Characterizing the Transition From Balanced to Unbalanced Motions in the Southern California Current

Chereskin, Teresa K.; Rocha, César B.; Gille, Sarah T.; Menemenlis, Dimitris; Passaro, Marcello

doi:10.1029/2018jc014583

Cited by 43 publications

(72 citation statements)

References 58 publications

(125 reference statements)

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“…Although BMs and IGWs occupy distinct regions in the spectral space (see Figure ), they do interact (Chereskin et al, ). Since Kunze (), many studies have revealed that IGW propagation is polarized by the sign of the relative vorticity and the sign of the stratification anomaly (or stretching) of mesoscale eddies (Danioux et al, ; Dunphy et al, ; Grisouard & Thomas, ; Joyce et al, ; Kunze, ; Young & Jelloul, ; Ponte & Klein, ; Thomas, ; Whitt & Thomas, ; Zaron & Egbert, ).…”

Section: Bms and Igwsmentioning

confidence: 99%

Ocean‐Scale Interactions From Space

Klein

Lapeyre

Siegelman

et al. 2019

Earth and Space Science

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109

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Satellite observations of the last two decades have led to a major breakthrough emphasizing the existence of a strongly energetic mesoscale turbulent eddy field in all the oceans. This ocean mesoscale turbulence is characterized by cyclonic and anticyclonic eddies (with a 100‐ to 300‐km size and depth scales of ∼500–1,000 m) that capture approximatively 80% of the total kinetic energy and is now known to significantly impact the large‐scale ocean circulation, the ocean's carbon storage, the air‐sea interactions, and therefore the Earth climate as a whole. However, ocean mesoscale turbulence revealed by satellite observations has properties that differ from those related to classical geostrophic turbulence theories. In the last decade, a large number of theoretical and numerical studies has pointed to submesoscale surface fronts (1–50 km), not resolved by satellite altimeters, as the key suspect explaining these discrepancies. Submesoscale surface fronts have been shown to impact mesoscale eddies and the large‐scale ocean circulation in counterintuitive ways, leading in particular to up‐gradient fluxes. The ocean engine is now known to involve energetic scale interactions, over a much broader range of scales than expected one decade ago, from 1 to 5,000 km. New space observations with higher spatial resolution are however needed to validate and improve these recent theoretical and numerical results.

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Section: Bms and Igwsmentioning

confidence: 99%

Ocean‐Scale Interactions From Space

Klein

Lapeyre

Siegelman

et al. 2019

Earth and Space Science

Self Cite

109

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“…From the spectral perspective, mesoscale fluxes have larger spatial and longer timescales than the submesoscale. The Omega equation, in contrast, provides a dynamics‐based decomposition, decomposing the eddy transport into a mesoscale component in balance with the geostrophic and ageostrophic horizontal flow and a submesoscale component associated with higher Rossby numbers (McWilliams, ; McWilliams et al, ; Chereskin et al, ).…”

Section: Introductionmentioning

confidence: 99%

The Contribution of Submesoscale over Mesoscale Eddy Iron Transport in the Open Southern Ocean

Uchida

Balwada

Abernathey

et al. 2019

J Adv Model Earth Syst

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Biological productivity in the Southern Ocean is limited by iron availability. Previous studies of iron supply have focused on mixed-layer entrainment and diapycnal fluxes. However, the Southern Ocean is a region highly energetic mesoscale and submesoscale turbulence. Here we investigate the role of eddies in supplying iron to the euphotic zone, using a flat-bottom zonally re-entrant model, configured to represent the Antarctic Circumpolar Current region, that is coupled to a biogeochemical model with a realistic seasonal cycle. Eddies are admitted or suppressed by changing the model's horizontal resolution. We utilize cross spectral analysis and the generalized Omega equation to temporally and spatially decompose the vertical transport attributable to mesoscale and submesoscale motions. Our results suggest that the mesoscale vertical fluxes provide a first-order pathway for transporting iron across the mixing-layer base, where diapycnal mixing is weak, and must be included in modeling the open-Southern Ocean iron budget. Plain Language SummaryOcean currents at the surface on the spatial scales of 1-200 km are energetic due to heating by the sun and stirring by the winds. These currents contribute to the climate system by transporting heat and carbon horizontally towards the poles and vertically into the deep ocean. By running a numerical simulation at very high spatial resolution that resolve these currents, we show that these currents are also responsible for transporting iron from the ocean interior to the surface in the Southern Ocean, where phytoplankton growth is limited by the lack of iron-a key nutrient for most living organisms on Earth. Our results highlight the importance of accurately representing these ocean currents and associated iron transport, in order to understand the Southern Ocean ecosystem and its impact on the climate via photosynthesis, the process in which carbon dioxide is converted to organic carbon and oxygen is produced as a bi-product.

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“…We did not find spectra transitioning from k −3 to k −2 near surface, characterising a transition between balanced and unbalanced flows. Instead, we found slopes close to k −2 in three regions (ECAL, SCAL, VAUB), as in regions of weaker EKE such the North Equatorial Current region (Qiu et al, 2017) and the southern California Current System (Chereskin et al, 2019).…”

Section: Regional Dependencementioning

confidence: 57%

“…flattening of the spectral slopes, from k −3 to k −2 in eddy-active regions. However, this flattening does not occur everywhere in the ocean as the KE spectra computed from ADCP observations in the North Equatorial Current region (Qiu et al, 2017) and in the Southern California Current (Chereskin et al, 2019) decrease monotonously, approximately following a k −2 law.…”

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confidence: 95%

Scale-dependent analysis of in situ observations in the mesoscale to submesoscale range around New Caledonia

Sérazin¹,

Marin²,

Gourdeau³

et al. 2019

Preprint

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Abstract. Small-scale ocean dynamics around New Caledonia (22° S) in the Southwest Pacific Ocean occur in regions with substantial mesoscale eddies, complex bathymetry, complex intertwined currents, islands, and strong internal tides. Using second order structure functions applied to observational ADCP and TSG dataset, these small-scale dynamics are characterised in the range of scales 3–100 km in order to determine the turbulent regime at work. A Helmholtz decomposition is used to analyse the contribution of rotational and divergent motions. A surface intensified regime is shown to be at work south and east of New Caledonia, involving substantial rotational motions such as submesoscale structures generated by mixed layer instabilities and frontogenesis. This regime is however absent north of New Caledonia, where mesoscale eddies are weaker and surface available potential energy is smaller at small scales. North of New Caledonia and below 200 m in the regions south and east of New Caledonia, the dynamical regime at work could be explained by stratified turbulence as divergent and rotational motions have similar contribution, but weakly nonlinear interaction between inertia gravity waves are also possible as structure functions get close to the empirical spectrum model for inertia gravity waves. Seasonal variations of the available potential energy reservoir, associated with a change in the vertical profile rather than in horizontal density variance, suggest that submesoscale motions would also seasonally vary around New Caledonia. Overall, a loss of geostrophic balance is likely to occur at scales smaller than 10 km, where the contribution of divergent motions become significant.

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Characterizing the Transition From Balanced to Unbalanced Motions in the Southern California Current

Cited by 43 publications

References 58 publications

Ocean‐Scale Interactions From Space

Ocean‐Scale Interactions From Space

The Contribution of Submesoscale over Mesoscale Eddy Iron Transport in the Open Southern Ocean

Scale-dependent analysis of in situ observations in the mesoscale to submesoscale range around New Caledonia

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