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Abrupt Climate Change: Inevitable Surprises
FIGURE 2.4 Global extent of terrestrial (pollen) and ice core (isotopic) evidence where the Younger Dryas cooling (11,500 – 13,000 BP) has been found. While northern hemispheric evidence is consistently strong for cooling, southern hemispheric sites contain controversial evidence and in some cases lack of evidence for a cooling during the YD interval. Possible upwelling in the Cariaco Basin during this time is also indicated, attributed to trade wind increase. Strong cooling ranges from 13-4° C; controversial means some sites show cooling and some do not (after Peteet, 1995).
decrease was not observed on the western Panamanian slope (Piperno et al., l990; Bush et al., l992).
In Colombia, the El Abra stadial (a Younger Dryas equivalent) was a cold interval about 13,000-11,700 years ago characterized by low temperature and low precipitation (van der Hammen and Hooghiemstra, 1995). The upper forest line during the stadial was 600-800 m lower than today, and average temperatures were about 4-6°C lower than today. This evi-