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As first noted by Heinrich, 1988, glacial age

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...

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Radiocarbon ages on CaCO3 from deep‐sea cores offer constraints on the nature of the CaCO3 dissolution process. The idea is that the toll taken by dissolution on grains within the core top bioturbation zone should be in proportion to their time of residence in this zone. If so, dissolution would shift the mass distribution in favor of younger grains, thereby reducing the mean radiocarbon age for the grain ensemble. We have searched in vain for evidence supporting the existence of such an age reduction. Instead, we find that for water depths of more than 4 km in the tropical Pacific the radiocarbon age increases with the extent of dissolution. We can find no satisfactory steady state explanation and are forced to conclude that this increase must be the result of chemical erosion. The idea is that during the Holocene the rate of dissolution of CaCO3 has exceeded the rain rate of CaCO3. In this circumstance, bioturbation exhumes CaCO3 from the underlying glacial sediment and mixes it with CaCO3 raining from the sea surface.

Radiocarbon ages for benthic and planktonic foraminifera from the late glacial sections of two Atlantic and two Pacific cores are reported. The differences for benthic‐planktonic pairs suggest that the radiocarbon age for deep Atlantic water was somewhat larger than today's (i.e., 600±250, as opposed to 400 years) and that the radiocarbon age for deep Pacific water was also slightly larger than today's (2100±400, as opposed to 1600, years). Our results suggest that during glacial time, the deep Pacific was, as it is today, significantly depleted in radiocarbon relative to the deep Atlantic. As many questions remain unanswered regarding the reliability of this approach, these conclusions must be considered to be preliminary.

Radiocarbon ages determined by the AMS method on hand-picked foraminifera shells are reported. The results allow estimates of the ventilation rate of the deep Atlantic and Pacific Oceans during glacial time. They also extend our knowledge of the chronology of events associated with the transition from full glacial conditions ca 15,000 years ago to full interglacial conditions ca 8000 years ago. This and the previous lists (Broecker et al 1988c) contain all the results obtained as part of this program through the fall of 1989.

As a test of the reliability of paleocean ventilation rates reconstructed from radiocarbon age differences between planktonic and benthic foraminifera, measurements have been made on coexisting species of planktonic foraminifera. While ideally no differences should exist, we do find them. In this paper we discuss the possible causes for these differences and attempt to evaluate their impact on the interpretation of benthic‐planktonic age differences.