Sites 1098 and 1099 in Palmer Deep were the first ultra high resolution Ocean Drilling Program (ODP) targets in the Southern Hemisphere and represented the first coordinated effort aimed at obtaining such a record from the Antarctic continental shelf (Barker, Camerlenghi, Acton, et al., 1999; Barker et al., 1998). Three offset holes at Site 1098 (1098A, 1098B, and 1098C) and two intersecting holes at Site 1099 (1099A and 1099B) were drilled during Leg 178. To date, detailed investigations have been completed at only Site 1098, focused around the completion of a composite depth scale (Acton et al., Chap. 5, this volume) and a detailed radiocarbon chronology (Domack et al., 2001). The chronology and stratigraphy of Site 1099 will be reported at a later date. The purpose of this paper is to summarize the scientific results dealing with Site 1098.
At Site 1098, ~45 m of diatomaceous mud and ooze underlain by a stiff glacial diamicton was recovered. The sequence represents a single deglaciation through the Holocene with unprecedented temporal resolution for Antarctic sediments. Hence, one of the stated objectives of Leg 178 was met by the completion of drilling at this site. Published studies for Site 1098 cover the following topics:
These results provide a consensus regarding general stratigraphy and paleoenvironmental interpretation. They also indicate some divergence of opinion regarding the paleoceanographic history of Palmer Deep. This paper summarizes the general consensus as well as different interpretations. The paper is organized around thematic issues related to basin physiography, origin of laminated intervals, sediment provenance, and deepwater vs. surface water signals during the Holocene. Suggestions for future avenues of study are highlighted.
Palmer Deep is an informal name given to an inner shelf depression of unusual depth and relief recently surveyed with swath mapping (SeaBeam) during cruise NBP-99-03 of the N.B. Palmer (Fig. F1). Palmer Deep appears to be located at an intersection of three ice drainage systems and contains at least two distinct subbasins (Figs. F1, F2). Glacial drainage systems included those from the Anvers Island ice cap in the northeast, valley glaciers that reached the area across the shelf from the south, and ice that entered the eastern end of Palmer Deep from the Bismark Strait via the Neumayer Channel and southernmost Gerlache Strait (Fig. F2). Palmer Deep is tectonically controlled by a half-graben that is still an active structure (Rebesco et al, 1998; Sniffen, 2001). The convergence of flow probably helped to overdeepen the basin and most probably originated an ice stream that extended some 200 km across the entire continental shelf until the shelf break (Fig. F2). The basin is one of the deepest inner shelf basins found along the Antarctic margin. Crystalline rocks of the Peninsula Volcanic and Trinity Groups comprise most of the underlying bedrock (British Antarctic Survey, 1982). Only in the deepest reaches of Subbasin III does postglacial deposition clearly mask the scoured bedrock surface.
Site 1098 is located in the axis of the ~2-km-wide perched Subbasin I, which trends in a southwest-northeast direction (Fig. F1). Acoustic imagery revealed a draped sequence of pelagic and hemipelagic sediments at this site (Rebesco et al., 1998; Barker, Camerlenghi, Acton, et al., 1999). Although the contour trend does allow connection between Subbasins III and I, the floors of the two subbasins within Palmer Deep are clearly separated by a narrow sill of 10-m relief (Fig. F1). Early bathymetric maps of Palmer Deep (Griffith 1987; Kirby et al., 1998) indicated a third subbasin ("Basin II"); however, this feature is an artifact of imprecise navigation and incomplete bathymetric soundings.
Palmer Deep Subbasin III reaches depths >1400 m and is elongated in an east-west direction, occupying ~192 km2 (Kirby et al., 1998; Rebesco et al., 1998). Steep and irregular basement rocks encircle Subbasin III, shallowing abruptly to depths of 300 to 400 m (Fig. F1). The floor of Subbasin III is characterized by a more or less flat eastern deep that slopes gently up to depths of ~1100 m toward the western end. Here, the subbasin floor is dissected by a nearly straight (west to east) canyon that feeds into the deeper, eastern end of the basin. This canyon itself is incised 100 m into the subbasin floor and has tributaries from the southern margin that deepen toward the northwest before merging with the main axial canyon as it turns eastward. Site 1099 and previous piston cores, located within the eastern, deeper portion of Subbasin III, not surprisingly, recovered an alternation of hemipelagic diatom mud/ooze and thick (>30 m) diatom mud turbidites to depths of just over 108 meters below seafloor (mbsf) (Barker, Camerlenghi, Acton, et al., 1999; Kirby et al., 1998).