Modelled seabed response to possible climate change scenarios over the next 50 years in the Australian Northeast - Stationary scenario datasets with Sedsim input files and output files

Brief description

Using data from ocean forecast models, field observations and seabed sampling we ran a numerical sediment transport model to estimate the Australian Shelf seabed evolution under three climate change scenarios. This data collection is for the Stationary climate change scenario in which the present climate continues for next 50 years.

In this study, the interaction of seabed sediment types and hydrodynamic forces in the northeastern region has been investigated using a state-of-the-art numerical model, Sedsim. The simulation area for this collection covers the northeast Australia continental shelf and abyssal basins which include the Great Barrier Reef, the Marion and Queensland plateaus, the Cato, Townsville and Queensland troughs, the New South Wales Shelf and the coast from south of Jervis Bay up to Princess Charlotte Bay in the North.

The model uses the known grain-size distribution of the present-day seabed based on a comprehensive analysis of currently available seabed data Information available from this data source includes grainsize, mud content, rock exposure, and estimates of critical seabed shear stress. This sediment layer is incorporated in the latest high-resolution (0.0025°) seabed bathymetry obtained from the Australian National Oceans Office (NOO). The seabed topography and present-day sediment layer are represented by a 566 (columns) by 550 (rows) grid with a spatial resolution of 2.1 km. The environmental forcing factors considered in the present model are sediment-laden river flows and turbidity currents, waves, tides, wind-driven currents, sea level change, submarine slope failure and carbonate sediment production.

Lineage

Long-term seabed change is the cumulative result of dynamic forcing and sediment responses. The environmental forces integrated in the model are:
sediment-laden river flows,
temperature and salinity variations,
waves and tides regimes,
wind-driven currents,
ocean geostrophic currents,
sea-level changes,
submarine slope failures and turbidity currents.

The Defence Oceanographic Data Centre has provided the wind climate in a monthly form. The data consist of mean and maximum wind speed and simultaneous wind direction when maximum speed occurred. The original wind data cover the time period from July 1999 to May 2004 at a resolution of 0.25°.
CSIRO WAM wave model has been used to define wave condition around the Australian Shelf. The data are six-hourly predictions of significant wave height, period and mean wave direction, gridded at 0.1° spatial resolution, for the period of March 1997 to February 2002.
The National Tidal Centre has provided the tidal range and depth-averaged tidal current speed (5 minutes resolution). In addition, bottom current fields simulated by the Ocean Forecasting Australia Model (0.1° spatial resolution) are used as input into the sediment-transport model. High-frequency water movement caused by wave and tides are the major factors affecting the seabed sediment availability to long-term and large scale transport although the net sediment movement by waves and tides may be negligible, at least in deep water.
In the model, seabed mobility index (ratio between the total and critical Shields parameter (induced by wave, tidal current and wind-driven current)) serves as the major indicator of the level of intensity and frequency of seabed sediment available for movement. Modification of the mobility index formulation integrates effects of reef, algae and mangroves on sediment transport and mobility. The mobility index is calculated under the condition of monthly mean and extreme climate.
The Australian Shelf has been divided in nine regions. This data collection is for the Northeast and Eastern regions. Depending on the area, several meshes have been used with cell size ranging between 2000 and 2400 metres. The construction of an existing seabed deposit layer is mainly based on the comprehensive sediment database auSEABED. The data collected are mostly retrieved from grabbed samples and bottom photographs. Based on this compilation the mean sediment grain size, the rock membership, the gravel and carbonates content have been estimated. Very little data is available to determine the thickness of loose sediment. The main reason being that the thinness of the sediment veneer covering the hard ground makes gravity coring almost impossible. Thus initial seabed loose sediment thickness is built on available data and according to simple rules for depth and rock membership.
For the Australian Shelf simulation, 131 major river and inlet systems have been identified and evaluated in terms of their annual sediment carrying capacity. Mean annual river discharge and sediment yield have been mainly extracted from the OzEstuaries database and converted into discharge rates and sediment concentration.