Samples from Sites 1209–1212 were obtained from continuous U-channels through the PETM. Samples of ~1 cm3 were rinsed in distilled water, dried for 24 hr, weighed, washed with buffered water (pH ~10) and 5% Calgon solution, then disaggregated on a gyratory table for ~12 hr. Samples were then washed through 38- and 63-µm sieves, dried at ~40°C for 24 hr, and reweighed. Since the >38- and >63-µm fractions have very similar trends at all four sites (Fig. F3), the >63-µm fraction is referred to as the coarse fraction.
Detailed counts were performed to characterize preservation. Samples were dry-sieved to isolate specimens >125 µm, poured onto a picking tray, and observed using a binocular light microscope. The first ~300 grains encountered in traverses of the picking tray were counted per sample. Grains were identified as whole planktonic foraminifers, fragmented planktonic foraminifers, benthic foraminifers, pyrite, or fish debris. Fragmented foraminifers include specimens showing notable deterioration, including missing chambers and substantial breakage. Three samples were recounted to ensure consistency; reproducibility is ±10% (Fig. F4). Calcium carbonate content for each site was measured from dried bulk samples using a CO2 coulometer. External precision based on replicate measurements is ±2%.
Foraminiferal preservation was documented using a scanning electron microscope (SEM) for comparison with other preservational proxies. Foraminifers used for preservational analyses were ultrasonified for ~5 s to remove nannofossils and clay, resieved, and dried. Representative specimens were mounted on SEM stubs, broken with a metal pick, and photographed to assess chamber infilling and secondary calcite overgrowth and reprecipitation. We illustrate the range of foraminiferal preservation observed in several samples (Pls. P1, P2, P3, P4, P5, P6, P7).
Stable isotope analyses were carried out on 100–500 µg of freeze-dried bulk sample using Autocarb common acid bath systems coupled to either a PRISM or OPTIMA mass spectrometer. All values are reported relative to Vienna Peedee belemnite as calibrated by replicate analyses of National Bureau of Standards (NBS)-19 and in-house standard Cararra marble.