Date of Award

6-2012

Document Type

Open Access

Degree Name

Bachelor of Arts

Department

Environmental Science and Policy

First Advisor

Donald Rodbell

Language

English

Keywords

sidement, glaciers, holocene, lakes, wetlands, cores

Abstract

Lake sediment cores taken from glacial lakes and wetlands are valuable proxies of glacial activity because they offer a continuous record of sediment input. Tropical alpine glaciers are especially sensitive to changes in precipitation and temperature, and thus the history of glaciation can be used in the reconstruction of past climates. Owing to a steep east-­‐to-­‐west moisture gradient across the Andes, glaciers in the eastern cordillera are more sensitive to changes in temperature whereas those in the drier, western, cordillera are more sensitive to changes in precipitation. Multiple lacustrine sediment cores were taken from two sites in the central Peruvian Andes in June 2011: one set from the wet, eastern cordillera of the Andes and one set from the dry, western cordillera. These cores were measures for three proxy indicators of glacial erosion: magnetic susceptibility (MS), dry bulk density, and organic carbon content (TOC); cores were dated by radiocarbon. An ~6.7 meter-­‐long core from a bog at the upper end of Laguna Shiurococha, located in the western cordillera (11.905°S, 75.960°W; 4585 m asl), records more than 3550 years of sedimentation. This core reveals a sharp decline in glacigenic sedimentation around 3550 cal yr BP, with very little glacial input thereafter. Laguna Yanacocha, located in the eastern cordillera of the Peruvian Andes (10.558°S, 75.927°W; 4358 m asl) yielded an ~2.6 meter-­‐long sediment core that spans more than 13,700 cal yr. The sediment record reveals a two-­‐step last deglaciation; the initial decline in glacigenic sediment input began about 14,000 cal yr BP and lasted until about 13,000 cal yr BP at which time glacial erosion increases and remained high until about 8,000 cal yr BP. For the past 8,000 cal yr, glacigenic sediment input into Laguna Yanacocha has been at a minimum. Cores from the western cordillera reveal significant ice expansion during the late Holocene that is not seen in the cores from the eastern cordillera. The δ18Oprecip record from nearby Laguna Pumococha reveal a period of aridity from the late Glacial through the early Holocene followed by a gradual increase in precipitation throughout the Holocene. Deglaciation of both cordillera appears to have been driven by the onset of drier and/or warmer conditions during the late Glacial. The relatively large readvance of glaciers in the western cordillera during the late Holocene was due to the onset of wetter conditions, which is evident in the depleted isotope values in regional carbonate lake cores. Western glaciers advanced more during this interval because these glaciers are more moisture sensitive than those in the eastern cordillera.

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