TESTATE RHIZOPODS IN THE DRY VALLEY LAKES, ANTARCTICA-AN ANALOGUE FOR A MARS ENVIRONMENT?

The McMurdo Dry Valleys comprise the largest ice-free area in Antarctica and are characterized by limited precipitation. There are many permanent lakes with permanent ice cover, that limit the amount of solar radiation reaching the water column, reducing the interaction between atmosphere and lakes. However these lakes provide a shelter from the harsh Antarctic climate, maintaining the lake ecosystem. Two cores were collected in Lake Hoare, in the Taylor Valley and the samples were examined for their thecamoebian (i.e. testate rhizopod) content. The testate rhizopods in these lakes have only chitinous organic tests with no agglutinated material, unlike most testate rhizopods, which use detrital material to build a test. The few species here are referred to the genus Arcella which is completely organic walled. The testate rhizopod concentration is generally higher in the layers where bacterial mat-fragments were more abundant which are net producers of oxygen. Additionally there were a limited number of ostracod carapaces and a rotifer resting stage? This reflects the sedimentation pattern occurring here where there are intervals with mat growth alternating with sediment accumulation on the ice surface and subsequent fallout to the lake bottom. New data from cores collected by others in 2002-03 penetrated to 2m depth with the upper 20cm being almost 5000ybp and having mixed layers of organics and sand, similar to the cores here, but below 20cm the sediment was partly unsorted, with gravel, sand and gravel mixed with sand which may mean that Lake Hoare has only had life forms in the last 5000yrs.