Northwestern Tasmania Research Articles

Insights into the Liquid Bismuth Collector Model Through Analysis of the Bi-Au Stormont Skarn Prospect, Northwest Tasmania

The liquid bismuth collector model has previously been proposed to explain the common association between gold and bismuth seen in many ore deposits, and involves the scavenging of gold from hydrothermal fluid by liquid bismuth. Here, textural relationships and temperature and chemical conditions of mineralization at the Stormont Bi-Au skarn prospect in northwestern Tasmania are analyzed to investigate whether the liquid bismuth collector model can explain gold accumulation at this prospect. The calc-silicate skarn assemblage containing grandite, hedenbergite, actinolite, magnetite, epidote, quartz, and calcite suggests that initial metasomatism involved temperatures >400° to 500°C. Visible gold is associated with native bismuth, bismuthinite, maldonite, galena, and an unknown Bi-Te-S mineral. Native bismuth is directly associated with grandite, which formed during initial stages of metasomatism. This implies that bismuth would have precipitated from a hydrothermal fluid as a liquid. Heating experiments showed that bismuth alloy inclusions in garnet melt between temperatures of 250° and 288°C. The mineralization setting at Stormont and textural relationships suggest that gold was scavenged from hydrothermal fluids by liquid bismuth. Rhythmically zoned grandite crystals provide evidence for fluctuating hydrothermal fluid conditions, which may have contributed to dissolution and reprecipitation of gold, thus facilitating an ore zone refining process within the prospect. This refining process is made possible by the tendency of liquid bismuth to scavenge gold from significantly under-saturated fluids. Infiltrating gold-undersaturated fluids can dissolve gold not in contact with bismuth, which can then be preferentially redeposited upon encountering a bismuth droplet, enhancing the correlation between the two elements. A long-lived and focused fluid flow system would maximize the efficiency of this ore zone refining process, which is likely to be relevant to gold deposition at a range of deposit types.

Cryogenian glaciations on the southern tropical paleomargin of Laurentia (NE Svalbard and East Greenland), and a primary origin for the upper Russøya (Islay) carbon isotope excursion

Neoproterozoic successions in NE Svalbard and East Greenland host a pair of glacigenic formations, the younger of which are correlated with the terminal Cryogenian (Marinoan) glaciation based on their lithologically and isotopically diagnostic cap dolostones. A deep negative carbon isotope excursion (CIE) occurs stratigraphically beneath the older glacigenic formations in both areas, but no CIE is preserved beneath the younger glacial horizon in either area. This led to uncertainty over the age of the CIE and the paleoenvironmental significance of the units separating the glacigenic formations. 87Sr/86Sr ratios in Sr-rich limestone associated with the CIEs are ≤0.7064 in East Greenland and ≤0.7068 in NE Svalbard, consistent with early Cryogenian values globally and inconsistent with late Cryogenian ratios, which are exclusively ≥0.7071. The CIEs are tentatively correlated with the Islay excursion in the Scottish and Irish Caledonides, and potentially correlative subglacial CIEs in northwestern Canada, northwestern Tasmania and the southwestern United States. In NE Svalbard, newly-acquired δ13Corg data covary with δ13Ccarb across the CIE, but the organic excursion is roughly half the amplitude of the inorganic excursion. δ13Ccarb and δ18Ocarb do not covary, nor does δ13Corg vary as a function of total organic carbon content. A primary origin for the CIE is supported and the accompanying proliferation of stromatolites suggests rising carbonate saturation (falling pCO2) prior to glaciation. New data suggest that the hiatus responsible for the missing Trezona CIE occurs at the top, not the bottom, of the Bråvika member sandstone in NE Svalbard. A dramatic decline in regional average thickness of older Cryogenian glacial deposits from the paleomagnetically-determined subtropics (British Isles) to the deep tropics (Svalbard) is consistent with meteoric net accumulation and sublimation zones on a snowball Earth, and inconsistent with the Jormungand climate zonation.

Man and megafauna in Tasmania: closing the gap

Recent discussion on the late Pleistocene extinction of the Australian megafauna has revolved around interpretation of several key fossil sites in Tasmania. It has been suggested that humans did not arrive in Tasmania until after the megafauna became extinct, or did not hunt now extinct megafauna, and therefore that humans cannot be implicated in the extinctions. Radiocarbon results from these sites indicate that the youngest extinct megafauna are close to charcoal ages from the oldest archaeological deposits, although difficulties have arisen in establishing chronologies because most relevant sites have ages near the limit for radiocarbon analysis.We report a series of new radiocarbon ages, δ13C, δ15N and C:N ratios on collagen and dentine fractions from skeletal remains in the Mount Cripps karst area and the Mowbray Swamp, both in northwestern Tasmania, and discuss the reliability of ages from these and other sites. We also report the discovery of an articulated Simosthenurus occidentalis skeleton at Mt Cripps, that represents only the second directly-dated extinct megafaunal taxon with a reliable age <50 ka cal BP from Tasmania.Our results suggest that C:N ratios measured on collagen or dentine are not an infallible guide to radiocarbon age reliability. We confirm previous reports of a temporal overlap between the megafaunal and archaeological records in Tasmania, but the presence of archaeological evidence and megafauna with the same age at the same site has not yet been demonstrated. At least two megafaunal taxa—the now-extinct Protemnodon anak and a giant Pleistocene form of the extant Macropus giganteus—were still present in Tasmania after 43 ka, when human crossing of the Bassian landbridge from mainland Australia first became sustainable.

Impacts of future climate scenarios on the balance between productivity and total greenhouse gas emissions from pasture based dairy systems in south-eastern Australia

The challenge for agriculture is to increase production in warmer climates in order to meet the demands of an increasing global population, while also meeting targets for reduced greenhouse gas (GHG) emissions. Our aim was to quantify the net effect of future climate scenarios on the productivity and total GHG emissions from pasture based dairy systems in 4 regions of south-eastern Australia using the biophysical model DairyMod. In each region, a single paddock in the grazing rotation of a dairy farm was simulated. This paddock was grazed at a stocking density of 50 lactating dairy cows/ha for a period of one day each time the pasture biomass reached 2.2t dry matter (DM)/ha. In this way, the annual stocking rate (i.e., cows/ha) reflected the number of times that the paddock was grazed annually. No supplementary feed was offered to the animals. Model estimates of annual pasture intake, stocking rate, milk production, CH4 and N2O emissions were compared at each site in a baseline climate (1971–2000) and 3 future climate scenarios representing increasingly warm and dry conditions, termed the ‘2030’, ‘2070 mid’ and ‘2070 high’ scenarios. At Kyabram (northern Victoria) summer irrigated perennial pastures were modelled in the baseline scenario, with supplementary irrigated annual pasture systems simulated in the baseline scenario for comparison, and in the future scenarios. At Terang (south-western Victoria), Ellinbank (south-eastern Victoria) and Elliott (north-western Tasmania) dryland perennial pastures were modelled. In dryland systems, increased pasture intake, stocking rate and milk production was modelled in all future scenarios for the cool temperate climate at Elliott, with reduced production in the ‘2070 mid’ and ‘2070 high’ scenarios at Ellinbank and Terang. At Kyabram, productivity of the annual system was lower than the perennial system in the baseline scenario, but increased in future climates, assuming adequate irrigation water availability. Among sites and climate scenarios, annual per cow GHG emissions were 3.4–5.5t CO2 equivalents (CO2e), with CH4 making 0.63–0.89 of total emissions. Annual emissions per unit area ranged from 2.6 to 13.1t CO2e/ha among sites and climate scenarios, and generally reflected stocking rates. However, in the future scenarios, there were changes in N2O emissions at dryland sites due to increased direct N2O losses and lower indirect N2O through volatilisation and leaching. Annual emission intensities ranged from 7.5 to 10.9t CO2e/t milk protein plus fat among sites and climate scenarios. The lowest emissions intensity was at Elliott, which also had little change in future climates. At Terang and Ellinbank, the emission intensity was 8.8t CO2e/t MS in the baseline climate, but this increased by more than 20% in the 2070 high scenario. Results suggest that pasture based production systems can continue as the basis of the dairy industry in north-western Tasmania, but lower production and higher emission intensity at Terang and Ellinbank suggest that systems adaptations are required to meet future GHG emissions reduction goals.This paper is part of the special issue entitled: Greenhouse Gases in Animal Agriculture – Finding a Balance between Food and Emissions, Guest Edited by T.A. McAllister, Section Guest Editors: K.A. Beauchemin, X. Hao, S. McGinn and Editor for Animal Feed Science and Technology, P.H. Robinson.

The genetic variation in the timing of heteroblastic transition in Eucalyptus globulus is stable across environments

Eucalyptus globulus is one of the best known examples of a heteroblastic plant. It exhibits a dramatic phase change from distinctive juvenile to adult leaves, but the timing of this transition varies markedly. We examined the genetic variation in the timing of heteroblastic transition using five large open-pollinated progeny trials established in north-western Tasmania. We used univariate and multi-variate mixed models to analyse data on the presence/absence of adult or intermediate foliage at age 2 years from a total of 14 860 trees across five trials, as well as height to heteroblastic phase change from one trial. Up to 566 families and 15 geographic subraces of E. globulus were represented in the trials. The timing of the heteroblastic transition was genetically variable and under strong genetic control at the subrace and within-subrace level, with single-trial narrow-sense heritability estimates for the binary trait averaging 0.50 (range 0.44–0.65). The degree of quantitative trait differentiation in the timing of heteroblastic transition among subraces, as measured by QST, exceeded the published level of neutral molecular marker (FST) differentiation in all cases, arguing that diversifying selection has contributed to shaping broad-scale patterns of genetic differentiation. Most inter-trial genetic correlations were close to one at the subrace and additive genetic levels, indicating that the genetic variation in this important developmental change is expressed in a stable manner and that genotype-by-environment interaction is minimal across the environments studied.

Spatial analysis of Tasmania’s native vegetation cover and potential implications for biodiversity conservation

Summary The landscape modification model proposed by McIntyre and Hobbs (1999) was used to assess the modification of Tasmania’s native vegetation and its potential implications for biodiversity conservation. The inclusion of new ‘substates’ in the model allowed the varying degrees of landscape variegation and fragmentation observed in Tasmania to be quantified. The mapped extent of Tasmania’s native vegetation is approximately 5.06 million ha or 74% of the land area. The extent of native vegetation varies across bioregions from a low of around 36% in the Tasmanian Northern Midlands bioregion to a high of 94% in the Tasmanian West bioregion. Overall, the Tasmanian landscape can be described as medium variegated as the State retains 76% cover of native vegetation, by area. Two of Tasmania’s nine bioregions are in an intact state, four are variegated, and three are fragmented. Seven of the State’s 48 catchments are in an intact state, 24 catchments are variegated, and 17 are fragmented. Tasmania was estimated to support 33 760 patches of native vegetation. Fewer than 3% of these patches exceed 50 ha in area. Small and medium patches occur predominantly on freehold land with grazing as a major land use, whereas large patches occur predominantly on crown land with conservation and production forestry as the major land uses. One feature of the State’s native vegetation is the large tract of native vegetation ecosystems in western Tasmania. Opportunities arise to sustain the resilience of these native ecosystems both by consolidating the formal protection of vegetation within catchments such as the Arthur and Pieman and by strengthening environmental management in adjacent areas. Bioregions and catchments where climate change may be of particular concern for biodiversity conservation and management include the Tasmanian Northern Midlands bioregion and Cam catchment in north-western Tasmania. The maintenance and enhancement of patches of remnant vegetation in these areas will be challenging and appears likely to require strategic, multiscale and coordinated natural resource management over decades. Limiting the loss of native vegetation across the entire range of landscape states in Tasmania appears essential to mitigate the further decline of biodiversity.

Cryptic genetic divergence in the giant Tasmanian freshwater crayfish Astacopsis gouldi (Decapoda: Parastacidae): implications for conservation

The giant Tasmanian freshwater crayfish Astacopsis gouldi prized by fisherman, is the world's largest freshwater invertebrate. Astacopsis gouldi is known only from river drainages in northern Tasmania. A narrow distribution, pollution of habitat and over-harvesting has led to the rapid decline of populations and subsequent loss from a number of drainages. We collected mitochondrial DNA sequences to assess population structure and genetic diversity from throughout the species' distribution. We found a lineage from north-eastern Tasmania, which was genetically divergent compared with the remaining distribution in north-western Tasmania. Populations from the remaining distribution, including haplotypes found across a noted faunal barrier (Tamar River), were genetically homogeneous with <1% sequence divergence. This finding is concordant with a hypothesis of more interconnected drainages associated with lower sea levels in the past. The new cryptic lineage from north-east Tasmania requires further investigation and may be of extremely high conservation value. Conservation efforts for A. gouldi, combining habitat restoration with in situ management of wild populations and some population augmentation into once occupied rivers, will also have a positive impact for conservation of freshwater ecosystems in northern Tasmania.

A new aglaspidid arthropod from the Upper Cambrian of Tasmania

Abstract: The aglaspidid arthropod, Australaglaspis stonyensis gen. et sp. nov., is described from the Idamean (Upper Cambrian) of Stony Point, Montagu, north-western Tasmania. The dorsal exoskeleton comprises a semicircular cephalon with a well-defined marginal rim, acute genal angles, oval eyes, subtriangular glabella area and a subtrapezoidal hypostome. The trunk bears eleven somites with well-developed pleural spines that progressively curve backwards. Paired postventral plates cover the last trunk tergites and the base of the tailspine, which is long and characterized by a medial cleft. Bilobed ventral impressions indicate the presence of homopodous appendages, forming a food groove along the trunk. The fossil assemblage and its mode of preservation suggest that Australaglaspis originally possessed a phosphatic cuticle, but chemical traces of it have been lost because of regional metamorphism and weathering. Australaglaspis appears to be closely related to the North American aglaspidid Chraspedops modesta Raasch, 1939, based on its medially cleft tailspine.

Early Miocene silicified limestone from Temma, northwestern Tasmania: further evidence of substantial post-Early Miocene uplift or tilting of Tasmania

Silicified shallow-water Early Miocene (Longfordian) marine limestone occurs in altitudes to over 160m, 12km east of Temma in northwestern Tasmania, the highest elevation known to date for rocks of this age and environment of deposition. Age and environmental data are provided by Foraminifera, calcareous algae and poorly preserved macrofauna. Mode of silicification of Foraminifera varies systematically between suborders - miliolids and agglutinated species as internal moulds, nodosariids, rotaliids and cibicidids as vohune-for-volume replacements. Foraminifera are benthic only. Miliolids dominate but preservation is too poor to allow statistically valid analysis. The locality provides only the second occurrence of Tenisonina tasmaniae Quilty, and, for the first time, it occurs with Sherbornina atkinsoni Chapman.

Association of allelic variation in xylem genes with wood properties in Eucalyptus nitens

Summary We used association studies to identify allelic variation in genes that influence wood fibre development in Eucalyptus nitens (Deane & Maiden). Genes selected for analysis were differentially expressed in wood with contrasting properties such as cellulose and lignin content, pulp yield and microfibril angle (MFA). Single nucleotide polymorphisms (SNPs) were identified by sequencing the candidate genes in a number of unrelated individuals. Selected SNPs were genotyped across 420 unrelated E. nitens trees from central Victorian populations and growing in a provenance trial at Meunna in north-western Tasmania. Significantly associated SNPs were genotyped across two other populations in northern Tasmania in order to validate associated SNPs. We have compiled a database of phenotypic information relating particularly to wood fibre properties for each individual in the association and validation populations. Associations between SNPs and wood properties were identified by comparing trait means in different SNP genotype classes. Several significantly associated SNPs identified in the Meunna population were validated in the other populations. The direction of the allele effect was reversed for two SNPs that were associated with kraft pulp yield. DNA markers identified in this research may be used to complement existing selection methods in breeding programs.

Correlation of Sturtian diamictite successions in southern Australia and northwestern Tasmania by Re–Os black shale geochronology and the ambiguity of “Sturtian”-type diamictite–cap carbonate pairs as chronostratigraphic marker horizons

Recent geochronological studies have raised concerns regarding the accuracy of regional and global correlations of Neoproterozoic sedimentary successions using relative dating methods such as carbon isotope chemostratigraphy and glaciogenic diamictite–cap carbonate lithological and geochemical characteristics. Precise and accurate radio-isotopic age constraints for Neoproterozoic sedimentary rocks thus remain a high priority for establishing a reliable Neoproterozoic chronostratigraphy. Here, we present a new Re–Os age of 640.7±4.7Ma from black shales of the upper Black River Dolomite (Togari Group, northwestern Tasmania) that represents a minimum age for deposition of the immediately underlying, diamictite-bearing Julius River Member. The upper Black River Dolomite Re–Os age is statistically identical to a Re–Os age of 643.0±2.4Ma previously determined for the Sturtian post-glacial Tindelpina Shale Member (Umberatana Group, Adelaide Rift Complex, southern Australia). Consistent with previous lithostratigraphic and stromatolite biostratigraphic evidence, the Re–Os ages suggest broadly coeval deposition of the Julius River Member and Sturtian diamictites and overlying organic-rich marine shales. Consideration of the Neoproterozoic geochronological database suggests that “Sturtian”-type diamictite–cap carbonate pairs cannot be used as chronostratigraphic marker horizons for global correlation of the Neoproterozoic rock record.

Potential of deficit irrigation to increase marginal irrigation response of perennial ryegrass (Lolium perenne L.) on Tasmanian dairy farms

In the cool temperate dairy regions of Tasmania, there is heavy reliance on irrigation to maximise pasture performance by ensuring that plants do not suffer water stress. Consequently, irrigation water has often been applied at a greater amount than plant water requirements, resulting in low efficiencies. An irrigation experiment was undertaken in north-western Tasmania between October 2007 and April 2008, examining the effect of deficit irrigation treatments on pasture growth and water-use efficiency. A rainfall deficit (potential evapotranspiration minus rainfall) of 20 mm was implemented to schedule irrigation, at which point 20, 16, 12, 8, or 0 mm of irrigation water was applied, referred to as treatments I100%, I80%, I60%, I40%, and I0%, respectively. The trial was a randomised complete block design with 4 replications. There were 21 irrigation events between October and April. The experimental area was grazed by 60 Holstein Friesian heifers at a grazing interval coinciding with emergence of 2.5–3.0 new ryegrass leaves/tiller of the I100% treatment. Cumulative pasture consumption for the irrigated period was 9.2, 8.9, 7.6, 6.9, and 3.7 t dry matter (DM)/ha for the I100%, I80%, I60%, I40%, and I0% treatments, respectively. The resulting marginal irrigation water-use index (MIWUI; marginal production due to irrigation) was 1.29, 1.54, 1.55, and 1.87 t DM/ML, for the I100%, I80%, I60%, and I40% treatments, respectively. The results of this study were modelled using the biophysical model DairyMod, with strong agreement between observed and modelled data. DairyMod was then used to simulate the MIWUI for 5 differing dairy regions of Tasmania using 40 years of climatic data (1968–2007) under 3 differing nitrogen management strategies by the 5 irrigation treatments. The modelling indicated that a MIWUI greater than 2 t DM/ML can be achieved in all regions. The current study has shown that the opportunity exists for irrigated pastoral systems to better manage an increasingly scarce resource and substantially improve responses to irrigation.

Post-pollination capsule development in Eucalyptus globulus seed orchards

Low capsule set is a major factor limiting seed production in Eucalyptus globulus seed orchards. Trials were conducted in E. globulus seed orchards in Tasmania, Australia, to identify the timing of capsule development and abortion, as well as the influence of pollination type, the number of ovules fertilised and weather events on capsule set. Controlled pollination (CP), mass supplementary pollination (MSP), open pollination (OP) and isolated unpollinated control (UP) treatments were performed on 21 genotypes in an orchard in southern Tasmania in 2004–2005 and on six genotypes in a higher-altitude orchard in north-western Tasmania in 2005–2006. No capsules were set in the UP control treatment, and capsule set was significantly lower following CP than OP and MSP. The major period of capsule abortion occurred between 20 and 80 days after pollination for all pollination methods across both sites, coinciding with the period of capsule growth. A positive correlation between the number of fertilised ovules per aborted capsule and the length of time capsules were held on the tree was recorded. Given that capsule abortion occurred during a period of fruit growth and that capsules with the lowest number of fertilised ovules aborted first, it is argued that fertilisation level and the level of resource competition are major factors determining capsule abortion.

Predicting Mycosphaerella leaf disease severity in a Eucalyptus globulus plantation using digital multi-spectral imagery

Digital remote sensing is rapidly developing into an operational tool for forest health assessment at a range of scales. A key aspect of this development is the derivation of models relating spectral data contained in the images to the extent and severity of plant stress symptoms. This study assesses the utility of high spatial resolution (0.5m &#215 0.5m pixel size) airborne digital imagery to assess the presence and severity of defoliation and necrosis from Mycosphaerella leaf disease at the crown scale across a small plantation in north-western Tasmania, Australia. The best model of defoliation included the variance of reflectance at 780nm within the crown (r 2 = 0.5; p 2 = 0.3; p Keywords: disease severity, Eucalyptus globulus , Mycosphaerella , remote sensing Southern Hemisphere Forestry Journal 2007, 69(3): 175–182

New and little‐known species of Didemnidae (Ascidiacea, Tunicata) from Australia (part 4)

Forty‐eight species (including nine that are new) of the 288 Didemnidae now known from Australian waters are reported on in the present work. Dredged material is from benthic habitats in inter‐reefal areas of the Great Barrier Reef and from deeper water canyons off northeastern and northwestern Tasmania. Collections from shallower waters of Port Davey (western Tasmania) and Kangaroo Island (South Australia) were hand‐collected by scuba divers. Seven of the eight known genera of the Didemnidae are represented. Despite this emphasis on sampling in temperate waters, only 14 species (all indigenous) are recorded from around the southern half of the continent. The species diversity of this family is greater in the tropics, with 34 species being recorded. Nearly half of these are known also from the tropical western Pacific and some from the Indian Ocean as well. Tropical indigenous species are relatively few.

Acaste (Trilobita: Phacopina) from the Early Devonian of Tasmania

Edgecombe, G.D. March 2007. Acaste (Trilobita: Phacopina) from the Early Devonian of Tasmania. Alcheringa 31, 59-66. ISSN 0311-5518. The widespread Siluro-Devonian acastid trilobites Acaste and Acastella are known from few occurrences in Australasia, these being confined to Lochkovian strata in Victoria and New Zealand. A new species, Acaste andersoni, is described from a correlative of the Bell Shale near St Valentines Peak in north-western Tasmania. Acaste supplements the biogeographic links between the Early Devonian faunas of New Zealand, Victoria and Tasmania. Gregory D. Edgecombe [greged@austmus.gov.au], Australian Museum, 6 College Street, Sydney, NSW 2010, Australia; received 2.3.2005, revised 6.4.2005.

Persistent improvements in the structure and hydraulic conductivity of a Ferrosol due to liming

Changes in the soil structure and hydraulic conductivity of an Acidic Red Ferrosol were measured in a long-term (1968–2003) fertiliser experiment on pasture in north-western Tasmania, Australia. Studies were initiated following observations of both softer soil surface and cracking on plots that had received 15 t/ha of ground agricultural limestone. Liming decreased penetration resistance and increased hydraulic conductivity. These structural improvements were associated with increased mean dry aggregate size, a small increase in wet aggregate stability, higher exchangeable calcium levels, and increased plant growth, but a 9% decrease in total soil organic carbon in the surface 50 mm. This decrease in organic carbon was not associated with deterioration in soil structure, as may have been anticipated. This was probably because total organic C was still 82 g/kg on unlimed plots. Decreases in soil penetration resistance due to liming increased the likelihood of pugging from livestock but may improve ease of tillage. This research demonstrates that liming can improve the structure of a well-aggregated Ferrosol as well as its previously reported effects of increasing soil pH and yields of pasture and barley despite decreasing organic C.

Anatomy and relationships of SuterillaThiele (Caenogastropoda: Assimineidae) with descriptions of four new species

The assimineid genus Suterilla, previously known only from New Zealand, including the Kermadec Islands, is revised using shell, radular and anatomical characters. In addition to the type species S. neozelanica (Murdoch, 1899), four new species are described, S. climoi and S. imperforata from northern New Zealand, S. julieae from northwestern Tasmania and S. fluviatilis from Norfolk Island. All species except the last are found in marine high tidal and supratidal locations, while the Norfolk Island species lives amphibiously in a freshwater stream. These five species are distinguishable chiefly by the characters of the penis and pallial oviduct. A morphology-based cladistic analysis places Suterilla as a primitive member of the subfamily Omphalotropidinae. New information is provided for the amphibious freshwater Tutuilana striata Hubendick, from Samoa, the sister taxon of Suterilla.

OH and HO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; chemistry in clean marine air during SOAPEX-2

Abstract. Model-measurement comparisons of HOx in extremely clean air ([NO]&lt;3 ppt) are reported. Measurements were made during the second Southern Ocean Photochemistry Experiment (SOAPEX-2), held in austral summer 1999 at the Cape Grim Baseline Air Pollution Station in north-western Tasmania, Australia. The free-radical chemistry was studied using a zero-dimensional box-model based upon the Master Chemical Mechanism (MCM). Two versions of the model were used, with different levels of chemical complexity, to explore the role of hydrocarbons upon free-radical budgets under very clean conditions. The "detailed" model was constrained to measurements of CO, CH4 and 17 NMHCs, while the "simple" model contained only the CO and CH4 oxidation mechanisms, together with inorganic chemistry. The OH and HO2 (HOx) concentrations predicted by the two models agreed to within 5–10%. The model results were compared with the HOx concentrations measured by the FAGE (Fluorescence Assay by Gas Expansion) technique during four days of clean Southern Ocean marine boundary layer (MBL) air. The models overestimated OH concentrations by about 10% on two days and about 20% on the other two days. HO2 concentrations were measured during two of these days and the models overestimated the measured concentrations by about 40%. Better agreement with measured HO2 was observed by using data from several MBL aerosol measurements to estimate the aerosol surface area and by increasing the HO2 uptake coefficient to unity. This reduced the modelled HO2 overestimate by ~40%, with little effect on OH, because of the poor HO2 to OH conversion at the low ambient NOx concentrations. Local sensitivity analysis and Morris One-At-A-Time analysis were performed on the "simple" model, and showed the importance of reliable measurements of j(O1D) and [HCHO] and of the kinetic parameters that determine the efficiency of O(1D) to OH and HCHO to HO2 conversion. A 2σ standard deviation of 30–40% for OH and 25–30% for HO2 was estimated for the model calculations using a Monte Carlo technique coupled with Latin Hypercube Sampling (LHS).

Late Middle Cambrian trilobites from St Valentines Peak and Native Track Tier, northwestern Tasmania

Late Middle Cambrian trilobites are described from two localities in northwestern Tasmania. Twenty-four trilobite taxa are documented. The 15 agnostoid species include Paraclavagnostus longus sp. nov. which is placed in the Utagnostinae, a new subfamily of the Clavagnostidae. The nine polymeroid species include a new member of the Rhyssometopidae, Tasmana truncata gen. et sp. nov. Three other new species of polymeroids are erected: Fuchouia tasmaniensis, Nepea delicata and Nepea hellyeri. Both faunas correlate with the Lejopyge laevigata Zone on the northern Australia biostratigraphic scale, possibly with the L. laevigata II Zone. When compared with Hunan, China, correlation is with the upper part of the Lejopyge laevigata Zone, and particularly with the lower part of the Proagnostus bulbus Zone.