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doi:10.2204/iodp.proc.346.202.2018

Methods and materials

This study is based on 455 samples that were collected at almost uniform intervals within Holes U1427A, U1427B, and U1427C. Sample preparation for light microscopy observation was conducted as follows:

Freeze-dried sediment samples were weighed and treated with 10% H₂O₂ and 10% HCl solution to remove organic matter and calcium carbonate, respectively.
The samples were then wet sieved and rinsed using a 45 µm mesh sieve, after which two types of slides were made of the residue for two purposes: quantify abundance (Q-slide) and faunal analysis (F-slide).
To prepare Q-slides, residue was transferred to a 200 mL beaker containing 100 mL of water. The solution was then mixed well, after which a 0.5 mL sample was taken from the suspension using a micropipette and dropped onto a glass slide. The sample was then dried and mounted with Norland optical adhesive and covered with a 22 mm × 18 mm cover glass.
F-slides were made from the remaining residue in the beaker. Because our samples had large lithogenic grain content, opal particles were extracted from the residue using the elutriation method (Itaki, 2006). The extracted particles were mounted with Norland optical adhesive and covered with 22 mm × 36 mm cover glasses. The adhesive was solidified by placing the slide under UV light for ~15 min.
Slides were partially examined at 50× to 400× for stratigraphic markers and other common taxa under a Zeiss Axio imager microscope.

The total number of radiolarians in 1 g of dry sediment was estimated using the following equation:

Relative abundance (percent of total assemblage) of subtropical species was estimated by counting and identifying more than 200 individuals on the F-slide; however, when radiolarian individuals were scarce, as many as could be identified were counted. The absolute abundance of subtropical species (individuals/g) was converted using the following equation:

Although very few counts often cause inaccurate relative percent data, the absolute abundance (individuals/g) estimated from the few counts shows low values regardless of count numbers. Therefore, the absolute abundance is used for illustrating abundance changes of subtropical species in this report (Table T1).

For key species used as biostratigraphic datums, their occurrence or absence was checked over the entire slide (Table T1). Taxonomic framework was adapted from Itaki et al. (2007) and Matsuzaki et al. (2014).

This report follows the Geological Time Scale 2012 (GTS 2012) of Gradstein et al. (2012).

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