Isopycnal stirring and diapycnal mixing in the Eastern North Atlantic inferred from Argo observations
Isopycnal stirring and diapycnal mixing in the Eastern North Atlantic inferred from Argo observations
The variability of isopycnal stirring and diapycnal mixing associated with mesoscale and microscale turbulence, respectively, is assessed using Argo float observations in the eastern subtropical North Atlantic. A new method is introduced combining a finescale parameterization with a triple decomposition framework to separate isopycnal stirring and diapycnal mixing. Our approach is validated by comparing with microstructure measurements from an independent North Atlantic tracer release experiment in the 1990s. Both sets of diagnostics reveal that diapycnal mixing dominates in the upper thermocline and that isopycnal stirring prevails in deeper, intermediate layers, influenced by Mediterranean Outflow Water. The analysis of Argo data for years 2014–24 reveals substantial interannual variations in stirring and mixing rates and in the relative contributions of mesoscale and microscale processes to thermohaline variance dissipation, which persisted in time (~3 yr) and across isopycnal layers (26.75–27.5 kg m -3). A shift in the relative contributions to the variance dissipation occurred over the period, with more prevalent isopycnal stirring in the thermocline after 2018. This enhancement of isopycnal stirring, which concurred with lower isopycnal diffusivities, is attributed to increased property gradient along-isopycnals induced by a large-scale cooling and freshening of the eastern subtropical North Atlantic. Our results highlight how property contrasts in the thermocline, induced originally by ocean ventilation, are modified by isopycnal stirring and diapycnal mixing. This application of finescale parameterizations constitutes a powerful tool that has the potential to capture and quantify the temporal evolution of isopycnal stirring and diapycnal mixing rates from Argo observations across the global ocean.
Diapycnal mixing, Isopycnal mixing, Mixing, North Atlantic Ocean, Turbulence, Ventilation
627-641
Broullón, Espe
044ead43-6ce8-4418-b5c4-724eb2a181f9
Castro, Bieito Fernández
8017e93c-d5ee-4bba-b443-9c72ca512d61
Naveira Garabato, Alberto C.
97c0e923-f076-4b38-b89b-938e11cea7a6
Clément, Louis
bd1aafc4-3240-46e3-88d4-141f2b9cc1cc
Oltmanns, Marilena
92c7996f-062c-43a7-8577-174b9c6a22fa
Williams, Richard G.
6686109a-abe3-41f7-8636-14cb8daaa6db
1 March 2026
Broullón, Espe
044ead43-6ce8-4418-b5c4-724eb2a181f9
Castro, Bieito Fernández
8017e93c-d5ee-4bba-b443-9c72ca512d61
Naveira Garabato, Alberto C.
97c0e923-f076-4b38-b89b-938e11cea7a6
Clément, Louis
bd1aafc4-3240-46e3-88d4-141f2b9cc1cc
Oltmanns, Marilena
92c7996f-062c-43a7-8577-174b9c6a22fa
Williams, Richard G.
6686109a-abe3-41f7-8636-14cb8daaa6db
Broullón, Espe, Castro, Bieito Fernández, Naveira Garabato, Alberto C., Clément, Louis, Oltmanns, Marilena and Williams, Richard G.
(2026)
Isopycnal stirring and diapycnal mixing in the Eastern North Atlantic inferred from Argo observations.
Journal of Physical Oceanography, 56 (3), .
(doi:10.1175/JPO-D-25-0090.1).
Abstract
The variability of isopycnal stirring and diapycnal mixing associated with mesoscale and microscale turbulence, respectively, is assessed using Argo float observations in the eastern subtropical North Atlantic. A new method is introduced combining a finescale parameterization with a triple decomposition framework to separate isopycnal stirring and diapycnal mixing. Our approach is validated by comparing with microstructure measurements from an independent North Atlantic tracer release experiment in the 1990s. Both sets of diagnostics reveal that diapycnal mixing dominates in the upper thermocline and that isopycnal stirring prevails in deeper, intermediate layers, influenced by Mediterranean Outflow Water. The analysis of Argo data for years 2014–24 reveals substantial interannual variations in stirring and mixing rates and in the relative contributions of mesoscale and microscale processes to thermohaline variance dissipation, which persisted in time (~3 yr) and across isopycnal layers (26.75–27.5 kg m -3). A shift in the relative contributions to the variance dissipation occurred over the period, with more prevalent isopycnal stirring in the thermocline after 2018. This enhancement of isopycnal stirring, which concurred with lower isopycnal diffusivities, is attributed to increased property gradient along-isopycnals induced by a large-scale cooling and freshening of the eastern subtropical North Atlantic. Our results highlight how property contrasts in the thermocline, induced originally by ocean ventilation, are modified by isopycnal stirring and diapycnal mixing. This application of finescale parameterizations constitutes a powerful tool that has the potential to capture and quantify the temporal evolution of isopycnal stirring and diapycnal mixing rates from Argo observations across the global ocean.
Text
phoc-JPO-D-25-0090.1
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More information
Accepted/In Press date: 5 January 2026
e-pub ahead of print date: 6 February 2026
Published date: 1 March 2026
Keywords:
Diapycnal mixing, Isopycnal mixing, Mixing, North Atlantic Ocean, Turbulence, Ventilation
Identifiers
Local EPrints ID: 510068
URI: http://eprints.soton.ac.uk/id/eprint/510068
ISSN: 0022-3670
PURE UUID: 8397e94b-04bd-4b0a-8e67-f0090f69bbf0
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Date deposited: 17 Mar 2026 17:31
Last modified: 18 Mar 2026 03:01
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Contributors
Author:
Espe Broullón
Author:
Louis Clément
Author:
Marilena Oltmanns
Author:
Richard G. Williams
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