Interview with Nozomu Takeuchi: Impact of snow algae on melting rate of snow & ice

Snow algae are a fascinating and unique aspect of the microbial world. These cold-tolerant microbes grow on snowpacks and are commonly observed in polar and alpine areas worldwide. During the snow melting season, they grow on the snow surface and can form visible blooms of red, green, or yellow. While snow algae have been studied for decades, the ecological impacts of their blooms are only now becoming better understood.

In an exclusive interview, Ground Report spoke with Nozomu Takeuchi of Chiba University, a renowned expert in the field of snow and ice ecology. Over the past 20 years, Takeuchi has carried out extensive research on the ecology of microbes living on snow and ice. Furthermore, their effects on surface albedo and glacier melting, and their role in hydrological processes on supraglacial lakes. With a wide range of field experiences in locations such as the Nepali Himalayas, Tienshan, Pamir, and Svalbard, Takeuchi brings a unique perspective to the study of snow algae and their ecological impacts.

We'll explore his findings on the formation of snow algal blooms, the environmental factors that contribute to their growth, and the potential impact of snow algae on the snow and ice they grow on and downstream ecosystems.

Excerpts

Q: Can you explain what snow algal blooms are and how are they formed?

A: Snow algae are cold-tolerant photosynthetic microbes growing on snowpacks and are commonly observed in polar and alpine areas worldwide. During the snow melting season (i.e. usually spring), they grow on the snow surface. When the number of algal cells in the snow (cell concentrations) reaches a certain level, the snow surface visibly becomes red, green, or yellow, which is called as snow algal bloom.

The algae on the snow surface originally come from soil under the snowpacks. Resting cells (spores) of snow algae stay in the soil from summer to winter. They wake up in spring when the snowpack starts to melt. The algal cells change from spores to motile cells and swim up from soil to the snow surface, and grow by photosynthesis (i.e. increase their cell number by cell divisions). Then, they finally appear on the snow surface as blooms.

Q: What environmental factors contribute to the growth of snow algal blooms?

A: The appearance of snow algal blooms requires certain amounts of snow, melting periods for their growth, sun light and nutrients in snowpacks. The snow algae could not grow in case of sub-zero temperature (without melting of snow), of too small snow abundance (melt too fast for algal growth), and of lack of nutrients (too clean snow), which is usually provided by air including anthropogenic pollution. In Japan, because of winter monsoon (westerly), heavy snow falls more than 3 meters in mountain areas every winter and warm temperatures in spring, allowing the snow algal blooms.

Q: How do snow algal blooms impact the snow and ice they grow on?

A: Algal blooms reduce the light reflectivity (albedo) of the snow surface, which is originally very high (i.e. white colour). When the reflectivity becomes lower, the snow surface absorbs more sunlight and thus melts faster.

Hence, the appearance of algal blooms affects the melt rate of snow and ice, which currently became significant in polar glaciers and snowpacks. The snow algal blooms spend nutrients in snow and produce various organic materials through photosynthesis and their metabolisms.

This is another impact of the snow algae on the material cycles in snowpacks or glacier systems. As snow melt proceeds, melt water is supplied to downstream ecosystems. The substances produced by the snow algae may play a role in the ecosystems.

Q: Have you observed any changes in the frequency or extent of snow algal blooms in recent years?

A: Unfortunately, there is no information on the long-term trend of the appearance of snow algal blooms in Japan as well as in the world. In the case of glaciers in polar regions, studies suggest that snow algal blooms recently increase and could accelerate the melting rate of snow and ice due to their darkening effect since climate warming can extend the melting period (algal growth period) during summer.

However, seasonal snowpacks, which are different systems from glaciers, could decrease in Japan as climate warming proceeds, which is a major concern for Japan. In this sense, I would think that the snow algal blooms might rather decline. I am doing a monitoring study of snow algae in Japan, but only for 17 years yet. The result shows that there are some years of appearance of very intensive algal blooms, but no clear long-term trend. The data is still insufficient yet.

Q: What are the implications of snow algal blooms for the wider ecosystem, including the Arctic and Antarctic regions?

A: Besides snow algae, there are diverse living organisms in snow and ice, which are just been discovered recently. The organisms include bacteria, insects (some species of snow-flea (springtails) and stoneflies), fungi as well as snow algae, which can be active only in snowy environments and are distinctive form other general organisms living in usual temperature environments.

They are strongly associated with each other as a food web and form ecosystems on glaciers or snowpacks, which are referred to as glacier or snowpack ecosystems.

The glacier and snowpack ecosystems in both of Arctic and Antarctic regions are one of the most vulnerable ecosystems because snow and ice are sensitive to climate warming, so they are likely to change rapidly at present. The appearance of snow algal blooms may be a part of the changes of ecosystems, however, we still have limited knowledge about the ecosystems and need to study more.

Q: Are there any measures that can be taken to mitigate the growth of snow algae blooms and their impact on the environment?

A: I would say that the presence of snow algae and their blooms is an essential part of natural ecosystems, therefore, we do not need to be afraid of the occurrence of algal blooms and not to mitigate their growth.

Recent studies have revealed the presence of the chytrid fungus, which parasitizes and kills snow algae. While this could inhibit snow algae growth, there are various interactions between microbes in the ecosystem, making it difficult to predict the outcome of any mitigation effort.

Furthermore, snow algae and its blooms play an essential role in natural ecosystems. They contribute to the global carbon cycle by storing carbon and generate at least 40% of Earth's oxygen through photosynthesis. However, snow algae blooms can have a significant impact on the global water cycle by reducing the albedo of glaciers and snowpacks, leading to accelerated melting and potentially causing sea level rise.

Therefore, rather than trying to mitigate the growth of snow algae blooms, it is important to study and understand their natural balance in the ecosystem. This will allow us to better predict the impact of climate change on these ecosystems and develop strategies for their preservation.

Q: Algae generate at least 40% of the earth’s oxygen through photosynthesis and store carbon, then how it is not good when growing on snow?

A: Again, as the snow algae and their blooms are parts of natural ecosystems, I would say that it is not a matter of good or bad. In terms of global cycles of oxygen and carbon, snow algae account for only a limited amount, negligible, compared with the other photosynthetic organisms including terrestrial plants and ocean phytoplanktons or see weeds.

However, the blooms of snow algae would have a significant impact on the global water cycle, as they have an effect of albedo reduction of glaciers and snowpacks, i.e. accelerate the melting of snow and ice, which possibly cause global sea level rise.

Therefore, too much snow algal blooms may have a potential impact on the global environment. However, as we still have limited knowledge of the present status of snow algal blooms, it is important to study what is the natural balance of snow algal growth and how their growth is going to be in future.

Q: Algae are common in snow, why it is a matter of concern now?

A: It has been believed that no organism can be alive in near-freezing environments such as glaciers and snowpacks because metabolisms of organisms usually require a certain warm temperature, the best temperature for biological activity is around +30 degree. However, recent studies revealed that various microbes are living in snow and ice. We knew just recently that algae are common in snow.

The algae thriving in snow may come as a surprise, as it was previously believed that no living organism could survive in environments so close to freezing. However, recent studies have shown that various microbes, including algae, are common on snow and ice.

The unique abilities of these organisms to adapt to low temperatures and thrive in such extreme conditions is a topic of great interest to scientists. They believe that understanding the functions and enzymes that allow these organisms to survive in these conditions could have potential applications in medical and industrial products.

Furthermore, the study of these organisms in snow and ice environments could provide insight into the potential for extraterrestrial life on icy planets beyond Earth. Overall, the study of snow algae has significant implications for global environmental problems, as well as for industrial applications and the search for life beyond our planet.

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