It is not customary to perform paleoclimate modeling hand in hand with data collection. The separation of data collection and modeling is generally beneficial, but for this particular problem—characterizing the tropics in a poorly understood time interval and clarifying the relationship between the tropics and global climate—it is appropriate to make an exception. This cruise and its companion (Ocean Drilling Program [ODP] Leg 198 to Shatsky Rise) are not the first to collect data on the early Paleogene tropical climate. Rather, these cruises returned to answer questions that have plagued the early Paleogene community for almost two decades. It is important to note that climate models themselves have evolved recently. We can now make predictions that are entirely independent of climate proxies because stable, fully coupled, comprehensive (atmosphere-ocean-land surface-sea ice), and well-validated climate models are now available. Results from these paleoclimate modeling studies allow us to construct a "straw man" for the sake of clarifying the differences between what climate proxies tell us and what, based on well-understood physical processes, we expect.
The early Paleogene is usually characterized as having near-modern (~25°C) tropical sea-surface temperatures (SSTs) and warm winters in extratropical continental interiors. Together, these features have proven difficult to reconcile with our current understanding of climate (Barron, 1987; Sloan and Barron, 1990; Wolfe, 1994; Zachos et al., 1994; Bralower et al., 1995; Greenwood and Wing, 1995). Existing tropical SST reconstructions may not, however, necessitate a fundamental rethinking of climate dynamics because