Two equilibria of the Antarctic Circumpolar Current and its associated Meridional Overturning Circulation

2011 ◽  
Vol 55 (2) ◽  
pp. 315-322 ◽  
Author(s):  
JiPing Chao ◽  
YaoKun Li
Keyword(s):  
Antarctic Circumpolar Current ◽  
Meridional Overturning Circulation ◽  
Overturning Circulation ◽  
Meridional Overturning ◽  
Circumpolar Current ◽  
The Antarctic ◽  
Two Equilibria

Upper-Ocean Eddy Heat Flux across the Antarctic Circumpolar Current in Drake Passage from Observations: Time-Mean and Seasonal Variability

2020 ◽  
Vol 50 (9) ◽  
pp. 2507-2527
Author(s):  
Manuel O. Gutierrez-Villanueva ◽  
Teresa K. Chereskin ◽  
Janet Sprintall
Keyword(s):  
Heat Flux ◽  
Antarctic Circumpolar Current ◽  
Drake Passage ◽  
Polar Front ◽  
Meridional Overturning Circulation ◽  
Time Varying ◽  
Eddy Heat Flux ◽  
Meridional Overturning ◽  
Circumpolar Current ◽  
The Antarctic

AbstractEddy heat flux plays a fundamental role in the Southern Ocean meridional overturning circulation, providing the only mechanism for poleward heat transport above the topography and below the Ekman layer at the latitudes of Drake Passage. Models and observations identify Drake Passage as one of a handful of hot spots in the Southern Ocean where eddy heat transport across the Antarctic Circumpolar Current (ACC) is enhanced. Quantifying this transport, however, together with its spatial distribution and temporal variability, remains an open question. This study quantifies eddy heat flux as a function of ACC streamlines using a unique 20-yr time series of upper-ocean temperature and velocity transects with unprecedented horizontal resolution. Eddy heat flux is calculated using both time-mean and time-varying streamlines to isolate the dynamically important across-ACC heat flux component. The time-varying streamlines provide the best estimate of the across-ACC component because they track the shifting and meandering of the ACC fronts. The depth-integrated (0–900 m) across-stream eddy heat flux is maximum poleward in the south flank of the Subantarctic Front (−0.10 ± 0.05 GW m−1) and decreases toward the south, becoming statistically insignificant in the Polar Front, indicating heat convergence south of the Subantarctic Front. The time series provides an uncommon opportunity to explore the seasonal cycle of eddy heat flux. Poleward eddy heat flux in the Polar Front Zone is enhanced during austral autumn–winter, suggesting a seasonal variation in eddy-driven upwelling and thus the meridional overturning circulation.

scholarly journals Inferring the Pattern of the Oceanic Meridional Transport from the Air–Sea Density Flux

2008 ◽  
Vol 38 (12) ◽  
pp. 2722-2738 ◽  
Author(s):  
Timour Radko ◽  
Igor Kamenkovich ◽  
Pierre-Yves Dare
Keyword(s):  
Antarctic Circumpolar Current ◽  
Water Mass ◽  
Meridional Overturning Circulation ◽  
Diagnostic Model ◽  
Global Budget ◽  
Meridional Transport ◽  
Meridional Overturning ◽  
The Difference ◽  
Circumpolar Current ◽  
The Antarctic

Abstract An extension of Walin’s water mass transformation analysis is proposed that would make it possible to assess the strength of the adiabatic along-isopycnal component of the meridional overturning circulation (MOC). It is hypothesized that the substantial fraction of the adiabatic MOC component can be attributed to the difference in subduction rates at the northern and southern outcrops of each density layer—the “push–pull” mechanism. The GCM-generated data are examined and it is shown that the push–pull mode accounts for approximately two-thirds of the isopycnal water mass transport in the global budget and dominates the Atlantic transport. Much of the difference between the actual interhemispheric flux and the push–pull mode can be ascribed to the influence of the Antarctic Circumpolar Current, characterized by the elevated (at least in the GCM) values of the diapycnal transport. When the diagnostic model is applied to observations, it is discovered that the reconstructed MOC is consistent, in terms of the magnitude and sense of overturning, with earlier observational and modeling studies. The findings support the notion that the dynamics of the meridional overturning are largely controlled by the adiabatic processes—time-mean and eddy-induced advection of buoyancy.

scholarly journals Improving Estimates of the Antarctic Circumpolar Current Streamlines in Drake Passage

2008 ◽  
Vol 38 (5) ◽  
pp. 1000-1010 ◽  
Author(s):  
Yueng-Djern Lenn ◽  
Teresa K. Chereskin ◽  
Janet Sprintall
Keyword(s):  
Southern Ocean ◽  
Antarctic Circumpolar Current ◽  
Acoustic Doppler Current Profiler ◽  
Drake Passage ◽  
Meridional Overturning Circulation ◽  
Dynamic Height ◽  
Current Profiler ◽  
Meridional Overturning ◽  
The Mean ◽  
Circumpolar Current

Abstract Accurately resolving the mean Antarctic Circumpolar Current (ACC) is essential for determining Southern Ocean eddy fluxes that are important to the global meridional overturning circulation. Previous estimates of the mean ACC have been limited by the paucity of Southern Ocean observations. A new estimate of the mean surface ACC in Drake Passage is presented that combines sea surface height anomalies measured by satellite altimetry with a recent dataset of repeat high-resolution acoustic Doppler current profiler observations. A mean streamfunction (surface height field), objectively mapped from the mean currents, is used to validate two recent dynamic height climatologies. The new streamfunction has narrower and stronger ACC fronts separated by quiescent zones of much weaker flow, thereby improving on the resolution of ACC fronts observed in the other climatologies. Distinct streamlines can be associated with particular ACC fronts and tracked in time-dependent maps of dynamic height. This analysis shows that varying degrees of topographic control are evident in the preferred paths of the ACC fronts through Drake Passage.

Preliminary biostratigraphy of IODP Expedition 383 sites

2021 ◽  
Author(s):  
Mariem Saavedra-Pellitero ◽  
Anieke Brombacher ◽  
Oliver Esper ◽  
Alexandre de Souza ◽  
Elisa Malinverno ◽  
...  
Keyword(s):  
High Resolution ◽  
Water Mass ◽  
Global Climate ◽  
Drake Passage ◽  
Meridional Overturning Circulation ◽  
The Pacific ◽  
Meridional Overturning ◽  
Circumpolar Current ◽  
Oceanic Carbon ◽  
The Antarctic

<p>The Antarctic Circumpolar Current (ACC) is a major driver of global climate. It connects all three ocean basins, integrating global climate variability, and its vertical water mass structure plays a key role in oceanic carbon storage. The Atlantic and Indian sectors of the ACC are well studied, but the Pacific sector lacks deep-sea drilling records. Therefore, past water mass transport through the Drake Passage and its effect on Atlantic Meridional Overturning Circulation are not well understood. To fill this gap, IODP Expedition 383 recovered sediments from three sites in the central South Pacific and three sites from the southern Chilean Margin.</p><p>Here we present the preliminary biostratigraphy developed during the expedition. The sediments contained abundant nannofossils, foraminifera, radiolarians, diatoms and silicoflagellates which produced age models that were in excellent agreement with the shipboard magnetostratigraphy. Two sites contain high-resolution Pleistocene records, one site goes back to the Pliocene, and two others reach back to the late Miocene. Post-cruise research will further refine these age models through high-resolution bio-, magneto- and oxygen isotope stratigraphies that are currently being generated.</p>

The Antarctic Circumpolar Current in Three Dimensions

2006 ◽  
Vol 36 (4) ◽  
pp. 651-669 ◽  
Author(s):  
Timour Radko ◽  
John Marshall
Keyword(s):  
Antarctic Circumpolar Current ◽  
Three Dimensional ◽  
Perturbation Expansion ◽  
Dimensional Structure ◽  
Residual Circulation ◽  
Mean Flow ◽  
Overturning Circulation ◽  
The Mean ◽  
Circumpolar Current ◽  
The Antarctic

Abstract A simple theory is developed for the large-scale three-dimensional structure of the Antarctic Circumpolar Current and the upper cell of its overturning circulation. The model is based on a perturbation expansion about the zonal-average residual-mean model developed previously by Marshall and Radko. The problem is solved using the method of characteristics for idealized patterns of wind and buoyancy forcing constructed from observations. The equilibrium solutions found represent a balance between the Eulerian meridional overturning, eddy-induced circulation, and downstream advection by the mean flow. Depth and stratification of the model thermocline increase in the Atlantic–Indian Oceans sector where the mean wind stress is large. Residual circulation in the model is characterized by intensification of the overturning circulation in the Atlantic–Indian sector and reduction in strength in the Pacific Ocean region. Predicted three-dimensional patterns of stratification and residual circulation in the interior of the ACC are compared with observations.

scholarly journals The Force Balance of the Southern Ocean Meridional Overturning Circulation

2013 ◽  
Vol 43 (6) ◽  
pp. 1193-1208 ◽  
Author(s):  
Matthew R. Mazloff ◽  
Raffaele Ferrari ◽  
Tapio Schneider
Keyword(s):  
Southern Ocean ◽  
Drake Passage ◽  
Meridional Overturning Circulation ◽  
Force Balance ◽  
Pressure Gradients ◽  
Meridional Transport ◽  
Overturning Circulation ◽  
Mean Pressure ◽  
Meridional Overturning ◽  
Circumpolar Current

Abstract The Southern Ocean (SO) limb of the meridional overturning circulation (MOC) is characterized by three vertically stacked cells, each with a transport of about 10 Sv (Sv ≡ 106 m3 s−1). The buoyancy transport in the SO is dominated by the upper and middle MOC cells, with the middle cell accounting for most of the buoyancy transport across the Antarctic Circumpolar Current. A Southern Ocean state estimate for the years 2005 and 2006 with ⅙° resolution is used to determine the forces balancing this MOC. Diagnosing the zonal momentum budget in density space allows an exact determination of the adiabatic and diapycnal components balancing the thickness-weighted (residual) meridional transport. It is found that, to lowest order, the transport consists of an eddy component, a directly wind-driven component, and a component in balance with mean pressure gradients. Nonvanishing time-mean pressure gradients arise because isopycnal layers intersect topography or the surface in a circumpolar integral, leading to a largely geostrophic MOC even in the latitude band of Drake Passage. It is the geostrophic water mass transport in the surface layer where isopycnals outcrop that accomplishes the poleward buoyancy transport.

A Simple Dynamical Model of the Warm-Water Branch of the Middepth Meridional Overturning Cell

2009 ◽  
Vol 39 (5) ◽  
pp. 1216-1230 ◽  
Author(s):  
R. M. Samelson
Keyword(s):  
Meridional Overturning Circulation ◽  
Warm Water ◽  
Ekman Transport ◽  
Overturning Circulation ◽  
Diabatic Processes ◽  
Meridional Overturning ◽  
Eddy Fluxes ◽  
Circumpolar Current ◽  
Diabatic Forcing ◽  
Current Dissipation

Abstract A reduced-gravity model is presented of the warm-water branch of the middepth meridional overturning circulation in a rectangular basin with a circumpolar connection. The model describes the balance between production of warm water by Ekman advection across the circumpolar current, dissipation of warm water by eddy fluxes southward across the current, and the net production or dissipation of warm water by diabatic processes north of the current. The results emphasize the role of the eastern boundary condition in setting the thermocline structure north of the current and the nonlinear interactions between wind forcing, eddy fluxes, and diabatic mixing, which together control the structure and amplitude of the model meridional overturning circulation. Solutions are shown to exist in which the northward Ekman transport across the circumpolar current is completely compensated by southward eddy fluxes and the meridional overturning north of the current is entirely driven by diabatic forcing and interior upwelling through the base of the layer. Other solutions are shown to exist in which the interior upwelling into the warm layer at midlatitudes is negligible and the meridional overturning circulation consists of a continuous cell that carried the fluid delivered by the northward Ekman transport across the circumpolar current through midlatitudes to the Northern Hemisphere subpolar gyre, where it cools and returns to depth. The results emphasize that the coupled elements of wind driving, eddy fluxes, and diabatic processes are inextricably intertwined in the middepth meridional overturning circulation.

scholarly journals The Global Overturning Circulation

2019 ◽  
Vol 11 (1) ◽  
pp. 249-270 ◽  
Author(s):  
Paola Cessi
Keyword(s):  
Wind Stress ◽  
Conceptual Models ◽  
Meridional Overturning Circulation ◽  
Diapycnal Mixing ◽  
Overturning Circulation ◽  
Meridional Overturning ◽  
The Antarctic ◽  
Global Overturning Circulation

In this article, I use the Estimating the Circulation and Climate of the Ocean version 4 (ECCO4) reanalysis to estimate the residual meridional overturning circulation, zonally averaged, over the separate Atlantic and Indo-Pacific sectors. The abyssal component of this estimate differs quantitatively from previously published estimates that use comparable observations, indicating that this component is still undersampled. I also review recent conceptual models of the oceanic meridional overturning circulation and of the mid-depth and abyssal stratification. These theories show that dynamics in the Antarctic circumpolar region are essential in determining the deep and abyssal stratification. In addition, they show that a mid-depth cell consistent with observational estimates is powered by the wind stress in the Antarctic circumpolar region, while the abyssal cell relies on interior diapycnal mixing, which is bottom intensified.

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