Time-Lapse Seismic Imaging of Oceanic Fronts and Transient Lenses within South Atlantic Ocean

• Main Authors: Gunn, Kathryn L., White, Nicholas J., Caulfield, Colm-cille P.
• Format: Article in Journal/Newspaper
• Language: English
• Published: AGU 2020
• Subjects: 02 - Geodynamics; Geophysics and Tectonics; South Atlantic Ocean
• Online Access: http://eprints.esc.cam.ac.uk/4765/; http://eprints.esc.cam.ac.uk/4765/1/gunn-et-al-2020-v8_revision_2_compressed.pdf

Oceanic fronts play a pivotal role in controlling water mass transfer, although little is known about deep frontal structure on appropriate temporal and spatial scales. Here, we present a sequence of calibrated time-lapse images from a three-dimensional seismic survey that straddles the Brazil-Malvinas Confluence— a significant feature of the merid- ional overturning circulation. Eight vertical transects reveal the evolution of a major front. It is manifest as a discrete planar surface that dips at less than 2 ◦ and is traceable to 1.5–2 km depth. Its shape and surface expression are consistent with sloping isopycnal surfaces of the calculated potential density field and with coeval sea surface tempera- ture measurements, respectively. Within the top ∼1 km, where cold fresh water subducts beneath warm salty water, a series of tilted lenses are banked up against the sharply de- fined front. The largest of these structures is centered at 700 m depth and is cored by cold fresh water. Time-lapse imagery demonstrates that this tilted lens grows and de- cays over nine days. It has a maximum diameter of < 34 ± 0.13 km and a maximum height of < 750±10 m. Beneath 1 km, where horizontal density gradients are negligi- ble, numerous deforming lenses and filaments on length scales of 10–100 km are being swept toward the advecting front.