Figure 7

Percentage of N. pachyderma (sin) in core-top sediments from the northern North Atlantic and Norwegian Sea versus temperature of the overlying surface waters. N. pachyderma (sin) percentage appears to have a range of temperature sensitivity of about 5°C. The inset map shows the location of the sediment cores used in the calibration. Data used in this figure were supplied by David Anderson of the National Geophysical Data Center, NOAA.

Average rates of deposition at the core location were 5 m/kyr during deglaciation, some 20 to 50 times higher than at other high-deposition-rate locations in the open Atlantic. The core site is located a few degrees east of the main axis of Atlantic water inflow to the Norwegian Sea basin (Figure 6b). Atlantic water bleeding off the main axis of inflow and into the North Sea greatly influences SST and salinity over the core site, as is clearly apparent in satellite images of the region (see Figure 8, in the color well). Instrumental data suggest that changes in salinity and SST of the North Sea reflect similar changes in the open North Atlantic (Dickson et al., 1984; Heath et al., 1991). These observations suggest that the location Troll 3.1 provides a suitable monitor of surface water exchange between the open North Atlantic and the Nordic Seas.

The down-core variation in percentage of N. pachyderma (sin) and associated accelerator mass spectrometer (AMS) 14C dates in Troll 3.1 are given in Figure 9. These match closely the faunal variations from another AMS 14C-dated sediment core located off Ireland (core V23-81), just upstream of Troll 3.1 in the present-day circulation (Figure 6b; Ruddiman et al., 1977; Broecker et al., 1988). The agreement between these records provides additional evidence that faunal changes in the western North Sea were diagnostic of conditions in the open Atlantic during the last deglaciation. While the two records are complementary in this regard, the record in Troll 3.1 offers a key advantage in that rates of deposition are high enough to permit resolu-

Figure 9

Percentage of N. pachyderma (sin) against depth. The panel for core Troll 3.1 includes AMS 14C dates from Lehman et al. (1991). Despite the large difference in depth scales, the downcore pattern is similar to that in core V23-81 panel, which is from Ruddiman et al. (1977, reprinted with permission of the Royal Society) and includes dates from Broecker et al. (1988, 1990b). The largest N. pachyderma (sin) peak in each core occurred during the Younger Dryas. Although dates of the N. pachyderma (sin) peak just prior to the Younger Dryas in V23-81 are discordant with those for a similar event in Troll 3.1, bracketing dates on subpolar foraminifera (Globoratalia bulloides) are similar. Detailed analyses of photographs of V23-81 indicate that out-of-sequence dates come from worm burrows (G. Bond, personal communication). Arrows mark faunal transitions in Troll 3.1 corresponding to SST changes of about 5°C in 40 years or less. (From Lehman and Keigwin, 1992; reprinted with permission of MacMillan Magazines.)

The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement