Articles | Volume 17, issue 1
Research article 10 Feb 2021
Research article | 10 Feb 2021
Seasonal variability of the Atlantic Meridional Overturning Circulation at 11° S inferred from bottom pressure measurements
Josefine Herrford et al.
No articles found.
Arne Biastoch, Franziska U. Schwarzkopf, Klaus Getzlaff, Siren Rühs, Torge Martin, Markus Scheinert, Tobias Schulzki, Patricia Handmann, Rebecca Hummels, and Claus W. Böning
Ocean Sci., 17, 1177–1211,Short summary
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.
Francesca Doglioni, Robert Ricker, Benjamin Rabe, and Torsten Kanzow
Earth Syst. Sci. Data Discuss.,
Manuscript not accepted for further reviewShort summary
This paper presents a new satellite-derived gridded dataset of sea surface height and geostrophic velocity, over the Arctic ice-covered and ice-free regions up to 88° N. The dataset includes velocities north of 82° N, which were not available before. We assess the dataset by comparison to one independent satellite dataset and to independent mooring data. Results show that the geostrophic velocity fields can resolve seasonal to interannual variability of boundary currents wider than about 50 km.
Josefine Maas, Susann Tegtmeier, Yue Jia, Birgit Quack, Jonathan V. Durgadoo, and Arne Biastoch
Atmos. Chem. Phys., 21, 4103–4121,Short summary
Cooling-water disinfection at coastal power plants is a known source of atmospheric bromoform. A large source of anthropogenic bromoform is the industrial regions in East Asia. In current bottom-up flux estimates, these anthropogenic emissions are missing, underestimating the global air–sea flux of bromoform. With transport simulations, we show that by including anthropogenic bromoform from cooling-water treatment, the bottom-up flux estimates significantly improve in East and Southeast Asia.
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,Short summary
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
Ocean Sci., 15, 891–904,Short summary
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.
Tim Fischer, Annette Kock, Damian L. Arévalo-Martínez, Marcus Dengler, Peter Brandt, and Hermann W. Bange
Biogeosciences, 16, 2307–2328,Short summary
We investigated air–sea gas exchange in oceanic upwelling regions for the case of nitrous oxide off Peru. In this region, routine concentration measurements from ships at 5 m or 10 m depth prove to overestimate surface (bulk) concentration. Thus, standard estimates of gas exchange will show systematic error. This is due to very shallow stratified layers that inhibit exchange between surface water and waters below and can exist for several days. Maximum bias occurs in moderate wind conditions.
Yao Fu, Johannes Karstensen, and Peter Brandt
Ocean Sci., 14, 589–616,Short summary
Hydrographic analysis in the Atlantic along 14.5° N and 24.5° N shows that between the periods of 1989/92 and 2013/15, the Antarctic Intermediate Water became warmer and saltier at 14.5° N, and that the Antarctic Bottom Water became lighter at both latitudes. By applying a box inverse model, the Atlantic Meridional Overturning Circulation (AMOC) was determined. Comparison among the inverse solution, GECCO2, RAPID, and MOVE shows that the AMOC has not significantly changed in the past 20 years.
Fabrice Ardhuin, Yevgueny Aksenov, Alvise Benetazzo, Laurent Bertino, Peter Brandt, Eric Caubet, Bertrand Chapron, Fabrice Collard, Sophie Cravatte, Jean-Marc Delouis, Frederic Dias, Gérald Dibarboure, Lucile Gaultier, Johnny Johannessen, Anton Korosov, Georgy Manucharyan, Dimitris Menemenlis, Melisa Menendez, Goulven Monnier, Alexis Mouche, Frédéric Nouguier, George Nurser, Pierre Rampal, Ad Reniers, Ernesto Rodriguez, Justin Stopa, Céline Tison, Clément Ubelmann, Erik van Sebille, and Jiping Xie
Ocean Sci., 14, 337–354,Short summary
The Sea surface KInematics Multiscale (SKIM) monitoring mission is a proposal for a future satellite that is designed to measure ocean currents and waves. Using a Doppler radar, the accurate measurement of currents requires the removal of the mean velocity due to ocean wave motions. This paper describes the main processing steps needed to produce currents and wave data from the radar measurements. With this technique, SKIM can provide unprecedented coverage and resolution, over the global ocean.
Eike E. Köhn, Sören Thomsen, Damian L. Arévalo-Martínez, and Torsten Kanzow
Ocean Sci., 13, 1017–1033,
Sandrine Djakouré, Moacyr Araujo, Aubains Hounsou-Gbo, Carlos Noriega, and Bernard Bourlès
Revised manuscript has not been submitted
Yao Fu, Johannes Karstensen, and Peter Brandt
Ocean Sci., 13, 531–549,Short summary
Meridional Ekman transport in the tropical Atlantic was estimated directly by using observed ageostrophic velocity, and indirectly by using wind stress data. The direct and indirect methods agree well with each other. The top of the pycnocline represents the Ekman depth better than the mixed layer depth and a constant depth. The Ekman heat and salt fluxes calculated from sea surface temperature and salinity or from high-resolution temperature and salinity profile data differ only marginally.
Johannes Hahn, Peter Brandt, Sunke Schmidtko, and Gerd Krahmann
Ocean Sci., 13, 551–576,Short summary
Recent studies have shown that the eastern tropical North Atlantic is subject to a strong decrease of the oceanic oxygen concentration in the upper 1000 m from the 1960s to today. By analyzing a broad observational data set, this study found an even stronger oxygen decrease in the upper 400 m throughout the past decade, whereas oxygen increase was found below (400–1000 m). Changes in the strength of the zonal currents are the most likely reason for the observed decadal oxygen changes.
Amelie Driemel, Eberhard Fahrbach, Gerd Rohardt, Agnieszka Beszczynska-Möller, Antje Boetius, Gereon Budéus, Boris Cisewski, Ralph Engbrodt, Steffen Gauger, Walter Geibert, Patrizia Geprägs, Dieter Gerdes, Rainer Gersonde, Arnold L. Gordon, Hannes Grobe, Hartmut H. Hellmer, Enrique Isla, Stanley S. Jacobs, Markus Janout, Wilfried Jokat, Michael Klages, Gerhard Kuhn, Jens Meincke, Sven Ober, Svein Østerhus, Ray G. Peterson, Benjamin Rabe, Bert Rudels, Ursula Schauer, Michael Schröder, Stefanie Schumacher, Rainer Sieger, Jüri Sildam, Thomas Soltwedel, Elena Stangeew, Manfred Stein, Volker H Strass, Jörn Thiede, Sandra Tippenhauer, Cornelis Veth, Wilken-Jon von Appen, Marie-France Weirig, Andreas Wisotzki, Dieter A. Wolf-Gladrow, and Torsten Kanzow
Earth Syst. Sci. Data, 9, 211–220,Short summary
Our oceans are always in motion – huge water masses are circulated by winds and by global seawater density gradients resulting from different water temperatures and salinities. Measuring temperature and salinity of the world's oceans is crucial e.g. to understand our climate. Since 1983, the research icebreaker Polarstern has been the basis of numerous water profile measurements in the Arctic and the Antarctic. We report on a unique collection of 33 years of polar salinity and temperature data.
Florian Schütte, Johannes Karstensen, Gerd Krahmann, Helena Hauss, Björn Fiedler, Peter Brandt, Martin Visbeck, and Arne Körtzinger
Biogeosciences, 13, 5865–5881,Short summary
Mesoscale eddies with very low–oxygen concentrations at shallow depth have been recently discovered in the eastern tropical North Atlantic. Our analysis shows that low oxygen eddies occur more frequent than expected and are found even close to the equator (8° N). From budget calculations we show that an oxygen reduction of 7 µmol/kg in the depth range of 50–150 m in the eastern tropical North Atlantic (peak reduction is 16 µmol/kg at 100 m depth) can be associated with the dispersion of these eddies.
Florian Schütte, Peter Brandt, and Johannes Karstensen
Ocean Sci., 12, 663–685,Short summary
We want to examine the characteristics of mesoscale eddies in the tropical northeastern Atlantic. They serve as transport agents, exporting water from the coast into the open ocean. Traditionally eddies are categorized with respect to their rotation: cyclonic and anticyclonic. But we could identify, with a combination of different satellite products, a third type called "anticyclonic mode-water eddy" transporting much larger anomalies. We propose a distinction into three classes for further studies.
K. A. Reeve, O. Boebel, T. Kanzow, V. Strass, G. Rohardt, and E. Fahrbach
Earth Syst. Sci. Data, 8, 15–40,Short summary
We present spatially gridded, time-composite mapped data of temperature and salinity of the upper 2000m of the Weddell Gyre through the objective mapping of Argo float data. This was realized on fixed-pressure surfaces ranging from 50 to 2000 dbar. Pressure, temperature and salinity are also available at the level of the sub-surface temperature maximum, which represents the core of Warm Deep Water, the primary heat source of the Weddell Gyre. A detailed description of the methods is provided.
L. Stramma, R. Czeschel, T. Tanhua, P. Brandt, M. Visbeck, and B. S. Giese
Ocean Sci., 12, 153–167,Short summary
The subsurface circulation in the eastern tropical North Atlantic OMZ is derived from velocity, float and tracer data and data assimilation results, and shows a cyclonic flow around the Guinea Dome reaching into the oxygen minimum zone. The stronger cyclonic flow around the Guinea Dome in 2009 seem to be connected to a strong Atlantic Meridional Mode (AMM) event. A continuous deoxygenation trend of the low oxygen layer was confirmed. Eddy influence is weak south of the Cape Verde Islands.
J. Karstensen, B. Fiedler, F. Schütte, P. Brandt, A. Körtzinger, G. Fischer, R. Zantopp, J. Hahn, M. Visbeck, and D. Wallace
Biogeosciences, 12, 2597–2605,Short summary
This study is the first report of the formation of dead zones in the open ocean. A combination of multiple ocean observing system elements (mooring, floats, satellites, ships) allowed us to reconstruct the generation of the dead zones and to connect the formation to enhanced respiration within mesoscale ocean eddies. The dead zones present specific threats to the ecosystem, such as the interruption of the diurnal migration of zooplankters.
P. Brandt, H. W. Bange, D. Banyte, M. Dengler, S.-H. Didwischus, T. Fischer, R. J. Greatbatch, J. Hahn, T. Kanzow, J. Karstensen, A. Körtzinger, G. Krahmann, S. Schmidtko, L. Stramma, T. Tanhua, and M. Visbeck
Biogeosciences, 12, 489–512,Short summary
Our observational study looks at the structure of the eastern tropical North Atlantic (ETNA) oxygen minimum zone (OMZ) in comparison with the less-ventilated, eastern tropical South Pacific OMZ. We quantify the OMZ’s oxygen budget composed of consumption, advection, lateral and vertical mixing. Substantial oxygen variability is observed on interannual to multidecadal timescales. The deoxygenation of the ETNA OMZ during the last decades represents a substantial imbalance of the oxygen budget.
T. Fischer, D. Banyte, P. Brandt, M. Dengler, G. Krahmann, T. Tanhua, and M. Visbeck
Biogeosciences, 10, 5079–5093,
Bachèlery, M.-L., Illig, S., and Dadou, I.: Interannual variability in the South-East Atlantic Ocean, focusing on the Benguela Upwelling System: Remote versus local forcing, J. Geophys. Res.-Oceans, 121, 284–310, https://doi.org/10.1002/2015JC011168, 2016.
Bentamy, A. and Croizé-Fillon, D.: Gridded surface wind fields from Metop/ASCAT measurements, Int. J. Remote Sens., 33, 1729–1754. https://doi.org/10.1080/01431161.2011.600348, 2012.
Biastoch, A., Böning, C. W., and Lutjeharms, J. R. E.: Agulhas leakage dynamics affects decadal variability in Atlantic overturning circulation, Nature, 456, 489–492, https://doi.org/10.1038/nature07426, 2008.
Bingham, R. J. and Hughes, C. W.: The relationship between sea‐level and bottom pressure variability in an eddy permitting ocean model, Geophys. Res. Lett., 35, L03602, https://doi.org/10.1029/2007GL032662, 2008.
Boebel, O., Schmid, C., and Zenk, W.: Kinematic elements of Antarctic Intermediate Water in the western South Atlantic, Deep-Sea Res. Pt. II, 46, 355–392, https://doi.org/10.1016/S0967-0645(98)00104-0, 1999.
Brandt, P., Claus, M., Greatbatch, R. J., Kopte, R., Toole, J. M., Johns, W. E., and Böning, C. W.: Annual and semiannual cycle of equatorial Atlantic circulation associated with basin mode resonance. J. Phys. Oceanogr., 46, 3011–3029, https://doi.org/10.1175/JPO-D-15-0248.1, 2016.
Buckley, M. W. and Marshall, J.: Observations, inferences, and mechanisms of the Atlantic Meridional Overturning Circulation: A review, Rev. Geophys., 54, 5–63, https://doi.org/10.1002/2015RG000493, 2016.
Chidichimo, M. P., Kanzow, T., Cunningham, S. A., Johns, W. E., and Marotzke, J.: The contribution of eastern-boundary density variations to the Atlantic meridional overturning circulation at 26.5∘ N, Ocean Sci., 6, 475–490, https://doi.org/10.5194/os-6-475-2010, 2010.
Chu, P. C., Ivanov, L. M., Melnichenko, O. V., and Wells, N. C.: On long baroclinic Rossby waves in the tropical North Atlantic observed from profiling floats, J. Geophys. Res., 112, C05032, https://doi.org/10.1029/2006JC003698, 2007.
Codiga, D. L.: Unified Tidal Analysis and Prediction Using the UTide Matlab Functions, Technical Report 2011-01, Graduate School of Oceanography, University of Rhode Island, Narragansett, RI. 59 pp., available at: ftp://www.po.gso.uri.edu/pub/downloads/codiga/pubs/2011Codiga-UTide-Report.pdf (latest access: 15 August 2019), 2011.
Cunningham, S. A., Kanzow, T., Rayner, D., Baringer, M. O., Johns, W. E., Marotzke, J., Longworth, H. R., Grant, E. M., Hirschi, J. J.-M., Beal, L. M., Meinen, C. S., and Bryden, H. L.: Temporal variability of the Atlantic meridional overturning circulation at 26.5∘ N, Science, 317, 935–938, https://doi.org/10.1126/science.1141304, 2007.
Cunningham, S. A.: RRS Discovery Cruise D334, 27 Oct-24 Nov 2008, RAPID Mooring Cruise Report, 2009.
da Silveira, I. C. A., Miranda, L. B., and Brown, W. S.: On the origins of the North Brazil Current, J. Geophys. Res., 99, 22501–22512, https://doi.org/10.1029/94JC01776, 1994.
Dengler, M., Schott, F. A., Eden, C., Brandt, P., Fischer, J., and Zantopp, R. J.: Break-up of the Atlantic deep western boundary current into eddies at 8 degrees S, Nature, 432, 1018–1020, https://doi.org/10.1038/nature03134, 2004.
Donohue, K. A., Watts, D. R., Tracey, K. L., Greene, A. D., and Kennelly, M.: Mapping circulation in the Kuroshio Extension with an array of current and pressure recording inverted echo sounders, J. Atmos. Ocean. Technol., 27, 507–527, https://doi.org/10.1175/2009JTECHO686.1, 2010.
Döös, K.: Influence of the Rossby waves on the seasonal cycle in the tropical Atlantic, J. Geophys. Res., 104, 29591–29598, https://doi.org/10.1029/1999JC900126, 1999.
Drakkar Group: DRAKKAR: developing high resolution ocean components for European Earth system models, Clivar Exchanges, 65, 18–21, 2014.
Durgadoo, J. V., Loveday, B. R., Reason, C. J. C., 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.
Frajka-Williams, E., Lankhorst, M., Koelling, J., and Send, U.: Coherent circulation changes in the Deep North Atlantic from 16∘ N and 26∘ N transport arrays. J. Geophys. Res., 123, 3427-3443, https://doi.org/10.1029/2018JC013949, 2018.
Frajka-Williams, E., Ansorge, I. J, Baehr, J., Bryden, H. L., Chidichimo, M. P., Cunningham, S. A., Danabasoglu, G., Dong, S., Donohue, K. A., Elipot, S., Heimbach, P., Holliday, N., P., Hummels, R., Jackson, L., C., Karstensen, J., Lankhorst, M., Le Bras, I. A., Lozier, M. S., McDonagh, E. L., Meinen, C. S., Mercier, H., Moat, B. I., Perez, R. C., Piecuch, C. G., Rhein, M., Srokosz, M. A., Trenberth, K. E., Bacon, S., Forget, G., Goni, G., Kieke, D., Koelling, J., Lamont, T., McCarthy, G. D., Mertens, C., Send, U., Smeed, D. A., Speich, S., van den Berg, M., Volkov, D., and Wilson, C.: Atlantic Meridional Overturning Circulation: Observed transport and variability, Front. Mar. Sci., 6, 260, https://doi.org/10.3389/fmars.2019.00260, 2019.
Hansen, B., Húsgarð Larsen, K. M., Hátún, H., and Østerhus, S.: A stable Faroe Bank Channel overflow 1995–2015, Ocean Sci., 12, 1205–1220, https://doi.org/10.5194/os-12-1205-2016, 2016.
Herrford, J., Brandt, P., and Zenk, W.: Property Changes of Deep and Bottom Waters in the western tropical Atlantic, Deep-Sea Res. Pt. I, 124, 103–125, https://doi.org/10.1016/j.dsr.2017.04.007, 2017.
Herrford, J., Brandt, P., and Krahmann, G.: Estimating seasonal AMOC variability at 11∘ S using Bottom Pressure Recorders (2013–2018), PANGAEA, https://doi.org/10.1594/PANGAEA.907589, 2019.
Hirschi, J., Baehr, J., Marotzke, J., Stark J., Cunningham, S., and Beismann, J.-O.: A monitoring design for the Atlantic meridional overturning circulation, Geophys. Res. Lett., 30, 1413, https://doi.org/10.1029/2002GL016776, 2003.
Hirschi, J. J., Killworth, P. D., and Blundell, J. R.: Subannual, Seasonal, and Interannual Variability of the North Atlantic Meridional Overturning Circulation. J. Phys. Oceanogr., 37, 1246–1265, https://doi.org/10.1175/JPO3049.1, 2006.
Hummels, R., Brandt, P., Dengler, M., Fischer, J., Araujo, M., Veleda, D., and Durgadoo, J. V.: Interannual to decadal changes in the western boundary circulation in the Atlantic at 11∘ S, Geophys. Res. Lett., 42, 7615–7622, https://doi.org/10.1002/2015GL065254, 2015.
Illig, S., Dewitte, B., Ayoub, N., du Penhoat, Y., Reverdin, G., De Mey, P., Bonjean, F., and Lagerloef, G. S. E.: nterannual long equatorial waves in the tropical Atlantic from a high‐resolution ocean general circulation model experiment in 1981–2000, J. Geophys. Res., 109, C02022, https://doi.org/10.1029/2003JC001771, 2004.
Illig, S., Bachèlery, M.-L., and Cadier, E.: Subseasonal coastal-trapped wave propagations in the southeastern Pacific and Atlantic Oceans: 2. Wave characteristics and connection with the equatorial variability. J. Geophys. Res., 123, 3942–3961, https://doi.org/10.1029/2017JC013540, 2018.
Imbol Koungue, R. A., Illig, S., and Rouault, M.: Role of interannual Kelvin wave propagations in the equatorial Atlantic on the Angola Benguela Current system. J. Geophys. Res.-Oceans, 122, 4685–4703, https://doi.org/10.1002/2016JC012463, 2017.
Jochumsen, K., Moritz, M., Nunes, N., Quadfasel, D., Larsen, K. M. H., Hansen, B., Valdimarsson, H., and Jonsson, S.: Revised transport estimates of the Denmark Strait overflow, J. Geophys. Res.-Oceans, 122, 3434–3450, https://doi.org/10.1002/2017JC012803, 2017.
Johns, W. E., Kanzow, T., and Zantopp, R.: Estimating ocean transports with dynamic height moorings: An application in the Atlantic Deep Western Boundary Current at 26∘ N, Deep-Sea Res. Pt. I, 52, 1542–1567. https://doi.org/10.1016/j.dsr.2005.02.002, 2005.
Johns, W. E., Baringer, M. O., Beal, L. M., Cunningham, S. A., Kanzow, T., Bryden, H. L., Hirschi, J. J., Marotzke, J., Meinen, C. S., Shaw, B., and Curry, R.: Continuous, Array-Based Estimates of Atlantic Ocean Heat Transport at 26.5∘ N, J. Climate, 24, 2429–2449, https://doi.org/10.1175/2010JCLI3997.1, 2011.
Kajikawa, H. and Kobata, T.: Reproducibility of calibration results by 0-A-0 pressurization procedures for hydraulic pressure transducers, Meas. Sci. Technol., 5, 015008, https://doi.org/10.1088/0957-0233/25/1/015008, 2014.
Kanzow, T., Send, U., Zenk, W., Chave, A. D., and Rhein, M.: Monitoring the integrated deep meridional flow in the tropical North Atlantic: long-term performance of a geostrophic array, Deep-Sea Res. Pt. I, 53, 528–546, https://doi.org/10.1016/j.dsr.2005.12.007, 2006.
Kanzow, T., Cunningham, S. A., Rayner, D., Hirschi, J. J.-M, Johns, W. E., Baringer, M. O., Bryden, H. L., Beal, L. M., Meinen, C. S., and Marotzke, J.: Observed flow compensation associated with the MOC at 26.5∘ N in the Atlantic, Science, 317, 938–941, https://doi.org/10.1126/science.1141293, 2007.
Kanzow, T., Send, U., and McCartney, M.: On the variability of the deep meridional transports in the tropical North Atlantic, Deep-Sea Res. Pt. I, 55, 1601–1623, https://doi.org/10.1016/j.dsr.2008.07.011, 2008.
Kanzow, T., Cunningham, S. A., Johns, W. E., Hirschi, J. J., Marotzke, J., Baringer, M. O., Meinen, C. S., Chidichimo, M. P., Atkinson, C., Beal, L. M., Bryden, H. L., and Collins, J.: Seasonal Variability of the Atlantic Meridional Overturning Circulation at 26.5∘ N, J. Climate, 23, 5678–5698, https://doi.org/10.1175/2010JCLI3389, 2010.
Kersalé, M., Meinen, C. S., Perez, R. C., Le Henaff, M., Valla, D., Lamont, T., Sato, O. T., Dong, S., Terre, T., van Caspel, M. Chidichimo, M. P., van den Berg, M., Speich, S., Piola, A. R., Campos, E. J. D., Ansorge, I., Volkov, D. L., Lumpkin, R., and Garzoli, S.: Highly Variable Upper and Abyssal Overturning Cells in the South Atlantic, Sci. Adv., 6, eaba7573, https://doi.org/10.1126/sciadv.aba7573, 2020.
Kolodziejczyk, N., Reverdin, G., Gaillard, F., and Lazar, A.: Low-frequency thermohaline variability in the Subtropical South Atlantic pycnocline during 2002–2013, Geophys. Res. Lett., 41, 6468–6475, https://doi.org/10.1002/2014GL061160, 2014.
Kopte, R., Brandt, P., Dengler, M., Tchipalanga, P. C. M., Macuéria, M., and Ostrowski, M.: The Angola Current: Flow and hydrographic characteristics as observed at 11∘ S, J. Geophys. Res. Oceans, 122, 1177–1189, https://doi.org/10.1002/2016JC012374, 2017.
Kopte, R., Brandt, P., Claus, M., Greatbatch, R. J., and Dengler, M.: Role of equatorial basin-mode resonance for the seasonal variability of the Angola Current at 11∘ S, J. Phys. Oceanogr., 48, 261–281, https://doi.org/10.1175/JPO-D-17-0111.1, 2018. Large, W. G. and Yeager S. G.: The global climatology of an interannually varying air-sea flux data set, Clim. Dyn., 33, 341–364, https://doi.org/10.1007/s00382-008-0441-3, 2009.
Lavin, A., Bryden, H. L., and Parilla, G.: Meridional transport and heat flux variations in the subtropical North Atlantic, Global Atmos. Ocean Sys., 6, 269–293, 1998.
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.
Lozier, M. S., Li, F., Bacon, S., Bahr, F., Bower, A. S., Cunningham, S. A., de Jong, M. F., de Steur, L., DeYoung, B., Fischer, J., Gary, S. F., Greenan, N. J. W., Holliday, N. P., Houk, A., Houpert, L., Inall, M. E., Johns, W. E., Johnson, H. L., Johnson, C., Karstensen, J., Koman, G., LeBras, I. A., Lin, X., Mackay, N., Marshall, D. P., Mercier, H., Oltmanns, M., Pickart, R. S., Ramsey, A. L., Rayner, D., Straneo, F., Thierry, V., Torres, D. J., Williams, R. G., Wilson, C., Yang, J., Yashayaev, I., and Zhao, J.: A Sea Change in Our View of Overturning in the Subpolar North Atlantic, Science, 363, 516–521, https://doi.org/10.1126/science.aau6592, 2019.
Lübbecke, J. F., Durgadoo, J. V., and Biastoch, A.: Contribution of Increased Agulhas Leakage to Tropical Atlantic Warming, J. Clim., 28, 9697–9706, https://doi.org/10.1175/JCLI-D-15-0258.1, 2015.
Lumpkin, R. and Speer, K.: Large-Scale Vertical and Horizontal Circulation in the North Atlantic Ocean, J. Phys. Oceanogr., 33, 1902–1920, https://doi.org/10.1175/1520-0485(2003)033<1902:LVAHCI>2.0.CO;2, 2003.
Lumpkin, R. and Speer, K.: Global ocean meridional overturning. J. Phys. Oceanogr., 37, 2550–2562, https://doi.org/10.1175/JPO3130.1, 2007.
Madec, G.: NEMO ocean engine, Note du Pole de modelisation, No. 27. Inst. Pierre-Simon Laplace (IPSL), France, 2008.
McCarthy, G. D., Smeed, D. A., Johns, W. E., Frajka-Williams, E., Moat, B. I., Rayner, D., Baringer, M. O., Meinen, C. S., Collins, J., Bryden, H. L.: Measuring the Atlantic meridional overturning circulation at 26∘ N, Prog. Oceanogr., 130, 91–111, https://doi.org/10.1016/j.pocean.2014.10.006, 2015.
Meinen, C. S., Johns, W. E., Garzoli, S. L., van Sebille, E., Rayner, D., Kanzow, T., and Baringer, M. O.: Variability of the Deep Western Boundary Current at 26.5∘ N during 2004-2009, Deep-Sea Res. Pt. II, 85, 154–168, https://doi.org/10.1016/j.dsr2.2012.07.036, 2013.
Meinen, C. S., Speich, S., Piola, A. R., Ansorge, I., Campos, E., Kersalè, M., Terre, T., Chidichimo, M.-P., Lamont, T., Sato, O. T., Perez, R. C., Valla, D., van den Berg, M., Le Henaff, M., Dong, S., and Garzoli, S. L.: Meridional Overturning Circulation transport variability at 34.5∘ S during 2009-2017: Baroclinic and barotropic flows and the dueling influence of the boundaries, Geophys. Res. Lett., 45, 4180–4188, https://doi.org/10.1029/2018GL077408, 2018.
Philander, S. G. H. and Pacanowski, R. C.: A model of the seasonal cycle in the tropical Atlantic Ocean, J. Geophys. Res., 91, 14192–14206, https://doi.org/10.1029/JC091iC12p14192, 1986.
Polo, I., Lazar, A., Rodriguez-Fonseca, B., and Arnault, S.: Oceanic Kelvin waves and tropical Atlantic intraseasonal variability: 1. Kelvin wave characterization, J. Geophys. Res., 113, C07009, https://doi.org/10.1029/2007JC004495, 2008.
Pujol, M.-I., Faugère, Y., Taburet, G., Dupuy, S., Pelloquin, C., Ablain, M., and Picot, N.: DUACS DT2014: the new multi-mission altimeter data set reprocessed over 20 years, Ocean Sci., 12, 1067–1090, https://doi.org/10.5194/os-12-1067-2016, 2016.
Richardson, P. L.: On the history of meridional overturning circulation schematic diagrams, Prog. Oceanogr., 76, 466–486. https://doi.org/10.1016/j.pocean.2008.01.005, 2008.
Rodrigues, R. R., Rothstein, L. M., and Wimbush, M.: Seasonal Variability of the South Equatorial Current Bifurcation in the Atlantic Ocean: A Numerical Study, J. Phys. Oceanogr., 37, 16–30, https://doi.org/10.1175/JPO2983.1, 2007.
Roessler, A., Rhein, M., Kieke, D., and Mertens, C.: Long-term observations of North Atlantic Current transport at the gateway between western and eastern Atlantic, J. Geophys. Res.-Oceans, 120, 4003–4027. https://doi.org/10.1002/2014JC010662, 2015.
Rühs, S., Getzlaff, K., Durgadoo, J. V., Biastoch, A., and Böning, C. W.: On the suitability of North Brazil current transport estimates for monitoring basin-scale AMOC changes, Geophys. Res. Lett., 42, 8072–8080, https://doi.org/10.1002/2015GL065695, 2015.
Schmidtko, S. and Johnson, G. C.: Multidecadal warming and shoaling of Antarctic Intermediate Water, J. Clim., 25, 207–221, https://doi.org/10.1175/JCLI-D-11-00021.1, 2012.
Schott, F. A., Dengler, M., Zantopp, R., Stramma, L., Fischer, J., and Brandt, P.: The Shallow and Deep Western Boundary Circulation of the South Atlantic at 5∘ –11∘ S, J. Phys. Oceanogr., 35, 2031–2053, https://doi.org/10.1175/JPO2813.1, 2005.
Send, U., Lankhorst, M., and Kanzow, T.: Observation of decadal change in the Atlantic meridional overturning circulation using 10 years of continuous transport data, Geophys. Res. Lett., 38, L24606, https://doi.org/10.1029/2011GL049801, 2011.
Srokosz, M. A. and Bryden, H. L.: Observing the Atlantic meridional overturning circulation yields a decade of inevitable surprises, Science 348, 1255575, https://doi.org/10.1126/science.1255575, 2015.
Stramma, L. and England, M.: On the water masses and mean circulation of the South Atlantic Ocean, J. Geophys. Res., 104, 20863–20883, https://doi.org/10.1029/1999JC900139, 1999.
Stramma, L., Fischer, J., and Reppin, J.: The North Brazil Undercurrent, Deep-Sea Res. Pt. I, 42, 773–795, https://doi.org/10.1016/0967-0637(95)00014-W, 1995.
Talley, L. D.: Shallow, intermediate and deep overturning components of the global heat budget, J. Phys. Oceanogr., 33, 530–560, https://doi.org/10.1175/1520-0485(2003)033<0530:SIADOC>2.0.CO;2, 2003.
Tchipalanga, P., Dengler, M., Brandt, P., Kopte, R., Macueria, M., Coelho, P., Ostrowski, M., and Keenlyside, N. S.: Eastern Boundary Circulation and Hydrography Off Angola: Building Angolan Oceanographic Capacities, Bull. Am. Meteorol. Soc., 99, 1589–1605, https://doi.org/10.1175/BAMS-D-17-0197.1, 2018.
Toole, J. M., Andres, M., Le Bras, I. A., Joyce, T. M., and McCartney, M. S.: Moored observations of the deep western boundary current in the NW Atlantic: 2004–2014, J. Geophys. Res.-Oceans 122, 7488–7505, https://doi.org/10.1002/2017JC012984, 2017.
Veleda, D. R. A., Araujo, M., Silva, M., Montagne, R., and Araujo, R.: Seasonal and interannual variability of the southern south equatorial bifurcation and meridional transport along the eastern Brazilian edge, Trop. Oceanogr., 39, 27–59, https://doi.org/10.5914/tropocean.v39i1.5176, 2011.
Watts, D. R. and Kontoyiannis, H.: Deep-ocean bottom pressure measurement–Drift removal and performance, J. Atmos. Ocean. Tech., 7, 296–306, https://doi.org/10.1175/1520-0426(1990)007<0296:DOBPMD>2.0.CO;2, 1990.
Wienders, N., Arhan, M., and Mercier, H.: Circulation at the western boundary of the South and Equatorial Atlantic: exchanges with the ocean interior, J. Mar. Res., 58, 1007–1039, https://doi.org/10.1357/002224000763485782, 2000.
Worthington, E. L., Frajka-Williams, E., and McCarthy, G. D.: Estimating the deep overturning transport variability at 26∘ N using bottom pressure recorders, J. Geoph. Res.-Oceans, 124, 335–348, https://doi.org/10.1029/2018JC014221, 2019.
Zantopp, R., Fischer, J., Visbeck, M., and Karstensen, J.: From interannual to decadal: 17 years of boundary current transports at the exit of the Labrador Sea. J. Geophys. Res.-Oceans, 122, 1724–1748. https://doi.org/10.1002/2016JC012271, 2017.
Zhang, D., Msadek, R., McPhaden, M. J., and Delworth, T.: Multidecadal variability of the North Brazil Current and its connection to the Atlantic meridional overturning circulation, J. Geophys. Res., 116, https://doi.org/10.1029/2010JC006812, 2011.
Zhao, J. and Johns, W. E.: Wind-forced interannual variability of the Atlantic Meridional Overturning Circulation at 26.5∘ N, J. Geophys. Res.-Oceans, 119, 2403–2419, https://doi.org/10.1002/2013JC009407, 2014.
The Atlantic Meridional Overturning Circulation (AMOC) is an important component of the climate system. Understanding its structure and variability is a key priority for many scientists. Here, we present the first estimate of AMOC variations for the tropical South Atlantic from the TRACOS array at 11° S. Over the observed period, the AMOC was dominated by seasonal variability. We investigate the respective mechanisms with an ocean model and find that different wind-forced waves play a big role.
The Atlantic Meridional Overturning Circulation (AMOC) is an important component of the climate...