Subduction of water masses in an eddying ocean
Abstract
Mesoscale eddies modify the rate at which a water mass transfers from the surface mixed layer of the ocean into the interior thermocline, in particular in regions of intense baroclinic instability such as the Antarctic Circumpolar Current, open-ocean convective chimneys, and ocean fronts. Here, the time-mean subduction of a water mass, evaluated following the meandering surface density outcrops, is found to incorporate a rectified contribution from eddies, arising from correlations between the area over which the water mass is outcropped at the sea surface and the local subduction rate. Alternatively, this eddy subduction can be interpreted in terms of an eddy-driven secondary circulation associated with baroclinic instability. The net subduction rate, incorporating both Eulerian-mean and eddy contributions, can be further related to buoyancy forcing of the surface mixed layer using a formula by Walin (1982). Solutions from an idealized two-dimensional ocean model are presented to illustrate the eddy contribution to subduction rates in the Southern Ocean and in an open-ocean convective chimney. In the Southern Ocean, the net subduction rate is the residual of the Eulerian-mean and eddy contributions, which cancel at leading order; given plausible patterns of surface buoyancy forcing, one can obtain subduction of Antarctic Intermediate Water and Antarctic Bottom Water, with entrainment of North Atlantic Deep Water in between. In a convective chimney, in contrast, the Eulerian-…
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In the Southern Ocean, air-sea buoyancy fluxes are much more informative than the wind forcing with respect to the meridional tracer transport.
“There air-sea buoyancy fluxes are, somewhat counterintuitively, much more informative than the wind forcing with respect to the meridional tracer transport (Marshall 1997;Gent 2016).”
From Competition between Baroclinic Instability and Ekman Transport under Varying Buoyancy Forcings in Upwelling Systems: An Idealized Analog to the Southern Ocean (2021) · cites this paper as Marshall 1997
Air-sea buoyancy fluxes constrain rates of fluid transfer across isopycnals in the mixed layer, hence also subduction and obduction rates at the base of the mixed layer in steady state.
“Indeed, they constrain rates of fluid transfer across isopycnals in the mixed layer, hence also subduction and obduction rates at the base of the mixed layer in steady state [subduction (obduction) being related to a convergence (divergence) of diapycnal flux of fluid, Fig. 1].”
From Competition between Baroclinic Instability and Ekman Transport under Varying Buoyancy Forcings in Upwelling Systems: An Idealized Analog to the Southern Ocean (2021) · cites this paper as Marshall 1997
Neglecting mixing in the ocean interior, the time-averaged residual meridional transport is entirely determined by the knowledge of air-sea buoyancy fluxes.
“Neglecting mixing in the ocean interior the time-averaged residual meridional transport is thus entirely determined by the knowledge of airsea buoyancy fluxes (Walin 1982;Marshall 1997).”
From Competition between Baroclinic Instability and Ekman Transport under Varying Buoyancy Forcings in Upwelling Systems: An Idealized Analog to the Southern Ocean (2021) · cites this paper as Marshall 1997
The results can be interpreted using steady-state Walin-type reasoning: given the mean frontal thermohaline structure of an upwelling system, vanishing or negative air-sea buoyancy fluxes would imply that the surface Ekman flow produces diapycnal transport of mass unless counteracted by eddy transport, resulting in partial or total cancellation of mean buoyancy advection by the Ekman flow.
“our results can be interpreted using a steady-state Walin type reasoning (Marshall 1997): given the mean frontal thermohaline structure of an upwelling system vanishing (or negative) air-sea buoyancy fluxes would imply that the surface Ekman flow produces diapycnal transport of mass unless it is counteracted by eddy transport, resulting in partial or total cancellation of the mean buoyancy advect”
From Competition between Baroclinic Instability and Ekman Transport under Varying Buoyancy Forcings in Upwelling Systems: An Idealized Analog to the Southern Ocean (2021) · cites this paper as Marshall 1997
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Thomsen, S., Capet, X., & Echevin, V. (2021) · Journal of Physical Oceanography · doi:10.1175/jpo-d-20-0294.1 · Cited by 17 · see citing works
- Authors
- Marshall, D.
- Corresponding author
- Marshall, David
- ORCID
- Marshall, David
- Venue
- Journal of Marine Research
- Publisher
- Journal of Marine Research/Yale
- Published
- 1997-03-01
- Volume
- 55
- Issue
- 2
- Pages
- 201-222
- ISSN
- 0022-2402 (ISSN-L)
- 1543-9542
- OpenAlex
- W2015825648
- Cited by
- 217
- References
- 0
- Citations by year
- 2026: 1 · 2025: 3 · 2024: 12 · 2023: 3 · 2022: 9 · 2021: 10 · 2020: 8 · 2019: 6 · 2018: 8 · 2017: 5 · 2016: 9 · 2015: 9 · 2014: 11 · 2013: 8 · 2012: 10
- FWCI
- 4.56
- Type
- journal article
- Language
- en
- Open access
- closed
- Locations
- Journal of Marine Research (publishedVersion)
- The journal
- Topics
- Physical Sciences › Earth and Planetary Sciences › Oceanography › Oceanographic and Atmospheric Processes
- Physical Sciences › Earth and Planetary Sciences › Atmospheric Science › Meteorological Phenomena and Simulations
- Physical Sciences › Earth and Planetary Sciences › Atmospheric Science › Arctic and Antarctic ice dynamics
- Keywords
- mesoscale eddies, baroclinic instability, secondary circulation, Antarctic Circumpolar Current, Southern Ocean, Antarctic Intermediate Water, Antarctic Bottom Water, thermocline
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