GEOMACS (Geological and Oceanographic Model of Australias Continental Shelf) Q25

Full description

Geoscience Australias GEOMACS model was utilised to produce hindcast hourly time series of continental shelf (~20 to 300 m depth) bed shear stress (unit of measure: Pascal, Pa) on a 0.1 degree grid covering the period March 1997 to February 2008 (inclusive). The hindcast data represents the combined contribution to the bed shear stress by waves, tides, wind and density-driven circulation. Included in the parameters that represent the magnitude of the bulk of the data are the quartiles of the distribution; Q25, Q50 and Q75 (i.e. the values for which 25, 50 and 75 percent of the observations fall below). Q25, or the 0.25 Quartile of the Geomacs output, represents the values for which 25% of the observations fall below (Hughes and Harris 2008). This dataset is a contribution to the CERF Marine Biodiversity Hub and is hosted temporarily by CMAR on behalf of Geoscience Australia.

Lineage

Progress Code: completed

Maintenance and Update Frequency: notPlanned

Statement: The Geological and Oceanographic Model of Australias Territory (GEOMAT- Harris et al., 2000) developed at Geoscience Australia provides maps indicative of seabed exposure on the Australian continental shelf in depths between approximately 20 m and 300 m. GEOMAT v.1 proposed a classification of the Australian underwater territory based on sediment mobility induced by distinct processes such as tidal currents and gravity waves (Porter-Smith et al., 2004). GEOMAT v.2 (GEOMACS) proposed an improved classification of the continental shelf area based on a seabed exposure index (Hemer, 2006). The seabed exposure index was derived from the statistical distribution of the sediment transport rate, which reflected the strength and frequency of the combined wave-current bed shear stress. The bed shear stress was derived from a bottom boundary layer model (SEDTRANS - Li and Amos, 2001), which integrated the combined action of tidal currents (Egbert et al., 1994), oceanic currents (OCCAM; Webb et al., 1998), and gravity waves (AUSWAM - Greenslade, 2001) over a given mean sediment fraction (MARS; Geoscience Australia, 2006). Additional Referencs: Egbert, G.D., Bennett, A.F., and Foreman, M.G.G., 1994. TOPEX/POSEIDON tides estimated using a global inverse mode. Journal of Geophysical Research 99, 24821-24852. Greenslade, D.J.M., 2001. The Assimilation of ERS-2 Significant Wave Height Data in the Australian region. Journal of Marine Systems 28, 141-160. Harris, P. T., Smith, R., Anderson, O., Coleman, R., and Greenslade, D., 2000. GEOMAT modelling of continental shelf sediment mobility in support of Australias regional marine planning process. Australian Geological Survey Organisation Record 2000/41. Geoscience Australia, Canberra. 53pp. Hemer, M.A., 2006. The magnitude and frequency of combined flow bed shear stress as a measure of exposure on the Australian continental shelf. Continental Shelf Research 26, 1258-1280. Hughes, M., Harris, P. T., 2008. Progress Report on Disturbance Task C1, Surrogates Program, Marine Biodiversity Hub. Geoscience Australia, Canberra. Li, M.Z., and Amos, C.L., 2001. SEDTRANS96: the upgraded and better calibrated sediment transport model for continental shelves. Computers and Geosciences 27, 619-645. Porter_Smith, R., Harris, P.T., Anderson, O., Coleman, R., Greenslade, D.J.M., and Jenkins, C.J., 2004. Classification of the Australian continental shelf based on predicted sediment threshold exceedance from tidal currents and swell waves. Marine Geology 211, 1-20. Webb, D.J., Cuevas, B.A., and Coward, A.C., 1998. The first main run of the OCCAM global ocean model. Internal Report of James Rennell Division, Southampton Oceanography Centre, UK. 50pp. See also:http://www.noc.soton.ac.uk/JRD/OCCAM.

Notes

Credit
Dr Michael Hughes Dr Peter Harris