The Younger Dryas Cooling Event

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Presentation transcript:

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.

Introduction . The Younger Dryas: Late Pleistocene(12,900- 11,600 cal yr. BP) . 3-4˚C depression, dry. temperature + moisture proxies . Retreat of the Laurentide Ice Sheet (26,000-16,000 cal yr. BP)

Role of the Atlantic meridional overturning circulation

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

Studies in Slotseng, Denmark

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).

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

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

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

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

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.

Conn.

Maine

Borns (2011)

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

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

Global AMOC