Ga. Islebe et al., A COOLING EVENT DURING THE YOUNGER DRYAS CHRON IN COSTA-RICA, Palaeogeography, palaeoclimatology, palaeoecology, 117(1-2), 1995, pp. 73-80
A fossil pollen record from the Costa Rican Cordillera de Talamanca pr
esents the first AMS radiocarbon-dated evidence of a temperature decre
ase during the Younger Dryas Chron. This cooling event is named La Cho
nta stadial after the bog at 2310 m altitude, located at the actual lo
wer to upper montane forest boundary. High-resolution pollen analysis
revealed that between 11,070 +/- 130 (AMS C-14 age) and 10,400 yr B.P.
(interpolated age) vegetation comparable to present-day subalpine for
est occurred about 300-400 m lower than in the previous warmer interva
l, and 600 to 700 m lower than at present time. The radiocarbon dates
ale close to the earlier estimated ages of 11,080-10,500 yr B.P. for t
his interval, based on interpolation and pollen concentration rates (H
ooghiemstra et al., 1992). The downslope shift of the upper forest lin
e indicates an estimated temperature drop of 2-3 degrees C during the
La Chonta stadial. The local vegetation development is indicative of a
drier climate. From 10,400 to 9800 +/- 120 yr B.P. (AMS C-14 age) sub
alpine rain forest was replaced by upper montane forest, a transitiona
l period to Holocene environmental conditions.