Variability and decline in the number of severe tropical cyclones making land-fall over eastern Australia since the late nineteenth century

Recent studies have raised concerns that tropical cyclones (TCs), particularly severe TCs, have become more frequent in many places in response to global warming. Other studies discuss errors in TC data that can cause large inaccuracies in some of the observed trends. Additional studies conclude that TCs are likely to become more intense in the future in response to global warming, while regional modelling studies for the south-west Pacific near north-eastern Australia project an intensification of TCs and either a decrease or no change in TC numbers. Here we describe and use a new data base of severe land-falling TCs for eastern Australia derived from numerous historical sources, that has taken over a decade to develop. It provides one of the world??s longest reliable records of tropical cyclone activity, and allows us to document changes over much longer periods than has been done previously for the Southern Hemisphere. Land-fall numbers are shown to vary a great deal on interannual, decadal and longer time-scales. The interannual variability is consistent with previous studies using much shorter data sets: land-fall numbers are well-simulated as a Poisson process and are modulated by the El Ni?o-Southern Oscillation (ENSO). Land-falls occurred almost twice as often in La Ni?a years as they did in El Ni?o years, and multiple land-falls only occurred during La Ni?a years. The statistical link between land-falls and pre-season values of the Southern Oscillation Index provides a modest predictive capability. Decadal variability in ENSO drives some of the decadal variability in land-fall numbers. The sign and magnitude of trends calculated over 30?years periods vary substantially, highlighting that caution needs to be taken in making inferences about trends based on e.g. satellite era data only. The linear trend in the number of severe TCs making land-fall over eastern Australia declined from about 0.45 TCs/year in the early 1870s to about 0.17 TCs/year in recent times??a 62% decline. This decline can be partially explained by a weakening of the Walker Circulation, and a natural shift towards a more El Ni?o-dominated era. The extent to which global warming might be also be partially responsible for the decline in land-falls??if it is at all??is unknown.     

Climate warming and the onset of salinization: Rapid changes in the limnology of two northern plains lakes

Water resources of the interior plains region of North America may be adversely affected by climate warming. The climate records of the Battleford region (west central Saskatchewan) indicate that mean annual temperatures have risen by 0.71 °C and mean annual minimum temperatures have risen by 1.03 °C from 1894 to 2007. Snowfall has also increased but total precipitation has not. Concomitant with periodic declines in precipitation, lake elevation has declined and salinity has increased in Jackfish and Murray lakes from 1938 to 2004. This long term increase in salinity is predicted to have caused an approximate 30% loss in diversity of macrobenthos. Phosphorus concentrations have also increased significantly, and Jackfish and Murray lakes would be classified as eutrophic by freshwater trophic indices. However, despite large increases in nutrients in both lakes, algal biomass has not increased and water transparency has not decreased. Although the total amount of planktonic biomass in Jackfish and Murray’s food web is similar to that of freshwater lakes, these lakes contain very low algal biomass (measured as chlorophyll a). In fact, such low algal biomass has not been previously observed in such dilute systems. The algal community in these shallow Prairie lakes appears to be very sensitive to slight changes in climate, and future climate driven increases in salinity of prairie lakes may result in large reductions in algal primary productivity.     

He,Ne and Ar in peridotitic and eclogitic paragenesis diamonds from the Jwaneng kimberlite,Botswana—Implications for mantle evolution and diamond formation ages

We have undertaken helium, neon and argon step-heating, isotopic analyses of eleven polycrystalline diamonds of known peridotite/eclogite paragenesis from the Jwaneng kimberlite pipe, Botswana. In contrast to the findings of crustal noble gases in framesites from the same kimberlite pipe (Honda et al., 2004. Unusual noble gas compositions in polycrystalline diamonds: preliminary results from the Jwaneng kimberlite, Botswana. Chem. Geol. 203, 347–358.), the Jwaneng polycrystalline diamonds appear to contain similar noble gas isotopic compositions (particularly Ne) to those representing a mantle source for MORBs. This implies that the Jwaneng polycrystalline diamonds may have formed in recent times, possibly close to the time of kimberlite emplacement at ~ 235 Ma. In contrast, Jwaneng framesites could be as old as gem diamonds (mineral inclusion ages of ~ 2.9 Ga). Furthermore, the data indicate that the sub-continental mantle lithosphere in the region has heterogeneous Ne isotopic compositions, or that these compositions changed over time from crustal Ne (as observed in the framesites) to MORB-like (as observed in the polycrystalline diamonds).     

Household perceptions of climate change and preferences for mitigation action: the case of the Carbon Pollution Reduction Scheme in Australia

The study aims to reveal Australian households?? perceptions of climate change and their preferences for mitigation action. A web-based survey was conducted in November 2008 in which over 600 households from the state of New South Wales were asked for their willingness to bear extra household expenditure to support the ??Carbon Pollution Reduction Scheme??, an emissions trading scheme proposed by the Australian government. The results of the study can be summarized in four key findings. First, respondents?? willingness to pay for climate change mitigation is significantly influenced by their beliefs of future temperature rise. Support for the policy increased at a decreasing rate as the perceived temperature change rose. Second, perceptions of policy failure have a significant negative impact on respondents?? support for the proposed mitigation measure. The higher the perceived likelihood that the measure would not deliver any outcome, the lower was the likelihood that respondents would support the policy. Third, respondent preferences for the proposed policy are influenced by the possibility of reaching a global agreement on emissions reduction. Sample respondents stated significantly higher values for the policy when the biggest polluting countries implement a similar scheme. Finally, respondents?? willingness to take action against climate change, both at the national and household level, is found to be influenced by their level of mass-media exposure. Particularly, those respondents who watched ??An Inconvenient Truth?? were significantly more likely to act for climate change mitigation than others.     

Stability and equation of state of post-aragonite BaCO3

At ambient conditions, witherite is the stable form of BaCO₃ and has the aragonite structure with space group Pmcn. Above ~10 GPa, BaCO₃ adopts a post-aragonite structure with space group Pmmn. High-pressure and high-temperature synchrotron X-ray diffraction experiments were used to study the stability and equation of state of post-aragonite BaCO₃, which remained stable to the highest experimental P–T conditions of 150 GPa and 2,000 K. We obtained a bulk modulus K ₀ = 88(2) GPa with $K'$  = 4.8(3) and V ₀ = 128.1(5) ų using a third-order Birch-Murnaghan fit to the 300 K experimental data. We also carried out density functional theory (DFT) calculations of enthalpy (H) of two structures of BaCO₃ relative to the enthalpy of the post-aragonite phase. In agreement with previous studies and the current experiments, the calculations show aragonite to post-aragonite phase transitions at ~8 GPa. We also tested a potential high-pressure post–post-aragonite structure (space group C222 ₁ ) featuring four-fold coordination of oxygen around carbon. In agreement with previous DFT studies, ΔH between the C222 ₁ structure and post-aragonite (Pmmn) decreases with pressure, but the Pmmn structure remains energetically favorable to pressures greater than 200 GPa. We conclude that post–post-aragonite phase transformations of carbonates do not follow systematic trends observed for post-aragonite transitions governed solely by the ionic radii of their metal cations.     

Chemically stabilized soil organic carbon fractions in a reclaimed minesoil chronosequence: implications for soil carbon sequestration

With adoption of appropriate reclamation strategies, minesoils can sequester significant amount of soil organic carbon (SOC). The objective of this study was to isolate different SOC fractions and coal-C in a reclaimed minesoil chronosequence and assess effects of increasing time since reclamation on each SOC fraction and selected soil properties. The chronosequence was comprised of four minesoils with time since reclamation ranging between 2 and 22 years. Total SOC (TSOC, summation of all SOC fractions), ranged between 20 and 8 g kg^?1, respectively, at the oldest (Mylan Park) and youngest (WVO1) minesite, indicating increasing SOC sequestration along the chronosequence. The humin fraction accounted for about 43 and 7 % of TSOC, respectively, at Mylan Park and WVO1, indicating increasing humification and biochemical stabilization of SOC with increasing time since reclamation. At WVO1, >60 % of TSOC was apportioned among the acid-hydrolysable (labile) and mineral-bound SOC fractions. Total soil carbon (TSC, TSOC + coal-C) were significantly (p < 0.05) related to the humin fraction in older minesoils, whereas with the acid-hydrolysable (labile) fraction in the younger minesoils indicating that C stabilization mechanisms differed substantially along the chronosequence. Coal-C was unrelated to any SOC fraction at all minesites indicating that SOC sequestration estimations in this chronosequence was unaffected by coal-C. Soil cation exchange capacity and electrical conductivity were significantly (p < 0.05) related to the humin fraction at Mylan Park while to the acid-hydrolysable and mineral-bound SOC fractions at WVO1 indicating that the relative influences of different SOC fractions on soil quality indicators differed substantially along the chronosequence.     

Radio-continuum study of the nearby Sculptor group Galaxies. Part 2: NGC 55 at λ=20, 13, 6 and 3 cm

A series of new radio-continuum (λ=20, 13, 6 and 3 cm) mosaic images focused on the NGC 55 galactic system were produced using archived observational data from the Australia Telescope Compact Array. These new images are both very sensitive (down to rms=33 μJy) and feature high angular resolution (down to <4″). Using these newly created images, 66 previously unidentified discrete sources are identified. Of these sources, 46 were classified as background sources, 11 as H?ii regions and 6 as supernova remnant candidates. This relatively low number of SNR candidates detected coupled with the low number of large H?ii regions is consistent with the estimated low star formation rate of the galaxy at 0.06 M _⊙?year^?1. Our spectral index map shows that the core of galaxy appears to have a shallow spectral index between α=?0.2 and ?0.4. This indicates that the core of the galaxy is a region of high thermal radiation output.     

Automated Extraction of Natural Drainage Density Patterns for the Conterminous United States through High-Performance Computing

Hydrographic networks form an important data foundation for cartographic base mapping and for hydrologic analysis. Drainage density patterns for these networks can be derived to characterize local landscape, bedrock and climate conditions, and further inform hydrological and geomorphological analysis by indicating areas where too few headwater channels are represented. Natural drainage density patterns are not consistently available in existing hydrographical data bases for the United States because compilation and capture criteria historically varied, along with climate, during the period of data collection over the various terrain types throughout the country. This paper demonstrates an automated workflow that is being tested in a high-performance computing environment by the U.S. Geological Survey (USGS) to map natural drainage density patterns at the 1:24,000-scale (24K) for the conterminous United States. Hydrographic network drainage patterns may be extracted from elevation data to guide corrections for existing hydrographic network data. The paper describes three stages in this workflow including data pre-processing, natural channel extraction, and generation of drainage density patterns from extracted channels. The workflow is implemented in parallel fashion by simultaneously executing procedures on multiple subbasin watersheds within the U.S. National Hydrography Dataset (NHD). Pre-processing defines parameters needed for the extraction process. Extraction proceeds in standard fashion: filling sinks, developing flow direction and weighted flow accumulation rasters. Drainage channels with assigned Strahler stream order are extracted within a subbasin and simplified. Drainage density patterns are then estimated with 100-m resolution and subsequently smoothed with a low-pass filter. The extraction process is found to be of better quality in higher slope terrains. Concurrent processing through the high-performance computing environment is shown to facilitate and refine the choice of drainage density extraction parameters and more readily improve extraction procedures than conventional processing.