Previously published work on the Holocene environment of southeastern Australia includes descriptions and analyses of sedimentary sequences and pollen assemblages from Lake Tyrrell. Mineralogy and sedimentary textures are excellent proxies for processes occurring within the lake; however, they are not necessarily reflective of catchment-wide conditions. Pollen analyses are a useful to fill this gap. Unfortunately, pollen assemblages in an arid environment are heavily impacted by aeolian transport, such that taxa whose pollen is windborne will be over-represented in ephemeral lacustrine sediments. In addition, some plants do not produce pollen that is readily preserved in dry, oxidizing sediments such as those of the modern Tyrrell sequence.

    In order to generate a more complete picture of changes in the plant community and supplement pollen data, we performed compound specific stable carbon isotope analyses on long chain n-alkanes extracted from the top 1.35 m of the lake bed. All higher plants produce long chain n-alkanes, such that plant types should be fairly evenly represented. In addition, chain-length of n-alkanes can be correlated with plant type, so that signals from grasses and trees/shrubs may be distinguished. In addition to extracting lipids from the core, we also examined the sediments for the presence of macro-scopic charcoal particles, to assess the claim that fire was a major factor in plant community shifts.

    Shifts in lipid abundance patterns and in isotopic signatures of individual lipids were interpreted as shifts in the plant community within the Lake Tyrrell catchment; the absence of macroscopic charcoal particles indicated that fire was not a major factor in precipitating community change. The rapid nature of the changes in lipid abundances and isotopic signatures points to a sudden shift in membership from a community dominated by C4 grasses to one containing a mixture of C4 and C3 grasses and relatively more C3 shrubs and/or trees. As this shift occurs in the top 6 cm of sediment, deposited during the last 10 ka, community change over this interval may be attributable to the shift from colder, arid conditions prevailing during the LGM to the relatively warmer, wetter conditions of the present interglacial.