Geoscience Australia undertook seabed mapping surveys in the eastern Bonaparte Gulf in 2009/2010 to deliver integrated
information relevant to marine biodiversity conservation and offshore infrastructure development. The survey objectives were to characterise the physical, chemical and biological properties of the seabed, document potential geohazards and identify unique or sensitive benthic habitats. Different clustering methods were applied to a 124 sample dataset comprising 74 physical and chemical variables which convey important baseline information about sediment sources, carbon reactivity/ redox and sedimentary environments. Results of the UPGMA clustering method were interpreted due to the high cophenetic correlation (0.82), and these clusters discriminated infauna better than clusters based on geomorphology. Major geochemical dimensions evident amongst clusters included grain-size and a cross-shelf transition from Mn and as enrichment (inner shelf) to P enrichment (outer-shelf). Higher P was due to enhanced authigenic-P accumulation.
Sponge/gorgonian occurrences were constrained by low Nd/Sr (pointing to a diminishing terrestrial source) and relatively high δ15N, and subsurface seepage was shown to enhance the ‘terrestrial’ (e.g. rare-earth element and Si) signature in outer-shelf sediments. Sponge-dominated shallow bank/terrace clusters with abundant reactive organic matter differentiated on the basis of Si-Al relations (and redox). These habitats shed materials to peripheral Gorgonian-dominated scree environments which had surface-area normalised TOC concentrations that were elevated over usual continental shelf ranges. Trichodesmium were identified as an important source of carbon to inner-shelf plains. Pair-wise ANOSIM results for infauna are brought together in a summary model which highlights the influence of the clusters on benthic biodiversity.
Abstract presented at the AMSA2013 Golden Jubilee Conference 7-11 July 2013 Gold Coast, Qld.