scholarly journals Paleo Agulhas rings enter the subtropical gyre during the penultimate deglaciation

2013 ◽  
Vol 9 (2) ◽  
pp. 2095-2114
Author(s):  
P. Scussolini ◽  
E. van Sebille
Keyword(s):  
Ocean Circulation ◽  
Circulation Model ◽  
South Atlantic ◽  
Meridional Overturning Circulation ◽  
Global Ocean ◽  
The South ◽  
Cape Basin ◽  
Globorotalia Truncatulinoides ◽  
Density Perturbations ◽  
Global Ocean Circulation

Abstract. A maximum in the strength of Agulhas Leakage has been registered at the interface between Indian and South Atlantic oceans during glacial Termination II (T II), presumably transporting the salt and heat necessary to maintain the Atlantic Meridional Overturning Circulation (AMOC) at rates similar to the present day. However, it was never shown whether these were effectively incorporated in the South Atlantic gyre, or whether they retroflected into the Indian and/or Southern Oceans. To solve this question, we investigate the presence of paleo Agulhas rings from a sediment core on the central Walvis Ridge, almost 1800 km farther into the Atlantic basin than previously studied. Analysis of a 20 yr dataset from a global ocean circulation model allows us to relate density perturbations, at the depth of the thermocline, to the passage of individual rings over the core site. Using this relation from the numerical model as the basis for a proxy, we generate a time series of δ18O variability of Globorotalia truncatulinoides single specimens, revealing high levels of pycnocline depth variability at the site, suggesting enhanced numbers of Agulhas rings moving into the South Atlantic gyre around and before T II. Our record closely follows the published quantifications of Agulhas Leakage from the east of the Cape Basin, and thus shows that Indian Ocean waters entered the South Atlantic circulation. This provides crucial support to the view of a prominent role of the Agulhas Leakage in the shift from a glacial to an interglacial mode of AMOC.

scholarly journals Paleo Agulhas rings enter the subtropical gyre during the penultimate deglaciation

2013 ◽  
Vol 9 (6) ◽  
pp. 2631-2639 ◽  
Author(s):  
P. Scussolini ◽  
E. van Sebille ◽  
J. V. Durgadoo
Keyword(s):  
South Atlantic ◽  
The South ◽  
Data Set ◽  
The Core ◽  
Walvis Ridge ◽  
Core Site ◽  
Cape Basin ◽  
Globorotalia Truncatulinoides ◽  
Density Perturbations

Abstract. A maximum in the strength of Agulhas leakage has been registered at the interface between the Indian and South Atlantic oceans during glacial Termination II (T-II). This presumably transported the salt and heat necessary for maintaining the Atlantic circulation at rates similar to the present day. However, it was never shown whether these waters were effectively incorporated into the South Atlantic gyre, or whether they retroflected into the Indian and/or Southern oceans. To resolve this question, we investigate the presence of paleo Agulhas rings from a sediment core on the central Walvis Ridge, almost 1800 km farther into the Atlantic Basin than previously studied. Analysis of a 60 yr data set from the global-nested INALT01 model allows us to relate density perturbations at the depth of the thermocline to the passage of individual rings over the core site. Using this relation from the numerical model as the basis for a proxy, we generate a time series of variability of individual Globorotalia truncatulinoides δ18O. We reveal high levels of pycnocline depth variability at the site, suggesting enhanced numbers of Agulhas rings moving into the South Atlantic Gyre around T-II. Our record closely follows the published quantifications of Agulhas leakage from the east of the Cape Basin, and thus shows that Indian Ocean waters entered the South Atlantic circulation. This provides crucial support for the view of a prominent role of the Agulhas leakage in the shift from a glacial to an interglacial mode of the Atlantic circulation.

scholarly journals Impact of partial steps and momentum advection schemes in a global ocean circulation model at eddy-permitting resolution

2006 ◽  
Vol 56 (5-6) ◽  
pp. 543-567 ◽  
Author(s):  
Barnier Bernard ◽  
Gurvan Madec ◽  
Thierry Penduff ◽  
Jean-Marc Molines ◽  
Anne-Marie Treguier ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
Circulation Model ◽  
Global Ocean ◽  
Ocean Circulation Model ◽  
Advection Schemes ◽  
Global Ocean Circulation

scholarly journals First satellite tracks of South Atlantic sea turtle ‘lost years’: seasonal variation in trans-equatorial movement

2017 ◽  
Vol 284 (1868) ◽  
pp. 20171730 ◽  
Author(s):  
Katherine L. Mansfield ◽  
Milagros L. Mendilaharsu ◽  
Nathan F. Putman ◽  
Maria A. G. dei Marcovaldi ◽  
Alexander E. Sacco ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
Environmental Changes ◽  
Circulation Model ◽  
Sea Turtle ◽  
South Atlantic ◽  
Swimming Velocity ◽  
The South ◽  
Frontal Zones ◽  
Few Data ◽  
Passive Drift

In the South Atlantic Ocean, few data exist regarding the dispersal of young oceanic sea turtles. We characterized the movements of laboratory-reared yearling loggerhead turtles from Brazilian rookeries using novel telemetry techniques, testing for differences in dispersal during different periods of the sea turtle hatching season that correspond to seasonal changes in ocean currents. Oceanographic drifters deployed alongside satellite-tagged turtles allowed us to explore the mechanisms of dispersal (passive drift or active swimming). Early in the hatching season turtles transited south with strong southward currents. Late in the hatching season, when currents flowed in the opposite direction, turtles uniformly moved northwards across the Equator. However, the movement of individuals differed from what was predicted by surface currents alone. Swimming velocity inferred from track data and an ocean circulation model strongly suggest that turtles' swimming plays a role in maintaining their position within frontal zones seaward of the continental shelf. The long nesting season of adults and behaviour of post-hatchlings exposes young turtles to seasonally varying ocean conditions that lead some individuals further into the South Atlantic and others into the Northern Hemisphere. Such migratory route diversity may ultimately buffer the population against environmental changes or anthropologic threats, fostering population resiliency.

scholarly journals An evaluation of the barotropic and internal tides in a high-resolution global ocean circulation model

2012 ◽  
Vol 117 (C10) ◽  
pp. n/a-n/a ◽  
Author(s):  
J. F. Shriver ◽  
B. K. Arbic ◽  
J. G. Richman ◽  
R. D. Ray ◽  
E. J. Metzger ◽  
...  
Keyword(s):  
High Resolution ◽  
Ocean Circulation ◽  
Circulation Model ◽  
Internal Tides ◽  
Global Ocean ◽  
Ocean Circulation Model ◽  
Global Ocean Circulation

scholarly journals Moored observations of mesoscale features in the Cape Basin: characteristics and local impacts on water mass distributions

Ocean Science ◽  
2018 ◽  
Vol 14 (5) ◽  
pp. 923-945 ◽  
Author(s):  
Marion Kersalé ◽  
Tarron Lamont ◽  
Sabrina Speich ◽  
Thierry Terre ◽  
Remi Laxenaire ◽  
...  
Keyword(s):  
Water Mass ◽  
Complex Dynamics ◽  
South Atlantic ◽  
Meridional Overturning Circulation ◽  
Data Sets ◽  
The South ◽  
Mesoscale Dynamics ◽  
Cape Basin ◽  
Independent Observations ◽  
The Impact

Abstract. The eastern side of the South Atlantic Meridional overturning circulation Basin-wide Array (SAMBA) along 34.5° S is used to assess the nonlinear, mesoscale dynamics of the Cape Basin. This array presently consists of current meter moorings and bottom mounted Current and Pressure recording Inverted Echo Sounders (CPIES) deployed across the continental slope. These data, available from September 2014 to December 2015, combined with satellite altimetry allow us to investigate the characteristics and the impact of mesoscale dynamics on local water mass distribution and cross-validate the different data sets. We demonstrate that the moorings are affected by the complex dynamics of the Cape Basin involving Agulhas rings, cyclonic eddies and anticyclonic eddies from the Agulhas Bank and the South Benguela upwelling front and filaments. Our analyses show that exchange of water masses happens through the advection of water by mesoscale eddies but also via wide water mass intrusions engendered by the existence of intense dipoles. These complex dynamics induce strong intra-seasonal upper-ocean velocity variations and water mass exchanges between the shelf and the open ocean but also across the subantarctic and subtropical waters. This work presents the first independent observations comparison between full-depth moorings and CPIES data sets within the eastern South Atlantic region that gives some evidence of eastern boundary buoyancy anomalies associated with migrating eddies. It also highlights the need to continuously sample the full water depth as inter-basin exchanges occur intermittently and affect the whole water column.

scholarly journals Stability of the Global Ocean Circulation: Basic Bifurcation Diagrams

2005 ◽  
Vol 35 (6) ◽  
pp. 933-948 ◽  
Author(s):  
Henk A. Dijkstra ◽  
Wilbert Weijer
Keyword(s):  
Ocean Circulation ◽  
General Circulation ◽  
Multiple Equilibria ◽  
Stable Solution ◽  
Circulation Model ◽  
Ocean Model ◽  
Global Ocean ◽  
Freshwater Flux ◽  
Surface Salinity ◽  
Global Ocean Circulation

Abstract A study of the stability of the global ocean circulation is performed within a coarse-resolution general circulation model. Using techniques of numerical bifurcation theory, steady states of the global ocean circulation are explicitly calculated as parameters are varied. Under a freshwater flux forcing that is diagnosed from a reference circulation with Levitus surface salinity fields, the global ocean circulation has no multiple equilibria. It is shown how this unique-state regime transforms into a regime with multiple equilibria as the pattern of the freshwater flux is changed in the northern North Atlantic Ocean. In the multiple-equilibria regime, there are two branches of stable steady solutions: one with a strong northern overturning in the Atlantic and one with hardly any northern overturning. Along the unstable branch that connects both stable solution branches (here for the first time computed for a global ocean model), the strength of the southern sinking in the South Atlantic changes substantially. The existence of the multiple-equilibria regime critically depends on the spatial pattern of the freshwater flux field and explains the hysteresis behavior as found in many previous modeling studies.

scholarly journals Oceanic Fluxes in the South Atlantic

2005 ◽  
Vol 35 (1) ◽  
pp. 109-122 ◽  
Author(s):  
Elaine L. McDonagh ◽  
Brian A. King
Keyword(s):  
Heat Flux ◽  
Ocean Circulation ◽  
World Ocean ◽  
South Atlantic ◽  
Freshwater Flux ◽  
Intermediate Water ◽  
The South ◽  
Cape Basin ◽  
Small Gain ◽  
The Difference

Abstract A box inverse of the World Ocean Circulation Experiment A10 (30°S) and A11 (nominally 45°S) sections in the South Atlantic Ocean was undertaken. The authors find a heat flux across A10 of 0.22 ± 0.08 PW, consistent with previous studies, and a heat flux of 0.43 ± 0.08 PW across A11. The A11 heat flux is lower than some previous analyses of this section but implies a plausible oceanic heat convergence (heat loss to the atmosphere) of 0.21 ± 0.10 PW. The difference is principally due to adding a cyclonic component to the circulation in the Cape Basin. As compared with the solution of other studies, the anticyclonic circulation in the surface and intermediate water of the subtropical gyre is weakened. The circulation of the deep water is cyclonic rather than anticyclonic; this is in better agreement with previously published circulation schemes based on examination of water properties. A southward freshwater flux of 0.7 Sv (1 Sv ≡ 106 m3 s−1) at A11, consistent with previous inverse studies, is still inconsistent with the net Atlantic evaporation inferred from integrated surface climatologies. Results suggest a small gain of freshwater (0.2 ± 0.1 Sv) between the sections.

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