Ocean dynamics in the equatorial Pacific drive tropical climate patterns that affect marine and terrestrial ecosystems worldwide. How this region will respond to global warming has profound implications for global climate, economic stability and ecosystem health. As a result, numerous studies have investigated equatorial Pacific dynamics during the Pliocene (5.3–2.6 million years ago) and late Miocene (around 6 million years ago) as an analogue for the future behaviour of the region under global warming1,2,3,4,5,6,7,8,9,10,11,12. Palaeoceanographic records from this time present an apparent paradox with proxy evidence of a reduced east–west sea surface temperature gradient along the equatorial Pacific1,3,7,8—indicative of reduced wind-driven upwelling—conflicting with evidence of enhanced biological productivity in the east Pacific13,14,15 that typically results from stronger upwelling. Here we reconcile these observations by providing new evidence for a radically different-from-modern circulation regime in the early Pliocene/late Miocene16 that results in older, more acidic and more nutrient-rich water reaching the equatorial Pacific. These results provide a mechanism for enhanced productivity in the early Pliocene/late Miocene east Pacific even in the presence of weaker wind-driven upwelling. Our findings shed new light on equatorial Pacific dynamics and help to constrain the potential changes they will undergo in the near future, given that the Earth is expected to reach Pliocene-like levels of warming in the next century.
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The code used in this paper to produce pH from d11B (and to produce all the proxy-related figures) is publicly available as Matlab scripts on GitHub (https://github.com/Maddie-Sh/ShankleEtAl2021_Pliocene-pH). The CESM 220.127.116.11 code is available from https://svn-ccsm-models.cgd.ucar.edu/cesm1/release_tags/cesm1_2_2_1. The Python code used to create select model figures is available at https://github.com/nburls/ShankleEtAl2021. Source data are provided with this paper.
Wara, M. W., Ravelo, A. C. & Delaney, M. L. Permanent El Niño-like conditions during the Pliocene warm period. Science 309, 758–761 (2005).
Fedorov, A. V. et al. The Pliocene paradox (mechanisms for a permanent El Niño). Science 312, 1485–1490 (2006).
Zhang, Y. G., Pagani, M. & Liu, Z. A 12-million-year temperature history of the tropical Pacific Ocean. Science 344, 84–88 (2014).
Fedorov, A. V., Burls, N. J., Lawrence, K. T. & Peterson, L. C. Tightly linked zonal and meridional sea surface temperature gradients over the past five million years. Nat. Geosci. 8, 975–980 (2015).
Ford, H. L., Ravelo, A. C., Dekens, P. S., LaRiviere, J. P. & Wara, M. W. The evolution of the equatorial thermocline and the early Pliocene El Padre mean state. Geophys. Res. Lett. 42, 4878–4887 (2015).
Tierney, J. E., Haywood, A. M., Feng, R., Bhattacharya, T. & Otto‐Bliesner, B. L. Pliocene warmth consistent with greenhouse gas forcing. Geophys. Res. Lett. 46, 9136–9144 (2019).
Lawrence, K. T., Liu, Z. & Herbert, T. D. Evolution of the eastern tropical Pacific through Plio-Pleistocene glaciation. Science 312, 79–83 (2006).
Dekens, P. S., Ravelo, A. C. & McCarthy, M. D. Warm upwelling regions in the Pliocene warm period. Paleoceanography 22, PA3211 (2007).
Ford, H. L., Ravelo, A. C. & Hovan, S. A deep Eastern Equatorial Pacific thermocline during the early Pliocene warm period. Earth Planet. Sci. Lett. 355, 152–161 (2012).
Fedorov, A. V. et al. Patterns and mechanisms of early Pliocene warmth. Nature 496, 43–49 (2013).
O’Brien, C. L. et al. High sea surface temperatures in tropical warm pools during the Pliocene. Nat. Geosci. 7, 606–611 (2014).
Ravelo, A. C., Lawrence, K. T., Fedorov, A. & Ford, H. L. Comment on “A 12-million-year temperature history of the tropical Pacific Ocean”. Science 346, 1467 (2014).
Lyle, M. Neogene carbonate burial in the Pacific Ocean. Paleoceanography 18, 1059 (2003).
Lyle, M. & Baldauf, J. Biogenic sediment regimes in the Neogene equatorial Pacific, IODP Site U1338: burial, production, and diatom community. Palaeogeogr. Palaeoclimatol. Palaeoecol. 433, 106–128 (2015).
Ma, Z., Ravelo, A. C., Liu, Z., Zhou, L. & Paytan, A. Export production fluctuations in the eastern equatorial Pacific during the Pliocene‐Pleistocene: reconstruction using barite accumulation rates. Paleoceanography 30, 1455–1469 (2015).
Burls, N. J. et al. Active Pacific meridional overturning circulation (PMOC) during the warm Pliocene. Sci. Adv. 3, e1700156 (2017).
Bjerknes, J. Atmospheric teleconnections from the equatorial Pacific. Mon. Wea. Rev 97, 163–172 (1969).
Philander, S. G. El Niño, La Niña, and the southern oscillation. Int. Geophys. Ser. 46, 289 (1989).
Iizumi, T. et al. Impacts of El Niño SOUTHERN OSCILLATION on the global yields of major crops. Nat. Commun. 5, 3712 (2014).
Anderson, W., Seager, R., Baethgen, W. & Cane, M. Crop production variability in North and South America forced by life-cycles of the El Niño Southern Oscillation. Agric. For. Meteorol. 239, 151–165 (2017).
Heede, U. K., Fedorov, A. V. & Burls, N. J. Time scales and mechanisms for the tropical Pacific response to global warming: a tug of war between the ocean thermostat and weaker Walker. J. Clim. 33, 6101–6118 (2020).
Foster, G. L., Royer, D. L. & Lunt, D. J. Future climate forcing potentially without precedent in the last 420 million years. Nat. Commun. 8, 14845 (2017).
Haywood, A. M. et al. Large-scale features of Pliocene climate: results from the Pliocene Model Intercomparison Project. Clim. Past 9, 191–209 (2013).
Haywood, A. M., Dowsett, H. J. & Dolan, A. M. Integrating geological archives and climate models for the mid-Pliocene warm period. Nat. Commun. 7, 10646 (2016).
Prescott, C. L. et al. Assessing orbitally-forced interglacial climate variability during the mid-Pliocene warm period. Earth Planet. Sci. Lett. 400, 261–271 (2014).
Haywood, A. M. et al. The Pliocene Model Intercomparison Project Phase 2: large-scale climate features and climate sensitivity. Clim. Past 16, 2095–2123 (2020).
Brierley, C. M. & Fedorov, A. V. Relative importance of meridional and zonal sea surface temperature gradients for the onset of the ice ages and Pliocene‐Pleistocene climate evolution. Paleoceanography 25, PA2214 (2010).
McClymont, E. L. et al. Lessons from a high-CO2 world: an ocean view from ∼3 million years ago. Clim. Past 16, 1599–1615 (2020).
Burls, N. J. et al. Simulating Miocene warmth: insights from an opportunistic multi-model ensemble (MioMIP1). Paleoceanogr. Paleoclimatology 36, e2020PA004054 (2021).
Ravelo, A. C., Dekens, P. S. & McCarthy, M. Evidence for El Niño-like conditions during the Pliocene. GSA Today 16, 4–11 (2006).
Liu, J. et al. Eastern equatorial Pacific cold tongue evolution since the late Miocene linked to extratropical climate. Sci. Adv. 5, eaau6060 (2019).
Wycech, J. B., Gill, E., Rajagopalan, B., Marchitto, T. M. Jr & Molnar, P. H. Multiproxy reduced‐dimension reconstruction of Pliocene equatorial Pacific sea surface temperatures. Paleoceanogr. Paleoclimatology 35, e2019PA003685 (2020).
White, S. M. & Ravelo, A. C. The benthic B/Ca record at Site 806: new constraints on the temperature of the West Pacific Warm Pool and the “El Padre” state in the Pliocene. Paleoceanogr. Paleoclimatology 35, e2019PA003812 (2020).
Rae, J. W. B., Foster, G. L., Schmidt, D. N. & Elliott, T. Boron isotopes and B/Ca in benthic foraminifera: proxies for the deep ocean carbonate system. Earth Planet. Sci. Lett. 302, 403–413 (2011).
Rae, J. W. B. in Boron Isotopes (eds. Marschall, H. & Foster, G.) 107–143 (Springer, 2018).
Henehan, M. J. et al. A new boron isotope-pH calibration for Orbulina universa, with implications for understanding and accounting for ‘vital effects’. Earth Planet. Sci. Lett. 454, 282–292 (2016).
Takahashi, T. et al. Climatological mean and decadal change in surface ocean pCO2, and net sea–air CO2 flux over the global oceans. Deep Sea Res. Part II Top. Stud. Oceanogr. 56, 554–577 (2009).
Burls, N. J. & Fedorov, A. V. Simulating Pliocene warmth and a permanent El Niño‐like state: the role of cloud albedo. Paleoceanography 29, 893–910 (2014).
Burls, N. J. & Fedorov, A. V. What controls the mean east–west sea surface temperature gradient in the equatorial Pacific: the role of cloud albedo. J. Clim. 27, 2757–2778 (2014).
Dowsett, H. J. et al. Sea surface temperature of the mid-Piacenzian ocean: a data-model comparison. Sci. Rep. 3, 2013 (2013).
Brierley, C., Burls, N., Ravelo, C. & Fedorov, A. Pliocene warmth and gradients. Nat. Geosci. 8, 419–420 (2015).
Sautter, L. R. & Thunell, R. C. Planktonic foraminiferal response to upwelling and seasonal hydrographic conditions; sediment trap results from San Pedro Basin, Southern California Bight. J. Foraminifer. Res. 21, 347–363 (1991).
Rebotim, A. et al. Factors controlling the depth habitat of planktonic foraminifera in the subtropical eastern North Atlantic. Biogeosciences 14, 827–859 (2017).
Buckley, M. W. & Marshall, J. Observations, inferences, and mechanisms of the Atlantic Meridional Overturning Circulation: a review. Rev. Geophys. 54, 5–63 (2016).
Thomas, M. D. & Fedorov, A. V. The eastern subtropical Pacific origin of the equatorial cold bias in climate models: a Lagrangian perspective. J. Clim. 30, 5885–5900 (2017).
Sarmiento, J. L., Hughes, T. M. C., Stouffer, R. J. & Manabe, S. Simulated response of the ocean carbon cycle to anthropogenic climate warming. Nature 393, 245–249 (1998).
Fedorov, A. V., Brierley, C. M. & Emanuel, K. Tropical cyclones and permanent El Niño in the early Pliocene epoch. Nature 463, 1066–1070 (2010).
Christensen, V., De la Puente, S., Sueiro, J. C., Steenbeek, J. & Majluf, P. Valuing seafood: the Peruvian fisheries sector. Mar. Policy 44, 302–311 (2014).
Gutierrez, D., Akester, M. & Naranjo, L. Productivity and sustainable management of the Humboldt Current large marine ecosystem under climate change. Environ. Dev. 17, 126–144 (2016).
Clark, P. U. et al. Consequences of twenty-first-century policy for multi-millennial climate and sea-level change. Nat. Clim. Chang. 6, 360–369 (2016).
Martínez-Botí, M. A. et al. Plio-Pleistocene climate sensitivity evaluated using high-resolution CO2 records. Nature 518, 49–54 (2015).
Mayer, L. A. et al. Proceedings of the Ocean Drilling Program: Initial Reports Vol. 138 (Ocean Drilling Program, 1992).
Kroenke, L. W. et al. Proceedings of the Ocean Drilling Program: Initial Reports Vol. 130 (Ocean Drilling Program, 1991).
Edgar, K. M., Anagnostou, E., Pearson, P. N. & Foster, G. L. Assessing the impact of diagenesis on δ11B, δ13C, δ18O, Sr/Ca and B/Ca values in fossil planktic foraminiferal calcite. Geochim. Cosmochim. Acta 166, 189–209 (2015).
Foster, G. L., Lear, C. H. & Rae, J. W. B. The evolution of pCO2, ice volume and climate during the middle Miocene. Earth Planet. Sci. Lett. 341, 243–254 (2012).
Penman, D. E., Hönisch, B., Zeebe, R. E., Thomas, E. & Zachos, J. C. Rapid and sustained surface ocean acidification during the Paleocene‐Eocene thermal maximum. Paleoceanography 29, 357–369 (2014).
Hönisch, B. & Hemming, N. G. Ground‐truthing the boron isotope‐paleo‐pH proxy in planktonic foraminifera shells: partial dissolution and shell size effects. Paleoceanography 19, PA4010 (2004).
Chaisson, W. P. & Ravelo, A. C. Pliocene development of the east‐west hydrographic gradient in the equatorial Pacific. Paleoceanography 15, 497–505 (2000).
Karnauskas, K. B., Mittelstaedt, E. & Murtugudde, R. Paleoceanography of the eastern equatorial Pacific over the past 4 million years and the geologic origins of modern Galapagos upwelling. Earth Planet. Sci. Lett. 460, 22–28 (2017).
Lisiecki, L. E. & Raymo, M. E. A Pliocene‐Pleistocene stack of 57 globally distributed benthic δ18O records. Paleoceanography 20, (2005).
Zhang, Y. G., Pagani, M., Henderiks, J. & Ren, H. A long history of equatorial deep-water upwelling in the Pacific Ocean. Earth Planet. Sci. Lett. 467, 1–9 (2017).
Ogg, J. G., Gradstein, F. M. & Smith, A. G. (eds.) A Geologic Time Scale 2004 (Cambridge Univ. Press, 2004).
Spezzaferri, S. et al. Fossil and genetic evidence for the polyphyletic nature of the planktonic foraminifera "Globigerinoides", and description of the new genus Trilobatus. PLoS ONE 10, e0128108 (2015).
Martínez-Botí, M. A. et al. Boron isotope evidence for oceanic carbon dioxide leakage during the last deglaciation. Nature 518, 219–222 (2015).
Key, R. M. et al. A global ocean carbon climatology: results from Global Data Analysis Project (GLODAP). Global Biogeochem. Cycles 18, GB4031 (2004).
Olsen, A. et al. GLODAPv2. 2020–the second update of GLODAPv2. Earth Syst. Sci. Data 12, 3653–3678 (2020).
Suzuki, T. et al. PACIFICA Data Synthesis Project (Carbon Dioxide Information Analysis Center, 2013).
Schlitzer, R. Electronic atlas of WOCE hydrographic and tracer data now available. Eos Trans. 81, 45 (2000).
Schlitzer, R. Ocean Data View. (2018). Available at: https://www.odv.awi.de.
Dickson, A. G., Sabine, C. L. & Christian, J. R. Guide to Best Practices for Ocean CO2 Measurements (North Pacific Marine Science Organization, 2007).
Lewis, E. R. & Wallace, D. W. R. Program Developed for CO2 System Calculations (Environmental System Science Data Infrastructure for a Virtual Ecosystem, 1998).
Huang, B. et al. Extended reconstructed sea surface temperature, version 5 (ERSSTv5): upgrades, validations, and intercomparisons. J. Clim. 30, 8179–8205 (2017).
NOAA Climate Prediction Center Internet Team. Cold and Warm Episodes by Season. (2021). Available at: https://origin.cpc.ncep.noaa.gov/products/analysis_monitoring/ensostuff/ONI_v5.php. (Accessed: 22 March 2021)
Zeebe, R. E. & Tyrrell, T. History of carbonate ion concentration over the last 100 million years II: revised calculations and new data. Geochim. Cosmochim. Acta 257, 373–392 (2019).
Foster, G. L. Seawater pH, pCO2 and [CO2−3] variations in the Caribbean Sea over the last 130 kyr: a boron isotope and B/Ca study of planktic foraminifera. Earth Planet. Sci. Lett. 271, 254–266 (2008).
Kiss, E. Ion-exchange separation and spectrophotometric determination of boron in geological materials. Anal. Chim. Acta 211, 243–256 (1988).
Okai, T., Suzuki, A., Kawahata, H., Terashima, S. & Imai, N. Preparation of a new Geological Survey of Japan geochemical reference material: Coral JCp‐1. Geostand. Newsl. 26, 95–99 (2002).
Al-Ammar, A. S., Gupta, R. K. & Barnes, R. M. Elimination of boron memory effect in inductively coupled plasma-mass spectrometry by ammonia gas injection into the spray chamber during analysis. Spectrochim. Acta Part B At. Spectrosc. 55, 629–635 (2000).
Berner, E. K. & Berner, R. A. Global Environment: Water, Air, and Geochemical Cycles (Prentice-Hall, 1996).
Broecker, W. S. & Peng, T. S. Tracers in the Sea (Eldigio, 1982).
Fantle, M. S. & DePaolo, D. J. Sr isotopes and pore fluid chemistry in carbonate sediment of the Ontong Java Plateau: calcite recrystallization rates and evidence for a rapid rise in seawater Mg over the last 10 million years. Geochim. Cosmochim. Acta 70, 3883–3904 (2006).
Lowenstein, T. K., Timofeeff, M. N., Brennan, S. T., Hardie, L. A. & Demicco, R. V. Oscillations in Phanerozoic seawater chemistry: evidence from fluid inclusions. Science 294, 1086–1088 (2001).
Horita, J., Zimmermann, H. & Holland, H. D. Chemical evolution of seawater during the Phanerozoic: implications from the record of marine evaporites. Geochim. Cosmochim. Acta 66, 3733–3756 (2002).
Chalk, T. B. et al. Causes of ice age intensification across the mid-Pleistocene transition. Proc. Natl Acad. Sci. USA 114, 13114–13119 (2017).
Greenop, R. et al. Orbital forcing, ice volume, and CO2 across the Oligocene‐Miocene transition. Paleoceanogr. Paleoclimatology 34, 316–328 (2019).
Sosdian, S. M., Babila, T. L., Greenop, R., Foster, G. L. & Lear, C. H. Ocean carbon storage across the middle Miocene: a new interpretation for the Monterey event. Nat. Commun. 11, 134 (2020).
Evans, D. & Müller, W. Deep time foraminifera Mg/Ca paleothermometry: nonlinear correction for secular change in seawater Mg/Ca. Paleoceanography 27, PA4205 (2012).
Tierney, J. E., Malevich, S. B., Gray, W., Vetter, L. & Thirumalai, K. Bayesian calibration of the Mg/Ca paleothermometer in planktic foraminifera. Paleoceanogr. Paleoclimatology 34, 2005–2030 (2019).
Anand, P., Elderfield, H. & Conte, M. H. Calibration of Mg/Ca thermometry in planktonic foraminifera from a sediment trap time series. Paleoceanography 18, 1050 (2003).
Gray, W. R. et al. Deglacial upwelling, productivity and CO2 outgassing in the North Pacific Ocean. Nat. Geosci. 11, 340–344 (2018).
Lemarchand, D., Gaillardet, J., Lewin, E. & Allegre, C. J. Boron isotope systematics in large rivers: implications for the marine boron budget and paleo-pH reconstruction over the Cenozoic. Chem. Geol. 190, 123–140 (2002).
Simon, L., Lécuyer, C., Maréchal, C. & Coltice, N. Modelling the geochemical cycle of boron: implications for the long-term δ11B evolution of seawater and oceanic crust. Chem. Geol. 225, 61–76 (2006).
Greenop, R. et al. A record of Neogene seawater δ11B reconstructed from paired δ11B analyses on benthic and planktic foraminifera. Clim. Past 13, 149–170 (2017).
Foster, G. L., Pogge von Strandmann, P. A. E. & Rae, J. W. B. Boron and magnesium isotopic composition of seawater. Geochem. Geophys. Geosystems 11, Q08015 (2010).
Shields, C. A. et al. The low-resolution CCSM4. J. Clim. 25, 3993–4014 (2012).
Moore, J. K., Doney, S. C. & Lindsay, K. Upper ocean ecosystem dynamics and iron cycling in a global three‐dimensional model. Global Biogeochem. Cycles 18, GB4028 (2004).
Tan, I., Storelvmo, T. & Zelinka, M. D. Observational constraints on mixed-phase clouds imply higher climate sensitivity. Science 352, 224–227 (2016).
Erfani, E. & Burls, N. J. The strength of low-cloud feedbacks and tropical climate: a CESM sensitivity study. J. Clim. 32, 2497–2516 (2019).
Li, R. L., Storelvmo, T., Fedorov, A. V. & Choi, Y.-S. A positive IRIS feedback: insights from climate simulations with temperature-sensitive cloud–rain conversion. J. Clim. 32, 5305–5324 (2019).
Mauritsen, T. & Stevens, B. Missing iris effect as a possible cause of muted hydrological change and high climate sensitivity in models. Nat. Geosci. 8, 346–351 (2015).
Williams, I. N. & Pierrehumbert, R. T. Observational evidence against strongly stabilizing tropical cloud feedbacks. Geophys. Res. Lett. 44, 1503–1510 (2017).
Sagoo, N. & Storelvmo, T. Testing the sensitivity of past climates to the indirect effects of dust. Geophys. Res. Lett. 44, 5807–5817 (2017).
Thomas, M. D., Fedorov, A. V., Burls, N. J. & Liu, W. Oceanic pathways of an active Pacific meridional overturning circulation (PMOC). Geophys. Res. Lett. 48, e2020GL091935 (2021).
Blanke, B. & Raynaud, S. Kinematics of the Pacific equatorial undercurrent: an Eulerian and Lagrangian approach from GCM results. J. Phys. Oceanogr. 27, 1038–1053 (1997).
Gent, P. R. & Mcwilliams, J. C. Isopycnal mixing in ocean circulation models. J. Phys. Oceanogr. 20, 150–155 (1990).
Van Sebille, E. et al. Lagrangian ocean analysis: fundamentals and practices. Ocean Model. 121, 49–75 (2018).
Arakawa, A. & Lamb, V. R. Computational design of the basic dynamical processes of the UCLA general circulation model. Gen. Circ. Model. Atmos. 17, 173–265 (1977).
Marshall, B. J. et al. Morphometric and stable isotopic differentiation of Orbulina universa morphotypes from the Cariaco Basin, Venezuela. Mar. Micropaleontol. 120, 46–64 (2015).
Raitzsch, M. et al. Boron isotope-based seasonal paleo-pH reconstruction for the Southeast Atlantic – a multispecies approach using habitat preference of planktonic foraminifera. Earth Planet. Sci. Lett. 487, 138–150 (2018).
Guillermic, M. et al. Seawater pH reconstruction using boron isotopes in multiple planktonic foraminifera species with different depth habitats and their potential to constrain pH and pCO2 gradients. Biogeosciences 17, 3487–3510 (2020).
Bartoli, G., Hönisch, B. & Zeebe, R. E. Atmospheric CO2 decline during the Pliocene intensification of Northern Hemisphere glaciations. Paleoceanography 26, PA4213 (2011).
Hönisch, B., Hemming, N. G., Archer, D., Siddall, M. & McManus, J. F. Atmospheric carbon dioxide concentration across the mid-Pleistocene transition. Science 324, 1551–1554 (2009).
Seki, O. et al. Alkenone and boron-based Pliocene pCO2 records. Earth Planet. Sci. Lett. 292, 201–211 (2010).
Sosdian, S. M. et al. Constraining the evolution of Neogene ocean carbonate chemistry using the boron isotope pH proxy. Earth Planet. Sci. Lett. 498, 362–376 (2018).
de la Vega, E., Chalk, T. B., Wilson, P. A., Bysani, R. P. & Foster, G. L. Atmospheric CO2 during the mid-Piacenzian warm period and the M2 glaciation. Sci. Rep. 10, 11002 (2020).
Medina-Elizalde, M. & Lea, D. W. The mid-Pleistocene transition in the tropical Pacific. Science 310, 1009–1012 (2005).
Liu, Z. & Herbert, T. D. High-latitude influence on the eastern equatorial Pacific climate in the early Pleistocene epoch. Nature 427, 720–723 (2004).
Regenberg, M. et al. Global dissolution effects on planktonic foraminiferal Mg/Ca ratios controlled by the calcite‐saturation state of bottom waters. Paleoceanography 29, 127–142 (2014).
Pagani, M., Liu, Z., LaRiviere, J. & Ravelo, A. C. High Earth-system climate sensitivity determined from Pliocene carbon dioxide concentrations. Nat. Geosci. 3, 27–30 (2010).
Conte, M. H. et al. Global temperature calibration of the alkenone unsaturation index (UK′ 37) in surface waters and comparison with surface sediments. Geochem. Geophys. Geosystems 7, Q02005 (2006).
Kim, J.-H. et al. New indices and calibrations derived from the distribution of crenarchaeal isoprenoid tetraether lipids: implications for past sea surface temperature reconstructions. Geochim. Cosmochim. Acta 74, 4639–4654 (2010).
Evans, D., Brierley, C., Raymo, M. E., Erez, J. & Müller, W. Planktic foraminifera shell chemistry response to seawater chemistry: Pliocene–Pleistocene seawater Mg/Ca, temperature and sea level change. Earth Planet. Sci. Lett. 438, 139–148 (2016).
Coggon, R. M., Teagle, D. A. H., Smith-Duque, C. E., Alt, J. C. & Cooper, M. J. Reconstructing past seawater Mg/Ca and Sr/Ca from mid-ocean ridge flank calcium carbonate veins. Science 327, 1114–1117 (2010).
Rausch, S., Böhm, F., Bach, W., Klügel, A. & Eisenhauer, A. Calcium carbonate veins in ocean crust record a threefold increase of seawater Mg/Ca in the past 30 million years. Earth Planet. Sci. Lett. 362, 215–224 (2013).
Dekens, P. S., Lea, D. W., Pak, D. K. & Spero, H. J. Core top calibration of Mg/Ca in tropical foraminifera: refining paleotemperature estimation. Geochemistry, Geophys. Geosystems 3, 1–29 (2002).
Müller, P. J., Kirst, G., Ruhland, G., Von Storch, I. & Rosell-Melé, A. Calibration of the alkenone paleotemperature index U37K′ based on core-tops from the eastern South Atlantic and the global ocean (60° N-60° S). Geochim. Cosmochim. Acta 62, 1757–1772 (1998).
The authors acknowledge and appreciate the aid of J. Robbins, W. Strojie, D. Asael and S. Zhang in supervising clean lab chemistry, boron and trace element analysis, and data processing. The authors also appreciate discussion with J. Rae. This work was supported by NSF Award 1602557 and 170251 to P.M.H., NSF Award 1844380 and 2002448 to N.J.B. and Sloan Ocean Fellowships to P.M.H. and N.J.B. Additional funding to A.V.F. was provided by the Guggenheim Fellowship and the ARCHANGE project (ANR-18-MPGA-0001, France). We acknowledge high-performance computing support from Cheyenne (https://doi.org/10.5065/D6RX99HX) provided by NCAR’s Computational and Information Systems Laboratory, sponsored by the NSF.
The authors declare no competing interests.
Peer review information Nature thanks Kelsey Dyez, Julia Tindall and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Peer reviewer reports are available.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Extended data figures and tables
Extended Data Fig. 1 pCO2 from this study’s western equatorial Pacific (WEP) pH values match previous δ11B-derived studies.
a, b, pCO2 estimates (blue markers and shaded areas showing 68% and 95% confidence intervals) from this study’s pH data from the WEP, a region in equilibrium with the atmosphere37, assuming a modern-like alkalinity of 2,275 ± 200 μmol kg−1 (a) versus a modern-like calcite saturation state (Ω = 5 ± 2 (error bars), Ω = 4 (lower black squares) and Ω = 6 (upper black squares); b). Grey data points show δ11B-deried estimates of pCO2 from previously published studies, with shading showing reported confidence intervals51,84,111,112,113,114,115.
Extended Data Fig. 2 δ11B-reconstructed pH matches model output over 25–75 m depth (top left, bottom); reconstructed pH data from ~3 Ma compared to model output also provided for reference (top right).
a, Modelled pH along the equator (at 55 m depth (red solid and blue dashed lines) and across the 25–75 m depth range (shaded areas)) and δ11B-derived pH (circles with 2σ uncertainty from a Monte Carlo simulation, as in Fig. 2b). Markers placed at their approximate longitudes (159.362°E for western ODP Site 806 and 269.182°E for eastern ODP Site 846). The observed (see Methods) modern gradient in surface pH averaged across the 25–50 m depth range is included for reference (yellow crosses), as well as the range of pH from available modern observations (vertical yellow bars on crosses). b–g, Climatological model output of pH and d11B-reconstructed pH with proxy data (circles) from ~3 Ma instead of ~6 Ma (b, c) and model output (contours) at distinct depths of 25 m ad 55 m (bracketing O. universa’s depth habitat) instead of averaged over the 25–55 m range (d–g). In all panels, more acidic waters (or more acidic waters in the past) are shown in yellow-green colours.
Extended Data Fig. 3 Extended physical oceanographic model output links pH changes to a Pacific meridional overturning circulation.
a–d, Timeseries of PMOC strength (blue lines), zonal Pacific pH gradient (ΔpH, black lines), and zonal Pacific SST gradient (ΔSST, red lines) for the model control run (a, b) and early Pliocene/late Miocene run (c, d). PMOC strength (Max PMOC Streamfunction) is defined as the maximum streamfunction north of 25°N and below 500 m depth in sverdrups (1 Sv = 106 m3 s−1). The pH gradient is defined as the pH difference between a western (5°S–5°N, 150–170°E) and eastern Pacific box (5°S–5°N, 260–280°E), taken at 55 m depth. The SST gradient is defined as the SST difference between the same boxes taken at the surface. Note that while the zonal SST gradient equilibrates within ~500 years in the early Pliocene/late Miocene experiment (d) and is hardly influenced by the appearance of the PMOC between ~800–1,600 years, the zonal pH gradient increases in phase with the PMOC (c). e–h, Zonally averaged streamfunction over the Pacific (e, g) and Atlantic (f, h) basins for the control run (e, f) and early Pliocene/late Miocene (g, h) runs of the model Positive (green values) denote clockwise circulation, and negative (pink) values denote counterclockwise rotation. Panel g is the same as Fig. 4b in the main text.
Extended Data Fig. 4 This study’s ~1 Ma samples fall in different stages of the glacial–interglacial cycles, and δ11B-pH core top calibration used in this study recreates observed ambient pH.
a, b, High-resolution sea surface temperature records from western equatorial Pacific site ODP 806 G. ruber-derived Mg/Ca data116 (a) and eastern equatorial Pacific ODP Site 846 alkenone (UK′37) data117 (b). In both panels the ages of the ~1 Ma samples in this study are overlain as green lines, falling at different points in the glacial–interglacial cycles. c, Core top, net tow, and sediment trap d11B data36,109,110 converted to pH using the calibration of Henehan et al.36 shows good agreement with reported in situ pH. For the odd point to the far right (dark orange, x), Raitzsch et al109. calculated in situ pH using an anomalous low value of alkalinity (~200 μmol kg−1 lower than alkalinity for the location reported in datasets such as GLODAPv266. Recalculating pH using the same in situ temperature and salinity as Raitzsch et al. but an alkalinity value derived from GLODAPv2 (2,325 μmol kg−1) brings the point in agreement with the other data (empty dark orange circle). For the odd point in the lower part of the figure (dark green, x), Guillermic and colleagues110. report an unrealistic value for temperature at this site: ~18 °C whereas the same site (in the central Indian Ocean) appears to be closer to ~26 °C on average according to GLODAPv2. When we re-calculate δ11B-pH derived pH using GLODAPv2’s 26 °C, this brings the point into better agreement with the other data (empty dark green circle). The line of best fit and 2σ shading was calculated with the original odd data points, however, and note that the core top data is still in good agreement with reported in situ pH following this calibration.
a–d, Observed pH (or pH calculated from alkalinity and total dissolved inorganic carbon (DIC)) from all cruises within 5° latitude and longitude of our study sites (pale profiles) during neutral-ENSO (a), El Niño (b) and La Niña conditions (c). Thick lines in panels a–c show average profiles from all stations on a given cruise. d, Average pH-depth profiles from all neutral-ENSO observations. Modern reference values of pH (that is, diamonds on the y axis in Fig. 2) were derived from averaging panel d’s profiles over 25–50 m depth (approximate depth habitat of O. universa). e–g, Modern pH derived from cruise-based observations of alkalinity and total DIC. Data compiled from the GLODAPv2 dataset66 and plotted using the Ocean Data View software (R. Schlitzer, Ocean Data View, https://www.osv.awi.de, 2018). Overlain are this study’s sites (black diamonds) as well as the site of the additional 3 Ma pH values51 included in Fig. 2 (blue square).
Extended Data Fig. 6 An enhanced early Pliocene/late Miocene zonal pH gradient is observed under different treatments of the data.
δ11B-derived pH from O. universa from the east (blue) and west (red) with 2σ uncertainty from a Monte Carlo simulation (empty circles; averages at ~1 Ma, ~3 Ma and ~6 Ma in filled circles) showing: all observations of modern pH used in producing average modern pH reference values (diamonds) given as individual dashes (a), the range of pH from using varied SST records in the pH calculation (grey bars) (b), pH as calculated using the SST record derived from calibrating this study’s Mg/Ca data with the BAYMAG calibration88 (c), and pH as calculated using dissolution-corrected118 Mg/Ca SSTs from this study (yellow squares) (d). In panel b, pH ranges cover pH calculated using: TEX86-derived3 SSTs, Mg/Ca-derived SSTs (this study) using a linear correction for Mg/CaSW, and Mg/Ca-derived SSTs (this study) using a power-law correction87 for Mg/CaSW. Both Mg/Ca-SST calibrations were done using the Mg/CaSW record of Fantle and DePaolo81.
a–c, Mg/Ca-derived SSTs for eastern (blue) and western (red) equatorial Pacific at ~1 Ma, ~3 Ma and ~6 Ma calculated using the O. universa calibration of Anand et al.89, using a linear (dark squares) and power-law (light squares) relationship between Mg/CaSW and Mg/Catest, and using the Bayesian calibration BAYMAG88, also corrected for Mg/CaSW. Error bars denote calibration errors on O. universa calibration (squares) and 95% confidence intervals on the BAYMAG-calibrated data (circles). Dark squares are plotted at corrects ages; other markers are offset for ease of viewing. d–f, δ11B-derived pH at the time points calculated using SST records from UK′377,119 (crosses, using the SST calibration of Conte et al.120), TEX863 (asterisks, using the SST calibration of Kim et al.120), and Mg/Ca data (this study, using the O. universa SST calibration of Anand et al.89) (assuming a linear (circles) and power-law87 (triangles) relationship between Mg/CaSW and Mg/Catest). Note that because the western-site UK′37 record119 (red crosses, bottom panels) only extends back to ~5.3 Ma, we assume the maximum temperature calculable by this calibration (~28.5 °C121) for our western points at ~6 Ma (red crosses, panel f), towards which the record of Pagani et al.119 was trending and had nearly approached even by ~5.3 Ma (~28.3–28.4 °C)). All error bars on pH depict uncertainty (2σ) returned from a Monte Carlo simulation.
Extended Data Fig. 8 Different Mg/Caseawater records influence sea surface temperatures but have only a modest impact on pH.
a, Various published Mg/CaSW reconstructions11,81,88,122 (lines) plotted alongside proxy-based estimates (orange points) from carbonate veins123,124 (orange triangle and diamond) and fluid inclusions82,83 (orange circle and square) with error reported in those studies (where there are error bars). b–d, Using different Mg/CaSW records only slightly affect SSTs and even less so pH results. b, SSTs calculated from T. sacculifer Mg/Ca data1 using the species-specific calibration of Dekens et al.125 and various Mg/CaSW reconstructions11,81,88,122. c, SSTs calculated from O. universa Mg/Ca data (this study) using the species-specific calibration of Anand et al.89 a and various Mg/CaSW reconstructions11,81,88,122. d, δ11B-derived pH (this study) using the various SST reconstructions in panel c. Note that the Mg/CaSW records of O’Brien et al.11 and Evans et al.122 (blue and purple lines in panel a) do note extend back far enough to apply to the ~6 Ma data, ending at ~4.8 Ma and ~5 Ma, respectively.
Extended Data Fig. 9 Different sea surface temperature proxies record varying reductions in the zonal sea surface temperature gradient, and a dissolution correction and different Mg/CaSW record is applied to this study’s data.
a, b, SST records from the eastern (blue) and western (red) equatorial Pacific. a, SST records which evince a collapse of the modern zonal SST gradient include: T. sacculifer Mg/Ca data1 calibrated and corrected for Mg/CaSW with the Bayesian BAYMAG calibration88 with 95% confidence intervals (pale blue and red bands); UK′37 data7,119 using a global ocean annual-mean calibration126 with its associated 1 s.e. (±1.1 °C) (dark blue and red bands, dashed line shows upper saturation limit of the proxy); T. sacculifer Mg/Ca data1 using a species-specific calibration125 and corrected for Mg/CaSW by O’Brien et al.11 (bright blue and red lines, no uncertainty reported); and O. universa Mg/Ca data (this study) using a species-specific calibration89 and the Mg/CaSW record of Fantle and DePaolo81, assuming a linear relationship between Mg/CaSW and Mg/Catest (square markers with calibration error in error bars). Note that the three Mg/Ca records in this panel all use different Mg/CaSW records11,81,88. As the goal of this figure is to depict the range of temperature (and temperature gradient) reconstructions from the literature, we have not standardized them all to the same Mg/CaSW record. b, SST records which evince the modern zonal SST gradient being roughly maintained back into the early Pliocene/late Miocene, derived from TEX86 data3 using the calibration of Kim et al.121, with its associated calibration error (±2.5 °C) (blue and red bands). c, SSTs calculated from O. universa Mg/Ca data in this study both with (solid squares) and without (empty squares) applying the dissolution correction of Regenberg and colleagues118. d, Western equatorial Pacific (WEP) SSTs according to T. sacculifer Mg/Ca data1 (lines) versus O. universa (this study, points). Depending on choice of Mg/CaSW record (light versus darker colours), even T. sacculifer may record cooler-than-modern temperatures in the WEP. Average annual modern WEP SST (from GLODAPv266) given in the dashed line.
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Shankle, M.G., Burls, N.J., Fedorov, A.V. et al. Pliocene decoupling of equatorial Pacific temperature and pH gradients. Nature 598, 457–461 (2021). https://doi.org/10.1038/s41586-021-03884-7
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