The Palmer Deep Sites recovered a continuous, high-resolution section of Holocene sediments. Two nearshore basins were cored: Basin I (Site 1098), a shallow inner basin with little evidence of turbidites in previously collected piston cores; and Basin III (Site 1099), a deeper basin with significant terrigenous deposits reported. Approximately half of the section at Site 1099 is in fact composed of debris flows and turbidites (see "Lithostratigraphy"). The preservation of microfossils in Palmer Deep is generally good. The paleoenvironmental evolution of Palmer Deep as recorded by diatoms, radiolarians, and foraminifers suggests a low-salinity, restricted marine environment with a strong glacial influence in the oldest sediments. There is also a gradual transition to open-marine conditions and periodic CDW influx.

Samples from Holes 1098C, 1099A, and 1099B core catchers and toothpick samples (from characteristic lithologies, including laminae) were analyzed. Diatom assemblages are excellently preserved and very diverse except in the lower portion of Core 178-1098C-5H, which was barren of diatoms. Many fine laminae were observed at both sites, each having a distinct assemblage, often different from the others. Most diatomaceous laminae are olive green to olive brown and composed of a nearly monospecific assemblage of Chaetoceros spp. spores. Light gray "fluffy" laminae that are dominantly Corethron criophilum occur sporadically. The overall background assemblage at both sites is dominated by several species of diatoms: Chaetoceros spp. spores, Eucampia antarctica, Fragilariopsis curta, Fragilariopsis kerguelensis, Fragilariopsis ritscherii, Odontella spp., Rhizosolenia spp., Thalassiosira antarctica, Thalassiosira lentiginosa, and Thalassiothrix spp. Only one biostratigraphic zone is represented at these two sites, the Thalassiosira lentiginosa Zone. Changes in assemblage were observed downhole, with more open-marine species abundant in the upper parts at the two sites. Species living in more restricted environments increase downhole (see "Lithostratigraphy").

At Site 1098, radiolarians are common and well preserved in the upper 28 mbsf with relatively diverse assemblages (Fig. F15). Diversity and abundance gradually decrease to zero at the bottom of the hole (47 mbsf). This pattern is interpreted as a transition from restricted circulation at the bottom of the core to open-marine conditions at the top.

Radiolarians at Site 1099 exhibit a pattern of decreasing abundance and diversity downcore similar to that at Site 1098. This pattern, however, occurs over 108 m, in contrast to 47 m at Site 1098. The interval from 24 to 62 mbsf is diluted by large amounts of terrigenous material, which diminishes radiolarian abundance. The radiolarians at Sites 1098 and 1099 appear to record the same events; the section at Site 1099 is thicker because of increased terrigenous supply.

Because of reduced shipboard sampling, no material from Site 1098 was available for analysis of foraminifers. At Site 1099, 12 core-catcher samples of ~10 cm³ were processed for foraminifers. An additional 13 samples of ~2 cm³ were processed from material scraped from the core surface. Benthic foraminifers are abundant and well preserved in the upper 87 mbsf; they decrease below that depth to a rare and poorly preserved assemblage in the lowest samples (Fig. F15). The planktonic foraminifer Neogloboquadrina pachyderma sinistral is rare throughout Holes 1099A and 1099B.

Preliminary analysis indicates that the benthic foraminifers in the upper 87 mbsf of Hole 1099A are similar to previously reported benthic foraminiferal fauna of the Bellingshausen Sea (Ishman and Domack, 1994). Ishman and Domack (1994) report two benthic foraminiferal assemblages: the Bulimina aculeata assemblage, related to CDW; and the Fursenkoina assemblage, related to shelf water. Fluctuations between these two assemblages have been recognized in piston cores from Palmer Deep and tied to 200-yr productivity cycles (Leventer et al., 1996).

Beneath 87 mbsf in Hole 1099B (depth of the highest black interval), however, B. aculeata is rare; Globocassidulina biora and the agglutinated genus Miliammina become more common. Miliammina spp. is linked to CDW by Ishman and Domack (1994), but G. biora is not closely related to either end-member. Both G. biora and Miliammina were found to be related to ice-front conditions in the Ross Sea (Osterman and Kellogg, 1979). In addition, the numbers of both foraminifers and diatoms observed in the sieved sediments decrease downcore in this lower interval. Sample 178-1099B-5H-CC (108.15 mbsf) at the bottom of the hole contains a large amount of pyrite as well as a decreased number of foraminifers, suggesting restricted basin circulation (Fig. F15).