Dry Valleys desert

• Category: Desert Biomes.
• Geographic Location: Antarctica.
• Summary: Scientists use this unique, hyperarid polar desert in the middle of Antarctica to study life forms in extreme environments.

The Antarctic Dry Valleys, also called McMurdo Dry Valleys, comprise the largest ice-free region of Antarctica over a total of 5,792 square miles (15,000 square kilometers). This hyperarid polar desert, located roughly 2,200 miles (3,541 kilometers) south of New Zealand and extending toward McMurdo Sound, is perhaps the most extreme desert in the world. Temperatures average 1.4 degrees Fahrenheit (-17 degrees Celsius), and precipitation is four inches (100 millimeters) per year. Snowstorms here typically bring less than 0.4 inch (ten millimeters) of snow at a time.

Geology and Hydrology

The region has many special geologic features, including glaciers, mountains, lakes, seasonal streams, unique soil formations, permafrost, and sand dunes. The valleys are nestled between the one-mile-high (1.6-kilometer-high) Transantarctic Mountains, and were formed when glaciers retreated. The main ice-free valleys are called Taylor, Write, McKelvy, Balham, Victoria, and Barwickthey all have similar characteristics. The valleys are each three to six miles (five to ten kilometers) wide and from nine to ninety-three miles (fifteen to one hundred fifty kilometers) long. They cause dense, cold air coming over the mountaintops to sink. The temperature gradient from the bottom of the valleys to the top of the mountains creates high winds in the area, and any water vapor evaporates as the sinking cold air warms in a process called katabaticdownhillheating. Liquid water is the main control on biological, physical, and chemical processes in this polar desert, much as it is such a key factor in life processes elsewhere. Million-year-old ice has been found buried under soil layers here; the chemistry of this ice and of the air bubbles trapped in it can yield clues to past climate conditions and today's climate change.

Some of the valleys have lakes at their floor that remain frozen most of the year. Much of this glacial meltwater, an interesting component of the watersheds, fell as precipitation thousands of years ago. The Onyx is largest river in Antarctica and runs through the Dry Valleys. For six to fourteen weeks during the summer, small streams form from water melting off the glaciers; this carries down to recharge the lakes. The streams also carry scant nutrients and salts into the valleys. Smaller ponds here can contain so much salt that they remain liquid water, often under the frozen surface. The lakes of the Dry Valleys contain very high concentrations of nitrous oxide, higher than measured in any other lakes in the world, because they are not well mixed and the gases are trapped.

The Dry Valleys have three microclimate zones—the coastal thaw, inland mixed, and stable upland—which are differentiated by summertime measurements of air temperature, soil moisture, and relative humidity. These climate factors vary subtly but create noticeable differences in geologic features, including large-scale gullies, midsize ice wedges, and fine-scale features such as wind erosion effects.

Biodiversity

Little can survive in these harsh conditions except extremophiles, organisms that thrive in exceedingly harsh environments. Some of the extremophiles found in the Dry Valleys include lichen and mosses, yeasts, microbes, and nematodesmicroscopic worms that live in the soils. Rotifers and tardigrades are other tiny invertebrate animals found in the valleys. The Dry Valleys may be the only place in the world where nematodes are found at the top of the food chain—indicating a very simple food chain. Many of the invertebrates within the Dry Valleys are known to travel and spread primarily by wind.

The valleys are specially designated as protected areas because of some unique bacterial life forms here, including specially adapted cyanobacteria. Scientist Craig Cary has reported that the soils of the Antarctic Dry Valleys have a surprisingly wide variety of unique microbes. Much of the research in this area has been conducted using molecular DNA analysis; results have partially debunked the old hypotheses that the soils here had almost no biota.

Some bacteria live in the moist interiors of rocks, producing food and energy directly through metabolizing the mineral nutrients within their surroundings. This process has yet to be fully understood. These rock dwellers, or endoliths, are cyanobacteria, an algae that can survive in numerous tough environmental nichesthey live in rocks or the pores between minerals in the soil. One remarkable bacterium within the Taylor Glacier apparently uses no oxygen as it metabolizes iron and sulfur deposits.

It was once thought that various of these organisms turned the water red here, whereas scientists now know that iron oxides provide the red tint to the glacial meltwaters that form the waterfalls known as Blood Falls. Fungal microflora, too, have been found in the Dry Valleys, living in small bits of soil in cracks of rocks, inside colonies of moss, in sediment deposited along shorelines, in calcium-carbonate formations, and on microbial mat formations. Lichens grow primarily in an altitude range of 3,281 to 6,562 feet (1,000 to 2,000 meters), as this zone has more moisture from frequent cloud cover.

Research

Many scientists travel to the Dry Valleys to study unique life forms. The United States maintains a Long Term Ecological Research site in the McMurdo Dry Valleys, which allows researchers to work together on studies of aquatic and terrestrial ecosystems in this unique setting. The study site joined the National Science Foundation's Long Term Ecological Research Network in 1993 and is funded through the Office of Polar Programs in six-year funding periods. Strict rules govern what types of activities can be carried out, as well as who can carry them out and where, in order to protect this fragile ecosystem.

Studying the changing climate in Antarctica is important to understanding global climate change. Warming temperatures have caused the ground to soften, creating swampy patches called thermokarst. They are caused by permafrost thawing. Scientists believe that this is sign that global warming is changing the Dry Valleys.

Studies conducted between 2020 and 2023 documented accelerating changes in the Dry Valleys ecosystem. Scientists have observed increased glacier melt rates, expanding thermokarst formations, and shifts in microbial communities. The warming has caused some previously permanently frozen lakes to experience more frequent melting, potentially affecting the unique extremophile communities that have evolved in these stable environments for thousands of years.

Geologists and astrophysicists also use the Dry Valleys to infer what may one day be found on Mars as the valleys are considered the most similar place on Earth to the Martian surface. Both areas have generally cold, dry climates and similar landforms, such as mountains, valleys, and ancient stream beds. The arid climates create a high concentration of salts in the soils that can affect the temperature at which water changes from liquid to ice. Geologists are interested in the Dry Valley's land forms, such as ice wedges and how they change over time; this too enables researchers to infer more details about the history of Mars and its climate. Additionally, scientists often test new scientific equipment in the Dry Valleys before deploying it on rovers to Mars so that it is put through its routines in an extreme environment before being deployed, providing the chance to uncover shortcomings and adapt the technology to correct form before it is sent to Mars.

Bibliography

Cary, S. Craig, et al. “On the Rocks: The Microbiology of Antarctic Dry Valley Soils.” Nature Review Microbiology, vol. 8, no. 1, 2010.

Friedmann, E. Imre, and Roseli Ocampo. “Endolithic Blue-Green Algae in the Dry Valleys: Primary Producers in the Antarctic Desert Ecosystem.” Science, vol. 193, no. 4259, 1976.

Gooseff, M. N., et al. "Long-term Ecological Responses to Climate Change in the McMurdo Dry Valleys." Nature Climate Change, vol. 13, 2023, pp. 892-901. Accessed 9 Nov. 2024.

Marchant, D. R., et al. “Antarctic Dry Valleys: Microclimate Zonation, Variable Geomorphic Processes, and Implications for Assessing Climate Change on Mars.” Icarus, 192, no. 1 (2007).

National Science Foundation LTER Network. “McMurdo Dry Valleys LTER.” National Science Foundation LTER Network, http://www.mcmlter.org. Accessed 11 Nov. 2024.

Sommers, P., et al. "Comparison of Microbial Communities in the Sediments and Water Columns of Frozen Cryoconite Holes in the McMurdo Dry Valleys, Antarctica." Frontiers in Microbiology, vol. 12, 2021, pp. 1-14. Accessed 9 Nov. 2024.

Zych, Ariel. "The Ground Is Softening. Something Is Shifting in Antarctica's McMurdo Dry Valley." Massive Science, 21 May 2021, massivesci.com/articles/antarctica-dry-valley-melting-ozone-water-climate-change-science-friday/. Accessed 1 Aug. 2022.