Terrestrial Paleotemperature Estimates for 10,000 to >50,000 14C yr BP from the Southern Andes, Chile
Calvin J. Heusser, (100 Clinton Road, Tuxedo, NY 10987); Linda E.
Heusser, (Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964); Thomas V. Lowell, (Dept. Of Geology, University of Cincinnati, Cincinnati, OH, 45221-0013 Internet Thomas.Lowell@uc.edu)
Glacial and vegetation records from mid-latitudes of the Southern
Hemisphere constrain various mechanisms of millennial-scale global
climate change. The Southern Andes at 40 to 420S latitude, where we extracted high-resolution, terrestrial paleotemperature data, are near the
present northern boundary of the westerly wind circulation. We highlight a record >from the mire at Taiquem= (420 10'S, 730 36'W) as 30 14C ages define a sequence back through the LGM to at least 50,000 14C yr BP. Within that record, fifteen different pollen assemblage zones reflect vegetation changes prior to the Holocene.
Pollen assemblage zonal boundaries lie at 11,400, 13,000, 15,300,
21,400, 23,000, 24,900, 26,000, 32,100, 35,600, 45,200, 47,100 14C yr BP and at two lower levels with infinite ages. By analogy with the present vegetation zones and their elevation distribution, paleovegetation zones provide an estimate of the temperature depression near present-day sea level. Values have an estimated error of 00.50C.
This temperature index shows two features: a long-term cooling from
>50,000 to 14,700 14C yr BP, and at least seven superposed millennial-scale temperature depressions. The long-term trend shows a maximum 50C summer temperature depression below present values (140C) at 16,000 14C yr BP. The short-term events show an additional 1 to 30C temperature decrease. The amplitude of the short-term events increases after 35,000 14C yr BP. Prior to 35,000 14C yr BP, temperature oscillations are+1.50C but most are lower; younger oscillations are as much 2.50C.
Four glacial expansions between 29,400 and 14,800 14C yr BP reached similar maximum positions. This indicates that the effective ELA was comparable. These expansions occur during cool spikes, but the exact phasing may differ somewhat.
We point out that the 14,800 14C yr BP expansion in the Southern
Andes overran older limits, suggesting a southerly displacement of the main moisture source. This implies that displacement of the westerly wind circulation belt was less just prior to the termination than during
earlier glacial expansions. These records imply that atmospheric changes operating on millennial time scales lie superposed on an overall LGM cooling cycle.