The Paleocene/Eocene (P/E) boundary (~55 Ma) records a ~200-k.y. interval of extreme global warming associated with the massive release of greenhouse gases into the ocean and atmosphere (Bains et al., 1999; Dickens 2001). Drilling during ODP Leg 171B recovered an expanded section of siliceous chalk across the P/E boundary at Sites 1050 and 1051 (Norris, Kroon, Klaus, et al., 1998; Norris et al., 2001b; Norris and Röhl, 1999). A notable feature of the entire Paleocene and early Eocene section at both sites was the pervasive cyclicity in sediment color and other physical properties that has made it possible to produce detailed orbital chronologies for the early Paleogene. For example, Röhl et al. (2001) used scanning X-ray fluorescence logs of split cores from Site 1050 to revise the Paleogene time scale and calibrate the durations of magnetochrons independent of models for seafloor spreading. Norris and Röhl (1999) and Röhl et al. (2000) used physical property cycles to estimate the age of the P/E boundary and the duration of the transient warm period associated with it. Modeling studies suggest that the region around Blake Nose should have been particularly sensitive to orbital forcing and may have salinities and seasonal responses to orbital forcing that depart greatly from those observed over the Atlantic as a whole (Sloan and Huber, 2001).
Results from studies of Site 1051 have contributed to our understanding of the climatology and origins of the P/E boundary event. Katz et al. (1999) presented geochemical data, foraminifer assemblage results, and seismic analysis to suggest that Blake Nose may have contributed greenhouse gases during venting of methane hydrate reservoirs at the P/E boundary. Coring and seismic evidence suggests that if Blake Nose was a gas hydrate reservoir in the Paleocene and early Eocene, the hydrate must have been shallowly seated and could not have contributed large volumes of greenhouse gases during the P/E event (Norris et al., 2001b). Sanfillipo and Blome (2001) demonstrated that there is no major change in radiolarian assemblages or taxonomic diversity associated with the P/E boundary event, in agreement with previous work on planktonic foraminifers. Bains et al. (1999) showed that stable isotope records can be correlated in detail between Site 1051 in the North Atlantic and Leg 113 Site 690 in the Southern Ocean. Together with the cyclostratigaphic chronology of Norris and Röhl (1999) and Röhl et al. (2000) the results of Bains et al. (1999) show that global warming and greenhouse gas outgassing was very abrupt and occurred in several pulses over a total of ~50 k.y. Recently, Bains et al. (2000) found evidence for an increase in export production during the P/E boundary event at several deep-sea sites, including Site 1051. These authors proposed that the increase in carbon sequestration by phytoplankton may have contributed to CO2 drawdown and the termination of greenhouse warming at the end of the P/E boundary event.
The broad-scale evolution of the Paleocene and Eocene oceans has also been investigated. For example, Faul and Delaney (Chap. 1, this volume) have examined the oceanographic history of phosphorus accumulation. They showed that the dramatic rise in d13C of marine carbonates during the Paleocene is accompanied by an increase in phosphorus accumulation rates consistent with a large increase in export production leading up to the P/E boundary event. Pletsch (2001) examined the history of palygorskite clay deposition over the same time interval. The widespread prevalence of these clays in North Atlantic sediments during the lower Eocene may reflect the formation and outflow of highly saline deep and intermediate waters from Tethys into the North Atlantic and provide a valuable tracer for the often sought, but rarely found, "warm saline deep water."