This year, we went back to Lake Joyce to study the benthic biology in the McMurdo Dry Valleys. The 3D microbial structures that are growing out of the mat are particularly interesting because most of them have a calcite skeleton. This is the only lake in the Dry Valleys where microbial mats have such distinctive calcite skeletons.

The calcite skeleton makes these microbialites particularly interesting for geobiology, where modern microbial mats are studied to enable a better interpretation of microbialite fossils from early Earth. 

Over the last three weeks we collected samples that will allow us to investigate if the water chemistry, light and sedimentation effect the growth of microbialites in the lake. We also collected mat material to carry out DNA and microscopy analysis to evaluate the role that cyanobacteria, other bacteria and eukaryotes play on the formation of microbialites and their calcite skeleton.

Microscopy image of Phormidium cyanobacterial filaments in Lake Joyce mats. Most of the Phormidium filaments have a strong purple pigmentation though the production of Phycoerythrin for a better utilisation of the limited light that is available in Lake Joyce.

Anne working at the microscope.

Close-up image of microbialites with calcite skeleton covered by thin microbial mat webs .

Microbialite structures with calcite skeleton collected from Lake Joyce by diving.

The team getting ready for a dive to collect microbial mats.

The main efforts of the field event led by researchers from UC Davis, California, were to map the distribution of the microbial structures in the lake and to test what the influence of sedimentation is on the microbial structures.

The imaging is done by a drop camera that is held on a rope through a hole in the ice. The team installed several traps in the ice that will collect sediment from now until next season.Each hole is individually drilled with a jiffy drill in order to insert the traps and document the microbial mas and microbial structures.

The team drilling a hole in the ice.

Most of the cyanobacterial mats that we have found were orange pigmented and the macroscopic structure was flaky to cohesive. The orange colour is due to carotenoids which are an protection against UV and oxidative stress.

I had a small light micrscope with me in the field and the genus Leptolyngbya dominated the orange mats. Leptolyngbya are filamentous non-branching cyanobacteria belonging to the order Oscillatoriales. They are mostly between 0.5-3 micrometre thick. However, the lower side of the orange layers sometimes had green pigmentation, which besides the Leptolyngbya also had some Phormidium. The genus Phormidium also belong to the order Oscillatoriales, but they are thicker with a width of around 5 micrometres.

   Flaky orange-pigmented cyanobacterial mats dominated by Leptolyngbya

Cohesive orange-pigmented cyanobacterial mats

green lower side of cyanobacterial mat with Phormidium

Interestingly, we also found some cyanobacterial mats which were dark purple to black. This colour is due to the UV-screening Scytonemin. We found the genus Schizothrix sp. (Oscillatoriales)  in the mats which is known to produce Scytonemin. We also found several ponds with large accumulations of the genus Nostoc, which belongs to the order Nostocales and has specialist cells called heterocysts for nitrogen-fixation.

Cyanobacterial mats with the Scytonemin-producing genus Schizothrix

Nostoc accumulations in a meltwater pond

We also found a few ponds with green algae. Green algae biofilms are easy to distinguish from cyanobacteria as green algae are very bright green.

Green algae