Mixing around a shallow seamount
| dc.contributor.author | Mudge, Todd Douglas | en_US |
| dc.date.accessioned | 2024-08-14T22:54:59Z | |
| dc.date.available | 2024-08-14T22:54:59Z | |
| dc.date.copyright | 1994 | en_US |
| dc.date.issued | 1994 | |
| dc.degree.department | School of Earth and Ocean Sciences | |
| dc.degree.level | Master of Science M.Sc. | en |
| dc.description.abstract | Microstructure measurements were taken as part of a multi-disciplinary study of a shallow seamount in the North Pacific. Cobb Seamount, approximately 500 km west of Washington state, rises from the abyssal sea-floor at 3000 m to within 27 m of the surface. The waters around Cobb contain high concentrations of planktonic and fish communities whose presence is believed to be the result of interactions between physical processes and phytoplankton. The microstructure measurements at Cobb were unique because they were the first to include observations within the bottom boundary layer (bbl) of a seamount. Within the bbl, t he diurnal tide and internal waves dominate t he mean flow around the seamount. Bot tom mixing and bottom mixed layer thickness are intermittent; with periods ranging from a few hours to 24 hours. The effective vertical eddy diffusivity within the bbl of the seamount is 2-10 x 10⁻⁴ m² s⁻¹. Hence, the mixing within the bbl of Cobb can be as great as the mixing occurring in 1000 km² of the open ocean. Internal tides t hat are generated and internal waves that are reflected by the bottom produce enhanced and persistent turbulence within 8 km of the flank of Cobb. Most of the turbulence is generated by semi-diurnal internal tidal waves originating from the rim of the seamount. The average vertical diffusivity 3 km from the flank was > 10⁻³ m² s⁻¹, more than 2 orders of magnitude larger than what is observed in the open ocean. The mixing that occurs at Cobb is equivalent to the mixing that occurs in 10,000- 100 ,000 km² of the open ocean. If all seamounts are as efficient mixers as Cobb, then they could produce 1- 10 times more mixing in the deep Pacific Ocean than occurs within the ocean's interior . Internal wave driven motions over the seamount obscure the bending of isopycnals by the geostrophic-mean flow. Previous claims of isopycnal doming over and around Cobb were made without accounting for this effect. Therefore, the existence of doming over Cobb is still an open question. Microstructure measurements made with airfoil shear probes contain anomalous signals that are mostly caused by particle hits. I have determined that these particles are on the order of 0.3 mm and greater. The particles are primarily biological in origin, but may be either living or dead. It may be possible to use these anomalous signals to determine relative and perhaps absolute particle concentrations. | en |
| dc.format.extent | 127 pages | |
| dc.identifier.uri | https://hdl.handle.net/1828/19058 | |
| dc.rights | Available to the World Wide Web | en_US |
| dc.title | Mixing around a shallow seamount | en_US |
| dc.type | Thesis | en_US |
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