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Materials and methods

A total of 343 samples were taken from the upper 550 m in Hole U1352B. The cores consist mainly of unconsolidated mud intercalated with fine sand layers. Sediment was sampled using 20 cm3 plastic tubes. Freeze-dried samples were washed over 125, 250, and 500 µm stacked sieves. From several to ~40 tests of benthic foraminifer N. flemingi were picked from subsamples of the medium to fine sand–size fraction (125–500 µm). Three to six well-preserved tests were selected for isotope analysis from each sample and sonicated repeatedly in methanol for 1–2 min to remove clay-size particles. After removal of impurities from the surfaces of the tests, the tests were broken with a needle and sonicated in methanol to remove internal impurities.

Oxygen and stable carbon isotopic analyses were carried out at the Kochi Core Center using an IsoPrime mass spectrometer. Automated reaction with hot (90°C) phosphoric acid was performed on cleaned samples in individual vials, and the resulting purified CO2 gas was fed directly into the mass spectrometer. Oxygen isotope results are expressed as per mil (‰) relative to the Vienna Peedee belemnite standard. We measured 21 samples for each measurement cycle. We measured four working standards (NBS 19; δ18O = –2.2‰ and δ13C = 1.95‰) at the beginning of each measurement cycle, one additional standard every seven samples, and three further standards at the end of the measurement cycle. Analytical precision is better than 0.14‰ for δ18O and 0.07‰ for δ13C. We made 369 measurements on the 343 samples because we replicated measurements for 24 of the samples (Tables T1, T2).