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Methods and materials

A total of 279 samples were examined from Holes U1334A–U1334C, and 418 samples were examined from Holes U1338A–U1338C. The meter subbottom depth scale references are based upon the original shipboard splice (see the “Expedition 320/321 summary” chapter [Pälike et al., 2010]). Wilkens et al. (2013) and Westerhold et al. (2012) subsequently revised the original shipboard splice.

Samples from Site U1334 were processed for semiqualitative analysis with strewn slides prepared following the methods of Baldauf (1984). The total number of diatoms, radiolarians, and silicoflagellates from typically the first 50 fields of view was tabulated. The relative percentage of diatom fragments was also estimated (<25%, 25%–50%, 50%–75%, or >75%) for each sample. Preservation (poor, moderate, or good) was defined based on the condition of the valve, breakage, and degree of silicification. For example,

Poor = contains typically fragments, partial dissolution may be observed, and finely silicified forms typically are not observed.

Moderate = significant fragmentation and finer silicified forms are present. Dissolution, if present, is much reduced when compared to the poorly preserved assemblages.

Good = minimal fragmentation with a balance of finely and coarsely silicified assemblages typical for the late Eocene–early Oligocene.

Samples from Site U1338 were processed for qualitative analysis using a modified method described by Scherer (1994). The primary adjustment to Scherer’s method was to process typically 0.1 g of sediment and neutralize the residue in the same vial. Once the residue was neutral, the entire vial content was decanted into a settling chamber. This eliminated the potential loss of residue. Typically, the total number of diatoms, radiolarians, and silicoflagellates was tabulated for the first 100 fields of view or the first 300 diatoms encountered. In the case where a significant number of diatoms was present, the total number of diatoms, radiolarians, and silicoflagellates was tabulated for 50 fields of view or the first 600 diatoms encountered. The total numbers of diatom valves per gram sediment, as well as radiolarian and silicoflagellate skeletons per gram sediment, was calculated following the procedures of Scherer (1994).

All samples (from both sites) were examined at 500× using a Zeiss Axio ImagerA2. Species identifications were completed at 1250×. The counting techniques of Gersonde and Schrader (1978) were utilized for all samples. The total number of diatoms was not tabulated for the few samples where diatoms were rare or absent.