Multisensor track (MST) and color reflectance data (650-750 nm) collected from Holes 1094A-1094D were used to determine depth offsets in the composite section. Gamma-ray attenuation (GRA) bulk density and magnetic susceptibility data were collected at 2- to 4-cm intervals on cores recovered from Holes 1094A-1094D. Color reflectance data were collected at 4- to 6-cm intervals on cores from Holes 1094A-1094D (see "Physical Properties" and "Lithostratigraphy" for details about these MST and color reflectance data sets).
The composite data show that the cores from Site 1094 provide a nearly continuous overlap to 121 mcd (base of Core 177-1094D-11H). The data used to construct the composite section and determine core overlaps are presented on a composite depth scale in Figures F13, F14, and F15. The depth offsets that comprise the composite section for Holes 1094A-1094D are given in Table T5 (also in ASCII format in the TABLES directory).
Stretching and compression of sedimentary features in aligned cores indicate distortion of the cored sequence. Because of the distortion within individual cores on depth scales of <9 m, it was not possible to align every feature in the MST and color reflectance records accurately by simply adding a constant to the mbsf core depth. Within-core scale changes will require postcruise processing to align smaller sedimentary features. Only after allowing variable adjustments of peaks within each core can an accurate estimate of core gaps be made.
Following construction of the composite depth section for Site 1094, a single spliced record was assembled for the aligned cores over the upper 121 mcd by using cores from Holes 1094A-1094D. The composite depths were aligned so that tie points between adjacent holes occurred at exactly the same depths in mcd. Intervals having significant disturbance or distortion were avoided whenever possible. The Site 1094 splice (Table T6, also in ASCII format in the TABLES directory) can be used as a sampling guide to recover a single sedimentary sequence between 0 and 121 mcd. Spliced records of magnetic susceptibility, GRA bulk density, and color reflectance are shown in Figure F16.
In the Site 1094 spliced record there is one known core gap between Cores 177-1094A-7H and 8H. The offset of 8H was arbitrarily set to the cumulative offset of Core 7H. Furthermore, the Site 1094 splice contains seven ambiguous tie points. Ambiguities in the splice points result from insufficient overlap between adjacent cores (e.g., <1 m), lack of strong features that can be correlated across the overlapping segments of adjacent cores (e.g., diatom-mat intervals), or disagreement in magnetic susceptibility, GRA bulk density, and/or color reflectance data across the spliced interval. We have identified the ambiguous tie points with an asterisk in Table T6.
Sediments recovered from Site 1094 provide a nearly continuous late to early Pleistocene record. Calcareous nannofossils in this interval are abundant to rare and are characterized by low diversity and by medium to poor preservation. Several barren intervals characterize the Pleistocene record (Table T7, also in ASCII format in the TABLES directory). The biostratigraphic zones of Martini (1971) and Okada and Bukry (1980), as well as some additional events according to Raffi et al. (1993) and Wei (1993) (see "Explanatory Notes" chapter), were recognized. Tables T7, T8, and T9 (all also in ASCII format in the TABLES directory), and Figure F17, summarize the main calcareous nannofossil biostratigraphic results.
The first occurrence (FO) of Emiliania huxleyi is present from 39.97 to 40.31 mcd (base of Zone NN21). The last occurrence (LO) of Pseudoemiliania lacunosa is present between 81.09 and 84.71 mcd, defining the base of Zone NN20. The LO of Reticulofenestra asanoi is recognized from 106.87 to 114.36 mcd. The reentrance of medium Gephyrocapsa (4-5.5 µm) is present between 125.07 and 125.29 mcd. The FO of R. asanoi is identified from 130.72 to 133.04 mcd. The LO of large Gephyrocapsa (>5.5 µm) is observed between 139.23 and 143.90 mcd, whereas its FO is present between 165.29 and 165.86 mcd. The continuous record of medium Gephyrocapsa (4-5.5 µm) from the lower portion of this site allows us to assign an early Pleistocene age to the bottom of the sequence (Table T7; Figs. F17, F18).
The sediment recovered from the four holes drilled at Site 1094 is dominated by foraminifer-bearing diatom ooze. The abundance of planktic foraminifers is generally higher below ~82 mcd. The pattern of increasing abundance with increasing depth is similar to Site 1093. The higher abundance of planktic foraminifers at Site 1094 compared to Site 1093 could possibly be explained by lower sedimentation rates at Site 1094 because of less dilution by biogenic silica. However, the relatively high sedimentation rates at Site 1094, as well as the shallower water depth, are probably additional important factors for the abundance and preservation of planktic foraminifers. Preservation is good to moderate in all studied core-catcher (CC) samples, and even in samples where only rare occurrences of planktic foraminifers were recorded. The dominant species at Site 1094 is, as expected, Neogloboquadrina pachyderma (sinistral). In addition to this species, Globigerina bulloides, Globigerina quinqueloba, and Globigerinita glutinata were recorded in some of the samples. Moreover, single specimens of two species, Globorotalia inflata and Globorotalia puncticuloides, were recorded in a few of the studied CC samples (Table T10, also in ASCII format in the TABLES directory). A nearly continuous planktic foraminifer stable isotopic record measured on Neogloboquadrina pachyderma (sinistral) will be achievable at Site 1094.
Benthic foraminifers at Site 1094 are generally not very abundant and vary considerably in their state of preservation from poor to good. Highly abundant, needle-like remains of the diatom genus Thalassiothrix in the >63-µm fraction made it necessary to wet-sieve sediment samples at 150 µm.
Benthic foraminifers are highly variable, typically constituting between 5% and 100% of the total foraminifer fauna from the >150-µm fraction studied. Absolute foraminifer abundances are variable and low, reaching a maximum of 22 specimens/cm3 in Sample 177-1094A-16H-CC, 0-10 cm (147.07 mcd). There is a general trend toward higher abundances below ~120 mcd. Low benthic foraminifer abundance may be explained by relatively high sedimentation rates (see "Stratigraphic Summary"). No barren intervals are observed, but some of the glacial intervals, characterized by low color reflectance and high magnetic susceptibility (Fig. F16), only contain very sparse benthic foraminiferal assemblages that are dominated by low-diversity agglutinated forms such as Martinotiella sp. Continuous benthic diatom isotopic records may be difficult to obtain from this site. However, Cibicidoides wuellerstorfi appears to be present fairly consistently in 12 out of 17 CC samples from Hole 1094A, suggesting that a benthic stable isotopic record, albeit discontinuous, should be achievable.
Quantitative estimates of relative species abundance were made from Holes 1094A, 1094C, and 1094D, with counts of up to 239 specimens/20-cm3 sample. Species richness is variable, with a maximum of 33 taxa recorded in Sample 177-1094A-14H-CC, 0-10 cm (126.38 mcd). High-diversity, relatively abundant assemblages correspond to interglacial intervals, and low-diversity, low-abundance assemblages correspond to glacial intervals. This pattern is clearly seen in the intervals adjacent to MIS 11, centered at 65 mcd (Table T11, also in ASCII format in the TABLES directory).
The most common benthic taxa recorded at Site 1093 include C. wuellerstorfi, Eggerella bradyi, Epistominella exigua, Globocassidulina subglobosa, Melonis barleeanum, Melonis pompiliodes, Oridorsalis umbonatus, Pullenia bulloides, Pullenia quinqueloba, and Pullenia subcarinata. The assemblages present are very similar to those recorded at Sites 1091 and 1093. No biostratigraphic subdivision, other than glacial-interglacial cyclicity, can be suggested on the basis of the recovered benthic foraminifer assemblages.
Site 1094 sediments provide a continuous Pleistocene record with a basal age of lower early Pleistocene. For biostratigraphic age assignments we used the late Pliocene-Pleistocene zonation proposed by Gersonde and Bárcena (1998), although this zonation scheme could be applied only partially because of the trace abundance of the marker species Hemidiscus karstenii. All diatom stratigraphic information from the four holes cored at Site 1094 was combined and converted to the mcd scale (Tables T8, T9, and T12; all also in ASCII format in the TABLES directory).
Diatoms are generally abundant, and preservation is good to moderate. Silicoflagellates, which were also examined during diatom analyses, were encountered in trace to rare abundances in half of the samples. Sponge spicules and Ebridians are sporadic (Table T12).
Trace occurrence of the marker species H. karstenii precluded the subdivision of the Thalassiosira lentiginosa Zone into its three subzones according to the zonation proposed by Gersonde and Bárcena (1998) for the northern area of the Southern Ocean. Because H. karstenii is most abundant in warmer waters north of the present PF (see "Chronostratigraphy" in the "Site 1093" chapter), this datum could not be used for the identification of MISs 7, 9, and 11. The boundary between the T. lentiginosa and the underlying Actinocyclus ingens Subzone c, reflecting an age of 0.65 Ma, was observed at 88 mcd (Fig. F17). The marker species Thalassiosira elliptipora, whose first abundant appearance datum at ~1.07 Ma is used to define the underlying boundary of the A. ingens Subzone b (Gersonde and Bárcena, 1998), was not encountered until ~130 mcd. The transition to A. ingens Subzone a at ~143 mcd, corresponding to an age of 1.3 Ma, is marked by the last appearance datum of Fragilariopsis barronii (Gersonde and Bárcena, 1998). Common occurrences of specimen, which probably document the transition between F. barronii and the extant F. kerguelensis, make the definition of A. ingens Subzone b difficult. However, ages older than 1.24 Ma derived from calcareous nannofossil biostratigraphy (see above) support the assignment of these sediments to A. ingens Subzone a, spanning the time interval between 1.3 and 1.8 Ma (Fig. F18).
Radiolarian biostratigraphy at Site 1094 is based on the examination of 22 samples (Table T13, also in ASCII format in the TABLES directory). Radiolarian abundance at Site 1094 varies from abundant to rare, depending on the relative amount of diatoms in the samples, and preservation is excellent throughout the recovered sequence.
The boundary between the Omega and Psi Zones, marked by the LO of Stylatractus universus at 0.46 Ma, is placed at 67.83 mcd (Table T9). Except for Stylatractus universus, no marker species were found in the lower portion of the recovered sequence. Calcareous nannofossils and diatoms provide datums of 1.46 and 1.3-1.8 Ma below ~160 mcd, respectively (see above), which indicates that samples from the lower portion can be assigned to the Chi Zone. Samples 177-1094A-14H-CC, 0-10 cm (126.38 mcd), and 16H-CC, 0-10 cm (147.07 mcd), contain reworked specimens of Desmospyris spongiosa, Eucyrtidium carvertense, and Helotholus vema, all of which are characteristic species below the Chi Zone.
The occurrence of Pterocanium trilobum, defining the top of the Chi Zone, is generally very rare; this fact has also been noted by previous studies (e.g., Lazarus, 1990). A significant revision may be necessary for the Pliocene-Pleistocene radiolarian biostratigraphy of the Antarctic region to establish reliable datums.
Archive halves of APC cores recovered at Site 1094 were measured using the shipboard pass-through magnetometer. Measurements were made at 5-cm intervals. Sections obviously affected by drilling disturbance were not measured. All core sections from Site 1094 were measured after alternating-field (AF) demagnetization at peak fields of 0 (natural remanent magnetization [NRM]), 5, 10, 15, 20, and 25 mT.
NRM intensities are ~5 × 10-2 A/m throughout most of the APC section. After AF demagnetization at peak fields of 25 mT, intensities generally decreased to ~10-2 A/m. NRM inclinations are typically downward or shallow as a result of a downward-directed magnetic overprint, possibly a viscous remanent magnetization attributable to the drill string. The drill-string remagnetization was largely removed at peak demagnetization fields in excess of 10 mT. The resulting inclination values (Fig. F19) define a normal polarity zone (Brunhes Chron) overlying a reversed polarity zone (Matuyama Chron). In Hole 1094D, several normal polarity zones are recognized within the Matuyama Chron. Interpretation of these normal polarity intervals should be clarified by shore-based study of discrete samples. The normal polarity interval between 120 and 128 mbsf at Hole 1094D may represent the Jaramillo Subchron. The Brunhes/Matuyama boundary is best identified in the 95.4- to 100.0-mbsf interval at Hole 1094A (Fig. F19; Table T9).
At Site 1094, the sedimentary section is nearly continuous to a depth of 121 mcd (base of Core 177-1093D-10H, early Pleistocene), and has a total thickness of ~170 mcd (base of Core 177-1094D-16H) (Figs. F13, F14, F15, F16). Holes 1094A-1094D were cored with the APC to 159.6, 38.0, 73.1, and 171.1 mbsf, respectively. The depth offset of cores below the spliced record is the same as the greatest cumulative offset of the overlying cores.
An expanded and continuous Pleistocene sequence was recovered at Site 1094. The lowermost biostratigraphic datum is the FO of large Gephyrocapsa (>5.5 µm) at 165.86 mcd (Sample 177-1094D-16H-2, 87 cm), which suggests an age older than 1.46 Ma.
All biostratigraphic datums, including calcareous nannofossil, diatom, and radiolarian events and available magnetostratigraphic events, yield consistent age assignments throughout the record at Site 1094. The sedimentation rates in the diatom-dominated upper to mid-Pleistocene sequences at Site 1094 average ~140 m/m.y. The transition between the Brunhes and Matuyama Chrons is identified between 98.20 and 101.58 mcd in Hole 1094A. Early Pleistocene sedimentation rates are lower, averaging ~90 m/m.y. This pattern of higher sedimentation rates during the last ~0.45 m.y. is similar to the pattern observed Site 1093.
The extremely expanded upper and mid-Pleistocene sediments provide a unique opportunity for paleoceanographic reconstructions at ultra-high time resolution in a pelagic environment. Sedimentation rates of ~140 m/m.y. throughout this interval will allow sampling at millennial and submillennial time-scale resolution. Such records can be correlated in detail with paleoclimatic records from Greenland and Antarctic ice cores. In addition, they will allow a detailed study of the sea-ice record as reflected in the abundance fluctuations of sea-ice diatoms. Based on the examination of CC samples, it seems likely that a nearly continuous planktic stable isotopic stratigraphy (N. pachyderma [sinistral]) and a more or less continuous benthic foraminiferal stable isotopic record can be established for Site 1094.