Abstract
During the last ice age, the Laurentide Ice Sheet exhibited extreme iceberg discharge events that are recorded in North Atlantic sediments1. These Heinrich events have far-reaching climate impacts, including widespread disruptions to hydrological and biogeochemical cycles2,3,4. They occurred during Heinrich stadials—cold periods with strongly weakened Atlantic overturning circulation5,6,7. Heinrich-type variability is not distinctive in Greenland water isotope ratios, a well-dated site temperature proxy8, complicating efforts to assess their regional climate impact and phasing against Antarctic climate change. Here we show that Heinrich events have no detectable temperature impact on Greenland and cooling occurs at the onset of several Heinrich stadials, and that both types of Heinrich variability have a distinct imprint on Antarctic climate. Antarctic ice cores show accelerated warming that is synchronous with increases in methane during Heinrich events, suggesting an atmospheric teleconnection9, despite the absence of a Greenland climate signal. Greenland ice-core nitrogen stable isotope ratios, a sensitive temperature proxy, indicate an abrupt cooling of about three degrees Celsius at the onset of Heinrich Stadial 1 (17.8 thousand years before present, where present is defined as 1950). Antarctic warming lags this cooling by 133 ± 93 years, consistent with an oceanic teleconnection. Paradoxically, proximal sites are less affected by Heinrich events than remote sites, suggesting spatially complex event dynamics.
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Data availability
GISP2 δ15N–N2 and CH4 data are available via the NSF Arctic Data Center (https://doi.org/10.18739/A2639K65M) and in the Supplementary Data. Source data are provided with this paper.
Code availability
The code for stacking the records is available with ref. 80.
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Acknowledgements
The work was supported financially by the US National Science Foundation grant 1702920 to C.B. and E.J.B.; NSF grant 2102944 to C.B.; the Global Climate Change Foundation (GCCF24, to C.B.) and the Gary Comer Science and Education Foundation (CP116, to J.P.S.). We thank the NSF ice-core facility (ICF) for their curation and assistance in preparation of ice-core samples.
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The paper was prepared by K.C.M. and C.B. The data analysis was conducted by K.C.M., C.B., J.S.E. and E.J.B. The chronology was developed by C.B. and K.C.M. The methane data were produced by K.C.M., C.B., E.J.B., J.S.E., B.R.-Y., M.L.K. and T.A.S. The δ15N data were produced by R.B. and J.P.S. All authors contributed to the final paper.
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Extended data figures and tables
Extended Data Fig. 1 Far- and near-field climate proxies indicative of Heinrich Stadial conditions.
a, U1308 IRD (black; ref. 11). b, North Atlantic IRD Stack with arbitrary units (brown; ref. 82). c, Summit Calcium (note concentration units on reversed axis with log scale, black; ref. 38). d, Speleothem composite of East Asian Monsoon strength (orange is raw data, black is 5-point running average; ref. 39) and Hulu δ18O (blue, from stalagmite PD offset by −4‰; ref. 51). e, North Atlantic stack (dark red) and Iberian Margin (dark blue) SST reconstruction transferred from GICC05 to BIC (ref. 36). f, Bermuda Rise 231Pa/230Th (blue squares50, teal circles37,green triangles5). Light blue bars denote the duration of Heinrich Stadials. Solid and dashed vertical lines indicate timing of Heinrich Events and DO stadial to interstadial transitions, respectively, inferred by the midpoint of CH4 features.
Extended Data Fig. 2 Paleoclimate records during HS1.
a, North Atlantic IRD from site U1308A (black; ref. 11). b, Cariaco Basin Sediment Reflectance (note reversed axis; teal; ref. 19). c, WD CH4 (green; ref. 17) and GISP2 CH4 (black; this study). d, GISP2 δ15N (modeled reconstruction in blue, data in black; this study). e, Speleothem composite of East Asian Monsoon strength (orange is raw data, black is 5-point running average; ref. 39). f, Summit δ18O (GISP2 and GRIP average, purple; ref. 48). g, Summit Ca2+ (black; ref. 38). h, 6-core Antarctic average δ18O (gold; refs. 9,49). i, North Atlantic stack (dark red) and Iberian Margin (dark blue) SST reconstruction transferred from GICC05 to BIC (ref. 36). j, Bermuda Rise 231Pa/230Th (blue squares50, teal circles37); The light blue bar denotes duration of Heinrich Stadial 1. Solid black line indicates timing of Heinrich Event 1 based on IRD and CH4. The vertical dark blue line is the midpoint of Greenland δ15N change at 18008 years BP, which is synchronous with the midpoint of cooling. The vertical gold line indicates the inflection of 6-core Antarctic δ18O stack identified by Breakfit81 at 17875 years BP.
Extended Data Fig. 3 Offsets between the synchronized and original chronologies for WD and GISP2.
Upper panel: Gas age differences between synchronized chronology and GICC05 (black) and WD2014 (green). Changes after 31ka in gas age differences are largely due to removing the 1.0063 scaling factor in WD24. Lower panel: Ice age differences between synchronized chronology and GICC05 (black) and WD2014 (green). Note that there is a 0-year ice age difference in GISP2 older than 31,000 years; WD has a 0-year ice age offset from 0-31,000 years.
Extended Data Fig. 4 Heinrich Event Sensitivity experiment results and experiment forcings.
a, magnitude and duration of forcings for peaked/triangular experiments. b, magnitude and duration of forcings for sustained/square experiments. c, δ15N data (black circles), control experiment (black line), and experimental output for a range of peaked forcings with abrupt recovery (colored lines). Cooler colors indicate more extreme temperature anomalies, dashed curves indicate model output outside of the control RMSD. d, Data to model RMSD evaluation for a range of model runs. Each circle corresponds to the integrated temperature forcing for an experiment, green to blue color gradient corresponds to panel C, cool and warm colors correspond to example runs from peak and sustained forcings respectively.
Extended Data Fig. 5 Comparison between Greenland ice core records over Heinrich Stadial 1.
a, GISP2 δ18O (purple; ref. 26). b, GISP2 Ca2+ (brown; ref. 26). c, NGRIP δ18O (purple; ref. 26). d, NGRIP Ca2+ (brown; ref. 26). e, NEEM δ18O (purple; ref. 83). f, NEEM Ca2+ (brown; ref. 84). Note that Ca2+ is in concentration units on a reverse log scale, on their original chronologies26. Vertical brown line indicates a cohesive change in Ca2+ across all cores at the midpoint of abrupt Ca2+ increase. Vertical solid line indicates timing of HE1 inferred from CH4.
Extended Data Fig. 6 Comparison between geochemical and climate model temperature reconstructions at Summit, Greenland.
The firn model reconstruction produced in this study (blue) is compared against existing reconstructions. a, Badgeley et al. (2020) reconstruction using data assimilation with δ18Oice (green; ref. 34). b, Cuffey and Clow (1997) δ18O-T scaling applied to our Summit δ18O and scaled Ca+2 stack (black; ref. 85). c, Buizert et al. (2018) firn reconstruction (purple; ref. 86). d, He et al. (2021) reconstruction accounting for modified seasonality of precipitation (black; ref. 20). e–f, transient, globally coupled climate model simulations of Liu et al. (2009) (teal; ref. 87) and Obase and Abe-Ouchi (2019) (light blue; ref. 88).
Extended Data Fig. 7 Phasing of Antarctic δ18O and CH4 during HS2b and HS2a.
a, WD CH4 (green; ref. 17) and GISP2 CH4 (black; this study). b, GISP2 δ15N (modeled reconstruction in blue, data in black; this study). c, Antarctic average δ18O (gold; ref. 9). d, Summit Ca2+ (black; ref. 38). Light blue bars denote Heinrich Stadials, and dashed vertical lines indicate Heinrich Event timings inferred by CH4 peaks for HE2b and HE2a. Red diamonds indicate CH4 (gas-phase) match points; blue squares indicate volcanic match points between WD and GISP2 (ref. 27).
Extended Data Fig. 8 Gas-phase synchronization of GISP2 and WD CH4 records over DO12.
CH4 match-points (red circles) and GISP2 CH4 record (black; this study), WD CH4 record17 (green). The use of an automated correlation scheme indicates that visual match-points are accurate to +/− 14 years.
Extended Data Fig. 9 Lead-Lag analysis of CH4 and Greenland δ18O.
Top panel: Summit (Su, average of GRIP and GISP2) δ18O (black); GISP2 CH4 stack, base record in blue and age-shifted record in red; Vertical dashed lines indicate correlation window. Bottom panel: squared correlation coefficient between GISP2 CH4 and Su δ18O for a range of age-offsets between records. Dashed lines indicate the 95% confidence level for correlations. Both records are the 25-year running average. Results are insensitive to changes in the window of correlation and the amount of smoothing.
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Supplementary Data
This data file includes the bipolar ice-core chronology, GISP2 CH4, GISP2 δ15N–N2, bipolar CH4 matchpoints between the GISP2 and WD ice cores, empirical GISP2 Δage constraints, model output for GISP2 δ15N–N2 and Δage, and a temperature reconstruction for Summit, Greenland.
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Martin, K.C., Buizert, C., Edwards, J.S. et al. Bipolar impact and phasing of Heinrich-type climate variability. Nature 617, 100–104 (2023). https://doi.org/10.1038/s41586-023-05875-2
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DOI: https://doi.org/10.1038/s41586-023-05875-2
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