scholarly journals Baroclinic Transport Time Series of the Antarctic Circumpolar Current Measured in Drake Passage

2014 ◽  
Vol 44 (7) ◽  
pp. 1829-1853 ◽  
Author(s):  
María Paz Chidichimo ◽  
Kathleen A. Donohue ◽  
D. Randolph Watts ◽  
Karen L. Tracey
Keyword(s):  
Time Series ◽  
Standard Deviation ◽  
Deep Water ◽  
Antarctic Circumpolar Current ◽  
Drake Passage ◽  
Polar Front ◽  
Intermediate Water ◽  
Circumpolar Deep Water ◽  
Circumpolar Current ◽  
Baroclinic Transport

Abstract The first multiyear continuous time series of Antarctic Circumpolar Current (ACC) baroclinic transport through Drake Passage measured by moored observations is presented. From 2007 to 2011, 19 current- and pressure-recording inverted echo sounders and 3 current-meter moorings were deployed in Drake Passage to monitor the transport during the cDrake experiment. Full-depth ACC baroclinic transport relative to the bottom has a mean strength of 127.7 ± 1.0 Sverdrups (Sv; 1 Sv ≡ 106 m3 s−1) with a standard deviation of 8.1 Sv. Mean annual baroclinic transport is remarkably steady. About 65% of the baroclinic transport variance is associated with time periods shorter than 60 days with peaks at 20 and 55 days. Nearly 28% of apparent energy in the spectrum computed from transport subsampled at the 10-day repeat cycle of the Jason altimeter results from aliasing of high-frequency signals. Approximately 80% of the total baroclinic transport is carried by the Subantarctic Front and the Polar Front. Partitioning the baroclinic transport among neutral density γn layers gives 39.2 Sv for Subantarctic Surface Water and Antarctic Intermediate Water (γn < 27.5 kg m−3), 57.5 Sv for Upper Circumpolar Deep Water (27.5 < γn < 28.0 kg m−3), 27.7 Sv for Lower Circumpolar Deep Water (28.0 < γn < 28.2 kg m−3), and 3.3 Sv for Antarctic Bottom Water (γn > 28.2 kg m−3). The transport standard deviation in these layers decreases with depth (4.0, 3.1, 2.1, and 1.1 Sv, respectively). The transport associated with each of these water masses is statistically steady. The ACC baroclinic transport exhibits considerable variability and is a major contributor to total ACC transport variability.

Changes in the Atlantic Sector of the Southern Ocean estimated from the CESM Last Millennium Ensemble

2019 ◽  
Vol 31 (1) ◽  
pp. 37-51 ◽  
Author(s):  
Ilana Wainer ◽  
Peter R. Gent
Keyword(s):  
Time Series ◽  
Standard Deviation ◽  
Wind Stress ◽  
Antarctic Circumpolar Current ◽  
Current System ◽  
Intermediate Water ◽  
Atlantic Sector ◽  
Southward Shift ◽  
Circumpolar Current ◽  
The Antarctic

AbstractThe changes in the Antarctic Circumpolar Current system associated with the Polar, sub-Antarctic and Subtropical Fronts in the Atlantic are examined in a ten-member ensemble using the Community Earth System Model. Results for the ensemble average mean show that the Polar Front at 25°W shifts to the south by 0.8° during 1970–2000 compared to its mean latitude over the period 1050–1950. This shift is significant because it is more than twice the standard deviation of the mean latitude time series during 1050–1950. The shift is caused by a slight southward displacement of the Antarctic Circumpolar Current, which in turn is caused by a southward shift in the latitude of the maximum zonal wind stress. The sub-Antarctic Front also shows a small southward shift after 1970, with a maximum latitudinal displacement of 0.2°. However, this shift is not significant compared to the standard deviation of the time series during 1050–1950. The Subtropical Front does not change its latitude during 1970–2000 compared to 1050–2000 because there is very little change in the wind-stress curl in the subtropics. Differences in temperature and salinity throughout the water column at 25°W reveal that during 1970–2000 there is freshening of Antarctic Intermediate Water, whereas the Circumpolar Deep Water becomes saltier.

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 Transport of warm Upper Circumpolar Deep Water onto the western Antarctic Peninsula continental shelf

Ocean Science ◽  
2012 ◽  
Vol 8 (4) ◽  
pp. 433-442 ◽  
Author(s):  
D. G. Martinson ◽  
D. C. McKee
Keyword(s):  
Continental Shelf ◽  
Antarctic Peninsula ◽  
Deep Water ◽  
Antarctic Circumpolar Current ◽  
Western Antarctic Peninsula ◽  
Dominant Mechanism ◽  
Circumpolar Deep Water ◽  
Marguerite Bay ◽  
Circumpolar Current ◽  
The Antarctic

Abstract. Five thermistor moorings were placed on the continental shelf of the western Antarctic Peninsula (between 2007 and 2010) in an effort to identify the mechanism(s) responsible for delivering warm Upper Circumpolar Deep Water (UCDW) onto the broad continental shelf from the Antarctic Circumpolar Current (ACC) flowing over the adjacent continental slope. Historically, four mechanisms have been suggested: (1) eddies shed from the ACC, (2) flow into the cross-shelf-cutting canyons with overflow onto the nominal shelf, (3) general upwelling, and (4) episodic advective diversions of the ACC onto the shelf. The mooring array showed that for the years of deployment, the dominant mechanism is eddies; upwelling may also contribute but to an unknown extent. Mechanism 2 played no role, though the canyons have been shown previously to channel UCDW across the shelf into Marguerite Bay. Mechanism 4 played no role independently, though eddies may be advected within a greater intrusion of the background flow.

Medium-scale heat fluxes across the Antarctic Circumpolar Current in the Drake Passage and western Scotia Sea

1996 ◽  
Vol 8 (4) ◽  
pp. 369-378
Author(s):  
Alberto R. Piola ◽  
Monica B. Grasselli
Keyword(s):  
Antarctic Circumpolar Current ◽  
Heat Content ◽  
Drake Passage ◽  
Polar Front ◽  
Heat Fluxes ◽  
Scotia Sea ◽  
Medium Scale ◽  
Scale Temperature ◽  
Circumpolar Current ◽  
The Antarctic

Closely spaced continuous temperature profiles from expendable bathythermographs launched along two sections across the Drake Passage and western Scotia Sea in the summer 1981–1982 are used to examine the vertical medium-scale (∼10–100 m) temperature fine structure. The large-scale temperature structure across the frontal regimes characteristic of the Antarctic Circumpolar Current and the cross-frontal structure of the upper ocean are discussed. In the Drake Passage the heat content drops about 0.5 × 102 Kcal cm−2 (2 × 109 J m−2) across the Subantarctic Zone and 0.9 × 102 Kcal cm−2 (3.6 − 109 J m−2) across the Polar Front. In the Scotia Sea the heat content changes across the front are not as prominent. The statistical model of Joyce (1977) is used to quantify the heat fluxes across the fronts produced by the medium-scale temperature interleaving. In the Drake Passage the estimated heat flux is 0.32 × 10−3 °C m s−1 (1.3 × 103 W m−2) across the Subantarctic Front and 0.46 × 10−3 °C m s−1 (1.9 × 103 W m−2) across the Polar Front. In the Scotia Sea the estimated heat flux is larger in the Polar Front reaching 0.71 × 10−3 °C m s−1 (2.9 × 103 W m−2). The medium-scale fine structure heat fluxes are about 10% of the existing estimates of the mesoscale eddy heat fluxes and comparable to heat fluxes associated with the meridional flow of deep and bottom waters across the Antarctic Circumpolar Current.

scholarly journals Transport of warm upper circumpolar deep water onto the Western Antarctic Peninsula Continental Shelf

2011 ◽  
Vol 8 (6) ◽  
pp. 2479-2502 ◽  
Author(s):  
D. G. Martinson
Keyword(s):  
Continental Shelf ◽  
Antarctic Peninsula ◽  
Deep Water ◽  
Antarctic Circumpolar Current ◽  
Western Antarctic Peninsula ◽  
Dominant Mechanism ◽  
Circumpolar Deep Water ◽  
Marguerite Bay ◽  
Circumpolar Current ◽  
The Antarctic

Abstract. Five thermistor-moorings were placed on the continental shelf of the Western Antarctic Peninsula (between 2007 and 2010) in an effort to identify the mechanism(s) responsible for delivering warm Upper Circumpolar Deep Water (UCDW) onto the broad continental shelf from the Antarctic Circumpolar Current (ACC) flowing over the adjacent continental slope. Historically, four mechanisms have been suggested (or assumed): (1) eddies shed from the ACC, (2) flow into the cross-shelf-cutting canyons with overflow onto the nominal shelf, (3) general upwelling, and (4) episodic sweeping of ACC meanders over the shelf. The mooring array showed that for the years of deployment, the dominant mechanism is eddies; upwelling may also contribute but to an unknown extent. Mechanisms 2 and 4 played no role, though the canyons have been shown previously to channel UCDW across the shelf into Marguerite Bay.

scholarly journals Intrinsic variability of the Antarctic Circumpolar Current system: low- and high-frequency fluctuations of the Argentine Basin flow

Ocean Science ◽  
2014 ◽  
Vol 10 (2) ◽  
pp. 201-213 ◽  
Author(s):  
G. Sgubin ◽  
S. Pierini ◽  
H. A. Dijkstra
Keyword(s):  
High Frequency ◽  
Antarctic Circumpolar Current ◽  
Current System ◽  
Low Frequency ◽  
Drake Passage ◽  
Ocean Model ◽  
Intrinsic Variability ◽  
Circumpolar Current ◽  
The Antarctic ◽  
Argentine Basin

Abstract. In this paper, the variability of the Antarctic Circumpolar Current system produced by purely intrinsic nonlinear oceanic mechanisms is studied through a sigma-coordinate ocean model, implemented in a large portion of the Southern Ocean at an eddy-permitting resolution under steady surface heat and momentum fluxes. The mean transport through the Drake Passage and the structure of the main Antarctic Circumpolar Current fronts are well reproduced by the model. Intrinsic variability is found to be particularly intense in the Subantarctic Front and in the Argentine Basin, on which further analysis is focused. The low-frequency variability at interannual timescales is related to bimodal behavior of the Zapiola Anticyclone, with transitions between a strong and collapsed anticyclonic circulation in substantial agreement with altimeter observations. Variability on smaller timescales shows clear evidence of topographic Rossby-wave propagation along the eastern and southern flanks of the Zapiola Rise and of mesoscale eddies, also in agreement with altimeter observations. The analysis of the relationship between the low- and high-frequency variability suggests possible mechanisms of mutual interaction.

scholarly journals Silicon pool dynamics and biogenic silica export in the Southern Ocean inferred from Si-isotopes

Ocean Science ◽  
2011 ◽  
Vol 7 (5) ◽  
pp. 533-547 ◽  
Author(s):  
F. Fripiat ◽  
A.-J. Cavagna ◽  
F. Dehairs ◽  
S. Speich ◽  
L. André ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Silicic Acid ◽  
Mixed Layer ◽  
Deep Water ◽  
Biogenic Silica ◽  
Polar Front ◽  
Intermediate Water ◽  
Subtropical Zone ◽  
Isotopic Signatures ◽  
The Antarctic

Abstract. Silicon isotopic signatures (δ30Si) of water column silicic acid (Si(OH)4) were measured in the Southern Ocean, along a meridional transect from South Africa (Subtropical Zone) down to 57° S (northern Weddell Gyre). This provides the first reported data of a summer transect across the whole Antarctic Circumpolar Current (ACC). δ30Si variations are large in the upper 1000 m, reflecting the effect of the silica pump superimposed upon meridional water transfer across the ACC: the transport of Antarctic surface waters northward by a net Ekman drift and their convergence and mixing with warmer upper-ocean Si-depleted waters to the north. Using Si isotopic signatures, we determine different mixing interfaces: the Antarctic Surface Water (AASW), the Antarctic Intermediate Water (AAIW), and thermoclines in the low latitude areas. The residual silicic acid concentrations of end-members control the δ30Si alteration of the mixing products and with the exception of AASW, all mixing interfaces have a highly Si-depleted mixed layer end-member. These processes deplete the silicic acid AASW concentration northward, across the different interfaces, without significantly changing the AASW δ30Si composition. By comparing our new results with a previous study in the Australian sector we show that during the circumpolar transport of the ACC eastward, the δ30Si composition of the silicic acid pools is getting slightly, but significantly lighter from the Atlantic to the Australian sectors. This results either from the dissolution of biogenic silica in the deeper layers and/or from an isopycnal mixing with the deep water masses in the different oceanic basins: North Atlantic Deep Water in the Atlantic, and Indian Ocean deep water in the Indo-Australian sector. This isotopic trend is further transmitted to the subsurface waters, representing mixing interfaces between the surface and deeper layers. Through the use of δ30Si constraints, net biogenic silica production (representative of annual export), at the Greenwich Meridian is estimated to be 5.2 ± 1.3 and 1.1 ± 0.3 mol Si m−2 for the Antarctic Zone and Polar Front Zone, respectively. This is in good agreement with previous estimations. Furthermore, summertime Si-supply into the mixed layer of both zones, via vertical mixing, is estimated to be 1.6 ± 0.4 and 0.1 ± 0.5 mol Si m−2, respectively.

scholarly journals Observed Storm Track Dynamics in Drake Passage

2019 ◽  
Vol 49 (3) ◽  
pp. 867-884 ◽  
Author(s):  
Annie Foppert
Keyword(s):  
Mean Field ◽  
Storm Track ◽  
Drake Passage ◽  
Polar Front ◽  
Mean Flow ◽  
Track Dynamics ◽  
Flow Interactions ◽  
Circumpolar Current ◽  
Eddy Potential Energy ◽  
Shackleton Fracture Zone

AbstractThe dynamics of an oceanic storm track—where energy and enstrophy transfer between the mean flow and eddies—are investigated using observations from an eddy-rich region of the Antarctic Circumpolar Current downstream of the Shackleton Fracture Zone (SFZ) in Drake Passage. Four years of measurements by an array of current- and pressure-recording inverted echo sounders deployed between November 2007 and November 2011 are used to diagnose eddy–mean flow interactions and provide insight into physical mechanisms for these transfers. Averaged within the upper to mid-water column (400–1000-m depth) and over the 4-yr-record mean field, eddy potential energy is highest in the western part of the storm track and maximum eddy kinetic energy occurs farther away from the SFZ, shifting the proportion of eddy energies from to about 1 along the storm track. There are enhanced mean 3D wave activity fluxes immediately downstream of SFZ with strong horizontal flux vectors emanating northeast from this region. Similar patterns across composites of Polar Front and Subantarctic Front meander intrusions suggest the dynamics are set more so by the presence of the SFZ than by the eddy’s sign. A case study showing the evolution of a single eddy event, from 15 to 23 July 2010, highlights the storm-track dynamics in a series of snapshots. Consistently, explaining the eddy energetics pattern requires both horizontal and vertical components of W, implying the importance of barotropic and baroclinic processes and instabilities in controlling storm-track dynamics in Drake Passage.

scholarly journals Coupling Influences of ENSO and PDO on the Inter-Decadal SST Variability of the ACC around the Western South Atlantic

2019 ◽  
Vol 11 (18) ◽  
pp. 4853
Author(s):  
You-Lin Wang ◽  
Yu-Chen Hsu ◽  
Chung-Pan Lee ◽  
Chau-Ron Wu
Keyword(s):  
Antarctic Circumpolar Current ◽  
Water Mass ◽  
Southern Oscillation ◽  
Drake Passage ◽  
South Atlantic ◽  
Sst Variability ◽  
The Pacific ◽  
Circumpolar Current ◽  
The Antarctic

The Antarctic Circumpolar Current (ACC) plays an important role in the climate as it balances heat energy and water mass between the Pacific and Atlantic Oceans through the Drake Passage. However, because the historical measurements and observations are extremely limited, the decadal and long-term variations of the ACC around the western South Atlantic Ocean are rarely studied. By analyzing reconstructed sea surface temperatures (SSTs) in a 147-year period (1870–2016), previous studies have shown that SST anomalies (SSTAs) around the Antarctic Peninsula and South America had the same phase change as the El Niño Southern Oscillation (ENSO). This study further showed that changes in SSTAs in the regions mentioned above were enlarged when the Pacific Decadal Oscillation (PDO) and the ENSO were in the same warm or cold phase, implying that changes in the SST of higher latitude oceans could be enhanced when the influence of the ENSO is considered along with the PDO.

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