One of the most abrupt and dramatic global warming events in the geologic record took place ~55 Ma in the late Paleocene epoch. This event, known as the Late Paleocene Thermal Maximum (LPTM), coincided with widespread extinction of deep-sea faunas and rapid radiation in surface ocean and terrestrial ecosystems. The proposed four-year study will build an integrated reconstruction of ocean, atmosphere, and biosphere immediately before and at the peak of the LPTM. We will define the timing of effusive volcanism relative to the LPTM, and we will generate and compile extensive data bases related to the LPTM. These data will be used to constrain oceanic and climatic conditions preceding and during the LPTM. The defined conditions will serve as boundary conditions and validation for atmospheric, oceanic and coupled climate models that will be used to test theories of climate change related to the LPTM.