No abstract

A palaeoclimatic Holocene rainfall history is reported for Lake Broadwater in southeast Queensland, Australia. This naturally occurring semi-permanent freshwater lake is part of the Condamine-Balonne Catchment on the Darling Downs. It is an important natural habitat for waterbirds and other wildlife, but it dried-out completely during the Australian Millennium Drought from 2001-2008. Lake sediments were sampled to a depth of about 1.7 m from the centre of the lake in March 2007. A detailed chronology developed from radiocarbon ('*C) dating indicates that sedimentation was fairly constant into the lake and averaged ~0.16 mm year' since about 11 kyr cal B.P. An interpretation of the palaeoclimatic record indicates higher rainfall and moist conditions prevailed from ~11 kyr to ~3.5 kyr cal B.P., followed by lower rainfall, decreasing further from ~2.2 kyr cal B.P to the present day. This change to drier conditions most likely reflects an increase in frequency and/or intensity of El Nifio-Southern Oscillation (ENSO) cycles which began in the mid-late Holocene and has been identified from other proxy records elsewhere in eastern Australia. The change to a lower rainfall regime suggests large-scale ocean/atmospheric circulation changes affecting not only coastal regions, but also inland regions of eastern Australia including the northern parts of the Murray-Darling Basin.

Abstract. Much of southern and eastern Australia including Queensland have experienced rainfall declines over recent decades affecting agricultural production and accelerating water infrastructure development. Rainfall declines from southern Australia have now been directly related to changes in the Southern Annular Mode (SAM) and the subtropical ridge. In southern and coastal Queensland, the rainfall declines have occurred mostly in the austral summer and autumn. Observations from this region reveal the rainfall decline is correlated to an increase in the mean sea level pressure (MSLP) at many stations. The largest increases in MSLP are over southeast Queensland and coastal regions, where some of the largest rainfall declines occur. This study indicates the subtropical ridge as one of the main factors in the rainfall decline over this region. SAM is also likely to be important, although its seasonal influence, apart from winter, is harder to determine.