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

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.

[1]  H. Hass,et al.  History of anthropogenic nitrogen input to the German Bight/SE North Sea as reflected by nitrogen isotopes in surface sediments, sediment cores and hindcast models , 2010 .

[2]  E. Kristensen.  Organic matter diagenesis at the oxic/anoxic interface in coastal marine sediments, with emphasis on the role of burrowing animals , 2000, Hydrobiologia.

[3]  M. Delaney,et al.  Sequential extraction and analysis of phosphorus in marine sediments: Streamlining of the SEDEX procedure , 2000 .

[4]  M. Lucotte,et al.  The Differential Geochemical Behavior of Arsenic and Phosphorus in the Water Column and Sediments of the Saguenay Fjord Estuary, Canada , 2000 .

[5]  P. Herman,et al.  Macrobenthic species response surfaces along estuarine gradients: prediction by logistic regression , 2002 .

[6]  F. Millero,et al.  A comparison of the equilibrium constants for the dissociation of carbonic acid in seawater media , 1987 .

[7]  J. Oades,et al.  Comparative organic geochemistries of soils and marine sediments , 1997 .

[8]  K. Ruttenberg.  The Global Phosphorus Cycle , 2003 .

[9]  T. Ferdelman,et al.  How depositional conditions control input, composition, and degradation of organic matter in sediments from the Chilean coastal upwelling region , 2007 .

[10]  M. German,et al.  The Karbonat-Bombe, a simple device for the determination of the carbonate content in sediments, soils, and other materials , 1971 .

[11]  M. Burford,et al.  Sources of nutrients driving production in the Gulf of Carpentaria, Australia: a shallow tropical shelf system. , 2009 .

[12]  Carrie V. Kappel,et al.  A Global Map of Human Impact on Marine Ecosystems , 2008, Science.

[13]  B. Toman,et al.  New Guidelines for d13C Measurements , 2006 .

[14]  T. Ferdelman,et al.  Chlorin Index: A new parameter for organic matter freshness in sediments , 2002 .

[15]  P. Harris,et al.  Predicted benthic disturbance regimes on the Australian continental shelf: a modelling approach , 2012 .

[16]  L. A. Trott,et al.  Strong tidal currents and labile organic matter stimulate benthic decomposition and carbonate fluxes on the southern Great Barrier Reef shelf , 2011 .

[17]  Zhi Huang,et al.  Developing physical surrogates for benthic biodiversity using co-located samples and regression tree models: a conceptual synthesis for a sandy temperate embayment , 2012, Int. J. Geogr. Inf. Sci..

[18]  V. Ramaswamy,et al.  Stable nitrogen isotopic ratios of sinking particles and sediments from the northern Indian Ocean , 2005 .

[19]  P. Tester,et al.  Toxic effect of the bloom-forming Trichodesmium sp. (Cyanophyta) to the copepod Acartia tonsa. , 1994, Natural toxins.

[20]  J. Hedges,et al.  Fluxes and reactivities of organic matter in a coastal marine bay , 1988 .

[21]  Pierre Legendre,et al.  Numerical Ecology with R , 2011 .

[22]  P. Herman,et al.  Spatial distribution in sediment characteristics and benthic activity on the northwestern Black Sea shelf , 1999 .

[23]  P. Moody,et al.  Tracing the source of sediment and phosphorus into the Great Barrier Reef lagoon , 2003 .

[24]  Gerald Müller,et al.  The 'Karbonat-Bombe', a simple device for the determination of carbonate content in sediment, soils, and other materials , 1971 .

[25]  K. Pye,et al.  GRADISTAT: a grain size distribution and statistics package for the analysis of unconsolidated sediments , 2001 .

[26]  S. Jeffrey,et al.  Spectrophotometric and fluorometric equations in common use in oceanography , 1997 .

[27]  K. R. Clarke,et al.  Change in marine communities : an approach to statistical analysis and interpretation , 2001 .

[28]  P. Baisch,et al.  Calcareous algae bioclast contribution to sediment enrichment by arsenic on the Brazilian subtropical coast , 2011 .

[29]  M. Chapman,et al.  Ecological patterns in multivariate assemblages: information and interpretation of negative values in ANOSIM tests , 1999 .

[30]  J. W. Valentine,et al.  Out of the Tropics: Evolutionary Dynamics of the Latitudinal Diversity Gradient , 2006, Science.

[31]  B. Toman,et al.  New Guidelines for δ13C Measurements , 2006 .

[32]  R. Rosenberg,et al.  Marine benthic hypoxia: a review of its ecological effects and the behavioural responses of benthic macrofauna , 1995 .

[33]  R. Berner,et al.  Degree of Pyritization of Iron as a Paleoenvironmental Indicator of Bottom-Water Oxygenation , 1988 .

[34]  P. Choquette,et al.  Geologic Nomenclature and Classification of Porosity in Sedimentary Carbonates , 1970 .

[35]  Hilairy E. Hartnett,et al.  Influence of oxygen exposure time on organic carbon preservation in continental margin sediments , 1998, Nature.

[36]  C. Vale,et al.  Record of diagenesis of rare earth elements and other metals in a transitional sedimentary environment , 2009 .

[37]  T. Algeo,et al.  Environmental analysis of paleoceanographic systems based on molybdenum–uranium covariation , 2009 .

[38]  Zhi Huang,et al.  Methodologies for seabed substrate characterisation using multibeam bathymetry, backscatter and video data: A case study from the carbonate banks of the Timor Sea, Northern Australia , 2013 .

[39]  C. Lorenzen,et al.  DETERMINATION OF CHLOROPHYLL AND PHEO‐PIGMENTS: SPECTROPHOTOMETRIC EQUATIONS1 , 1967 .

[40]  T. H. Andel,et al.  Morphology and sediments of the Timor Sea , 1954 .

[41]  T. Lyons,et al.  Trace metals as paleoredox and paleoproductivity proxies: An update , 2006 .

[42]  B. Eyre,et al.  Organic matter and benthic metabolism in euphotic sediments along shallow sub-tropical estuaries, northern New South Wales, Australia , 2003 .

[43]  H. Dulfer,et al.  Pockmark development in the Petrel Sub-basin, Timor Sea, Northern Australia: Seabed habitat mapping in support of CO2 storage assessments , 2014 .

[44]  Brendan P. Brooke,et al.  On the use of abiotic surrogates to describe marine benthic biodiversity , 2010 .

[45]  C. Culberson,et al.  MEASUREMENT OF THE APPARENT DISSOCIATION CONSTANTS OF CARBONIC ACID IN SEAWATER AT ATMOSPHERIC PRESSURE1 , 1973 .

[46]  P. Harris,et al.  Seafloor geomorphology as benthic habitat : GeoHAB atlas of seafloor geomorphic features and benthic habitats , 2012 .

[47]  P. Quay,et al.  Loss of organic matter from riverine particles in deltas , 1997 .

[48]  Scott M. McLennan,et al.  Relationships between the trace element composition of sedimentary rocks and upper continental crust , 2001 .

[49]  T. Pietsch,et al.  Delineation of sediment sources to a coastal wetland in the Great Barrier Reef catchment: influence of climate variability and land clearing since European arrival , 2010 .

[50]  K Norrish,et al.  An accurate X-ray spectrographic method for the analysis of a wide range of geological samples , 1969 .

[51]  S. Taylor,et al.  The continental crust: Its composition and evolution , 1985 .

[52]  P. T. Harris,et al.  Geomorphology of the Australian margin and adjacent seafloor , 2008 .

[53]  G. Chaillou,et al.  The behaviour of arsenic in muddy sediments of the Bay of Biscay (France) , 2003 .

[54]  Craig J. Brown,et al.  Benthic habitat mapping: A review of progress towards improved understanding of the spatial ecology of the seafloor using acoustic techniques , 2011 .

[55]  Walter Jetz,et al.  Global patterns and predictors of marine biodiversity across taxa , 2010, Nature.

[56]  D. Burdige.  Geochemistry of Marine Sediments , 2006 .

[57]  M. Chapman,et al.  Chapman MG, Underwood AJ.. Ecological patterns in multivariate assemblages: Information and interpretation of negative values in ANOSIM tests. Mar Ecol Prog Ser 180: 257-265 , 1999 .

[58]  C. Heip,et al.  Ecology of estuarine macrobenthos , 1999 .