Moraines in mountain ranges along the Pole-Equator-Pole: Americas (PEP 1) transect document positions reached by glaciers during the last glacial cycle. Acom-mon perception has been that the outermost moraines define the CLIMAP (Climate: Long-Range Investigation, Mapping, and Prediction) (1981) last glacial maximum (LGM, 18,000 14C B.P.), and moraines within this zone were formed during recessional stages. However, it now seems likely that mountain glaciers advanced and retreated many times during the last glacial cycle (e.g., Lowell et al., 1995; Benson et al., 1996; Phillips et al., 1996), perhaps in synchrony with glacial age climate variability indicated by analyses of Greenland ice cores (Dansgaard et al., 1993) and North Atlantic sediments (Bond et al., 1993). Moreover, maximum glaciation rarely occurred at 18,000 14C B.P., which is important when the relationship between snow line depression and CLIMAP's (CLIMAP, 1981) estimates of sea surface temperature (SST) at the LGM (e.g., Klein et al., 1999; Thompson et al., 1995) is being considered. The extent reached by glaciers during Marine Isotope Stage 2 (MIS 2) depended on the available precipitation as well as on the degree of thermal decline. For this reason, it may be inappropriate to assume that all mountain glaciers reached their maximum extents at the CLIMAP LGM, or that they all reached their maximum limits at the same time.
This chapter presents a brief review of published chronologies for MIS 2 (-32,000-15,000 14C B.P.) glacier advances along the PEP 1 transect (Fig. 1). The analysis is based largely on overviews of glacial chronologies published in the last 15 years, but incorporates information from recent papers on specific areas where appropriate. This chapter discusses the last glaciation in the cordilleras of North and South America prior to a discussion of the patterns that emerge (Fig. 2).
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