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South‐west Australia has been identified as a global hotspot for the occurrence of meteotsunamis. In this study, a numerical hydrodynamic model (Regional Ocean Modelling System) was configured to investigate the generation of meteotsunamis through propagating thunderstorms. A range of simulations were performed using realistic and synthetic atmospheric forcing to establish the sensitivity of meteotsunami wave heights and waveforms along different parts of the coast to variations in the propagation speed and bandwidths of propagating pressure jumps associated with the thunderstorms. When a pressure jump propagated from the north and north‐west quadrants with a speed (U) of 8–15 ms−1, both the Proudman and Greenspan resonances were possible mechanisms for the generation of meteotsunamis. However, the response changed for different bandwidths of the propagating pressure jump and resulted in different meteotsunami waveforms at the coast. When U > 15 ms−1, long waves were amplified initially through shoaling at the shelf slope, with Proudman resonance enhancing the wave heights at corresponding resonant depths on the shelf, and then propagated as free waves on the continental shelf. The waves were further amplified at the coast through refraction and shoaling effects and resulted in an elevation wave at the coast. Numerical simulations also indicated that edge waves can also be excited near the coast when the incoming free wave wavelengths were equal to or half the edge wave wavelength. The study provides observational and numerical evidence to suggest that the bandwidth of propagating air pressure jumps plays a major role in meteotsunami generation and their waveforms. Plain Language Summary: The numerical simulation results show that meteotsunamis on the southwest Australian coast can be generated over a range of traveling pressure jump speeds and bandwidths, where Proudman resonance, Greenspan edge wave, refraction, and shoaling were responsible for the initial wave amplification. The simulations also revealed that resonance and shoaling amplification were determined by both the speed and bandwidth of the propagating pressure jumps. The pressure jump with constant translational speed can cause significantly different wave heights and waveform meteotsunami when the bandwidths were different. As the wave propagates southward with speeds of 15–28 ms−1, it undergoes subcritical, critical, and supercritical states over the shelf. The findings of this study provide preliminary guidelines for forecasting meteotsunamis generated by summer thunderstorms along the south‐west Australian coastline. Key Points: A range of moving atmospheric pressure jump speeds were conducive to meteotsunami generation on the southwest Australian coastProudman resonance, Greenspan edge waves, refraction, and shoaling were responsible for the generation and amplification of meteotsunamisThe resonance and shoaling amplification were influenced by both the speed of propagation and the bandwidths of the pressure jumps [ABSTRACT FROM AUTHOR]

Kelp forests may contribute substantially to ocean carbon sequestration, mainly through transporting kelp carbon away from the coast and into the deep sea. However, it is not clear if and how kelp detritus is transported across the continental shelf. Dense shelf water transport (DSWT) is associated with offshore flows along the seabed and provides an effective mechanism for cross-shelf transport. In this study, we determine how effective DSWT is in exporting kelp detritus beyond the continental shelf edge, by considering the transport of simulated sinking kelp detritus from a region of Australia's Great Southern Reef. We show that DSWT is the main mechanism that transports simulated kelp detritus past the continental shelf edge, and that export is negligible when DSWT does not occur. We find that 51% per year of simulated kelp detritus is transported past the continental shelf edge, or 17–29% when accounting for decomposition while in transit across the shelf. This is substantially more than initial global estimates. Because DSWT occurs in many mid-latitude locations around the world, where kelp forests are also most productive, export of kelp carbon from the coast could be considerably larger than initially expected. [ABSTRACT FROM AUTHOR]

Dynamics of ocean boundary currents and associated shelf processes can influence onshore and offshore water transport, critically impacting marine organisms that release long-lived pelagic larvae into the water column. The western rock lobster, Panulirus cygnus , endemic to Western Australia, is the basis of Australia's most valuable wild-caught commercial fishery. After hatching, western rock lobster larvae (phyllosoma) spend up to 11 months in offshore waters before ocean currents and their ability to swim transports them back to the coast. The abundance of western rock lobster post-larvae (puerulus) provides a puerulus index used by fishery managers as a predictor of lobster abundance 3–4 years later. This index has historically been positively correlated with the strength of the Leeuwin Current. In 2008 and 2009, the Leeuwin Current was strong, yet a settlement failure occurred throughout the fishery, prompting management changes and a rethinking of environmental factors associated with their settlement. Thus, understanding factors that may have been responsible for the settlement failure is essential for fishery management. Oceanographic parameters likely to influence puerulus settlement were derived for 17 years to investigate correlations. Analysis indicated that puerulus settlement at adjacent monitoring sites has similar oceanographic forcing, with kinetic energy in the offshore and the strength of the Leeuwin Current being key factors. Settlement failure years were synonymous with "hiatus" conditions in the southeast Indian Ocean and periods of sustained cooler water present offshore. Post-2009, there has been an unusual but consistent increase in the Leeuwin Current during the early summer months, with a matching decrease in the Capes Current, which may explain an observed settlement timing mismatch compared to historical data. Our study has revealed that a culmination of these conditions likely led to the recruitment failure and subsequent changes in puerulus settlement patterns. [ABSTRACT FROM AUTHOR]

Dynamics of ocean boundary currents and associated shelf processes can influence onshore/offshore transport of water, critically impacting marine organisms that release long-lived pelagic larvae into the water column. The western rock lobster, Panulirus cygnus, endemic to Western Australia, is the basis of Australia's most valuable wild-caught commercial fishery. After hatching, western rock lobster larvae (phyllosoma) spend up to 11 months in offshore waters before ocean currents and their ability to swim, transport them back to the coast. The abundance of western rock lobster puerulus (settlement phase post phyllosoma) has historically been observed to be positively correlated with the strength of the Leeuwin Current, and an index of puerulus numbers is used by fisheries managers as a predictor of subsequent lobster abundance 3-4 years later. In 2008 and 2009 the Leeuwin Current was strong, yet a settlement failure occurred throughout the fishery prompting management changes and a rethinking of environmental factors associated with their settlement. Thus, understanding factors that may have been responsible for the settlement failure is important for fisheries management. Oceanographic parameters likely to influence puerulus settlement were derived for a 17 year period to investigate correlations. Analysis indicated that puerulus settlement at adjacent monitoring sites have similar oceanographic forcing with kinetic energy in the offshore and the strength of the Leeuwin Current being key factors. Settlement failure years were synonymous with 'hiatus' conditions in the south-east Indian Ocean, and periods of sustained cooler water present offshore. Post 2009, there has been an unusual but consistent increase in the Leeuwin Current during the early summer months with a matching decrease in the Capes Current, that may explain an observed settlement timing mismatch compared to historical data. Our study has revealed that a culmination of these conditions likely led to the recruitment failure and subsequent changes in puerulus settlement patterns. [ABSTRACT FROM AUTHOR]

A multi-year ocean glider dataset, obtained along a representative cross-shelf transect along the Rottnest continental shelf, south-west Australia, was used to characterise the seasonal and inter-annual variability of water column properties (temperature, salinity, and chlorophyll fluorescence distribution). All three variables showed distinct seasonal and inter-annual variations that were related to local and basin-scale ocean atmosphere processes. Controlling influences for the variability were attributed to forcing from two spatial scales: (1) the local scale (due to Leeuwin Current and dense shelf water cascades, DSWC) and (2) the basin scale (El Niño–Southern Oscillation, ENSO, events). In spring and summer, inner-shelf waters were well mixed due to strong wind mixing, and deeper waters (>50 m) were vertically stratified in temperature that contributed to the presence of a subsurface chlorophyll maximum (SCM). On the inner shelf, chlorophyll fluorescence concentrations were highest in autumn and winter. DSWCs were also the main physical feature during autumn and winter. Chlorophyll fluorescence concentration was higher closer to the seabed than at the surface in spring, summer, and autumn. The seasonal patterns coincided with changes in the wind field (weaker winds in autumn) and air–sea fluxes (winter cooling and summer evaporation). Inter-annual variation was associated with ENSO events. Lower temperatures, higher salinity, and higher chlorophyll fluorescence (>1 mg m -3) were associated with the El Niño event in 2010. During the strong La Niña event in 2011, temperatures increased and salinity and chlorophyll fluorescence decreased (<1 mg m -3). It is concluded that the observed seasonal and inter-annual variabilities in chlorophyll fluorescence concentrations were related to the changes in physical forcing (wind forcing, Leeuwin Current, and air–sea heat and moisture fluxes). [ABSTRACT FROM AUTHOR]

A multiyear, ocean glider dataset, obtained along a representative cross-shelf transect along the Rottnest continental shelf, south-west Australia, was used to characterise the seasonal and inter-annual variability of water column properties (temperature, salinity, and chlorophyll fluorescence distribution). All three variables showed distinct seasonal and inter-annual variations. Local and basin-scale ocean-atmosphere processes also affected the spatial distributions of the water column properties. The controlling influences for the variability were derived from (a) at the local scale, the Leeuwin Current and dense shelf water cascades (DSWC); and, (2) at the basin scale, the El Niño Southern Oscillation (ENSO). In spring and summer, shallow waters were well mixed due to strong wind mixing and the deeper waters (> 50 m) were vertically stratified in temperature that contributed to the formation of a subsurface chlorophyll maximum (SCM). With the onset of storms in late autumn, the water column was well mixed with the SCM absent. On the inner shelf, chlorophyll fluorescence concentrations were highest in autumn and winter; DSWCs were also the main physical feature during autumn and winter. Chlorophyll fluorescence concentration was higher closer to the sea bed than at the surface in spring, summer, and autumn. The seasonal patterns coincided with changes in the wind field (weaker winds in autumn) and air-sea fluxes (winter cooling and summer evaporation). Inter-annual variation was associated with ENSO events. Lower temperatures, higher salinity, and higher chlorophyll fluorescence (> 1 mg m-3) were associated with the El Niño event in 2010. During the strong La Niña event in 2011, temperatures increased (a marine heat wave), and salinity and chlorophyll fluorescence decreased (< 1 mg m-3). These changes were mainly associated with changed to the strength of the Leeuwin current. Over subsequent years, the temperatures gradually decreased, the salinity increased, and the chlorophyll fluorescence continued to decrease (< 0.25 mg m-3). These changes were mainly associated with an increase in the strength of the Leeuwin current that transported warmer, lower salinity, low nutrient water into the region. In the autumn of 2014, the chlorophyll fluorescence increased (> 1 mg m-3). It is concluded that the observed seasonal and inter-annual variability in chlorophyll fluorescence concentrations were related to the changes in physical forcing (wind forcing, Leeuwin Current and air-sea fluxes). [ABSTRACT FROM AUTHOR]

Bahmanpour, M.H.; Pattiaratchi, C., Wijeratne, E.M.S., Steinberg, C., and D'Adamo, N., 2016. Multi-year observation of a boundary current along the shelf edge of North Western Australia. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 517-521. Coconut Creek (Florida), ISSN 0749-0208. Analysis of multi-year current meter data across North West shelf of Australia identified various aspects of the mean flow in a macro-tidal environment. Main features of the flow appear to be a continuous alongshore south-westward flow, i.e., Holloway current located along the continental shelf edge in depth 100-200 m. Annually, the current transports ∼ 1 Sv of lower salinity, higher temperature water from the tropical regions to North West Cape. The Holloway current is at its maximum intensity (up to 2 Sv) during autumn/winter (Apr-Jul) when the winds are either weak or the region is dominated by south-east trade winds. Unlike alongshore flow, cross-shore structure of the flow is fairly complex and shows variations with depth and season. A new mechanism is proposed to justify the observed intensification of the flow in austral autumn that is closely related to the seasonal cycle of sea level around Australia. Each year, due to the monsoon cycles there is a high sea level anomaly that peaks in February in the Gulf of Carpentaria in the upstream side of the Holloway current that manifests itself as southward progressive high sea level anomalies in the following months along the West Australian coastline. Observed onshore fluxes can also have some implications for the strength of the Holloway current. [ABSTRACT FROM AUTHOR]

Mahjabin, T.; Pattiaratchi, C., and Hetzel, Y., 2016. Factors influencing the occurrence of Dense Shelf Water Cascades in Australia. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 527-531. Coconut Creek (Florida), ISSN 0749-0208. Transport of inshore waters and suspended material off the continental shelf by Dense Shelf Water Cascades (DSWC) has important ecological and biogeochemical implications in Australian waters. Because of high rates of evaporation, denser saline water occurs in the shallow coastal regions around Australia, setting up horizontal density gradients that can drive DSWC. Ocean glider data available from the Integrated Marine Observing System (IMOS), which is operated by the Australian National Facility for Ocean Gliders (ANFOG) located at the University of Western Australia, were used to measure cross-shelf density profiles under varying wind and tide conditions for seven contrasting regions around the entire continent. Overall 97 sets of spatial and temporal resolution data from year 2008 to 2015 collected by the ocean gliders and analysed with a subset presented here. Data from 19 transects covering the years 2012 to 2015 for the Pilbara region of Western Australia, indicated that cascades occur during the autumn and winter due to cooling of the coastal waters which already have higher salinity due to evaporation during the summer months. The cross-shelf density gradient in this continental shelf was found to be maximum in July with a value of 14.23×10−6 kg m−4. [ABSTRACT FROM AUTHOR]

Understanding of measured and predicted waves has an impact on wave energy extraction, efficiency and economics and is therefore a focus for optimisation of Carnegie Wave Energy’s CETO technology. Improvements in weather prediction have enabled the generation of updated wave hindcasts by the National Oceanic and Atmospheric Administration (NOAA) and the Centre for Australian Weather and Climate Research (CAWCR). These were validated for Garden Island, Rottnest Island and Cape Naturaliste in south-west Australia for March to December 2009. The CAWCR data set provides a more extensive list of wave parameters as opposed to three-hourly major wave parameter sets (significant wave height (Hs), peak period (Tp) and peak direction (Dp)) provided by NOAA, and overall performed better. The CAWCR hindcast will form the underpinning data for the Australian Wave Energy Atlas Project, a CSIRO and Bureau of Meteorology project in which Carnegie is a collaborator. [ABSTRACT FROM PUBLISHER]

The incidence of major storm surges in the last decade have dramatically emphasized the immense destructive capabilities of extreme water level events, particularly when driven by severe tropical cyclones. Given this risk, it is vitally important that the exceedance probabilities of extreme water levels are accurately evaluated to inform risk-based flood and erosion management, engineering and for future land-use planning and to ensure the risk of catastrophic structural failures due to under-design or expensive wastes due to over-design are minimised. Australia has a long history of coastal flooding from tropical cyclones. Using a novel integration of two modeling techniques, this paper provides the first estimates of present day extreme water level exceedance probabilities around the whole coastline of Australia, and the first estimates that combine the influence of astronomical tides, storm surges generated by both extra-tropical and tropical cyclones, and seasonal and inter-annual variations in mean sea level. Initially, an analysis of tide gauge records has been used to assess the characteristics of tropical cyclone-induced surges around Australia. However, given the dearth (temporal and spatial) of information around much of the coastline, and therefore the inability of these gauge records to adequately describe the regional climatology, an observationally based stochastic tropical cyclone model has been developed to synthetically extend the tropical cyclone record to 10,000 years. Wind and pressure fields derived for these synthetically generated events have then been used to drive a hydrodynamic model of the Australian continental shelf region with annual maximum water levels extracted to estimate exceedance probabilities around the coastline. To validate this methodology, selected historic storm surge events have been simulated and resultant storm surges compared with gauge records. Tropical cyclone induced exceedance probabilities have been combined with estimates derived from a 61-year water level hindcast described in a companion paper to give a single estimate of present day extreme water level probabilities around the whole coastline of Australia. Results of this work are freely available to coastal engineers, managers and researchers via a web-based tool (). The described methodology could be applied to other regions of the world, like the US east coast, that are subject to both extra-tropical and tropical cyclones. [ABSTRACT FROM AUTHOR]

The occurrence of extreme water levels along low-lying, highly populated and/or developed coastlines can lead to considerable loss of life and billions of dollars of damage to coastal infrastructure. Therefore it is vitally important that the exceedance probabilities of extreme water levels are accurately evaluated to inform risk-based flood management, engineering and future land-use planning. This ensures the risk of catastrophic structural failures due to under-design or expensive wastes due to over-design are minimised. This paper estimates for the first time present day extreme water level exceedence probabilities around the whole coastline of Australia. A high-resolution depth averaged hydrodynamic model has been configured for the Australian continental shelf region and has been forced with tidal levels from a global tidal model and meteorological fields from a global reanalysis to generate a 61-year hindcast of water levels. Output from this model has been successfully validated against measurements from 30 tide gauge sites. At each numeric coastal grid point, extreme value distributions have been fitted to the derived time series of annual maxima and the several largest water levels each year to estimate exceedence probabilities. This provides a reliable estimate of water level probabilities around southern Australia; a region mainly impacted by extra-tropical cyclones. However, as the meteorological forcing used only weakly includes the effects of tropical cyclones, extreme water level probabilities are underestimated around the western, northern and north-eastern Australian coastline. In a companion paper we build on the work presented here and more accurately include tropical cyclone-induced surges in the estimation of extreme water level. The multi-decadal hindcast generated here has been used primarily to estimate extreme water level exceedance probabilities but could be used more widely in the future for a variety of other research and practical applications. [ABSTRACT FROM AUTHOR]

Plastics represent the vast majority of human-made debris present in the oceans. However, their characteristics, accumulation zones, and transport pathways remain poorly assessed. We characterised and estimated the concentration of marine plastics in waters around Australia using surface net tows, and inferred their potential pathways using particle-tracking models and real drifter trajectories. The 839 marine plastics recorded were predominantly small fragments (“microplastics”, median length = 2.8 mm, mean length = 4.9 mm) resulting from the breakdown of larger objects made of polyethylene and polypropylene (e.g. packaging and fishing items). Mean sea surface plastic concentration was 4256.4 pieces km−2, and after incorporating the effect of vertical wind mixing, this value increased to 8966.3 pieces km−2. These plastics appear to be associated with a wide range of ocean currents that connect the sampled sites to their international and domestic sources, including populated areas of Australia's east coast. This study shows that plastic contamination levels in surface waters of Australia are similar to those in the Caribbean Sea and Gulf of Maine, but considerably lower than those found in the subtropical gyres and Mediterranean Sea. Microplastics such as the ones described here have the potential to affect organisms ranging from megafauna to small fish and zooplankton. [ABSTRACT FROM AUTHOR]

Abstract: Tropical cyclones (termed hurricanes and typhoons in other regions), are extreme events associated with strong winds, torrential rain and storm surges (in coastal areas) and cause extensive damage as a result of strong winds and flooding (caused by either heavy rainfall or ocean storm surges) in the immediate area of impact. The eastern Indian Ocean, particularly in the northwest region of Australia, is impacted by up to 10 tropical cyclones during the cyclone season, although direct impact of cyclones along the west and southwest coastlines is rare. However, the sub-tidal frequency component of sea level records along the west and south coasts of Western Australia indicates lagged correspondence with the occurrence of tropical cyclones. It is demonstrated that the tropical cyclones generate a continental shelf wave which travels along the west and south coasts of Australia up to 3500km with speeds of 450–500kmday−1 (5.2–5.8ms−1) with maximum trough to crest wave height of 0.63m, comparable with the mean daily tidal range in the region. The shelf wave is identified in the coastal sea level records, initially as a decrease in water level, 1–2 days after the passage of the cyclone and has a period of influence up to 10 days. Amplitude of the shelf wave was strongly affected by the path of the tropical cyclone, with cyclones travelling parallel to the west coast typically producing the most significant signal due to resonance and superposition with local forcing. Analysis of water levels from Port Hedland, Geraldton, Fremantle and Albany together with cyclone paths over a ten year period (1988–1998) indicated that the tropical cyclones paths may be classified into 6 different types based on the amplitude of the wave. [ABSTRACT FROM AUTHOR]

Abstract: Surf zone drifters and a current meter were used to study the nearshore circulation patterns in the lee of groynes at Cottesloe Beach and City Beach in Western Australia. The circulation patterns revealed that a persistent re-circulation cell was present in the lee of the groyne which was driven by changes in wave set-up resulting from lower wave heights in the lee of the groyne. The re-circulation consisted of a longshore current directed towards the groyne which was deflected offshore due to groyne resulting in a rip current along the groyne face. The offshore-flowing rip current and the incoming waves converged at the offshore extent of this circulation cell, with the deflection of the rip current parallel to the shoreline and then completing the recirculation through an onshore component. The Eulerian measurements revealed that 55% of the currents on the lee side of the groyne were directed offshore and that these currents had a maximum speed of 2ms−1. Spectral analysis of the wave heights and the currents revealed several corresponding peaks in the measured spectral densities with timescales between 12s and 50min. Numerical simulations of an idealised beach with a shore-normal groyne were conducted using a circulation model driven by waves, and confirmed the formation of a persistent eddy in the lee of the groyne. Sensitivity studies indicated that the incident wave angle, wave period, and especially the wave height controlled the circulation. The eddy vorticity, a measure of an eddy''s strength, increased roughly proportional to an increase in the incident wave energy flux. [Copyright &y& Elsevier]

Tide gauge data collected from Sri Lanka (three stations) and Western Australia (eleven stations) during the Indian Ocean tsunamis, which occurred in December 2004, March 2005, July 2006, and September 2007, and incorporated five tsunamis, were examined to determine tsunami behaviour during these events. During the December 2004 tsunami, maximum wave heights of 3.87 m and 1.75 m were recorded at Colombo (Sri Lanka) and Bunbury (Western Australia), respectively. The results indicated that although the relative magnitudes of the tsunamis varied, the tsunami behaviour at each station was similar. This was due to the effect of the local and regional topography. At all tide gauges, the spectral energy corresponding to periods between 20 and 85 minutes increased during the tsunami. The sea-level data obtained from the west and south coasts of Sri Lanka (Colombo and Kirinda) indicated the importance of wave reflections from the Maldives Island chain, which produced the maximum wave two to three hours after the arrival of the first wave. In contrast, Trincomalee on the east coast did not show evidence of a reflected wave. Similarly, along the west coast of Australia, the highest waves occurred 15 hours after the arrival of the first wave. Here, based on travel times, we postulated that the waves were reflected from the Mascarene Ridge and/or the Island of Madagascar. Reflected waves were not present in the 2006 tsunami, where the primary waves propagated away from topographic features. One of the main influences of the tsunami was to set up oscillations at the local resonance frequency. Because Sri Lanka and Western Australia have relatively straight coastlines, these oscillations were related to the fundamental period of the shelf oscillation. For Colombo, this corresponded to 75-minute period, whereas in Geraldton and Busselton (Australia), the four-hour period was most prominent; at Jurien Bay and Fremantle, the resonance period was 2.7 hours. [ABSTRACT FROM AUTHOR]

Abstract: Conceptual models of circulation theorise that the dominant forces controlling estuarine circulation are freshwater discharge from the riverine section (landward), tidal forcing from the ocean boundary, and gravitational circulation resulting from along-estuary gradients in density. In micro-tidal estuaries, sub-tidal water level changes (classified as those with periods between 3 and 10 days) with amplitudes comparable to the spring tidal range can significantly influence the circulation and distribution of water properties. Field measurements obtained from the Swan River Estuary, a diurnal, micro-tidal estuary in south-western Australia, indicated that sub-tidal water level changes at the ocean boundary were predominantly from remotely forced continental shelf waves (CSWs). The sub-tidal water levels had maximum amplitudes of 0.8m, were comparable to the maximum tidal range of 0.6m, propagated into the estuary to its tidal limit, and modified water levels in the whole estuary over several days. These oscillations dominated the circulation and distribution of water properties in the estuary through changing the salt wedge location and increasing the bottom water salinity by 7 units over 3 days. The observed salt wedge excursion forced by CSW was up to 5km, whereas the maximum tidal excursion was 1.2km. The response of the residual currents and the salinity distribution lagged behind the water level changes by ∼24h. It was proposed that the sub-tidal forcing at the ocean boundary, which changed the circulation, salinity, and dissolved oxygen in the upper estuary, was due to a combination of two processes: (1) a gravity current generated by a process similar to a lock exchange mechanism and (2) amplified along-estuary density gradients in the upper estuary, which enhanced the gravitational circulation in the estuary. The salt intrusions under the sub-tidal forcing caused the rapid movement of anoxic water upstream, with significant implications for water quality and estuarine health. [Copyright &y& Elsevier]

Linear sandbanks are located globally in areas where there are strong currents and an abundance of sand. In the recent years, these sandbanks have become of strategic interest as a potential source of marine aggregates (sand and gravel) and mineral deposits. They form the seaward boundary of the nearshore zone and therefore are important for the stability of the coastal system. They also commonly reach the sea surface and thus pose a threat to navigation. Headland-associated linear sandbanks are a specific type of sandbanks which are located in the lee of coastal topographic features such as headlands and islands. Interaction between tidal currents and topographic features generate complex three-dimensional circulation patterns that significantly influence the distribution of sediments in the vicinity of the feature. Field and numerical model investigations of the three-dimensional flow structure have been undertaken on the Levillain Shoal, a headland-associated linear sandbank present in the lee of Cape Levillain (Shark Bay, Western Australia). The field data indicated the presence of secondary flows near the tip of the cape and around the bank which were re-produced in the numerical simulations. Numerical results have shown that residual eddies are not representative of the sediment transport and that secondary currents enhance the convergence of sediment towards the sandbank. Maintenance processes have been investigated. Sediment transport paths near the cape and the bank indicate that the sandbank is part of a sand circulation cell where the sand is circulating around the bank with exchanges between the sandbank and the headland. [ABSTRACT FROM AUTHOR]

Abstract: Shark Bay is a large inverse estuary on the west coast of Australia. Analytical and numerical approaches were used to predict the locations and causes of fronts in Shark Bay, and the results were compared with Sea Surface Temperature and field data. The study first applies an analytical theory, widely used in studies of traditional estuaries, to predict the location of fronts, and then applies a 3-D, baroclinic hydrodynamic model to analyze advection of temperature and salinity, and their ultimate influence on density fronts within the Bay. Analytical theory defines a front as a transitional region between mixed and stratified conditions, and it postulates that the location of fronts may be predicted through the balance of stratifying and de-stratifying energy input to the water column, ‘the stratification parameter’. In Shark Bay, fronts are predicted where the stratification parameter, S =3.0. Furthermore, the distribution of the mean tidal velocity magnitude was determined to correlate to regions of high bathymetric gradients, showing that changes in water depth influence the local tidal currents, the value of the stratification parameter and by extension, the location of the fronts. However, calculation of the balance of all major energy inputs reveals a balance between evaporation-driven gravitational flow and tidal mixing in Shark Bay. A numerical model was then used to investigate the hydrodynamic processes contributing to frontal dynamics in Shark Bay. Predicted residual velocities revealed a two-layer flow regime and temperature and salinity simulations accurately reproduced the major frontal features observed at the entrances of the Bay using only tidal forcing and gravitational circulation. However, it was found that wind forcing clearly influenced the distribution of salinity, defining the shape of the major frontal feature inside the Bay. [Copyright &y& Elsevier]

Estimates of extreme sea levels have mainly been derived using atmospheric and tidal forcing only, but surface gravity waves are a key process that can cause a substantial elevation of mean sea level at the coast. In this paper a coupled wave-circulation model was used to simulate storm surge and wave setup across a broad range of coastal topographies and storm types around Australia. The main aim was a practical assessment of the benefits and limitations of using a coupled wave-surge model to determine wave effects for extreme sea level studies on the continental scale. The simulations included: tropical cyclones Yasi (2011) and George (2007) on the northeast and northwest coasts of Australia; Cyclone Alby (1978) that underwent extratropical transition in southwest Australia; and a large extratropical winter storm in the Southern Ocean (2016). Predicted wave setup was highly variable both spatially and temporally, with values up to 0.45 m, 35% of maximum storm surge height, and 9% of incident significant wave heights. In general, where storm surge heights were smaller, the relative importance of wave setup increased in the presence of large waves. The model best resolved wave setup in shallow gently sloping coastal areas, whilst unrealistically low values were predicted for steep coastlines. Predictions improved when wave setup was included for most sites and events, however, these wave effects were often secondary to other assumptions implicit in modeling extreme events. This was especially true for tropical cyclones where reliable wind forcing was not available. The results showed similar contributions from wave setup to other studies but highlighted the high temporal and spatial variability of wave setup across a wider variety of storms and coastal morphologies. The results also revealed that the maximum wave setup did not always coincide with the maximum storm surge. Overall, the coupled wave-surge model presented a useful tool to predict extreme water levels including wave setup when accurate depth and atmospheric data are available, however, significant challenges still exist to model this process at the continental scale. [Display omitted] • Continental scale coupled wave storm surge model was applied to examine extreme events around Australia. • Maximum wave setup preceded arrival of slow-moving storms and co-occurred with fast-moving storms. • Predicted wave setup contributed up to 35% of total storm surge. [ABSTRACT FROM AUTHOR]

The land–sea breeze (LSB) system, driven by the thermal contrast between the land and the adjacent ocean is a widely known atmospheric phenomenon, which occurs in coastal regions globally. South-west Australia experiences a persistent and one of the strongest LSB systems globally with maximum wind speeds associated with the LSB system often exceeding 15 ms−1. In this paper, using field measurements and numerical simulations, we examine: (1) the local winds associated with the land–sea breeze with an emphasis on the ocean; and, (2) the response of the surface currents to the diurnal wind forcing. The measurements indicated that the wind speeds decreased between midnight and 0400 and increased rapidly after 1100, reaching maxima >10 ms−1 around 1800) associated with the sea breeze and decreased to midnight. Wind directions were such that they were blowing from south-east (120°) in the morning and changed to almost southerly (~200°) in the afternoon. Decomposition of the wind record to the diurnal and synoptic components indicated that the diurnal component of winds (i.e., LSB) was oriented along the south-west to north-east axis. However, the stronger synoptic winds were from the south-east to south quadrant and in combination with the LSB, the winds consisted of a strong southerly component. We examined the evolution, horizontal extent, and propagation properties of sea breeze fronts for characteristic LSB cycles and the sea breeze cell propagating offshore and inland. The results indicated that the sea breeze cell was initiated in the morning in a small area, close to 33° S, 115.5° E, with a width of ~25 km and expanded onshore, offshore and alongshore. The sea breeze cell expanded faster (30 kmh−1) and farther (120 km) in the offshore direction than in the onshore direction (10 kmh−1 and 30–40 km). Winds during the LSB cycle followed a counterclockwise rotation that was also reflected in the surface currents. The winds and surface currents rotated anticlockwise with the surface currents responding almost instantaneously to changes in wind forcing but were modified by topography. The diurnal surface currents were enhanced due to the resonance between the LSB forcing and the inertial response. [ABSTRACT FROM AUTHOR]

Evaporation and cooling during autumn and winter in south-western Australia results in denser water near the coast and a cross-shelf density gradient. These conditions drive a gravitational circulation, with offshore transport of higher density water along the seabed, defined as dense shelf water cascades (DSWCs). A field experiment with data collected from multiple platforms is described to identify the temporal variability and controlling mechanisms of DSWCs during the austral autumn and winter (May–June 2015) when DSWCs were most prevalent. Data analysis confirmed that both the wind intensity and direction were critical parameters to: (1) inhibit DSWC formation through vertical mixing; and, (2) enhance DSWCs, depending on the wind direction. An intense and persistent DSWC was initiated through the passage of a winter cold front with strong onshore winds. Here, onshore winds caused downwelling, resulting in onshore movement of surface water and offshore movement in the bottom layer, enhancing the cross-shelf density gradient and the cascade. Vertical mixing of the water column and shutdown of the DSWC occurred when the winds were strong and had an offshore component or were upwelling-favourable, which resulted in the advection of higher density water offshore at the surface and vertical mixing. • Density gradient is negative and DSWC is present during low wind • Onshore wind enhances density gradient and drives a strong DSWC • Offshore wind with cold front leads to vertically mixed water column • Eddy viscosity values 1 to 17 x10-5 m2s-1 for vertically stratified cases (DSWC) • Eddy viscosity values 33 to 90 x10-5 m2s-1 for vertically mixed conditions [ABSTRACT FROM AUTHOR]

Along the majority of Australian shallow coastal regions, summer evaporation increases the salinity of shallow waters, and subsequently in autumn/winter, the nearshore waters become cooler due to heat loss. This results in the formation of horizontal density gradients with density increasing toward the coast that generates gravity currents known as dense shelf water cascades (DSWCs) flowing offshore along the sea bed. DSWCs play important role in ecological and biogeochemical processes in Australian waters through the transport of dissolved and suspended materials offshore. In this study a numerical ocean circulation model of Rottnest continental shelf, validated using simultaneous ocean glider and mooring data, indicated that the passage of cold fronts associated with winter storms resulted in rapid heat loss through evaporative cooling. These conditions resulted in enhancement of the DSWCs due to modifications of the cross-shelf density gradient and wind effects. Specifically, onshore (offshore) directed winds resulted in an enhancement (inhibition) of DSWCs due to downwelling (vertical mixing). Consequently, the largest DSWC events occurred during the cold fronts when atmospheric temperatures reinforced density gradients and onshore winds promoted downwelling that enhanced DSWCs. Advection of DSWCs was also strongly influenced by the wind conditions, with significantly more transport occurring along-shelf compared to cross-shelf. [ABSTRACT FROM AUTHOR]

Abstract: The Regional Ocean Modelling System (ROMS v2.1) was used to investigate the physical processes that sustained the mesoscale eddy fields. The model was able to mimic the spatial, temporal, and migratory scales of the Leeuwin Current (LC) System''s mean flow and eddying characteristics. Importantly, eddy generation sites were consistent with those reported previously observed from satellite imagery, and two main regions were identified: site 1, adjacent to the Abrolhos Islands’ western edge (latitude 29°S); and site 2, adjacent to the shelf break (latitude 27.8°S). The description of the eddying dynamics suggested the eddy field evolution followed a similar pathway at both sites. An offshore flow impinged on the continental shelf and was redirected southward, intensifying the LC''s southward alongshore flow on the shelf. This southward redirection formed a current loop, which closed and formed a distinct clockwise eddy. The eddy remained near stationary and attached to the bottom topography, but it redirected LC and continental shelf waters offshore to dominate the local dynamics. The resulting offshore meander grew laterally, shallowed, and closed to form an anticlockwise eddy to the original clockwise eddy''s south, forming a characteristic LC eddy pair (dipole). The model demonstrated that the LC and Leeuwin Undercurrent coupling played an important role in the onset of eddies at both sites. An energy diagnostic scheme was used, and the dominant instability process linked to the developing anticlockwise eddy at site 1 was mixed mode barotropic and baroclinic instability. The baroclinic instability source was the available potential energy stored within the mean lateral density gradient between the eddy dipole. The LC''s meandering southward flow interacting with the undercurrent''s northward subsurface flow generated horizontal shear, which was the source of barotropic instability. The dominant instability process at site 2 was baroclinic in origin. At both sites, the baroclinic mechanism followed a series of phases coinciding with the physical description of the evolving eddies. [Copyright &y& Elsevier]

• The first expedition to the depths of the Southern Ocean facing Bremer canyon systems. • First ROV images of these unique deep-sea environments and inhabitants (180 to 3300 m) • Discovery of spectacular 'animal forests' in the Bremer and Hood canyons. • Scleractinian corals found well below the aragonite saturation horizon (>1000 m) • Major fossil coral deposits occur at all three study areas, especially Mount Gabi. Here we present the outcomes of the first deep-sea remotely operated vehicle study of previously unexplored submarine canyon systems along the southwest Australian continental margin. This was conducted around: (1) the Bremer Marine Park; (2) the Mount Gabi seamount and nearby slope-shelf margin at the interface of the Southern and Indian oceans; with new information from (3) the Perth Canyon Marine Park located in the SE Indian Ocean. These canyons differ from many explored around the world in having no connectivity to continental river systems, thus little detrital input, with the Bremer systems and Mount Gabi facing the Southern Ocean which plays a key role in the global ocean circulation and climate systems. Such studies in the vast deep waters around the Australian continent are rare given the lack of local ROV capability available for research, thus little is known about these environments. Using the resources of the Schmidt Ocean Institute, we characterised the submarine topography from high-resolution bathymetric mapping, geology, physical and chemical oceanography, and provide an overview of these environments including the fauna observed and collected. We show that these Southern Ocean-influenced environments incorporate South Indian Central Water, Subantarctic Mode Water, Antarctic Intermediate Water, and Upper and Lower Circumpolar Deep Water, with Antarctic Bottom Water present in deep water just south of the Bremer canyon systems. The richness in megabenthos, especially along the steep, rocky substrates of the canyon heads and walls around the Bremer canyon systems, contrasts to the comparatively depauperate fauna of the more northerly Perth Canyon. Various corals serve as important substrates for a range of other species and often exhibit particular faunal associations. Especially notable are distinct ecological zones including a bryozoan and sponge-dominated (animal) forest on the shelf edge, spectacular coral gardens along canyon margins, and the occurrence of solitary scleractinians well below the aragonite saturation horizon. Subfossil coral deposits were discovered across all three study areas, reflecting periodic waxing and waning of deep-water Scleractinia throughout this southwest region. Extensive pre-modern assemblages at Mount Gabi contrast markedly with the sparse populations of living species and suggest that it might have once been a major coral hotspot, or whether they reflect long-term coral aggregations is yet to be determined. Nevertheless, stark differences in both living and past coral distribution patterns across our study sites point to at least localised fluctuations in Southern Ocean-derived nutrient and/or oxygen supplies to these deep-sea communities. [ABSTRACT FROM AUTHOR]

Coastal setbacks are used to protect populations and infrastructure, and involve determining baselines and historic trends in shoreline movements. Assessing these movements can be difficult on coasts with especially complex geomorphology, such as due to rock and coral reefs. Reefs are often assumed to provide coastal protection and stability. However, little is known about the spatial variability of beach dynamics on beaches with reefs, over inter-annual and decadal time-scales. Spatial variability in inter-annual vegetation line and shoreline stability was assessed on three adjacent beaches at Yanchep, southwestern Australia, using 34 years (1974–2008) of aerial photographs. Over 96% of the study area, beach width narrowed over the 34 years. This trend was statistically significant on 83% of the middle beach, 43% of the northern beach, and only 29% of the southern beach. The maximum mean annual change in beach width was 1.7 m yr. − 1 at the south end of the southern beach, the first mode of the Empirical Orthogonal Function (EOF) explained 45% of the variability alongshore, and correlated significantly (p < 0.05) with the 90th percentile of annual wave height and annual mean sea level. Beach rotation and reef-controlled currents resulted in cellular beach morphodynamics, and vegetation line and shoreline movements varied greatly alongshore. On one occasion, the beach widened by more than 50 m inter-annually while other areas eroded by 50 m. The southern beach that was fronted by the most continuous and highest (supratidal) section of reef was the most temporally variable. Even the vegetation line here moved by up to 20 m inter-annually, so cannot be assumed to be a ‘stable’ baseline for setback. The impact of reefs on inter-annual shoreline and vegetation line stability should be considered in future guidelines for determining coastal setback. [ABSTRACT FROM AUTHOR]

Millimeter-sized plastics are abundant in most marine surface waters, and known to carry fouling organisms that potentially play key roles in the fate and ecological impacts of plastic pollution. In this study we used scanning electron microscopy to characterize biodiversity of organisms on the surface of 68 small floating plastics (length range = 1.7-24.3 mm, median = 3.2 mm) from Australia-wide coastal and oceanic, tropical to temperate sample collections. Diatoms were the most diverse group of plastic colonizers, represented by 14 genera. We also recorded 'epiplastic' coccolithophores (7 genera), bryozoans, barnacles (Lepas spp.), a dinoflagellate (Ceratium), an isopod (Asellota), a marine worm, marine insect eggs (Halobates sp.), as well as rounded, elongated, and spiral cells putatively identified as bacteria, cyanobacteria, and fungi. Furthermore, we observed a variety of plastic surface microtextures, including pits and grooves conforming to the shape of microorganisms, suggesting that biota may play an important role in plastic degradation. This study highlights how anthropogenic millimeter-sized polymers have created a new pelagic habitat for microorganisms and invertebrates. The ecological ramifications of this phenomenon for marine organism dispersal, ocean productivity, and biotransfer of plastic-associated pollutants, remains to be elucidated.