The Paleogene represents one of the more climatically dynamic periods in Earth history. Stable isotopebased reconstructions reveal a rather complex history of gradual and rapid warming and cooling (Miller et al., 1987; Miller and Katz, 1987; Stott and Kennet, 1990; Zachos et al., 1994, 2001). This includes a gradual 5-m.y.-long global warming trend that began in the late Paleocene and climaxed in the early Eocene in a 1- to 2-m.y.-long climatic optimum (early Eocene Climatic Optimum [EECO]), and a 12-m.y.-long steplike cooling trend that began in the early middle Eocene and culminated in the earliest Oligocene with the appearance of continental-scale ice sheets (Hambrey et al., 1991; Zachos et al., 1992). Among the more prominent events, however, is a brief but extreme greenhouse period known as the PaleoceneEocene Thermal Maximum (PETM). This event occurred at ~55.0 Ma, midway through the PaleoceneEocene warming trend, and was accompanied by major changes in ocean chemistry as inferred by shifts in carbon isotope patterns and in the distribution and preservation patterns of terrigenous and biogenic sediments on the seafloor (e.g., Bralower et al., 1995; Kennett and Stott, 1991; Robert and Kennett, 1997). In addition, this event was responsible for large-scale turnover of fauna and flora in the oceans and on land (e.g., Kelly et al., 1998; Koch et al., 1992, 1995; Thomas and Gooday, 1996; Thomas and Shackleton, 1996). Another notable transient is the earliest Oligocene Glacial Maximum (EOGM, also known as the Oi-1 Event), a brief but extreme glacial interval that occurred at ~33.4 Ma, coincident with the transition to permanent glacial conditions on Antarctica (e.g., Miller et al., 1987, 1991; Zachos et al., 1996). This transient, like the PETM, has been linked to major changes in ocean chemistry and ecology (Barrera and Huber, 1991, 1993; Salamy and Zachos, 1999; Thomas and Ward, 1990; Thunell and Corliss, 1986).
Multiple hypotheses exist to explain the large-scale, long-term changes in Paleogene climate, though none have gained universal acceptance. In general, among the many factors, ocean gateways (continental geography) and greenhouse gas levels are recognized as the two key variables. Theoretical models have invoked either higher greenhouse gas levels or the absence of a circum-Antarctic current or some combination of the two to account for the EECO (Barron, 1985; Bice et al., 2000; Sloan and Barron, 1992; Sloan and Rea, 1996; Sloan et al., 1992, 1995). Similarly, the Oligocene glaciation has been attributed to both a reduction in greenhouse levels and the initiation of the Antarctic circumpolar current (e.g., Kennett and Shackleton, 1976; Mikolajewicz et al., 1993; Oglesby, 1991; Raymo et al., 1990; Rind and Chandler, 1991). The more abrupt transient excursions are more likely to have been forced by rapid changes in greenhouse gas levels because they transpire over short timescales (e.g., 103104 yr) and, most importantly, are accompanied by geochemical and isotopic anomalies suggestive of major perturbations in the carbon and sulfur cycles (Dickens et al., 1995, 1997; Paytan et al., 1998; Pearson and Palmer, 2000; Schmitz et al., 1997; Stott and Kennet, 1990; Zachos et al., 1993).
Progress in characterizing Paleogene oceanography and climate history, particularly the transient events, has been hampered by the lack of high-quality, high-resolution multicored sequences. Most existing sites suffer from poor recovery and drilling disturbance, and few were multicored or drilled as part of depth transects. The few exceptions are sites recovered during recent Ocean Drilling Program (ODP) legs, including Sites 865, 999, 1001, 1051, and Bass River, New Jersey (Bralower et al., 1995, 1997; Miller et al., 1998; Norris and Röhl, 1999; Röhl et al., 2000). The high-resolution records produced from these sites have yielded a wealth of exciting, potentially important ideas about climate change that require additional data to be more fully explored. We currently lack the required sediment archives needed to characterize the changes in ocean circulation and chemistry that theoretically should have accompanied these climatic extremes. Gaining a more complete description of these events in a third dimension and at a higher temporal resolution is critical because such information is required for both formulating and testing hypotheses of what caused these events.
One of the more promising locations for recovering Paleogene sediments, including the PETM and EOGM, is Walvis Ridge in the South Atlantic Ocean. Walvis Ridge was the target of Deep Sea Drilling Project (DSDP) Leg 74, drilled in the summer of 1980, during which Sites 525529 were drilled as a depth transect along the northern flank of the ridge from 2500 to 4100 m water depth (Moore, Rabinowitz, et al., 1984). Paleogene pelagic sediments characterized by moderate sedimentation rates (~815 m/m.y.) and superb magnetic stratigraphy were recovered at each site. However, because of the poor recovery (~50%) and coring disturbances, especially with the extended core barrel (XCB) in relatively unlithified sediments, only short segments of the sequences were recovered fully intact, thereby preventing attempts to conduct high-resolution investigations. Nevertheless, subsequent shore-based studies of these cores were instrumental in improving our understanding of Maastrichtian and Paleogene paleoceanography (e.g., carbonate compensation depth [CCD], carbon isotope stratigraphy, deep-sea temperature/ice volume) (e.g., Moore, Rabinowitz, et al., 1984, and papers within). In addition, a nearly complete PETM interval was recovered from the deepest hole at Site 527. Bottom-water and sea-surface temperature (SST) estimates obtained from analysis of Site 527 samples have provided critical constraints on the scale of this event (Thomas et al., 1999; Thomas and Shackleton, 1996). At the shallower sites, the PETM was not recovered because of core gaps (poor recovery).
During the winter of 2000, a seismic survey of the southeastern Walvis Ridge was undertaken by the Meteor (cruise M49/1). The survey extended from the location of the Leg 74 sites to areas located north and northeast, a region where thicker sediment sequences were discovered (Fig. F1). The higher-fidelity multichannel seismic data generated during the survey allowed us to target a series of sites that will capture the PETM and other key intervals, possibly from penetration depths reachable by advanced hydraulic piston corer (APC), at least at the three shallowest sites. The sites have been positioned at depths that will provide a paleodepth range of 2200 m. This paleodepth transect will provide critical constraints on several aspects of the PETM event, as well as the EOGM, a lower-priority target. Advances in coring technology and drilling strategies (i.e., multihole composite sections) should allow for 100% recovery of sequences that were only partially recovered during Leg 74. In addition, recent advances in data acquisition and chronostratigraphy will enable high-precision correlation and dating of these sediments.
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