As shown by the work of Dansgaard and his colleagues, climate oscillations of one or so millennia duration punctuate much of glacial section of the Greenland ice cores. These oscillations are characterized by 5øC air temperature changes, severalfold dust content changes and 50 ppm CO2 changes. Both the temperature and CO2 change are best explained by changes in the mode of operation of the ocean. In this paper we provide evidence which suggests that oscillations in surface water conditions of similar duration are present in the record from a deep sea core at 50øN. Based on this finding, we suggest that the Greenland climate changes are driven by oscillations in the salinity of the Atlantic Ocean which modulate the strength of the Atlantic's conveyor circulation.
INTRODUCTIONOne of the most puzzling features of the ice core records from Greenland is the series of large and rather abrupt changes in oxygen isotope composition during the last period of glaciation [Dansgaard et al., 1971[Dansgaard et al., , 1982[Dansgaard et al., , 1989]. Based on the correlation between the b180 in present-day precipitation and mean annual temperature for high-latitude stations, these changes translate into 5øC jumps in air temperature. Correlating with the oxygen isotope changes are severalfold changes in the dust content of the ice (see Figure 1), Copyfight 1990 by the American Geophysical Union. Paper number 90PA01194. 0883-8305/90/90PA-01194 $10.00 50 ppm changes in the CO2 content of the air trapped in the ice [Stauffer et al., 1984], changes in the SO4 concentration in the ice [Finkle and Langway, 1985] and changes in 10Be content of the ice [Beer et al., 1984]. As the 180 signature for these events has now been found in three Greenland ice cores (Camp Century [Dansgaard et al., 1971], Dye 3 [Dansgaard et al., 1982], and Renland (W. Dansgaard personal communication, 1990)), they must be real climatic events. However, the validity of the CO2 signal as a record of atmospheric composition remains in limbo. The reason is that similar events were not found in a study of an Antarctic ice core [Neftel et al., 1988]. As discussed by Dansgaard and Oeschger [1989], this absence could reflect either a smoothing of the record in low deposition Antarctic record or meltwater layers in the Dye 3 ice. Oeschger et al. [1984], fin'st suggested that the Greenland events constitute jumps between two modes of operation of the climate system. Broecker et al. [1985] went a step further and postulated that Oeschger's modes involved a turning on and off of the Atlanfic's conveyor circulation system. Rather than pursuing the cause of the entire series of oscillations, recent attention has been focused on a single event, the Younger Dryas, which followed upon the heels of the last glacial termination. This event has roughly the same shape, amplitude, and duration as those during the glacial period. The lure of the Younger Dryas is that in contrast to the others it is well documented in pollen records from the lands surrounding the northern Atlantic [W...
