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

2021 ◽  
Vol 13 (1) ◽  
pp. 43-61 ◽  
Author(s):  
Carine G. van der Boog ◽  
J. Otto Koetsier ◽  
Henk A. Dijkstra ◽  
Julie D. Pietrzak ◽  
Caroline A. Katsman
Keyword(s):  
Heat Transport ◽  
Detection Algorithm ◽  
Argo Floats ◽  
Mixed Layers ◽  
Diffusive Mixing ◽  
Double Diffusive

Abstract. Thermohaline staircases are associated with double-diffusive mixing. They are characterized by stepped structures consisting of mixed layers of typically tens of metres thick that are separated by much thinner interfaces. Through these interfaces enhanced diapycnal salt and heat transport take place. In this study, we present a global dataset of thermohaline staircases derived from observations of Argo profiling floats and Ice-Tethered Profilers using a novel detection algorithm. To establish the presence of thermohaline staircases, the algorithm detects subsurface mixed layers and analyses the interfaces in between. Of each detected staircase, the conservative temperature, absolute salinity, depth, and height, as well as some other properties of the mixed layers and interfaces, are computed. The algorithm is applied to 487 493 quality-controlled temperature and salinity profiles to obtain a global dataset. The performance of the algorithm is verified through an analysis of independent regional observations. The algorithm and global dataset are available at https://doi.org/10.5281/zenodo.4286170.

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

2020 ◽  
Author(s):  
Carine G. van der Boog ◽  
J. Otto Koetsier ◽  
Henk A. Dijkstra ◽  
Julie D. Pietrzak ◽  
Caroline A. Katsman
Keyword(s):  
Heat Transport ◽  
Detection Algorithm ◽  
Research Data ◽  
Argo Floats ◽  
Mixed Layers ◽  
Diffusive Processes ◽  
Double Diffusive

Abstract. Thermohaline staircases arise from double diffusive processes. They are characterised by stepped structures consisting of mixed layers of typically tens of meters thick that are separated by much thinner gradient layers. Through these gradient layers enhanced diapycnal salt and heat transport take place. In this study, we present a global dataset of thermohaline staircases derived from observations of Argo profiling floats and Ice Tethered Profilers using a novel detection algorithm. To establish the presence of stepped thermohaline staircases, the algorithm detects subsurface mixed layers and analyses the gradient layers in between. Of each detected staircase, the temperature, salinity, depth and height, as well as some other properties of the mixed layers and gradient layers are computed. The algorithm is applied to 487,647 quality-controlled temperature and salinity profiles to obtain the global dataset. The performance of the algorithm is verified through an analysis of independent regional observations. The algorithm and global dataset are available at the 4TU centre for research data (van der Boog et al. 10 (2020), doi: https://doi.org/10.4121/uuid:f6529d31-b285-46ac-990b-5f45839f4e11).

scholarly journals Double-diffusive mixing makes a small contribution to the global ocean circulation

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Carine G. van der Boog ◽  
Henk A. Dijkstra ◽  
Julie D. Pietrzak ◽  
Caroline A. Katsman
Keyword(s):  
Ocean Circulation ◽  
Mechanical Energy ◽  
Global Ocean ◽  
Small Contribution ◽  
Global Ocean Circulation ◽  
Diffusive Fluxes ◽  
Diffusive Mixing ◽  
Diffusive Processes ◽  
Flowing Waters ◽  
Double Diffusive

AbstractDouble-diffusive processes enhance diapycnal mixing of heat and salt in the open ocean. However, observationally based evidence of the effects of double-diffusive mixing on the global ocean circulation is lacking. Here we analyze the occurrence of double-diffusive thermohaline staircases in a dataset containing over 480,000 temperature and salinity profiles from Argo floats and Ice-Tethered Profilers. We show that about 14% of all profiles contains thermohaline staircases that appear clustered in specific regions, with one hitherto unknown cluster overlying the westward flowing waters of the Tasman Leakage. We estimate the combined contribution of double-diffusive fluxes in all thermohaline staircases to the global ocean’s mechanical energy budget as 7.5 GW [0.1 GW; 32.8 GW]. This is small compared to the estimated energy required to maintain the observed ocean stratification of roughly 2 TW. Nevertheless, we suggest that the regional effects, for example near Australia, could be pronounced.

scholarly journals A Global Ocean Model with Double-Diffusive Mixing

1999 ◽  
Vol 29 (6) ◽  
pp. 1124-1142 ◽  
Author(s):  
William J. Merryfield ◽  
Greg Holloway ◽  
Ann E. Gargett
Keyword(s):  
Ocean Model ◽  
Global Ocean ◽  
Diffusive Mixing ◽  
Double Diffusive

Does Rotation Influence Double-Diffusive Fluxes in Polar Oceans?

2014 ◽  
Vol 44 (1) ◽  
pp. 289-296 ◽  
Author(s):  
J. R. Carpenter ◽  
M.-L. Timmermans
Keyword(s):  
Arctic Ocean ◽  
Heat Fluxes ◽  
Small Scale ◽  
Previous Theory ◽  
Thermal Interface ◽  
Diffusive Convection ◽  
Polar Oceans ◽  
Diffusive Fluxes ◽  
Mixed Layers ◽  
Double Diffusive

Abstract The diffusive (or semiconvection) regime of double-diffusive convection (DDC) is widespread in the polar oceans, generating “staircases” consisting of high-gradient interfaces of temperature and salinity separated by convectively mixed layers. Using two-dimensional direct numerical simulations, support is provided for a previous theory that rotation can influence DDC heat fluxes when the thickness of the thermal interface sufficiently exceeds that of the Ekman layer. This study finds, therefore, that the earth’s rotation places constraints on small-scale vertical heat fluxes through double-diffusive layers. This leads to departures from laboratory-based parameterizations that can significantly change estimates of Arctic Ocean heat fluxes in certain regions, although most of the upper Arctic Ocean thermocline is not expected to be dominated by rotation.

scholarly journals Diathermal Heat Transport in a Global Ocean Model

2019 ◽  
Vol 49 (1) ◽  
pp. 141-161 ◽  
Author(s):  
Ryan M. Holmes ◽  
Jan D. Zika ◽  
Matthew H. England
Keyword(s):  
Heat Transport ◽  
Seasonal Cycle ◽  
Vertical Mixing ◽  
Shear Instability ◽  
Tidal Mixing ◽  
Global Ocean ◽  
Surface Boundary ◽  
Diabatic Processes ◽  
Numerical Mixing ◽  
Diffusive Mixing

AbstractThe rate at which the ocean moves heat from the tropics toward the poles, and from the surface into the interior, depends on diabatic surface forcing and diffusive mixing. These diabatic processes can be isolated by analyzing heat transport in a temperature coordinate (the diathermal heat transport). This framework is applied to a global ocean sea ice model at two horizontal resolutions (1/4° and 1/10°) to evaluate the partioning of the diathermal heat transport between different mixing processes and their spatial and seasonal structure. The diathermal heat transport peaks around 22°C at 1.6 PW, similar to the peak meridional heat transport. Diffusive mixing transfers this heat from waters above 22°C, where surface forcing warms the tropical ocean, to temperatures below 22°C where midlatitude waters are cooled. In the control 1/4° simulation, half of the parameterized vertical mixing is achieved by background diffusion, to which sensitivity is explored. The remainder is associated with parameterizations for surface boundary layer, shear instability, and tidal mixing. Nearly half of the seasonal cycle in the peak vertical mixing heat flux is associated with shear instability in the tropical Pacific cold tongue, highlighting this region’s global importance. The framework presented also allows for quantification of numerical mixing associated with the model’s advection scheme. Numerical mixing has a substantial seasonal cycle and increases to compensate for reduced explicit vertical mixing. Finally, applied to Argo observations the diathermal framework reveals a heat content seasonal cycle consistent with the simulations. These results highlight the utility of the diathermal framework for understanding the role of diabatic processes in ocean circulation and climate.

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