Articles | Volume 22, issue 1
https://doi.org/10.5194/os-22-629-2026
© Author(s) 2026. 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-22-629-2026
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Research article
| 
16 Feb 2026
Research article |
| 16 Feb 2026
| 16 Feb 2026
Subpolar Atlantic meridional heat transports from OSNAP and ocean reanalyses – a comparison
Susanna Winkelbauer
CORRESPONDING AUTHOR
Department of Meteorology and Geophysics, University of Vienna, Vienna, Austria
Isabella Winterer
Department of Meteorology and Geophysics, University of Vienna, Vienna, Austria
Michael Mayer
Department of Meteorology and Geophysics, University of Vienna, Vienna, Austria
European Centre for Medium-Range Weather Forecasts, Bonn, Germany
College of Marine Science, University of South Florida, Florida, USA
Leopold Haimberger
Department of Meteorology and Geophysics, University of Vienna, Vienna, Austria
Related authors
Susanna Winkelbauer, Michael Mayer, and Leopold Haimberger
Geosci. Model Dev., 17, 4603–4620, https://doi.org/10.5194/gmd-17-4603-2024, https://doi.org/10.5194/gmd-17-4603-2024, 2024
Short summary
Short summary
Oceanic transports shape the global climate, but the evaluation and validation of this key quantity based on reanalysis and model data are complicated by the distortion of the used modelling grids and the large number of different grid types. We present two new methods that allow the calculation of oceanic fluxes of volume, heat, salinity, and ice through almost arbitrary sections for various models and reanalyses that are independent of the used modelling grids.
Michael Mayer, Takamasa Tsubouchi, Susanna Winkelbauer, Karin Margretha H. Larsen, Barbara Berx, Andreas Macrander, Doroteaciro Iovino, Steingrímur Jónsson, and Richard Renshaw
State Planet, 1-osr7, 14, https://doi.org/10.5194/sp-1-osr7-14-2023, https://doi.org/10.5194/sp-1-osr7-14-2023, 2023
Short summary
Short summary
This paper compares oceanic fluxes across the Greenland–Scotland Ridge (GSR) from ocean reanalyses to largely independent observational data. Reanalyses tend to underestimate the inflow of warm waters of subtropical Atlantic origin and hence oceanic heat transport across the GSR. Investigation of a strong negative heat transport anomaly around 2018 highlights the interplay of variability on different timescales and the need for long-term monitoring of the GSR to detect forced climate signals.
Magdalena Fritz, Michael Mayer, Leopold Haimberger, and Susanna Winkelbauer
Ocean Sci., 19, 1203–1223, https://doi.org/10.5194/os-19-1203-2023, https://doi.org/10.5194/os-19-1203-2023, 2023
Short summary
Short summary
The interaction between the Indonesian Throughflow (ITF) and regional climate phenomena indicates the high relevance for monitoring the ITF. Observations remain temporally and spatially limited; hence near-real-time monitoring is only possible with reanalyses. We assess how well ocean reanalyses depict the intensity of the ITF via comparison to observations. The results show that reanalyses agree reasonably well with in situ observations; however, some aspects require higher-resolution products.
Susanna Winkelbauer, Michael Mayer, Vanessa Seitner, Ervin Zsoter, Hao Zuo, and Leopold Haimberger
Hydrol. Earth Syst. Sci., 26, 279–304, https://doi.org/10.5194/hess-26-279-2022, https://doi.org/10.5194/hess-26-279-2022, 2022
Short summary
Short summary
We evaluate Arctic river discharge using in situ observations and state-of-the-art reanalyses, inter alia the most recent Global Flood Awareness System (GloFAS) river discharge reanalysis version 3.1. Furthermore, we combine reanalysis data, in situ observations, ocean reanalyses, and satellite data and use a Lagrangian optimization scheme to close the Arctic's volume budget on annual and seasonal scales, resulting in one reliable and up-to-date estimate of every volume budget term.
Kristian Strommen, Michael Mayer, Andrea Storto, Jonas Spaeth, and Steffen Tietsche
EGUsphere, https://doi.org/10.5194/egusphere-2025-6402, https://doi.org/10.5194/egusphere-2025-6402, 2026
This preprint is open for discussion and under review for Weather and Climate Dynamics (WCD).
Short summary
Short summary
Numerical weather forecasts of sea ice are unreliable, exhibiting an overly narrow range of plausible sea ice evolutions. Stochastic perturbations introduce randomness to the forecast in order to alleviate this by representing uncertainties in the representation of sea ice physics. We show that such including such perturbations in a forecast model improves the reliability of sea ice forecasts, and furthermore results in improved seasonal forecasts of the northern European winter circulation.
Gokhan Danabasoglu, Frederic S. Castruccio, Burcu Boza, Alice M. Barthel, Arne Biastoch, Adam Blaker, Alexandra Bozec, Diego Bruciaferri, Frank O. Bryan, Eric P. Chassignet, Yao Fu, Ian Grooms, Catherine Guiavarc'h, Hakase Hayashida, Andrew McC. Hogg, Ryan M. Holmes, Doroteaciro Iovino, Andrew E. Kiss, M. Susan Lozier, Gustavo Marques, Alex Megann, Franziska U. Schwarzkopf, Dave Storkey, Luke van Roekel, Jon Wolfe, Xiaobiao Xu, and Rong Zhang
EGUsphere, https://doi.org/10.5194/egusphere-2025-5406, https://doi.org/10.5194/egusphere-2025-5406, 2025
Short summary
Short summary
A comparison of simulated and observed overturning transports across the Overturning in the Subpolar North Atlantic Program sections for the 2014–2022 period is presented. Eighteen ocean simulations participate in the study. The simulated transports are in general agreement with observations. Analyzing overturning circulations in both depth and density space together provides a more complete picture of the overturning properties. The study serves as a benchmark for evaluation of ocean models.
Mona Zolghadrshojaee, Susann Tegtmeier, Sean M. Davis, Robin Pilch Kedzierski, and Leopold Haimberger
Atmos. Chem. Phys., 25, 12213–12232, https://doi.org/10.5194/acp-25-12213-2025, https://doi.org/10.5194/acp-25-12213-2025, 2025
Short summary
Short summary
The tropical tropopause layer (TTL) is a crucial region where the troposphere transitions into the stratosphere, influencing air mass transport. This study examines temperature trends in the TTL and lower stratosphere using data from weather balloons, satellites and reanalysis datasets. We found cooling trends in the TTL from 1980 to 2001, followed by warming from 2002 to 2023. These shifts are linked to changes in atmospheric circulation and impact water vapour transport into the stratosphere.
Lucie Bakels, Michael Blaschek, Marina Dütsch, Andreas Plach, Vincent Lechner, Georg Brack, Leopold Haimberger, and Andreas Stohl
Earth Syst. Sci. Data, 17, 4569–4585, https://doi.org/10.5194/essd-17-4569-2025, https://doi.org/10.5194/essd-17-4569-2025, 2025
Short summary
Short summary
Meteorological reanalyses are crucial datasets. Most reanalyses are Eulerian, providing data at specific, fixed points in space and time. When studying how air moves, it is more convenient to follow air masses through space and time, requiring a Lagrangian Reanalysis (LARA). We explain how the LARA dataset is organised and provide four examples of applications. These include studying the evolution of wind patterns, understanding weather systems, and measuring air mass travel time over land.
Susanna Winkelbauer, Michael Mayer, and Leopold Haimberger
Geosci. Model Dev., 17, 4603–4620, https://doi.org/10.5194/gmd-17-4603-2024, https://doi.org/10.5194/gmd-17-4603-2024, 2024
Short summary
Short summary
Oceanic transports shape the global climate, but the evaluation and validation of this key quantity based on reanalysis and model data are complicated by the distortion of the used modelling grids and the large number of different grid types. We present two new methods that allow the calculation of oceanic fluxes of volume, heat, salinity, and ice through almost arbitrary sections for various models and reanalyses that are independent of the used modelling grids.
Ulrich Voggenberger, Leopold Haimberger, Federico Ambrogi, and Paul Poli
Geosci. Model Dev., 17, 3783–3799, https://doi.org/10.5194/gmd-17-3783-2024, https://doi.org/10.5194/gmd-17-3783-2024, 2024
Short summary
Short summary
This paper presents a method for calculating balloon drift from historical radiosonde ascent data. The drift can reach distances of several hundred kilometres and is often neglected. Verification shows the beneficial impact of the more accurate balloon position on model assimilation. The method is not limited to radiosondes but would also work for dropsondes, ozonesondes, or any other in situ sonde carried by the wind in the pre-GNSS era, provided the necessary information is available.
Johannes Mayer, Leopold Haimberger, and Michael Mayer
Earth Syst. Dynam., 14, 1085–1105, https://doi.org/10.5194/esd-14-1085-2023, https://doi.org/10.5194/esd-14-1085-2023, 2023
Short summary
Short summary
This study investigates the temporal stability and reliability of winter-month trends of air–sea heat fluxes from ERA5 forecasts over the North Atlantic basin for the period 1950–2019. Driving forces of trends and the impact of modes of climate variability and analysis increments on air–sea heat fluxes are investigated. Finally, a new and independent estimate of the Atlantic Meridional Overturning Circulation weakening is provided and associated with a decrease in air–sea heat fluxes.
Michael Mayer, Takamasa Tsubouchi, Susanna Winkelbauer, Karin Margretha H. Larsen, Barbara Berx, Andreas Macrander, Doroteaciro Iovino, Steingrímur Jónsson, and Richard Renshaw
State Planet, 1-osr7, 14, https://doi.org/10.5194/sp-1-osr7-14-2023, https://doi.org/10.5194/sp-1-osr7-14-2023, 2023
Short summary
Short summary
This paper compares oceanic fluxes across the Greenland–Scotland Ridge (GSR) from ocean reanalyses to largely independent observational data. Reanalyses tend to underestimate the inflow of warm waters of subtropical Atlantic origin and hence oceanic heat transport across the GSR. Investigation of a strong negative heat transport anomaly around 2018 highlights the interplay of variability on different timescales and the need for long-term monitoring of the GSR to detect forced climate signals.
Jonathan Andrew Baker, Richard Renshaw, Laura Claire Jackson, Clotilde Dubois, Doroteaciro Iovino, Hao Zuo, Renellys C. Perez, Shenfu Dong, Marion Kersalé, Michael Mayer, Johannes Mayer, Sabrina Speich, and Tarron Lamont
State Planet, 1-osr7, 4, https://doi.org/10.5194/sp-1-osr7-4-2023, https://doi.org/10.5194/sp-1-osr7-4-2023, 2023
Short summary
Short summary
We use ocean reanalyses, in which ocean models are combined with observations, to infer past changes in ocean circulation and heat transport in the South Atlantic. Comparing these estimates with other observation-based estimates, we find differences in their trends, variability, and mean heat transport but closer agreement in their mean overturning strength. Ocean reanalyses can help us understand the cause of these differences, which could improve estimates of ocean transports in this region.
Magdalena Fritz, Michael Mayer, Leopold Haimberger, and Susanna Winkelbauer
Ocean Sci., 19, 1203–1223, https://doi.org/10.5194/os-19-1203-2023, https://doi.org/10.5194/os-19-1203-2023, 2023
Short summary
Short summary
The interaction between the Indonesian Throughflow (ITF) and regional climate phenomena indicates the high relevance for monitoring the ITF. Observations remain temporally and spatially limited; hence near-real-time monitoring is only possible with reanalyses. We assess how well ocean reanalyses depict the intensity of the ITF via comparison to observations. The results show that reanalyses agree reasonably well with in situ observations; however, some aspects require higher-resolution products.
Karina von Schuckmann, Audrey Minière, Flora Gues, Francisco José Cuesta-Valero, Gottfried Kirchengast, Susheel Adusumilli, Fiammetta Straneo, Michaël Ablain, Richard P. Allan, Paul M. Barker, Hugo Beltrami, Alejandro Blazquez, Tim Boyer, Lijing Cheng, John Church, Damien Desbruyeres, Han Dolman, Catia M. Domingues, Almudena García-García, Donata Giglio, John E. Gilson, Maximilian Gorfer, Leopold Haimberger, Maria Z. Hakuba, Stefan Hendricks, Shigeki Hosoda, Gregory C. Johnson, Rachel Killick, Brian King, Nicolas Kolodziejczyk, Anton Korosov, Gerhard Krinner, Mikael Kuusela, Felix W. Landerer, Moritz Langer, Thomas Lavergne, Isobel Lawrence, Yuehua Li, John Lyman, Florence Marti, Ben Marzeion, Michael Mayer, Andrew H. MacDougall, Trevor McDougall, Didier Paolo Monselesan, Jan Nitzbon, Inès Otosaka, Jian Peng, Sarah Purkey, Dean Roemmich, Kanako Sato, Katsunari Sato, Abhishek Savita, Axel Schweiger, Andrew Shepherd, Sonia I. Seneviratne, Leon Simons, Donald A. Slater, Thomas Slater, Andrea K. Steiner, Toshio Suga, Tanguy Szekely, Wim Thiery, Mary-Louise Timmermans, Inne Vanderkelen, Susan E. Wjiffels, Tonghua Wu, and Michael Zemp
Earth Syst. Sci. Data, 15, 1675–1709, https://doi.org/10.5194/essd-15-1675-2023, https://doi.org/10.5194/essd-15-1675-2023, 2023
Short summary
Short summary
Earth's climate is out of energy balance, and this study quantifies how much heat has consequently accumulated over the past decades (ocean: 89 %, land: 6 %, cryosphere: 4 %, atmosphere: 1 %). Since 1971, this accumulated heat reached record values at an increasing pace. The Earth heat inventory provides a comprehensive view on the status and expectation of global warming, and we call for an implementation of this global climate indicator into the Paris Agreement’s Global Stocktake.
Susanna Winkelbauer, Michael Mayer, Vanessa Seitner, Ervin Zsoter, Hao Zuo, and Leopold Haimberger
Hydrol. Earth Syst. Sci., 26, 279–304, https://doi.org/10.5194/hess-26-279-2022, https://doi.org/10.5194/hess-26-279-2022, 2022
Short summary
Short summary
We evaluate Arctic river discharge using in situ observations and state-of-the-art reanalyses, inter alia the most recent Global Flood Awareness System (GloFAS) river discharge reanalysis version 3.1. Furthermore, we combine reanalysis data, in situ observations, ocean reanalyses, and satellite data and use a Lagrangian optimization scheme to close the Arctic's volume budget on annual and seasonal scales, resulting in one reliable and up-to-date estimate of every volume budget term.
Noemi Imfeld, Leopold Haimberger, Alexander Sterin, Yuri Brugnara, and Stefan Brönnimann
Earth Syst. Sci. Data, 13, 2471–2485, https://doi.org/10.5194/essd-13-2471-2021, https://doi.org/10.5194/essd-13-2471-2021, 2021
Short summary
Short summary
Upper-air data form the backbone of reanalysis products, particularly in the pre-satellite era. However, historical upper-air data are error-prone because measurements at high altitude were especially challenging. Here, we present a collection of data from historical intercomparisons of radiosondes and error assessments reaching back to the 1930s that may allow us to better characterize such errors. The full database, including digitized data, images, and metadata, is made publicly available.
Cited articles
Bacon, S., Aksenov, Y., Fawcett, S., and Madec, G.: Arctic mass, freshwater and heat fluxes: methods and modelled seasonal variability, Phil. Trans. R. Soc. A, 373, https://doi.org/10.1098/rsta.2014.0169, 2015. a
Baker, J., Renshaw, R., Jackson, L., Dubois, C., Iovino, D., and Zuo, H.: Overturning variations in the subpolar North Atlantic in an ocean reanalyses ensemble, in: The Copernicus Marine Environment Monitoring Service Ocean State Report, vol. 15, S1–S142, https://doi.org/10.1080/1755876X.2022.2095169, 2022. a, b, c
Bryden, H. L., Johns, W. E., King, B. A., McCarthy, G., McDonagh, E. L., Moat, B. I., and Smeed, D. A.: Reduction in Ocean Heat Transport at 26°N since 2008 Cools the Eastern Subpolar Gyre of the North Atlantic Ocean, Journal of Climate, 33, 1677–1689, https://doi.org/10.1175/JCLI-D-19-0323.1, 2020. a
Buckley, M. W. and Marshall, J.: Observations, inferences, and mechanisms of the Atlantic Meridional Overturning Circulation: A review, Reviews of Geophysics, 54, 5–63, https://doi.org/10.1002/2015RG000493, 2016. a, b, c
Caesar, L., Rahmstorf, S., Robinson, A., Feulner, G., and Saba, V.: Observed fingerprint of a weakening Atlantic Ocean overturning circulation, Nature, 556, 191–196, https://doi.org/10.1038/s41586-018-0006-5, 2018. a
Calafat, F. M., Vallivattathillam, P., and Frajka-Williams, E.: Estimates of Atlantic meridional heat transport from spatiotemporal fusion of Argo, altimetry, and gravimetry data, Ocean Sci., 21, 2743–2762, https://doi.org/10.5194/os-21-2743-2025, 2025. a
Cheng, L., Pan, Y., Tan, Z., Zheng, H., Zhu, Y., Wei, W., Du, J., Yuan, H., Li, G., Ye, H., Gouretski, V., Li, Y., Trenberth, K. E., Abraham, J., Jin, Y., Reseghetti, F., Lin, X., Zhang, B., Chen, G., Mann, M. E., and Zhu, J.: IAPv4 ocean temperature and ocean heat content gridded dataset, Earth Syst. Sci. Data, 16, 3517–3546, https://doi.org/10.5194/essd-16-3517-2024, 2024a. a
Cheng, L., Tan, Z., Pan, Y., Zheng, H., Zhu, Y., Wei, W., Du, J., Li, G., Ye, H., and Gourteski, V.: IAP global ocean heat content 1° gridded analysis product (IAPv4), Marine Science Data Center of the Chinese Academy of Sciences [data set], https://doi.org/10.12157/IOCAS.20240117.001, 2024b. a
Collins, M., Sutherland, M., Bouwer, L., Cheong, S.-M., Frölicher, T., Jacot Des Combes, H., Koll Roxy, M., Losada, I., McInnes, K., Ratter, B., Rivera-Arriaga, E., Susanto, R. D., Swingedouw, D., and Tibig, L.: Extremes, Abrupt Changes and Managing Risks, in: IPCC Special Report on the Ocean and Cryosphere in a Changing Climate, edited by Pörtner, H.-O., Roberts, D. C., Masson-Delmotte, V., Zhai, P., Tignor, M., Poloczanska, E., Mintenbeck, K., Alegría, A., Nicolai, M., Okem, A., Petzold, J., Rama, B., and Weyer, N. M., Cambridge University Press, Cambridge, UK and New York, NY, USA, 589–655, https://doi.org/10.1017/9781009157964.008, 2019. a
Dee, D. P., Uppala, S. M., Simmons, A. J., Berrisford, P., Poli, P., Kobayashi, S., Andrae, U., Balmaseda, M. A., Balsamo, G., Bauer, P., Bechtold, P., Beljaars, A. C. M., van de Berg, L., Bidlot, J., Bormann, N., Delsol, C., Dragani, R., Fuentes, M., Geer, A. J., Haimberger, L., Healy, S. B., Hersbach, H., Hólm, E. V., Isaksen, L., Kållberg, P., Köhler, M., Matricardi, M., McNally, A. P., Monge-Sanz, B. M., Morcrette, J.-J., Park, B.-K., Peubey, C., de Rosnay, P., Tavolato, C., Thépaut, J.-N., and Vitart, F.: The ERA-Interim reanalysis: configuration and performance of the data assimilation system, Quarterly Journal of the Royal Meteorological Society, 137, 553–597, https://doi.org/10.1002/qj.828, 2011. a
Desportes, C., Garric, G., Régnier, C., Drévillon, M., Parent, L., Drillet, Y., Masina, S., Storto, A., Mirouze, I., Cipollone, A., Zuo, H., Balmaseda, M., Peterson, D., Wood, R., Jackson, L., Mulet, S., and Greiner, E.: Global Ocean Ensemble Physics Reanalysis, Marine Data Store (MDS) [data set], https://doi.org/10.48670/moi-00024, 2017. a, b
Dobricic, S. and Pinardi, N.: An oceanographic three-dimensional variational data assimilation scheme, Ocean Modelling, 22, 89–105, https://doi.org/10.1016/j.ocemod.2008.01.004, 2008. a
Duchez, A., Courtois, P., Harris, E., Josey, S. A., Kanzow, T., Marsh, R., Smeed, D. A., and Hirschi, J. J.-M.: Potential for seasonal prediction of Atlantic sea surface temperatures using the RAPID array at 26∘N, Climate Dynamics, 46, 3351–3370, https://doi.org/10.1007/s00382-015-2918-1, 2016. a
E.U. Copernicus Marine Service Information (CMEMS): Global Ocean Gridded L 4 Sea Surface Heights And Derived Variables Reprocessed 1993 Ongoing, Marine Data Store (MDS) [data set], https://doi.org/10.48670/moi-00148, 2024. a, b
Fasullo, J. T. and Trenberth, K. E.: The Annual Cycle of the Energy Budget. Part I: Global Mean and Land–Ocean Exchanges, Journal of Climate, 21, 2297–2312, https://doi.org/10.1175/2007JCLI1935.1, 2008. a
Fox-Kemper, B., Hewitt, H., Xiao, C., Aðalgeirsdóttir, G., Drijfhout, S., Edwards, T., Golledge, N., Hemer, M., Kopp, R., Krinner, G., Mix, A., Notz, D., Nowicki, S., Nurhati, I., Ruiz, L., Sallée, J.-B., Slangen, A., and Yu, Y.: Ocean, Cryosphere and Sea Level Change, Cambridge University Press, Cambridge, 1211–1362, https://doi.org/10.1017/9781009157896.011, 2023. a
Fritz, M., Mayer, M., Haimberger, L., and Winkelbauer, S.: Assessment of Indonesian Throughflow transports from ocean reanalyses with mooring-based observations, Ocean Sci., 19, 1203–1223, https://doi.org/10.5194/os-19-1203-2023, 2023. a, b
Fu, Y., Lozier, M. S., Biló, T. C., Bower, A. S., Cunningham, S. A., Cyr, F., de Jong, M. F., deYoung, B., Drysdale, L., Fraser, N., Fried, N., Furey, H. H., Han, G., Handmann, P., Holliday, N. P., Holte, J., Inall, M. E., Johns, W. E., Jones, S., Karstensen, J., Li, F., Pacini, A., Pickart, R. S., Rayner, D., Straneo, F., and Yashayaev, I.: Meridional Overturning Circulation Observed by the Overturning in the Subpolar North Atlantic Program (OSNAP) Array from August 2014 to June 2020, Georgia Institute of Technology [data set], https://doi.org/10.35090/gatech/70342, 2023. a, b
Gelaro, R., McCarty, W., Suárez, M. J., Todling, R., Molod, A., Takacs, L., Randles, C. A., Darmenov, A., Bosilovich, M. G., Reichle, R., Wargan, K., Coy, L., Cullather, R., Draper, C., Akella, S., Buchard, V., Conaty, A., da Silva, A. M., Gu, W., Kim, G.-K., Koster, R., Lucchesi, R., Merkova, D., Nielsen, J. E., Partyka, G., Pawson, S., Putman, W., Rienecker, M., Schubert, S. D., Sienkiewicz, M., and Zhao, B.: The Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2), Journal of Climate, 30, 5419–5454, https://doi.org/10.1175/JCLI-D-16-0758.1, 2017. a
GMAO: MERRA-2 tavgM_2d_flx_Nx: 2d,Monthly mean,Time-Averaged,Single-Level,Assimilation,Surface Flux Diagnostics V5.12.4, Greenbelt, MD, USA, Goddard Earth Sciences Data and Information Services Center (GES DISC) [data set], https://doi.org/10.5067/0JRLVL8YV2Y4, 2015. a
Good, S. A., Martin, M. J., and Rayner, N. A.: EN4: Quality controlled ocean temperature and salinity profiles and monthly objective analyses with uncertainty estimates, Journal of Geophysical Research: Oceans, 118, 6704–6716, https://doi.org/10.1002/2013JC009067, 2013. a
Haimberger, L., Tavolato, C., and Sperka, S.: Homogenization of the global radiosonde temperature dataset through combined comparison with reanalysis background series and neighboring stations, J. Climate, 25, 8108–8131, 2012. a
Hersbach, H., Bell, B., Berrisford, P., Hirahara, S., Horányi, A., Muñoz-Sabater, J., Nicolas, J., Peubey, C., Radu, R., Schepers, D., Simmons, A., Soci, C., Abdalla, S., Abellan, X., Balsamo, G., Bechtold, P., Biavati, G., Bidlot, J., Bonavita, M., De Chiara, G., Dahlgren, P., Dee, D., Diamantakis, M., Dragani, R., Flemming, J., Forbes, R., Fuentes, M., Geer, A., Haimberger, L., Healy, S., Hogan, R. J., Hólm, E., Janisková, M., Keeley, S., Laloyaux, P., Lopez, P., Lupu, C., Radnoti, G., de Rosnay, P., Rozum, I., Vamborg, F., Villaume, S., and Thépaut, J.-N.: The ERA5 global reanalysis, Quarterly Journal of the Royal Meteorological Society, 146, 1999–2049, https://doi.org/10.1002/qj.3803, 2020. a
Heuzé, C., Zanowski, H., Karam, S., and Muilwijk, M.: The Deep Arctic Ocean and Fram Strait in CMIP6 Models, Journal of Climate, 36, 2551–2584, https://doi.org/10.1175/JCLI-D-22-0194.1, 2023. a
Hollingsworth, A., Shaw, D. B., Lönnberg, P., Illari, L., and Simmons, A. J.: Monitoring of observation and analysis quality by a data assimilation system, Mon. Wea. Rev., 114, 861–879, 1986. a
Jackson, L. C., Kahana, R., Graham, T., Ringer, M. A., Woollings, T., Mecking, J. V., and Wood, R. A.: Global and European climate impacts of a slowdown of the AMOC in a high resolution GCM, Climate Dynamics, 45, 3299–3316, https://doi.org/10.1007/s00382-015-2540-2, 2015. a
Jackson, L. C., Peterson, K. A., Roberts, C. D., and Wood, R. A.: Recent slowing of Atlantic overturning circulation as a recovery from earlier strengthening, Nature Geoscience, 9, 518–522, https://doi.org/10.1038/ngeo2715, 2016. a
Jackson, L. C., Dubois, C., Forget, G., Haines, K., Harrison, M., Iovino, D., Köhl, A., Mignac, D., Masina, S., Peterson, K. A., Piecuch, C. G., Roberts, C. D., Robson, J., Storto, A., Toyoda, T., Valdivieso, M., Wilson, C., Wang, Y., and Zuo, H.: The Mean State and Variability of the North Atlantic Circulation: A Perspective From Ocean Reanalyses, Journal of Geophysical Research: Oceans, 124, 9141–9170, https://doi.org/10.1029/2019JC015210, 2019. a
Japan Meteorological Agency: JRA-55: Japanese 55-year Reanalysis, Monthly Means and Variances, NSF National Center for Atmospheric Research [data set], https://doi.org/10.5065/D60G3H5B, 2013. a
Jayne, S. R., Roemmich, D., Zilberman, N., Riser, S. C., Johnson, K. S., Johnson, G. C., and Piotrowicz, S. R.: The Argo Program: Present and Future, Oceanography, 30, 18–28, https://doi.org/10.5670/oceanog.2017.213, 2017. a
Kobayashi, S., Ota, Y., Harada, Y., Ebita, A., Moriya, M., Onoda, H., Onogi, K., Kamahori, H., Kobayashi, C., Endo, H., Miyaoka, K., and Takahashi, K.: The JRA-55 Reanalysis: General Specifications and Basic Characteristics, Journal of the Meteorological Society of Japan. Ser. II, 93, 5–48, https://doi.org/10.2151/jmsj.2015-001, 2015. a
Kosaka, Y., Kobayashi, S., Harada, Y., Kobayashi, C., Naoe, H., Yoshimoto, K., Harada, M., Goto, N., Chiba, J., Miyaoka, K., Sekiguchi, R., Deushi, M., Kamahori, H., Nakaegawa, T., Tanaka, T. Y., Tokuhiro, T., Sato, Y., Matsushita, Y., and Onogi, K.: The JRA-3Q Reanalysis, Journal of the Meteorological Society of Japan. Ser. II, 102, 49–109, https://doi.org/10.2151/jmsj.2024-004, 2024. a
Lellouche, J.-M., Greiner, E., Le Galloudec, O., Garric, G., Regnier, C., Drevillon, M., Benkiran, M., Testut, C.-E., Bourdalle-Badie, R., Gasparin, F., Hernandez, O., Levier, B., Drillet, Y., Remy, E., and Le Traon, P.-Y.: Recent updates to the Copernicus Marine Service global ocean monitoring and forecasting real-time 1∕12° high-resolution system, Ocean Sci., 14, 1093–1126, https://doi.org/10.5194/os-14-1093-2018, 2018 a, b
Li, F., Lozier, M. S., and Johns, W. E.: Calculating the Meridional Volume, Heat, and Freshwater Transports from an Observing System in the Subpolar North Atlantic: Observing System Simulation Experiment, Journal of Atmospheric and Oceanic Technology, 34, 1483–1500, https://doi.org/10.1175/JTECH-D-16-0247.1, 2017. a, b, c, d
Li, F., Lozier, M. S., Holliday, N. P., Johns, W. E., Le Bras, I. A., Moat, B. I., Cunningham, S. A., and de Jong, M. F.: Observation-based estimates of heat and freshwater exchanges from the subtropical North Atlantic to the Arctic, Progress in Oceanography, 197, 102640, https://doi.org/10.1016/j.pocean.2021.102640, 2021. a
Lozier, M. S., Bacon, S., Bower, A. S., Cunningham, S. A., de Jong, M. F., de Steur, L., deYoung, B., Fischer, J., Gary, S. F., Greenan, B. J. W., Heimbach, P., Holliday, N. P., Houpert, L., Inall, M. E., Johns, W. E., Johnson, H. L., Karstensen, J., Li, F., Lin, X., Mackay, N., Marshall, D. P., Mercier, H., Myers, P. G., Pickart, R. S., Pillar, H. R., Straneo, F., Thierry, V., Weller, R. A., Williams, R. G., Wilson, C., Yang, J., Zhao, J., and Zika, J. D.: Overturning in the Subpolar North Atlantic Program: A New International Ocean Observing System, Bulletin of the American Meteorological Society, 98, 737–752, https://doi.org/10.1175/BAMS-D-16-0057.1, 2017. a, b, c, d, e
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, B. J. W., Holliday, N. P., Houk, A., Houpert, L., Inall, M. E., Johns, W. E., Johnson, H. L., Johnson, C., Karstensen, J., Koman, G., Bras, I. A. L., 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. a
Lyman, J. M. and Johnson, G. C.: Global High-Resolution Random Forest Regression Maps of Ocean Heat Content Anomalies Using In Situ and Satellite Data, Journal of Atmospheric and Oceanic Technology, 40, 575–586, https://doi.org/10.1175/JTECH-D-22-0058.1, 2023. a
Lyman, J. M. and Johnson, G. C.: RFROM: Random Forest Regression Ocean Maps (v2.2), NOAA Pacific Marine Environmental Laboratory [data set], https://data.pmel.noaa.gov/pmel/erddap/files/argo_rfromv22/, last access: 10 June 2025. a
MacLachlan, C., Arribas, A., Peterson, K. A., Maidens, A., Fereday, D., Scaife, A. A., Gordon, M., Vellinga, M., Williams, A., Comer, R. E., Camp, J., Xavier, P., and Madec, G.: Global Seasonal forecast system version 5 (GloSea5): a high-resolution seasonal forecast system, Quarterly Journal of the Royal Meteorological Society, 141, 1072–1084, https://doi.org/10.1002/qj.2396, 2015. a, b
Mahajan, S., Zhang, R., and Delworth, T. L.: Impact of the Atlantic Meridional Overturning Circulation (AMOC) on Arctic Surface Air Temperature and Sea Ice Variability, Journal of Climate, 24, 6573–6581, https://doi.org/10.1175/2011JCLI4002.1, 2011. a
Mayer, J., Mayer, M., and Haimberger, L.: Mass-consistent atmospheric energy and moisture budget monthly data from 1979 to present derived from ERA5 reanalysis, Copernicus Climate Change Service (C3S) Climate Data Store (CDS) [data set], https://doi.org/10.24381/cds.c2451f6b, 2021a. a, b
Mayer, J., Mayer, M., and Haimberger, L.: Consistency and Homogeneity of Atmospheric Energy, Moisture, and Mass Budgets in ERA5, Journal of Climate, 34, 3955–3974, https://doi.org/10.1175/JCLI-D-20-0676.1, 2021b. a
Mayer, J., Haimberger, L., and Mayer, M.: A quantitative assessment of air–sea heat flux trends from ERA5 since 1950 in the North Atlantic basin, Earth Syst. Dynam., 14, 1085–1105, https://doi.org/10.5194/esd-14-1085-2023, 2023a. a, b, c, d
Mayer, M., Vidar, S. L., Kjell, A. M., von Schuckmann, K., Monier, M., and Greiner, E.: Ocean heat content in the HighNorth, Journal of Operational Oceanography, 14, S17–S23, https://doi.org/10.1080/1755876X.2021.1946240, 2021c. a, b
Mayer, M., Tsubouchi, T., von Schuckmann, K., Seitner, V., Winkelbauer, S., and Haimberger, L.: Atmospheric and oceanic contributions to observed Nordic Seas and Arctic Ocean Heat Content variations 1993–2020, Journal of Operational Oceanography, 15, S20–S28, https://doi.org/10.1080/1755876X.2022.2095169, 2022. a
Mayer, M., Tsubouchi, T., Winkelbauer, S., Larsen, K. M. H., Berx, B., Macrander, A., Iovino, D., Jónsson, S., and Renshaw, R.: Recent variations in oceanic transports across the Greenland–Scotland Ridge, in: 7th edition of the Copernicus Ocean State Report (OSR7), edited by: von Schuckmann, K., Moreira, L., Le Traon, P.-Y., Grégoire, M., Marcos, M., Staneva, J., Brasseur, P., Garric, G., Lionello, P., Karstensen, J., and Neukermans, G., Copernicus Publications, State Planet, 1-osr7, 14, https://doi.org/10.5194/sp-1-osr7-14-2023, 2023b. a
Mayer, M., Kato, S., Bosilovich, M., Bechtold, P., Mayer, J., Schröder, M., Behrangi, A., Wild, M., Kobayashi, S., Li, Z., and L'Ecuyer, T.: Assessment of Atmospheric and Surface Energy Budgets Using Observation-Based Data Products, Surveys in Geophysics, 45, 1827–1854, https://doi.org/10.1007/s10712-024-09827-x, 2024. a
McCarthy, G. D. and Caesar, L.: Can we trust projections of AMOC weakening based on climate models that cannot reproduce the past?, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 381, 20220193, https://doi.org/10.1098/rsta.2022.0193, 2023. a
Menary, M. B., Jackson, L. C., and Lozier, M. S.: Reconciling the Relationship Between the AMOC and Labrador Sea in OSNAP Observations and Climate Models, Geophysical Research Letters, 47, e2020GL089793, https://doi.org/10.1029/2020GL089793, 2020. a
Meyssignac, B., Fourest, S., Mayer, M., Johnson, G. C., Calafat, F. M., Ablain, M., Boyer, T., Cheng, L., Desbruyères, D., Forget, G., Giglio, D., Kuusela, M., Locarnini, R., Lyman, J. M., Llovel, W., Mishonov, A., Reagan, J., Rousseau, V., and Benveniste, J.: North Atlantic Heat Transport Convergence Derived from a Regional Energy Budget Using Different Ocean Heat Content Estimates, Surveys in Geophysics, 45, 1855–1874, https://doi.org/10.1007/s10712-024-09865-5, 2024. a
Moffa-Sánchez, P., Moreno-Chamarro, E., Reynolds, D. J., Ortega, P., Cunningham, L., Swingedouw, D., Amrhein, D. E., Halfar, J., Jonkers, L., Jungclaus, J. H., Perner, K., Wanamaker, A., and Yeager, S.: Variability in the Northern North Atlantic and Arctic Oceans Across the Last Two Millennia: A Review, Paleoceanography and Paleoclimatology, 34, 1399–1436, https://doi.org/10.1029/2018PA003508, 2019. a
Mogensen, K. and Balmaseda, W.: The NEMOVAR ocean data assimilation system as implemented in the ECMWF ocean analysis for System 4, https://doi.org/10.21957/x5y9yrtm, 2012. a
Muilwijk, M., Smedsrud, L. H., Ilicak, M., and Drange, H.: Atlantic Water Heat Transport Variability in the 20th Century Arctic Ocean From a Global Ocean Model and Observations, Journal of Geophysical Research: Oceans, 123, 8159–8179, https://doi.org/10.1029/2018JC014327, 2018. a
NASA/LARC/SD/ASDC: CERES Energy Balanced and Filled (EBAF) TOA and Surface Monthly means data in netCDF Edition 4.2.1, NASA Langley Atmospheric Science Data Center DAAC [data set], https://doi.org/10.5067/TERRA-AQUA-NOAA20/CERES/EBAF_L3B004.2.1, 2025. a, b
Palmer, M. D., Roberts, C. D., Balmaseda, M., Chang, Y.-S., Chepurin, G., Ferry, N., Fujii, Y., Good, S. A., Guinehut, S., Haines, K., Hernandez, F., Köhl, A., Lee, T., Martin, M. J., Masina, S., Masuda, S., Peterson, K. A., Storto, A., Toyoda, T., Valdivieso, M., Vernieres, G., Wang, O., and Xue, Y.: Ocean heat content variability and change in an ensemble of ocean reanalyses, Climate Dynamics, 49, 909–930, https://doi.org/10.1007/s00382-015-2801-0, 2017. a
Petit, T., Smeed, D., Blaker, A., Elipot, S., Johns, W., Kajtar, J. B., Rayner, D., Sinha, B., Smith, R. H., Volkov, D. L., and Moat, B.: Evaluation of a Reduced RAPID Array for Measuring the AMOC, Journal of Geophysical Research: Oceans, 130, e2025JC023093, https://doi.org/10.1029/2025JC023093,2025. a
Rahmstorf, S., Box, J. E., Feulner, G., Mann, M. E., Robinson, A., Rutherford, S., and Schaffernicht, E. J.: Exceptional twentieth-century slowdown in Atlantic Ocean overturning circulation, Nature Climate Change, 5, 475–480, https://doi.org/10.1038/nclimate2554, 2015. a
Rayner, D., Hirschi, J. J.-M., Kanzow, T., Johns, W. E., Wright, P. G., Frajka-Williams, E., Bryden, H. L., Meinen, C. S., Baringer, M. O., Marotzke, J., Beal, L. M., and Cunningham, S. A.: Monitoring the Atlantic meridional overturning circulation, Deep Sea Research Part II: Topical Studies in Oceanography, 58, 1744–1753, https://doi.org/10.1016/j.dsr2.2010.10.056, 2011. a
Schauer, U. and Beszczynska-Möller, A.: Problems with estimation and interpretation of oceanic heat transport – conceptual remarks for the case of Fram Strait in the Arctic Ocean, Ocean Sci., 5, 487–494, https://doi.org/10.5194/os-5-487-2009, 2009. a
Scott, R. C., Rose, F. G., Stackhouse, P. W., Loeb, N. G., Kato, S., Doelling, D. R., Rutan, D. A., Taylor, P. C., and Smith, W. L.: Clouds and the Earth’s Radiant Energy System (CERES) Cloud Radiative Swath (CRS) Edition 4 Data Product, Journal of Atmospheric and Oceanic Technology, 39, 1781–1797, https://doi.org/10.1175/JTECH-D-22-0021.1, 2022. a
Serreze, M. C., Holland, M. M., and Stroeve, J.: Perspectives on the Arctic's Shrinking Sea-Ice Cover, Science, 315, 1533–1536, https://doi.org/10.1126/science.1139426, 2007. a
Shu, Q., Wang, Q., Årthun, M., Wang, S., Song, Z., Zhang, M., and Qiao, F.: Arctic Ocean Amplification in a warming climate in CMIP6 models, Science Advances, 8, eabn9755, https://doi.org/10.1126/sciadv.abn9755, 2022. a
Srokosz, M., Baringer, M., Bryden, H., Cunningham, S., Delworth, T., Lozier, S., Marotzke, J., and Sutton, R.: Past, Present, and Future Changes in the Atlantic Meridional Overturning Circulation, Bulletin of the American Meteorological Society, 93, 1663–1676, https://doi.org/10.1175/BAMS-D-11-00151.1, 2012. a
Storto, A. and Masina, S.: C-GLORSv5: an improved multipurpose global ocean eddy-permitting physical reanalysis, Earth Syst. Sci. Data, 8, 679–696, https://doi.org/10.5194/essd-8-679-2016, 2016. a, b
Storto, A., Masina, S., Simoncelli, S., Iovino, D., Cipollone, A., Drevillon, M., Drillet, Y., Schuckmann, K., Parent, L., Garric, G., Greiner, E., Desportes, C., Zuo, H., Balmaseda, M., and Peterson, K.: The added value of the multi-system spread information for ocean heat content and steric sea level investigations in the CMEMS GREP ensemble reanalysis product, Climate Dynamics, 53, https://doi.org/10.1007/s00382-018-4585-5, 2019. a
Thornalley, D. J. R., Oppo, D. W., Ortega, P., Robson, J. I., Brierley, C. M., Davis, R., Hall, I. R., Moffa-Sanchez, P., Rose, N. L., Spooner, P. T., Yashayaev, I., and Keigwin, L. D.: Anomalously weak Labrador Sea convection and Atlantic overturning during the past 150 years, Nature, 556, 227–230, https://doi.org/10.1038/s41586-018-0007-4, 2018. a
Trenberth, K. E., Zhang, Y., Fasullo, J. T., and Cheng, L.: Observation-Based Estimates of Global and Basin Ocean Meridional Heat Transport Time Series, Journal of Climate, 32, 4567–4583, https://doi.org/10.1175/JCLI-D-18-0872.1, 2019. a, b
Tsubouchi, T., Bacon, S., Naveira Garabato, A. C., Aksenov, Y., Laxon, S. W., Fahrbach, E., Beszczynska-Möller, A., Hansen, E., Lee, C. M., and Ingvaldsen, R. B.: The Arctic Ocean in summer: A quasi-synoptic inverse estimate of boundary fluxes and water mass transformation, Journal of Geophysical Research: Oceans, 117, https://doi.org/10.1029/2011JC007174, 2012. a
Tsubouchi, T., von Appen, W.-J., Schauer, U., Kanzow, T., Lee, C., Curry, B., de Steur, L., Ingvaldsen, R., and Woodgate, R. A.: The Arctic Ocean volume, heat and fresh water transports time series from October 2004 to May 2010, PANGAEA [data set], https://doi.org/10.1594/PANGAEA.909966, 2019. a
Tsubouchi, T., Våge, K., Hansen, B., Larsen, K. M. H., Østerhus, S., Johnson, C., Jónsson, S., and Valdimarsson, H.: Increased ocean heat transport into the Nordic Seas and Arctic Ocean over the period 1993–2016, Nature Climate Change, 11, 21–26, https://doi.org/10.1038/s41558-020-00941-3, 2021. a
Tsubouchi, T., von Appen, W.-J., Kanzow, T., and de Steur, L.: Temporal Variability of the Overturning Circulation in the Arctic Ocean and the Associated Heat and Freshwater Transports during 2004–10, Journal of Physical Oceanography, 54, 81–94, https://doi.org/10.1175/JPO-D-23-0056.1, 2024. a
UNESCO Ocean Decade: Marine Environment Reanalyses Evaluation Project (MER-EP), https://oceandecade.org/actions/marine-environment-reanalyses-evaluation-project/ (last access: 21 August 2025), 2025. a
von Schuckmann, K., Cheng, L., Palmer, M. D., Hansen, J., Tassone, C., Aich, V., Adusumilli, S., Beltrami, H., Boyer, T., Cuesta-Valero, F. J., Desbruyères, D., Domingues, C., García-García, A., Gentine, P., Gilson, J., Gorfer, M., Haimberger, L., Ishii, M., Johnson, G. C., Killick, R., King, B. A., Kirchengast, G., Kolodziejczyk, N., Lyman, J., Marzeion, B., Mayer, M., Monier, M., Monselesan, D. P., Purkey, S., Roemmich, D., Schweiger, A., Seneviratne, S. I., Shepherd, A., Slater, D. A., Steiner, A. K., Straneo, F., Timmermans, M.-L., and Wijffels, S. E.: Heat stored in the Earth system: where does the energy go?, Earth Syst. Sci. Data, 12, 2013–2041, https://doi.org/10.5194/essd-12-2013-2020, 2020. a
Winkelbauer, S.: susannawinkelbauer/StraitFlux: StraitFlux v1.1.0 (v1.1.0), Zenodo [code], https://doi.org/10.5281/zenodo.14620858, 2025. a
Winkelbauer, S., Mayer, M., and Haimberger, L.: StraitFlux – precise computations of water strait fluxes on various modeling grids, Geosci. Model Dev., 17, 4603–4620, https://doi.org/10.5194/gmd-17-4603-2024, 2024. a, b, c, d
Yeager, S. and Danabasoglu, G.: The Origins of Late-Twentieth-Century Variations in the Large-Scale North Atlantic Circulation, Journal of Climate, 27, 3222–3247, https://doi.org/10.1175/JCLI-D-13-00125.1, 2014. a
Zhang, J. and Rothrock, D. A.: Modeling Global Sea Ice with a Thickness and Enthalpy Distribution Model in Generalized Curvilinear Coordinates, Monthly Weather Review, 131, 845–861, https://doi.org/10.1175/1520-0493(2003)131<0845:MGSIWA>2.0.CO;2, 2003. a
Zou, S., Lozier, M. S., Li, F., Abernathey, R., and Jackson, L.: Density-compensated overturning in the Labrador Sea, Nature Geoscience, 13, 121–126, https://doi.org/10.1038/s41561-019-0517-1, 2020. a
Zuo, H., Balmaseda, M. A., Tietsche, S., Mogensen, K., and Mayer, M.: The ECMWF operational ensemble reanalysis–analysis system for ocean and sea ice: a description of the system and assessment, Ocean Sci., 15, 779–808, https://doi.org/10.5194/os-15-779-2019, 2019. a, b
Short summary
Ocean reanalyses combine models and observations to reconstruct past ocean conditions. We evaluate their performance against measurements from the OSNAP (Overturning in the Subpolar North Atlantic Program) section. While reanalyses capture long-term averages and broad circulation patterns, they miss some more regional features and variability. This highlights both their value and their limitations, stressing the need for improved observations and higher-resolution models.
Ocean reanalyses combine models and observations to reconstruct past ocean conditions. We...
