Western Coast Of Australia Research Articles

Under no-tillage and stubble retention, soil water content and crop growth are poorly related to soil water repellency

In southern and western Australia up to 10 million hectares of farmed land is water repellent or at risk of developing repellency. The majority of these soils are sandy. Their high susceptibility to erosion has led to the adoption of practices such as no-tillage and stubble retention. However, retention of stubbles can lead to increases in soil organic matter and consequently aggravate soil water repellency. In a 4-year study on sandy soils on the south coast of Western Australia, soil organic C (LECO), soil water repellency (measured by the Molarity of Ethanol Drop (MED) method), soil water contents (using a hand held time domain reflectometer (TDR)) and crop performance (emergence and grain yields) were monitored in four treatment combinations; no-tillage, stubble retained or burnt; cultivated, stubble retained or burnt. Over time, higher levels of soil organic C were measured under no-tillage than cultivation, and under stubble retention than stubble burning. Soil water repellency followed a similar pattern to soil organic C with the most severe repellency under no-tillage and stubble retention and least under stubble burning and cultivation (R2=0.67). However, soil water contents measured in the field contradicted the findings on water repellency and indicated that water infiltration was best under no-tillage and stubble retention and poorest under stubble burning and cultivation, and this impacted on crop performance. The results suggest that mechanisms other than just soil water repellency are involved in determining soil water content and crop performance. Visualisation of water infiltration using blue dye indicated that under no-tillage, old and current crop rows provide pathways for water movement in the soil, thereby by-passing the repellent surface layer. These findings challenge traditional thinking on soil water repellency and have implications for crop management.

High Sulfide Intrusion in Five Temperate Seagrasses Growing Under Contrasting Sediment Conditions

Five temperate seagrasses (Amphibolis antartica, Halophila ovalis, Posidonia australis, Posidonia sinuosa and Zostera nigricaulis) were surveyed along the south-west coast of Western Australia. These morphological different seagrasses grow in contrasting sediments with large variations in sedimentary organic matter, carbonate and iron contents. We tested if sulfur composition in the plants responded to sulfur dynamics in the sediments and if plant morphology affected the sulfur composition of the plants. The sediments were characterized by low sulfate reduction rates (<9 mmol m−2day−1), low concentrations of dissolved sulfides in the pore waters (<74 μM) and low burial of sulfides (total reducible sulfur <0.8 mol m−2) in the sediments. However, all seagrasses showed high intrusion in the below-ground parts with up to 84 % of the sulfur derived from sedimentary sulfides. There were no direct links between sulfur in the plants and sulfur dynamics in the sediments, probably due to low iron contents in the sediments limiting the buffering capacity of the sediments and exposing the plants to sulfides despite low rates of production and low pools of sulfides. The intrusion was linked between plant compartments (roots, rhizomes and leaves) for the two small species (H. ovalis and Z. nigricaulis), whereas the intrusion into the leaves was limited for the larger species (P. australis and P. sinuosa) and for A. antarctica, where extensive rhizomes and roots and the long stem for A. antarctica separate the leaves from the sediment compartment. Elevated intrusion was observed at two study locations, where natural deposition of organic matter or nutrient enrichment may be contributing factors to enhanced sulfide pressure.

Interannual Variations of Wind Regimes off the Subtropical Western Australia Coast during Austral Winter and Spring

Abstract Off the Western Australia coast, interannual variations of wind regime during the austral winter and spring are significantly correlated with the Indian Ocean dipole (IOD) and the southern annular mode (SAM) variability. Atmospheric general circulation model experiments forced by an idealized IOD sea surface temperature anomaly field suggest that the IOD-generated deep atmospheric convection anomalies trigger a Rossby wave train in the upper troposphere that propagates into the southern extratropics and induces positive geopotential height anomalies over southern Australia, independent of the SAM. The positive geopotential height anomalies extended from the upper troposphere to the surface, south of the Australian continent, resulting in easterly wind anomalies off the Western Australia coast and a reduction of the high-frequency synoptic storm events that deliver the majority of southwest Australia rainfall during austral winter and spring. In the marine environment, the wind anomalies and reduction of storm events may hamper the western rock lobster recruitment process.

Bait Effects in Sampling Coral Reef Fish Assemblages with Stereo-BRUVs

Baited underwater video techniques are increasingly being utilised for assessing and monitoring demersal fishes because they are: 1) non extractive, 2) can be used to sample across multiple habitats and depths, 3) are cost effective, 4) sample a broader range of species than many other techniques, 5) and with greater statistical power. However, an examination of the literature demonstrates that a range of different bait types are being used. The use of different types of bait can create an additional source of variability in sampling programs. Coral reef fish assemblages at the Houtman Abrolhos Islands, Western Australia, were sampled using baited remote underwater stereo-video systems. One-hour stereo-video recordings were collected for four different bait treatments (pilchards, cat food, falafel mix and no bait (control)) from sites inside and outside a targeted fishery closure (TFC). In total, 5209 individuals from 132 fish species belonging to 41 families were recorded. There were significant differences in the fish assemblage structure and composition between baited and non-baited treatments (P<0.001), while no difference was observed with species richness. Samples baited with cat food and pilchards contained similar ingredients and were found to record similar components of the fish assemblage. There were no significant differences in the fish assemblages in areas open or closed to fishing, regardless of the bait used. Investigation of five targeted species indicated that the response to different types of bait was species-specific. For example, the relative abundance of Pagrus auratus was found to increase in areas protected from fishing, but only in samples baited with pilchards and cat food. The results indicate that the use of bait in conjunction with stereo-BRUVs is advantageous. On balance, the use of pilchards as a standardised bait for stereo-BRUVs deployments is justified for use along the mid-west coast of Western Australia.

Preparation of Calcium Hexaluminate Using Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3 &lt;/sub&gt;and White Beach Sand from Western Australia &lt;sub&gt; &lt;/sub&gt;

Calcium hexaluminate (CA6) because of its high stability, high melting point and low thermal conductivity properties make it as a new high-temperature insulation materials are valued. In this paper, chemical analysis and XRD were used to investigate the composition of the white beach sand mineral from Perth coast of Western Australia. The main composition of it was carbonate. White beach sand as calcium source respectively, and industrial alumina as aluminum source synthesized CA6 at 1550°C-1650°C for 3h. The results showed that: synthetic CA6 shapes in platelet crystalline. Influence of different amounts of alumina and sintering temperature on synthesis of calcium hexaluminate are studied.The main phase of the samples with different amounts of alumina which decrease or increase 5%, 10% and 15% alumina around theory are CA6. The porosity of the samples obtained is about 53%. The bending strength of Sample S-0 of theoretical ratio values up to 7.73Mpa. Sintering temperature from 1500°C to 1650°C is not conductive to the improvement of apparent porosity of CA6 materials.

Plutonium and uranium contamination in soils from former nuclear weapon test sites in Australia

The British government performed a number of nuclear weapon tests on Australian territory from 1952 through to 1963 with the cooperation of the Australian government. Nine fission bombs were detonated in South Australia at Emu Junction and Maralinga, and a further three fission weapons were detonated in the Monte Bello Islands off the coast of Western Australia. A number of soil samples were collected by the Australian Radiation Laboratories in 1972 and 1978 during field surveys at these nuclear weapon test sites. They were analysed by gamma spectrometry and, for a select few samples, by alpha spectrometry to measure the remaining activities of fission products, activation products and weapon materials. We have remeasured a number of these Montebello Islands and Emu Junction soil samples using the ANTARES AMS facility, ANSTO. These samples were analysed for plutonium and uranium isotopic ratios and isotopic concentrations. Very low 240Pu/239Pu ratios were measured at both sites (∼0.05 for Alpha Island and ∼0.02 for Emu Field), substantially below global fallout averages. Well correlated but widely varying 236U and plutonium concentrations were measured across both sites, but 233U did not correlate with these other isotopes and instead showed correlation with distance from ground zero, indicating in situ production in the soils.

Fussy feeders: phyllosoma larvae of the Western Rocklobster (Panulirus cygnus) demonstrate prey preference.

The Western Rocklobster (Panulirus cygnus) is the most valuable single species fishery in Australia and the largest single country spiny lobster fishery in the world. In recent years a well-known relationship between oceanographic conditions and lobster recruitment has become uncoupled, with significantly lower recruitment than expected, generating interest in the factors influencing survival and development of the planktonic larval stages. The nutritional requirements and wild prey of the planktotrophic larval stage (phyllosoma) of P. cygnus were previously unknown, hampering both management and aquaculture efforts for this species. Ship-board feeding trials of wild-caught mid-late stage P. cygnus phyllosoma in the eastern Indian Ocean, off the coast of Western Australia, were conducted in July 2010 and August-September 2011. In a series of experiments, phyllosoma were fed single and mixed species diets of relatively abundant potential prey items (chaetognaths, salps, and krill). Chaetognaths were consumed in 2–8 times higher numbers than the other prey, and the rate of consumption of chaetognaths increased with increasing concentration of prey. The highly variable lipid content of the phyllosoma, and the fatty acid profiles of the phyllosoma and chaetognaths, indicated they were from an oligotrophic oceanic food chain where food resources for macrozooplankton were likely to be constrained. Phyllosoma fed chaetognaths over 6 days showed significant changes in some fatty acids and tended to accumulate lipid, indicating an improvement in overall nutritional condition. The discovery of a preferred prey for P. cygnus will provide a basis for future oceanographic, management and aquaculture research for this economically and ecologically valuable species.

The impact of a locust plague on mangroves of the arid Western Australia coast

Mangroves generally grow in nutrient-poor environments and maintain high levels of productivity through unique adaptations for nutrient conservation (Reef et al. 2010). One such adaptation in mangroves is highly efficient resorption of limiting nutrients from senescing leaves prior to abscission (Feller et al. 2003). Thus processes that lead to loss of foliage prior to senescence and nutrient resorption (e.g. storms and herbivory) can be detrimental to tree growth and productivity (Bryant et al. 1983, May &amp; Killingbeck 1992). Furthermore, decomposition of fallen leaves by soil microbial communities (Alongi 1994, Holguin et al. 2001) and crabs (Nagelkerken et al. 2008) is another important process contributing to the recycling of nutrients that are in short supply. Therefore, processes that lead to a substantial reduction in litterfall can have a strong negative effect on nutrient cycling and forest productivity. Mangroves have long been recognized as an important source of organic carbon (both particulate and dissolved) for the surrounding tropical coastal ecosystems (Bouillon et al. 2008, Kristensen et al. 2008). Thus, processes affecting litterfall in mangroves can affect the surrounding marine food webs.

The effects of roughness on transmission loss in regions with elastic bottoms

On rough elastic interfaces, incident acoustic waves couple more readily into the shear mode due to the steeper local angle relative to the nominal incident angle. This effect has a profound influence on transmission loss in shallow water areas with elastic bottoms. Although rock interfaces are often covered with sand or other sediment, the effect is still significant even for overlying sediment layers several acoustic wavelengths thick. In this study, the effects of roughness on transmission loss in an area with a hard elastic bottom with and without an overlying sediment layer are studied using a finite element transmission loss model. Results are compared with transmission loss data measured in an area with sediment layers over hard rock off the Western coast of Australia. [Work supported by ONR, Ocean Acoustics]

The biological characteristics of Scorpis aequipinnis (Kyphosidae), including relevant comparisons with those of other species and particularly of a heavily exploited congener

This study has determined the biological characteristics of Scorpis aequipinnis on the south coast of Western Australia. It thus supplements the limited amount of data for members of the widely distributed and speciose Kyphosidae, which contains species that make an important contribution to certain ecosystems and local commercial and recreational fisheries and have considerable aquaculture potential. S. aequipinnis was aged using the number of annuli in sectioned otoliths and its growth described using the Schnute growth equation. This species attains a greater maximum fork length (FL), i.e. 477 vs. 330mm, and greater maximum age, i.e. 68 vs. 54years, than S. lineolatus on the eastern Australian coast, where its stock has apparently experienced excessive exploitation. S. aequipinnis thus exhibits characteristics that would make it particularly susceptible to over-fishing should fishing effort on the south coast increase as anticipated. S. aequipinnis and S. lineolatus exhibit similar and very rapid growth initially, reaching 90% of their asymptotic fork lengths (FL∞) at 14-16 and 12years, respectively, and then grow only slightly for much of the remainder of their extensive life spans. The FL50s at maturity for female and male S. aequipinnis (363 and 379mm, respectively) and for both sexes of S. lineolatus combined (172mm) were each far greater than would be expected given their respective FL∞s. There have thus been strong selection pressures for the attainment by both species of a relatively large size prior to maturation. The main spawning period of S. aequipinnis, which occurs between late autumn and mid-winter when water temperatures are declining rapidly, and those of other recreational and commercial species on the south coast of Western Australia vary markedly, thereby reducing the potential for inter-specific competition for resources by their larvae and juveniles. The estimate of fishing mortality for male S. aequipinnis was greater than expected, possibly reflecting a combination of site fidelity and the localisation of commercial fishing.

Impact of air gun noise on the behaviour of marine fish and squid

In this study various species of captive marine fish and one species of squid were exposed to the noise from a single air gun. Six trials were conducted off the coast of Western Australia with each trial using a different noise exposure regime. Noise levels received by the animals ranged between 120 and 184dBre1μPa2.s (SEL).Behavioural observations of the fish and squid were made before, during and after air gun noise exposure. Results indicate that as air gun noise levels increase, fish respond by moving to the bottom of the water column and swimming faster in more tightly cohesive groups. Significant increases in alarm responses were observed in fish and squid to air gun noise exceeding 147–151dBre1μPa SEL. An increase in the occurrence of alarm responses was also observed as noise level increased.

Growth of Western Australian Corals in the Anthropocene

Anthropogenic increases of atmospheric carbon dioxide lead to warmer sea surface temperatures and altered ocean chemistry. Experimental evidence suggests that coral calcification decreases as aragonite saturation drops but increases as temperatures rise toward thresholds optimal for coral growth. In situ studies have documented alarming recent declines in calcification rates on several tropical coral reef ecosystems. We show there is no widespread pattern of consistent decline in calcification rates of massive Porites during the 20th century on reefs spanning an 11° latitudinal range in the southeast Indian Ocean off Western Australia. Increasing calcification rates on the high-latitude reefs contrast with the downward trajectory reported for corals on Australia's Great Barrier Reef and provide additional evidence that recent changes in coral calcification are responses to temperature rather than ocean acidification.

Climate-change induced tropicalisation of marine communities in Western Australia

A major observed and predicted impact of climate change on marine species is the poleward shift in their distributions and the resulting changes in community structure. Here, we used a Dynamic Bioclimate Envelope Model to project range shift of exploited marine fishes and invertebrates in Western Australia. We combined published data and expert knowledge to predict current species distributions for 30 tropical, sub-tropical and temperate species that occur along the coast of Western Australia. Using outputs from both a Regional Oceanographic Model and a Global Circulation Model, we simulated change in the distribution of each species. Our study shows that under the SRES (Special Report for Emission Scenarios) A1B scenario, the median rate of distribution shift is around 19 km decade–1 towards higher latitudes and 9 m deeper decade–1 by 2055 relative to 2005. As a result, species gains and losses are expected along the south coast and north coast of Western Australia, respectively. Also, the coast of Western Australia is expected to experience a ‘tropicalisation’ of the marine community in the future, with increasing dominance of warmer-water species. Such changes in species assemblages may have large ecological and socio-economic implications through shifts in fishing grounds and unexpected trophic effects.

Entanglements of baleen whales off the coast of Western Australia between 1982 and 2010: patterns of occurrence, outcomes and management responses.

Baleen whale population sizes have increased in Western Australian waters since the cessation of commercial whaling activities. This has been followed by a coincident increase in the number of reported entanglements of baleen whales in fishing gear. During their annual migration, whales pass through Western Australian waters used by commercial fisheries targeting rock lobster, octopus and shark as well as aquaculture industries producing abalone, pearls and mussels. We reviewed the 63 baleen whale entanglement records in the Western Australian Cetacean Strandings Database (1982-2010). Of the four baleen whale species observed entangled in fishing gear in Western Australian waters, the Humpback Whale Megaptera novaeangliae accounted for 56 (89%) entanglements, followed by the Southern Right Whale Eubalaena australis, five (8%) entanglements, and one record each for both the Bryde s Balaenoptera edeni and Minke Whale Balaenoptera acutorostrata. Almost half of entanglements occurred in rock lobster fishing gear (n = 31; 49%). There is an upward trend in the number of entanglements reported since 1990 in rock lobster fishing gear despite fishing effort reducing over the same period of time. This can, at least partly, be attributed to the increase in humpback whale population size. Fisheries and conservation agencies have responded by developing cooperative relationships and protocols that reduce entanglement risk and improve outcomes when entanglement does occur.

Occurrence of non-volant mammals on islands along the Kimberley coast of Western Australia

Occurrence of non-volant mammals on islands along the Kimberley coast of Western Australia

U–Pb ages of metamorphic monazite and detrital zircon from the Northampton Complex: evidence of two orogenic cycles in Western Australia

The Pinjarra Orogen, stretching along the western coast of Western Australia, is one of the least understood orogens on the continent. Exposure is limited to fault-bound basement blocks within the Phanerozoic Perth Basin, which have been interpreted as either remnants of a Mesoproterozoic orogen or as allochthonous blocks within a Neoproterozoic orogen. Thus even the timing of orogenesis is controversial. However, since the orogen is in a critical position for reconstructions of both Rodinia and Gondwana, a better understanding is highly desirable. New U–Pb ages of detrital zircon cores, metamorphic zircon rims and metamorphic monazites from the Northampton Complex, the northernmost and largest of the exposed basement blocks, provide better insights into the sedimentary provenance and metamorphic history of the metasediments exposed in this part of the orogen. Both the monazite ages and the youngest metamorphic zircon rims constrain metamorphism in the Northampton Complex to 1090–1020Ma. Additionally, a large number of older metamorphic zircon rims pre-date this event and were inherited from the Albany-Fraser Orogen in southwestern Australia, which is also identified as the main source region for the detrital zircon cores. Additional sources of detrital zircons are the Mawson Continent (the South Australian Craton and parts of East Antarctica) and possibly the North Australian Craton, as well as synsedimentary volcanic rocks. However, the combination of ages from the cores and inherited metamorphic rims shows that zircons from the Mawson Continent/North Australian Craton were not directly transported to the Northampton Complex but arrived there after being incorporated into the Albany-Fraser Orogen and then eroded from there. The dataset records therefore two orogenic cycles: (1) erosion of the Mawson Continent/North Australian Craton, deposition along the craton margins, collision between the Mawson Continent and North-West Australian Craton and metamorphism in the Albany-Fraser Orogen and (2) erosion of the Albany-Fraser Orogen, deposition along Australia's western margin and metamorphism during the Pinjarra Orogeny. This highlights the care that must be taken in detrital zircon studies, since many of the detrital cores record a second-order provenance. It also explains how zircons from the Mawson Continent could be transported across the Albany-Fraser Orogen that should normally have been a barrier to northwest-directed sediment transport. Finally, in light of these new and previously published data, we support the interpretation that the Pinjarra Orogen is a Mesoproterozoic orogen formed along Australia's western margin.

The truth is in there: Analysis of grave relics to help solve a mystery linked to the loss of the HMAS Sydney II

In February 1942, three months after the HMAS Sydney II sank off the coast of Western Australia, taking with it all 645 crew members, the unidentified body of a man washed ashore in a Carley float on Christmas Island. The body was buried and two eyewitness accounts of the situation recorded. A 2006 recovery mission to find the grave site and give the unknown sailor a proper burial was successful. Relics found in the original grave included four somewhat degraded and corroded press-studs–the only remaining components of the sailor’s clothing. These relics were accessioned into the Australian War Memorial’s collection. Analysis of some of the press-studs was conducted in an attempt to help determine who this sailor may have been, or whether he was likely to have been from the HMAS Sydney II. Elemental and molecular analyses using a range of instrumental techniques including X-ray fluorescence (XRF), Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS), X-ray tomography, Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR) have been conducted in conjunction with the Australian Federal Police and Australian National University. Strong evidence for an inscription on one of the press-studs and a blue colourant from fragments of fabric preserved within the press-studs have been revealed.

High-Value Engineering Center: Implementing a Major Capital Project - Gorgon

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 145708, ’Use of a High- Value Engineering Center in Execution of a Major Capital Project, Gorgon,’ by Siva Malladi, SPE, Parag Shah, and David Cruikshank, Chevron, prepared for the 2011 SPE Asia Pacific Oil and Gas Conference and Exhibition, Jakarta, 20-22 September. The paper has not been peer reviewed. The Chevron-operated Gorgon Project is off the northwest coast of Western Australia and encompasses several megaprojects, including an all-subsea upstream development of the Greater Gorgon gas fields. Because of its sheer size, scale, and complexity, in addition to several unique characteristics, the Gorgon Project required an extraordinary level of project management. A key project-management strategy was appointment of a high-value engineering center (HVEC) in Jakarta. Introduction This project is one of the world’s largest natural-gas projects and the largest single-resource project in Australia’s history. The development program includes several megaproject components. Gorgon Upstream—comprising subsea production facilities, pipeline facilities, and domestic gas-export facilities. Gorgon Downstream—comprising a 15×106 t/a liquefied-natural-gas (LNG) plant on Barrow Island, gas-receiving and processing facilities (e.g., slug catchers, heaters/coolers, acid-gas-removal plants, gas-dehydration plants for pretreatment of feed gas to the LNG plant), condensate-stabilization facilities, monoethylene glycol regeneration, LNG/condensate storage and offloading, power-generation and -distribution facilities, and other utilities to support the LNG plant. A domestic gas plant with the capacity to provide 300 TJ/d to supply gas to Western Australia. Carbon dioxide (CO2) injection. LNG-export terminal. Infrastructure facilities—camp, buildings, logistics, telecommunications, and other facilities to support the construction and operation of the LNG-plant facilities on Barrow Island. The full-length paper details the scope associated with the HVEC work for the Gorgon-Downstream project, the evaluation undertaken of the Jakarta HVEC, and the challenges encountered and remedial tac-tics used during the execution of the HVEC work. The engineering and procurement portions of the downstream project were completed at the main execution centers (ECs) in London (two offices), Singapore (one office), and Jakarta (one office). Part of the execution strategy was the use of an HVEC in Jakarta to support the main ECs in the UK, operating as a remote design resource. The project-execution plan for performing this work was the following. The main EC would perform the detailed engineering, begin the 3D-modeling work, bring the model up to between 40 and 60% maturity for various disciplines, and transfer the design-work scope to the HVEC. The workscope transition would occur in a staggered sequence for various work areas—modules, preassembled racks (PARs), preassembled units (PAUs), and stick-built areas—in accordance with the EC execution sequence and in line with the overall project schedule. The HVEC would pick up the 3D model from that point and develop it to final completion to generate the required deliverables, as described in the following section.

The role of vegetation in mitigating the effects of landscape clearing upon dryland stream response trajectory and restoration potential

ABSTRACTDryland rivers are recognized for limited research and high uncertainties with respect to understanding biogeomorphic processes. This study uses aerial photography, sediment analysis, palynology indicators and hydraulic modelling to investigate the role of riparian vegetation in influencing the response of systems to disturbance, the trajectory of channel evolution and the potential for management. The study focuses on cleared and uncleared sites in the Yerritup catchment, along the south coast of Western Australia, that occur along a transect with a consistent stream gradient and landscape topographic setting.Downstream reaches show no gross botanical change, but gradual sediment deposition across the floodplain of up to 40 cm based on palynological and sedimentary indicators. Channel response in the cleared section by incision, widening and floodplain degradation began rapidly after land clearing, but is driven by large flood events. Degradation of riparian vegetation has significantly increased the sensitivity of the system. The cleared reaches have transformed from a low‐capacity channel, under‐adjusted to the prevailing flow regime, to the large present channel that is now over‐adjusted to the predominantly low to moderate seasonal (occasional flood) flow regime. Modelling of pre‐settlement erosive potential reveals that the entire system was naturally sensitive to change, and was primed to erode once riparian vegetation was removed.The trajectory of channel evolution and the role of riparian vegetation is examined in relation to undisturbed reaches in the system and an appreciation of the historical range of variability in geomorphic response. Analysis of the patterns of contemporary vegetation growth identify the potential to re‐establish vegetation where it is elevated from saline baseflow. However, the system is assessed as being close to a threshold where restoration is no longer possible and remediation options become more limited as eco‐hydraulic and hydrochemical changes continue. Copyright © 2011 John Wiley &amp; Sons, Ltd.

A continental shelf scale examination of the Leeuwin Current off Western Australia during the austral autumn–winter

A continental shelf scale survey from 22°S to 34°S along the Western Australia coast provides the first detailed synoptic examination of the structure, circulation and modification of the southward flowing Leeuwin Current (LC) during the late austral autumn–early winter (May–June 2007). At lower latitudes (22°S–25°S), the LC was masked within a broad expanse of warm ambient surface water, which extended across the shelf and offshore before becoming constrained at the shelf break and attaining its maximum velocity of ∼1.0 m s −1 at 28°S. The temperature and salinity signature of the LC experienced substantial modification as it flowed poleward; surface temperature of the LC decreased by ∼5.25 °C while surface salinity increased by ∼0.72, consistent with climatology estimates and smaller (larger) for temperature (salinity) than those found during summer. Subsequently, LC water was denser by ∼2 σ T in the south compared to the north, and the surface mixed layer of the LC revealed only a small deepening trend along its poleward trajectory. Modification of the LC resulted from a combination of mixing due to geostrophic inflow and entrainment of cooler, more saline surrounding subtropical waters, and convective mixing driven by large heat loss to the atmosphere. Air–sea heat fluxes accounted for 50% of the heat lost from the LC in the south, whilst only accounting for 25% in the north, where large geostrophic inflow occurred and the LC displayed its maximum flow. The onshore transport was characterised by distinct jet-like structures, enhanced in the upper 200 m of the water column, and the presence of eddies in the vicinity of the shelf break generated offshore transport.