A total of 157 samples were collected from lithologic Unit I in Cores 185-1149A-1H through 13H. The sampling interval was ~75 cm, beginning with Section 185-1149A-1H-1 at 00.61 meters below seafloor (mbsf) (Table T1). Approximately 1 g of air-dried sediment from each sample was cleaned and disaggregated in 15% hydrogen peroxide, followed by a 2% sodium hexametaphosphate (Calgon) solution and sonication in an ultrasonic bath for 5 s. When disaggregation was completed, each sample was washed five times by repeated decantations with deionized water to remove any suspended clays and sodium hexametaphosphate residue. Samples were allowed to stand undisturbed for 24 hr between decantations. A known quantity of Lycopodium sp. pollen grains and Rose Bengal dye were added to each sample to permit later estimations of diatom abundance (diatom number).
Strewn slides were prepared from the cleaned bulk sample using a settling method modified after Laws (1983). Prior to settling, some bulk wet samples were split to produce a concentration that would settle as a single layer on the coverslips. The 22 mm x 22 mm coverslips containing the settled sample were affixed to glass slides with Hyrax mounting medium. All diatoms were identified and counted at 1250x using the ribbon counting method (Laws, 1983) until at least 500 specimens were counted or 15 traverses (ribbons) were completed, whichever came first.
All samples collected, prepared, and analyzed for this report are shown in Table T1. The counts yield a raw data matrix of number of frustules for each species in each sample. The raw data for species present were converted to relative percents and are reported in Table T2 according to the following convention:
Diatom abundance, as number of frustules per gram of sediment (diatom number), was calculated according to the following formula.
where