dicted) at the cold, wintertime values reconstructed for the last glacial maximum (the LGM, which occurred about 18,000 yr BP) by CLIMAP (1981). As can be seen in Figure 4, a similar pattern of cooling (in this case, wintertime) was achieved. Although the presence of large ice sheets contributed to oceanic cooling during the LGM (Manabe and Broccoli, 1985), in both this and the coupled atmosphere/ocean experiment ice sheets were not introduced, and all other climate boundary conditions were those of today. Figures 3 and 4 provide an impression of the influence of a cold ("conveyor off") ocean alone.
The main purpose of the present paper is to assess the capacity of the ocean to undergo circulation changes of the magnitude and rapidity suggested by the climate proxy
record around the Atlantic region, through a review of the evidence for such changes in the ocean sediments themselves. Following up on the discussion brought forward in this introduction, I will begin by assessing the magnitude of heat transport into the circum-Atlantic region by the ocean's conveyor circulation system. I will then outline the approach used in reconstructing past changes in conveyor circulation and present results from studies of new Atlantic sediment records with sub-century-scale resolution and climate sensitivity sufficient to capture the amplitude and rates of climate change implied by ice-core studies and numerical models (Lehman and Keigwin, 1992; Koc-Karpuz and Jansen, 1992). These provide a test of the proposed conveyor model of circum-Atlantic climate change, as well as an assessment of the frequency and abruptness with which the conveyor circulation may vary.
The net transports of heat and salt in the world's oceans are characterized by a southward, trans-equatorial flow of relatively cold, salty North Atlantic Deep Water (NADW) formed by cooling and sinking in the northern North Atlantic, and an apparently compensatory, northward, trans-equatorial flow of warm, salty water in the Atlantic thermocline (Gordon, 1986; Broecker, 1991 a). Cooling and sinking occurs predominantly in the Labrador and the Nordic seas (Figure 5). The dense products of surface cooling in the