Although detailed interpretations of the combined data sets must await further work, a few conclusions can be presented at this time. In the whole debate about Antarctic cryospheric evolution during the Pliocene, some authors have classified all authors as belonging to one of two categories: "dynamicists" and "stabilists." Such labels should be abandoned because if we ask, "Who is right, the stabilists or the dynamicists?" The answer must be "both" (see also Quilty, 1996): there is no doubt about the antiquity of landscape features and glacial ice in the mountains near the Dry Valleys as proposed (e.g., Marchant and Lewis, 2002), based on 75 laser-fusion age dates of ash fall deposits and numerous cosmogenic-nuclide analyses of boulders. At the same time, the interpretation of seismic lines and stable isotopic records (e.g., Hart, 2001) suggests that the margin of the ice sheet has advanced and retreated across the continental margin several times during the Pliocene, suggesting a dynamic behavior, at least of the ice sheet margin. In addition, field work in the Vestfold Hills (Soersdal Formation) suggests that during parts of the early Pliocene the ice sheet grounding line was far landward of its present location (Whitehead et al., 2001). However, vertical movements of the coastal area need to be better constrained for an evaluation of absolute grounding-line movements.
Our analyses likewise suggest a dynamic behavior of the ice sheet margin, reflected by the somewhat surprising fluctuations in all measured parameters, particularly magnetic parameters, brightness and color, stable isotopes, and clays and clay mineral composition. For instance, at 34 mbsf, brightness, ARM, k, and ARM/IRM all change. Smectite percent decreases upsection while kaolinite percent increases. Most investigators agree that these changes reflect changes in the specific location of the source area within the Lambert Graben drainage area. This conclusion is in agreement with similar conclusions drawn by the Shipboard Scientific Party (2001) for the older Miocene portion of Site 1165. The remarkable change at 34 mbsf occurred in the lowermost normal interval of the Gauss Chron, at ~3.4-3.5 Ma(?). A correlation with nearby drill sites of ODP Legs 119 and 120 is not immediately obvious, perhaps because the review of the results of these sites (Ehrmann et al., 1992) essentially dealt with the "big picture" of Antarctic climate evolution. In addition, there are sites on the Kerguelen Plateau that yielded a record of ice rafting for the last 10 m.y. (Ehrmann et al., 1992). The combined Sites 745/74 show a strong influx of ice-rafted debris at 4.5-4.3 Ma. Site 751 shows an increase in ice rafting at 3.2-2.9 Ma. None of these records can be confidently correlated with ours.
Going farther afield, we speculate that the "big change" at Site 1165 at 34 mbsf may be coeval with the beginning of ice rafting at Leg 114 Site 704 in the South Atlantic. This beginning occurred during marine isotope Stage (MIS) MG2 and suggests a drop in sea-surface temperature at that location (i.e., a northward movement of the polar frontal systems).
In the HiRISC interval at Site 1165, starting from the bottom, smectite percent decreases upsection to ~34 mbsf. Above a transitional interval from ~34 to ~22 mbsf the clay mineralogy is characterized by a smectite-poor assemblage. Illite concentrations do not seem constant but fluctuate in concert (antiparallel) with smectite. At this stage, we have no straightforward explanation for these changes. A possible explanation is that there were temporal variations in supply from the source rocks (for example, by progressive erosion through successive units in the source area or by switching of source regions). A second explanation is that these changes possibly reflect a climatic modulation of weathering type and transport mechanism of these sediments. The clay mineral assemblage and the likely presence of maghemite below ~35 mbsf (factor 4) may be due to enhanced pedogenesis associated with a relatively warmer and wetter climate. If our "weathering hypothesis" is correct, then this observation further supports the hypothesis that the change at 34 mbsf may coincide with the beginning of ice rafting observed at Site 704 in the South Atlantic during MIS MG2. Details, causes, and correlations of these changes must still be worked out.
Another important result of detailed, integrated magnetostratigraphic and biostratigraphic work is the identification of significant hiatuses (i.e., 100 k.y. or more) within the HiRISC interval, suggesting occasional strong erosional events on the continental rise. Similar conclusions were recently drawn by Escutia et al. (2003) for the continental rise area off Wilkes Land, East Antarctica.
Our cooperative research will hopefully continue. Some of the changes indicated in the integrated data set for the East Antarctic Ice Sheet need to be better constrained, characterized, and correlated with events on the Antarctic Peninsula (West Antarctic Ice Sheet) and elsewhere.