Date of Award

6-2014

Document Type

Open Access

Degree Name

Bachelor of Science

Department

Geology

First Advisor

Donald Rodbell

Language

English

Keywords

glaciers, climate change, glaciation, geology

Abstract

Alpine glaciers respond rapidly to changes in climate and the growth and decay of alpine glaciers is recorded in sediment cores extracted from lakes immediately downvalley from the margins of former glaciers. These records provide continuous archives of glaciation and climate change that complement the inherently discontinuous records of glaciation preserved by moraines. The aim of this study is to generate a continuous record of glaciation in Jaico cirque from lake sediment cores, which is located on the southeastern side of the quartz-monzonite dominated Huaguruncho Massif (5789 masl) in the eastern Peruvian Andes. The lakes are Laguna Jaico (10.56° S, 75.92° W; 4,271 masl) and Laguna Yanacocha (10.56° S, 75.93° W; 4,357 masl). The records generated will be combined with the record of glaciation preserved in upvalley moraines that are dated by the cosmogenic radionuclide 10Be. The lake cores were obtained using both a Livingstone square-rod piston corer and a modified Nesje Percussion corer from an inflatable raft. Cores were analyzed for total carbon (TC), total inorganic carbon (TIC), bulk density (BD), magnetic susceptibility (MS), stable isotopes of C and O, and major element composition (by scanning XRF). Age control for cores was achieved by radiocarbon dating using accelerator mass spectrometry on detrital charcoal fragments (>250 µm) isolated by sieving. Records of glacigenic sediment input from both lakes reveal similar broad scale patterns; here we describe in detail the record from Laguna Jaico. Glacial flour dominates the core, with little to no organic material (TC8264 ± 61/58 cal yr BP); thereafter, the sediment record transitions into a brecciated, high TC (3-9%), low MS (~0 SI) section from ~225 – 90 cm depth (8264 ± 61/58 – 1426 ± 86/48 cal yr BP). Extending upcore to the core top (<1426 >± 86/48 cal yr BP) the record then reveals a section of intermediate TC (.1-3%) and low MS (0-1 SI). These results combined with those from Laguna Yanacocha show that over that last 12,000 years the influx of glacigenic sediment (low TC, high MS and BD) was low from ~13,000 – 11,500 and from ~8,500 – 1,500 cal yr BP. In contrast, from ~11,500 – 7,500 cal yr BP and since 1500 cal yr BP, glacigenic sediment input increased significantly. The intervals of increased glacigenic sediment input correlate well with the age of upvalley moraines, and with a recent summary of glacigenic sediment records from the western cordillera of central Peru (Stansell et al., 2013).

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