Dry valleys: Unlike anywhere else on Earth
The McMurdo Dry Valleys are located on the western coast of McMurdo Sound and form the largest relatively ice-free area in Antarctica. Covering a surface area of approximately 4,800 square kilometres this ice-free area is unique in that its frozen lakes and extensive areas of exposed soil are subject to low temperatures, limited precipitation and salt accumulation and therefore represent a region of Earth where life approaches its absolute environmental limits. The Dry Valleys are ice-free, or dry, because any precipitation that falls as snow on the valley floor is blown away by strong, dry katabatic winds, through the process of sublimation. The result is the Dry Valleys being cold, dry deserts. The only ice that is found in the valleys is in the form of alpine glaciers along the steep valley sides and the permanent ice that covers the lakes on the valley floor.
Life in the Dry Valleys
When Captain Scott and his Antarctica expedition first discovered the Dry Valleys in 1903 they believed the valleys to be void of any life. However, it turns out that a large variety of aquatic ecosystems thrive in the harsh climate due to glacier melt-streams that flow into the ice-covered lakes. However, this flow is not constant: instead the volume of melt-water is dependent on a combination of temperature, wind and sun, with ice able to melt in temperatures below 0 °C: if it absorbs enough solar energy. This results in variable flow levels – from a trickle to a torrent – throughout the day, month and year. This means only extreme organisms can survive in an environment where water may only be available for a few days or week in addition to extreme winter temperatures of up to -50 °C. These organisms are usually cyanobacteria, known to be ‘stress-tolerant’ species, which also have dark pigments for protection from high UV rays that can be damaging when the species are in dried or frozen states. Surprisingly, there are diverse varieties of these species despite the climate as there are no other plants or animals competing with or eating them.
One of the most amazing aspects of cyanobacteria is their ability to kick-start the photosynthesis process within 48 hours of liquid water returning, despite being in a freeze-dried state. Because of the low temperatures it also means metabolic rates are slow giving them increased chance of surviving in the harsh environment.
Ice-covered lakes in the Dry Valleys
Ice-covered lakes in the Dry Valleys, which have ice around 3-5 metres thick throughout the year, provide a unique habitat for life to thrive. Some of the key characteristics of the lakes include:
- The ice-cover prevents wind-mixing resulting in a stable water column. This allows salt-water layers to persist over many years
- It limits the speed at which nutrients, that accumulate in deep waters, can return to the upper layer of the lake
- The thick ice blocks 80-99% of the sun’s energy
These characteristics lead to the Dry Valleys lakes being dark, cold with a slow supply of nutrients and a slow-growth environment for different species. The most common production found in the lakes is microbial mats on the lakebeds with the main organisms being cyanobacteria. Despite the cold temperatures inhibiting their growth, lake mats grow in large accumulations due to limited disturbance and lack of grazing. One interesting aspect of these mats is they grow annual layers with each layer appearing as alternate bands of black (winter) and white (summer), enabling researchers to determine past temperature changes in the dry valleys. Lake levels are determined by the volume of melt-water available, which fluctuates over time. For example, Lake Vanda’s depth has varied from 130 m deep around 5,000 years ago to bone dry levels around 1,200 years ago, leaving a brine pool. During the 1970s the lake depth was 65 m. Because of the lack of wind mixing the water, the brine pool dating from 1,000 years ago is still at the bottom of the lake.
Discovery of groundwater in the Dry Valleys
Recently researchers discovered beneath the Dry Valleys a salty aquifer that potentially could support previously unknown microbial ecosystems. UC Santa Cruz glaciologist Slawek Tulaczyk – a professor of Earth and planetary sciences – along with other researches gathered evidence of groundwater by using a helicopter-borne sensor to penetrate below the surface. The study found brines, or salty water, form aquifers below the Dry Valleys’ glaciers and lakes and within its frozen soil. The study also found evidence of the brines flowing towards the Antarctic coast from around 18 kilometres inland, eventually discharging into the Southern Ocean. The study speculates the nutrients carried in the brine is released into the ocean affecting biological productivity in and around the shoreline areas. Another discovery was the detection of microbial habitats in the surface and near-surface of the Dry Valleys: an amazing feat of life given the tiny pore spaces are filled with hyper-saline brine that stay liquid down to -15 °C This study is part of an international, interdisciplinary team that is using an electromagnetic sensor called SkyTEM mounted to a helicopter to produce imagery of the subsurface of the Dry Valleys, with the technology developed at Aarhus University in Denmark. The SkyTEM lead Esben Auken has flown the sensor in many places around the world and this was the first time the technology was deployed to Antarctica. Overall, the data from the project will provide scientists with a greater understanding of how the Dry Valleys have change over time and how this history influences what scientists see today.
Science in the dry valley
The McMurdo Dry Valleys Long Term Ecological Research (LTER) project is an interdisciplinary study of the Dry Valleys’ aquatic and terrestrial ecosystems. The site was selected in 1992 for the National Science Foundation’s Long-term Ecological Research Program. With the project funding in 2010 renewed for another 6 years, the McMurdo LTER project conducts long-term ecological research with the aim of leaving a legacy of well-designed and well-document long-term field experiments and observations for future generations to improve their understanding of the basic components of the ecosystem as well as factors that cause widespread changes. Specifically, the McMurdo LTER goal is to understand the influence of physical and biological constraints on the structure and function of Dry Valley ecosystems.
The McMurdo LTER a barometer of global change
McMurdo’s LTER project states the research conducted in the Dry Valleys is important for science as while all ecosystems are dependent on liquid water for survival seldom are there places on Earth in which a minor change in climate can affect the capabilities of organisms to grow and reproduce. With the data collected by the LTER indicating the Dry Valleys are very sensitive to small variations in solar radiation and temperature this can provide researchers with a natural regional-scale laboratory for studying responses to human activities that alter the climate. Importantly, Antarctic ice sheets respond to climate change over periods of thousands of years while the streams and ice-covered lakes in McMurdo’s Dry Valleys respond to change almost immediately: The McMurdo Dry Valleys will be the first place on Earth where the impacts climate change will be observed immediately.