GEOMACS (Geological and Oceanographic Model of Australias Continental Shelf) Interquartile range

Brief 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 will be calculated to 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). The interquartile range, , of the GEOMACS output takes the observations from between Q25 and Q75 to provide an accurate representation of the spread of observations. The interquartile range was shown to provide a more robust representation of the observations than the standard deviation, which produced highly skewed observations (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