http://www.researchonline.mq.edu.au/vital/access/services/Feed ${session.getAttribute("locale")} 5 http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:24228 6 page(s) 2013-02-18T06:32:12.680Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:24229 10 page(s) 2013-02-18T06:32:11.272Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:15246 Savannas are defined based on vegetation structure, the central concept being a discontinuous tree cover in a continuous grass understorey. However, at the high-rainfall end of the tropical savanna biome, where heavily wooded mesic savannas begin to structurally resemble forests, or where tropical forests are degraded such that they open out to structurally resemble savannas, vegetation structure alone may be inadequate to distinguish mesic savanna from forest. Additional knowledge of the functional differences between these ecosystems which contrast sharply in their evolutionary and ecological history is required. Specifically, we suggest that tropical mesic savannas are predominantly mixed tree–C₄ grass systems defined by fire tolerance and shade intolerance of their species, while forests, from which C₄ grasses are largely absent, have species that are mostly fire intolerant and shade tolerant. Using this framework, we identify a suite of morphological, physiological and life-history traits that are likely to differ between tropical mesic savanna and forest species. We suggest that these traits can be used to distinguish between these ecosystems and thereby aid their appropriate management and conservation. We also suggest that many areas in South Asia classified as tropical dry forests, but characterized by fire-resistant tree species in a C₄ grass-dominated understorey, would be better classified as mesic savannas requiring fire and light to maintain the unique mix of species that characterize them. 2011-10-05T13:10:28.363Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13425 We present an interactive 3-D computer program (LitMod3D) developed to perform combined geophysical-petrological modeling of the lithosphere and sublithospheric upper mantle. In contrast to other available modeling software, LitMod3D is built within an internally consistent thermodynamic-geophysical framework, where all relevant properties are functions of temperature, pressure, and composition. By simultaneously solving the heat transfer, thermodynamic, rheological, geopotential, and isostasy (local and flexural) equations, the program outputs temperature, pressure, surface heat flow, density (bulk and single phase), seismic wave velocities, geoid and gravity anomalies, elevation, and lithospheric strength for any given model. These outputs can be used to obtain thermal and compositional models of the lithosphere and sublithospheric upper mantle that simultaneously fit all available geophysical and petrological observables. We illustrate some of the advantages and limitations of LitMod3D using synthetic models and comparing our predictions with those from other modeling methods. In particular, we show that (1) temperature at midlithosphere depths may be overestimated by as much as 200 K when compositional heterogeneities in the mantle and T-P effects are not considered in lithospheric models and (2) the neglect of mantle phase transformations on gravity-based models in thin-crust settings can result in a significant overestimation and underestimation of the derived crustal thickness and its internal density distribution, respectively. 2011-08-26T04:32:32.646Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:14151 Coral disease is a growing problem for reef corals and a primary driver of reef degradation. Incidences of coral disease on the Great Barrier Reef (GBR) are increasing; however, our understanding of differences among species in their potential for contracting disease is poor. In this study, we integrate observations of coral disease on the GBR from the primary literature as well as morphological, ecological and biogeographical traits of coral species that have been hypothesised to influence “disease potential.” Most of the examined traits influence species’ disease potential when considered alone. However, when all traits are analysed together, diversity of predators, geographical range size and characteristic local abundance are the primary predictors of disease potential. Biases associated with species’ local abundance and phylogeny are tested but do not overpower relationships. This large-scale macroecological 2011-08-01T06:26:50.705Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13928 Original Russian Text © M.V. Mints, A.N. Konilov, K.A. Dokukina, T.V. Kaulina, E.A. Belousova, L.M. Natapov, W.L. Griffin, S.Y. O’Reilly, 2010, published in Doklady Akademii Nauk, 2010, Vol. 434, No. 6, pp. 776–781. 2011-07-06T14:21:04.951Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13996 Original Russian Text © N.B. Kuznetsov, L.M. Natapov, E.A. Belousova, W.L. Griffin, S.Y. O’Reilly, 2009, published in Doklady Akademii Nauk, 2009, Vol. 426, No. 4, pp. 504–510. 2011-07-06T06:07:26.125Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13995 Original Russian Text © N.B. Kuznetsov, L.M. Natapov, E.A. Belousova, U.L. Griffin, S. O’Reilly, A.A. Soboleva, K.V. Kulikova, O.V. Udoratina, A.A. Morgunova, 2009, published in Doklady Akademii Nauk, 2009, Vol. 424, No. 3, pp. 363–368. 2011-07-06T06:07:20.671Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13971 Detailed LAM-ICPMS U–Pb dating and LAM-MC-ICPMS Lu–Hf isotope analysis were carried out on zircons from nine samples of basement metamorphic rocks in the southern Cathaysia Block, South China. The chemical compositions of these metamorphic rocks and zircon morphology indicate that their protoliths were sedimentary; zircon U–Pb dating results show they mainly formed during the late Neoproterozoic. The Precambrian crust of the Cathaysia Block can be divided into two distinct tectonic domains, the Wuyishan terrane to the northeast and the Nanling-Yunkai terrane to the southwest. The nearly E–W boundary between these two terranes is also supported by geophysical, petrological and geochemical evidence, and the basement rocks of the two terranes are comprised of different components. The Wuyishan terrane is characterized by dominant Paleoproterozoic (1.86 Ga) and lesser Neoarchean magmatism, and the southern-central part of the terrane suffered strong Neoproterozoic and early Paleozoic tectonothermal reworking. The zircon data suggest that there were five important episodes of juvenile crust generation (3.6 Ga, 2.8 Ga, 2.6–2.4 Ga, 1.85 Ga and 0.8–0.7 Ga) in the Wuyishan terrane. Strong Paleoproterozoic (1.85 Ga) magmatism in northern Wuyishan and Neoproterozoic (0.8–0.7 Ga) magmatism in central and southern Wuyishan both principally involved the remelting of old crust with minor input of juvenile material. In contrast, the Nanling-Yunkai terrane contains abundant Neoarchean and Grenvillian zircons, some evidence of Mesoproterozoic activity and rare Paleo- to Meso-Archean and Neoproterozoic zircons. U–Pb ages and Hf-isotopic compositions of the detrital zircons from the late Neoproterozoic to early Paleozoic meta-sedimentary rocks in the Nanling-Yunkai area suggest that the growth of juvenile crust mainly occurred at ~3.6 Ga, ~3.3 Ga, 2.5–2.6 Ga, ~1.6 Ga, ~1.0 Ga and 0.8–0.7 Ga. Neoarchaean (2.6–2.5 Ga), Grenvillian (~1.0 Ga) and Neoproterozoic (0.8–0.7 Ga) magmatism mainly involved the recycling of old crust. Minor remnants of ~4.1 Ga crust may remain in the terrane. This crustal history is distinct from that of the Wuyishan terrane and analogous to those recorded for the eastern India–East Antarctic domain of northern Gondwanaland, suggesting that they probably were once linked. 2011-07-04T12:20:24.857Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13936 Integrated U–Pb dating, Hf-isotope and trace-element analysis of detrital zircons from the Fanjingshan and Xiajiang sediments in the southeastern part of the Yangtze Block has been used to identify ancient crustal remnants and the provenance of clastic sediments, and to provide an overview of crustal evolution in the now-covered parts of the Yangtze Block. The zircon dating indicates that the Fanjingshan Group, which previously was regarded as 870 Ma old, actually was deposited in a ~800 Ma rift basin similar to other contemporaneous basins in the Yangtze Block; the regional unconformity separating the Fanjingshan Group from the overlying Xiajing Group is dated to 800–740 Ma. Differences in clast compositions and the trace-element and Hf-isotope signatures of zircons between the Fanjingshan Group and the Xiajiang Group suggest changes in the source areas within the Yangtze Block. The combined ages and Hf-isotope data for each group show different histories of crustal evolution in their source areas. In the Yangtze Block, a previously unrecognized source (~4.3 Ga) is suggested by the Hf model ages of the oldest zircons. Both recycling of ancient crustal materials and minor addition of juvenile material took place in the time intervals 2.5–2.4 Ga, 2.0–1.7 Ga and 0.85–0.8 Ga. The most important generation of juvenile crust appears to have occurred at 1.6–1.4 Ga in the source area of the Fanjingshan Group, and at 0.95–0.85 Ga and 0.78–0.74 Ga in the source area of the Xiajiang Group. This is the first documentation of early Mesoproterozoic (1.6–1.4 Ga) juvenile crust in South China. 2011-07-01T09:40:41.360Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13896 Analysis of U–Pb ages, Hf isotopes and trace-element compositions in zircon collected from modern drainages is a robust methodology for tracking crustal and magmatic evolution. The application of the technique to zircons from the Luebo area in the central part of the Congo-Kasai Craton indicates the presence of a ~3.6 Ga crust that underwent late Archean (2.9–2.5 Ga) reworking. Very low initial Hf-isotope ratios in zircons with U–Pb ages between 1.9 and 2.6 Ga suggest the presence of crust even older than 3.6 Ga at depth. The Archean crust underwent further reworking during Paleoproterozoic, Mesoproterozoic and Neoproterozoic thermal events. Post-Archean generation of juvenile crust appears to have occurred only sporadically during Meoproterozoic–Neoproterozoic time. The magmatic activity and tectonic events observed in the Neoproterozoic Katangan Belt had a regional extent as they also impacted the Congo-Kasai Craton where alkaline magmatism has occurred from late Archean to early Cambrian time. The ages of zircons with low HREE and U contents suggest three separate episodes of kimberlite magmatism in the central part of the Congo-Kasai Craton, in late Archean (2.8–2.6 Ga), Neoproteorozoic (850–582 Ma) and Cretaceous (116–70 Ma) time. 2011-06-30T15:10:57.984Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13776 A revised set of propositions about ecology in arid Australia is presented, based on research literature since publication of Stafford Smith and Morton (1990). Fourteen propositions distil our argument that most features of the Australian deserts are explicable in terms of two dominant physical and climatic elements: rainfall variability, leading to extended droughts and occasional flooding rains; and widespread nutrient poverty. Different landscapes within the arid zone show these features to varying degrees, and so it is important to think about different places separately when considering our propositions. Plant life-histories strongly reflect temporal patterns of soil moisture; because Australian deserts receive more variable rainfall than most others, there is a distinctive spectrum of life-histories. Low levels of phosphorus (together with abundant soil moisture on irregular occasions) favour plants producing a relative excess of carbohydrate (C). In turn, C-rich plant products sometimes lead to fire-prone ecosystems, assemblages dominated by consumers of sap and other C-based products, and abundant detritivores (particularly termites). Fluctuations in production due to variable rainfall provide openings for consumers with opportunistic life-histories, including inhabitants of extensive but ephemeral rivers and lakes. Most consumer species exhibit some dietary flexibility or utilise more dependable resources; these strategies give rise to greater stability in species dynamics and composition of assemblages than might first be imagined under the variable rainfall regime. Aboriginal people have had long-standing ecological influence as they accessed resources. For each proposition we suggest the extent to which it is ‘different’, ‘accentuated’ or ‘universal’ in comparison with other deserts of the world, recognising that this categorisation is in need of critical testing. Further tests of each proposition are also suggested to fill the many gaps that still exist in our knowledge of the structure and functioning of Australia’s deserts. 2011-06-24T23:31:18.602Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13482 As climate is changing rapidly, there is an increasing need to understand how water and soil resources respond to climate change. Soil and sediment dynamics are sensitive to several external factors such as climate, vegetation type and distribution, human activity, and tectonic activity. However, the relationship between erosion and changes in these factors is difficult to constrain with current available approaches. Here we show that uranium isotopes in sediments from river paleochannels can be used to reconstruct variations in the residence time of sediments in a catchment over the past 100 k.y. We find that sediment residence times increase by an order of magnitude during interglacials compared to glacial periods. This is interpreted as a change in sediment stores in the landscape that are tapped by catchment erosion: young, upland soils during glacial periods, reworking of old alluvial sediments during interglacials. A direct correlation is found between the sediment residence time and climatic parameters (sea-surface temperature, atmospheric carbon dioxide content, and paleorainfall estimates), suggesting that during a glacial cycle, sediment dynamics closely follow variations in climate. However, this relationship is not simple because there is no correlation between sediment residence time and paleodischarge estimates. Because sediment residence time variations correlate with changes in vegetation inferred from pollen data, it is hypothesized that the influence of climate on erosion over a glacial cycle may be indirect, and operates via the influence of climate on the type of plant ecosystems within a catchment. If verified elsewhere, this conclusion would emphasize the important role of biology in the physical evolution of Earth's surface, here observed over a 100 k.y. time scale. 2011-06-03T12:30:23.048Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12321 As climate is changing rapidly, there is an increasing need to understand how water and soil resources respond to climate change. Soil and sediment dynamics are sensitive to several external factors such as climate, vegetation type and distribution, human activity, and tectonic activity. However, the relationship between erosion and changes in these factors is difficult to constrain with current available approaches. Here we show that uranium isotopes in sediments from river paleochannels can be used to reconstruct variations in the residence time of sediments in a catchment over the past 100 k.y. We find that sediment residence times increase by an order of magnitude during interglacials compared to glacial periods. This is interpreted as a change in sediment stores in the landscape that are tapped by catchment erosion: young, upland soils during glacial periods, reworking of old alluvial sediments during interglacials. A direct correlation is found between the sediment residence time and climatic parameters (sea-surface temperature, atmospheric carbon dioxide content, and paleorainfall estimates), suggesting that during a glacial cycle, sediment dynamics closely follow variations in climate. However, this relationship is not simple because there is no correlation between sediment residence time and paleodischarge estimates. Because sediment residence time variations correlate with changes in vegetation inferred from pollen data, it is hypothesized that the influence of climate on erosion over a glacial cycle may be indirect, and operates via the influence of climate on the type of plant ecosystems within a catchment. If verified elsewhere, this conclusion would emphasize the important role of biology in the physical evolution of Earth's surface, here observed over a 100 k.y. time scale. 2011-05-30T00:10:07.696Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13381 Ancient cratons are typically characterized by thick lithospheric-mantle roots that provide them with buoyancy and rigidity. Once formed, cratons, including their roots, move around Earth's surface as parts of rigid plates that are normally unaffected by later magmatism or tectonic activity. Considerable geophysical and geochemical evidence, however, suggests that the ancient lithospheric mantle beneath the Chinese portion of the eastern Sino-Korean craton was replaced by thinner, hotter, juvenile mantle during the Jurassic to Early Cretaceous. The extent and cause of the changes to this lithospheric mantle have been debated. Keys to deciphering the history of the changes include knowledge of both the lateral extent of the lithospheric modifications and the relative timing of change across the craton. Discerning the age and structure of lithospheric mantle underlying North Korea, the easternmost part of the Sino-Korean craton, is thus particularly important. Here we report mineral compositions and Re-Os isotopic data for peridotite xenoliths from North Korean Triassic kimberlite and Tertiary basalts. The data suggest that, from the Triassic to the present, North Korea has been underlain by young, hot and fertile lithospheric mantle, unlike typical cratonic lithospheric roots, but similar to the juvenile lithospheric mantle underlying Chinese portions of the craton. Given the generally ancient nature of the crust composing North Korea, our findings suggest that modification of underlying cratonic roots extended to the eastern edge of the craton. The Triassic eruption age of the kimberlite suggests that the lithospheric changes may have occurred earlier than in China, indicating that lithospheric removal evolved from east to west. These results are most consistent with the conclusion that lithospheric loss was initially triggered by extension that followed the collision between the Sino-Korean and Yangtze cratons. 2011-05-27T04:30:35.259Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12964 Lavas erupted in back-arc basins afford the opportunity to explore the extent to which decompression and subduction-related components influence partial melting in this setting. We present U-Th-Ra disequilibria data from 24 well-characterized lavas from the Manus Basin behind the New Britain volcanic arc, supplemented by some additional trace element and Sr-Nd-Pb isotope data. The lavas range in composition from 49.6 to 57.7 wt % SiO₂ and can be subdivided into those that are broadly like mid-ocean ridge basalts (MORB) with Ba/Nb < 16 and back-arc basin basalts (BABB) that are variably influenced by subduction components and have Ba/Nb > 16. Rifts closest to the arc are dominated by BABB, whereas both lavas types erupt further away at the Manus Spreading Center. The MORB have small ²³⁰Th excesses (up to 5%) and are displaced below the global correlation of (²³⁰Th/²³⁸U) with ridge depth. In most respects the BABB closely resemble lavas erupted along the New Britain arc front, including ²³⁸U excesses that reach 26%. The Pb isotope data can be explained by mixing of a subduction component into an Indian MORB mantle source. The Pb in the subduction component is derived from both the subducted sediment (5%) and fluids from the subducting altered Solomon Sea oceanic crust (95%), and these were mixed prior to addition to the mantle wedge. U/Th ratios, Fe³⁺/ΣFe, and H2O contents all increase with increasing ²⁰⁶Pb/²⁰⁴Pb. A model in which addition of the subduction component to the mantle wedge is followed by 230Th in-growth during decompression and dynamic melting all less than 140 kyr prior to eruption can simulate the data. However, our preferred model is one of dynamic decompression melting in which subduction-modified, more oxidized mantle had DU ≪ DTh leading to ²³⁸U excesses in contrast to unmodified mantle that yields ²³⁰Th excess. Large ²²⁶Ra excesses in some southern rift samples require addition of a fluid <8 kyr ago but elsewhere reflect melting under low-porosity conditions. 2011-05-25T21:53:40.967Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12966 In order to undertake a preliminary assessment of the extent of symmetry in source composition and melting dynamics in the Azores plume we present new ICP-MS trace element data along with Sr, Nd, Pb, and U-Th-Ra isotope data for samples from the islands Flores and Corvo west of the Mid-Atlantic Ridge. We also present data from a picrite from Faial and new ICP-MS trace element data for 28 basaltic lavas from the eastern Azores Plateau to augment data published previously from these samples. Rare earth element data for primitive lavas (MgO ≥ 5% and Mg # ≥ 60) have La/YbN ∼ 10 and variable Ce and/or Eu anomalies. Multi-incompatible trace element patterns normalized to primitive mantle are convex upward with small negative Th and K ± Pb anomalies. While lavas to the east are characterized by low Nb/Zr and generally lower La/Yb ratios (with the notable exception of eastern São Miguel), lavas from the western islands have slightly higher Nb/Zr and La/Yb inferred to reflect smaller degrees of partial melting. The Sr-Nd-Pb isotope systematics imply that Corvo and Flores sample components which range from an isotopic source commonly found in the Azores (e.g., at the eastern island of Graciosa) to a more depleted, MORB-like mantle sampled at the Mid-Atlantic Ridge. However, in common with uncontaminated samples from São Miguel, the Corvo and Flores samples appear to have slightly lower ²³⁰Th excesses and higher La/Yb, Tb/Yb than the other Azores islands or the Mid-Atlantic Ridge samples. The trace element and isotope data indicate a relatively symmetric pattern with distance across the MAR, while U-Th disequilibria, and thus inferred melting dynamics, appear less symmetric. Nevertheless, the data suggest that heterogeneities in source composition do not have a large effect on melting dynamics, at least within the Azores islands. 2011-05-25T21:53:36.535Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12195 Biological soil crusts cover large areas of the Gurbantunggut Desert in northwestern China where they make a significant contribution to soil stability and fertility. The aim of this study was to quantify the potential nitrogen-fixing activity (NA) of different types of biological soil crusts in the Gurbantunggut Desert. The results suggest that NA (nmol C₂H₄m⁻⁴h⁻²) for each type of crusts was highly variable. Seasonal variation was also important, with all three types of crusts responding in a similar way to changes in environmental conditions. From March to May, NA was relatively low for all crust types. During this season, NA was 2.26 × 10³ for cyanobacterial crust followed by lichen crust (6.54 × 10²) and moss crust (6.38 × 10²). From June to October, all crust types reached their highest level of NA, especially lichen crust and moss crust (p < 0.01). The NA of cyanobacterial crust (9.81 × 10³) was higher than that of lichen crust (9.06 × 10³) and moss crust (2.03 × 10³). From November to February, when temperatures were consistently low (<0 °C), NA was at its lowest level, especially in cyanobacterial crust (4.18 × 10²) and moss crust (5.43 × 10²) (p < 0.01). Our results indicate that species composition is critical when estimating N inputs in desert ecosystems. In addition, all three types of crusts generally responded in a similar way to environmental conditions. The presence of N fixation activity in all crusts may contribute to the maintenance of fertility in sparsely vegetated areas and provide surrounding vascular plant with fixed nitrogen. 2011-03-14T06:00:47.973Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12196 The responses of canopy conductance to variation in solar radiation, vapour pressure deficit and soil moisture have been extensively modelled using a Jarvis–Stewart (JS) model. Modelled canopy conductance has then often been used to predict transpiration using the Penman–Monteith (PM) model. We previously suggested an alternative approach in which the JS model is modified to directly estimate transpiration rather than canopy conductance. In the present study we used this alternative approach to model tree water fluxes from an Australian native forest over an annual cycle. For comparative purposes we also modelled canopy conductance and estimated transpiration via the PM model. Finally we applied an artificial neural network as a statistical benchmark to compare the performance of both models. Both the PM and modified JS models were parameterised using solar radiation, vapour pressure deficit and soil moisture as inputs with results that compare well with previous studies. Both models performed comparably well during the summer period. However, during winter the PM model was found to fail during periods of high rates of transpiration. In contrast, the modified JS model was able to replicate observed sapflow measurements throughout the year although it too tended to underestimate rates of transpiration in winter under conditions of high rates of transpiration. Both approaches to modelling transpiration gave good agreement with hourly, daily and total sums of sapflow measurements with the modified JS and PM models explaining 87% and 86% of the variance, respectively. We conclude that these three approaches have merit at different time-scales. 2011-03-14T06:00:47.559Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:11977 Many continental flood basalt provinces contain rhyolites with ‘A-type’ compositions and many studies have concluded that these higher silica rocks are crustal melts from metapelitic or tonalitic country rock. However, although many of the low-Ti continental flood basalt sequences exhibit a marked a silica gap from ∼55–65 wt. SiO2, many incompatible element ratios, and the calculated eruption temperatures (950–1100°C) are strikingly similar between the rhyolites and associated basalts. Using experimental evidence, derivation of the low-Ti rhyolites from a basaltic parent is shown to be a viable alternative to local crustal melting. Comparison of liquid compositions from experimental melting of both crustal and mantle-derived (basaltic) source materials allows the two to be distinguished on the basis of Al₂O₃ and FeO content. The basalt experiments are reversible, such that the same melts can be produced by melting or crystallisation. The effect of increased water content in the source is also detectable in the liquid composition. The majority of rhyolites from continental flood basalt provinces fall along the experimental trend for basalt melting/ crystallisation at relatively low water content. The onset of the silica gap in the rhyolites is accompanied by an abrupt decrease in TiO₂ and FeO*, marking the start of Fe–Ti oxide crystallisation. Differentiation from 55–65 wt. SiO₂ requires ∼30 fractional crystallisation in which magnetite is an important phase, sometimes accompanied by limited crustal contamination. The rapid increase in silica occurs over a small temperature interval and for relatively small changes in the amount of fractional crystallisation, thus intermediate compositions are less likely to be sampled. It is argued that the presence of a silica gap is not diagnostic of a crustal melting origin for either A-type granites or rhyolites in continental flood basalt provinces. The volume of these rhyolites erupted over the Phanerozoic is significant and models for crustal growth should take this substantial contribution from the mantle into account. 2011-02-28T14:20:20.660Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:11918 The observation of oil inclusions trapped prior to 2.0 Ga in Palaeoproterozoic rocks and the ability to obtain detailed molecular geochemical information from them provide a robust way for understanding the early biogeochemical evolution of the Earth. Oil-bearing fluid inclusions (FI) in ca. 2.45 Ga fluvial metaconglomerate of the Matinenda Formation at Elliot Lake, Canada were trapped in quartz and feld-spar during diagenesis and early metamorphism of the host rock, probably before ca. 2.2 Ga. The 2.1 Ga FA Formation sandstone of the Franceville Basin in Gabon that hosts the Oklo natural fission reactors has also been discovered to contain abundant Palaeoproterozoic oil-bearing FIs. This oil occurs within H2O and CO2-dominated inclusions trapped in syntaxial quartz overgrowths and intragranular and transgranular microfractures in detrital quartz, and was most likely trapped 2.1–1.98 Ga. Molecular geochemical analyses of both FI oils reveal a wide range of compounds, including n-alkanes, isoprenoids, monomethylalkanes, aromatic hydrocarbons, and trace amounts of complex multi-ring biomarkers including terpanes, hopanes, methylhopanes, steranes and diasteranes. To ensure a reliable interpretation of oil inclusions, a comprehensive series of outside-rinse blanks and procedural system blanks was analysed by gas chromatography-mass spectrometry; quantitative amounts of the hydrocarbons in these blanks were compared to the FI extracts, so as to provide confidence limits on the experimental integrity of each compound class. Maturity ratios based on reliably detected compound classes show that the FI oils were generated in the oil window, with no evidence of extensive thermal cracking. The presence of biomarkers for cyanobacteria and eukaryotes derived from and trapped in rocks deposited prior to 2.0 Ga is consistent with early evolution of oxygenic photosynthesis and suggests that some aquatic settings had become sufficiently oxygenated for sterol biosynthesis by this time. The extraction of biomarker molecules from Palaeoproterozoic oil-bearing FIs thus establishes a new method, using low detection limits and system blank levels, to trace evolution through Earth’s early history that avoids the potential contamination problems affecting shale-hosted hydrocarbons. 2011-02-23T07:50:55.362Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:11831 16 page(s) 2011-02-15T08:10:25.051Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:11581 The terrestrial biosphere is a key regulator of atmospheric chemistry and climate. During past periods of climate change, vegetation cover and interactions between the terrestrial biosphere and atmosphere changed within decades. Modern observations show a similar responsiveness of terrestrial biogeochemistry to anthropogenically forced climate change and air pollution. Although interactions between the carbon cycle and climate have been a central focus, other biogeochemical feedbacks could be as important in modulating future climate change. Total positive radiative forcings resulting from feedbacks between the terrestrial biosphere and the atmosphere are estimated to reach up to 0.9 or 1.5 W m−2 K−1 towards the end of the twenty-first century, depending on the extent to which interactions with the nitrogen cycle stimulate or limit carbon sequestration. This substantially reduces and potentially even eliminates the cooling effect owing to carbon dioxide fertilization of the terrestrial biota. The overall magnitude of the biogeochemical feedbacks could potentially be similar to that of feedbacks in the physical climate system, but there are large uncertainties in the magnitude of individual estimates and in accounting for synergies between these effects. 2011-02-02T05:30:49.068Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:11425 The importance of orbital forcing and ocean impact on the Asian summer monsoon in the Holocene is investigated by comparing simulations with a fully coupled ocean–atmosphere general circulation model (FOAM) and with the atmospheric component of this model (FSSTAM) forced with prescribed modern sea-surface temperatures (SSTs). The results show: (1) the ocean amplifies the orbitally-induced increase in African monsoon precipitation, makes somewhat increase in southern India and damps the increase over the southeastern China. (2) The ocean could change the spatial distribution and local intensity of the orbitally-induced latitudinal atmospheric oscillation over the southeastern China and the subtropical western Pacific Ocean. (3) The orbital forcing mostly enhances the Asian summer precipitation in the FOAM and FSSTAM simulations. However, the ocean reduces the orbitally-induced summer precipitation and postpones the time of summer monsoon onset over the Asian monsoon region. (4) The orbital forcing considerably enhances the intensity of upper divergence, which is amplified by ocean further, over the eastern hemisphere. But the divergence is weaker in the FOAM simulations than in the FSSTAM simulations when the orbital forcing is fixed. (5) The orbital forcing can enhance the amplitude of precipitation variability over the subtropical Africa, the southeastern China and northwestern China, inversely, reduce it over central India and North China in the FOAM and FSSTAM simulations. The ocean obviously reduces the amplitude of precipitation variability over most of the Asian monsoon regions in the fixed orbital forcing simulations. (6) The areas characterized by increased summer precipitation in the long-term mean are mostly characterized by increased amplitude of short-term variability, whereas regions characterized by decreased precipitation are primarily characterized by decreased amplitude of short-term variability. However, the influences of orbital forcing or dynamical ocean on regional climate depend on the model. 2011-01-21T03:20:07.619Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:11409 A compilation of wildfire records spanning six continents and 2,000 years reveals global patterns in biomass burning to be temporally linked with changes in climate, population and land use. An abrupt decline in biomass burning beginning about 150 years ago may be related to the expansion of intensive grazing, agriculture and fire management activities. 2011-01-20T23:40:25.517Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:11410 A coupled atmosphere-ocean-vegetation general circulation model (AOVGC M) is used to investigate the climate of the early Holocene. It is found that th e coupled AOVGCM can simulate the early Holocene climate successfully. In winter the averaged global surface temperature is 1.6 K less than today's, and 0.3 K less than today's in summer. The solar radiation has important effect on the high level atmospheric temperature, while the atmosphere temperature in the lower levels is sensitive to the land surface (for example ice sheets, vegetation and ocean, etc.). The simulated early-Holocene climate is drier than modern time in winter, but there are more precipitations in the tropical Pacific ocean some areas in the South Hemisphere. The climate in most areas in summer is wetter than today, especially in Asia and Africa monsoon areas where the monsoon is strong and the precipitation is abundant. 2011-01-20T23:40:24.869Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:11198 The impacts of dynamic vegetation on interannual and interdecadal variability of Asian summer monsoon in modern (0 kyr) and mid-Holocene (6 kyr) climates are investigated by contrasting simulations with and without dynamic vegetation in a coupled ocean-atmosphere model. According to a dynamic index of South Asian summer monsoon, it has been found that the strengths of interannual and interdecadal westerly wind tend not to be affected by the dynamic vegetation over South Asia in the lower troposphere for 0 kyr and 6 kyr. However, based on a dynamic index of western North Pacific (WNP) monsoon, the strengths of tropical westerly wind and south–north cross-equatorial transport are weakened over the tropical western Pacific in the lower troposphere for 0 kyr and 6 kyr. It suggests the impact of dynamic vegetation is more obvious for the WNP monsoon than for the South Asian monsoon. Also, it implies the impact of dynamic vegetation on the interannual and interdecadal circulations is distinctly regional. Singular value decomposition (SVD) analysis shows that the impact of dynamic vegetation can remodel the leading correlation mode (SVD1) between precipitation and surface temperature. All of the interannual and interdecadal precipitation patterns with and without the impact of dynamic vegetation are associated with positive anomalies over India and southeastern China. However, the impact of dynamic vegetation tends to enhance (keep) the positive interannual temperature anomalies of SVD1 over the midlatitudinal Eurasia (WNP) for 0 kyr, but to reduce the anomalies over the midlatitudinal Eurasia and WNP for 6 kyr. Furthermore, the La Niña-like sea surface temperature (SST) anomalies always dominate the tropics for 0 kyr and 6 kyr. It suggests La Niña-like SST anomalies are the important mechanism to induce the above-mentioned precipitation pattern no matter whether for 0 kyr or for 6 kyr. For the interdecadal surface temperature pattern of SVD1, the impact of dynamic vegetation tends to enhance (reduce) positive anomalies over the midlatitudinal Eurasia (WNP) for 0 kyr, but to reduce (keep) positive anomalies over the midlatitudinal Eurasia (WNP) for 6 kyr. Also, all of the above implies the impact of dynamic vegetation is a mechanism to induce the long-term change of leading interannual and interdecadal surface temperature pattern over the midlatitudinal Eurasia and/or WNP. 2011-01-10T05:40:41.430Z ]]>