Physical characterization and benthic megafauna distribution and species composition on Orphan Knoll and Orphan Seamount, NW Atlantic

Meredyk, Shawn P. (2017) Physical characterization and benthic megafauna distribution and species composition on Orphan Knoll and Orphan Seamount, NW Atlantic. Masters thesis, Memorial University of Newfoundland.

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Abstract

Orphan Knoll (OK) is an 'orphaned' fragment of the North American continental crust that contains ~250 mounds of unknown composition ranging from 60 to 600 m of meters tall and 1 to 3 km wide. The adjacent “Orphan Seamount” (OS) is located 9 km NE of the SE portion of OK and is a volcanic seamount. The purpose of this study was to: determine the age and composition of the enigmatic OK mounds and OS, in an effort to better understand their origin and thus physical deep-sea habitat; to identify the distribution and abundance of the benthic megafauna of OK and OS; to examine the effects of bathymetry, oceanography and geology on deep-sea community composition. A multipurpose survey using the remotely operated vehicle (ROV) ROPOS was used to collect geological substrate samples, biological presence data (HD video), oceanographic data (conductivity, temperature and density (CTD)) and high and low resolution multibeam imagery. Rock samples on OS were identified as basaltic bedrock with limestone-filled vesicles (mid-Miocene aged through identification of Globigerina spp. and Orbulina spp. of pelagic foraminifera); thereby, identifying the OS as a volcanic seamount having been formed between the lower Cretaceous and the mid Miocene. Rock samples from the OK mounds identified mid-Miocene bedded pelagic limestone bedrock as the upper layer of limestone on top of the OK mounds. An unconformity was discovered between units 2 and 3 of the bedded OK mound limestone, identifying tilting of the faulted-blocks that are the Orphan Knoll mounds. The formation of the OK mounds possibly occurred through Neogene faulting through plate movements along the White Sail fault and quaternary faulting along the Charlie Gibbs Fracture Zone (CGFZ). On six ROV dives, 18 identified species of coral, 4 species of sponges, and 10 species of other deep-sea megafauna were identified. Amongst all of the recorded megafaunal species, 10 large concentrations (>20% area coverage) were grouped in an effort to further examine community turnover factors. Statistical analysis using gradientForest identified that bathymetry data of an intermediate scale (100 m spatial resolution) was the most accurate data to collect to explain megafaunal distribution and abundance through examining changes in community turnover along driver gradients in the deep-sea megafaunal species; however, surficial geology and oceanographic data were also important drivers in distribution and abundance of deep-sea megafauna. The variables depth, slope and aspect were found as being the most accurate descriptors when assessing changes in deep-sea megafaunal community turnover.

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