Lagrangian surface signatures reveal upper-ocean vertical displacement conduits near oceanic density fronts

Aravind, H.M.; Sarkar, Sutanu; Freilich, Mara; Mahadevan, Amala; Haley, Patrick J.; Lermusiaux, Pierre F. J.; Allshouse, Michael

doi:10.1016/j.ocemod.2022.102136

Cited by 6 publications

(10 citation statements)

References 59 publications

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“…Submesoscale stirring in the upper ocean could arise from a variety of causes, including internal waves and mesoscale straining described by QG dynamics, and followed on by typically submesoscale processes such as frontogenesis, centrifugal instabilities, mixed layer instabilities, and other secondary instabilities (McWilliams, 2016; Shcherbina et al., 2015). Mixed layer instabilities (Fox‐Kemper et al., 2008) are usually active within the mixed layer and may suppress vertical mixing (Smith et al., 2015), but entrainment and secondary instabilities facilitated by the intense frontogenesis formed between them is a potential mechanism (Aravind et al., 2023). Considering the conditions for the occurrence of other instabilities featuring loss of balance in stratified flow (McWilliams et al., 1998), we can rule out the mesoscale strain‐induced frontogenesis within the eddy core due to weak straining within the eddy (Figure S6 in Supporting Information ), although this process may be important in the eddy periphery.…”

Section: Potential Dynamical Mechanismmentioning

confidence: 99%

Isopycnal Submesoscale Stirring Crucially Sustaining Subsurface Chlorophyll Maximum in Ocean Cyclonic Eddies

Cao,

Freilich,

Song

et al. 2024

Geophysical Research Letters

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Mesoscale and submesoscale processes have crucial impacts on ocean biogeochemistry, importantly enhancing the primary production in nutrient‐deficient ocean regions. Yet, the intricate biophysical interplay still holds mysteries. Using targeted high‐resolution in situ observations in the South China Sea, we reveal that isopycnal submesoscale stirring serves as the primary driver of vertical nutrient transport to sustain the dome‐shaped subsurface chlorophyll maximum (SCM) within a long‐lived cyclonic mesoscale eddy. Density surface doming at the eddy core increased light exposure for phytoplankton production, while along‐isopycnal submesoscale stirring disrupted the mesoscale coherence and drove significant vertical exchange of tracers. These physical processes play a crucial role in maintaining the elevated phytoplankton biomass in the eddy core. Our findings shed light on the universal mechanism of how mesoscale and submesoscale coupling enhances primary production in ocean cyclonic eddies, highlighting the pivotal role of submesoscale stirring in structuring marine ecosystems.

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Section: Potential Dynamical Mechanismmentioning

confidence: 99%

Isopycnal Submesoscale Stirring Crucially Sustaining Subsurface Chlorophyll Maximum in Ocean Cyclonic Eddies

Cao,

Freilich,

Song

et al. 2024

Geophysical Research Letters

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“…It can also determine the origin (backward tracking) and fate (forward tracking) of material transported via general circulation and driven by meso-to submesoscale currents. In particular, since the number of submesoscale current studies has steadily grown over the past two decades, Lagrangian methods, such as particle tracking, are increasingly being used to evaluate the effect of surface material transport occurring within this scale range (Choi et al, 2017;Freilich and Mahadevan, 2021;Aravind et al, 2023).…”

Section: Particle Trackingmentioning

confidence: 99%

The role of submesoscale filaments in restratification of the surface mixed layer and dissolved oxygen variability in large Lake Geneva: field evidence complemented by Lagrangian particle-tracking

Hamze-Ziabari,

Foroughan,

Lemmin

et al. 2023

Front. Mar. Sci.

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Theoretical studies on oceans and large lakes have shown that submesoscale instabilities in frontal zones tend to reduce horizontal density gradients and enhance vertical density gradients, thereby re-stratifying the Surface Mixed Layer (SML). Submesoscale filament dynamics are primarily studied using numerical models and remote sensing imagery. However, in large lakes, this concept remains without substantial field validation, mainly due to the difficulty in conducting the necessary high-resolution water column measurements. Using a procedure we recently developed to predict the time and location of mesoscale and submesoscale features generated by strong wind fields, this work presents direct field evidence demonstrating the role of submesoscale cold filaments in re-stratifying the SML under weakly stratified conditions in a large lake (Lake Geneva). The dynamics of the observed filaments were further investigated with a high-resolution three-dimensional (3D) numerical model and Lagrangian particle-tracking. The numerical model accurately captured the formation of these filaments. The enhancement of thermal stratification strength, N2, reached O(10-5) s-2 in areas adjacent to cold filaments under atmospheric cooling and heating conditions. In the pelagic zone (offshore), strong vertical velocities of O(100 m d-1) were associated with secondary circulation that rapidly transports and accumulates passive particles in the thermocline and hypolimnion layers, as confirmed by Acoustic Doppler Current Profiler (ADCP) backscattering intensity data. The field observations indicate that under weak stratification, Dissolved Oxygen (DO) variability reaches 0.5 mg l-1 near cold filaments. This documentation of strong vertical motions associated with submesoscale filaments is expected to contribute to the understanding of the vertical exchange of heat, contaminants and oxygen between the atmosphere and the pelagic zone of large lakes, as well as in oceans where carrying out such field measurements is very challenging.

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“…Regarding simulations of submesoscale processes, earlier studies emphasized the significance of model resolution in accurately representing vertical motion (e.g., Mahadevan & Tandon, 2006). Recent advancements in box models (e.g., Aravind et al., 2023; Cornejo & Bahamonde, 2023) and Lagrangian trajectory modeling (Freilich & Mahadevan, 2021; Mahadevan et al., 2020) have improved the understanding of submesoscale processes far beyond the simple Eady model proposed by Eady (1949). However, computational limitations in Earth System Models or General Circulation Models often prevent the resolution of submesoscale or even mesoscale processes and often assume hydrostatic and geostrophic relationships.…”

Section: Introductionmentioning

confidence: 99%

Stepwise Subduction Observed at a Front in the Marginal Ice Zone in Fram Strait

Hofmann,

von Appen,

Kanzow

et al. 2024

JGR Oceans

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At high latitudes, submesoscale dynamics act on scales of (100 m–1 km) and are associated with the breakdown of geostrophic balance, vertical velocities, and energy cascading to small scales. Submesoscale features such as fronts, filaments, and eddies are ubiquitous in marginal ice zones forced by the large horizontal density gradients. In July 2020, we identified multiple fronts and filaments using a towed undulating vehicle near the sea ice edge in central Fram Strait, the oceanic gateway to the Arctic Ocean between Greenland and Svalbard. Sea ice covered the entire study region 1–2 weeks earlier, and a stratified meltwater layer was present. We observed a front between warm and saline Atlantic Water (AW) and cold and fresh Polar Water (PW) at 30–85 m depth, where we identified a subsurface maximum in chlorophyll fluorescence and other biogeochemical properties extending along the tilted isopycnals down to 75 m, indicating subduction of AW (mixed with meltwater) that had previously occurred. The meltwater layer also featured multiple shallow fronts, one of which exhibited high velocities and a subsurface maximum in chlorophyll fluorescence, possibly indicating subduction of PW below the meltwater layer. The fronts at different depth levels suggest a stepwise subduction process near the ice edge, where water subducts from the surface below the meltwater and then further down along subsurface fronts. The submesoscale features were part of a larger‐scale mesoscale pattern in the marginal ice zone. As sea ice continuously retreats, such features may become more common in the Arctic Ocean.

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Lagrangian surface signatures reveal upper-ocean vertical displacement conduits near oceanic density fronts

Cited by 6 publications

References 59 publications

Isopycnal Submesoscale Stirring Crucially Sustaining Subsurface Chlorophyll Maximum in Ocean Cyclonic Eddies

Isopycnal Submesoscale Stirring Crucially Sustaining Subsurface Chlorophyll Maximum in Ocean Cyclonic Eddies

The role of submesoscale filaments in restratification of the surface mixed layer and dissolved oxygen variability in large Lake Geneva: field evidence complemented by Lagrangian particle-tracking

Stepwise Subduction Observed at a Front in the Marginal Ice Zone in Fram Strait

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