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Weakening of the Atlantic Meridional Overturning Circulation abyssal limb in the North Atlantic


The abyssal limb of the global Meridional Overturning Circulation redistributes heat and carbon as it carries Antarctic Bottom Water from the Southern Ocean towards the Northern Hemisphere. Using mooring observations and hydrographic data from multiple sources in the North Atlantic, we show that northward-flowing Antarctic Bottom Water is constrained below 4,500 m with a mean volume transport of 2.40 ± 0.25 Sv at 16° N. We find that during 2000–2020, the Antarctic Bottom Water northward transport weakened by approximately 0.35 ± 0.13 Sv, corresponding to a 12 ± 5% decrease. The weakening of the Atlantic Meridional Overturning Circulation abyssal cell is a probable response to reduced Antarctic Bottom Water formation rates over the past several decades and is associated with abyssal warming observed throughout the western Atlantic Ocean. We estimate that the warming of the Antarctic Bottom Water layer in the subtropical North Atlantic is, on average, 1 m°C per year in the last two decades due to the downward heaving of abyssal isopycnals, contributing to the increase of abyssal heat content and, hence, sea-level rise in the region (1 m°C = 0.001 °C). This warming trend is approximately half of the Antarctic Bottom Water warming trend observed in the South Atlantic and parts of the Southern Ocean, indicating a dilution of the signal as the Antarctic Bottom Water crosses the Equator.

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Fig. 1: AABW distribution and its primary pathways in the North Atlantic.
Fig. 2: MOVE data analysis showing the AABW flow weakening in the twenty-first century at 16° N.
Fig. 3: MOVE data analysis showing that warming due to isopycnal heaving near the MAR decreased the abyssal geostrophic shear at 16° N.
Fig. 4: Analysis of the hydrographic observations showing the AABW distribution and its warming signal at 24.5° N–26.5° N.

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Data availability

All data used in this study are freely available and can be accessed as follows: MOVE (link for the OceanSITES Global Data Assembly Center Public FTP Server can be found at (ref. 72)); GAGE ( (ref. 73)); WOCE and GOSHIP A05 line ( (ref. 74)); RAPID ( (ref. 75)); Deep Argo ( (ref. 76)); WBTS (link for the AOML-NOAA’s public FTP server can be found at (ref. 77)); WOA18 ( (ref. 78)); GEBCO ( (ref. 55).

Code availability

All the codes used in this study are freely available in public repositories. As mentioned in Methods, all relevant seawater parameters, properties and dynamic height were computed using the Python Gibbs Seawater Oceanographic 3.4.2 software available at The γn routine can be found at The Python pyMannKendall software for the MK trends statistical tests is available at Finally, all data handling, mathematical operations, data interpolation and data filtering procedures were performed using standard functions found in the Xarray 0.20.1 (, Numpy 1.21.5 ( and Scipy 1.7.3 ( Python 3 packages.


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We thank the many scientists, engineers and mariners from many institutions worldwide who supported several projects that developed instruments and collected, processed and published the data we used in this work. That includes all CTD, Deep Argo and moored profiles. Without their collaboration and hard work, studies like this would not happen. We offer special thanks to M. Lankhorst and the MOVE team for providing the MOVE dataset, to the WBTS team (R. Smith, D. Volkov, R. Garcia, J. Hooper) for providing the WBTS mooring and CTD dataset, to C. Meinen, M. Harrison, D. Volkov, M. Le Henaff and L. Chomiak for the useful discussions. We also thank S.-K. Lee for reading the manuscript and providing useful comments. T.C.B., R.C.P. and S.D. gratefully acknowledge the funding from the National Oceanic and Atmospheric Administration (NOAA)’s Global Ocean Monitoring and Observing programme (FundRef number 100007298); NOAA’s Climate Program Office, Climate Observations and Monitoring and Climate Variability and Predictability programmes under NOFO NOAA-OAR-CPO-2021-2006389 with additional NOAA Atlantic Oceanographic and Meteorological Laboratory support. Support for W.J.’s participation in the research was provided by the US National Science Foundation under grants OCE-1332978 and OCE-1926008. T.K. is funded by the EU’s Horizon 2020 Research and Innovation Program under the grant agreement number 821001 (SO-CHIC) and therein is a contribution to its Work Packages 3 and 6. This study is further a contribution to the project T3 of the Collaborative Research Centre TRR 181 ‘Energy Transfers in Atmosphere and Ocean’ funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation; project number 274762653). This research was carried out in part under the auspices of the Cooperative Institute for Marine and Atmospheric Studies, a cooperative institute of the University of Miami and the National Oceanic and Atmospheric Administration (NOAA), cooperative agreement NA 20OAR4320472.

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T.C.B. led this study from the idea conception to the data analysis, results interpretation and paper writing. R.C.P. and S.D. contributed to the idea conception, results interpretation, discussion and paper preparation. W.J. and T.K. contributed to the data analysis, results interpretation and discussion and paper preparation.

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Correspondence to Tiago Carrilho Biló.

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Extended data

Extended Data Fig. 1 MOVE data analysis showing that most of the vertical geostrophic shear variability below 4500 m at 16 N, ranging from interannual to decadal time scales, is driven primarily by density changes within the DWBC domain.

Curves represent the detrended eighteen-month low-passed filtered abyssal geostrophic shear time anomalies series averaged between 4500-5000 m discussed in Fig. 3.

Extended Data Fig. 2 MOVE potential temperature analysis showing the period after 2017 is characterized by colder temperatures than the previous years at 16 N (see blue arrows).

Curves represent the detrended eighteen-month low-passed filtered potential temperature time anomalies series averaged between 4500-5000 m.

Supplementary information

Supplementary Information

Supplementary Figs. 1–5, Discussion and Tables 1–5.

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Biló, T.C., Perez, R.C., Dong, S. et al. Weakening of the Atlantic Meridional Overturning Circulation abyssal limb in the North Atlantic. Nat. Geosci. 17, 419–425 (2024).

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