The vertical structure of open-ocean submesoscale variability during a full seasonal cycle

Type Article
Date 2020-01
Language English
Author(s) Erickson Zachary K1, Thompson Andrew F1, Callies Jörn1, Yu Xiaolong2, Naveira Garabato Alberto3, Klein Patrice
Affiliation(s) 1 : California Institute of Technology, Division of Geological and Planetary Sciences, Pasadena, CA, USA
2 : Ifremer, Université de Brest, CNRS, IRD, Laboratoire d’Océanographie Physique et Spatiale, IUEM, Brest, France
3 : Department of Ocean and Earth Sciences, University of Southampton, UK
4 : Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
Source Journal Of Physical Oceanography (0022-3670) (American Meteorological Society), 2020-01 , Vol. 50 , N. 1 , P. 145-160
DOI 10.1175/JPO-D-19-0030.1
WOS© Times Cited 17
Keyword(s) Instability, Mixing, Small scale processes, Buoy observations, Profilers, oceanic

Submesoscale dynamics are typically intensified at boundaries and assumed to weaken below the mixed layer in the open ocean. Here, we assess both the seasonality and the vertical distribution of submesoscale motions in an open ocean region of the northeast Atlantic. Second-order structure functions, or variance in properties separated by distance, are calculated from submesoscale-resolving ocean glider and mooring observations, as well as a 1/48° numerical ocean model. This data set combines a temporal coverage that extends through a full seasonal cycle, a horizontal resolution that captures spatial scales as small as 1 km, and vertical sampling that provides near-continuous coverage over the upper 1000 m. While kinetic and potential energies undergo a seasonal cycle, being largest during the winter, structure function slopes, influenced by dynamical characteristics, do not exhibit a strong seasonality. Furthermore, structure function slopes show weak vertical variations; there is not a strong change in properties across the base of the mixed layer. Additionally, we compare the observations to output from a high-resolution numerical model. The model does not represent variability associated with superinertial motions and does not capture an observed reduction in submesoscale kinetic energy that occurs throughout the water column in spring. Overall, these results suggest that the transfer of mixed layer submesoscale variability down to depths below the traditionally-defined mixed layer is important throughout the weakly stratified subpolar mode waters.

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