Lake Tyrrell is of particular interest to climate scientists, due to the time period represented in its sediment sequence and its emplacement on the northern margin of a region dominated by westerlies, midway between the arid interior of the continent and the coastal highlands. The Tyrrell beds, whose age extends through the Holocene (~11.5 ka – present) and into the late-Pleistocene (1.8 Ma – 11.5 ka) are underlain by a sequence of fresh water clays whose thickness varies with geographic location. Termed the Blanchetown Clay, the sequence was deposited by the Plio-Pleistocene megalake, Lake Bungunnia. Together, the Tyrrell Beds and Blanchetown Clay preserve records of multiple glacial-interglacial cycles comprising a period of significant environmental change on the Australian continent.

    In addition to preserving an extensive sediment sequence, Lake Tyrrell possesses one other considerable attraction for climate scientists: its location. The Tyrrell Basin lies midway between a tropical/sub-tropical region dominated by summer rains, and an arid coastal region dominated by winter rains. An equator ward compression of the dominant westerly winds, such as is thought to have occurred during Pleistocene glaciations, would have altered the precipitation regime in the catchment, and so the water balance in the lake. The resulting fluctuations in salinity would be recorded in the sedimentary sequence, and would provide information on the changes in the dominant wind pattern.

    Based on the suites of lipid biomarkers extracted from 20 subsamples taken at core depths from 20 - 1013 cm, and correlation of those biomarkers with pollen and mineral assemblages and sedimentary textures, we are able to show that the Tyrrell Beds preserve records of 2 glacial-interglacial cycles, and that salinity in the lake fluctuated from <3 g/L to > 330 g/L during the Pleistocene.