CONCLUSIONS

1. Documented dissolution of calcareous foraminifers in the core repository has affected the foraminifer content of the sediment (Table T9). Any interpretation of the calcareous foraminifers of this site is questionable, but the agglutinated species are presumed to be intact and can be used for paleoenvironmental interpretations. The overall trend of higher percentages of calcareous foraminifers in the bioturbated interval and lower percentages in the laminated interval is believed to be syndepositional but has also been altered by an unknown amount of postdepositional carbonate dissolution.
2. The presence of mobile epifaunal agglutinated benthic foraminifers in all samples from Hole 1098C indicates that the bottom water was oxygenated at all times and that laminated sediments do not represent periods of anoxia (Fig. F4). The formation of the laminations by mat-forming diatoms may have suppressed bioturbation by macrobenthos (Pike and Kemp, 1999). The increased numbers of benthic foraminifers, possibly due to decreased competition from larger metazoans (Bernhard and Reimers, 1991), indicate that any anoxia that might have occurred was minor (seasonal, not decadal).
3. The climatic model proposed by Leventer et al. (1996) appears to be supported by data from our intervals A and B, but a revision of the foraminiferal interpretation is necessary (see conclusion 4, below). In intervals A and B, MS lows are characterized by laminated sediments and diatoms, indicating increased meltwater and a more stratified ocean (Fig. F3). Total dissolution of calcareous foraminifers in the low-susceptibility laminated sediments may be related in part to decreased bottom-water pH due to decay of diatom organic matter (Fig. F6).

   High values of magnetic susceptibility occur in massive bioturbated sediments, which contain a diatom assemblage indicating reduced meltwater stratification. Preservation of calcareous foraminifers during the susceptibility highs (Fig. F6) likely reflects normal bottom-water pH.

4. There are no major changes in the assemblage composition of the agglutinated benthic foraminifers or the isotopic values of the calcareous benthic foraminifers in the laminated and massive sediments within each sample interval (Figs. F4, F6). This suggests that the driving force behind the laminated sediments and the susceptibility fluctuations within each interval is probably not a change in the bottom-water mass but lies in changes in the diatom productivity of the surface water (see conclusion 3, above). It appears that UCDW was a feature of the AP continental shelf throughout the Holocene. Our results disagree with the idea that bottom-water fluctuations played a role in the climatic fluctuations of the Palmer Deep (Leventer et al., 1996).
5. Diatoms indicate that the early and middle Holocene climatic optimum (intervals C and D) was a time of reduced sea-ice formation. These conditions led to the highest accumulation rates of diatoms and benthic foraminifers and the greatest primary productivity occurrence during interval C (Tables T1, T2). During the late Holocene (intervals A and B), diatoms record increased meltwater stratification of the AP shelf water and expansion of sea-ice conditions.
6. Early Holocene interval D records a significantly different environmental condition. This conclusion is based on several lines of evidence. First, both the presence of the asymmetrical morphotype of E. antarctica (Table T3) and the presence of increased numbers of the planktonic foraminifer N. pachyderma (Table T8) suggest the intrusion of more open-ocean surface water into this region. Second, a change in the oxygen isotopic values of benthic foraminifers suggests a different bottom water. Third, a change in the faunal assemblage of benthic foraminifers, including a decrease in P. eltaninae and B. pseudopunctata and the increased percentage of rare calcareous species diversity (Fig. F4; Table T7), indicates a change in the bottom water mass. All the data suggest the presence of more open-ocean CDW on the AP continental shelf during the early Holocene.