scholarly journals Subantarctic and Polar Fronts of the Antarctic Circumpolar Current and Southern Ocean Heat and Freshwater Content Variability: A View from Argo

2016 ◽  
Vol 46 (3) ◽  
pp. 749-768 ◽  
Author(s):  
Donata Giglio ◽  
Gregory C. Johnson
Keyword(s):  
Southern Ocean ◽  
Antarctic Circumpolar Current ◽  
Potential Temperature ◽  
Local Maximum ◽  
Potential Density ◽  
Argo Data ◽  
Circumpolar Current ◽  
The Antarctic ◽  
Ekman Upwelling

AbstractArgo profiling floats initiated a revolution in observational physical oceanography by providing numerous, high-quality, global, year-round, in situ (0–2000 dbar) temperature and salinity observations. This study uses Argo’s unprecedented sampling of the Southern Ocean during 2006–13 to describe the position of the Antarctic Circumpolar Current’s Subantarctic and Polar Fronts, comparing and contrasting two different methods for locating fronts using the same dataset. The first method locates three fronts along dynamic height contours, each corresponding to a local maximum in vertically integrated shear. The second approach locates the fronts using specific features in the potential temperature field, following Orsi et al. Results from the analysis of Argo data are compared to those from Orsi et al. and other more recent studies. Argo spatial resolution is not adequate to resolve annual and interannual movements of the fronts on a circumpolar scale since they are on the order of 1° latitude (Kim and Orsi), which is smaller than the resolution of the gridded product analyzed. Argo’s four-dimensional coverage of the Southern Ocean equatorward of ~60°S is used to quantify variations in heat and freshwater content there with respect to the time-mean front locations. These variations are described during 2006–13, considering both pressure and potential density ranges (within different water masses) and relations to wind forcing (Ekman upwelling and downwelling).

scholarly journals Topographic Control of Southern Ocean Gyres and the Antarctic Circumpolar Current: A Barotropic Perspective

2019 ◽  
Vol 49 (12) ◽  
pp. 3221-3244 ◽  
Author(s):  
Ryan D. Patmore ◽  
Paul R. Holland ◽  
David R. Munday ◽  
Alberto C. Naveira Garabato ◽  
David P. Stevens ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Antarctic Circumpolar Current ◽  
Large Scale ◽  
Volume Transport ◽  
Topographic Features ◽  
Conservation Of Momentum ◽  
Ridge Width ◽  
Circumpolar Current ◽  
The Antarctic ◽  
Ridge Geometry

AbstractIn the Southern Ocean the Antarctic Circumpolar Current is significantly steered by large topographic features, and subpolar gyres form in their lee. The geometry of topographic features in the Southern Ocean is highly variable, but the influence of this variation on the large-scale flow is poorly understood. Using idealized barotropic simulations of a zonal channel with a meridional ridge, it is found that the ridge geometry is important for determining the net zonal volume transport. A relationship is observed between ridge width and volume transport that is determined by the form stress generated by the ridge. Gyre formation is also highly reliant on the ridge geometry. A steep ridge allows gyres to form within regions of unblocked geostrophic (f/H) contours, with an increase in gyre strength as the ridge width is reduced. These relationships among ridge width, gyre strength, and net zonal volume transport emerge to simultaneously satisfy the conservation of momentum and vorticity.

scholarly journals Estimating the Four-Dimensional Structure of the Southern Ocean Using Satellite Altimetry

2011 ◽  
Vol 28 (4) ◽  
pp. 548-568 ◽  
Author(s):  
A. J. S. Meijers ◽  
N. L. Bindoff ◽  
S. R. Rintoul
Keyword(s):  
Southern Ocean ◽  
Satellite Altimetry ◽  
Velocity Structure ◽  
Velocity Fields ◽  
Optimal Interpolation ◽  
Dimensional Structure ◽  
Strongly Correlated ◽  
Circumpolar Current ◽  
The Antarctic

Abstract A gravest empirical mode (GEM) projection of temperature and salinity fields over the circumpolar Southern Ocean is presented and is used in combination with satellite altimetry to produce gridded, full-depth, time-evolving temperature, salinity, and velocity fields. Optimal interpolation of historical hydrography, including Argo floats, is used to produce GEM projections of the circumpolar temperature and salinity fields. Parameterizing these fields by dynamic height allows the use of altimetric SSH values from 1992–2006 to create synoptic temperature and salinity fields at weekly intervals on a ⅓° grid at 36 depth levels. The satellite-derived temperature and salinity fields generally capture over 90% of the property variance below the thermocline, with RMS residuals of 1.16°C and 0.132 in salinity at the surface, decreasing to less than 0.45°C and 0.05 below 500 dbar. The combination of altimetry with the GEM fields allows the resolution of the subsurface structure of the filamentary fronts and eddy features. Velocity fields derived from the time-evolving temperature and salinity fields reproduce the Antarctic Circumpolar Current (ACC) velocity structure well, and are strongly correlated (r > 0.7) with in situ measurements from current meters and drifters, with RMS velocity residuals of 4.8–14.8 cm−1 in the Subantarctic Front.

scholarly journals Multiple Jets of the Antarctic Circumpolar Current South of Australia*

2007 ◽  
Vol 37 (5) ◽  
pp. 1394-1412 ◽  
Author(s):  
Serguei Sokolov ◽  
Stephen R. Rintoul
Keyword(s):  
Southern Ocean ◽  
Antarctic Circumpolar Current ◽  
Sea Surface ◽  
Mean Flow ◽  
Nonlinear Fitting ◽  
Fitting Procedure ◽  
Multiple Jets ◽  
Gradient Fields ◽  
Circumpolar Current ◽  
The Antarctic

Abstract Maps of the gradient of sea surface height (SSH) and sea surface temperature (SST) reveal that the Antarctic Circumpolar Current (ACC) consists of multiple jets or frontal filaments. The braided and patchy nature of the gradient fields seems at odds with the traditional view, derived from hydrographic sections, that the ACC is made up of three continuous circumpolar fronts. By applying a nonlinear fitting procedure to 638 weekly maps of SSH gradient (∇SSH), it is shown that the distribution of maxima in ∇SSH (i.e., fronts) is strongly peaked at particular values of absolute SSH (i.e., streamlines). The association between the jets and particular streamlines persists despite strong topographic and eddy–mean flow interactions, which cause the jets to merge, diverge, and fluctuate in intensity along their path. The SSH values corresponding to each frontal branch are nearly constant over the sector of the Southern Ocean between 100°E and 180°. The front positions inferred from SSH agree closely with positions inferred from hydrographic sections using traditional water mass criteria. Recognition of the multiple branches of the Southern Ocean fronts helps to reconcile differences between front locations determined by previous studies. Weekly maps of SSH are used to characterize the structure and variability of the ACC fronts and filaments. The path, width, and intensity of the frontal branches are influenced strongly by the bathymetry. The “meander envelopes” of the fronts are narrow on the northern slope of topographic ridges, where the sloping topography reinforces the β effect, and broader over abyssal plains.

scholarly journals Time-Mean Flow as the Prevailing Contribution to the Poleward Heat Flux across the Southern Flank of the Antarctic Circumpolar Current: A Case Study in the Fawn Trough, Kerguelen Plateau

2013 ◽  
Vol 43 (3) ◽  
pp. 583-601 ◽  
Author(s):  
H. Sekma ◽  
Y.-H. Park ◽  
F. Vivier
Keyword(s):  
Heat Flux ◽  
Southern Ocean ◽  
Antarctic Circumpolar Current ◽  
Mean Flow ◽  
Kerguelen Plateau ◽  
The Mean ◽  
The Cross ◽  
Circumpolar Current ◽  
The Antarctic ◽  
Southern Flank

Abstract The major mechanisms of the oceanic poleward heat flux in the Southern Ocean are still in debate. The long-standing belief stipulates that the poleward heat flux across the Antarctic Circumpolar Current (ACC) is mainly due to mesoscale transient eddies and the cross-stream heat flux by time-mean flow is insignificant. This belief has recently been challenged by several numerical modeling studies, which stress the importance of mean flow for the meridional heat flux in the Southern Ocean. Here, this study analyzes moored current meter data obtained recently in the Fawn Trough, Kerguelen Plateau, to estimate the cross-stream heat flux caused by the time-mean flow and transient eddies. It is shown that the poleward eddy heat flux in this southern part of the ACC is negligible, while that from the mean flow is overwhelming by two orders of magnitude. This is due to the unusual anticlockwise turning of currents with decreasing depth, which is associated with significant bottom upwelling engendered by strong bottom currents flowing over the sloping topography of the trough. The circumpolar implications of these local observations are discussed in terms of the depth-integrated linear vorticity budget, which suggests that the six topographic features along the southern flank of the ACC equivalent to the Fawn Trough case would yield sufficient poleward heat flux to balance the oceanic heat loss in the subpolar region. As eddy activity on the southern flank of the ACC is too weak to transport sufficient heat poleward, the nonequivalent barotropic structure of the mean flow in several topographically constricted passages should accomplish the required task.

Following the Antarctic Circumpolar Current: patterns and processes in the biogeography of the limpetNacella(Mollusca: Patellogastropoda) across the Southern Ocean

2016 ◽  
Vol 44 (4) ◽  
pp. 861-874 ◽  
Author(s):  
Claudio A. González-Wevar ◽  
Mathias Hüne ◽  
Nicolas I. Segovia ◽  
Tomoyuki Nakano ◽  
Hamish G. Spencer ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Antarctic Circumpolar Current ◽  
Circumpolar Current ◽  
Patterns And Processes ◽  
The Antarctic
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