Development and application of subfossil chironomid-based methods for late Quaternary climate reconstructions in eastern Australia

Chang, Jie Christine (2015). Development and application of subfossil chironomid-based methods for late Quaternary climate reconstructions in eastern Australia PhD Thesis, School of Geography, Planning and Environmental Management, The University of Queensland. doi:10.14264/uql.2015.1000

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Author Chang, Jie Christine
Thesis Title Development and application of subfossil chironomid-based methods for late Quaternary climate reconstructions in eastern Australia
School, Centre or Institute School of Geography, Planning and Environmental Management
Institution The University of Queensland
DOI 10.14264/uql.2015.1000
Publication date 2015-11-06
Thesis type PhD Thesis
Total pages 235
Total colour pages 26
Total black and white pages 209
Language eng
Subjects 040605 Palaeoclimatology
040203 Isotope Geochemistry
060206 Palaeoecology
Formatted abstract
The lack of tools to quantify past climate has hindered the development of our knowledge of climate change in the late Quaternary in eastern Australia. This thesis developed two methods using subfossil remains of non-biting midge larvae (Chironomid, Diptera: Chironomidae) preserved in lake sediments to reconstruct past changes in the Australian climate system during and since the Last Glacial Maximum (LGM). Firstly a transfer function model for reconstructing past summer temperatures based on the temperature tolerance of modern Australian chironomid taxa was created. Secondly the stable oxygen and hydrogen isotope composition (δ18O, δ2H) of the chitinous head capsules was used to determine temperature changes from chironomids from the same lakes. Both techniques were tested and the complexities of applying these methods as independent temperature proxies in Australia were explored.

In order to develop the transfer function, forty-five lakes were examined in eastern Australia for eighteen physical and chemical parameters. The physical and chemical analysis of the lakes suggests that sub-humid and semi-arid sites are naturally eutrophic, whereas high altitude and actively managed sites were mostly mesotrophic. Thirty-four lakes were subsequently used in the transfer function. The transfer function first axis was Mean February Temperature which explains 9.5% of the variance and the secondary axis is pH which also explains 9.5% of the variance. Despite these low values the function appears robust. The transfer function had an r2jack-knifed of 0.69 and a root mean squared error of prediction (RMSEP) of 2.33°C.

The transfer function method was then applied to subfossil chironomids from a subtropical site on North Stradbroke Island, Australia that spans the LGM and the last deglaciation. This has provided the first quasi-continuous quantitative temperature reconstruction from mainland terrestrial Australia covering these critical periods (between c. ~ 23.2 and 15.5 cal ka BP). The results of this reconstruction show a maximum cooling of c. ~6.5°C had occurred at c. ~18.5 cal ka BP during the LGM. A rapid warming followed and temperatures reached near Holocene values by c. ~17.3 cal ka BP. The warming trend started at c. ~18.1 cal ka BP and is consistent with the start of deglaciation from Antarctic records. The records suggest high latitude influencing of subtropical climate during the LGM.

Stable isotopes (δ18O and δ2H) from a single genus of chironomid head capsules (Chironomus spp.) were evaluated to reconstruct past temperatures also. Results suggest that both δ18O and δ2H are potentially valuable tools for reconstructing temperature in humid and low nutrient regions of Australia (e.g. Tasmania and the southeastern highlands). The correlation between δ18O of chironomid head capsules and temperature is consistent with observations from Europe and indicates that there is potential for this technique. However, the collection of enough material from ancient sites is challenging and the use of stable isotopes is recommended for late Holocene and modern studies, perhaps focused on nutrient changes rather than temperature.
Keyword Southeast Australia
Freshwater lakes
Subfossil chironomids
Transfer function
Temperature
Palaeoclimate reconstruction
Last Glacial Maximum
Last deglaciation
Stable Isotopes

Document type: Thesis
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Created: Fri, 30 Oct 2015, 04:34:22 EST by Christine Chang on behalf of Scholarly Communication and Digitisation Service