The modern Pacific Ocean, the largest ocean basin, occupies slightly more than 50% of modern global ocean surface area but accounted for almost 65% of total ocean area at the beginning of the Cenozoic. It has been a large medium-term reservoir of heat, carbon, and nutrients for the entire Cenozoic and is a major locus of carbon cycling to and from the ocean interior. For example, 20%–60% of total marine primary production occurs in the modern equatorial Pacific (Chavez and Barber, 1987), and ~1 Gt of carbon is exchanged from the ocean to the atmosphere annually through upwelling of CO2-enriched subsurface waters (Chavez et al., 1999).

Pacific Ocean circulation, temperature, primary productivity, and chemistry have all changed radically over the Cenozoic. Earth cooled from the extreme warmth of the early Cenozoic to the dual-pole icecaps of the Pleistocene. Study of the Cenozoic equatorial Pacific provides an opportunity to understand how different Earth systems interact under different boundary conditions of global temperature and geography.

Leg 199 is one of a set of recent Ocean Drilling Program (ODP) drilling legs that target Paleogene and Mesozoic paleoceanography. During Leg 171B, a transect of sites was drilled in the subtropical western North Atlantic (Blake Nose). During Legs 181 and 189 sites were drilled around New Zealand and the Tasman Rise to study the evolution of Pacific deepwater circulation and the development of circulation through the Tasman Gateway. During Leg 198, a depth transect was drilled on the Shatsky Rise to study the Mesozoic and early Cenozoic tropical Pacific, and during Leg 207 a similarly aged sequence was drilled on the margin of Suriname, Demerara Rise, in the equatorial Atlantic. Leg 208, on Walvis Ridge, studied the evolution of the South Atlantic.

In this paper we summarize the research from the Leg 199 shipboard scientific party and their collaborators since the end of Leg 199 drilling in December 2001. The contributions range from the rigorously metric to the posing of more speculative hypotheses (e.g., from developing the first continuous oxygen isotope stratigraphy for the Oligocene in the Pacific [Wade and Pälike, 2004; Lear et al., 2004; Pälike et al., submitted (N1)] to the use of the geographic fixity of equatorial upwelling to explore Cenozoic Hawaiian hotspot movement [Parés and Moore, 2005]).

After a brief description of the setting of the Eocene Pacific and a synopsis of ODP Leg 199 drilling, we describe stratigraphic efforts during Leg 199. Then we summarize studies of the Eocene/Oligocene (E/O) boundary event and Oligocene, followed by an exploration of interactions between Greenhouse Eocene conditions and the carbon cycle. Finally, we examine the Paleocene/Eocene (P/E) boundary event, also known as the Paleocene/Eocene Thermal Maximum (PETM) (Zachos et al., 2001).