ALBERT

Description: Millimeter-sized plastics are numerically abundant and widespread across the world's ocean surface. These buoyant macroscopic particles can be mixed within the upper water column due to turbulent transport. Models indicate that the largest decrease in their concentration occurs within the first few meters of water, where subsurface observations are very scarce. By using a new type of multi-level trawl at 12 sites within the North Atlantic accumulation zone, we measured concentrations and physical properties of plastics from the air–seawater interface to a depth of 5 m, at 0.5 m intervals. Our results show that plastic concentrations drop exponentially with water depth, but decay rates decrease with increasing Beaufort scale. Furthermore, smaller pieces presented lower rise velocities and were more susceptible to vertical transport. This resulted in higher depth decays of plastic mass concentration (mg m−3) than numerical concentration (pieces m−3). Further multi-level sampling of plastics will improve our ability to predict at-sea plastic load, size distribution, drifting pattern, and impact on marine species and habitats.

Description: Field measurements, collected at several low energy, microtidal beaches in south-western Australia were used to study the cross-shore transport and sediment resuspension over different sand ripple types. The measurements included simultaneous records of the water surface elevation, cross-shore current velocity, and suspended sediment concentration, as well as free diver measurements of the ripple dimensions. The observed ripples were classified according to their geometry and sediment suspension patterns into six categories: flat bed, post-vortex ripples, two-dimensional (2-D) ripples, two/three-dimensional (2-D/3-D) ripples, three-dimensional (3-D) ripples, and cross ripples. Flat bed conditions were observed under the highest flow mobility numbers. Post-vortex ripples were observed under slightly lower mobility numbers. The other ripple types occurred under low mobility numbers, with no significant difference in the mobility number among them. Two-dimensional ripples were observed more than the other ripple types in the presence of coarse grains. The suspended sediment concentration at ∼0.05 m above the bed was greater over steep ripples. The net cross-shore suspended sediment flux close to the seabed (at ∼0.05 m) in the swell frequency band varied over the different ripples types: onshore over a flat bed, offshore over post-vortex ripples, onshore over 2-D and 2-D/3-D ripples, and offshore over 3-D ripples. The suspended sediment flux direction over the cross ripples varied between onshore and offshore.

Description: 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 straight-forward – 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 take-away bundle, and use it to run the model of their choice. Models supported by WebMARVL 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.

Description: Sri Lanka occupies a unique location within the equatorial belt in the northern Indian Ocean with the Arabian Sea on its western side and the Bay of Bengal on its eastern side. The region is characterised by bi-annually reversing monsoon winds resulting from seasonal differential heating and cooling of the continental land mass and the ocean. This study explored elements of the dynamics of the surface circulation and coastal upwelling in the waters around Sri Lanka using satellite imagery and the Regional Ocean Modelling System (ROMS) configured to the study region and forced with ECMWF interim data. The model was run for 2 yr to examine the seasonal and shorter term (∼10 days) variability. The results confirmed the presence of the reversing current system in response to the changing wind field: the eastward flowing Southwest Monsoon Current (SMC) during the Southwest (SW) monsoon transporting 11.5 Sv and the westward flowing Northeast Monsoon Current (NMC) transporting 9.5 Sv during the Northeast (NE) monsoon, respectively. A recirculation feature located to the east of Sri Lanka during the SW monsoon, the Sri Lanka Dome, is shown to result from the interaction between the SMC and the Island of Sri Lanka. Along the eastern and western coasts, during both monsoon periods, flow is southward converging along the south coast. During the SW monsoon the Island deflects the eastward flowing SMC southward whilst along the east coast the southward flow results from the Sri Lanka Dome recirculation. The major upwelling region, during both monsoon periods, is located along the south coast and is shown to be due to flow convergence and divergence associated with offshore transport of water. Higher surface chlorophyll concentrations were observed during the SW monsoon. The location of the flow convergence and hence the upwelling centre was dependent on the relative strengths of wind driven flow along the east and west coasts: during the SW (NE) monsoon the flow along the western (eastern) coast was stronger and hence the upwelling centre was shifted to the east (west). The presence of upwelling along the south coast during both monsoon periods may explain the blue whale (Balaenoptera musculus) aggregations in this region.

Description: Sri Lanka occupies a unique location within the equatorial belt in the northern Indian Ocean, with the Arabian Sea on its western side and the Bay of Bengal on its eastern side, and experiences bi-annually reversing monsoon winds. Aggregations of blue whale (Balaenoptera musculus) have been observed along the southern coast of Sri Lanka during the northeast (NE) monsoon, when satellite imagery indicates lower productivity in the surface waters. This study explored elements of the dynamics of the surface circulation and coastal upwelling in the waters around Sri Lanka using satellite imagery and numerical simulations using the Regional Ocean Modelling System (ROMS). The model was run for 3 years to examine the seasonal and shorter-term (~10 days) variability. The results reproduced correctly the reversing current system, between the Equator and Sri Lanka, in response to the changing wind field: the eastward flowing Southwest Monsoon Current (SMC) during the southwest (SW) monsoon transporting 11.5 Sv (mean over 2010–2012) and the westward flowing Northeast Monsoon Current (NMC) transporting 9.6 Sv during the NE monsoon, respectively. A recirculation feature located to the east of Sri Lanka during the SW monsoon, the Sri Lanka Dome, is shown to result from the interaction between the SMC and the island of Sri Lanka. Along the eastern and western coasts, during both monsoon periods, flow is southward converging along the southern coast. During the SW monsoon, the island deflects the eastward flowing SMC southward, whilst along the eastern coast, the southward flow results from the Sri Lanka Dome recirculation. The major upwelling region, during both monsoon periods, is located along the southern coast, resulting from southward flow converging along the southern coast and subsequent divergence associated with the offshore transport of water. Higher surface chlorophyll concentrations were observed during the SW monsoon. The location of the flow convergence and hence the upwelling centre was dependent on the relative strengths of wind-driven flow along the eastern and western coasts: during the SW (NE) monsoon, the flow along the western (eastern) coast was stronger, migrating the upwelling centre to the east (west).

Description: Millimetre-sized plastics are numerically abundant and widespread across the world's ocean surface. These buoyant macroscopic particles can be mixed within the upper water column by turbulent transport. Models indicate that the largest decrease in their concentration occurs within the first few metres of water, where in situ observations are very scarce. In order to investigate the depth profile and physical properties of buoyant plastic debris, we used a new type of multi-level trawl at 12 sites within the North Atlantic subtropical gyre to sample from the air–seawater interface to a depth of 5 m, at 0.5 m intervals. Our results show that plastic concentrations drop exponentially with water depth, and decay rates decrease with increasing Beaufort number. Furthermore, smaller pieces presented lower rise velocities and were more susceptible to vertical transport. This resulted in higher depth decays of plastic mass concentration (milligrams m−3) than numerical concentration (pieces m−3). Further multi-level sampling of plastics will improve our ability to predict at-sea plastic load, size distribution, drifting pattern, and impact on marine species and habitats.