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Geosciences 2018, 8(6), 195; https://doi.org/10.3390/geosciences8060195

Origin of High Density Seabed Pockmark Fields and Their Use in Inferring Bottom Currents

1
Geoscience Australia, Crn Jerrabombera and Hindmarsh Avenue, Symonston 2607, Australia
2
Australian Institute of Marine Science, Arafura Timor Research Facility, University Ave., North Darwin 0811, Australia
3
GeoQuEST Research Centre, School of Earth & Environmental Sciences, University of Wollongong, Wollongong 2522, Australia
4
British Geological Survey, The Lyell Centre, Research Avenue South, Edinburgh EH14 4AP, UK
*
Author to whom correspondence should be addressed.
Received: 19 March 2018 / Revised: 24 April 2018 / Accepted: 23 May 2018 / Published: 30 May 2018
(This article belongs to the Special Issue Marine Geomorphometry)
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Abstract

Some of the highest density pockmark fields in the world have been observed on the northwest Australian continental shelf (>700/km2) where they occur in muddy, organic-rich sediment around carbonate banks and paleochannels. Here we developed a semi-automated method to map and quantify the form and density of these pockmark fields (~220,000 pockmarks) and characterise their geochemical, sedimentological and biological properties to provide insight into their formative processes. These data indicate that pockmarks formed due to the release of gas derived from the breakdown of near-surface organic material, with gas accumulation aided by the sealing properties of the sediments. Sources of organic matter include adjacent carbonate banks and buried paleochannels. Polychaetes biodiversity appears to be affected negatively by the conditions surrounding dense pockmark fields since higher biodiversity is associated with low density fields. While regional bi-directionality of pockmark scours corresponds to modelled tidal flow, localised scattering around banks suggests turbulence. This multi-scale information therefore suggests that pockmark scours can act as proxy for bottom currents, which could help to inform modelling of benthic biodiversity patterns. View Full-Text
Keywords: multibeam sonar; carbonate banks; semi-automated mapping; polychaete; Northwestern Australia; Oceanic Shoals Australian Marine Park; Bonaparte Basin; Timor Sea multibeam sonar; carbonate banks; semi-automated mapping; polychaete; Northwestern Australia; Oceanic Shoals Australian Marine Park; Bonaparte Basin; Timor Sea
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Picard, K.; Radke, L.C.; Williams, D.K.; Nicholas, W.A.; Siwabessy, P.J.; Howard, F.J.F.; Gafeira, J.; Przeslawski, R.; Huang, Z.; Nichol, S. Origin of High Density Seabed Pockmark Fields and Their Use in Inferring Bottom Currents. Geosciences 2018, 8, 195.

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