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Cited by 17Oceanographic and Atmospheric ProcessesMeteorological Phenomena and SimulationsOcean Waves and Remote Sensing

Competition between Baroclinic Instability and Ekman Transport under Varying Buoyancy Forcings in Upwelling Systems: An Idealized Analog to the Southern Ocean

Open access
Thomsen, Soeren, Capet, Xavier, Echevin, Vincent·2021·Journal of Physical Oceanography
DOI 10.1175/jpo-d-20-0294.1
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Abstract

Coastal upwelling rates are classically determined by the intensity of the upper-ocean offshore Ekman transport. But (sub)mesoscale turbulence modulates offshore transport, hence the net upwelling rate. Eddy effects generally oppose the Ekman circulation, resulting in so-called ‘‘eddy cancellation,” a process well studied in the Southern Ocean. Here we investigate how air–sea heat/buoyancy fluxes modulate eddy cancellation in an idealized upwelling model. We run CROCO simulations with constant winds but varying heat fluxes with and without submesoscale-rich turbulence. Eddy cancellation is consistently evaluated with three different methods that all account for the quasi-isopycnal nature of ocean circulation away from the surface. For zero heat fluxes the release of available potential energy by baroclinic instabilities is strongest and leads, near the coast, to nearly full cancellation of the Ekman cross-shore circulation by eddy effects, i.e., zero net mean upwelling flow. With increasing heat fluxes eddy cancellation is reduced and the transverse flow progressively approaches the classical Ekman circulation. Sensitivity of the eddy circulation to synoptic changes in air–sea heat fluxes is felt down to 125-m depth despite short experiments of tens of days. Mesoscale dynamics dominate the cancellation effect in our simulations which might also hold for the real ocean as the relevant processes act below the surface boundary layer. Although the idealized setting overemphasizes the role of eddies and thus studies with more realistic settings should follow, our findings have important implications for the overall understanding of upwelling system dynamics.

AI snapshot

Written from the paper’s full text.

TL;DR

In idealized CROCO upwelling simulations with constant winds, eddy cancellation of the Ekman cell is strongest when air–sea heat fluxes are zero and weakens as heat flux increases, so the residual cross-shore flow approaches the classical Ekman circulation. The cancellation is dominated by mesoscale turbulence and is sensitive to heat-flux changes down to ~125 m, though the idealized periodic channel overemphasizes eddy effects relative to real EBUS.

Key findings

  • For zero heat flux (NF), available potential energy release by baroclinic instability is strongest; near the coast, eddy effects nearly fully cancel the Ekman cross-shore circulation, i.e., zero net mean upwelling flow. With increasing heat flux, eddy cancellation is reduced and the transverse flow progressively approaches the classical Ekman circulation.
  • At 70-m depth and 64 km offshore, eddies cancel 72%–87% of the Ekman transport in NF, 46%–60% in MF, and around 40% in HF across three streamfunction methods. The eddy streamfunction reaches −2.8 m² s⁻¹ in NF, stronger in opposing direction than the mean Eulerian streamfunction (2.3 m² s⁻¹).
  • The APE release term \(w'b'\) averaged between 16 and 112 km offshore decreases from 1.44 × 10⁻⁷ m² s⁻³ in NF to 1.06 × 10⁻⁷ m² s⁻³ in HF, a decrease of about 25%; at 75-m depth it is reduced by about 50% in HF compared with NF. Sensitivity to heat flux reaches down to 125-m depth, while below 125 m the domain-averaged \(w'b'\) curves show almost no difference and vanish around 200 m.
  • Mesoscale dynamics dominate the cancellation: a factor-of-10 resolution change (800 m vs. 8 km) does not dramatically alter \(w'b'\) below 50 m, though mixed-layer values differ by about 25%. The paper’s EKE exceeds real EBUS values by a factor of 2–10; rescaling suggests real EBUS cancellation of roughly 3%–6% in the northern Benguela to 10%–30% in the California Current System.

Methods

  • CROCO is used in an idealized upwelling configuration: 400 km alongshore × 600 km cross-shore, periodic alongshore, closed coast and offshore boundaries, shelf/slope/flat bottom, 100 sigma levels, constant \(f\) corresponding to ~14.5°S, constant wind stress of 0.075 N m⁻² after a ramp, and a prescribed alongshore pressure gradient driving an onshore return flow.
  • Heat-flux sensitivity experiments use restoring with \(dQ/dT = 0\) (NF), 225 (MF), and 250 W m⁻² K⁻¹ (HF); MF receives on average about 200 W m⁻² near the coast and 50 W m⁻² 200 km offshore. Each experiment has 12 ensemble runs at 800-m and 8-km horizontal resolution; runs last 120 days including 80-day spinup, with analysis over days 81–120.
  • Eddy and residual circulations are quantified with three streamfunction formulations: transformed Eulerian mean (TEM), isopycnal averaging at constant cross-shore distance, and isopycnal averaging at constant depth. Baroclinic instability strength is evaluated as APE release via the covariance \(w'b'\).

Limitations

  • Paper-stated: the idealized periodic channel lacks a beta effect, so EKE is 2–10 times higher than in the real EBUS; the rescaling to real EBUS assumes eddy overturning scales linearly with EKE. Experiments are only 40 days and not in statistical equilibrium, and wind variability and alongshore pressure-gradient variability are ignored.
  • Paper-stated: the idealized setting overemphasizes the role of eddies, and more realistic EBUS studies are needed; negative buoyancy-flux cases and biogeochemical tracers were not investigated. The choice of pure flux versus restoring surface buoyancy boundary condition may also matter.
  • Evident from the text: constant wind forcing, no seasonal cycle, simplified bathymetry/coastline, a closed offshore boundary with a sponge layer, and short ensemble duration may further limit realism and statistical robustness.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1175/jpo-d-20-0294.1

Cites

65 of 65 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

11 of 66 cited sources checked · 3 supported · 0 flagged · accuracy not yet measured

  • Premisecitation

    (Sub)mesoscale turbulence modulates offshore transport and hence the net upwelling rate.

    “But (sub)mesoscale turbulence modulates offshore transport, hence the net upwelling rate.”
    Quote in the paperSubstantial claim1 of 3 sources checked
    • cites Lathuilière et al. 2010 source

      The Summary (§5, paragraph 51; page unavailable) says mesoscale filaments export nitrate and phytoplankton offshore, supporting the transport part. But it also says the eddying and non-eddying simulations have the same upwelling mass flux, so the paper does not support the claimed change in net upwelling rate. (LLM, conf=0.91)

      Experimental — accuracy not yet measured
    • cites Gruber et al. 2011 source
    • cites Colas et al. 2013 source
  • Interpretationcitation

    Feeding the surface Ekman flow would involve bottom Ekman transport, thereby limiting the realism of the model for most upwelling sectors.

    “Feeding the surface Ekman flow would therefore involve bottom Ekman transport, thereby limiting the realism of the model for most upwelling sectors (Lentz and Chapman 2004).”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites Lentz and Chapman 2004 source

      The Estimation of the nonlinear cross-shelf momentum flux section describes a model in which onshore transport in the bottom boundary layer and interior balances offshore surface Ekman transport. But the Numerical model results section says return flow can occur predominantly in the interior, with essentially none in the bottom boundary layer. The paper therefore does not establish that feeding the surface flow necessarily involves bottom Ekman transport or that this limits a model’s realism for most upwelling sectors. (LLM, conf=0.84)

      Experimental — accuracy not yet measured
  • Premisecitation

    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].”
    Quote in the paperSubstantial claim1 of 2 sources checked
    • cites Marshall 1997 source
    • cites Gent 2016 source

      The Introduction discusses how surface boundary conditions affect eddy compensation of the overturning circulation, and the Discussion’s Figure 1 caption identifies atmospheric forcing and fluxes. Neither passage states that air–sea buoyancy fluxes constrain fluid transfer across isopycnals or steady-state subduction and obduction at the mixed-layer base. Searches for those relationships, including “mixed layer,” “subduction,” and “obduction,” found no supporting passage in our copy. (LLM, conf=0.72)

      Experimental — accuracy not yet measured
  • Premisecitation

    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).”
    Quote in the paperSubstantial claim1 of 2 sources checked
    • cites Walin 1982 source

      Section 4 says that surface heat flux can directly estimate the poleward surface drift and associated circulation when the mixing term is negligible, particularly at low and medium temperatures. It does not establish that air–sea buoyancy fluxes entirely determine the time-averaged residual meridional transport; for high temperatures, it says the mixing term is vital. (LLM, conf=0.84)

      Experimental — accuracy not yet measured
    • cites Marshall 1997 source
  • Interpretationcitation

    The recirculation confined in the mixed layer revealed by C_TEM Eddy, and to a lesser extent C_iso2y Eddy, is the signature of submesoscale-driven mixed layer restratification.

    “The recirculation confined in the mixed layer revealed by C TEM Eddy (and to a lesser extent C iso2y Eddy ) is the signature of submesoscaledriven mixed layer restratification (Fox-Kemper et al. 2008).”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites Fox-Kemper et al. 2008 source
  • May combine two claims. 38
  • Classified as probably not a substantial claim. 40

  • May combine two claims.

    Premisecitation

    Eddy effects generally oppose the Ekman circulation, resulting in eddy cancellation, a process well studied in the Southern Ocean.

    “Eddy effects generally oppose the Ekman circulation, resulting in so-called ''eddy cancellation,'' a process well studied in the Southern Ocean.”
    Quote in the paperSubstantial claim2 of 3 sources checked
    • cites Marshall and Radko 2003 source
    • cites Hallberg and Gnanadesikan 2006 source
    • cites Morrison et al. 2011 source

  • May combine two claims.

    Premisecitation

    Quasi-balanced mesoscale and submesoscale turbulence is responsible for rectified eddy transport which also tends to counteract the Ekman upwelling cell.

    “quasi-balanced mesoscale and submesoscale turbulence is responsible for rectified eddy transport which also tends to counteract the Ekman upwelling cell.”
    Quote in the paperSubstantial claim1 of 3 sources checked
    • cites Lathuilière et al. 2010 source

      The Summary (§5; page unavailable) reports that mesoscale circulation and filaments transport nitrate and phytoplankton offshore. But the Discussion (§4; page unavailable) explicitly says that rectification of the mean flow by mesoscale dynamics was not addressed. The paper does not establish that eddy transport counteracts the Ekman upwelling cell; its Physical Model (§2.1; page unavailable) attributes compensating onshore transport to an imposed alongshore pressure gradient. (LLM, conf=0.84)

      Experimental — accuracy not yet measured
    • cites Gruber et al. 2011 source
    • cites Colas et al. 2013 source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductreasoning

    Spurious diapycnal mixing associated with the WENO scheme has negligible effects in this study.

    “Spurious diapycnal mixing associated with this scheme cannot be entirely avoided but shall have negligible effects in our study”
    Quote in the paperNot a substantial claim1 of 2 sources checked
    • cites Marchesiello et al. (2009)

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

    • cites Lemarié et al. (2012) source

      Section 2, “Active Tracer Advection,” says numerical schemes must respect small levels of diapycnal mixing, and Section 2.1 says spurious mixing should be kept as small as possible. But the paper describes a modified RSUP3 scheme, not WENO, and does not establish that WENO-associated mixing has negligible effects in the citing authors’ study. Section 6.1 instead reports significant mixing for diffusion along σ-surfaces in long-term simulations. (LLM, conf=0.78)

      Experimental — accuracy not yet measured

  • Classified as probably not a substantial claim.

    Premisecitation

    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).”
    Quote in the paperSubstantial claim1 of 2 sources checked
    • cites Marshall 1997 source
    • cites Gent 2016 source

      The Introduction says the Southern Ocean overturning circulation affects uptake of heat, carbon dioxide, and other tracers. The Discussion reports that buoyancy-driven variability produced a much larger change than Southern Hemisphere winds in the North Atlantic overturning circulation. Neither passage establishes that air–sea buoyancy fluxes are more informative than winds for meridional tracer transport in the Southern Ocean; the comparison concerns a different region and quantity. (LLM, conf=0.78)

      Experimental — accuracy not yet measured

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    In many upwelling sectors, alongshore pressure gradients can yield onshore velocities that counteract, or more infrequently reinforce, the Ekman flow.

    “In many upwelling sectors they can yield onshore velocities that counteract, or more infrequently reinforce, the Ekman flow (Colas et al. 2008;Marchesiello et al. 2010;Ndoye et al. 2017;Jacox et al. 2018).”
    Quote in the paperNot a substantial claim1 of 3 sources checked
    • cites Colas et al. 2008 source
    • cites Marchesiello et al. 2010 source
    • cites Ndoye et al. 2017 source

      Section 3.3 reports that alongshore gradients produce onshore geostrophic flow over the southern Senegal shelf, reducing or reversing the offshore flow expected from Ekman transport. The paper does not establish that this happens in many upwelling sectors, or that reinforcement of Ekman flow occurs less frequently. Page numbers are not available in our copy. (LLM, conf=0.86)

      Experimental — accuracy not yet measured

  • May combine two claims.

    Findingown data

    For zero heat fluxes, the release of available potential energy by baroclinic instabilities is strongest and leads, near the coast, to nearly full cancellation of the Ekman cross-shore circulation by eddy effects, i.e., zero net mean upwelling flow.

    “For zero heat fluxes the release of available potential energy by baroclinic instabilities is strongest and leads, near the coast, to nearly full cancellation of the Ekman cross-shore circulation by eddy effects, i.e., zero net mean upwelling flow.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    With increasing heat fluxes, eddy cancellation is reduced and the transverse flow progressively approaches the classical Ekman circulation.

    “With increasing heat fluxes eddy cancellation is reduced and the transverse flow progressively approaches the classical Ekman circulation.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Findingnone given

    The first baroclinic Rossby Radius is around 57 km within the idealized setting.

    “The first baroclinic Rossby Radius is around 57 km within our idealized setting.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    Because the mean cross-shore buoyancy gradient b_y is weakly sensitive to resolution, similar reductions of about 25% are found for the intensity of C_TEM Eddy in the mixed layer.

    “The mean cross-shore buoyancy gradient b y being weakly sensitive to resolution similar reductions of about 25% are found for the intensity of C TEM Eddy in the mixed layer (cf.Figs.7b,e).”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    At the chosen location, eddies cancel between 72% (C_iso2y Eddy) and 87% (C_iso2h Eddy) of the Ekman transport for NF, while cancellation reduces to between 46% (C_iso2y Eddy) and 60% (C_iso2h Eddy) for MF.

    “At the chosen location, the eddies cancel between 72% (C iso2y Eddy ) and 87% (C iso2h Eddy ) of the Ekman transport for NF while the cancellation reduces to between 46% (C iso2y Eddy ) and 60% (C iso2h Eddy )for MF (Fig. 10b).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    C_TEM Eddy sign is systematically negative and almost mirrors the structure of the mean streamfunction C_Mean.

    “Its sign is systematically negative, and it almost mirrors the structure of the mean streamfunction (C Mean ) shown in Fig. 8a.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Several smaller-scale cyclonic vortices are formed around the anticyclone with cold filaments at the edges of the mesoscale structures.

    “Several smaller-scale cyclonic vortices are formed around the anticyclone with cold filaments at the edges of the mesoscale structures (Figs.6a,b).”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    Below 125-m depth, domain-averaged w'b' curves for all air-sea flux cases show almost no difference and vanish at around 200-m depth.

    “Below 125-m depth the domain-averaged w 0 b 0 curves for all airsea flux cases show almost no difference and vanish at around 200-m depth (Fig. 7c)”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Findingown data

    Within the filaments the SST can drop down to about 18°C.

    “Within the filaments the SST can drop down to about 188C.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    Although a large degree of eddy-mean cancellation is still present at HF, its residual circulation has recovered a structure that more closely resembles the mean Ekman circulation, with some streamlines connecting the offshore-subsurface to the nearshore-surface sectors.

    “Although a large degree of eddy-mean cancellation is still present at HF its residual circulation has recovered a structure that more closely resembles the mean Ekman circulation, with some streamlines unambiguously connecting the offshoresubsurface to the nearshore-surface sectors.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    The entire region of interest is in close proximity to the mean mixed-layer base and is subjected to intense intermittent mixing.

    “Second, and more importantly, our entire region of interest is in close proximity to the mean ML base, and it is subjected to intense intermittent mixing.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Eddy streamfunction reaches values down to -2.8 m2 s-1, stronger in opposing direction than the mean Eulerian streamfunction (2.3 m2 s-1).

    “The eddy streamfunction reaches values down to 22.8 m 2 s 21 , which is stronger (in opposing direction) than the mean Eulerian streamfunction (2.3 m 2 s 21 , Fig. 5d).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    The Ekman cell (C_Mean) is closed by a return flow reaching down to 200-m depth and has a maximum strength of 2.3 m^2 s^-1 around 50-m depth.

    “The Ekman cell (C Mean ) is closed by a return flow reaching down to 200-m depth and has a maximum strength of 2.3 m 2 s 21 around 50-m depth (Fig. 5d).”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Findingown data

    Submesoscale frontal dynamics are richer at the higher resolution.

    “Submesoscale frontal dynamics are obviously richer at the higher resolution.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    The eddies play an important role, so that the neglect of the bolus velocity in Eq. (A9) is invalid; this is also the case in the Southern Ocean.

    “In contrast we find that the eddies play an important role so that the neglect of the bolus velocity in (A9) is invalid (this is also the case in Southern Ocean).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Over the relatively short study periods (40 days) analyzed, the temporal tendency term could contribute to the balance, but it is not found to be important.

    “Over relatively short study periods (40 days for the analyses we carried out) temporal tendency could contribute to the balance but we do not find this term to be important.”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim.

    Premisereasoning

    It is widely accepted that the sole knowledge of the wind forcing does not provide useful insight into the mean cross-frontal circulation of the Southern Ocean.

    “As a result, it is widely accepted that the sole knowledge of the wind forcing does not provide useful insight into the mean cross-frontal circulation of the SO.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    The initial temperature profile T_o(z) is typical of (sub)tropical eastern boundary upwelling systems.

    “It is chosen to be typical of (sub)tropical EBUS.”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites Ridgway et al. 2002 source
    • cites Condie and Dunn 2006 source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisenone given

    The first part of Eq. (3) prescribes the intensified stratification within the upper 250 m as typically found in eastern boundary systems.

    “The first part of Eq. ( 3) prescribes the intensified stratification within the upper 250 m as typically found in eastern boundary systems.”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim.

    Premisecitation

    In the Southern Ocean, transport transverse to the Antarctic Circumpolar Current axis computed in isopycnal coordinates is a small residual between the mean Ekman-driven circulation due to wind pumping/suction (the Deacon cell) and eddy-induced transfers of mass driven by baroclinic instability processes.

    “In the SO, transport in the direction transverse to the Antarctic Circumpolar Current (ACC) axis computed in isopycnal coordinates is a small residual between the mean Ekman-driven circulation due to wind pumping/suction (the so-called Deacon cell) and eddy-induced transfers of mass driven by baroclinic instability processes (Marshall and Radko 2006;Marshall and Speer 2012).”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites Marshall and Radko 2006 source
    • cites Marshall and Speer 2012 source

  • Probably not a substantial claim: may not pass S4 (based). May combine two claims.

    Premisereasoning

    Due to the turbulent nature of the ocean, eddy fluxes are not solely determined by the forcings and are subjected to intrinsic stochastic variability, in addition to not being in statistical equilibrium.

    “Due to the turbulent nature of the ocean the eddy fluxes are not solely determined by the forcings and are subjected to intrinsic stochastic variability (in addition to not being in statistical equilibrium).”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premiseown data

    These heat flux values are typical of net heat flux forcings in EBUS although large variability exists.

    “These values are typical of net heat flux forcings in EBUS although large variability exists (Fig. 2).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites Fig. 2

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • Classified as probably not a substantial claim.

    Study design and conductnone given

    Eddy cancellation is consistently evaluated with three different methods that all account for the quasi-isopycnal nature of ocean circulation away from the surface.

    “Eddy cancellation is consistently evaluated with three different methods that all account for the quasi-isopycnal nature of ocean circulation away from the surface.”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim.

    Study design and conductcitation

    Applying all three approaches to determine residual overturning streamfunctions ensures that the main findings are robust.

    “Thus, we apply all three of them to ensure that our main findings are robust, as previously done for the SO or in the atmosphere.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationnone given

    The choice of parameters makes the results applicable to the Peruvian, West African, and northern Benguelan upwelling systems, and the main findings should also be valid at higher latitude.

    “This choice of parameters makes our results applicable to the Peruvian, West African, and northern Benguelan upwelling systems, but the main findings should also be valid at higher latitude.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    The transformed Eulerian mean formulation explicitly involves the rate of APE release and is able to accommodate outcropping situations.

    “The first formulation explicitly involves the rate of APE release and is able to accommodate outcropping situations.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites Held and Schneider (1999) source

  • Probably not a substantial claim: may not pass S4 (based). May combine two claims.

    Interpretationnone given

    Upwelling systems lack the periodicity attribute, so the ACC framework and theory are not directly applicable.

    “One practical difficulty is that upwelling systems lack the periodicity attribute, so the ACC framework and theory are not directly applicable.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation

    The eddy-induced circulation attempts to flatten isopycnal surfaces, reduce available potential energy, and therefore largely opposes the thermally direct Deacon cell.

    “The eddy-induced circulation attempts to flatten isopycnal surfaces, reduce available potential energy, and therefore largely opposes the thermally direct Deacon cell.”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites Marshall and Radko 2006 source
    • cites Marshall and Speer 2012 source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Interpretationcitation

    The absence of beta effect is presumably responsible for eddy kinetic energy levels above typical values found in the real ocean for EBUS sectors.

    “but is presumably responsible for eddy kinetic energy (EKE) levels above typical values found in the real ocean for EBUS sectors (Haney et al. 2001;Marchesiello et al. 2003;Gruber et al. 2011).”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites Haney et al. 2001 source
    • cites Marchesiello et al. 2003 source
    • cites Gruber et al. 2011 source

  • Classified as probably not a substantial claim.

    Premisecitation

    Baroclinic instability processes are essential in upwelling systems as a source of mesoscale and submesoscale turbulence.

    “Baroclinic instability (hereafter BCI) processes are known to be essential in upwelling systems as a source of mesoscale and submesoscale turbulence (Marchesiello et al. 2003).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites Marchesiello et al. 2003 source

  • Classified as probably not a substantial claim.

    Study design and conductreasoning

    The model uses 100 vertical sigma levels for all configurations to resolve sharp vertical velocity and temperature gradients in the upper ocean.

    “To resolve sharp vertical velocity and temperature gradients in the upper ocean, we use 100 vertical sigma levels for all configurations.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Rare occurrences of warm water conditions at the surface strongly imprint on the form of C_iso2h_Res and its remapping.

    “In addition, rare occurrences of warm water conditions at the surface strongly imprint on the form of C iso2h Res and its remapping (Nurser and Lee 2004a).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites Nurser and Lee 2004a

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • Probably not a substantial claim: may not pass S4 (based).

    Study design and conductnone given

    Performing 12 ensemble runs for each experiment provides statistically reliable averages.

    “to get statistically reliable averages.Thus we perform 12 ensemble runs for each experiment listed in Table 1.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S4 (based).

    Interpretationnone given

    The rate at which water is transferred from the ocean interior into the mixed layer may not be simply related to the Ekman transport.

    “However, the rate at which water is being transferred from the ocean interior into the mixed layer may not be simply related to the Ekman transport.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S4 (based).

    Study design and conductnone given

    The degree of resemblance between C_TEM_Eddy, C_iso2h_Eddy, and C_iso2y_Eddy will be considered as an indication of robustness.

    “The degree of resemblance between C TEM Eddy , C iso2h Eddy , and C iso2y Eddy will be considered as an indication of robustness.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Study design and conductown data

    The circulation pattern is very similar for C_iso2y Eddy and C_iso2h Eddy, providing confidence in its robustness despite the proximity of the ocean surface and coastline.

    “This circulation pattern is very similar for C iso2y Eddy and C iso2h Eddy which provides confidence in its robustness, despite the proximity of the ocean surface and coastline.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    The result is consistent with the limited vertical extension of submesoscale turbulence, which is typically confined into the mixed layer in most oceanic regimes.

    “Although this may seem surprising given the shallow nature of the problem under consideration, this is consistent with the limited vertical extension of submesoscale turbulence, which is typically confined into the mixed layer in most oceanic regimes [see Capet et al. (2016) for a counterexample where Charney instability is present].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites Capet et al. (2016) source

  • May combine two claims.

    Interpretationown data

    The level of cancellation can be subjected to spatiotemporal modulations due to air-sea buoyancy flux variability, which can lead to changes in the degree to which eddy fluxes counteract the mean advection by the Ekman flow central in coastal upwelling dynamics.

    “and (ii) the level of cancellation can be subjected to spatiotemporal modulations due to air-sea buoyancy flux variability, which can lead to changes in the degree to which eddy fluxes counteract the mean advection by the Ekman flow that is central in coastal upwelling dynamics.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationcitation

    In the mixed layer, C_iso2y Res displays a reduction of the submesoscale restratification tendency consistent with theory, confirming the superiority of this formulation near the ocean surface.

    “In the mixed layer, C iso2y Res displays a reduction of the submesoscale restratification tendency consistent with theory, which confirms the superiority of this formulation near the ocean surface (Held and Schneider 1999).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites Held and Schneider 1999 source

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Study design and conductown data

    Eddy and residual streamfunctions exhibit small spatial variations in their cross-shore-depth structures at different resolution, so the single-point comparison in Fig. 10 should not be overinterpreted.

    “Also note that eddy and residual streamfunctions exhibit small spatial variations in their crossshore-depth structures at different resolution, so the single point comparison in Fig. 10 should not be overinterpreted.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Isothermal averaging at constant z is strongly impacted near side boundaries where the structure of C_iso2y_Res can be difficult to interpret.

    “On the other hand, isothermal averaging at constant z is strongly impacted near side boundaries where the structure of C iso2y Res can be difficult to interpret (Nurser and Lee 2004a;Lee and Nurser 2012).”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites Nurser and Lee 2004a

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

    • cites Lee and Nurser 2012 source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Interpretationcitation

    Eddy fluxes may also have an appreciable time-averaged effect on tracer advection in sectors of the California Current System where standing meanders yield intensified mesoscale and submesoscale activity.

    “Eddy fluxes may also have an appreciable timeaveraged effect on tracer advection in sectors of the California Current System where standing meanders yield intensified mesoscale and submesoscale activity (Centurioni et al. 2008;Colas et al. 2013).”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites Centurioni et al. 2008 source
    • cites Colas et al. 2013 source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Interpretationreasoning

    In the northern Benguela and southern Canary Current sectors, where eddy cancellation is particularly weak, the alongshore pressure gradient effect and its temporal variability may be difficult to discern.

    “In the northern Benguela and southern Canary current sectors where the eddy cancellation is particularly weak this effect and its temporal variability may thus be difficult to discern.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationown data

    The modulation of the eddy cancellation process in response to environmental changes should occur on synoptic and longer time scales, including seasonal and interannual, but not on shorter time scales such as a diurnal cycle.

    “From this we infer that the modulation of the eddy cancellation process in response to environmental changes should occur on synoptic and longer times scales (including seasonal and interannual) but not on shorter time scales, e.g., as a response to a diurnal cycle.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Interpretationreasoning

    In the real ocean, wind and air-sea buoyancy flux variability may be correlated and combine to produce results distinct from those found in this study.

    “In the real ocean wind and air-sea buoyancy flux variability may be correlated and combine to produce results distinct from those found in this study.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationown data

    The results point to the possible importance of eddy-induced circulations during periods when air-sea buoyancy forcings are weak and perhaps more so when they are temporarily negative.

    “But they point to the possible importance of eddy-induced circulations during periods when air-sea buoyancy forcings are weak and perhaps more so when they are temporarily negative (see Fig. 2).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationown data

    The study suggests that a regional ocean model need not resolve submesoscale processes because eddy cancellation of the Ekman flow depends on subsurface turbulence that remains overwhelmingly linked to the mesoscale despite strong frontality.

    “Our study suggests that such model need not resolve submesoscale processes: eddy cancellation of the Ekman flow depends on subsurface turbulence which, our study demonstrates, remains overwhelmingly linked to the mesoscale despite the strong frontality of the environment under investigation.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationcitation

    Cancellation estimates derived from Fig. 11 ignore that beta drift is more effective at low latitude, which fundamentally alters the w'b'-EKE relationship.

    “Thus, cancellation estimates derived from Fig. 11 ignore, for instance, the fact that beta drift is more effective at low latitude which fundamentally alters the w 0 b 0 -EKE relationship.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Alongshore pressure gradient variability is another factor that can modulate upwelling intensity on synoptic, seasonal, and longer time scales, frequently in the sense of an upwelling reduction.

    “Finally, note that alongshore pressure gradient variability is another factor that can modulate upwelling intensity on synoptic, seasonal, and longer time scales (Werner and Hickey 1983;Huyer et al. 1987;Colas et al. 2008;Marchesiello et al. 2010;McCabe et al. 2015;Jacox et al. 2018), frequently in the sense of an upwelling reduction.”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites Werner and Hickey 1983 source
    • cites Huyer et al. 1987 source
    • cites Colas et al. 2008 source

  • Classified as probably not a substantial claim.

    Interpretationreasoning

    Identifying and quantifying eddy cancellation in realistic model simulations is far more difficult, mainly because the alongshore periodicity of the numerical configuration offers a much simpler framework for analyses.

    “Identifying and quantifying eddy cancellation in realistic model simulations is far more difficult, mainly because the alongshore periodicity of our numerical configuration offers a much simpler framework for analyses.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Study design and conductnone given

    Limitations imposed by the idealized framework do not allow the study to work in steady state and limit the duration of experiments to periods of tens of days.

    “Limitations imposed by our idealized framework do not allow us to work in steady state and limit the duration of our experiments to periods of tens of days.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Study design and conductown data

    The study used three different standard methods and found good agreement between them in the idealized setting.

    “Concerned by the methodological limitations inherent to eddy flux estimations and descriptions we used three different standard methods and found good agreement between them in our idealized setting.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premiseown data

    In all EBUS, air-sea buoyancy fluxes exhibit fluctuations of large magnitude on synoptic and seasonal time scales.

    “In all EBUS air-sea buoyancy fluxes exhibit fluctuations of large magnitude on synoptic and seasonal time scales as illustrated in Fig. 2 for nearshore sites.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationreasoning

    The findings on the cancellation process itself do not specifically depend on the 40-day time scale, but the modulation of cancellation in response to air-sea buoyancy fluctuations may.

    “Our findings on the cancellation process itself do not specifically depend on this particular time scale but the modulation of the cancellation in response to air-sea buoyancy fluctuations may.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Interpretationown data

    In the northern Humboldt, eddy cancellation is presumably stronger but still modest in magnitude, about 10%-20%.

    “In the northern Humboldt the eddy cancellation is presumably stronger but still modest in magnitude (;10%-20%,”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S1 (asserted), S3 (load-bearing), S4 (based).

    Premisenone given

    Strong ocean cooling events from -200 to -500 W m-2 can occasionally occur in three of the four EBUS.

    “Strong ocean cooling events (from 2200 to 2500 W m 22 ) can occasionally occur in three of the four EBUS.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Correlations between wind and air-sea buoyancy flux variability vary from place to place.

    “Such correlations vary from place to place (Send et al. 1987;Beardsley et al. 1998;Flynn et al. 2017;Lübbecke et al. 2019).”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites Send et al. 1987 source
    • cites Beardsley et al. 1998 source
    • cites Flynn et al. 2017 source

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Study design and conductreasoning

    Wind variability has been ignored throughout the study, whereas it is an important aspect of upwelling dynamics.

    “Third, for simplicity, wind variability has been ignored throughout the study whereas it is an important aspect of upwelling dynamics.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationcitation

    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”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites Marshall 1997 source

  • May combine two claims.

    Interpretationcitation

    By analogy with Southern Ocean functioning and general understanding of baroclinic processes, the intensity of eddy cancellation mechanisms should roughly scale with that of the Ekman flow, so that increasing upwelling winds steepen isopycnals and increase the counteracting effect of eddies.

    “By analogy with the SO functioning and in agreement with the general understanding of baroclinic processes the intensity of the eddy cancellation mechanisms shall roughly scale with that of the Ekman flow, i.e., we expect compensation (Marshall and Radko 2003) to occur whereby increasing upwelling winds steepens the isopycnals which increases the counteracting effect of eddies.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites Marshall and Radko 2003 source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisenone given

    The two studies (Nagai et al. 2015 and Colas et al. 2013) use very similar numerical configurations.

    “Note that the two studies use very similar numerical configurations.”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites Nagai et al. (2015) source
    • cites Colas et al. (2013) source

  • May combine two claims.

    Interpretationown data

    Net heat flux values are more typically in the range 0-150 W m-2, consistent with the forcings used in this study, so the results should be relevant to the real ocean provided that the rescaling of cancellation based on EKE levels is correct.

    “Net heat fluxes values are more typically in the range 0-150 W m 22 (Fig. 2b), i.e., consistent with the forcings used in this study whose results should therefore be relevant to the real ocean, provided that the rescaling of cancellation based on EKE levels proposed above is correct.”
    Quote in the paperSubstantial claim
    • The authors state this as an assumption: The intensity of the eddy overturning streamfunctions scales linearly with EKE.
    • Rests on an assumption: The rescaling of cancellation based on EKE levels proposed in the study is correct.

  • May combine two claims.

    Interpretationnone given

    Upper range values correspond to situations with about zero net air-sea buoyancy fluxes, which are not very common in the California Current System when upwelling conditions prevail.

    “Upper range values correspond to situations with '0 net air-sea buoyancy fluxes, which are not very common in this latter system when upwelling conditions prevail.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductown data

    The study was based on numerical simulations analyzed only over specific time periods of 40 days.

    “Second, our study was based on numerical simulations that were analyzed only over specific time periods of 40 days.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S2 (checkable).

    Study design and conductreasoning

    The simplifications taken advantage of have important implications in terms of model realism.

    “However, the simplifications we take advantage of have important implications in terms of model realism.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationreasoning

    In real upwelling systems the eddy terms are not as strong as in the idealized simulations, but the upper-ocean buoyancy balance can also involve a mean alongshore advection term because of lack of periodicity.

    “In real upwelling systems the eddy terms are not as strong (see section 4), but the upper-ocean buoyancy balance can also involve mean alongshore advection term because of lack of periodicity.”
    Quote in the paperNot a substantial claim
71 of 71

  • The paper relies on this without support.

    Coastal upwelling rates are classically determined by the intensity of the upper-ocean offshore Ekman transport.

    “Coastal upwelling rates are classically determined by the intensity of the upper-ocean offshore Ekman transport.”

  • The authors state this as an assumption.

    The net buoyancy supply to the mixed layer (B_ml) mainly results from air-sea exchanges in the sector where coastal upwelling is taking place.

    “The term B ml is the net buoyancy supply to the mixed layer, supposed to mainly result from air-sea exchanges sector where coastal upwelling is taking place (Fig. 2).”

  • The paper relies on this without support.

    Net buoyancy input can arise from lateral fluxes at the northern and southern edges of the upwelling region, and this is an important source of complication.

    “Net buoyancy input can arise from lateral fluxes at the northern and southern edges of the upwelling region, and this is an important source of complication.”

  • The paper relies on this without support.

    Twelve ensemble runs per experiment are sufficient to obtain statistically reliable averages.

    “Thus we perform 12 ensemble runs for each experiment listed in Table 1.”

  • The paper relies on this without support.

    Simple Eulerian averaging produces transport fields with unrealistically large diapycnal components.

    “Simple Eulerian averaging is well known to produce transport fields with unrealistically large diapycnal components (i.e., the flow associated with C Mean crosses the mean isopycnal surfaces and is therefore inconsistent with the weakly diabatic nature of interior ocean circulation).”

  • The paper relies on this without support.

    The ocean sector where upwelling takes place is in close proximity to the eastern boundary and not situated very deep below the surface, with the depth range of interest from below the mixed layer down to 150-200 m or less.

    “The ocean sector where upwelling takes place is in close proximity to the eastern boundary and not situated very deep below the surface.Indeed we are typically interested in the depth range from below the mixed layer down to 150-200-m depth or less, i.e., the source region of the upwelled water.”

  • The paper relies on this without support.

    Submesoscale permitting simulations represent the turbulent processes more accurately.

    “This is done for the submesoscale permitting simulations which represent the turbulent processes more accurately.”

  • The paper relies on this without support.

    The proximity to the ocean surface has no effect on the isopycnal averaging at constant height method.

    “The proximity to the ocean surface has no effect on this method.”

  • The authors state this as an assumption.

    The intensity of the eddy overturning streamfunctions scales linearly with EKE.

    “To make progress despite this important caveat we assume that the intensity of the eddy overturning streamfunctions scales linearly with EKE.”

  • The paper relies on this without support.

    The rescaling of cancellation based on EKE levels proposed in the study is correct.

    “provided that the rescaling of cancellation based on EKE levels proposed above is correct.”

  • The authors state this as an assumption.

    The upwelling channel is alongshore periodic, making the alongshore eddy flux component u0b0 irrelevant.

    “taking advantage of the alongshore periodicity of our upwelling channel (which makes the eddy flux component in that direction u 0 b 0 irrelevant)”

  • The authors state this as an assumption.

    The flow is 2D laminar and steady-state, with Ekman circulation as the only flow component.

    “In the situation of a 2D laminar and steady-state upwelling where the Ekman circulation is the only flow component”

  • The authors state this as an assumption.

    The buoyancy gradient in the mixed layer is horizontal (no vertical stratification) and independent of depth.

    “the buoyancy gradient is supposed to be horizontal (no vertical stratification) and independent of depth”

  • The authors state this as an assumption.

    Heat is neglected in the mixed layer integration.

    “neglecting heat”
14 of 14

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

  • Heat-flux relaxation coefficient has conflicting units

    Minor

    The methods describe dQ/dT in W K−1, whereas Table 1 labels the same parameter in W m−2 K−1.

  • Table lists 80-day runs, but the text describes 120-day runs

    Minor

    Table 1 gives a duration of 80 days for every run, while the text says the experiments run for 120 days, including an 80-day spinup.

  • Sponge-layer endpoints imply 94 km, not 96 km

    Minor

    The stated sponge layer begins at 506 km and ends at the boundary at 600 km, giving a width of 94 km rather than 96 km.

    Reported 96 · recomputed 94

  • Figure 8 assigns panel (k) to two different results

    Minor

    The caption labels panel (k) as the HF residual streamfunction and also as the HF-minus-NF difference.

4 of 4

Cites

Flagged first, then by citations

Research works printed but not linked: 65

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Cited by

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Authors
Thomsen, S., Capet, X., & Echevin, V.
Affiliations
  • LOCEAN-IPSL, IRD/CNRS/Sorbonne Universités (UPMC)/MNHN, UMR 7159, Paris, France
  • Centre National de la Recherche Scientifique (FR)
Venue
Journal of Physical Oceanography
Publisher
American Meteorological Society
Published
2021-09-02
ISSN
  • 0022-3670 (ISSN-L)
  • 1520-0485
DOI
10.1175/jpo-d-20-0294.1
OpenAlex
W3198774622
Cited by
17
References
65
Citations by year
2025: 3 · 2024: 6 · 2023: 5 · 2022: 2 · 2021: 1
FWCI
1.68
Type
journal article
Language
en
Open access
Licence
other-oa
Locations
  • Journal of Physical Oceanography (publishedVersion, other-oa)
  • HAL (Le Centre pour la Communication Scientifique Directe) (submittedVersion)
Funders
  • European Commission (HORIZON2020, 749699)
  • Deutsche Forschungsgemeinschaft (SFB‐754)
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 › Oceanography › Ocean Waves and Remote Sensing
Keywords
coastal upwelling, baroclinic instability, Ekman transport, air-sea heat flux, buoyancy forcing, submesoscale turbulence, mesoscale eddies, available potential energy

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