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ABSTRACT Atmospheric CO2 fluctuations over glacial–interglacial cycles remain a major challenge to our understanding of the carbon cycle and the climate system. Leading hypotheses put

forward to explain glacial–interglacial atmospheric CO2 variations invoke changes in deep-ocean carbon storage1,2, probably modulated by processes in the Southern Ocean, where much of the

deep ocean is ventilated3. A central aspect of such models is that, during deglaciations, an isolated glacial deep-ocean carbon reservoir is reconnected with the atmosphere, driving the

atmospheric CO2 rise observed in ice-core records4,5,6. However, direct documentation of changes in surface ocean carbon content and the associated transfer of carbon to the atmosphere

during deglaciations has been hindered by the lack of proxy reconstructions that unambiguously reflect the oceanic carbonate system. Radiocarbon activity tracks changes in ocean

ventilation6, but not in ocean carbon content, whereas proxies that record increased deglacial upwelling4,7 do not constrain the proportion of upwelled carbon that is degassed relative to

that which is taken up by the biological pump. Here we apply the boron isotope pH proxy in planktic foraminifera to two sediment cores from the sub-Antarctic Atlantic and the eastern

equatorial Pacific as a more direct tracer of oceanic CO2 outgassing. We show that surface waters at both locations, which partly derive from deep water upwelled in the Southern Ocean8,9,

became a significant source of carbon to the atmosphere during the last deglaciation, when the concentration of atmospheric CO2 was increasing. This oceanic CO2 outgassing supports the view

that the ventilation of a deep-ocean carbon reservoir in the Southern Ocean had a key role in the deglacial CO2 rise, although our results allow for the possibility that processes operating

in other regions may also have been important for the glacial–interglacial ocean–atmosphere exchange of carbon. Access through your institution Buy or subscribe This is a preview of

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ADDITIONAL ACCESS OPTIONS: * Log in * Learn about institutional subscriptions * Read our FAQs * Contact customer support SIMILAR CONTENT BEING VIEWED BY OTHERS INDIAN OCEAN GLACIAL

DEOXYGENATION AND RESPIRED CARBON ACCUMULATION DURING MID-LATE QUATERNARY ICE AGES Article Open access 10 August 2023 ABRUPT UPWELLING AND CO2 OUTGASSING EPISODES IN THE NORTH-EASTERN

ARABIAN SEA SINCE MID-HOLOCENE Article Open access 09 March 2022 SOUTHERN OCEAN CONTRIBUTION TO BOTH STEPS IN DEGLACIAL ATMOSPHERIC CO2 RISE Article Open access 11 November 2021 REFERENCES *

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samples from ODP Leg 202, R. Gersonde and A. Mackensen for the PS2498-1 core material, J. F. McManus for sharing his unpublished benthic isotope data for ODP1238, and E. J. Rohling, M. P.

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for samples from the National Institute for Water and Atmospheric Research, Wellington, and B. J. Marshall and R. Thunell for samples from the Cariaco Basin sediment trap time series. J. A.

Milton, M. J. Cooper and A. Michalik provided assistance during ICP-MS analyses and sample preparation in the laboratory. C. Alt and M. T. Horigome helped with foraminifera picking. We thank

the other members of ‘The B-Team’ at the National Oceanography Centre Southampton for their contributions. Financial support was provided by the European Community through a Marie Curie

Intra-European Fellowship for Career Development to M.A.M.-B., the Universitat Autònoma de Barcelona through a Postdoctoral Research Grant to G.M., the Spanish Ministry of Science and

Innovation (PROCARSO project CGL2009-10806) to G.M., P.Z. and P.G.M., a NERC PhD studentship awarded to M.J.H., a NOAA/UCAR Climate and Global Change Postdoctoral Fellowship to J.W.B.R., and

NERC grant NE/D00876/X2 to G.L.F. G.M. was also supported by the Australian Laureate Fellowship project FL120100050 (E. J. Rohling). AUTHOR INFORMATION Author notes * M. A. Martínez-Botí

and G. Marino: These authors contributed equally to this work. AUTHORS AND AFFILIATIONS * Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton

Waterfront Campus, Southampton SO14 3ZH, UK, M. A. Martínez-Botí, G. L. Foster & M. J. Henehan * Institute of Environmental Science and Technology (ICTA), Universitat Autònoma de

Barcelona, Bellaterra, Catalonia, 08193, Spain, G. Marino, P. Ziveri & P. G. Mortyn * Research School of Earth Sciences, The Australian National University, Canberra, Australian Capital

Territory 2601, Australia, G. Marino * Institució Catalana de Recerca i Estudis Avançats, ICREA, Barcelona, Catalonia, 08010, Spain, P. Ziveri * Department of Earth Sciences, Earth and

Climate Cluster, Faculty of Earth and Life Sciences, VU Universiteit Amsterdam, 1081HV Amsterdam, The Netherlands, P. Ziveri * Department of Geology and Geophysics, Yale University, New

Haven, 06511, Connecticut, USA M. J. Henehan * Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, 91125, California, USA J. W. B. Rae * Department

of Earth and Environmental Sciences, University of St Andrews, St Andrews KY16 9AL, UK, J. W. B. Rae * Department of Geography, Universitat Autònoma de Barcelona, Bellaterra, Catalonia,

08193, Spain, P. G. Mortyn * Department of Earth Sciences, Institute of Geochemistry and Petrology, ETH Zürich, NW D81.4, Zürich 8092, Switzerland, D. Vance Authors * M. A. Martínez-Botí

View author publications You can also search for this author inPubMed Google Scholar * G. Marino View author publications You can also search for this author inPubMed Google Scholar * G. L.

Foster View author publications You can also search for this author inPubMed Google Scholar * P. Ziveri View author publications You can also search for this author inPubMed Google Scholar *

M. J. Henehan View author publications You can also search for this author inPubMed Google Scholar * J. W. B. Rae View author publications You can also search for this author inPubMed 

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inPubMed Google Scholar CONTRIBUTIONS M.A.M.-B., G.M., G.L.F. and P.Z. designed the study; G.M. and M.A.M.-B. produced the δ11B and trace element records for PS2498-1; M.A.M.-B. produced the

δ11B and trace element records for ODP1238; G.M. produced the δ18O and δ13C data; M.J.H. developed the _G. bulloides_ δ11B–pH calibration; J.W.B.R. sampled sediment core PS2498-1. M.A.M.-B.

and G.M. wrote the first draft jointly, and all authors contributed to the interpretation and the preparation of the final manuscript. CORRESPONDING AUTHORS Correspondence to M. A.

Martínez-Botí or G. Marino. ETHICS DECLARATIONS COMPETING INTERESTS The authors declare no competing financial interests. EXTENDED DATA FIGURES AND TABLES EXTENDED DATA FIGURE 1 COMPARISON

OF PS2498-1 (BLUE) AND ODP1238 (RED) RECORDS. A, δ11B. B, pH. C, . EXTENDED DATA FIGURE 2 Δ11B-DERIVED COMPILATION FOR THE EQUATORIAL PACIFIC DURING THE LAST DEGLACIATION AND HOLOCENE.

Foraminifera-based record from the western equatorial Pacific21 (grey), _Porites_ coral-based record from the central equatorial Pacific22,23 (as published in ref. 22, green), and

foraminifera-based record from the EEP (this study, red). The records of refs 21, 22 have been smoothed by fitting a LOESS function with degrees of smoothing (span) of 0.2 and 0.4,

respectively (Methods), to allow a better comparison with the ODP1238 record (see main text). ODP1238 is located in the EEP, and therefore represents a direct record of upwelling of CO2-rich

waters, while the signal at central and western equatorial sites may have been modified during the westward transit of waters by, for example, equilibration with the atmosphere and/or

nutrient utilization by the biological pump. EXTENDED DATA FIGURE 3 PLANKTIC Δ18O AND Δ13C RECORDS FROM ODP1238. A, Planktic δ18O records from OPD1238. Red, _G. ruber_ sensu stricto (ss)

250–355 μm; green, _G. sacculifer_ (mixed morphotypes) 355–425 μm; black, _N. dutertrei_ 355–500 μm. B, Planktic δ13C records from OPD1238. To facilitate comparison between species, δ13C

data has been normalized53. Red, _G. ruber_ ss 250–355 μm; green, _G. sacculifer_ (mixed morphotypes) 355–425 μm; black, _N. dutertrei_ 355–500 μm. EXTENDED DATA FIGURE 4 RECORDS FROM THE

SAA AND THE EEP DURING THE LAST DEGLACIATION, COMPARED WITH INDICATORS OF DUST INPUT. A–C, SAA; D–F, EEP. A, δ11B-derived in core PS2498-1. B, Logarithm of the mass accumulation rates (MAR)

of iron (Fe) in the sub-Antarctic site ODP109013. C, F, measured on a suite of Antarctic ice cores5. D, δ11B-derived in core ODP1238. E, Dust fluxes in the EEP29. Dust fluxes from ref. 29

were de-meaned and divided by their own standard deviation, and are displayed in standard deviation units. EXTENDED DATA FIGURE 5 AGE MODEL FOR PS2498-1. A, Chronology of SAA core PS2498-1.

Carbon-14 calendar age/depth relationships in core PS2498-1. Grey shading indicates 95% confidence limits of calendar ages. B, PS2498-1 _G. bulloides_ δ11B record plotted using the different

chronologies described in Methods and compared with atmospheric CO2 (green; refs 5, 87, 88) and with Antarctic opal flux4 (orange) records. Red, constant Δ_R_ = 300 yr; green, Δ_R_ = 900 yr

for intervals older than 16 kyr and Δ_R_ = 300 yr for younger intervals6; magenta, variable Δ_R_ correction38 (ranging between 500 and 900 yr between 13 and 16 kyr ago). EXTENDED DATA

FIGURE 6 AGE MODEL FOR ODP1238. A, Radiocarbon ages for ODP1238 determined from _N. dutertrei_ tests at LLNL-CAMS. B, Chronology of EEP core ODP1238. Orange circles, calendar ages; black

line, linear fit; red line, third-order polynomial fit (Methods). EXTENDED DATA FIGURE 7 BENTHIC AND PLANKTIC Δ18O STRATIGRAPHY FOR ODP1238. A, Benthic δ18O stratigraphy for ODP1238 compared

with other benthic δ18O stratigraphies from EEP cores. Black circles, unpublished benthic δ18O data for ODP1238 generated by J. F. McManus (LDEO, Columbia University); red line, site

TR163-2240; blue line, sites RC13-140, RC23-22 and RC23-1544. B, _Globigerinoides ruber_ δ18O stratigraphy for ODP1238 compared with other _G. ruber_ stratigraphies from EEP cores. Black

circles, ODP1238 (Methods); green squares, site TR163-197; red line, site TR163-2240; blue line, site ODP124041. EXTENDED DATA FIGURE 8 Δ11B–PH CALIBRATIONS FOR _G. BULLOIDES_ AND _G. 

SACCULIFER_. A, Data tabulated; B, Data plotted. The green symbols and text show a new calibration for _G. bulloides_ (with associated 2_σ_ uncertainties). Horizontal error bars for core-top

samples are 2_σ_ of intra-annual variability in calculated monthly δ11Bborate, and for sediment trap samples reflect the range of δ11Bborate between December 2006 and February 2007.

Vertical error bars represent the analytical reproducibility (2_σ_) as calculated using equation (1). The most recent PS2498-1 sample (2.2 kyr old) (black-filled circle) was not used in the

calibration process, and is included to show its agreement with the calibration line. The red symbols and text show a calibration for _G. sacculifer_ (with associated 2_σ_ uncertainties).

The calibration line incorporates both culture78 (empty symbols) and core-top (red-filled symbols) data17. Culture data analysed by N-TIMS (grey symbols and text)78 has been corrected by

applying a laboratory offset of −3.32‰ (Methods) (the vertical grey arrow indicates an original N-TIMS calibration data point that falls outside the plot area). The ODP1238 late-Holocene

average (black-filled square) was not used to produce the calibration equation, and is included to show its agreement with the calibration line. Horizontal error bars for core-top samples

are 2_σ_ of intra-annual variability in calculated monthly δ11Bborate, and for culture samples represent quoted uncertainties78 in pH. Vertical error bars represent quoted uncertainties in

δ11B measurements17,78 (2_σ_). To calculate monthly pH variations at ODP1238, the method described in the _G. bulloides_ calibration section has been used62 (with total alkalinity derived

using the total alkalinity/salinity/temperature relationship for the ‘Equatorial upwelling Pacific Zone’ in ref. 72). The black line denotes a 1:1 relationship, that is, a pH sensitivity

equal to that of borate ion. Heavily and lightly shaded regions around calibration lines represent 1_σ_ and 2_σ_ uncertainties, respectively. EXTENDED DATA FIGURE 9 EFFECT OF Δ11B–PH

CALIBRATION, TOTAL ALKALINITY AND CHRONOLOGICAL UNCERTAINTIES IN AND RECORDS. A, PS2498-1 δ11B-based record calculated with the _G. bulloides_ calibration equation (thick blue line), and its

associated 2_σ_ uncertainty (blue shaded envelope). B, PS2498-1 δ11B-based record assuming a constant total alkalinity of (i) modern values at PS2498-1 (blue), (ii) modern values minus 25 

μmol kg−1 (green) and (iii) modern values plus 125 μmol kg−1 (red). C, PS2498-1 record calculated using (i) age derived from our age model (blue), (ii) age plus 0.5 kyr (green) and (iii) age

minus 0.5 kyr (red). D, ODP1238 δ11B-based record calculated with the _G. sacculifer_ calibration equation (thick red line), and its associated 2_σ_ uncertainty (shaded red envelope). E,

ODP1238 δ11B-based record assuming a constant total alkalinity of (i) modern values at ODP1238 (blue), (ii) modern values minus 25 μmol kg−1 (green) and (iii) modern values plus 125 μmol 

kg−1 (red). F, ODP1238 record calculated using (i) age derived from our age model (blue), (ii) age plus 0.5 kyr (green) and (iii) age minus 0.5 kyr (red). Note the different horizontal and

vertical axes in each panel. EXTENDED DATA FIGURE 10 _GLOBIGERINOIDES SACCULIFER_ MG/CA-BASED SEA SURFACE SST (RED) AND _N. DUTERTREI_ MG/CA-BASED THERMOCLINE TEMPERATURE (TT; GREEN) AT

ODP1238. POWERPOINT SLIDES POWERPOINT SLIDE FOR FIG. 1 POWERPOINT SLIDE FOR FIG. 2 POWERPOINT SLIDE FOR FIG. 3 SOURCE DATA SOURCE DATA TO FIG. 1 SOURCE DATA TO FIG. 2 RIGHTS AND PERMISSIONS

Reprints and permissions ABOUT THIS ARTICLE CITE THIS ARTICLE Martínez-Botí, M., Marino, G., Foster, G. _et al._ Boron isotope evidence for oceanic carbon dioxide leakage during the last

deglaciation. _Nature_ 518, 219–222 (2015). https://doi.org/10.1038/nature14155 Download citation * Received: 22 August 2014 * Accepted: 11 December 2014 * Published: 11 February 2015 *

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