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We examine baseline water properties and bottom water patterns in hadal trench environments across the Southern Ocean, Indian Ocean, and western Pacific. Significant differences are identified in the South Fiji Basin and surrounding the Philippine Sea, primarily due to the movement of cold Lower Circumpolar Deep Water along topographic features, highlighting the importance of a trench's geospatial position. We present the first hydrographic profiles in the Java Trench, warranting further research. Salinity increases with increasing depth for profiles over 10 000 dbar, with potential causes including instrumentation error, internal mixing, and saline pore water expulsion. These hadopelagic variations are crucial for assessing climate change impacts, especially regarding Antarctic Bottom Water. The study underscores the importance of incorporating these adiabatic conditions to gain insights into ecological biodiversity, alongside the indispensable baseline conditions presented, which are crucial for future oceanographic research across multiple disciplines. [ABSTRACT FROM AUTHOR]

We examine baseline water properties and bottom water patterns in hadal trench environments across the Southern Ocean, Indian Ocean, and Western Pacific. Significant differences are identified in the South Fiji Basin and surrounding the Philippine Sea, primarily due to the movement of cold Lower Circumpolar Deep Water along topographic features, highlighting the importance of a trench's geospatial position. We present the first hydrographic profiles in the Java Trench, warranting further research. Increases in salinity patterns in depths over 10,000 dbar are investigated, with potential causes including instrumentation error, internal mixing, and saline pore water expulsion. These hadopelagic variations are crucial for assessing climate change impacts, especially regarding Antarctic Bottom Water. The study underscores the importance of incorporating these adiabatic conditions for insights into ecological biodiversity, alongside the baseline conditions presented being indispensable for future oceanographic research across multiple disciplines. [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]

Plastic debris is the most common and exponentially increasing human pollutant in the world's ocean. The distribution and impact of plastic in the Pacific and Atlantic oceans have been the subject of many publications but not so the Indian Ocean (IO). Some of the IO rim countries have the highest population densities globally and mismanagement of plastic waste is of concern in many of these rim states. Some of the most plastic-polluted rivers empty into the IO, with all this suggesting that the IO receives a tremendous amount of plastic debris each year. However, the concentration, distribution, and impacts of plastics in the IO are poorly understood as the region is under-sampled compared to other oceans. In this review, we discuss sources and sinks, which are specific to the IO. We also discuss unique atmospheric, oceanographic, and topographic features of the IO that control plastic distribution, such as reversing wind directions due to the monsoon, fronts, and upwelling regions. We identify hotspots of possible plastic accumulation in the IO, which differ between the two hemispheres. In the southern IO, plastics accumulate in a garbage patch in the subtropical gyre. However, this garbage patch is not well defined, and plastics may leak into the southern Atlantic or the Pacific Ocean. There is no subtropical gyre and associated garbage in the northern IO due to the presence of landmasses. Instead, the majority of buoyant plastics most likely end up on coastlines. Finally, we identify the vast knowledge gaps concerning plastics in the IO and point to the most pressing topics for future investigation. [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]

Plastic debris are the most common and exponentially increasing human pollutant in the world's oceans. The distribution and impact of plastics in the Pacific and Atlantic Oceans have been the subject of many studies but not so for the Indian Ocean (IO). Some of the IO rim countries have the highest population densities in the world and mis-management of plastic waste is of concern in many of these IO rim states. Some of the highest plastic-polluted rivers end up in the IO with all this suggesting that the IO receives a tremendous amount of plastic debris each year. However, the concentration, distribution and impacts of plastics in the IO are poorly understood as the region is under-sampled compared to other oceans. In this review, we discuss sources and sinks, which are specific for the IO as well as unique atmospheric, oceanographic and topographic features of the IO such as reversing wind directions due to the monsoon, fronts and upwelling regions that control plastic distribution. We identified hotspots of possible plastic accumulation in the IO, which were different in the two hemispheres. In the northern Indian Ocean, the majority of the plastic material will most likely end up being beached due to the absence of a sub-tropical gyre, whereas in the southern Indian Ocean, the garbage patch is not well defined and there may be leakage of plastics into the southern Atlantic Ocean. Hotspots of predicted plastic accumulations are identified here as well as the vast knowledge gaps about the plastic issue of the IO and point to the most striking future investigation topics. [ABSTRACT FROM AUTHOR]

A large percentage of global ocean plastic waste enters the Northern Hemisphere Indian Ocean (NIO). Despite this, it is unclear what happens to buoyant plastics in the NIO. Because the subtropics in the NIO are blocked by landmass, there is no subtropical gyre and no associated subtropical garbage patch in this region. We therefore hypothesize that plastics "beach" and end up on coastlines along the Indian Ocean rim. In this paper, we determine the influence of beaching plastics by applying different beaching conditions to Lagrangian particle-tracking simulation results. Our results show that a large amount of plastic likely ends up on coastlines in the NIO, while some crosses the Equator into the Southern Hemisphere Indian Ocean (SIO). In the NIO, the transport of plastics is dominated by seasonally reversing monsoonal currents, which transport plastics back and forth between the Arabian Sea and the Bay of Bengal. All buoyant plastic material in this region beaches within a few years in our simulations. Countries bordering the Bay of Bengal are particularly heavily affected by plastics beaching on coastlines. This is a result of both the large sources of plastic waste in the region and the ocean dynamics that concentrate plastics in the Bay of Bengal. During the intermonsoon period following the southwest monsoon season (September, October, November), plastics can cross the Equator on the eastern side of the NIO basin into the SIO. Plastics that escape from the NIO into the SIO beach on eastern African coastlines and islands in the SIO or enter the subtropical SIO garbage patch. [ABSTRACT FROM AUTHOR]

A large percentage of global ocean plastic waste enters the northern hemisphere Indian Ocean (NIO). Despite this, it is unclear what happens to buoyant plastics in the NIO. Because the subtropics in the NIO is blocked by landmass, there is no subtropical gyre and no associated subtropical garbage patch in this region. We therefore hypothesise that plastics "beach" and end up on coastlines along the Indian Ocean rim. In this paper, we determine the influence of beaching plastics by applying different beaching conditions to Lagrangian particle tracking simulation results. Our results show that a large amount of plastic likely ends up on coastlines in the NIO, while some crosses the equator into the southern hemisphere Indian Ocean (SIO). In the NIO, the transport of plastics is dominated by seasonally reversing monsoonal currents, which transport plastics back and forth between the Arabian Sea and the Bay of Bengal. All buoyant plastic material in this region beaches within a few years in our simulations. Countries bordering the Bay of Bengal are particularly heavily affected by plastics beaching on coastlines. This is a result of both the large sources of plastic waste in the region, as well as ocean dynamics which concentrate plastics in the Bay of Bengal. During the intermonsoon period following the southwest monsoon season (September, October, November), plastics can cross the equator on the eastern side of the NIO basin into the SIO. Plastics that escape from the NIO into the SIO beach on eastern African coastlines and islands in the SIO or enter the subtropical SIO garbage patch. [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]

The Perth Canyon is a prominent submarine valley system in the southeast Indian Ocean that incises the southwest Australian continental shelf. It is characterised by two main steep-sided valleys forming a V-shaped configuration that extend from a depth of ~ 600 m to the abyssal plain at ~ 4000 m. Despite its prominence and location of only ~ 27 nautical miles (50 km) offshore, this study represents the first ROV-based exploration of the canyon and its inhabitants. ROV surveys revealed quiescent environments, the structure essentially representing a fossil canyon system with localised occurrences of significant mega- and macrobenthos in the depth range of ~ 680 to ~ 1800 m. The patchy distribution of canyon life comprised corals, sponges, molluscs, echinoderms, crustaceans, brachiopods, and worms, as well as plankton and nekton (various fish species) especially near benthic communities. High definition video surveys and biomass sampling were complemented by ship-based multi-beam bathymetry, and seawater CTD profiling and chemical analyses. ROV transects were conducted at six geomorphologically distinct locations, from the head to the mouth of the canyon and on the northern shelf plateau. The dives traversed the generally featureless muddy canyon floor, along near vertical walls, and onto the canyon rim. ROV imaging revealed typically massive and well-bedded sedimentary units that are variably lithified and mostly friable. Biostratigraphic and palaeoecological analysis of foraminifers from rock and sediment samples (~ 700 to 1600 m) indicate that they were deposited from the Late Paleocene to Early Oligocene within upper-middle bathyal (~ 200 to ~ 700 m) water depths, thus implying that significant subsidence has occurred. Strontium isotope (87Sr/86Sr) dating also suggests the presence of Early Miocene sediments at the shallower sites. Settlement of large benthic sessile organisms is largely limited to indurated substrates mostly along the canyon walls. Corals were specifically targeted, with solitary (Desmophyllum dianthus, Caryophyllia sp., Vaughanella sp., and Polymyces sp.) and colonial (Solenosmilia variabilis) scleractinians found sporadically distributed along the walls and beneath overhangs in the deeper canyon valleys as well as along the canyon rims. Gorgonian, bamboo, and proteinaceous corals were also present with noticeable patches of live Corallium hosting a diverse community of organisms. Extensive coral graveyards were discovered between ~ 690-720 m and 1560-1790 m comprising colonial (S. variabilis) and solitary (D. dianthus) scleractinians, which had flourished during the last ice age between ~ 18 ka to 33 ka (BP). Faunal sampling (674 m to 1815 m) spans the intermediate and deep waters, which were identified as Antarctic Intermediate Water and Upper Circumpolar Deep Water, with temperatures of ~ 2.5 to ~ 6 °C. The carbonate chemistry of those water depths show supersaturation (Ωcalc ~ 1.3 to 2.2) with respect to calcite, but mild saturation to undersaturation (Ωarag ~ 0.8 to 1.4) with respect to aragonite. Notably, some scleractinians inhabit depths below the aragonite saturation horizon (~ 1000 m). Depth profile measurements of δ13C and nuclear bomb produced δ14C show decreases within the upper canyon waters of up to ~ 0.8 ‰ (< 800 m) and 95 ‰ (< 500 m) respectively, relative to measurements taken nearby in 1978, thereby reflecting the ingress of anthropogenic carbon into upper intermediate waters. Thus, the canyon waters and its inhabitants are already being subject to the influences of CO2 induced climate change and ocean acidification. [ABSTRACT FROM AUTHOR]

Laboratory experiments were conducted in an open channel flume with a flat sandy bed to examine the role of turbulence on sediment resuspension. An acoustic Doppler velocimeter (ADV) was used to measure the instantaneous three-dimensional velocity components and acoustic backscatter as a proxy to suspended sediment concentration. Estimates of sediment transport assume that there is a mean critical velocity that needs to be exceeded before sediment transport is initiated. This approach does not consider the turbulent flow field that may initiate sediment resuspension through event-based processes such as the "bursting" phenomenon. In this paper, laboratory measurements were used to examine the sediment resuspension processes below and above the mean critical velocity. The results within a range above and below the measured mean critical velocity suggested that (1) the contribution of turbulent bursting events remained identical in both experimental conditions, (2) ejection and sweep events contributed more to the total sediment flux than up-acceleration and down-deceleration events, and (3) wavelet transform revealed a correlation between the momentum and sediment flux in both test conditions. Such similarities in conditions above and below the measured mean critical velocity highlight the need to re-evaluate the accuracy of a single time-averaged mean critical velocity for the initiation of sediment entrainment. [ABSTRACT FROM AUTHOR]

The technical steps involved in configuring a regional ocean model are analogous for all community models. All require the generation of a model grid, preparation and interpolation of topography, initial conditions, and forcing fields. Each task in configuring a regional ocean model is straightforward - but the process of downloading and reformatting data can be time-consuming. For an experienced modeller, the configuration of a new model domain can take as little as a few hours - but for an inexperienced modeller, it can take much longer. In pursuit of technical efficiency, the Australian ocean modelling community has developed the Web-based MARine Virtual Laboratory (WebMARVL). WebMARVL allows a user to quickly and easily configure an ocean general circulation or wave model through a simple interface, reducing the time to configure a regional model to a few minutes. Through WebMARVL, a user is prompted to define the basic options needed for a model configuration, including the model, run duration, spatial extent, and input data. Once all aspects of the configuration are selected, a series of data extraction, reprocessing, and repackaging services are run, and a "take-away bundle" is prepared for download. Building on the capabilities developed under Australia's Integrated Marine Observing System, WebMARVL also extracts all of the available observations for the chosen time-space domain. The user is able to download the takeaway bundle and use it to run the model of his or her choice. Models supported byWebMARVL include three community ocean general circulation models and two community wave models. The model configuration from the take-away bundle is intended to be a starting point for scientific research. The user may subsequently refine the details of the model set-up to improve the model performance for the given application. In this study,WebMARVL is described along with a series of results from test cases comparing WebMARVL-configured models to observations and manually configured models. It is shown that the automatically configured model configurations produce a good starting point for scientific research. [ABSTRACT FROM AUTHOR]