Paleoclimate studies of Greenland ice cores (Dansgaard et al., 1993) were the first to reveal a remarkable sequence of major, rapid, millennial-scale oscillations in the climate system during the last ice age superimposed on the more gradual, orbitally-driven insolation cycles. Because of high accumulation rates of snow over Greenland, ice cores from this location are able to resolve climate changes occuring within decades or less, revealing late Quaternary climate behavior never before observed. The initial ice core work demonstrated that the climate oscillations (now known as Dansgaard/Oeschger [D/O] cycles) essentially reflect a "flickering" of the climate system between warm and cold states (Fig.1), with air temperature shifts between these states estimated to be about 6° to 10°C. These shifts impart an almost bistable behavior in the climate system, with jumps between states occuring as briefly as a few decades or less (Alley and Clark, 1999). Even more remarkable was the discovery that the final switch from glacial to interglacial temperatures took place over a period of years to only a few decades at most (Alley and Clark, 1999). The oscillations also are recorded by significant changes in trace atmospheric greenhouse gases CO2 and CH4 in the ice cores. The discovery of millennial-scale climate variability of this magnitude contributed to a sweeping reevaluation of the processes that drive major changes in the climate system, since no obvious external forcing exists that can cause change on these time scales. While the ice core discoveries generated much excitement, it was initially unknown if this climate behavior was limited to the North Atlantic, with the peculiarities of ocean overturning in this region, or if the climate changes extended to other oceans and other parts of the globe. Were the tropics involved in climate flickering? Do these processes reflect global climate changes? Knowledge of the regional extent of the ocean's role in climate behavior was a critical first step to understanding possible mechanisms for abrupt climate changes. Investigation of other regions, especially oceans distant from the North Atlantic, was required. Ocean drilling became imperative since recovery of thick sediment sequences, deposited during the Quaternary at high sedimentation rates, was needed to resolve decadal-to millennial-scale climate change. Penetration of traditional piston cores was simply not long enough. Several locations offered the prospect of drilling for high quality records, including the Santa Barbara Basin off the coast of temperate southern California and the Cariaco Basin in the western tropical Atlantic. Studies of these two basin sequences represent an important legacy of the Ocean Drilling Program (ODP).
|Original language||English (US)|
|Number of pages||5|
|State||Published - Jan 1 2002|
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