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Materials and methods

We picked 36 samples for microscopic analysis of calcareous nannofossils every 0.83 to 4.52 m, with an average spacing of 1.5 m or one sample per section, from 180.4 to 122.37 m in Hole U1352B (Table T1) to determine the HO of P. lacunosa (Zone NN20/NN19).

Smear slides were examined under a polarized microscope at 1250× magnification. Three hundred calcareous nannofossils were identified to species level in each slide. The total abundance of calcareous nannofossils was defined as follows:

  • A = abundant; usually >10 specimens observed per field of view (FOV).
  • C = common; 1–10 specimens per FOV.
  • F = few; 1 specimen per FOV.
  • R = rare; 1 specimen per 1–10 FOVs.
  • VR = very rare; <1 specimen per 10 FOVs.
  • B = barren; no nannofossils.

Calcareous nannofossil preservation was recorded using the following criteria (see the “Methods” chapter [Expedition 317 Scientists, 2011a]):

  • M = moderate; some etching and/or recrystallization; primary morphological characteristics partially altered; most specimens identifiable at the species level.
  • P = poor; specimens severely etched or overgrown; primary morphological characteristics largely destroyed; fragmentation evident; most specimens not identifiable at the species and/or generic level.

Analyses of oxygen and stable carbon isotope ratios of benthic foraminifer N. flemingi were carried out on 23 samples from 62–68 m, 8 samples from 95–100 m, 41 samples from 123–151 m, 20 samples from 197–202 m, 21 samples from 247–253 m, 22 samples from 426–432 m, and 42 samples from 446–456 m. A total of 177 samples were measured. The spacing between our new measurements ranges from a minimum of 0.2 m to a maximum of 1.45 m and averages 0.5 m for 123–151 m, where the focus was on the HO of P. lacunosa and MIS 12 (Table T2). This 0.5 m sample interval represents ~3300 y.

Several U. perigrina tests were picked from each of 88 samples from Hole U1352B between 156.4 and 501 m. We measured their oxygen and carbon isotope ratios and compared the ratios with those of N. flemingi from the same horizons (Table T3).

Oxygen and stable carbon isotopic analyses were carried out at the Kochi Core Center using an IsoPrime mass spectrometer. We used the same sample preparation and analytical procedures as Hoyanagi et al. (2014). Analytical precision is better than 0.08‰ for δ18O and 0.05‰ for δ13C.