Phytoliths are classified by morphological type based on the classification schemes of Piperno (1988) and Kondo et al. (1994). Numbers of distinctive phytoliths observed at each sampling level are presented in Table T1. The presence of "plate" and "block" phytoliths with irregular and highly variable morphologies and other siliceous microfossils is noted by an asterisk symbol. The observed phytoliths have been compared to those previously described from other Cenozoic Antarctic samples: CRP cores (Carter, 1998b; Thorn, 2001), CIROS cores (70 km south of Cape Roberts) (Kondo et al., 1994), an undescribed Ross Sea core (J. Carter, pers. comm., 2002), Sirius Group cores from Mt. Feather (Carter, 1998a), and McMurdo Sound erratics (V.C. Thorn, unpubl. data). Comparisons have also been sought from the wider literature, including a Web-based database (Pearsall et al., 1998) on modern phytolith production.
Three phytoliths originating from grass bulliform (motor) cells are present at Site 1165 (329.13 mbsf: one fan shaped and one rectangular and 392.88 mbsf: one fan shaped) (Plate P1, fig. 3). The rectangular specimen has high relief, a rectangular outline with the long edges bevelled, a smooth surface, and is 12 µm long. The fan-shaped forms have a curved outline around half of the circumference, and the remainder tapers to a point (Fig. F1). The surface of the illustrated specimen is smooth (8 µm in diameter), and the second is rugulose (9 µm).
Fan-shaped and rectangular bulliform cells have also been observed in core CRP-2/2A (Thorn, 2001) and fan-shaped phytoliths from the CIROS-1 core and extant Rytidosperma (reed grass) in New Zealand (Kondo et al., 1994).
A single panicoid phytolith is present at 96.08 mbsf at Site 1165 (Plate P1, fig. 1). It has a smooth, dumbbell-shaped outline, is opaque, and is 16 µm long. Dark-colored or opaque phytoliths are related to high quantities of organic carbon occluded either within or coating the surface. Carbon coatings are also commonly produced when a plant is burned and can be an indication of vegetation fires (Piperno, 1988).
A transparent panicoid specimen with a narrow, wavy margin has been described from core CRP-3 (Thorn, 2001). Bukry (1979) notes the presence of panicoid phytoliths (and illustrates an opaque form) in the Pliocene sediments of deep-sea cores off the northwest coast of Africa (Deep Sea Drilling Project [DSDP] Site 397). He compares these forms to those found in the extant prairie grass Zea mays. Locker and Martini (1986) also illustrate both transparent and dark-colored panicoid phytoliths from the middle Miocene to Pleistocene sediments of DSDP Site 591 in the southwest Pacific. Here, they attribute the presence of grass phytoliths to distribution by westerly winds from Australia, where large open grasslands developed during the late Neogene in the north and central regions (Kemp, 1978). Bowdery (1999) has also described the modern eolian transport of panicoid phytoliths with reference to historical Mid-Atlantic shipboard samples sourced from the African dust plume. Panicoid phytoliths are known from the epidermal cells of Panicoideae, some Arundinoideae, some Eragrostoideae (Kondo et al., 1994), and a small number of Cyperaceae (sedge) species (Metcalfe, 1971). In general terms they are considered characteristic of "warm" climate grasses (Twiss, 1992).
A single striated plate comparable to those produced in modern fern tissue (Kondo et al., 1994) is present at 329.13 mbsf at Site 1165 (Plate P1, fig. 4). This specimen is 16 µm long, has a rectangular outline, medium relief, and deep, parallel striations across the upper surface. Kondo et al. (1994) noted similar striated plate forms within samples from the CIROS-1 core.
A jigsaw piece-shaped phytolith is present at 329.13 mbsf at Site 1165 (Plate P1, fig. 14). It is transparent, of medium relief, and has a smooth surface with well-defined edges and deep embayments. It is 42 µm long, which is within the size range of anticlinal phytoliths typically formed in the epidermal leaves of dicotyledonous trees and shrubs (12-85 µm) (Kondo et al., 1994). Another anticlinal specimen is present at 1.29 mbsf at Site 1166, which has broader embayments, is 16 µm wide, and is partially dissolved on the surface. Anticlinal epidermal forms have been described from ferns, but the latter are generally larger (70-200 µm) and longer in outline (Kondo et al., 1994).
Anticlinal epidermal phytoliths have also been observed in the CRP cores (Carter, 1998b; Thorn, 2001), Sirius Group (Carter, 1998a), and Permian Weller Coal Measures (Carter, 1999) at Mt. Feather, Antarctica.
Spherical phytoliths are the most common forms observed in the Prydz Bay samples. These forms are deposited within leaf epidermal and wood ray and parenchyma cells. Six different morphological subgroups are identified. Only spherical "pellet" forms are observed at Site 1166.
Seven specimens of this distinctive form are present between 291.28 and 392.88 mbsf at Site 1165 (Plate P1, fig. 10). The specimens are oval to kidney-shaped in outline with a high relief and a folded surface texture with sharp-edged ridges. The forms are dark in color and are commonly 6-8 µm long (two specimens are 4 and 12 µm long). No comparative phytoliths have been previously described, and the natural affinity of these forms is currently unknown.
Three irregular spherical phytoliths are present at Site 1165, one each at 329.13, 392.88, and 482.98 mbsf (Plate P1, fig. 6). These specimens are dark in color, have irregular but still approximately circular outlines, and medium relief. The surface textures include smooth or low widely spaced nodules, ranging in size from 7 to 8 µm in diameter. Irregular spherical phytoliths have not been described from other localities and are currently of unknown natural affinity.
This subgroup of spherical phytoliths is the most common form observed throughout samples from both Sites 1165 and 1166 (39 specimens) (Plate P1, fig. 5). The specimens are generally small (4-7 µm in diameter), dark in color, and of medium-high relief. The outlines are commonly irregular but remain approximately circular. The surface textures are varied and include smooth, low-relief rugulose, striated, and medium-relief folded.
Pellet sphericals are common throughout core CRP-2/2A and the upper portion of core CRP-3 (Thorn, 2001). These forms have not been described elsewhere, and their natural affinity remains unknown.
A single smooth spherical specimen is present at 2.29 mbsf at Site 1165 (Plate P1, fig. 7). It is opaque, 5 µm in diameter, and, like the opaque panicoid specimen described above, could reflect source vegetation burning.
Slightly larger smooth spherical phytoliths have been described from the Cape Roberts cores (8-10 µm in diameter) and are compared to those produced by the New Zealand mountain beech (Nothofagus solandri var. cliffortioides) (Thorn, 2001). Significant numbers ranging in size between 1 and 50 µm in diameter are also produced by deciduous angiosperms (Piperno, 1988).
One spinulose spherical specimen (5 µm in diameter) is present at 139.08 mbsf at Site 1165 (Plate P1, fig. 8). Spinulose sphericals commonly originate from a stegmata leaf cell with unevenly thickened walls. This specimen is approximately circular in outline and is covered with widely spaced narrow spinules with rounded apices.
This form has also been described from the CRP cores (Thorn, 2001). Spinulose spherical phytoliths are commonly found in modern Palmae (6-25 µm in diameter); however, the Bromeliaceae (monocotyledon herbs) also produce small forms (<2-8 µm in diameter). Phytoliths from the two families can generally be distinguished on the basis of size (Piperno, 1988), although this distinction requires further investigation.
Two spherical phytoliths with a distinctive verrucose surface texture are present at 64.58 (5 µm in diameter) and 973.40 mbsf (8 µm), respectively, at Site 1165 (Plate P1, figs. 9a, 9b). Both specimens have approximately circular outlines with verrucae projections of varying lengths (up to ~1 µm in diameter).
Verrucose sphericals have been previously described from core CRP-3 (Thorn, 2001) and a variety of extant plants including Nothofagus spp. (Kondo et al., 1994). Verrucose spherical phytoliths described from the CIROS-1 core are tentatively attributed to Nothofagus (Kondo et al., 1994); however, the CRP-3 core forms are more closely compared to those produced by the New Zealand honeysuckle (Proteaceae) (Thorn, 2001).
Three distinctive phytoliths of cubic form are present in the uppermost sample from Site 1166 (1.29 mbsf) (Plate P1, fig. 13). The specimens have smooth surfaces, well-defined edges, and sharp corners and are 7, 7, and 9 µm in diameter, respectively.
Carter (1998a) noted the presence of irregular cubic forms of slightly larger size (8-16 µm) in samples from the Sirius Group from Mt. Feather, which were also extracted from a diamicton at the same locality by Bleakley (1996). The natural affinity of these forms is currently unknown. The cubic phytoliths observed are superficially similar in appearance to starch grains comprising the powder supplied with disposable laboratory gloves. The glove starch grains are, however, generally larger (8-17 µm in diameter observed) and have a circular outline with conical relief.
This highly variable category contains irregular plate and block specimens of biogenic silica. Outline shapes include irregular, rectangular, embayed, and polygonal with commonly etched or smooth surface textures. These forms are present within samples from both Sites 1165 and 1166, but are observed predominantly between 291.28 and 855.78 mbsf at Site 1165 (Plate P1, figs. 11, 12).
Carter (1999) notes the occurrence of similar "etched polyhedral" phytoliths from the Devonian Aztec Siltstone at Mt. Crean and also within samples from an undescribed Ross Sea core (J. Carter, pers. comm., 2002). Similar forms are also described from the Cape Roberts cores (Carter, 1998b; Thorn, 2001) and the Sirius Group from Mt. Feather (Bleakley, 1996; Carter, 1998a) and Table Mountain (Bleakley, 1996). The natural affinity of these forms is currently unknown.
One festucoid phytolith is present at 106.34 mbsf at Site 1166 (Plate P1, fig. 2). It has crenulate margins, higher relief in the center compared to the edges, and is 24 µm long. This well-preserved specimen is considered to be a contaminant because of its presence in an otherwise barren sample.
The only other possible festucoid phytolith that has been reported from Antarctic sediments was reported from core CRP-3 (Thorn, 2001). Festucoid phytoliths form in the epidermal cells of extant Pooideae and some Arundinoideae.
The verrucose spherical specimen observed at 923.28 mbsf at Site 1165 is assumed to be a contaminant because of its presence in the otherwise barren zone at and below 692.48 mbsf. Further, it is considered that the verrucose surface texture is unlikely to have survived the diagenetic opal-A to opal-CT transition at ~600 mbsf.