red instead of brilliant white: In the course of climate change, more and more algae are spreading on the snowy areas on the coasts of the Antarctic Peninsula. The dark discoloration significantly increases light absorption and thus leads to increased heating of the surfaces, a study has now documented. The results show that the effect of green algae in particular can make a significant contribution to snowmelt. This is a factor to be reckoned with, say the scientists.
Icy surfaces are their home: Certain single-cell algae species have adapted to life on snow and ice. Temperatures at which thin water films form on the surface are sufficient for them. Blown dust or dirt can then serve them as mineral nutrient sources so that they can thrive on the cold surfaces. These so-called snow algae are widespread in the polar regions and also in the high mountains. They are noticeable there through characteristic discoloration.
Some species provide a greenish color, with others special pigments lead to red tones – this creates the phenomenon of so-called blood snow. It has long been known that the bizarre algae lower the so-called albedo, similar to dust pollution. It is the measure of how strongly the snow and ice surfaces reflect sunlight. If more radiation is absorbed, this leads to more intensive heating and thus to increased defrosting.
Warm green
In this context, the researchers led by Alia Khan from the University of Colorado in Boulder are now looking to the Antarctic Peninsula. As they report, the improved living conditions for the snow algae in the course of global warming are leading to ever stronger growth. Especially in coastal areas where seals, penguins and other birds provide sufficient fertilizer with their excrement, the warming can lead to increased algal blooms. “We see that these algae are spreading more and more on the snow surfaces over large areas along the coast. This creates a warming effect, as if you were wearing a dark T-shirt on a sunny day, ”says the scientist.
In order to be able to more precisely assess the importance of algal blooms when the snow melts in the coastal area of the Antarctic Peninsula, Khan and her colleagues have now carried out measurements of the spectral albedo of red and green snow algae at three locations. Their results show: compared to clean surfaces, green algae stains reduce the radiation of the snow by an average of 40 percent, while red spots only reduce the radiation by 20 percent. As the researchers explain, green snow algae contain more chlorophyll than the red versions and therefore absorb more solar radiation, which reduces the albedo by a greater amount for the same algae concentration in the snow.
Accelerated melting
According to the calculations of the researchers, the green algae growth increases the average energy consumption of the surfaces in summer by around 26 watts per square meter, with the red algae it is 13 watts. These values are comparable to those caused by dust on snow in the mid-latitudes and known to accelerate the melt there, say the researchers. Based on their data, the researchers also performed model calculations that show how much the warming effect caused by the snow algae could contribute to the melt. They came to the conclusion that the algae could lead to considerable snow loss on the coasts of Antarctica, so that areas are exposed.
This effect could have an important meaning on the climatic and ecological developments in the region, say the researchers. An intensification is to be expected in the future: “Warmth leads to an expansion and intensification of the snow algae bloom season, which could increase further in this region of the Antarctic if the climate change continues,” says Khan.
According to the researchers, their results show that snow algae play a significant role in ice melting in the coastal areas of the Antarctic Peninsula. Therefore, they should be taken into account in future estimates of the development of the ice-free areas. In order to gain even more detailed insights into the importance of this aspect, Khan and her colleagues are now planning to examine the areas where the algae spread in the region and the factors that lead to the intense growth spurts.
Source: University of Colorado, Article: The Cryosphere, doi: 10.5194 / tc-15-133-2021