Samples were collected during Ocean Drilling Program (ODP) Leg 198, three holes were drilled at Site 1209 (Shatsky Rise, N. Pacific 32°39.1081'N, 158°30.3564'E) at a water depth of 2387 m [Bralower et al., 2002], equivalent to a paleodepth during the PETM of ~ 1900 m [Takeda and Kaiho, 2007].
Sediment samples, collected at 1-3 cm resolution across a 2m interval spanning the carbon isotope excursion (CIE), were washed and sieved, and specimens of the mixed-layer dwelling planktic species Morozovella velascoensis and Acarinina soldadoensis were picked from the 250-300 and 300-425 µm size fraction. On the basis of shell size-d13C relations, these species likely harbored photosynthetic algal symbionts and were thus restricted to the photic zone of the surface ocean [D’Hondt et al., 1994]. Additionally, specimens of the smooth-walled, thermocline-dwelling genus Subbotina were picked from the 250-300 µm size fraction. Isotopic depth ranking suggests that this taxon was nonsymbiotic and occupied the thermocline [Berggren and Norris, 1997]. Boron isotope analyses at Site 1209 were restricted to M. velascoensis and complemented by low-resolution d11B analyses of the same taxon from Sites 1263 (Walvis Ridge, Southeast Atlantic, 28°31.98'S, 02°46.77'E, 2717 m depth; paleodepth ~1500 m; [Zachos et al., 2004]) and 865 (Allison Guyot, Equatorial Pacific, 18°26.41'N, 179°22.24'W, 1518 m depth; paleodepth ~ 1400 m; [Bralower et al., 1995]) to evaluate whether the Site 1209 record is representative of a global signal or compromised by local or preservational effects.
Trace element data are generated from a Finnegan Element XR Inductively Coupled Plasma Mass Spectrometer monitoring masses 11B, 24Mg, 43Ca, 55Mn (to detect contamination from Fe, Mn oxides), and 238U. Inter- and intra- run variability will be assessed utilizing both a solid foraminiferal standard (mixture of crushed foraminifera that will be cleaned as samples) and a liquid consistency standard of similar composition as the dissolved foraminifera. The solid foraminiferal consistency standard composed of crushed and homogenized Globigerinoides sacculifer from core top KNR 110 2-58 STN40-2 (without final sac; B/Ca = 92 +- 8 µmol/mol). 13C and 18O data from the dual Inlet gas source mass spectrometer systems at the University of California Santa Cruz – Stable Isotope Laboratory are measured against reference gases which have been calibrated relative to international reference materials (NBS-19, NBS-18) obtained from the National Institute of Standards and Technology (NIST) and the International Atomic Energy Agency (IAEA) to ensure accurate measurement and reporting of isotope ratios for the selected samples. These same international standards are analyzed on a daily basis, typically at the start and finish of each analytical round. In addition, internal laboratory standards are analyzed at a much greater frequency during each analytical round to assess data quality during the course of each analytical round. The analytical error on standards measured during the course of analyses conducted for this project will be monitored and reported for each analytical round.
Boron isotope data will be generated from a Thermo TRITON Thermal Ionization Mass Spectrometer at LDEO and from Thermo NEPTUNE multi-collector inductively coupled mass spectrometers at UC Santa Cruz and LDEO. Sample preparation for all analyses will be done in a boron filtered ultraclean environment, to avoid laboratory contamination. The international boric acid standard NBS 951 obtained from NIST is routinely measured on the TIMS with each sample wheel and shows no long-term drift for this method. MC-ICP-MS analyses are subject to daily drift and standard bracketing with NBS 951 will be applied to monitor and correct for drift. Additional routine in-house standards include NBS 951 precipitated in a CaCO3 matrix and seawater. For MC-ICP-MS analyses a natural carbonate from the Geological Survey of Japan (GSJ) geochemical reference sample collection will be used as an additional standard to monitor B purification consistency. Despite standardization to the same boric acid standard, absolute 11B values by TIMS are often higher than those measured by MC-ICP-MS. However, Fig. 4 and an international laboratory intercomparison study (Foster, Hönisch et al., in prep.) confirm that the TPI 7220824 relative difference in foraminiferal and coral 11B over the same pH-difference (determined from laboratory cultures and glacial/interglacial sediment samples) is the same for both methods, thus allowing for sound comparison of data from both methods, as long as method-specific calibrations are applied. 11B of the foraminifer species used in this study can thus be calibrated with Paleocene (pre-CIE) samples using both techniques, and the same slope and inflection point of the delta-11B/pH relationship (Fig. 4) will then be applied to estimate the pH-change during and after the PETM relative to the Paleocene baseline.
c) Organization and progression of trace metal and isotope analysis
- Analysis of B/Ca, Mg/Ca, Mn/Ca and U/Ca will take place at the UCSC Marine Analytical Laboratory.
- Analysis of delta-13C and delta-18O will take place at the UCSC-SIL.
- Analysis of delta-11B will take place at the LDEO.
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