An Australian Holocene climate reconstruction using Chironomidae from a tropical volcanic maar lake

Holocene sediments from Lake Barrine on the Atherton Tableland in tropical north-east Queensland, Australia (17°15′S, 145°38′E, 721 m asl) reveal 10 assemblage shifts in subfossil aquatic immature Chironomidae remains over the past 9000 years. Using the program CANOCO 3.12 and ordination analyses we examined relationships between the physico-chemistry of multiple local and regional water bodies and their chironomid fauna to assess the relative importance of various environmental and climatic parameters on the distribution of Australian chironomids. To derive palaeoclimates we used an extant assemblage to test reconstructions, over 50 calibrated radiocarbon dates from a 7.5-m sediment record, and the correlative distribution modelling programs DOMAIN and BIOCLIM to construct and overlap climate envelopes of species. In comparison with contemporary climate, reconstructed conditions were warmer annually by ∼2.5°C from 4650 calendar years before present (cal yr BP) to more recent times. Annual temperatures were slightly cooler between 5130 to 4650 cal yr BP and may have been cooler in the warmest quarter by ∼6.6°C between 6890 and 6090 cal yr BP. Precipitation estimates, although subject to greater errors, were reconstructed in the wettest quarter to be drier by around 500 mm at 5130-4650 and 6890-6090 cal yr BP. The inferred sensitivity of Chironomidae to climatic and environmental conditions at Lake Barrine suggests that Australian midges are reliable and informative biological indicators. Faunal changes were correlated with fluctuations in water levels, sediment influx, organic material, oxygen availability and nutrient status mediated by changes in the local climate and a shift from dry sclerophyll vegetation to rainforest within the catchment.