Observations of Submesoscale Variability and Frontal Subduction within the Mesoscale Eddy Field of the Tasman Sea
Submesoscale lenses of water with anomalous hydrographic properties have previously been observed in the East Australian Current (EAC) system, embedded within the thermocline of mesoscale anticyclonic eddies. The waters within these lenses have high oxygen content and temperature–salinity properties that signify a surface origin. However, it is not known how these lenses form. This study presents field observations that provide insight into a possible generation mechanism via subduction at upper-ocean fronts. High-resolution hydrographic and velocity measurements of submesoscale activity were taken across a front between a mesoscale eddy dipole downstream of the EAC separation point. The front had O(1) Rossby number, strong vertical shear, and flow conducive to symmetric instability. Frontogenesis was measured in conjunction with subduction of an anticyclonic water parcel, indicative of intrathermocline eddy formation. Twenty-five years of satellite imagery reveals the existence of strong mesoscale strain coupled with strong temperature fronts in this region and indicates the conditions that led to frontal subduction observed here are a persistent feature. These processes impact the vertical export of tracers from the surface and dissipation of mesoscale kinetic energy, implicating their importance for understanding regional ocean circulation and biological productivity.
© 2020 American Meteorological Society. (Manuscript received 28 May 2019, in final form 22 March 2020) We heartily thank the scientists, Australian Marine National Facility staff and crew of the R/V Investigator who made the voyage a success, under the guidance of chief scientist Iain Suthers, master John Highton, and voyage manager Don McKenzie. Special thanks to Paulina Cetina-Heredia, Carlos Rocha, and Eduardo Queiroz for their vital role in planning the instrument deployment, and Matt Boyd, Karl Malakoff, Jason Fazey, Sven Gastauer, and Kendal Sherrin for technical support and making the 2am–2pm shift so much fun. All data collected on the cruise are available through the Australian Ocean Data Network (www.aodn.org.au). The SSALTO/DUACS altimeter products were produced and distributed by the Copernicus Marine and Environment Monitoring Service (http://www.marine.copernicus.eu), the FSLE were provided in collaboration with LOcean and CTOH and distributed by Aviso+ (https://www.aviso.altimetry.fr/) with support from CNES. Ocean color and SST imagery was produced by NASA's Ocean Biology Processing Group (https://oceandata.sci.gsfc.nasa.gov/). We make use of "cmocean" colorbars developed by Kristen Thyng, and "brewermap" colorbars developed by Cynthia Brewer and colleagues. This research was partially supported by an Australian Research Council Linkage Project Grant to MR (LP150100064). We are thankful to the two reviewers whose insightful feedback helped improve the quality this manuscript.
Supplemental Material - 10.1175_jpo-d-19-0131.s1.pdf
Published - jpod190131.pdf