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An Annual Cycle of Submesoscale Vertical Flow and Restratification in the Upper Ocean

Yu, Xiaolong and Naveira Garabato, Alberto C. and Martin, Adrian P. and Buckingham, Christian E. and Brannigan, Liam and Su, Zhan (2019) An Annual Cycle of Submesoscale Vertical Flow and Restratification in the Upper Ocean. Journal of Physical Oceanography, 49 (6). pp. 1439-1461. ISSN 0022-3670. https://resolver.caltech.edu/CaltechAUTHORS:20190613-082314910

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Abstract

Numerical simulations suggest that submesoscale turbulence may transform lateral buoyancy gradients into vertical stratification and thus restratify the upper ocean via vertical flow. However, the observational evidence for this restratifying process has been lacking due to the difficulty in measuring such ephemeral phenomena, particularly over periods of months to years. This study presents an annual cycle of the vertical velocity and associated restratification estimated from two nested clusters of meso- and submesoscale-resolving moorings, deployed in a typical midocean area of the northeast Atlantic. Vertical velocities inferred using the nondiffusive density equation are substantially stronger at submesoscales (horizontal scales of 1–10 km) than at mesoscales (horizontal scales of 10–100 km), with respective root-mean-square values of 38.0 ± 6.9 and 22.5 ± 3.3 m day^(−1). The largest submesoscale vertical velocities and rates of restratification occur in events of a few days’ duration in winter and spring, and extend down to at least 200 m below the mixed layer base. These events commonly coincide with the enhancement of submesoscale lateral buoyancy gradients, which is itself associated with persistent mesoscale frontogenesis. This suggests that mesoscale frontogenesis is a regular precursor of the submesoscale turbulence that restratifies the upper ocean. The upper-ocean restratification induced by submesoscale motions integrated over the annual cycle is comparable in magnitude to the net destratification driven by local atmospheric cooling, indicating that submesoscale flows play a significant role in determining the climatological upper-ocean stratification in the study area.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1175/jpo-d-18-0253.1DOIArticle
ORCID:
AuthorORCID
Yu, Xiaolong0000-0001-7828-8161
Martin, Adrian P.0000-0002-1202-8612
Buckingham, Christian E.0000-0001-9355-9038
Su, Zhan0000-0002-2699-431X
Additional Information:© 2019 American Meteorological Society. Manuscript received 27 November 2018, in final form 28 March 2019. This research was funded by grants from the Natural Environmental Research Council (NE/1019999/1 and NE/101993X/1 as part of the OSMOSIS project). The responses of Baylor Fox-Kemper and four anonymous reviewers have greatly improved the manuscript. We acknowledge helpful discussions with George Nurser, Eleanor Frajka-Williams, Andrew Thompson, and Zachary Erickson. We are grateful to the engineers and scientists at NMFSS, captain and crew of the RRS Discovery, RRS James Cook, and R/V Celtic Explorer, and numerous scientists and technicians that helped during deployment and recovery of the moorings/gliders. All data are archived at the British Oceanographic Data Centre.
Funders:
Funding AgencyGrant Number
Natural Environment Research Council (NERC)NE/1019999/1
Natural Environment Research Council (NERC)NE/101993X/1
Subject Keywords:Ocean; Atlantic Ocean; Ageostrophic circulations; Frontogenesis/frontolysis; In situ oceanic observations
Issue or Number:6
Record Number:CaltechAUTHORS:20190613-082314910
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20190613-082314910
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:96358
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:13 Jun 2019 16:07
Last Modified:03 Oct 2019 21:21

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