Technical Comments

Early Deglaciation in the Tropical Andes

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Science  04 Oct 2002:
Vol. 298, Issue 5591, pp. 7
DOI: 10.1126/science.298.5591.7


  • Figure 1

    Climate records spanning the last deglaciation. The vertical gray box represents the timing of tropical deglaciation established in (1). (A) The GISP2 record of atmospheric methane (12, 13). Also shown are the ages of deglaciation from five glacier systems in western North America (no vertical scale). WR, weighted mean (20,100 + 1000 yr B.P.) of 10Be ages on boulders from LGM moraine in the Wind River Mountains, Wyoming (15). SN, weighted mean (21,000+ 3000 yr B.P.) of 36Cl ages on boulders from the LGM moraine in the Sierra Nevada Mountains, California (16, 17). I interpret these cosmogenic surface exposure ages as representing landform age, and thus the time since the moraine was last occupied. OM, weighted mean (22,800 + 100 yr B.P.) of calibrated 14C ages on organics from lake sediments directly above till associated with a moraine in the Olympic Mountains, Washington (18). CIS, weighted mean (22,100+ 100 yr B.P.) of calibrated 14C ages on organics directly above glacial sediments associated with an advance of the southern margin of the Cordilleran Ice Sheet into the Fraser Lowlands, British Columbia (19). YIC, weighted mean (22,400 ± 100 yr B.P.) of U-series ages on travertine associated with reduced ice cover in the valley occupied by the northern outlet glacier of the Yellowstone Ice Cap (20). (B) Smooth curves: midmonth insolation at 60oN for June and at 30oS for December (21). Jagged curves: GISP2 record of oxygen isotopes. Gray line represents high-resolution, bidecadal data published by Stuiver and Grootes (9); black line represents lower resolution data published by Grootes et al. (22). (C) Byrd Station record of oxygen isotopes on GISP2 time scale (12, 13).

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