Millennial-scale climate change and oceanic processes in the late Pliocene and early Pleistocene

Abstract

We generated 200-500 year resolution records of oceanic processes in the North Atlantic (Ocean Drilling Program Site 983, 60°24N, 23°38W, 1983 meters water depth) for intervals in the latest Pliocene (1.86-1.93 Ma) and the earliest Pleistocene (1.75-1.83 Ma) in order to examine the linkages between millennial-scale variations in the ocean and background glacial-interglacial climate change. Within glacial intervals we find evidence for variations similar to those observed in the late Pleistocene. We find discrete ice-rafted debris (IRD) events that reoccur every 2-5 kyr. These events are preceded by a short cooling and accompanied by a reorganization of glacial deep waters. The timing of IRD events in the late Pliocene and early Pleistocene intervals is similar to that of Dansgaard-Oeschger cycles, but we find no IRD events comparable in timing to late Pleistocene Heinrich events. Although interglacial intervals are much more stable, we do find evidence for low-amplitude variations in deep water properties that reoccur every ~2 kyr within interglacial intervals. The similarity between our late Pliocene-early Pleistocene records and late Pleistocene records implies that the mechanism driving millennial-scale variations cannot be uniquely attributed to the strongly nonlinear linkage between climate and insolation and the large ice sheets of the late Pleistocene.