michael bird

James Cook University, Science and Engineering, Faculty Member

James Cook University, College of Science, Technology and Engineering, Faculty Member

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I trained as a geologist at U. Sydney and the ANU (PhD 1988). After a postdoc at UWO in Canada, I returned to Australia as Research Fellow, QEII Fellow at Research School of Earth Sciences, ANU. In 2000 I took up a position in Singapore and in 2004, a Chair at St. Andrews, Scotland. In 2009 I returned to Australia as an ARC Federation Fellow and Laureate Fellow at JCU. My research interests include the terrestrial carbon cycle, biochar, geoarchaeology and environmental change in the tropics.

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Minimum founding populations for the first peopling of Sahul

by Sean Ulm, michael bird, and Frédérik Saltré

Nature Ecology and Evolution, 2019

The timing, context and nature of the first people to enter Sahul is still poorly understood owin... more The timing, context and nature of the first people to enter Sahul is still poorly understood owing to a fragmented archaeological record. However, quantifying the plausible demographic context of this founding population is essential to determine how and why the initial peopling of Sahul occurred. We developed a stochastic, age-structured model using demographic rates from hunter-gatherer societies, and relative carrying capacity hindcasted with LOVECLIM’s net primary productivity for northern Sahul. We projected these populations to determine the resilience and minimum sizes required to avoid extinction. A census founding population of between 1,300 and 1,550 individuals was necessary to maintain a quasi-extinction threshold of ≲0.1. This minimum founding population could have arrived at a single point in time, or through multiple voyages of ≥130 people over ~700–900 years. This result shows that substantial population amalgamation in Sunda and Wallacea in Marine Isotope Stages 3–4 provided the conditions for the successful, large-scale and probably planned peopling of Sahul.

Early human settlement of Sahul was not an accident

by michael bird, Sean Ulm, and Frédérik Saltré

Scientific Reports, 2019

The first peopling of Sahul (Australia, New Guinea and the Aru Islands joined at lower sea levels... more The first peopling of Sahul (Australia, New Guinea and the Aru Islands joined at lower sea levels) by anatomically modern humans required multiple maritime crossings through Wallacea, with at least one approaching 100 km. Whether these crossings were accidental or intentional is unknown. Using coastal-viewshed analysis and ocean drift modelling combined with population projections, we show that the probability of randomly reaching Sahul by any route is <5% until ≥40 adults are 'washed off' an island at least once every 20 years. We then demonstrate that choosing a time of departure and making minimal headway (0.5 knots) toward a destination greatly increases the likelihood of arrival. While drift modelling demonstrates the existence of 'bottleneck' crossings on all routes, arrival via New Guinea is more likely than via northwestern Australia. We conclude that anatomically modern humans had the capacity to plan and make open-sea voyages lasting several days by at least 50,000 years ago. Increased attention to maritime landscapes over the last two decades has re-invigorated investigation into the role of coastal environments and sea travel in the behavioural evolution of our species. New evidence has fundamentally changed our understanding of the cognitive capacity of anatomically modern humans 1,2 , genetic ancestry 3 , dispersal patterns from Africa 4 and the peopling of new environments 5,6. However, the role of coastlines and coastal resources in the dispersal of modern humans has been much debated. Proponents of a coastal migration model for H. sapiens out of Africa argue that coastlines would have provided for a fast, directional population expansion with predictable resources and supplies of potable water 7. Those opposing, point out that there is little direct evidence to support a coastal-highway hypothesis and that there is evidence that early humans were able to make use of savanna and rainforest environments 2,8. More recent papers propose a less dichotomous model featuring flexibility, involving use of coasts and estuaries, but not exclusively relying on them 4,5,9. Whatever the reality, it is clear that the ability to make even rudimentary watercraft and move directionally over water, both across large rivers and in traversing unknown sections of coastline, would have given H. sapiens a selective advantage over other hominins. Australia and the islands to its north (the Wallacean Archipelago) have been at the forefront of this debate because the maritime crossing from Sunda to Sahul requires lengthy water crossings that appear to have been beyond the capacity of earlier hominins.

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The climate reconstruction potential of Acacia cambagei (gidgee) for semi-arid regions of Australia using stable isotopes and elemental abundances

by B. Witt, michael bird, and Patricia Gadd

To provide multi-centennial, annually-resolved records of climate for arid and semi-arid areas of... more To provide multi-centennial, annually-resolved records of climate for arid and semi-arid areas of Australia it is necessary to investigate the potential climate signals in tree species in this large region. Using a stable isotope and x-ray fluorescence approach to dendrochronology in Acacia cambagei, this study demonstrates short (10 years) proxies of temperature and precipitation are possible. Because rings in A. cambagei are difficult to see, precluding traditional dendrochronology, we used elemental abundances of Ca and Sr as an annual chronometer back to 1962. Radiocarbon analysis confirmed that our dating of wood from two trees. We compared d 13 C and d 18 O from the a-cellulose of the dated wood over the most recent 10 years (n ¼ 10) to local climate records demonstrating significant relationships between d 18 O and precipitation (r ¼ À0.85, p < 0.002); mean monthly maximum temperature (r ¼ 0.69, p < 0.03); and drought indexes (CRU scPDSI 0.5 , r ¼ À0.89, p < 0.001) for February and March. Acacia cambagei may be useful in developing regional networks of climate proxies for drought. Using modern trees, in combination with architectural timbers, it may be possible to construct a multi-century, annually-resolved proxy-record of rainfall and temperature for semi-arid northeastern Australia.

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Complexities in the palaeoenvironmental and archaeological interpretation of isotopic analyses of the Mud Shell Geloina erosa (Lightfoot, 1786)

by Sean Ulm, Robin Twaddle, Christopher Wurster, and michael bird

Isotope signals derived from molluscan shell carbonates allow researchers to investigate palaeoen... more Isotope signals derived from molluscan shell carbonates allow researchers to investigate palaeoenvironments and the timing and periodicity of depositional events. However, it cannot be assumed that all molluscan taxa provide equally useful data owing to species-specific biological and ecological traits. The Mud Shell, Geloina erosa (Lightfoot, 1786) (syn. Polymesoda coaxans, syn. Polymesoda erosa), an infaunal mangrove bivalve, is a common component of archaeological deposits along Australia's tropical north coast and throughout the Indo-West Pacific. The ubiquity of G. erosa has led to numerous researchers incorporating this taxon into interpretations of associated deposits, particularly in the generation of radiocarbon chronologies and as a palaeoenvironmental proxy. Despite this, concerns have been expressed regarding the impact of G. erosa physiology and ecology on associated geochemical signals. Adaptations allowing the survival of this species within its highly changeable mangrove environment may introduce complexities into radiocarbon and environmental data archived within its shell. This study combines local environmental and hydrological data with isotopic analysis (δ18O, δ13C, and 14C) of live-collected specimens to explore the interpretability of geochemical proxies derived from G. erosa. Results suggest a number of factors may impact geochemical markers in unpredictable ways, eroding the usefulness of associated interpretations.

Spatial heterogeneity of soil-derived CO2 efflux in three tropical Australian savannas

by Kalu Davies, michael bird, and Jon Lloyd

Impact of temperature and moisture on heterotrophic soil respiration along a moist tropical forest gradient in Australia

by Kalu Davies and michael bird

Soil Research, 2015

ABSTRACT Tropical forests represent the largest store of terrestrial carbon (C) and are potential... more ABSTRACT Tropical forests represent the largest store of terrestrial carbon (C) and are potentially vulnerable to climatic variations and human impact. However, the combined influence of temperature and precipitation on aboveground and belowground C cycling in tropical ecosystems is not well understood. To simulate the impact of climate (temperature and rainfall) on soil C heterotrophic respiration rates of moist tropical forests, we translocated soil cores among three elevations (100, 700 and 1540 m a.s.l.) representing a range in mean annual temperature of 10.9°C and in rainfall of 6840 mm. Initial soil C stocks in the top 30 cm along the gradient increased linearly with elevation from 6.13 kg C m–2 at 100 m a.s.l. to 10.66 kg C m–2 at 1540 m a.s.l. Respiration rates of translocated soil cores were measured every 3 weeks for 1 year and were fitted to different model functions taking into account soil temperature, soil moisture, mean annual temperature and total annual rainfall. Measured data coul

The Niah Cave Project: the fourth (2003) season of fieldwork

by Jessica Manser, Huw Barton, michael bird, Ryan Rabett, and Franca Cole

Sarawak museum journal, 2003

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The Niah Cave Project: the third (2002) season of fieldwork

by Brian Pyatt, Huw Barton, michael bird, Franca Cole, and Jessica Manser

Sarawak museum journal, 2002

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Past Human Activity and Geomorphological Change in a Guano-Rich Tropical Cave Mouth: Initial Interpretations of the Late Quaternary Succession in the Great Cave of Niah, Sarawak

by Brian Pyatt and michael bird

Asian Perspectives, 2005

Page 1. Past Human Activity and Geomorphological Change in a Guano-Rich Tropical Cave Mouth: Init... more

Field-based cavity ring-down spectrometry of δ 13 C in soil-respired CO 2

by Kalu Davies, michael bird, and N. Munksgaard

Isotopes in Environmental and Health Studies, 2013

Measurement of soil-respired CO 2 at high temporal resolution and sample density is necessary to ... more

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Bird, M. I. et al. Terrestrial vegetation change inferred from n-alkane 13C analysis in the marine environment. Geochim. Cosmochim. Acta 59, 2853-2857

Geochimica et Cosmochimica Acta

We report gas chromatography-isotope ratio monitoring-mass spectrometry (GC-IRM-MS) measurements ... more We report gas chromatography-isotope ratio monitoring-mass spectrometry (GC-IRM-MS) measurements of the 613C values of individual biomarker compounds (n-alkanes) extracted from a 3 m marine sediment core taken near the mouth of the Johnstone River, North Queensland, Australia. The technique allows a purely terrestrial isotope signal to be discerned despite mixing of terrestrial and marinederived carbon.

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Determining the timing and pattern of human colonisation in Australia: Proposals for radiocarbon dating'early'sequences

Australian Archaeology

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Pyrogenic carbon from tropical savanna burning: production and stable isotope composition

Biogeosciences, 2015

Widespread burning of mixed tree-grass ecosystems represents the major natural locus of pyrogenic... more Widespread burning of mixed tree-grass ecosystems represents the major natural locus of pyrogenic carbon (PyC) production. PyC is a significant, pervasive and yet poorly understood "slow-cycling" form of carbon present in the atmosphere, hydrosphere, soils and sediments. We conducted 16 experimental burns on a rainfall transect through northern Australian savannas with C 4 grasses ranging from 35 to 99 % of total biomass. Residues from each fire were partitioned into PyC and further into recalcitrant (HyPyC) components, with each of these fluxes also partitioned into proximal components (> 125 µm), likely to remain close to the site of burning, and distal components (< 125 µm), likely to be transported from the site of burning. The median (range) PyC production across all burns was 16.0 (11.5) % of total carbon exposed (TCE), with HyPyC accounting for 2.5 (4.9) % of TCE. Both PyC and HyPyC were dominantly partitioned into the proximal flux. Production of HyPyC was strongly related to fire residence time, with shorter duration fires resulting in higher HyPyC yields. The carbon isotope (δ 13 C) compositions of PyC and HyPyC were generally lower by 1-3 ‰ relative to the original biomass, with marked depletion up to 7 ‰ for grasslands dominated by C 4 biomass. δ 13 C values of CO 2 produced by combustion were computed by mass balance and ranged from ∼ 0.4 to 1.3 ‰. The depletion of 13 C in PyC and HyPyC relative to the original biomass has significant implications for the interpretation of δ 13 C values of savanna soil organic carbon and of ancient PyC preserved in the geologic record, as well as for global 13 C isotopic disequilibria calculations.

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… NPP and impacts of climate change on sandy soils in Australia using a soil carbon model calibrated to measurements of soil carbon, nitrogen and carbon …

The CENTURY model was modified and calibrated to a robust data set from of 31 regions of sandy so... more The CENTURY model was modified and calibrated to a robust data set from of 31 regions of sandy soils using landscape average measurements of soil carbon, nitrogen and δ 13 C, δ 14 C and some remotely sensed data. The 31 regions covered the full range of climate experienced in Australia including temperature extremes from Katherine in the Northern Territory to Cape Grim in Tasmania, and rainfall extremes from desert sand hills in the interior to tropical rainforests of the east coast of Queensland. A genetic algorithm was used to calibrate generic parameters describing ecosystem attributes such as N inputs, N loss after fire, and plant growth sensitivity to temperature. In addition one or two site specific parameters relating to fire frequency were calibrated for each individual site. The model was spun up for a period of at least 5000 years to equilibrate isotope pools. Atmospheric δ 13 C and δ 14 C concentrations were varied annually to incorporate the Seuss effect and bomb pulse C. The modified model was able to describe the variation across sites in terms of C, N, δ 13 C and δ 14 C reasonably well but with some exceptions. Simulated NPP was close to estimates obtained independently from remotely sensed data. Following model calibration, climate change scenarios were run for 70 years in the future to assess the sensitivity of the tree-grass-soil system to future climate and increasing atmospheric CO 2 .

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Re-analysis of the nineteenth century hydrology and sediment load data for the ayeyarwady river, myanmar

The Ayeyarwady (Irrawaddy) River of Myanmar (formerly Burma) is generally though to have the 5 th... more The Ayeyarwady (Irrawaddy) River of Myanmar (formerly Burma) is generally though to have the 5 th largest suspended load of any world river, and the 4 th highest total dissolved load. From these flux estimates, the combined systems of the Ayeyarwady and Thanlwin (Salween) rivers are regarded as contributing 20% of the total flux of material from the Himalayan-Tibetan orogen and deliver it over a short length of coastline into the Gulf of Martaban in the eastern Indian Ocean. The estimates for the Ayeyarwady are taken from published quotes of a 19 th Century dataset (Gordon 1885) and there are no available published data for the Thanlwin. We present a re-analysis of the Ayeyarwady data from the original 550 page report of Gordon (1879) covering ten years of discharge (1869)(1870)(1871)(1872)(1873)(1874)(1875)(1876)(1877)(1878)(1879) and one year of sediment concentration measurements (1877) and demonstrate that the commonly cited values of sediment loads (and therefore chemical fluxes) are in error. Taken at face value, the sediment flux estimates are conservatively assessed as being underestimated by 18%, and possibly as much as 38%, due to omission of the fine particulate load. However, an early 20 th Century Ayeyarwady River engineer criticised Gordon's discharge measuring methods, suggesting they lead to over-estimation of both water and sediment fluxes. These two opposing uncertainties require careful review. We describe the approaches employed, evaluate Gordon's measurements, calculations, and subsequent adjustments and present our revised interpretation of daily and annual discharges and sediment fluxes along with an estimate of uncertainty. Our re-evaluation suggests that the annual sediment flux from the Ayeyarwady-Thanlwin system may be significant for ocean geochemistry and estimation of denudation rates. The new values suggest that the Ayeyarwady and Thanlwin rivers contribute half the present day Ganges-Brahmaputra flux to the Indian Ocean. The catchments of the Ayeyarwady and Thanlwin are affected by ongoing land-use change, and our recently collected water and sediment flux data suggest that modern sediment loads are lower than those in the late19 th Century.

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New ABOX AMS-14C ages remove dating anomalies at Puritjarra rock shelter

Australian Archaeology

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Impact of temperature and moisture on heterotrophic soil respiration along a moist tropical forest gradient in Australia

Soil Research, 2015

Submission to Joint Standing Committee on Treaties: Inquiry into the Kyoto Protocol. from Research School of Earth Sciences Australian National University

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The gateway for terrestrial material entering the ocean

Eos Transactions American Geophysical Union

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Woody cover and hominin environments in the past 6 million years

Nature, 2011

The role of African savannahs in the evolution of early hominins has been debated for nearly a ce... more The role of African savannahs in the evolution of early hominins has been debated for nearly a century. Resolution of this issue has been hindered by difficulty in quantifying the fraction of woody cover in the fossil record. Here we show that the fraction of woody cover in tropical ecosystems can be quantified using stable carbon isotopes in soils. Furthermore, we use fossil soils from hominin sites in the Awash and Omo-Turkana basins in eastern Africa to reconstruct the fraction of woody cover since the Late Miocene epoch (about 7 million years ago). 13 C/ 12 C ratio data from 1,300 palaeosols at or adjacent to hominin sites dating to at least 6 million years ago show that woody cover was predominantly less than 40% at most sites. These data point to the prevalence of open environments at the majority of hominin fossil sites in eastern Africa over the past 6 million years.

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