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RESEARCH ARTICLE

Characterising sediments of a tropical sediment-starved shelf using cluster analysis of physical and geochemical variables

Lynda C. Radke A C , Jin Li A , Grant Douglas B , Rachel Przeslawski A , Scott Nichol A , Justy Siwabessy A , Zhi Huang A , Janice Trafford A , Tony Watson A and Tanya Whiteway A
+ Author Affiliations
- Author Affiliations

A Coastal, Marine and Climate Change Group, Geoscience Australia, GPO Box 378, Canberra, ACT 2601, Australia.

B CSIRO Land and Water, Private Bag 5, Wembley WA 6913, Australia.

C Corresponding author. Email: lynda.radke@ga.gov.au

Environmental Chemistry 12(2) 204-226 https://doi.org/10.1071/EN14126
Submitted: 9 October 2014  Accepted: 11 December 2014   Published: 18 March 2015

Environmental context. Australia's tropical marine estate is a biodiversity hotspot that is threatened by human activities. Analysis and interpretation of large physical and geochemistry data sets provides important information on processes occurring at the seafloor in this poorly known area. These processes help us to understand how the seafloor functions to support biodiversity in the region.

Abstract. Baseline information on habitats is required to manage Australia's northern tropical marine estate. This study aims to develop an improved understanding of seafloor environments of the Timor Sea. Clustering methods were applied to a large data set comprising physical and geochemical variables that describe organic matter (OM) reactivity, quantity and source, and geochemical processes. Arthropoda (infauna) were used to assess different groupings. Clusters based on physical and geochemical data discriminated arthropods better than geomorphic features. Major variations among clusters included grain size and a cross-shelf transition from authigenic-Mn–As enrichments (inner shelf) to authigenic-P enrichment (outer shelf). Groups comprising raised features had the highest reactive OM concentrations (e.g. low chlorin indices and C : N ratios, and high reaction rate coefficients) and benthic algal δ13C signatures. Surface area-normalised OM concentrations higher than continental shelf norms were observed in association with: (i) low δ15N, inferring Trichodesmium input; and (ii) pockmarks, which impart bottom–up controls on seabed chemistry and cause inconsistencies between bulk and pigment OM pools. Low Shannon–Wiener diversity occurred in association with low redox and porewater pH and published evidence for high energy. Highest β-diversity was observed at euphotic depths. Geochemical data and clustering methods used here provide insight into ecosystem processes that likely influence biodiversity patterns in the region.

Additional keywords: ANOSIM, backscatter, carbonate banks, Commonwealth Marine Reserve, conceptual model, epifauna, marine, rare earth elements, subsurface seepage.


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