Craig Steinberg

Biophysical correlates of relative abundances of marine megafauna at Ningaloo Reef, Western Australia

Changes in the relative abundance of marine megafauna (whales, dolphins, sharks, turtles, manta rays, dugongs) from aerial survey sightings in the waters adjacent to Ningaloo Reef between June 2000 and April 2002 are described. Generalised linear models were used to explore relationships between different trophic guilds of animals (based on animal sighting biomass estimates) and biophysical features of the oceanscape that were likely to indicate foraging habitats (regions of primary/secondary production) including sea surface temperature (SST), SST gradient, chlorophyll-a (Chl-a), bathymetry (BTH) and bathymetry gradient (BTHg). Relative biomass of krill feeders (i.e. minke whales, whale sharks, manta rays) were related to SST, Chl-a and bathymetry (model [AICc] weight = 0.45) and the model combining these variables explained a relatively large amount (32.3%) of the variation in relative biomass. Relative biomass of fish/cephalopod feeders (dolphins, sharks) were weakly correlated with changes in SST, whereas that of other invertebrate/macroalgal feeders (turtles, dugong) was weakly correlated with changes in steepness of the shelf (bathymetry gradient). Our results indicate that biophysical variables describe only a small proportion of the variance in the relative abundance and biomass of marine megafauna at Ningaloo reef.

Intrusive upwelling in the Central Great Barrier Reef

In the Central Great Barrier Reef, the outer continental shelf has an open reef matrix that facilitates the exchange of waters with the Coral Sea. During austral summer, cool water intrudes onto the shelf along the seafloor. Temperature observations reveal cool, bottom intrusions during a 6 year period from the Queensland Integrated Marine Observing Systems Palm Passage mooring. A metric is used to identify 64 intrusion events. These intrusions predominantly occur from October to March including the wet season. During an event, the outer-shelfs near-bottom temperature decreases by 1–3°C typically over 1 week. The near-bottom salinity tends to increase, while near-surface changes do not reflect these tendencies. Intrusion events occur predominantly with either weakening equatorward winds or poleward wind bursts. A regional hydrodynamic model for the Great Barrier Reef captures the timing and amplitude of these intrusions. During intrusion events, isotherms tend to uplift over the continental slope and onto the shelf and the East Australian Current intensifies poleward. Over the shelf, a bottom-intensified onshore current coincides with bottom cooling. For numerous events, the model diagnostics reveal that the cross-shelf flow is dominated by the geostrophic contribution. A vertical circulation tilts the isopycnals upward on the southern side of the passage, causing an along-shelf density gradient and geostrophic onshore flow with depth. While wind fluctuations play a major role in controlling the along-shelf currents, model results indicate that a concurrent topographically induced circulation can assist the onshore spread of cool water.

Chapter 15 Merging scales in models of water circulation: perspectives from the great barrier reef

Publisher Summary This chapter describes the technique chosen to include the effect of the oceanic circulation in a 2-D model of the large-scale circulation on the continental shelf. This circulation is found to be modulated at an intermediate spatial scale by the interaction of the tidal circulation with individual reefs, and this process is modeled by merging large-scale and reef-scale 2-D circulation models. The oceanography of the Great Barrier Reef (GBR) is made particularly complex by the extraordinary complex bathymetry. In the GBR, the obstruction of the flow by the presence of reefs steers and modifies, even at these large scales, the oceanic inflow and the longshore currents. Obstruction by large reefs or a reef matrix steers prevailing currents toward areas of low reef density. This provides the modeler the challenge to merge the large-scale oceanic circulation with the shelf-scale general distribution of reefs over the shelf. The resulting currents through a reef matrix, and the deflection of the prevailing currents around a reef matrix, are modulated by the tides.

Real-time marine observing systems: Challenges, benefits and opportunities in Australian coastal waters

The Australian Integrated Marine Observing System (IMOS) is funded by the Australian Government, and designed to be a fully-integrated national array of observing equipment to monitor the open oceans and coastal marine environment around Australia. IMOS delivers physical, chemical and biological data comprising of observations from a wide spectrum of platforms including weather stations, oceanographic moorings, underway ship observations, seagliders, ocean surface radar, satellite image reception and reef based sensor networks. When data from ocean observing systems can be provided in near real-time, the operational aspects are further enhanced and provide potential for a range of value added products to be developed. Here we provide three examples of co-invested partnerships that have facilitated the development of real-time moored ocean observing systems in the coastal zone, operated by the Queensland IMOS node. For each of these examples, the project is introduced, a detailed technical description of the system is provided, operational aspects are summarised, and the uptake of data from stakeholders is discussed. These examples demonstrate the benefits of having a national collaborative approach to marine observing with a clear focus on open access to data. It is also demonstrated that the benefits and opportunities offered by real-time ocean observing can outweigh the technical challenges of developing and maintaining these complex systems.

Application of VHF high resolution radar to evaluating circulation around a seawater intake facility

The Australian Institute of Marine Science operates a research aquarium at Cape Ferguson in North Queensland which requires a high volume circulation of ocean water from the adjacent bay. Turbidity and water quality are significant issues which govern the location of the seawater intakes. A VHF high resolution ocean radar was deployed at the site of the sea water intakes in order to evaluate the circulation in an area of approximately 2 km × 2 km with spatial resolution of about 100 m. The short deployment showed that there are complex flow patterns at this scale, and identified three bodies of water which may affect the quality of water that enters the intakes.

Can vertical mixing from turbulent kinetic energy mitigate coral bleaching? An application of high frequency ocean radar

Coral bleaching is an ecological response to stressful physical conditions observed to occur when strong insolation coupled with stratification of the water column leads to anomalous warming of the surface water. Stratfication requires calm winds, the absence of waves, and an absence of currents: conditions which result in limited mixing of the water column and thus confine heat due to insolation at the ocean surface. There is a strong need to identify which of the physical parameters are more significant at any given time and, more importantly, to monitor the physical parameters in near realtime to serve as a tool for long-term planning and management for marine parks and coastal waters. This paper reviews the contribution that currents make to mixing in the water column through the dissipation of turbulent kinetic energy and takes a further step to evaluate the use of surface current data to provide an index of vertical mixing. In this work, when the surface current speed is greater than a critical value, the water column is found to be vertically mixed even in the absence of wind or waves. A phased array HF Ocean Radar deployed in the southern part of the Great Barrier Reef provides a map of surface currents with high spatial resolution (4km) every 10 minutes over the grid. These surface currents are used to predict vertical stratification and mixing which can then be used as an indication for conditions under which bleaching might occur.