1. The Younger Dryas Cooling Event
Exploring relations between geochemical and ecological expressions of the Younger Dryas in the North Atlantic, Nordic, and New England Regions.

2. Introduction
. The Younger Dryas: Late Pleistocene(12, ,600 cal yr. BP)
. 3-4˚C depression, dry.
temperature + moisture proxies
. Retreat of the Laurentide Ice Sheet (26,000-16,000 cal yr. BP)

4. Role of the Atlantic meridional overturning circulation

5. . Observations of Dryas in the Nordic pollen and macrofossil record (Dahl 1951)

6. Studies in Slotseng, Denmark

7. Pollen Data from Slotseng region of Denmark
Pollen Data from Slotseng region of Denmark. SL-8 representative of Younger Dryas. Note appearance of Dryas Octopetala and reduced Pine abundance (Morten & Fischer et al. 2011).

8. Geochemical Evidence
. Ice and sediment cores a) O18/O16 ratios b) Mg/Ca ratios
1837’th m section from total 3053m GISP2 Ice Core

9. Temperature Proxies
. O18/O16 ratios in ice cores . Preferential condensation and precipitation at lower latitude as cooler temperatures spread towards the equator
Greenland/North Atlantic ice and sediment core record (right) compared to Antarctic and SE Pacific ice and sediment core record

10. Adult (a,b) and juvenile (c,d) N. pachyderma

11. Temperature Proxies
. Mg/Ca ratios . Mg2+ substitution for Ca in biogenic calcium carbonate . Death, deposition, lithification.
Sedimentary Core Site 980 YD

12. Ecological Expressions in New England (Pollen and Macrofossil Records)
. Shift from post-glacial warming vegetation to boreal/sub-arctic vegetation. . Site studies in Maine and Conn. sediment cores from pond sites.

13. Conn.

14. Maine

15. Borns (2011)

16. Collapse of the AMOC and cause of the Younger Dryas: Threshold Meltwater Hypothesis
. Multi-decadal cyclicity: documented

17. Meltwater Hypothesis
. Retreat of the Laurentide Ice Sheet . Density Issues . Apparent Threshold . Abrupt end to the Younger Dryas

18. Global AMOC