Coronavirus Information for the UC San Diego Community

Our leaders are working closely with federal and state officials to ensure your ongoing safety at the university. Stay up to date with the latest developments. Learn more.

Persistent turbulence in the Samoan Passage

TitlePersistent turbulence in the Samoan Passage
Publication TypeJournal Article
Year of Publication2019
AuthorsCusack J.M, Voet G., Alford MH, Girton J.B, Carter G.S, Pratt L.J, Pearson-Potts K.A, Tan S.W
Date Published2019/12
Type of ArticleArticle
ISBN Number0022-3670
Accession NumberWOS:000501807300003
Keywordsabyssal circulation; abyssal transport; channel; efficiency; flow; gravity waves; lee waves; Mixing; model; ocean; oceanography; stability; thorpe; tides; turbulence; water

Abyssal waters forming the lower limb of the global overturning circulation flow through the Samoan Passage and are modified by intense mixing. Thorpe-scale-based estimates of dissipation from moored profilers deployed on top of two sills for 17 months reveal that turbulence is continuously generated in the passage. Overturns were observed in a density band in which the Richardson number was often smaller than 1/4, consistent with shear instability occurring at the upper interface of the fast-flowing bottom water layer. The magnitude of dissipation was found to be stable on long time scales from weeks to months. A second array of 12 moored profilers deployed for a shorter duration but profiling at higher frequency was able to resolve variability in dissipation on time scales from days to hours. At some mooring locations, near-inertial and tidal modulation of the dissipation rate was observed. However, the modulation was not spatially coherent across the passage. The magnitude and vertical structure of dissipation from observations at one of the major sills is compared with an idealized 2D numerical simulation that includes a barotropic tidal forcing. Depth-integrated dissipation rates agree between model and observations to within a factor of 3. The tide has a negligible effect on the mean dissipation. These observations reinforce the notion that the Samoan Passage is an important mixing hot spot in the global ocean where waters are being transformed continuously.

Student Publication: