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Freshwater forcing of the Atlantic Meridional Overturning Circulation revisited

Nature Climate Change volume 12, pages 449–454 (2022)Cite this article

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Abstract

Freshwater (FW) forcing is widely identified as the dominant mechanism causing reductions of the Atlantic Meridional Overturning Circulation (AMOC), a climate tipping point that led to past abrupt millennial-scale climate changes. However, the AMOC response to FW forcing has not been rigorously assessed due to the lack of long-term AMOC observations and uncertainties of sea-level rise and ice-sheet melt needed to infer past FW forcing. Here we show a muted AMOC response to FW forcing (~50 m sea-level rise from the final deglaciation of Northern Hemisphere ice sheets) in the early-to-middle Holocene ~11,700–6,000 years ago. Including this muted AMOC response in a transient simulation of the Holocene with an ocean–atmosphere climate model improves the agreement between simulated and proxy temperatures of the past 21,000 years. This demonstrates that the AMOC may not be as sensitive to FW fluxes and Arctic freshening as is currently projected for the end of the twenty-first century.

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Fig. 1: Holocene meltwater–AMOC paradox.
Fig. 2: Comparison of data and models for regional temperature stacks of the past 21,000 years.
Fig. 3: Differences in modelled surface temperature and precipitation during the early Holocene (9 –6 ka) between simulations with and without FW forcing in the Holocene.

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Data availability

The model datasets used for this study (Figs. 2 and 3) are available from the Open Science Framework (https://doi.org/10.17605/OSF.IO/NUQ2K). The TraCE-21K-I model data are available from the Earth System Grid (https://www.earthsystemgrid.org/project/trace.html), and the TraCE-21K-II model data are available from the Transient Climate Simulation Lab (https://trace-21k.nelson.wisc.edu).

Code availability

CCSM3 is freely available as open-source code from http://www.cesm.ucar.edu/models/ccsm3.0/

References

  1. Broecker, W. S., Peteet, D. M. & Rind, D. Does the ocean–atmosphere system have more than one stable mode of operation? Nature 315, 21–26 (1985).

    Article  CAS  Google Scholar 

  2. Rahmstorf, S. Bifurcations of the Atlantic thermohaline circulation in response to changes in the hydrological cycle. Nature 378, 145–149 (1995).

    Article  CAS  Google Scholar 

  3. Clark, P. U. et al. Freshwater forcing of abrupt climate change during the last glaciation. Science 293, 283–287 (2001).

    Article  CAS  Google Scholar 

  4. Shakun, J. D. et al. Global warming preceded by increasing carbon dioxide concentrations during the last deglaciation. Nature 484, 49–54 (2012).

    Article  CAS  Google Scholar 

  5. He, F. et al. Northern Hemisphere forcing of Southern Hemisphere climate during the last deglaciation. Nature 494, 81–85 (2013).

    Article  CAS  Google Scholar 

  6. Lenton, T. M. et al. Climate tipping points—too risky to bet against. Nature 575, 592–595 (2019).

    Article  CAS  Google Scholar 

  7. Jackson, L. C. et al. Global and European climate impacts of a slowdown of the AMOC in a high resolution GCM. Clim. Dyn. 45, 3299–3316 (2015).

    Article  Google Scholar 

  8. Yin, J., Schlesinger, M. E. & Stouffer, R. J. Model projections of rapid sea-level rise on the northeast coast of the United States. Nat. Geosci. 2, 262–266 (2009).

    Article  CAS  Google Scholar 

  9. Ritchie, P. D. L. et al. Shifts in national land use and food production in Great Britain after a climate tipping point. Nat. Food 1, 76–83 (2020).

    Article  Google Scholar 

  10. Caesar, L., Rahmstorf, S., Robinson, A., Feulner, G. & Saba, V. Observed fingerprint of a weakening Atlantic Ocean overturning circulation. Nature 556, 191–196 (2018).

    Article  CAS  Google Scholar 

  11. Fu, Y., Li, F. L., Karstensen, J. & Wang, C. Z. A stable Atlantic Meridional Overturning Circulation in a changing North Atlantic Ocean since the 1990s. Sci. Adv. 6, eabc7836 (2020).

    Article  Google Scholar 

  12. Moat, B. et al. Pending recovery in the strength of the meridional overturning circulation at 26 degrees N. Ocean Sci. 16, 863–874 (2020).

    Article  Google Scholar 

  13. Bakker, P. et al. Fate of the Atlantic Meridional Overturning Circulation: strong decline under continued warming and Greenland melting. Geophys. Res. Lett. 43, 12252–12260 (2016).

    Article  Google Scholar 

  14. Weijer, W., Cheng, W., Garuba, O. A., Hu, A. & Nadiga, B. T. CMIP6 models predict significant 21st century decline of the Atlantic Meridional Overturning Circulation. Geophys. Res. Lett. 47, e2019GL086075 (2020).

    Article  Google Scholar 

  15. Gregory, J. M. et al. A model intercomparison of changes in the Atlantic thermohaline circulation in response to increasing atmospheric CO2 concentration. Geophys. Res. Lett. 32, L12703 (2005).

    Article  CAS  Google Scholar 

  16. Jahn, A. & Holland, M. M. Implications of Arctic sea ice changes for North Atlantic deep convection and the meridional overturning circulation in CCSM4–CMIP5 simulations. Geophys. Res. Lett. 40, 1206–1211 (2013).

    Article  Google Scholar 

  17. Golledge, N. R. et al. Global environmental consequences of twenty-first-century ice-sheet melt. Nature 566, 65–72 (2019).

    Article  CAS  Google Scholar 

  18. Stouffer, R. J. et al. Investigating the causes of the response of the thermohaline circulation to past and future climate changes. J. Clim. 19, 1365–1387 (2006).

    Article  Google Scholar 

  19. Weijer, W. et al. Stability of the Atlantic Meridional Overturning Circulation: a review and synthesis. J. Geophys. Res. Oceans 124, 5336–5375 (2019).

    Article  Google Scholar 

  20. Rahmstorf, S. On the freshwater forcing and transport of the Atlantic thermohaline circulation. Clim. Dyn. 12, 799–811 (1996).

    Article  Google Scholar 

  21. Liu, W., Xie, S. P., Liu, Z. & Zhu, J. Overlooked possibility of a collapsed Atlantic Meridional Overturning Circulation in warming climate. Sci. Adv. 3, e1601666 (2017).

    Article  CAS  Google Scholar 

  22. Gnanadesikan, A., Kelson, R. & Sten, M. Flux correction and overturning stability: insights from a dynamical box model. J. Clim. 31, 9335–9350 (2018).

    Article  Google Scholar 

  23. Wunsch, C. Towards understanding the Paleocean. Quat. Sci. Rev. 29, 1960–1967 (2010).

    Article  Google Scholar 

  24. Condron, A. & Winsor, P. Meltwater routing and the Younger Dryas. Proc. Natl Acad. Sci. USA 109, 19928–19933 (2012).

    Article  CAS  Google Scholar 

  25. Kim, H.-J., An, S.-I., Kim, S.-K. & Park, J.-H. Feedback processes modulating the sensitivity of Atlantic thermohaline circulation to freshwater forcing timescales. J. Clim. 34, 5081–5092 (2021).

    Google Scholar 

  26. Jackson, L. C. & Wood, R. A. Hysteresis and resilience of the AMOC in an eddy-permitting GCM. Geophys. Res. Lett. 45, 8547–8556 (2018).

    Article  Google Scholar 

  27. Lozier, M. S. et al. A sea change in our view of overturning in the subpolar North Atlantic. Science 363, 516–521 (2019).

    Article  CAS  Google Scholar 

  28. Swingedouw, D. et al. Decadal fingerprints of freshwater discharge around Greenland in a multi-model ensemble. Clim. Dyn. 41, 695–720 (2012).

    Article  Google Scholar 

  29. Jackson, L. C. et al. Impact of ocean resolution and mean state on the rate of AMOC weakening. Clim. Dyn. 55, 1711–1732 (2020).

    Article  Google Scholar 

  30. Ullman, D. J. et al. Final Laurentide ice-sheet deglaciation and Holocene climate-sea level change. Quat. Sci. Rev. 152, 49–59 (2016).

    Article  Google Scholar 

  31. Cuzzone, J. K. et al. Final deglaciation of the Scandinavian Ice Sheet and implications for the Holocene global sea-level budget. Earth Planet. Sci. Lett. 448, 34–41 (2016).

    Article  CAS  Google Scholar 

  32. Lambeck, K., Rouby, H., Purcell, A., Sun, Y. & Sambridge, M. Sea level and global ice volumes from the Last Glacial Maximum to the Holocene. Proc. Natl Acad. Sci. USA 111, 15296–15303 (2014).

    Article  CAS  Google Scholar 

  33. Licciardi, J. M., Clark, P. U., Jenson, J. W. & Macayeal, D. R. Deglaciation of a soft-bedded Laurentide Ice Sheet. Quat. Sci. Rev. 17, 427–448 (1998).

    Article  Google Scholar 

  34. Licciardi, J. M., Teller, J. T. & Clark, P. U. in Mechanisms of Global Climate Change at Millennial Time Scales (eds Clark, P. U. et al.) 177–201 (Geophysical Monograph Series Vol. 112, AGU, 1999).

  35. Carlson, A. E. et al. Rapid early Holocene deglaciation of the Laurentide ice sheet. Nat. Geosci. 1, 620–624 (2008).

    Article  CAS  Google Scholar 

  36. Siegert, M. J. & Dowdeswell, J. A. Numerical reconstructions of the Eurasian Ice Sheet and climate during the Late Weichselian. Quat. Sci. Rev. 23, 1273–1283 (2004).

    Article  Google Scholar 

  37. Dixon, K. W., Delworth, T. L., Spelman, M. J. & Stouffer, R. J. The influence of transient surface fluxes on North Atlantic overturning in a coupled GCM climate change experiment. Geophys. Res. Lett. 26, 2749–2752 (1999).

    Article  Google Scholar 

  38. Haine, T. W. N. et al. Arctic freshwater export: status, mechanisms, and prospects. Glob. Planet. Change 125, 13–35 (2015).

    Article  Google Scholar 

  39. Clark, J., Mitrovica, J. X. & Alder, J. Coastal paleogeography of the California–Oregon–Washington and Bering Sea continental shelves during the latest Pleistocene and Holocene: implications for the archaeological record. J. Archaeol. Sci. 52, 12–23 (2014).

    Article  Google Scholar 

  40. Lippold, J. et al. Constraining the variability of the Atlantic Meridional Overturning Circulation during the Holocene. Geophys. Res. Lett. 46, 11338–11346 (2019).

    Article  Google Scholar 

  41. Lynch-Stieglitz, J. The Atlantic Meridional Overturning Circulation and abrupt climate change. Ann. Rev. Mar. Sci. 9, 83–104 (2017).

    Article  Google Scholar 

  42. McManus, J. F., Francois, R., Gherardi, J. M., Keigwin, L. D. & Brown-Leger, S. Collapse and rapid resumption of Atlantic meridional circulation linked to deglacial climate changes. Nature 428, 834–837 (2004).

    Article  CAS  Google Scholar 

  43. Ng, H. C. et al. Coherent deglacial changes in western Atlantic Ocean circulation. Nat. Commun. 9, 2947 (2018).

    Article  CAS  Google Scholar 

  44. Alley, R. B. et al. Holocene climatic instability: a prominent, widespread event 8200 yr ago. Geology 25, 483–486 (1997).

    Article  Google Scholar 

  45. Fleitmann, D. et al. Evidence for a widespread climatic anomaly at around 9.2 ka before present. Paleoceanography 23, PA1102 (2008).

    Article  Google Scholar 

  46. Bond, G. et al. A pervasive millennial-scale cycle in North Atlantic Holocene and glacial climates. Science 278, 1257–1266 (1997).

    Article  CAS  Google Scholar 

  47. Buizert, C. et al. Greenland temperature response to climate forcing during the last deglaciation. Science 345, 1177–1180 (2014).

    Article  CAS  Google Scholar 

  48. Liu, Z. et al. Transient simulation of last deglaciation with a new mechanism for Bolling–Allerod warming. Science 325, 310–314 (2009).

    Article  CAS  Google Scholar 

  49. He, F. Simulating Transient Climate Evolution of the Last Deglaciation with CCSM3. PhD thesis, Univ. Wisconsin–Madison (2011).

  50. Zhang, Y., Renssen, H., Seppä, H. & Valdes, P. J. Holocene temperature trends in the extratropical Northern Hemisphere based on inter-model comparisons. J. Quat. Sci. 33, 464–476 (2018).

    Article  Google Scholar 

  51. Renssen, H. et al. The spatial and temporal complexity of the Holocene thermal maximum. Nat. Geosci. 2, 411–414 (2009).

    Article  CAS  Google Scholar 

  52. Renold, M., Raible, C. C., Yoshimori, M. & Stocker, T. F. Simulated resumption of the North Atlantic meridional overturning circulation—slow basin-wide advection and abrupt local convection. Quat. Sci. Rev. 29, 101–112 (2010).

    Article  Google Scholar 

  53. Zhu, J., Liu, Z. Y., Zhang, X., Eisenman, I. & Liu, W. Linear weakening of the AMOC in response to receding glacial ice sheets in CCSM3. Geophys. Res. Lett. 41, 6252–6258 (2014).

    Article  Google Scholar 

  54. Du, J., Haley, B. A. & Mix, A. C. Evolution of the Global Overturning Circulation since the Last Glacial Maximum based on marine authigenic neodymium isotopes. Quat. Sci. Rev. 241, 106396 (2020).

    Article  Google Scholar 

  55. Missiaen, L. et al. Modelling the impact of biogenic particle flux intensity and composition on sedimentary Pa/Th. Quat. Sci. Rev. 240, 106394 (2020).

    Article  Google Scholar 

  56. Bova, S., Rosenthal, Y., Liu, Z., Godad, S. P. & Yan, M. Seasonal origin of the thermal maxima at the Holocene and the last interglacial. Nature 589, 548–553 (2021).

    Article  CAS  Google Scholar 

  57. Kaufman, D. S. et al. Holocene thermal maximum in the western Arctic (0–180° W). Quat. Sci. Rev. 23, 529–560 (2004).

    Article  Google Scholar 

  58. Marcott, S. A., Shakun, J. D., Clark, P. U. & Mix, A. C. A reconstruction of regional and global temperature for the past 11,300 years. Science 339, 1198–1201 (2013).

    Article  CAS  Google Scholar 

  59. Liu, Z. et al. The Holocene temperature conundrum. Proc. Natl Acad. Sci. USA 111, E3501–3505 (2014).

    CAS  Google Scholar 

  60. Park, H.-S., Kim, S.-J., Stewart, A. L., Son, S.-W. & Seo, K.-H. Mid-Holocene Northern Hemisphere warming driven by Arctic amplification. Sci. Adv. 5, eaax8203 (2019).

    Article  Google Scholar 

  61. He, F. et al. Simulating global and local surface temperature changes due to Holocene anthropogenic land cover change. Geophys. Res. Lett. 41, 623–631 (2014).

    Article  Google Scholar 

  62. Carlson, A. E. & Clark, P. U. Ice sheet sources of sea level rise and freshwater discharge during the last deglaciation. Rev. Geophys. 50, RG4007 (2012).

    Article  Google Scholar 

  63. Broecker, W. S. Was the Younger Dryas triggered by a flood? Science 312, 1146–1148 (2006).

    Article  CAS  Google Scholar 

  64. Rahmstorf, S. Ocean circulation and climate during the past 120,000 years. Nature 419, 207–214 (2002).

    Article  CAS  Google Scholar 

  65. Sigman, D. M., Hain, M. P. & Haug, G. H. The polar ocean and glacial cycles in atmospheric CO(2) concentration. Nature 466, 47–55 (2010).

    Article  CAS  Google Scholar 

  66. Collins, M. et al. in Climate Change 2013: The Physical Science Basis (eds Stocker, T. F. et al.) Ch. 12 (IPCC, Cambridge Univ. Press, 2013).

  67. Church, J. A. et al. in Climate Change 2013: The Physical Science Basis (eds Stocker, T. F. et al.) Ch. 13 (IPCC, Cambridge Univ. Press, 2013).

  68. Briner, J. P. et al. Rate of mass loss from the Greenland Ice Sheet will exceed Holocene values this century. Nature 586, 70–74 (2020).

    Article  CAS  Google Scholar 

  69. Aschwanden, A. et al. Contribution of the Greenland Ice Sheet to sea level over the next millennium. Sci. Adv. 5, eaav9396 (2019).

    Article  Google Scholar 

  70. Alley, R. B. The Younger Dryas cold interval as viewed from central Greenland. Quat. Sci. Rev. 19, 213–226 (2000).

    Article  Google Scholar 

  71. Yellowstone: IBM iDataPlex System (University Community Computing) (Computational Information Systems Laboratory, National Center for Atmospheric Research, 2016); http://n2t.net/ark:/85065/d7wd3xhc

  72. Cheyenne: HPE/SGI ICE XA System (University Community Computing) (Computational Information Systems Laboratory, National Center for Atmospheric Research, 2019); https://doi.org/10.5065/D6RX99HX

  73. Pedro, J. B. et al. The spatial extent and dynamics of the Antarctic Cold Reversal. Nat. Geosci. 9, 51–55 (2015).

    Article  CAS  Google Scholar 

  74. Rasmussen, S. O. et al. A new Greenland ice core chronology for the last glacial termination. J. Geophys. Res. 111, D06102 (2006).

    Google Scholar 

  75. Andersen, K. K. et al. The Greenland Ice Core Chronology 2005, 15–42 ka. Part 1: constructing the time scale. Quat. Sci. Rev. 25, 3246–3257 (2006).

    Article  Google Scholar 

  76. Stenni, B. et al. The deuterium excess records of EPICA Dome C and Dronning Maud Land ice cores (East Antarctica). Quat. Sci. Rev. 29, 146–159 (2010).

    Article  Google Scholar 

  77. Lemieux-Dudon, B. et al. Consistent dating for Antarctic and Greenland ice cores. Quat. Sci. Rev. 29, 8–20 (2010).

    Article  Google Scholar 

  78. Kawamura, K. et al. Northern Hemisphere forcing of climatic cycles in Antarctica over the past 360,000 years. Nature 448, 912–916 (2007).

    Article  CAS  Google Scholar 

  79. Petit, J. R. et al. Climate and atmospheric history of the past 420,000 years from the Vostok ice core, Antarctica. Nature 399, 429–436 (1999).

    Article  CAS  Google Scholar 

  80. Waelbroeck, C. et al. The timing of the last deglaciation in North Atlantic climate records. Nature 412, 724–727 (2001).

    Article  CAS  Google Scholar 

  81. Cacho, I. et al. Variability of the western Mediterranean Sea surface temperature during the last 25,000 years and its connection with the Northern Hemisphere climatic changes. Paleoceanography 16, 40–52 (2001).

    Article  Google Scholar 

  82. Bard, E., Rostek, F., Turon, J. L. & Gendreau, S. Hydrological impact of Heinrich events in the subtropical northeast Atlantic. Science 289, 1321–1324 (2000).

    Article  CAS  Google Scholar 

  83. Cacho, I. et al. Dansgaard–Oeschger and Heinrich event imprints in Alboran Sea paleotemperatures. Paleoceanography 14, 698–705 (1999).

    Article  Google Scholar 

  84. Castañeda, I. S. et al. Millennial-scale sea surface temperature changes in the eastern Mediterranean (Nile River Delta region) over the last 27,000 years. Paleoceanography 25, PA1208 (2010).

    Article  Google Scholar 

  85. Arz, H. W., Patzold, J., Muller, P. J. & Moammar, M. O. Influence of Northern Hemisphere climate and global sea level rise on the restricted Red Sea marine environment during termination I. Paleoceanography 18, 1053 (2003).

    Article  Google Scholar 

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Acknowledgements

We thank J. D. Shakun and C. Buizert for fruitful discussions and J. Lynch-Stieglitz for providing the AMOC data at the Florida Straits. This work was funded by the US National Science Foundation through grant numbers OPP-1936880, AGS-1502990 and AGS-1602771 (to F.H.), AGS-1503032 (to P.U.C.); the Climate, People, and the Environment Program (to F.H.); and the NOAA Climate and Global Change Postdoctoral Fellowship programme (to F.H.), administered by the University Corporation for Atmospheric Research. Support for this research was also provided by the University of Wisconsin–Madison Office of the Vice Chancellor for Research and Graduate Education with funding from the Wisconsin Alumni Research Foundation. This research used resources of the Oak Ridge Leadership Computing Facility at the Oak Ridge National Laboratory, which is supported by the Office of Science of the US Department of Energy under contract number DE-AC05-00OR22725.

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  1. Center for Climatic Research, Nelson Institute for Environmental Studies, University of Wisconsin–Madison, Madison, WI, USA

    Feng He

  2. College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR, USA

    Peter U. Clark

  3. School of Geography and Environmental Sciences, University of Ulster, Coleraine, UK

    Peter U. Clark

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F.H. designed and performed the research with input from P.U.C. and F.H. led the writing of the manuscript with input from P.U.C. All authors discussed the results and contributed towards improving the final manuscript.

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Correspondence to Feng He.

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Extended data

Extended Data Fig. 1 Site locations of the proxy data used in the regional temperature stacks.

Site locations for Greenland temperature stack and the Eastern Atlantic Ocean and Mediterranean Sea temperature stacks (top) and Antarctica temperature stack (bottom).

Extended Data Fig. 2 Comparison of data and models for regional temperature stacks of past 21,000 years over Greenland and Antarctica.

a-b, Surface air temperature (SAT) changes from the central Greenland at NGRIP and GISP2 sites. The composite of the central Greenland temperature was based on δ15N for 21-10 ka47 and δ18O for 10-0 ka at NGRIP74,75 and GISP2 sites70. c-f, SAT changes from the Antarctica at EDML76,77, Dome C76,77, Dome F78 and Vostok79 sites. g-h. Greenland and Antarctica stack. Proxy data in black; before and include the onset of the Bølling, TraCE-21K-I and TraCE-21K-II are identical (red); after the onset of the Bølling, simulation based on the protocol of prescribing the reconstructed AMOC in red (TraCE-21K-II) and prescribing the reconstructed FW forcing in cyan (TraCE-21K-I). See Methods for detailed information about the proxy data used in the regional temperature stacks. All modeled changes are referenced to the averages of corresponding proxy data during the Oldest Dryas (19-15 ka) to aid the comparison. LGM, Last Glacial Maximum. OD, Oldest Dryas. BA, Bølling-Allerød interstadial. YD, Younger Dryas. HMAP, Holocene Meltwater-AMOC Paradox. LH, Late Holocene. ka, thousand years before 1950.

Extended Data Fig. 3 Comparison of data and models for the regional temperature stack of past 21,000 years in the Eastern Atlantic Ocean/Mediterranean Sea.

a-h, sea surface temperature changes from a) core NA 87-22 in Northeast Atlantic Ocean80, b) Western Mediterranean (BS79-38)81, c) Iberian margin (SU81-18)82, d) Iberian margin (SU81-18)80, e) Gulf of Cadiz (M39-008)81, f) Alboran Sea (MD95-2043)83, g) Nile Delta (GeoB 7702-3)84 and h) Red Sea (GeoB 5844-2)85. i, Eastern Atlantic/Mediterranean sea surface temperature stack. Proxy data in black; before and include the onset of the Bølling, TraCE-21K-I and TraCE-21K-II are identical (red); after the onset of the Bølling, simulation based on the protocol of prescribing the reconstructed AMOC in red (TraCE-21K-II) and prescribing the reconstructed FW forcing in cyan (TraCE-21K-I). See Methods for detailed information about the proxy data used in the regional temperature stacks. All modeled changes are referenced to the proxy data during the Oldest Dryas (19-15 ka) to aid the comparison. LGM, Last Glacial Maximum. OD, Oldest Dryas. BA, Bølling-Allerød interstadial. YD, Younger Dryas. HMAP, Holocene Meltwater-AMOC Paradox. LH, Late Holocene. ka, thousand years before 1950.

Extended Data Fig. 4 Comparison of data and models for regional temperature stacks of past 21,000 years.

Same as Fig. 2, but with temperature anomalies of each regional stack (b-d) from the average value in the Oldest Dryas (19 ka-15 ka).

Extended Data Fig. 5 The temperature biases of the two Holocene simulations.

TraCE-21K-I in Cyan and TraCE-21K-II in red. Upper panel, the temperature differences and their uncertainties (one standard deviation) between the proxy data and the simulations during the early Holocene (9 ka - 6 ka) in the three regional temperature stacks in Fig. 2; Lower panel, the percentage of the biases with reference to the biases in TraCE-21K-I.

Extended Data Fig. 6 Location of FW forcing in TraCE-21K-I and TraCE-21K-II simulations.

The amount of FW forcing in TraCE-21K-I and TraCE-21K-II simulations was documented in Supplementary Tables 2 and 3. In the TraCE-21K-I simulation, locations of the FW forcing include the coastal region near the Mackenzie River (pink shaking), the Arctic Ocean in the Beaufort Sea and parts of the Canadian Arctic Archipelago (blue shading), the North Atlantic Ocean between 50°N and 70°N (hollow blue), the Barents Sea (orange shading), the North Sea (dark red shading), the Nordic Sea (hollow green), the coastal region near the St. Lawrence River (hollow black), Hudson Strait (hollow dark green), the Gulf of Mexico (red shading), the Weddell Sea (yellow shading) and Ross Sea (gray shading). In the TraCE-21K-II simulation, the FW forcing during the Younger Dryas was applied to the North Atlantic Ocean between 50°N and 70°N (hollow blue). In TraCE-21K-I, the Laurentide ice-sheet FW forcings are derived from Ref. 33 and Ref. 34 that are updated in timing by Ref. 35. The Scandinavian ice-sheet FW forcing comes from Ref. 36. Updates to these ice sheets’ deglacial chronologies by Ref. 30 and Ref. 31, respectively, have not changed the overall FW forcings. Ice divides were used to determine to which ocean basins the various fractions of the total ice-sheet FW were discharged following Ref. 34.

Extended Data Fig. 7 Total amount of freshwater forcing in the Northern Hemisphere (cyan) and Southern Hemisphere (blue) in TraCE-21K-I and TraCE-21K-II simulations.

m SLE 1000 yr-1, meter of sea level equivalent per thousand years. 1 m SLE 1000 yr−1 ~= 0.011 Sv. ka, thousand years before 1950. Refer Supplementary Tables 2 and 3 for the amount of meltwater discharge in specific locations in TraCE-21K-I and TraCE-21K-II simulations. Purple shading denotes the period of the HMAP.

Extended Data Fig. 8 Comparison of AMOC streamfunction and the changes of maximum mix layer depths between TraCE-21K-I and TraCE-21K-II during the early Holocene.

AMOC streamfunction (in sverdrup) during the early Holocene (9 ka – 6 ka) in TraCE-21K-II (top) and TraCE-21K-I simulations (middle) and the differences of maximum mix layer depths (m) in March between TraCE-21K-I and TraCE-21K-II during the early Holocene (9 ka – 6 ka) (bottom).

Extended Data Fig. 9 Comparison of global surface temperature evolution between TraCE-21K-I and TraCE-21K-II simulations.

Global surface temperature from TraCE-21K-I in cyan and TraCE-21K-II in red.

Extended Data Fig. 10 Comparison of regional surface temperature evolution between TraCE-21K-I and TraCE-21K-II simulations.

Northern Hemisphere mid-high latitude (top, 30N-90N), low-latitude (middle, 30S-30N) and Southern Hemisphere mid-high latitude (bottom, 30S-90S). Regional surface temperature from TraCE-21K-I in cyan and TraCE-21K-II in red.

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He, F., Clark, P.U. Freshwater forcing of the Atlantic Meridional Overturning Circulation revisited. Nat. Clim. Chang. 12, 449–454 (2022). https://doi.org/10.1038/s41558-022-01328-2

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