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Geological Setting

The North Atlantic Ocean is undoubtedly one of the most climatically sensitive regions on Earth because the ocean-atmosphere-cryosphere system is prone to mode jumps that are triggered by changes in freshwater delivery to source areas of deepwater formation. During the last glaciation, these abrupt jumps in climate state are manifest by Dansgaard/Oeschger (D/O) cycles and Heinrich events in ice and marine sediment cores. Given the paramount importance of the North Atlantic as a driver of global climate change, we drilled at nine key locations to extend the study of millennial-scale climate variability over the last few million years. What is the rationale for studying millennial-scale variability in the North Atlantic over the last few million years rather than just the last glacial cycle (recoverable by conventional piston cores)? Determining the long-term evolution of millennial-scale variability in surface temperature, ice sheet dynamics, and thermohaline circulation can provide clues to the mechanisms responsible for abrupt climate change. For example, the average climate state evolved toward generally colder conditions with larger ice sheets during the Pliocene–Pleistocene. This shift was accompanied by a change in the spectral character of climate proxies from dominantly 41 k.y. to 100 k.y. periods between ~920 and 640 ka (Schmieder et al., 2000). Among the numerous questions to be answered are the following:

• When did "Heinrich events" first appear in the sedimentary record of the North Atlantic?

• Are they restricted to the "100 k.y. world" when ice volume increased substantially?

• Is the quasi-periodic 1500 y cycle documented for the last climate cycle a stable feature of the North Atlantic throughout the Pleistocene?

• How has millennial-scale variability evolved during the Pleistocene as orbital and glacial boundary conditions changed?

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