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doi:10.2204/iodp.proc.323.203.2016

Methods and materials

0–64 m CCSF-A (MIS 1–6)

A total of 336 subsamples (40 cm³) were taken from Cores 323-U1344A-1H through 6H, 323-U1344D-1H through 7H, and 323-U1344E-1H through 6H following the site’s composite depth scale (0–64 m CCSF-A) at a sample spacing of 10 cm. Sediment samples were freeze-dried and washed on a 63 µm mesh sieve and then dried in an oven at 40°C. Dry samples were sieved through a 250 µm mesh. Two benthic foraminiferal species, Uvigerina senticosa and Elphidium batialis, were picked for isotope measurements. Both species are shallow infauna (Bubenshchikova et al., 2008; Asahi et al., in press). Three specimens of each species were used for each measurement. Brownish shells were excluded.

64–750 m CCSF-A (Pleistocene)

A total of 145 samples with an individual volume of 30–40 cm³ and spanning the overall stratigraphic section recovered at Site U1344 (746.6 m) were taken from Holes U1344A and U1344D at a sampling resolution of four samples per core (each core is approximately 9.5 m long). Shipboard results (see the “Site U1344” chapter [Expedition 323 Scientists, 2011b]) suggested that multiple species would be necessary to obtain a complete and continuous isotope record spanning the ~750 m section recovered from Hole U1344A because not a single benthic foraminifer species occurred abundantly and uninterruptedly throughout the cored sediment sequence. Therefore, the two most ubiquitous and abundant foraminifers (E. batialis and Valvulineria sadonica) were used to generate the isotope record. In samples where these taxa are absent or occur in very low abundance, the species U. senticosa, Globobulimina pacifica, and Nonionella labradorica were selected. Planktonic foraminifers are present and very low in abundance overall, and a planktonic oxygen isotope stratigraphy could not be established.

Cleaning procedures and stable isotopic analyses

Stable isotopic analyses were carried out at two different laboratories: the Center for Advanced Marine Core Research at Kochi University, Japan (KOCHI), and the Stable Isotope Geoscience Facility at Texas A&M University, USA (TAMU).

Cleaning of benthic foraminiferal shells followed a conventional procedure: crushing and cleaning by ultrasonification with 99.5% methyl alcohol and Milli-Q water (Asahi et al., in press). The cleaning steps were repeated two times. After confirming under a stereo microscope that all dirt had been removed, shells were rinsed in Milli-Q water and dried in an oven at 40°C overnight.

Dried samples used for the high-resolution section were analyzed using IsoPrime mass spectrometry with the Multicarb preparation system at Kochi University along with part of the samples from the low-resolution section. Analyses were calibrated to the NBS-19 standard (δ¹³C = +1.95‰, Vienna Peedee belemnite [VPDB]; δ¹⁸O = –2.20‰, VPDB), and the average analytical errors for δ¹³C and δ¹⁸O were less than 0.06‰ and 0.10‰, respectively. Benthic foraminifer samples used from the low-resolution section were measured on a KIEL IV carbonate device coupled to a 10 kV Thermo Scientific MAT 253 isotope ratio mass spectrometer at TAMU. The external precisions of the KIEL IV for δ¹³C and δ¹⁸O are 0.03‰ and 0.07‰, respectively.

The oxygen isotope species–specific offset between U. senticosa and E. batialis at Site U1344 was calculated at 0.9‰ ± 0.2‰ (1σ, N = 127), which is very close to the offset (0.82‰ ± 0.22‰) calculated between these species at nearby Site U1343 (Asahi et al., in press). Therefore, to correct the species-specific offset, δ¹⁸O values of E. batialis were adjusted by +0.9‰.

Age model

The age model for the uppermost 64 m CCSF-A at Site U1344 was established by correlating the derived composite δ¹⁸O record to the LR04 global stack (Lisiecki and Raymo, 2005). The comparison was made using the dynamic “MATCH 2.3” program (Lisiecki and Lisiecki, 2002). Prior to matching, all data were normalized. No biostratigraphic- or magnetostratigraphic-based age-depth tie points were provided prior to the matching process. The age model for the remaining part of the record (from ~64 to ~800 mbsf) is from shipboard stratigraphy (see the “Site U1344” chapter [Expedition 323 Scientists, 2011b]).

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