Tanzania Eocene-Oligocene d11B Data and PCO2atm Reconstruction ----------------------------------------------------------------------- World Data Center for Paleoclimatology, Boulder and NOAA Paleoclimatology Program ----------------------------------------------------------------------- NOTE: PLEASE CITE ORIGINAL REFERENCE WHEN USING THIS DATA!!!!! NAME OF DATA SET: Tanzania Eocene-Oligocene d11B Data and PCO2atm Reconstruction LAST UPDATE: 11/2009 (Original receipt by WDC Paleo) CONTRIBUTOR: Paul N. Pearson, Cardiff University IGBP PAGES/WDCA CONTRIBUTION SERIES NUMBER: 2009-121 WDC PALEO CONTRIBUTION SERIES CITATION: Pearson, P.N., et al. 2009. Tanzania Eocene-Oligocene d11B Data and PCO2atm Reconstruction. IGBP PAGES/World Data Center for Paleoclimatology Data Contribution Series # 2009-121. NOAA/NCDC Paleoclimatology Program, Boulder CO, USA. ORIGINAL REFERENCE: Pearson, P.N., G.L. Foster, and B.S. Wade. 2009. Atmospheric carbon dioxide through the Eocene-Oligocene climate transition. Nature, Vol 461, pp. 1110-1113, 22 October 2009. doi:10.1038/nature08447 ABSTRACT: Geological and geochemical evidence indicates that the Antarctic ice sheet formed during the Eocene-Oligocene transition, 33.5-34.0 million years ago. Modelling studies suggest that such ice-sheet formation might have been triggered when atmospheric carbon dioxide levels (pCO2atm) fell below a critical threshold of 750 p.p.m.v., but the timing and magnitude of pCO2atm relative to the evolution of the ice sheet has remained unclear. Here we use the boron isotope pH proxy on exceptionally well-preserved carbonate microfossils from a recently discovered geological section in Tanzania to estimate pCO2atm before, during and after the climate transition. Our data suggest that a reduction in pCO2atm occurred before the main phase of ice growth, followed by a sharp recovery to pre-transition values and then a more gradual decline. During maximum ice-sheet growth, pCO2atm was between 450 and 1,500 p.p.m.v., with a central estimate of 760 p.p.m.v. The ice cap survived the period of pCO2atm recovery, although possibly with some reduction in its volume, implying (as models predict) a nonlinear response to climate forcing during melting. Overall, our results confirm the central role of declining pCO2atm in the development of the Antarctic ice sheet (in broad agreement with carbon cycle modelling) and help to constrain mechanisms and feedbacks associated with the Earth's biggest climate switch of the past 65 Myr. ADDITIONAL REFERENCES: Anand, P., H. Elderfield, and M.H. Conte. 2003. Calibration of Mg/Ca thermometry in planktonic foraminifera from a sediment trap time series. Paleoceanography 18, 1050, doi:10.1029/2002PA000846. Foster, G.L. 2008. Seawater pH, pCO2 and [CO32-] variations in the Caribbean Sea over the last 130 kyr: a boron isotope and B/Ca study of planktic foraminifera. Earth Planet. Sci. Lett., Vol. 271, pp. 254–266. Key, R.M., et al. 2004. A global ocean carbon climatology: results from Global Data Analysis Project (GLODAP). Glob. Biogeochem. Cycles 18, GB4031, doi:10.1029/2004GB002247. Wilkinson, B.H. and T.J. Algeo. 1989. Sedimentary carbonate record of calcium-magnesium cycling at the Earth's surface. Am. J. Sci. 289, 1158–1194. GEOGRAPHIC REGION: East Africa PERIOD OF RECORD: Eocene-Oligocene transition, 33.5-34.0 MYrBP FUNDING SOURCE: Natural Environment Research Council (NERC) UK, grants to P.N.P., B.S.W., and G.L.F. DESCRIPTION: Boron isotope (d11B) data from upper-ocean planktonic foraminifera (Turborotalia ampliapertura, 212–250 mm) in sediments of the Kilwa Group, Tanzania. Reconstructed ocean pH based on the d11B data, plus inferred dissolved CO2 concentration (CO2aq) and pCO2atm. Foraminifera collected from Tanzania Drilling Project sites 12 (total depth 147.44m) and 17 (total depth 125.9m), approximately 4 km apart. TDP Site 12: UTM 37L 560222 8981309 (~39.548şS, ~9.215şE) TDP Site 17: UTM 37L 560539 8984483 (~39.551şS, ~9.186şE) DATA: 1. Table 1. Boron isotopic data T. ampliapertura (212-250 um) from TDP12 and TDP17 across the Eocene-Oligocene Transition pCO2atm (ppm)*i pCO2atm (ppm)*j Composite Age d11Bm-1 d11Bm-2 d11BmAv d11Bav-c [B] Temperature pH (total scale) *h Variable [CO32-] Constant [CO32-] Sample depth(m)*a C&K95*b (‰)*c 2se (‰)*c 2se (‰)*c (‰)*d 2se ng*f (şC)*g sw=37‰ sw=38‰ sw=39‰ surf.umol/kg sw=37‰ err+ err- sw=38‰ err+ err- sw=39‰ err+ err- surf.umol/kg sw=37‰ err+ err- sw=38‰ err+ err- sw=39‰ err+ err- TDP17/13/2 0-50cm 42.70 32.98 14.70 0.13 14.73 0.14 14.72 14.76 0.23 3 27.9 7.95 7.84 7.71 119 378 38 44 624 73 86 1142 162 202 119 378 40 41 624 76 82 1142 169 193 TDP17/19/1 0-50cm 59.70 33.17 14.47 0.15 14.09 0.17 14.28 14.31 0.23 4 28.5 7.89 7.77 7.63 115 457 49 57 786 100 121 1545 247 318 119 476 54 56 819 109 120 1609 266 319 TDP17/26/1 40-90c 75.45 33.33 13.94 0.09 13.86 0.10 13.90 13.93 0.22 6 29.0 7.84 7.71 7.55 125 615 68 80 1105 148 181 2346 407 538 119 589 69 72 1060 147 165 2249 402 498 TDP12/11/2 0-50cm 94.25 33.47 13.78 0.11 13.78 0.11 13.78 13.81 0.22 22 27.5 7.85 7.71 7.54 125 635 73 86 1160 162 201 2534 465 628 119 609 73 78 1112 162 184 2429 459 582 TDP17/34/2 0-50cm 99.15 33.59 14.33 0.08 14.31 0.11 14.32 14.34 0.22 17 27.9 7.90 7.78 7.64 115 445 46 54 763 94 113 1492 231 295 119 463 51 53 795 103 112 1554 249 295 TDP12/21/3 20-50c 125.40 33.96 13.73 0.16 14.03 0.17 13.88 13.93 0.23 25 29.8 7.83 7.71 7.54 106 533 62 73 959 134 166 2038 369 495 119 600 73 78 1079 157 178 2291 427 538 TDP12/32/1 0-50cm 154.70 34.21 13.86 0.23 13.69 0.18 13.78 13.81 0.23 8 29.7 7.82 7.69 7.52 110 589 70 83 1074 155 194 2345 443 605 119 637 79 85 1163 174 201 2539 494 635 TDP12/40/3 0-50cm 179.50 34.42 13.95 0.34 13.59 0.31 13.77 13.86 0.36 8 30.1 7.82 7.69 7.53 110 577 100 130 1046 217 304 2254 599 958 119 625 112 136 1133 241 320 2441 660 1015 TDP12/47/3 0-50cm 204.70 34.63 14.14 0.38 13.92 0.34 14.03 14.10 0.39 12 29.2 7.86 7.74 7.58 110 498 90 118 876 187 263 1791 477 763 119 539 100 123 949 207 277 1940 526 808 *a Composite depth in metres from Foster 2008. *b Age in Ma on timescale of Key et al 2004. *c Two measurements of d11B of T. ampliapertura and their average. 2se is the 2*standard error for each analysis = internal precision at 95% confidence. *d Blank corrected d11B of T. amplipertura. The blank correction was based on measured sample size and a total proceedural blank (d11B = +5 ‰, [B] = 50 pg) processed and measured at the same time. In all cases the blank correction is small but deemed necessary to ensure accuracy. *e Uncertainty at 95% confidence on d11B of T. ampliapertura. This figure represents either our external precision based on repeat measurements of our in house carbonate standard (ħ0.22 ‰; 2sd) or an average of the internal precisions of the two measurements if this is larger. Also includes a propagation of the uncertainty in the blank correction (d11B = +0-10 ‰, [B] = 30 to 70 pg). *f Sample size in ng's. *g Temperature calculated from tandem measurements of Mg/Ca and as described in text. *h pH (total scale) calculated from the blank corrected d11B, temperature, and salinity of 35 psu, for three values of seawater d11B (37, 38, 39 ‰). *i pCO2atm (ppm) calculated from d11B derived pH for the different seawater d11B values (37, 38, 39 ‰). [CO32-] mmol/kg is determined from a simple box model as described in the text. Uncertainty in this estimate are calculated from a propagation of the measurement uncertainties on d11B. *j pCO2atm (ppm) calculated from d11B derived pH for the different seawater d11B values (37, 38, 39 ‰). [CO32-] mmol/kg is held constant at late Oligocene values. Uncertainty in this estimate are calculated from a propagation of the measurement uncertainties on d11B. 2. Table 2. Mg/Ca data for samples from TDP12 and TDP17 Composite Age Mg/Ca *c Temperature Sample depth(m)*a (C&K'95)*b (mmol/mol) (şC)*d Turborotalia ampliapertura (212-250 um)*e TDP17/13/2 0-50cm 42.70 32.98 4.133 28.1 TDP17/13/2 0-50cm 42.70 32.98 3.961 27.8 TDP17/19/1 0-50cm 59.70 33.17 4.188 28.3 TDP17/19/1 0-50cm 59.70 33.17 4.285 28.6 TDP17/26/1 40-90cm 75.45 33.33 4.660 29.6 TDP17/26/1 40-90cm 75.45 33.33 4.729 29.6 TDP17/26/1 40-90cm 75.45 33.33 4.048 27.9 TDP12/11/2 0-50cm 94.25 33.47 4.027 27.9 TDP12/11/2 0-50cm 94.25 33.47 3.779 27.2 TDP12/11/2 0-50cm 94.25 33.47 3.822 27.2 TDP12/11/2 0-50cm 94.25 33.47 3.923 27.7 TDP17/34/2 0-50cm 99.15 33.59 4.287 28.6 TDP17/34/2 0-50cm 99.15 33.59 3.934 27.7 TDP17/34/2 0-50cm 99.15 33.59 3.863 27.4 TDP12/21/3 20-50cm 125.40 33.96 4.740 29.8 TDP12/32/1 0-50cm 154.70 34.21 4.697 29.7 TDP12/40/3 0-50cm 179.50 34.42 4.863 30.1 TDP12/47/3 0-50cm 204.70 34.63 4.516 29.2 Dentoglobigerina cf. tapuriensis (250-300 um)*f TDP/17/13/2 0-20cm 42.70 32.98 3.898 27.5 TDP/17/13/2 0-20cm 42.70 32.98 3.843 27.4 TDP/17/19/1 0-10cm 59.70 33.17 3.493 26.3 TDP/17/19/1 0-10cm 59.70 33.17 3.485 26.3 TDP/12/11/2 0-10cm 94.25 33.47 3.570 26.6 TDP/12/11/2 0-10cm 94.25 33.47 3.581 26.6 TDP/17/34/2 0-10cm 99.15 33.59 3.643 26.8 TDP/17/34/2 0-10cm 99.15 33.59 3.626 26.7 TDP/12/21/3 20-50cm 125.40 33.96 3.792 27.2 TDP/12/21/3 20-50cm 125.40 33.96 3.828 27.3 TDP/12/32/1 0-20cm 154.70 34.21 3.654 26.8 TDP/12/32/1 0-20cm 154.70 34.21 3.724 27.0 TDP/12/40/3 0-20cm 179.50 34.42 4.057 28.0 TDP/12/40/3 0-20cm 179.50 34.42 4.096 28.1 TDP/12/47/3 0-30cm 204.70 34.63 3.806 27.3 TDP/12/47/3 0-30cm 204.70 34.63 3.826 27.3 Hantkenina spp. (250-300 um)*f TDP/12/21/3 20-50cm 125.40 33.96 4.498 29.1 TDP/12/21/3 20-50cm 125.40 33.96 4.497 29.1 TDP/12/32/1 0-20cm 154.70 34.21 4.675 29.6 TDP/12/32/1 0-20cm 154.70 34.21 4.616 29.4 TDP/12/40/3 0-20cm 179.50 34.42 4.323 28.7 TDP/12/40/3 0-20cm 179.50 34.42 4.311 28.7 TDP/12/47/3 0-30cm 204.70 34.63 4.227 28.4 TDP/12/47/3 0-30cm 204.70 34.63 4.206 28.4 *a Composite depth in metres from Foster 2008. *b Age in Ma on timescale of Key et al. 2004. *c Uncertainty in the measured Mg/Ca ratio is 2% based on long reproducibility of consistency standards over the duration of this study. *d Temperature calculated using the generic temperature equation from Anand et al. 2003 and assuming a Mg/Ca ratio of 4.3 mol/mol (Wilkinson and Algeo 1989). *e Samples from the same depth are full procedral replicates *f Samples from the same depth are repeat analyses of the same dissolution