Thermohaline-turbulence instability and thermohaline staircase formation in the polar oceans

Ma, Yuchen; Peltier, W. R.

doi:10.1103/physrevfluids.7.083801

Cited by 7 publications

(6 citation statements)

References 53 publications

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“…In this case, clear, 10 m thick, thermohaline staircases can be generated, but the arrest of this vertical merging and the long term evolution are not fully elucidated as yet. The evolution of a diffusive regime is also discussed in Ma and Peltier (2022a); Ma and Peltier (2022b). They use parameterizations from stratified-turbulence of effective turbulent diapycnal diffusivities for heat and salt.…”

Section: Discussionmentioning

confidence: 99%

Density Staircases Are Disappearing in the Canada Basin of the Arctic Ocean

2022

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In the Canada Basin of the Arctic Ocean, warm and salty Atlantic‐origin Water (AW) lies in the intermediate layer (250–800 m) below a colder and fresher surface layer. It results in a depth range where vertical thermohaline gradients are propitious to double‐diffusion. Indeed, thermohaline staircases are commonly observed and associated with double‐diffusive processes. Using observations from the Beaufort Gyre Exploration Project large database and Ice‐Tethered Profilers, we document the presence of density staircases in the 300–700 m depth range with a striking strong spatial and temporal coherence. However, since 2007, a progressive smoothing of these staircases has occurred, beginning from the western half of the basin. Quantifying this evolution, we find that a general pattern is a clear evolution over time from numerous thick steps (≃40 m) with sharp interfaces to fewer and thinner steps (≃30 m) with smoother interfaces. After 2014, marked density staircases have almost disappeared in most of the Canada Basin. The vanishing of staircases occurs over a few years and coincides with modifications of the large scale circulation and thermohaline large scale horizontal gradients. As the small scale thermohaline structures are thought to play an important role for the vertical and horizontal exchanges of heat within the Canada Basin, the disappearance of the steps may impact the heat distribution at depth, with potential consequences for the evolution of the sea ice cover.

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Section: Discussionmentioning

confidence: 99%

Density Staircases Are Disappearing in the Canada Basin of the Arctic Ocean

2022

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“…2 of 11 and Peltier (2021) demonstrated a pathway by which general turbulence could lead to staircase development. Three-dimensional numerical simulations have also shown the development of staircases (Ma & Peltier, 2022;Yang et al, 2021), even for a theoretically stable initial state. The impact of shear is measured in terms of the Richardson number, defined as…”

Section: 1029/2022gl100605mentioning

confidence: 94%

“…In addition, the groundbreaking theoretical advancements of Ma and Peltier (2021) demonstrated a pathway by which general turbulence could lead to staircase development. Three‐dimensional numerical simulations have also shown the development of staircases (Ma & Peltier, 2022; Yang et al., 2021), even for a theoretically stable initial state. The impact of shear is measured in terms of the Richardson number, defined as

\mathrm{R}\mathrm{i}=\frac{{{N}^{\ast }}^{2}}{{\left(\frac{\partial {u}^{\ast }}{\partial {z}^{\ast }}\right)}^{2}},

where u * is the lateral fluid velocity and N * is the Brunt–Väisälä frequency.…”

Section: Introductionmentioning

confidence: 99%

Disruption of Arctic Staircases by Shear

Brown

Radko

2022

Geophysical Research Letters

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The origin and stability of thermohaline staircases remain topics of significance and mystery in studies of the Arctic Ocean. Thermohaline staircases take the form of layers of uniform temperature and salinity separated by thin interfaces with sharp gradients and typically exist in regions of the ocean that are strongly stratified with respect to both salt and temperature. Some well-studied examples include the thermocline at mid-latitudes in the western Atlantic (Schmitt et al., 1987(Schmitt et al., , 2005 and in the outflow of the Mediterranean (Magnell, 1976;Tait & Howe, 1968). The present study examines so-called diffusive staircases that are commonly observed in the Arctic. In the Eurasian Basin of the Arctic Ocean, warm water enters from the Atlantic and subducts beneath the cooler and fresher waters of the upper Arctic generating the Arctic thermocline. At the top of the thermocline, staircases have been observed in a number of studies, first by Neal et al. (1969) and more recently by Padman (1994),

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“…In order to investigate the structure of the diffusive-convection staircases and the vertical heat transport across the staircases, we have performed a series of numerical simulations to explore the influence of density ratio R ρ and the external forcing strength P on the staircase state that forms spontaneously in our numerical systems. By adjusting the value of P after a staircase is spontaneously formed from the thermohaline-turbulence instability described in Ma & Peltier (2022b) and Ma & Peltier (2022c), we found that the initial staircase state can either be maintained or when P is adjusted. Based on the energy sources of the system, we have further categorised all of our simulations into five regimes: the staircases can either be maintained in the double-diffusion-dominated regime, maintained in the turbulence-dominated regime, maintained in the hybrid regime, disrupted by diffusion or disrupted by turbulence.…”

Section: Discussionmentioning

confidence: 94%

“…In contrast to conventional understanding, our recent work (Ma & Peltier 2022 b , hereafter MP21; Ma & Peltier 2022 c , hereafter MP22) argues that stratified turbulence, rather than double-diffusion, may be the primary driver for the formation of diffusive-convection staircases. This theory demonstrates that the staircases will form spontaneously in a salinity-stratified ocean if the turbulent level is relatively low, which explained the widespread availability of staircases in the Arctic Ocean where both these conditions are well met.…”

Section: Introductionmentioning

confidence: 90%

Diffusive-convection staircases in the polar oceans: the interplay between double diffusion and turbulence

Ma,

Peltier

2024

J. Fluid Mech.

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Numerical simulations have been conducted to examine the structure of diffusive-convection staircases in the presence of vortical-mode-induced turbulent forcing. By modulating the input power $P$ and the background density ratio $R_\rho$ , we have identified three distinct types of staircase structures in these simulations: namely staircases maintained in the system driven by double-diffusion, by turbulence or by a combination of both double-diffusion and turbulence. While we showed that staircases maintained in the double-diffusion-dominated system are accurately characterised by the existing model originally proposed by Linden & Shirtcliffe (J. Fluid Mech., vol. 87, no. 3, 1978, pp. 417–432), we introduced new physical models to describe the staircase structures maintained in the turbulence-dominated system and the system driven by both turbulence and double-diffusion. Our integrated model reveals that turbulence fundamentally governs the entire life cycle of the diffusive-convection staircases, encompassing their formation, maintenance and eventual disruption in the Arctic Ocean's thermohaline staircases. While our previous work of Ma & Peltier (J. Fluid Mech., vol. 931, 2022b) demonstrated that turbulence could initiate the formation of Arctic staircases, these staircases are sustained by both turbulence and double-diffusion acting together after formation has occurred. Strong turbulence may disrupt staircase structures; however, the presence of weak turbulence could lead to unstable stratification within mixed layers of the staircases, as well as enhancing vertical heat and salt fluxes. Turbulence can even sustain a stable staircase structure factor when $R_\rho$ is relatively large, following a similar mechanism to the density staircases observed in laboratory experiments. Consequently, previous parameterisations (e.g. Kelley, J. Geophys. Res.: Oceans, vol. 95, no. C3, 1990, pp. 3365–3371) on the vertical heat flux across the diffusive-convection staircases may provide a significant underestimation of the heat transport by ignoring the influences of turbulence.

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Thermohaline-turbulence instability and thermohaline staircase formation in the polar oceans

Cited by 7 publications

References 53 publications

Density Staircases Are Disappearing in the Canada Basin of the Arctic Ocean

Density Staircases Are Disappearing in the Canada Basin of the Arctic Ocean

Disruption of Arctic Staircases by Shear

Diffusive-convection staircases in the polar oceans: the interplay between double diffusion and turbulence

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