Charophyte oogonia and amino acid geochronology
The summer monsoon is one of the primary sources of moisture over the semi-arid regions of central Australia. Often, dry lakes in the interior of Australia are used to reconstruct the timing and the intensity of monsoons in the past. Investigation of the stratigraphy surrounding these lakes shows that elevated shoreline deposits demarcate these prior highstands. A lack of suitable material for dating techniques has hampered our understanding of the exact timing of these monsoonal shifts.
Here I've used charophyte oogonia, the calcified algal fruiting bodies found in shallow lacustrine sediments, as a new sample material for amino acid geochronology. Improved instrumentation now allows the use of extremely small samples (~0.01 mg), reducing the required sample size and therefore enabling higher sampling precision of lacustrine sediments (e.g. beaches, lake cores). An assessment of sample quality regarding charophyte oogonia was made and several applications of amino acid racemization using these algae were explored. The majority of the oogonia analyzed in this experiment displayed random D/L variability between subsamples from the same stratum despite high levels of analytical reproducibility (< 8% variation). The concentration of amino acids in oogonia was investigated as a potential source of this D/L variability, but there was no correlation between the two parameters. It is this variability which hampered nearly all chronologic reconstructions based on amino acid racemization.