METHODS

Standard nannofossil smear slide techniques were used to prepare the samples. Norland optical adhesive was used as a mounting medium. Slides were examined using a Zeiss and/or Olympus polarizing compound microscope at 1000x. All core catchers were examined, along with selected samples from within the cores, which were picked from finer-grained, more calcareous material.

Etching and overgrowth are the most important features of nannofossil preservation. To establish a ranking of preservation, the code system adopted by the Leg 172 Shipboard Scientific Party (1998) was used:

G = good (little or no evidence of dissolution and/or secondary overgrowth of calcite; diagnostic characters fully preserved).

M = moderate (dissolution and/or secondary overgrowth; partially altered primary morphological characteristics [however, nearly all specimens can be identified at the species level]).

P = poor (severe dissolution, fragmentation, and/or secondary overgrowth with primary features largely destroyed; many specimens cannot be identified at the species level and/or generic level).

The total abundance of calcareous nannofossils, at 1000x, for each sample was estimated as follows:

A = abundant (>10-100 nannoliths per field of view).

C = common (1-10 nannoliths per field of view).

F = few (1 nannolith per 3-5 fields of view).

R = rare (<1 nannolith per 10 fields of view).

X = scarce (<3 nannoliths per traverse).

B = barren.

The nannofossil zonation schemes proposed by Okada and Bukry (1980) and Martini (1971) were used as the basic zonal reference for Leg 178. Ages of most calcareous nannofossil datums that are employed to construct the Leg 178 age model used for the Pliocene-Pleistocene interval are drawn from the work of Raffi et al. (1993) and Wei (1993). These are summarized in the Leg 172 Initial Reports volume "Explanatory Notes" chapter (Shipboard Scientific Party, 1998). The zonal scheme is illustrated in the Leg 178 Initial Reports volume "Explanatory Notes" chapter (Shipboard Scientific Party, 1999a); please refer to these for a complete discussion. All ages of the species events are correlated to the geomagnetic polarity timescales of Berggren et al. (1995). Reworked species were nearly nonexistent. One Braarudosphaera spp. (very dissolved) was observed in Core 178-1101A-5H, and a broken Sphenolithus spp. was noted in Section 178-1101A-10H-CC.

Table T1 lists the nannofossils considered in this study. Because of often poor preservation, the Gephyrocapsa spp. were utilized for the datums correlated with distinctive sizes, that is, the first occurrence (FO) and last occurrence (LO) of large Gephyrocapsa spp. (>6 µm) and the reentrance of medium-sized Gephyrocapsa spp. (>4 to <6 µm). Gephyocapsa oceanica and Gephyrocapsa caribbeanica, included in these size-based groupings, are included in the table of species but not in the data tables. Elsewhere in the world in the Pleistocene, episodes of temporary disappearances of medium Gephyrocapsa spp. are observed, leaving only the small form. This small variety was noted in this study to see if these episodes were present in sediments from this part of the Southern Ocean. As can be seen, the overall paucity of nannofossil intervals distributed throughout the holes did not allow this distinction. The small variety was never broken down into species level; this topic is further discussed in Raffi et al. (1993).