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dc.contributor.authorHosegood, Phil. J
dc.contributor.authorNimmo-Smith, W.A.M.
dc.contributor.authorProud, R.
dc.contributor.authorAdams, Kate
dc.contributor.authorBrierley, A. S.
dc.identifier.citationHosegood , P J , Nimmo-Smith , W A M , Proud , R , Adams , K & Brierley , A S 2019 , ' Internal lee waves and baroclinic bores over a tropical seamount shark ‘hot-spot’ ' , Progress in Oceanography , vol. 172 , pp. 34-50 .
dc.identifier.otherPURE: 257545910
dc.identifier.otherPURE UUID: fcd17675-09de-416f-a3da-bfabd236f9ae
dc.identifier.otherScopus: 85060541498
dc.identifier.otherORCID: /0000-0002-8647-5562/work/53548938
dc.identifier.otherORCID: /0000-0002-6438-6892/work/60427319
dc.identifier.otherWOS: 000460493500003
dc.descriptionThis work was supported by the Bertarelli Foundation and we thank them for their generous and sustained financial support in making the 2 cruises possible.en
dc.description.abstractOceanographic observations were made with a subsurface oceanographic mooring over the summit and flanks of two neighbouring seamounts in the tropical Indian Ocean to identify processes that may be responsible for the aggregation of silvertip sharks (Carcharhinus albimarginatus) in the deep water drop-off surrounding the summits. The seamounts, which are in the Chagos Archipelago in the British Indian Ocean Territories, are narrow in horizontal extent (<10 km), have steeply sloping (>15°) sides that rise from depths of > 600 m, and flat summits at a depth of 70 m. They are subjected to forcing at subinertial, basin-scales and local scales that include a mixed tidal regime and storm-generated near inertial waves. At the drop-off, at a depth of between 70 and 100 m, isotherms oscillate at both diurnal and semidiurnal frequencies with amplitudes of ∼ 20–30 m. The waves of tidal origin are accompanied by short period (∼5 min) internal waves with amplitudes O(10 m) and frequencies close to the local buoyancy frequency, N, within the thermocline which is the maximum frequency possible for freely propagating internal waves. The tidal oscillations result from internal lee waves with 30 m vertical wavelength generated by the prevailing currents over the supercritical seamount flanks, whereby the bottom slope is greater than the internal tide wave slope. The ‘near-N’ waves are due to enhanced shear associated with the hydraulic jumps that form from the lee waves due to the abrupt transition from steeply sloping sides to a relatively flat summit. The jumps manifest themselves as bottom-trapped bores that propagate up the slope towards the summit. Further observations over the summit reveal that the bores subsequently flush the summits with cold water with tidal periodicity. The bores, which have long wave phase speeds more than double that of the bore particle velocities, are characterised by intense vertical velocities (>0.1 m s−1) and inferred local resuspension but relatively little turbulence based on temperature overturns. Our results strongly implicate lee waves as the dynamic mechanism of leading order importance to the previously observed accumulation of biomass adjacent to the supercritical slopes that are commonplace throughout the archipelago. We propose that further investigation should identify the spatiotemporal correlation between internal wave activity and fish schooling around the summit, and whether such schooling attracts predators.
dc.relation.ispartofProgress in Oceanographyen
dc.rightsCopyright © 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (
dc.subjectChagos Archipelagoen
dc.subjectIndian Oceanen
dc.subjectLee wavesen
dc.subjectApex predatorsen
dc.subjectInternal wavesen
dc.subjectGC Oceanographyen
dc.subjectQH301 Biologyen
dc.titleInternal lee waves and baroclinic bores over a tropical seamount shark ‘hot-spot’en
dc.typeJournal articleen
dc.description.versionPublisher PDFen
dc.contributor.institutionUniversity of St Andrews.Scottish Oceans Instituteen
dc.contributor.institutionUniversity of St Andrews.School of Biologyen
dc.contributor.institutionUniversity of St Andrews.Pelagic Ecology Research Groupen
dc.contributor.institutionUniversity of St Andrews.Marine Alliance for Science & Technology Scotlanden
dc.contributor.institutionUniversity of St Andrews.Centre for Research into Ecological & Environmental Modellingen
dc.description.statusPeer revieweden

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