TY - JOUR T1 - A 17,000 year history of Andean climatic and vegetation change from Laguna de Chochos, Peru JF - Journal of Quaternary Science Y1 - 2005 A1 - Bush, M. B. A1 - Hansen, B. C. S. A1 - Rodbell, D. T. A1 - Seltzer, G. O. A1 - Young, K. R. A1 - Leon, B. A1 - Abbott, M. B. A1 - Silman, M. R. A1 - Gosling, W. D. AB - The manifestation of major climatic events such as the timing of deglaciation and whether, or not, the Younger Dryas affected Andean systems has garnered considerable recent attention. Even the Holocene is rapidly emerging as a time of considerable interest in Neotropical palaeoclimatology and palaeoecology. The Holocene of the Neotropics is now revealed as a time of some temperature change with precipitation:evaporation ratios fluctuating markedly. Major changes in lake level, ice-accumulation, and vegetation are indicative of changes both in precipitation and temperature regimes. Although global-scale forcing mechanisms may underlie some of these changes, e.g. the precessional rhythm, other variability appears to be localised. In a record from near the upper forest limit of the eastern Peruvian Andes, pollen, charcoal, and sedimentary data suggest that the deglaciational period from ca. 17 000 to ca. 11 500 cal. yr BP was a period of rapid climatic oscillations, set against an overall trend of warming. A warm-dry event is evident between ca. 9500 and ca. 7300 cal. yr BP, and comparisons with other regional archives suggest that it was regional in scale. A ca. 1500-yr periodicity in the magnetic susceptibility data is evident between 12 000 and 6000 cal. yr BP, reaching a peak intensity during the dry event. A weaker oscillation with a 500–600-yr periodicity is present throughout much of the Holocene. The uppermost sample of the pollen analysis reveals deforestation as modern human land use simplified the landscape. VL - 20 IS - 7-8 N1 - id: 1015 JO - A 17,000 year history of Andean climatic and vegetation change from Laguna de Chochos, Peru ER - TY - JOUR T1 - A late glacial-Holocene tephrochronology for glacial lakes in southern Ecuador JF - Quaternary Research Y1 - 2002 A1 - Rodbell, D. T. A1 - Bagnato, S. A1 - Nebolini, J. C. A1 - Seltzer, G. O. A1 - Abbott, M. B. AB - Despite the presence of numerous active volcanoes in the northern half of Ecuador, few, if any, distal tephras have been previously recognized in the southern one third of the country. In this article, we document the presence of thin (0.1-1.0-cm-thick) distal tephras comprising glass and/or phenocrysts of hornblende and feldspar in sediment cores from five glacial lakes and one bog in Las Cajas National Park (2degrees40'-3degrees00'S, 79degrees00'-79degrees25'W). The lake cores contain from 5 to 7 tephras, and each has a diagnostic major element geochemistry as determined from electron microprobe analysis of similar to710 glass shards and similar to440 phenocrysts of feldspar and hornblende. The loss of sodium with exposure to the electron microbeam causes a 10 +/- 7 wt.% (+/-1sigma) reduction in Na content, which we empirically determined and corrected for before correlating tephras among the sediment cores. We use a similarity coefficient to correlate among the sediment cores; pair-wise comparison of all tephras generally yields an unambiguous correlation among the cores. Six tephras can be traced among all or most of the cores, and several tephras are present in only one or two of the cores. Twenty-six accelerator mass spectrometry (14)C dates on macrofossils preserved in the sediment cores provide the basis for establishing a regional tephrochronology. The widespread tephras were deposited similar to9900, 8800,7300,5300,2500, and 2200 cal yr B.P. The oldest tephras were deposited similar to15,500 and 15,100 cal yr B.P., but these are not found in all cores. Two of the tephras appear correlative with volcaniclastic strata on the flanks of Volcan Cotopaxi and one tephra may correlate with strata on the flanks of Volcan Ninahuilca; both volcanoes are in central Ecuador. The absence of tephras in sediment cores correlative with the numerous eruptions of active volcanoes of the past two millennia implies that the earlier eruptions, which did deposit tephras in the lakes, must have been either especially voluminous, or southerly winds must have prevailed at the time of the eruption, or both. (C) 2002 University of Washington. VL - 57 IS - 3 N1 - 555kpTimes Cited:25Cited References Count:23 JO - A late glacial-Holocene tephrochronology for glacial lakes in southern Ecuador ER - TY - JOUR T1 - Subdivision of glacial deposits in southeastern Peru based on pedogenic development and radiometric ages JF - Quaternary Research Y1 - 2001 A1 - Goodman, A. Y. A1 - Rodbell, D. T. A1 - Seltzer, G. O. A1 - Mark, B. G. AB - The Cordillera Vilcanota and Quelccaya Ice Cap region of southern Peru (13 degrees 30'-14 degrees 00'S; 70 degrees 40'-71 degrees 25'W) contains a detailed record of late Quaternary glaciation in the tropical Andes, Quantification of soil development on 19 moraine crests and radiocarbon ages are used to reconstruct the glacial history. Secondary iron and day increase linearly in Quelccaya soils and clay accumulates at a linear rate in Vilcanota soils, which may reflect the semicontinuous addition of eolian dust enriched in secondary iron to all soils. In contrast, logarithmic rates of iron buildup in soils in the Cordillera Vilcanota reflect chemical weathering; high concentrations of secondary iron in Vilcanota tills may mask the role of eolian input to these soils. Soil-age estimates from extrapolation of field and laboratory data suggest that the most extensive late Quaternary glaciation occurred >70,000 yr B.P. This provides one of the first semiquantitative age estimates for maximum ice extent in southern Peru and is supported by a minimum-limiting age of similar to 41,520 C-14 yr B.P. A late glacial readvance culminated similar to 16,650 cal yr B.P. in the Cordillera Vilcanota, Following rapid deglaciation of unknown extent, an advance of the Quelccaya Ice Cap occurred between similar to 13,090 and 12,800 cal yr B.P., which coincides approximately with the onset of the Younger Dryas cooling in the North Atlantic region. Moraines deposited <394 cal yr B.P. in the Cordillera Vilcanota and <300 cal yr B.P. on the west side of the Quelccaya Ice Cap correlate with Little Ice Age moraines of other regions. (C) 2001 University or Washington. VL - 56 IS - 1 N1 - 452lzTimes Cited:27Cited References Count:51 JO - Subdivision of glacial deposits in southeastern Peru based on pedogenic development and radiometric ages ER - TY - JOUR T1 - Rapid ice margin fluctuations during the Bolling/Allerod and Younger Dryas intervals in the Peruvian Andes JF - Quaternary Research Y1 - 2000 A1 - Rodbell, D. T. A1 - Seltzer, G. O. VL - 54 N1 - id: 392 ER - TY - JOUR T1 - Rapid ice margin fluctuations during the Younger Dryas in the tropical Andes JF - Quaternary Research Y1 - 2000 A1 - Rodbell, D. T. A1 - Seltzer, G. O. AB - Radiocarbon dated lacustrine sequences in Peru show that the chronology of glaciation during the late glacial in the tropical Andes was significantly out-of-phase with the record of climate change in the North Atlantic region. Fluvial incision of glacial-lake deposits in the Cordillera Blanca, central Peru, has exposed a glacial outwash gravel; radiocarbon dates from peat stratigraphically bounding the gravel imply that a glacier advance culminated between similar to 11,280 and 10,990 C-14 yr B.P.; rapid ice recession followed. Similarly, in southern Peru, ice readvanced between similar to 11,500 and 10,900 C-14 yr B.P. as shown by a basal radiocarbon date of similar to 10,870 C-14 yr B.P. from a lake within 1 ion of the Quelccaya Ice Cap. By 10,900 C-14 yr B.P, the ice front had retreated to nearly within its modern limits. Thus, glaciers in central and southern Peru advanced and retreated in near lockstep with one another. The Younger Dryas in the Peruvian Andes was apparently marked by retreating ice fronts in spite of the cool conditions that are inferred from the partial derivative O-18 record of Sajama ice. This retreat was apparently driven by reduced precipitation, which is consistent with interpretations of other paleoclimatic indicators from the region and which may have been a nonlinear response to steadily decreasing summer insolation. (C) 2000 University of Washington. VL - 54 IS - 3 N1 - 388erTimes Cited:61Cited References Count:66 JO - Rapid ice margin fluctuations during the Younger Dryas in the tropical Andes ER - TY - JOUR T1 - A high resolution ~15,000 year record of El-Nino driven alluviation in southwestern Ecuador JF - Science Y1 - 1999 A1 - Rodbell, D. T. A1 - Seltzer, G. O. A1 - Anderson, D. M. A1 - Abbott, M. B. A1 - Enfield, D. B. A1 - Newman, J. H. VL - 283 N1 - id: 393 ER -