Cyclonic entrainment of preconditioned shelf waters into a frontal eddy

• Published in: Journal of geophysical research. Oceans 2015-02, Vol.120 (2), p.677-691
• Main Authors: Everett, J. D., Macdonald, H., Baird, M. E., Humphries, J., Roughan, M., Suthers, I. M.
• Format: Article
• Language: English
• Subjects: billow; boundary current; Computer simulation; Continental shelves; Cyclones; Eddies; Entrainment; filament; Fish; frontal eddy; Geophysics; Gliders; Habitats; larval fish; Marine ecology; Mathematical models; Nutrient transport; Oceanography; Shelves; Surface water
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1002/2014JC010301

The volume transport of nutrient‐rich continental shelf water into a cyclonic frontal eddy (entrainment) was examined from satellite observations, a Slocum glider and numerical simulation outputs. Within the frontal eddy, parcels of water with temperature/salinity signatures of the continental shelf (18–19°C and >35.5, respectively) were recorded. The distribution of patches of shelf water observed within the eddy was consistent with the spiral pattern shown within the numerical simulations. A numerical dye tracer experiment showed that the surface waters (≤50 m depth) of the frontal eddy are almost entirely (≥95%) shelf waters. Particle tracking experiments showed that water was drawn into the eddy from over 4° of latitude (30–34.5°S). Consistent with the glider observations, the modeled particles entrained into the eddy sunk relative to their initial position. Particles released south of 33°S, where the waters are cooler and denser, sunk 34 m deeper than their release position. Distance to the shelf was a critical factor in determining the volume of shelf water entrained into the eddy. Entrainment reduced to 0.23 Sv when the eddy was furthest from the shelf, compared to 0.61 Sv when the eddy was within 10 km of the shelf. From a biological perspective, quantifying the entrainment of shelf water into frontal eddies is important, as it is thought to play a significant role in providing an offshore nursery habitat for coastally spawned larval fish. Key Points: Observations showed parcels of water in the eddy were entrained from the shelf Particle tracking quantified the volume and origin of the entrained waters Frontal eddies play a significant role, providing habitat for larval fish