Articles | Volume 17, issue 4
https://doi.org/10.5194/os-17-1067-2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/os-17-1067-2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Research article
| 
16 Aug 2021
Research article |
| 16 Aug 2021
| 16 Aug 2021
Characteristics and robustness of Agulhas leakage estimates: an inter-comparison study of Lagrangian methods
Christina Schmidt
GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany
Franziska U. Schwarzkopf
GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany
Siren Rühs
GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany
GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany
Christian-Albrechts-Universität zu Kiel, Kiel, Germany
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Ocean Sci., 18, 1431–1450, https://doi.org/10.5194/os-18-1431-2022, https://doi.org/10.5194/os-18-1431-2022, 2022
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Ocean and climate scientists have used numerical simulations as a tool to examine the ocean and climate system since the 1970s. Since then, owing to the continuous increase in computational power and advances in numerical methods, we have been able to simulate increasing complex phenomena. However, the fidelity of the simulations in representing the phenomena remains a core issue in the ocean science community. Here we propose a cloud-based framework to inter-compare and assess such simulations.
Jens Zinke, Takaaki K. Watanabe, Siren Rühs, Miriam Pfeiffer, Stefan Grab, Dieter Garbe-Schönberg, and Arne Biastoch
Clim. Past, 18, 1453–1474, https://doi.org/10.5194/cp-18-1453-2022, https://doi.org/10.5194/cp-18-1453-2022, 2022
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Salinity is an important and integrative measure of changes to the water cycle steered by changes to the balance between rainfall and evaporation and by vertical and horizontal movements of water parcels by ocean currents. However, salinity measurements in our oceans are extremely sparse. To fill this gap, we have developed a 334-year coral record of seawater oxygen isotopes that reflects salinity changes in the globally important Agulhas Current system and reveals its main oceanic drivers.
Ioana Ivanciu, Katja Matthes, Arne Biastoch, Sebastian Wahl, and Jan Harlaß
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Greenhouse gas concentrations continue to increase, while the Antarctic ozone hole is expected to recover during the twenty-first century. We separate the effects of ozone recovery and of greenhouse gases on the Southern Hemisphere atmospheric and oceanic circulation, and we find that ozone recovery is generally reducing the impact of greenhouse gases, with the exception of certain regions of the stratosphere during spring, where the two effects reinforce each other.
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The Atlantic Meridional Overturning Circulation (AMOC) quantifies the impact of the ocean on climate and climate change. Here we show that a high-resolution ocean model is able to realistically simulate ocean currents. While the mean representation of the AMOC depends on choices made for the model and on the atmospheric forcing, the temporal variability is quite robust. Comparing the ocean model with ocean observations, we able to identify that the AMOC has declined over the past two decades.
Ioana Ivanciu, Katja Matthes, Sebastian Wahl, Jan Harlaß, and Arne Biastoch
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The Antarctic ozone hole has driven substantial dynamical changes in the Southern Hemisphere atmosphere over the past decades. This study separates the historical impacts of ozone depletion from those of rising levels of greenhouse gases and investigates how these impacts are captured in two types of climate models: one using interactive atmospheric chemistry and one prescribing the CMIP6 ozone field. The effects of ozone depletion are more pronounced in the model with interactive chemistry.
Josefine Maas, Susann Tegtmeier, Yue Jia, Birgit Quack, Jonathan V. Durgadoo, and Arne Biastoch
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Nele Tim, Eduardo Zorita, Kay-Christian Emeis, Franziska U. Schwarzkopf, Arne Biastoch, and Birgit Hünicke
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Our study reveals that the latitudinal position and intensity of Southern Hemisphere trades and westerlies are correlated. In the last decades the westerlies have shifted poleward and intensified. Furthermore, the latitudinal shifts and intensity of the trades and westerlies impact the sea surface temperatures around southern Africa and in the South Benguela upwelling region. The future development of wind stress depends on the strength of greenhouse gas forcing.
Franziska U. Schwarzkopf, Arne Biastoch, Claus W. Böning, Jérôme Chanut, Jonathan V. Durgadoo, Klaus Getzlaff, Jan Harlaß, Jan K. Rieck, Christina Roth, Markus M. Scheinert, and René Schubert
Geosci. Model Dev., 12, 3329–3355, https://doi.org/10.5194/gmd-12-3329-2019, https://doi.org/10.5194/gmd-12-3329-2019, 2019
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A family of nested global ocean general circulation model configurations, the INALT family, has been established with resolutions of 1/10°, 1/20° and 1/60° in the South Atlantic and western Indian oceans, covering the greater Agulhas Current (AC) system. The INALT family provides a consistent set of configurations that allows to address eddy dynamics in the AC system and their impact on the large-scale ocean circulation.
Josefine Maas, Susann Tegtmeier, Birgit Quack, Arne Biastoch, Jonathan V. Durgadoo, Siren Rühs, Stephan Gollasch, and Matej David
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In a large-scale analysis, the spread of disinfection by-products from oxidative ballast water treatment is investigated, with a focus on Southeast Asia where major ports are located. Halogenated compounds such as bromoform (CHBr3) are produced in the ballast water and, once emitted into the environment, can participate in ozone depletion. Anthropogenic bromoform is rapidly emitted into the atmosphere and can locally double around large ports. A large-scale impact cannot be found.
Siren Rühs, Franziska U. Schwarzkopf, Sabrina Speich, and Arne Biastoch
Ocean Sci., 15, 489–512, https://doi.org/10.5194/os-15-489-2019, https://doi.org/10.5194/os-15-489-2019, 2019
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We revisit the sources for the upper limb of the overturning circulation in the South Atlantic by tracking fluid particles in a high-resolution ocean model. Our results suggest that the upper limb’s transport is dominantly supplied by waters with Indian Ocean origin, but the contribution of waters with Pacific origin is substantially larger than previously estimated with coarse-resolution models. Yet, a large part of upper limb waters obtains thermohaline properties within the South Atlantic.
D. Le Bars, J. V. Durgadoo, H. A. Dijkstra, A. Biastoch, and W. P. M. De Ruijter
Ocean Sci., 10, 601–609, https://doi.org/10.5194/os-10-601-2014, https://doi.org/10.5194/os-10-601-2014, 2014
Cited articles
Ansorge, I. J., Speich, S., Lutjeharms, J. R., Göni, G. J., Rautenbach,
C. J., Froneman, P. W., Rouault, M., and Garzoli, S.: Monitoring the oceanic
flow between Africa and Antarctica: Report of the first GoodHope cruise,
S. Afr. J. Sci., 101, 29–35, 2005. a
Arhan, M., Mercier, H., and Lutjeharms, J. R.: The disparate evolution of
three Agulhas rings in the South Atlantic Ocean, J. Geophys.
Res.-Oceans, 104, 20987–21005, https://doi.org/10.1029/1998jc900047, 1999. a
Arhan, M., Speich, S., Messager, C., Dencausse, G., Fine, R., and Boye, M.:
Anticyclonic and cyclonic eddies of subtropical origin in the subantarctic
zone south of Africa, J. Geophys. Res.-Oceans, 116, 1–22,
https://doi.org/10.1029/2011JC007140, 2011. a
Backeberg, B. C., Penven, P., and Rouault, M.: Impact of intensified Indian
Ocean winds on mesoscale variability in the Agulhas system, Nat. Clim.
Change, 2, 608–612, https://doi.org/10.1038/nclimate1587, 2012. a
Beal, L. M., De Ruijter, W. P., Biastoch, A., Zahn, R., Cronin, M., Hermes,
J., Lutjeharms, J., Quartly, G., Tozuka, T., Baker-Yeboah, S., Bornman, T.,
Cipollini, P., Dijkstra, H., Hall, I., Park, W., Peeters, F., Penven, P.,
Ridderinkhof, H., and Zinke, J.: On the role of the Agulhas system in ocean
circulation and climate, Nature, 472, 429–436, https://doi.org/10.1038/nature09983,
2011. a, b
Beal, L. M., Elipot, S., Houk, A., and Leber, G. M.: Capturing the Transport
Variability of a Western Boundary Jet: Results from the Agulhas Current
Time-Series Experiment (ACT)*, J. Phys. Oceanogr., 45,
1302–1324, https://doi.org/10.1175/jpo-d-14-0119.1, 2015. a, b
Biastoch, A. and Böning, C. W.: Anthropogenic impact on Agulhas
leakage, Geophys. Res. Lett., 40, 1138–1143,
https://doi.org/10.1002/grl.50243, 2013. a, b, c
Biastoch, A., Lutjeharms, J. R., Böning, C. W., and Scheinert, M.:
Mesoscale perturbations control inter-ocean exchange south of Africa,
Geophys. Res. Lett., 35, 2000–2005, https://doi.org/10.1029/2008GL035132,
2008. a, b
Biastoch, A., Böning, C. W., Schwarzkopf, F. U., and Lutjeharms, J. R.:
Increase in Agulhas leakage due to poleward shift of Southern Hemisphere
westerlies, Nature, 462, 495–498, https://doi.org/10.1038/nature08519, 2009. a, b, c
Biastoch, A., Sein, D., Durgadoo, J. V., Wang, Q., and Danilov, S.: Simulating
the Agulhas system in global ocean models – nesting vs. multi-resolution
unstructured meshes, Ocean Modell., 121, 117–131,
https://doi.org/10.1016/j.ocemod.2017.12.002, 2018. a
Blanke, B. and Raynaud, S.: Kinematics of the Pacific Equatorial Undercurrent:
An Eulerian and Lagrangian approach from GCM results, J. Phys.
Oceanogr., 27, 1038–1053,
https://doi.org/10.1175/1520-0485(1997)027<1038:KOTPEU>2.0.CO;2, 1997. a, b
Blanke, B., Arhan, M., Madec, G., and Roche, S.: Warm water paths in the
equatorial Atlantic as diagnosed with a general circulation model, J. Phys. Oceanogr., 29, 2753–2768,
https://doi.org/10.1175/1520-0485(1999)029<2753:WWPITE>2.0.CO;2, 1999. a, b
Boebel, O., Lutjeharms, J., Schmid, C., Zenk, W., Rossby, T., and Barron, C.:
The Cape Cauldron: A regime of turbulent inter-ocean exchange, Deep Sea
Res. II, 50, 57–86, https://doi.org/10.1016/S0967-0645(02)00379-X, 2003. a
Capuano, T. A., Speich, S., Carton, X., and Blanke, B.: Mesoscale and
Submesoscale Processes in the Southeast Atlantic and Their Impact on the
Regional Thermohaline Structure, J. Geophys. Res.-Oceans,
123, 1937–1961, https://doi.org/10.1002/2017JC013396, 2018. a, b
Cheng, Y., Beal, L. M., Kirtman, B. P., and Putrasahan, D.: Interannual
Agulhas leakage variability and its regional climate imprints, J.
Clim., 31, 10105–10121, https://doi.org/10.1175/JCLI-D-17-0647.1, 2018. a, b, c, d
de Ruijter, W. P. M., Biastoch, A., Drijfhout, S. S., Lutjeharms, J. R. E.,
Matano, R. P., Pichevin, T., van Leeuwen, P. J., and Weijer, W.:
Indian-Atlantic interocean exchange: Dynamics, estimation and impact,
J. Geophys. Res.-Oceans, 104, 20885–20910,
https://doi.org/10.1029/1998jc900099, 1999. a
Debreu, L., Vouland, C., and Blayo, E.: AGRIF: Adaptive grid refinement in
Fortran, Comput. Geosci., 34, 8–13,
https://doi.org/10.1016/j.cageo.2007.01.009, 2008. a
Delandmeter, P. and van Sebille, E.: The Parcels v2.0 Lagrangian framework: new field interpolation schemes, Geosci. Model Dev., 12, 3571–3584, https://doi.org/10.5194/gmd-12-3571-2019, 2019. a, b, c, d
Doglioli, A. M., Veneziani, M., Blanke, B., Speich, S., and Griffa, A.: A
Lagrangian analysis of the Indian-Atlantic interocean exchange in a regional
model, Geophys. Res. Lett., 33, 1–5, https://doi.org/10.1029/2006GL026498,
2006. a, b
Donners, J. and Drijfhout, S. S.: The Lagrangian view of South Atlantic
interocean exchange in a global ocean model compared with inverse model
results, J. Phys. Oceanogr., 34, 1019–1035,
https://doi.org/10.1175/1520-0485(2004)034<1019:TLVOSA>2.0.CO;2, 2004. a
Durgadoo, J. V., Loveday, B. R., Reason, C. J., Penven, P., and Biastoch, A.:
Agulhas leakage predominantly responds to the southern hemisphere
westerlies, J. Phys. Oceanogr., 43, 2113–2131,
https://doi.org/10.1175/JPO-D-13-047.1, 2013. a, b, c, d
Fichefet, T. and Maqueda, M. A.: Sensitivity of a global sea ice model to the
treatment of ice thermodynamics and dynamics, J. Geophys.
Res.-Oceans, 102, 12609–12646, https://doi.org/10.1029/97JC00480, 1997. a
Gordon, A. L., Lutjeharms, J. R., and Gründlingh, M. L.: Stratification
and circulation at the Agulhas Retroflection, Deep Sea Res. A,
34, 565–599,
https://doi.org/10.1016/0198-0149(87)90006-9, 1987. a
Lange, M. and van Sebille, E.: Parcels v0.9: prototyping a Lagrangian ocean analysis framework for the petascale age, Geosci. Model Dev., 10, 4175–4186, https://doi.org/10.5194/gmd-10-4175-2017, 2017. a, b
Large, W. G. and Yeager, S. G.: The global climatology of an interannually
varying air – Sea flux data set, Clim. Dynam., 33, 341–364,
https://doi.org/10.1007/s00382-008-0441-3, 2009. a
Le Bars, D., Durgadoo, J. V., Dijkstra, H. A., Biastoch, A., and De Ruijter, W. P. M.: An observed 20-year time series of Agulhas leakage, Ocean Sci., 10, 601–609, https://doi.org/10.5194/os-10-601-2014, 2014. a, b
Laboratoire d'Océanographie Physique et Spatiale (LOPS): Ariane, available at: http://mespages.univ-brest.fr/~grima/Ariane/, last access:
10 August 2021. a
Loveday, B. R., Penven, P., and Reason, C. J.: Southern Annular Mode and
westerly-wind-driven changes in Indian-Atlantic exchange mechanisms,
Geophys. Res. Lett., 42, 4912–4921, https://doi.org/10.1002/2015GL064256,
2015. a, b, c, d
Lutjeharms, J. R.: The Agulhas Current, Springer, Berlin, ISBN 978-3-540-37212-7, 2006. a
OceanParcels project:
http://oceanparcels.org/, last access: 10 August 2021. a
Paris, C. B., Helgers, J., van Sebille, E., and Srinivasan, A.: Connectivity
Modeling System: A probabilistic modeling tool for the multi-scale tracking
of biotic and abiotic variability in the ocean, Environ. Model.
Soft., 42, 47–54, https://doi.org/10.1016/j.envsoft.2012.12.006, 2013. a
Patara, L., Böning, C. W., and Tanhua, T.: Multidecadal Changes in
Southern Ocean Ventilation since the 1960s Driven by Wind and Buoyancy
Forcing, J. Clim., 34, 1485–1502, https://doi.org/10.1175/jcli-d-19-0947.1,
2021. a, b
Putrasahan, D. A., Beal, L. M., Kirtman, B. P., and Cheng, Y.: A new Eulerian
method to estimate “spicy” Agulhas leakage in climate models, Geophys.
Res. Lett., 42, 4532–4539, https://doi.org/10.1002/2015GL064482, 2015. a
Qin, X., van Sebille, E., and Sen Gupta, A.: Quantification of errors
induced by temporal resolution on Lagrangian particles in an eddy-resolving
model, Ocean Model., 76, 20–30, https://doi.org/10.1016/j.ocemod.2014.02.002,
2014. a
Richardson, P. L.: Agulhas leakage into the Atlantic estimated with subsurface
floats and surface drifters, Deep-Sea Res. I, 54, 1361–1389, https://doi.org/10.1016/j.dsr.2007.04.010, 2007. a, b, c
Rimaud, J., Speich, S., Blanke, B., and Grima, N.: The exchange of
Intermediate Water in the southeast Atlantic: Water mass transformations
diagnosed from the Lagrangian analysis of a regional ocean model, J.
Geophys. Res.-Oceans, 117, 1–21, https://doi.org/10.1029/2012JC008059, 2012. a, b, c
Rouault, M., Penven, P., and Pohl, B.: Warming in the Agulhas Current system
since the 1980's, Geophys. Res. Lett., 36, 2–6,
https://doi.org/10.1029/2009GL037987, 2009. a, b
Rühs, S., Schwarzkopf, F. U., Speich, S., and Biastoch, A.: Cold vs. warm water route – sources for the upper limb of the Atlantic Meridional Overturning Circulation revisited in a high-resolution ocean model, Ocean Sci., 15, 489–512, https://doi.org/10.5194/os-15-489-2019, 2019. a
Rusciano, E., Speich, S., and Ollitrault, M.: Interocean exchanges and the
spreading of Antarctic Intermediate Water south of Africa, J.
Geophys. Res.-Oceans, 117, 1–21, https://doi.org/10.1029/2012JC008266, 2012. a, b, c, d
Schmid, C., Boebel, O., Zenk, W., Lutjeharms, J. R., Garzoli, S. L.,
Richardson, P. L., and Barron, C.: Early evolution of an Agulhas Ring,
Deep-Sea Res. II, 50, 141–166,
https://doi.org/10.1016/S0967-0645(02)00382-X, 2003. a
Schmidt, C., Schwarzkopf, F. U., Rühs, S., and Biastoch, A.: Supplementary Data to “Characteristics and robustness of Agulhas leakage estimates: an inter-comparison study of Lagrangian methods”, GEOMAR [code and data set], available at: https://hdl.handle.net/20.500.12085/b704e917-09dd-4a73-b6a1-ea24a549920c, 2021. a
Schubert, R., Schwarzkopf, F. U., Baschek, B., and Biastoch, A.: Submesoscale
Impacts on Mesoscale Agulhas Dynamics, J. Adv. Model. Earth
Syst., 11, 2745–2767, https://doi.org/10.1029/2019MS001724, 2019. a
Schubert, R., Gula, J., Greatbatch, R. J., Baschek, B., and Biastoch, A.: The
submesoscale kinetic energy cascade: Mesoscale absorption of submesoscale
mixed layer eddies and frontal downscale fluxes, J. Phys.
Oceanogr., 50, 2573–2589, https://doi.org/10.1175/JPO-D-19-0311.1, 2020. a
Schwarzkopf, F. U., Biastoch, A., Böning, C. W., Chanut, J., Durgadoo, J. V., Getzlaff, K., Harlaß, J., Rieck, J. K., Roth, C., Scheinert, M. M., and Schubert, R.: The INALT family – a set of high-resolution nests for the Agulhas Current system within global NEMO ocean/sea-ice configurations, Geosci. Model Dev., 12, 3329–3355, https://doi.org/10.5194/gmd-12-3329-2019, 2019. a, b, c, d, e, f
Shchepetkin, A. F. and McWilliams, J. C.: A method for computing horizontal
pressure-gradient force in an oceanic model with a nonaligned vertical
coordinate, J. Geophys. Res.-Oceans, 108, 1–34,
https://doi.org/10.1029/2001jc001047, 2003. a
Speich, S., Lutjeharms, J. R., Penven, P., and Blanke, B.: Role of bathymetry
in Agulhas Current configuration and behaviour, Geophys. Res.
Lett., 33, 2–6, https://doi.org/10.1029/2006GL027157, 2006. a
Tsujino, H., Urakawa, S., Nakano, H., Small, R. J., Kim, W. M., Yeager, S. G.,
Danabasoglu, G., Suzuki, T., Bamber, J. L., Bentsen, M., Böning, C. W.,
Bozec, A., Chassignet, E. P., Curchitser, E., Boeira Dias, F., Durack,
P. J., Griffies, S. M., Harada, Y., Ilicak, M., Josey, S. A., Kobayashi, C.,
Kobayashi, S., Komuro, Y., Large, W. G., Le Sommer, J., Marsland, S. J.,
Masina, S., Scheinert, M., Tomita, H., Valdivieso, M., and Yamazaki, D.:
JRA-55 based surface dataset for driving ocean–sea-ice models (JRA55-do),
Ocean Model., 130, 79–139, https://doi.org/10.1016/j.ocemod.2018.07.002, 2018. a
van Sebille, E., Barron, C. N., Biastoch, A., van Leeuwen, P. J., Vossepoel, F. C., and de Ruijter, W. P. M.: Relating Agulhas leakage to the Agulhas Current retroflection location, Ocean Sci., 5, 511–521, https://doi.org/10.5194/os-5-511-2009, 2009. a
van Sebille, E., van Leeuwen, P. J., Biastoch, A., and de Ruijter, W. P.: Flux
comparison of Eulerian and Lagrangian estimates of Agulhas leakage: A case
study using a numerical model, Deep-Sea Res. I, 57, 319–327, https://doi.org/10.1016/j.dsr.2009.12.006, 2010. a
van Sebille, E., England, M. H., Zika, J. D., and Sloyan, B. M.: Tasman
leakage in a fine-resolution ocean model, Geophys. Res. Lett., 39,
2–6, https://doi.org/10.1029/2012GL051004, 2012.
a
van Sebille, E., Sprintall, J., Schwarzkopf, F. U., Sen Gupta, A., Santoso,
A., England, M. H., Biastoch, A., and Böning, C. W.: Pacific-to-Indian
Ocean connectivity: Tasman leakage, Indonesian Throughflow, and the role of
ENSO, J. Geophys. Res.-Oceans, 129, 1365–1382,
https://doi.org/10.1038/175238c0, 2014. a
van Sebille, E., Griffies, S. M., Abernathey, R., Adams, T. P., Berloff, P.,
Biastoch, A., Blanke, B., Chassignet, E. P., Cheng, Y., Cotter, C. J.,
Deleersnijder, E., Döös, K., Drake, H. F., Drijfhout, S., Gary,
S. F., Heemink, A. W., Kjellsson, J., Koszalka, I. M., Lange, M., Lique, C.,
MacGilchrist, G. A., Marsh, R., Mayorga Adame, C. G., McAdam, R., Nencioli,
F., Paris, C. B., Piggott, M. D., Polton, J. A., Rühs, S., Shah, S. H.,
Thomas, M. D., Wang, J., Wolfram, P. J., Zanna, L., and Zika, J. D.:
Lagrangian ocean analysis: Fundamentals and practices, Ocean Model.,
121, 49–75, https://doi.org/10.1016/j.ocemod.2017.11.008, 2018. a
Weijer, W. and van Sebille, E.: Impact of Agulhas leakage on the Atlantic
overturning circulation in the CCSM4, J. Clim., 27, 101–110,
https://doi.org/10.1175/JCLI-D-12-00714.1, 2014. a
Weijer, W., de Ruijter, W. P., Sterl, A., and Drijfhout, S. S.: Response of
the Atlantic overturning circulation to South Atlantic sources of buoyancy,
Global Planet.Change, 34, 293–311,
https://doi.org/10.1016/S0921-8181(02)00121-2, 2002. a, b
Short summary
We estimate Agulhas leakage, water flowing from the Indian Ocean to the South Atlantic, in an ocean model with two different tools. The mean transport, variability and trend of Agulhas leakage is simulated comparably with both tools, emphasising the robustness of our method. If the experiments are designed differently, the mean transport of Agulhas leakage is altered, but not the trend. Agulhas leakage waters cool and become less salty south of Africa resulting in a density increase.
We estimate Agulhas leakage, water flowing from the Indian Ocean to the South Atlantic, in an...
