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doi:10.2204/iodp.proc.342.203.2017

Methods

Shipboard age models suggested sedimentation rates generally greater than 2 cm/ky in megasplice drift sequences at Sites U1411 and U1408 and less than 2 cm/ky in pelagic deposits at Sites U1406 and U1409 (see Fig. F53 in the “Expedition 342 summary” chapter [Norris et al., 2014a]). To capture orbital variability, we sampled every 2–3 thousand years (ky) in the drift deposits (i.e., Sites U1408 and U1411) and every ~5 ky in the pelagic sequences (i.e., Sites U1406 and U1409), based on shipboard sedimentation rate estimates and age models. By site, ESIC sampling included 1807 samples from Site U1411; 1550 samples from Site U1406; 5300 samples from Site U1408, and 2172 samples from Site U1409, most of which were sampled during the postcruise sampling party (February 2013 at the Bremen Core Repository [Germany]).

ESIC samples were distributed among 10 primary groups in six countries: H.K. Coxall, Stockholm University (Sweden); O. Friedrich, Universität Heidelberg (Germany); P.M. Hull, Yale University (USA); S.K. Turner, University of California Riverside (USA); K. Moriya, Waseda University (Japan); R.D. Norris, Scripps Institution of Oceanography (USA); B.N. Opdyke, Australian National University (Australia); P.F. Sexton, Open University (UK); P.A. Wilson, National Oceanography Centre Southampton (UK); and J.C. Zachos, University of California Santa Cruz (USA).

To provide consistency across the consortium, a common sample preparation protocol was developed. Samples were dried (in an oven at ~55°C or freeze-dried), massed, disaggregated in deionized water (DI water; typically for 1–12 h), washed in DI water over a 63 µm sieve, and redried. Samples that were difficult to wash (i.e., not clean within 30 min of misting with DI water) were rewashed. Rewashing involved a several hour soak in boron-free disaggregating solution (dilute sodium metaphosphate solution [20 g/10 L DI water] buffered to pH of 7–7.5) and up to 30 min of DI mist-washing on a 63 µm sieve. Drift sediments commonly required two washes, and those in the deeper sections of Site U1408 washed in the Hull and Zachos laboratories often required three to four such repeats. Samples were rinsed with ethanol (denatured). After drying (at 55°C), the greater than 63 µm size fraction (coarse fraction) was weighed and, with the sample dry weight mass, used to calculate wt% CF. It should be noted that we are technically measuring the mass percent coarse fraction, not the wt% CF. We use the term wt% CF here for consistency with paleoceanographic common usage (however technically incorrect it may be) and for linguistic consistency with other parameters measured shipboard, like weight percent carbonate (wt% carbonate), that are also properly mass percents.

Samples were then split equally into a geochemistry fraction (for benthic and planktonic foraminiferal stable isotope and trace metal geochemistry) and a faunal fraction for biotic studies. In some sections with very low wt% CF (see below) or low numbers of the target benthic species, faunal splits were not made.

Exceptions to the standard ESIC washing protocols were made by various groups based on local equipment availability, protocols, and scientific priorities, and are listed here as follows:

• Stockholm University: Followed protocol, except that samples were not split into faunal and geochemistry fractions because the late Eocene material from Sites U1411 and U1406 contained typically <2% coarse fraction and thus low numbers of benthic foraminifers. Efforts were made to keep a record of every specimen removed, and any unused specimens were returned to the vials.
• Heidelberg University: Followed protocol, except for drying oven temperature (set to 40°C).
• Yale University: None. Followed protocol for Hull, Norris, and Penman sample requests.
• University of California Riverside: Followed protocol, except samples were not rinsed in alcohol at any point and samples were not split into benthic and faunal fractions. Efforts were made to keep a record of every specimen removed, and any unused specimens were returned to the vials. All samples were washed until clean in a single wash (no second washes).
• Waseda University: Followed protocol, except for drying oven temperature (set to 50°C) after washes (initial sediments were freeze-dried). Washing was notably gentle, as electric foggers filled with DI water were used for mist-washing.
• Scripps Institution of Oceanography: None. All samples washed at Yale University (Hull Laboratory), and Yale followed protocol.
• Australian National University: Used several washing protocols optimized for local project goals and site-specific differences in lithology. Throughout, samples were washed in DI water and dried in a 35°–40°C oven. Site U1408 samples were initially washed according to four size fractions (<63, 63–100, 100–200, and >200 µm), a procedure that was quickly changed to saving the fine fraction (<63 µm sediment) and washing two independent splits (63–200 and >200 µm). Site U1408 >200 µm fractions were typically washed in three wash/dry cycles, and the 63–200 µm fractions were washed in 7–8 three wash/dry cycles. Site U1406 sample washing protocols differ from the final Site U1408 protocols in three ways. Calgon (a brand-name water softener similar in washing effect to the boron-free sodium metaphosphate solution used by other groups), diluted to 1 g Calgon/100 mL, was used. Samples were also ultrasonicated for 5 s between washes. Typical Site U1406 samples required 10 wet/dry cycles to clean the 63–200 µm fraction.
• Open University: None. Followed protocol.
• National Oceanography Centre Southampton: Followed protocol, except for the ethanol rise; samples were not rinsed in alcohol at any point.
• University of California Santa Cruz: Followed protocol, except samples were dried at room temperature.

All samples are listed in COARSE_FRACTION.csv in SPLICE in “Supplementary material” with the responsible principal investigator (PI). In the text, when referring to specific wt% CF values, we report the mean and standard deviation as mean ± standard devation %. For instance, an interval with a mean wt% CF of 3 and standard deviation of 1.5 would be reported as 3% ± 1.5%.

Shipboard splicing within drift deposits proved difficult in many intervals due to low magnetic susceptibility and (apparently) high lateral variability in sedimentation rates and the continuity of sedimentation. XRF scans of Fe at 10 kV were used to generate a revised spliced depth scale (meters composite depth [mcd]) for Sites U1408 and U1409 that we use here (see 342_REV_SPLICE in SPLICE in “Supplementary material”). For Sites U1406 and U1411, we use the shipboard splices (see 342_SPLICE in SPLICE in “Supplementary material”) and the corresponding site reports (see the “Site U1406” and “Site U1411” chapters [Norris et al., 2014b, 2014e). The splice from Site U1408 is still under revision and is being considered with a direct comparison with Site U1410, particularly for Magnetochrons C18, C19, and C20r. COARSE_FRACTION.csv in SPLICE in “Supplementary material” provides the original sample ID, meters below seafloor (mbsf; also known as core depth below seafloor, or CSF-A, in other Expedition 342 publications), current meters composite depth as described above (also known as core composite depth below seafloor, or CCSF, in other Expedition 342 publications), and shipboard bio- and magnetostrat-derived age models for every sample. Sample IDs for all shipboard stratigraphic tie points were obtained from the relevant site reports (see the “Site U1406,” “Site U1408,” “Site U1409,” and “Site U1411” chapters [Norris et al., 2014b, 2014c, 2014d, 2014e]). Several inconsistencies in the meters below seafloor assignments in the shipboard reports were identified by P. Blum on review, so we updated all assignments for the sample IDs of the stratigraphic tie points using the Laboratory Information Management System (LIMS) Report system (http://web.iodp.tamu.edu/LORE/). These updated meters below seafloor values are listed in BIO_PMAG_TIE_POINTS.csv in SPLICE in “Supplementary material,” and this table should be used for the generation of further “shipboard” age models. The midpoint depth of biostratigraphic datums and magnetostratigraphic boundaries were translated from meters below seafloor to meters composite depth using the updated splices (where applicable) as described above. Shipboard-like age models were then calculated via linear interpolation between these tie points. Here we calculate all sedimentation rate statistics (that is, interval averages and trends) based on sample specific values provided in COARSE_FRACTION.csv in SPLICE in “Supplementary material.” Multitaper Method (MTM) spectral analysis was performed on a (polynomial; period 500 ky) detrended subset of samples across Magnetochron C20n at Site U1408 (Yale interval) using the astrochron package in R.

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