Antarctic lakes are full of small surprises

Sarah Payne and Alyce Hancock are part way through a 17 month posting to Antarctica to study changes in the microbial communities living in the lakes near Davis station. The University of New South Wales (UNSW) scientists are part of Professor Rick Cavicchioli’s team, whose work at the lakes has recently featured in this magazine (Issue 25:12–13, 2013). Here Sarah gives an insight into their research so far.

Alyce and I are taking samples from three lakes and an ocean site to study the microorganisms present in Antarctic aquatic systems. Most of the samples we take will be used to determine what changes take place in the microbial communities throughout an entire Antarctic year. Other samples will be used to discover what microbes are present in a range of lakes that have never been studied before.

Building upon previous discoveries by Professor Rick Cavicchioli’s group, the work we are doing will help to determine:

  • which microbes are present;
  • why they are present;
  • if they are common or unique;
  • what functions they perform in the environment;
  • how they perform their functions;
  • how much the microbial communities and functions change throughout the seasons and across the years; and
  • what impact human activities and global ecosystem changes will have on Antarctic aquatic systems.

Because microbes are the beginning of the food chain and carry out critical processes in nutrient cycling that no other life-forms can perform, it is important that we study them. Also, about 85% of life on Earth exists in the cold (i.e. below 5°C), so learning about microbes in Antarctica not only informs us about life in this wonderful, pristine environment, but has broad implications for much of life on the planet.

I have learnt many surprising things so far. For example, the lakes we study were part of the ocean about 5000 years ago, so in essence we are learning how marine life has evolved to what we see now — there are hundreds of lakes and they are each unique ‘time capsules’.

Ace Lake, Organic Lake and Deep Lake, near Davis station, are the lakes we take most of our samples from, and each is very different.

Ace Lake has two distinct layers, an aerobic (contains oxygen) top, and anaerobic (no oxygen) bottom full of methane and hydrogen sulphide. Unique light-harvesting microbes, called green sulphur bacteria, grow right between these two layers in the lake and are critical for the nutrient cycling of the whole lake ecosystem.

The surface of Deep Lake sits 55m below sea level, and has a very high salt concentration. The temperature of the lake can drop to −20°C but it does not freeze because it is hypersaline — a bit like a very, very cold, Dead Sea. The lake is a real mystery because it contains ‘haloarchaea’, which are very promiscuous and readily exchange DNA with one another.

Organic Lake is also quite salty, but it contains a special virus called a ‘virophage’ which is actually a predator of a larger algal virus. The virophage is believed to benefit the microbial community in the lake by promoting algal growth cycles during summer. Since the discovery of the Organic Lake Virophage, these special viruses have also been found to be present in diverse aquatic systems around the planet.

The research we are part of shows just how surprising and unpredictable discoveries about Antarctic microbes can be, and also just how important the discoveries are for understanding life on Earth more broadly (see 'Extremophiles on and beyond Earth').

Our days are split between working in the laboratory, preparing for field trips, and being out on the lakes collecting the samples. A typical day for us can vary from being in the lab counting microbes under the microscope, to being out on a lake drilling through a metre of ice to collect water, trying to prevent it from freezing long enough to take our samples in air temperatures between −10°C and −30°C.

This is my third trip to Antarctica with the Australian Antarctic Division, but the first time I have stayed over winter. My first trip was in October 2010 when I spent five months at Davis station studying ecotoxicology on marine plankton. I returned to Davis in December 2012 for two months in a similar role.

The most surprising thing I have found over winter is just how devoid of life this vast continent becomes. During the summer there are many seals, seabirds and penguins, but once the last of these head north for the winter it becomes very quiet. On a windless day out in the field, if I stand still and listen, there is absolutely no sound or movement, and I feel like I could be the only living thing on the continent (except for the microbes of course).

Sarah Payne