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Persistently well-ventilated intermediate-depth ocean through the last deglaciation

Abstract

During the last deglaciation (~18–11 thousand years ago), existing radiocarbon (14C) reconstructions of intermediate waters in the mid- to low-latitude oceans show widely diverging trends, with some broadly tracking the atmosphere and others suggesting extreme depletions. These discrepancies cloud our understanding of the deglacial carbon cycle because of the diversity of hypotheses needed to explain these diverging records, for example, injections of 14C-dead geological carbon, mixing of extremely isolated waters from the abyssal ocean or changes in sites of deep-water ventilation. Here we present absolutely dated deglacial deep-sea coral 14C records of intermediate waters from the Galápagos Platform—close to the largest reported deglacial 14C depletions—together with data from the low-latitude Atlantic. Our records indicate coherent, well-equilibrated intermediate-water 14C ventilation in both oceans relative to the atmosphere throughout the deglaciation. The observed overall trend towards 14C-enriched signatures in our records is largely due to enhanced air–sea carbon isotope exchange efficiency under increasing atmospheric \({p_{{\rm {CO}}_2}}\). These results suggest that the 14C-depleted signatures from foraminifera are likely sedimentary rather than water mass features, and provide tight 14C constraints for modelling changes in circulation and carbon cycle during the last deglaciation.

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Fig. 1: Map of sample locations and estimated distribution of pre-bomb 14C concentration.
Fig. 2: The Δ14C records of the eastern Pacific over the past 20 kyr (refs. 5,10,12,13,14,34,35,36,37,38).
Fig. 3: The evolution of B-Atm age of our coral records together with other palaeoclimate reconstructions.

Data availability

Sample location information, U-series ages and radiocarbon data that support the findings of this study are available in Extended Data Tables 1–3 and Mendeley Data https://doi.org/10.17632/vxrmfch8h9.1. The atmosphere CO2 concentration records, radiocarbon data, 231Pa/230Th and authigenic uranium flux cited in this study were previously published in refs. 13,21,31,39,40,41 and are available in the Source Data. The calculated B-Atm age trend without circulation change as well as projection age of the low-latitude coral samples are also available in the Source Data. Detailed information on published foraminifera age and radiocarbon data are available from a recent comprehensive compilation58 (https://www.ncdc.noaa.gov/paleo/study/21390). Source data are provided with this paper.

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Acknowledgements

This study was funded by the European Research Council, the Natural Environment Research Council (NE/S001743/1; NE/N011716/1), the Philip Leverhulme Trust, the Strategic Priority Research Program of Chinese Academy of Sciences (XDB40010200), the National Natural Science Foundation of China (41822603), the US National Science Foundation (OCE-0926637, OCE-10309040 and OCE-0926491), a Marie Curie Reintegration Grant and the NOAA (National Oceanic and Atmospheric Administration) Ocean Exploration Trust. We also thank the JC094 cruise members, shipboard staff and science party on MV1007 (permit #111-2010), the Charles Darwin Research Station, the Charles Darwin Research Foundation, the Galápagos National Park and INOCAR (Instituto Oceanográfico de la Armada de Ecuador) for supporting the coral sampling.

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Contributions

T.C. and L.F.R. designed the study and wrote the paper. L.F.R., D.J.F. and K.S.H. collected the deep-sea coral samples. T.C., L.C., T.L. and T.D.J.K. did the U-series and 14C analysis. All authors contributed to the discussion on data interpretation and improving the manuscript draft.

Corresponding author

Correspondence to Tianyu Chen.

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Extended data

Extended Data Table 1 Radiocarbon data of the Galápagos deep-sea coral together with new data from the equatorial Atlantic intermediate waters.

The table includes the location, depth, calendar age, 14C age, Δ14C, ΔΔ14C, and B-Atm age of the deglacial samples reported in this study.

Extended Data Table 2 New U-Th age data of the deep-sea corals from the equatorial Atlantic.

The table includes the detailed U-series data of deep-sea corals analyzed in this study.

Extended Data Table 3 Test of the coral radiocarbon age reproducibility between AMS in UCI and Bristol.

The table includes 14C data measured by accelerator mass spectrometer in the University of Bristol as well as the University of California Irvine. Data published in Chen et al.13.

Extended Data Fig. 1 Compiled 14C evolution of mid-low latitude intermediate water records during the last deglaciation.

(a) Δ14C of the eastern Pacific; (b) Δ14C of the equatorial Pacific and Atlantic corals; (c) ΔΔ14Ccorr of eastern Pacific records that did not show large 14C depletions; (d) ΔΔ14Ccorr of eastern Pacific records with large 14C depletions in comparison to our data; (e) ΔΔ14Ccorr of mid-low latitude Atlantic records. Also shown in (a) is the atmosphere Δ14C evolution with ±2σ uncertainty39. The legend in (a) shows the materials used for the 14C reconstruction5,10,12,13,14,34,35,36,37,38,55,56]. Symbols are the same as in Fig. 1. For clarity, 2σ error ellipses of ΔΔ14Ccorr of published data are not shown.

Source data

Extended Data Fig. 2 Radiocarbon age offset of the deep-sea coral data from the expected trend forced by the atmospheric pCO2 induced air-sea isotope exchange efficiency change alone.

Note vertical axis is reversed. Zero 14C age offset means a Holocene-like 14C ventilation in the upper ocean.

Extended Data Fig. 3 The bathymetry and sample locations of the Galápagos platform.

VM21-3010 showed the most depleted benthic 14C content during the deglacial period reported so far.

Extended Data Fig. 4 Age-depth distribution for reported deglacial deep-sea corals.

Red dots represent samples from the EEP while the green diamonds represent samples from the Equatorial Atlantic.

Source data

Extended Data Fig. 5 Sample locations of this study and hydrography of the Pacific and Atlantic transections.

Upper panel: Pacific; Lower panel: Atlantic. Colour maps denote oxygen concentrations (μmol/kg) while contours denote neutral densities (kg/m3). These low-latitude corals located close to or within the oxygen minimum zone as a result of oxygen utilization by remineralization of the falling biogenic particles along the advection path from the high to low latitude oceans. Data were from GLODAP1 and were plotted with ODV.

Extended Data Fig. 6 Data comparison between published dataset and this study.

(a) Deglacial data from low latitude intermediate Atlantic. New data of YD and HS1 presented in this study are shown by orange diamond and hollow diamond, respectively. (b) The difference between 14C ages measured in the Bristol AMS and in the UCI AMS. Note the age differences also include the inhomogeneity of deep-sea coral samples.

Extended Data Fig. 7 Projection age calculated from data of the deep-sea corals in this study.

Note that the coral 14C data are projected to the average global surface ocean reservoir (that is, Marine13 calibration curve39). In this case, the projection age would be systematically lower than the B-Atm age which is compared to the atmosphere.

Source data

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Source Data Fig. 2

Statistical Source Data

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Source Data Extended Data Fig. 1

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Source Data Extended Data Fig. 4

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Source Data Extended Data Fig. 7

Statistical Source Data

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Chen, T., Robinson, L.F., Burke, A. et al. Persistently well-ventilated intermediate-depth ocean through the last deglaciation. Nat. Geosci. 13, 733–738 (2020). https://doi.org/10.1038/s41561-020-0638-6

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