Relationships among the monsoon-like southwest Australian circulation,the Southern Annular Mode,and winter rainfall over southwest Western Australia

This study examines the relationships among the monsoon-like southwest Australian circulation (SWAC), the Southern Annular Mode (SAM), and southwest Western Australia winter rainfall (SWR), based on observed rainfall, reanalysis datasets, and the results of numerical modeling. By decomposing the SWAC into two components using a linear model, i.e. the component related to SAM (RSAM) and the component unrelated to SAM (SWACI*), we find it is the SWACI* that shows a significant influence on SWR. Similarly, it is the component of SAM associated with SWAC that exhibits an impact on SWR, whereas the component unrelated to SAM. A similar result is obtained in terms of the circulation associated with SWAC and the SAM. These facts suggest the SAM plays an indirect role in influencing SWR, and raise the possibility that SWAC acts as a bridge between the SAM and SWR, by which the SAM passes its influences onto SWR. This is due to the fact that the variations of SWAC are closely linked to the thermal contrast between land and sea across the southern Indian Ocean and southwest Australia. By contrast, the SAM does not significantly relate to this thermal structure, particularly for the component unrelated to SWAC. The variations of surface sea temperature over the southern Indian Ocean contribute to the favored rainfall circulation patterns. This finding is supported by the numerical modeling results. The strong coupling between SWAC and SWR may be instrumental for understanding the interactions between SWR and the southern Indian Ocean, and provides another perspective in examining the variations in SWR.     

Detrital zircon geochronology of the Speewah Group,Kimberley region,Western Australia: evidence for intracratonic development of the Paleoproterozoic Speewah Basin

Field observations integrated with new petrographic and sensitive high-resolution ion microprobe (SHRIMP) U–Pb age data for detrital zircons from the Paleoproterozoic Speewah Group of northern Western Australia provide evidence of depositional conditions, source of detritus, timing and evolution of the sedimentary rocks in the Speewah Basin. The Speewah Group is a 1.5 km-thick succession of poorly outcropping, predominantly siliciclastic rocks that preserve a fluviatile to marine, transgressive and regressive event. The Speewah Group unconformably overlies crystalline rocks of the Lamboo Province that were stabilised by the 1870–1850 Ma Hooper Orogeny, then accreted as the Kimberley region onto the North Australian Craton during the 1835–1810 Ma Halls Creek Orogeny. Unconformably overlying the Speewah Group is about 4 km of predominantly siliciclastic marine sedimentary rocks of the Kimberley Group in the Kimberley Basin. This study has detected a detrital zircon component within the Speewah Basin at 1814 ± 10 Ma, with a youngest zircon at 1803 ± 12 Ma (1σ) in fluviatile sandstones located beneath a volcaniclastic rock with magmatic zircons that have been dated at ca 1835 Ma. Previous studies proposed that the Speewah Basin developed as a retro-arc foreland basin during accretion of the North Australian Craton. We interpret the ca 1835 Ma zircons in the volcaniclastic rocks to be xenocrystic in origin. This new 20 million years younger maximum depositional age indicates that the Speewah Group in the Speewah Basin, similarly to the overlying Kimberley Group in the Kimberley Basin, developed in a post-orogenic setting on the North Australian Craton rather than in a syn-orogenic setting associated with the 1835–1810 Ma Halls Creek Orogeny.     

Mapping mesoscale currents by optimal interpolation of satellite radiometer and altimeter data

 Mapping the mesoscale surface velocity stream function by combining estimates of surface height from satellite altimetry and surface currents from sequential infrared (sea-surface temperature) imagery using optimal interpolation is described. Surface currents are computed from infrared images by the method of maximum cross-correlations (MCC) and are combined with altimeter sea-level anomaly data from the TOPEX/Poseidon and ERS satellites. The analysis method was applied to 6 years of data from the East Australian Current region. The covariance of velocity and sea-level data is consistent with the statistical assumptions of homogeneous, isotropic turbulence, with typical length scales of order 220 km and time scales of 10 days in this region. Augmenting the analysis of altimeter data with MCC velocity observations improves the resolution of the surface currents, especially near the Australian coast, and demonstrates that the two data sources provide consistent and complementary observations of the surface mesoscale circulation. The volume of MCC data is comparable to that from a satellite altimeter, but with a more variable distribution of spatial and temporal resolution. In concert with altimetry, satellite radiometer velocimetry represents a technique useful for retrospective analysis of currents from high-resolution satellite radiometer data-sets. Received: 3 July 2001 / Accepted: 16 November 2001     

Bushmanship: The explorers' silent partner

Bushmanship, or the competence to interact meaningfully with newly encountered environments in the achievement of predetermined goals, is a factor overlooked in analyses of land-based exploration. The importance of bushmanship is examined in this paper through a comparison of George Grey's inept exploration of north-western Australia in 1836-37 with Edward Eyre's increasingly successful overlanding ventures in south-eastern Australia at approximately the same time. Grey's impetuosity, inexperience and lack of competence contrast sharply with Eyre's growing confidence to handle unfamiliar conditions. The comparison reveals many of the factors that differentiate externally initiated expeditions such as Grey's from forays by settlers determined to wrest a living from newly settled territories.     

Three-dimensional seismic structure beneath the Australasian region from refracted wave observations

The earthquakes in the seismicity belt extending through Indonesia, New Guinea, Vanuatu and Fiji to the Tonga–Kermadec subduction zone recorded at the 65 portable broad-band stations deployed during the Skippy experiment from 1993–1996 provide good coverage of the lithosphere and mantle under the Australian continent, Coral Sea and Tasman Sea.
The variation in structure in the upper part of the mantle is characterized by deter-mining a suite of 1-D structures from stacked record sections utilizing clear P and S arrivals, prepared for all propagation paths lying within a 10° azimuth band. The azimuth of these bands is rotated by 20° steps with four parallel corridors for each azimuth. This gives 26 separate azimuthal corridors for which 15 independent 1-D seismic velocity structures have been derived, which show significant variation in P and S structure.
The set of 1-D structures is combined to produce a 3-D representation by projecting the velocity values along the ray path using a turning point approximation and stacking into 3-D cells (5° by 50 km in depth). Even though this procedure will tend to underestimate wave-speed perturbations, S -velocity deviations from the ak135 reference model exceed 6 per cent in the lithosphere.
In the uppermost mantle the results display complex features and very high S -wave speeds beneath the Precambrian shields with a significant low-velocity zone beneath. High velocities are also found towards the base of the transition zone, with high S -wave speeds beneath the continent and high P -wave speeds beneath the ocean. The wave-speed patterns agree well with independent surface wave studies and delay time tomography studies in the zones of common coverage.     

中原末次冰期间冰阶以来的古季风气候变迁

中原邙山黄土地层以巨厚的马兰黄土为特色。本文研究了末次冰期间冰阶以来邙山黄土－古土壤序列的粗颗粒含量和磁化率值曲线反映的冬夏季风变迁及其相互关系,发现在万年尺度上夏季风增强对应于冬季风减弱,冬季风增强对应于夏季风减弱,但在千年尺度上冬季风变化比夏季风强烈得多,而且末次间冰段开始时冬季风减弱明显早于夏季风增强。通过中原黄土记录与深海及冰芯Ｏ同位素记录的对比,发现短时间尺度气候变化阶段明显具有很大的区域性特征,它们不能简单地进行等时性全球对比,而应该通过各自独立的时间标尺来建立古气候变化的远距离联系。     

Redating the onset of burning at Lynch's Crater (North Queensland): implications for human settlement in Australia

Lynch's Crater preserves a continuous, high‐resolution record of environmental changes in north Queensland. This record suggests a marked increase in burning that appears to be independent of any known major climatic boundaries. This increase is accompanied, or closely followed, by the virtually complete replacement of rainforest by sclerophyll vegetation. The absence of any major climatic shift associated with this increase in fire frequency therefore has been interpreted as a result of early human impact in the area. The age for this increase in burning, on the basis of conventional radiocarbon dating, was previously thought to be approximately 38 000 ¹⁴C yr BP, supporting the traditional model for human arrival in Australia at 40 000 ¹⁴C yr BP Here we have applied a more rigorous pre‐treatment and graphitisation procedure for radiocarbon dating samples from the Lynch's Crater sequence. These new dates suggest that the increase in fire frequency occurred at 45 000 ¹⁴C yr BP, supporting the alternative view that human occupation of Australia occurred by at least 45 000–55 000 cal. yr BP. Copyright © 2001 John Wiley & Sons, Ltd.     

Do boat licences have a role in fisheries managed through individual quotas? Experience in Australian fisheries

Some economists have questioned the need for retaining boat licences in fisheries managed through rights-based systems on the assumption that licences act as an impediment to autonomous adjustment. In this paper, the role of boat licences in fisheries managed through rights-based instruments is explored through examining their use in several fisheries in Australian and elsewhere. The study concludes that any impediment to autonomous adjustment that is produced by boat licences is likely to be small relative to other factors. Further, boat licences play an important role in offsetting imperfections in the rights-based management systems that exist in most countries.     

Paleoclimate implications of high latitude precession-scale mineralogic fluctuations during early Oligocene Antarctic glaciation: the Great Australian Bight record

Sediments from ODP Site 1128 in the Great Australian Bight record isotopic and mineralogic variations corresponding to orbital parameters and regional climate change during the early Oligocene climate transition and Oi1 glacial event. Bulk carbonate stable isotope analyses reveal prominent positive oxygen and carbon isotope shifts related to the inferred major increase in glaciation at approximately 33.6 to 33.48 Ma. The oxygen isotope excursion corresponds to a prolonged period of low eccentricity, suggesting ice-sheet growth during low seasonality conditions. The clay mineralogy is dominated by smectite throughout. The exclusive occurrence of highly crystalline smectite from 33.6 to 33.5 Ma suggests the occurrence of explosive volcanism that correlates with the positive oxygen isotope shift. The dominance of mixed-layer smectite from 33.5 to 33.4 Ma and an increase in illite following 33.4 Ma indicates a transition from cool, wet conditions to cool, dry conditions over Australia during the Oi1 glaciation. Clay mineralogy and carbonate percentages reveal precession-scale oscillations during the Oi1 event. Kaolinite varies inversely with smectite and percent carbonate. Variations in precipitation and runoff, and wind velocities during southern hemisphere summer perihelion and high eccentricity intervals may account for the precession-scale oscillations.