Submesoscale Features and Turbulent Mixing of an Oblique Anticyclonic Eddy in the Gulf of Alaska Investigated by Marine Seismic Survey Data

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.

Time‐Lapse Acoustic Imaging of Mesoscale and Fine‐Scale Variability within the Faroe‐Shetland Channel

“…This lack of correspondence suggests that regions of high shear do not generate local turbulent dissipation. Instead, energy could be carried away from the core of the vortex by internal waves that break within weaker stratification located away from the core (Tang et al, 2019). In general, variations in calculated values of K are probably caused by a combination of changes in stratification and in the strength of turbulent mixing that are brought about by passage of the vortex.…”

Geostatistical Seismic Inversion for Temperature and Salinity in the Madeira Abyssal Plain

“…A smaller lenticular feature is also observed at shallow depths (around 750 m) that could be associated with the transition to Mediterranean waters or a secondary feature associated with that eddy (Figure 10B). Oblique reflections between 750 and 2,250 m might be related to oceanic fronts within the MOW or an inclined eddy of smaller dimensions as imaged in Tang et al (2020). A possible double diffusion phenomenon can be detected by the continuous, parallel and bright reflections at approximately 1,500 ms for almost all the profile (Figure 10C).…”

Observations of Internal Structure Changes in Shoaling Internal Solitary Waves Based on Seismic Oceanography Method

“…With the development of seismic oceanography (Holbrook et al, 2003), seismic reflection surveying has been applied to study various oceanographic phenomena including fronts (Holbrook et al, 2003;Tsuji et al, 2005), water mass boundaries (Nandi et al, 2004), mesoscale eddies (Pinheiro et al, 2010), internal waves (Holbrook and Fer, 2005;Bai et al, 2017), the Mediterranean undercurrent (Buffett et al, 2009;Biescas et al, 2010), and submesoscale processes (Sallarès et al, 2016;Tang et al, 2020). More recently, seismic reflection studies have now been used to look at the evolution of oceanic processes over time (Dickinson et al, 2020;Gunn et al, 2020;Zou et al, 2021).…”