Submesoscale Features and Turbulent Mixing of an Oblique Anticyclonic Eddy in the Gulf of Alaska Investigated by Marine Seismic Survey Data. Issue 1 (4th January 2020)

• Record Type: Journal Article
• Authors: Tang, Qunshu; Gulick, Sean P. S.; Sun, Jie; Sun, Longtao; Jing, Zhiyou
• Is Part Of: Journal of geophysical research. Volume 125:Issue 1(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-01-04
• Subjects: tilting eddy -- submesoscale feature -- mesoscale structure -- turbulent mixing -- Gulf of Alaska -- seismic oceanography; Oceanography -- Periodicals; 551.4605
• DOI: 10.1029/2019JC015393
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: Mesoscale eddies are ubiquitous in the global ocean and can be captured by marine multichannel seismic surveys. In this study, a short‐lived anticyclonic eddy is characterized along the seismic line STEEP11 acquired on 30 September 2008 in northern Gulf of Alaska. Fine‐scale eddy stratification with alternative strong striae and weak layers is regarded as a typical eddy structure of the study region. The eddy center dips along a NW tilted axis of 1.9 ± 0.2° from the horizontal. Submesoscale structures including fronts and filaments coexist around the eddy periphery and dominate ~70% of the eddy volume. The estimated geostrophic current is asymmetric and ageostrophic components must play a significant role in balancing the eddy system. Nonlinearity of the eddy is strong as its rotation speed is much higher than its translation speed. We suggest that Ekman transport is probably responsible for the skewed shape with regards to the asymmetric geostrophic current and asymmetric submesoscale processes. Detailed turbulent diffusivities in and around the eddy are quantified, with an average level of 6.5 × 10 −5 m 2 s −1 . The diapycnal diffusivities show an increasing pattern from the eddy center to the surrounding water. With the pervasive submesoscale processes as the transitional dynamics, a forward cascade of energy could be expected from the mesoscale eddy to the fine‐scale wave‐breaking and turbulence. The irregular vortex structure may reduce the structural stability, facilitate the energy conversion, and accelerate the eddy dissipation. Plain Language Summary: Mesoscale eddies are the weather of the global ocean and can be captured by marine multichannel seismic surveys. Vertical axes of mesoscale eddies could be tilt rather than canonically straight, and therefore, their detailed internal structures may also be asymmetric. Here we use high‐resolution seismic methods to characterize a skewed, short‐lived (eight weeks) anticyclonic eddy in northern Gulf of Alaska for the first time. The eddy center is strongly displaced at depth with a NW tilted axis of ~2° from the horizontal. Geostrophic currents, submesoscale structures, and turbulent diffusivities are asymmetrically distributed in and around the eddy. Except for the standard description/interpretation of a seismic imaged eddy, this study strives to derive numerous and detailed physical oceanographic characteristics from seismic data and stems from a close collaboration between seismologists and oceanographers. Key Points: A marine seismic image reveals a strongly tilted mesoscale warm eddy in the Gulf of Alaska Submesoscale structures including fronts and filaments coexist around the eddy periphery Diapycnal turbulent diffusivity of the eddy center is lower than that of its surroundings