Global dataset of thermohaline staircases obtained from Argo floats and Ice-Tethered Profilers

Boog, Carine G. van der; Koetsier, J. Otto; Dijkstra, Henk A.; Pietrzak, Julie D.; Katsman, Caroline A.

doi:10.5194/essd-13-43-2021

Cited by 10 publications

(10 citation statements)

References 41 publications

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“…Since the diffusive-convection stratification mostly exists in the Arctic region (see the discussion of the global dataset of thermohaline staircases of Van Der Boog et al. (2021), for example), our theory cannot be directly migrated to apply to determine the staircase formation process in the low- and mid-latitude oceans in which temperature usually dominates the stratification in the thermocline, and turbulence levels are usually much higher than in the Arctic Ocean. In the low- and mid-latitude oceans, the staircases develop in the salt-fingering environment, and the turbulence so produced may form thermohaline staircases via the instability theory of Radko (2003).…”

Section: Summary and Discussionmentioning

confidence: 99%

Thermohaline staircase formation in the diffusive convection regime: a theory based upon stratified turbulence asymptotics

Peltier

2021

J. Fluid Mech.

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We describe a mechanism that leads to the spontaneous formation of a thermohaline staircase in the high-latitude oceans. Our analysis of this mechanism is based upon a model in which uniform gradients of temperature and salinity are assumed and is applied to a simplified mean-field model of stratified turbulence. Detailed analysis employs a parametrization of turbulent diapycnal diffusivities (Bouffard & Boegman, Dyn. Atmos. Oceans, vol. 61, 2013, pp. 14–34). This parametrization is apparently unique in that it distinguishes between the diapycnal diffusivities for heat and salt on the basis of their Prandtl (Schmidt) numbers. Our model predicts that the temperature and salinity profiles will be susceptible to linear instability if the buoyancy Reynolds number lies in the range 0.18–91, and a nonlinear mean-field model simulation demonstrates that it evolves into a well-defined thermohaline staircase that matches the characteristics of those found in the high-latitude oceans. The criterion for initial instability is furthermore shown to be consistent with the observed regional variability of staircase occurrence in the Arctic Ocean as determined by the most recent observational datasets.

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Section: Summary and Discussionmentioning

confidence: 99%

Thermohaline staircase formation in the diffusive convection regime: a theory based upon stratified turbulence asymptotics

Peltier

2021

J. Fluid Mech.

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“…In order to gather all features and to exclude sharp temperature and salinity gradients compensated in density, resulting from pure isopycnal stirring, we choose to perform our detection on density profiles. As such, our method, tracking alternance of strong and weak vertical gradients of density, follows the method of van der Boog, Koetsier, et al (2021), who have censused thermohaline staircases in the global ocean, using Argo floats and ITP data. However, in contrast to our study, they wanted to exclude staircases that could be the result of intrusions and thus removed steps alternating SF and DC conditions from their statistics.…”

Section: Measurements and Methodsmentioning

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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“…The method we presented here has certain advantages in particular circumstances. For example, all of the other methods referred to herein (Timmermans et al, 2008; Shibley et al, 2017; van der Boog et al, 2021b; Lu et al, 2022) require setting one or multiple thresholds on gradients in temperature, salinity, or density which are used to identify sections of profiles where layers may be present. However, choosing reasonable values for these thresholds requires precise prior knowledge of the staircase properties, which may not be available before identifying staircases in that particular region and time period.…”

Section: Discussionmentioning

confidence: 99%

“…Shibley et al (2017) extended the automated detection method of Timmermans et al (2008) by including two additional conditions: (1) For each experiment, they visually determined different threshold values on both and on the temperature difference between neighboring points and (2) after then running the detection method, those authors only considered staircases that consisted of at least three layers. van der Boog et al (2021b) developed a similar staircase detection algorithm, but chose threshold values of vertical density gradients that were expected to be applicable to staircases in all of the world’s oceans, not just the Arctic. Specifically, they set a vertical gradient threshold of , where is the density anomaly referenced to dbar.…”

Section: Introductionmentioning

confidence: 99%

Unsupervised clustering identifies thermohaline staircases in the Canada Basin of the Arctic Ocean

Schee,

Rosenblum,

Lilly

et al. 2024

Environ. Data Science

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Thermohaline staircases are a widespread stratification feature that impacts the vertical transport of heat and nutrients and are consistently observed throughout the Canada Basin of the Arctic Ocean. Observations of staircases from the same time period and geographic region form clusters in temperature-salinity (T–S) space. Here, for the first time, we use an automated clustering algorithm called the hierarchical density-based spatial clustering of applications with noise to detect and connect individual well-mixed staircase layers across profiles from ice-tethered profilers. Our application only requires an estimate of the typical layer thickness and expected salinity range of staircases. We compare this method to two previous studies that used different approaches to detect layers and reproduce several results, including the mean lateral density ratio $ {R}_L $ and that the difference in salinity between neighboring layers is a magnitude larger than the salinity variance within a layer. We find that we can accurately and automatically track individual layers in coherent staircases across time and space between different profiles. In evaluating the algorithm’s performance, we find evidence of different physical features, namely splitting or merging layers and remnant intrusions. Further, we find a dependence of $ {R}_L $ on pressure, whereas previous studies have reported constant $ {R}_L $ . Our results demonstrate that clustering algorithms are an effective and parsimonious method of identifying staircases in ocean profile data.

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Global dataset of thermohaline staircases obtained from Argo floats and Ice-Tethered Profilers

Cited by 10 publications

References 41 publications

Thermohaline staircase formation in the diffusive convection regime: a theory based upon stratified turbulence asymptotics

Thermohaline staircase formation in the diffusive convection regime: a theory based upon stratified turbulence asymptotics

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

Unsupervised clustering identifies thermohaline staircases in the Canada Basin of the Arctic Ocean

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