Stansell, Nathan Derek
(2005)
LAST GLACIAL MAXIMUM EQUILIBRIUM-LINE ALTITUDE RECONSTRUCTIONS, PALEO-TEMPERATURE ESTIMATES AND DEGLACIAL CHRONOLOGY OF THE MÉRIDA ANDES, VENEZUELA.
Master's Thesis, University of Pittsburgh.
(Unpublished)
Abstract
The magnitude and underlying cause of glacial variability in the Venezuelan Andes during the late Quaternary are investigated in order to better understand tropical climate and its forcing mechanisms. Paleo-glaciers were mapped using field observations, aerial photographs, satellite imagery and high-resolution digital topographic data. Paleo-glacier equilibrium-line altitudes (ELAs) were reconstructed using the accumulation-area ratio (AAR) and the accumulation-area balance ratio (AABR) methods. During the local Last Glacial Maximum (LGM) in Venezuela (~20,600 to 17,800 cal yr BP), ELAs were ~870 to 1420 m lower. Paleo-temperature estimates were calculated for the northern Sierra de Santo Domingo region which had a ÄELA of -980 m. Using a combined energy and mass-balance equation (Kuhn, 1989) it appears that temperatures were at least 8.8 ± 2°C cooler than today. This is greater than that estimated by an atmospheric lapse rate calculation, which yields a value of 6.4 ± 1°C cooler. The paleo-ELAs presented here are consistent with other northern tropical sites and the maximum estimates from southern tropical/sub-tropical Andean records. Our paleo-temperature results, based on estimates that take into account the total energy budget across a glacier's surface, are greater than Porter's (2001) overall tropical average of 5.4 ± 0.8°C cooler temperatures during the LGM using an atmospheric lapse rate calculaion. The pattern of the LGM gradient in ELA values of Venezuela is consistent with the modern precipitation and cloud cover patterns suggesting similar moisture sources and circulation patterns at both times. The regional deglacial history is characterized using lake sediments and bog deposits. Analyses include AMS radiocarbon dating, sedimentology studies and magnetic susceptibility on a series of cores from 7 lakes and 2 bogs in the Venezuelan Andes. Results show that by 15,950 cal yr BP, glaciers began to retreat. This retreat was interrupted by at least one readvance between 14,000 and 10,000 cal yr BP. Glaciers rapidly retreated after 10,000 cal yr BP in arid areas, whereas ice remained in north facing humid areas until after 6,200 cal yr BP. The deglacial history of the Venezuelan Andes cannot be attributed to insolation forcing alone and must be combined with changes in temperature and moisture availability.
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Details
| Item Type: |
University of Pittsburgh ETD
|
| Status: |
Unpublished |
| Creators/Authors: |
| Creators | Email | Pitt Username | ORCID  |
|---|
| Stansell, Nathan Derek | nas12@pitt.edu | NAS12 | |
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| ETD Committee: |
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| Date: |
9 June 2005 |
| Date Type: |
Completion |
| Defense Date: |
28 March 2005 |
| Approval Date: |
9 June 2005 |
| Submission Date: |
17 April 2005 |
| Access Restriction: |
No restriction; Release the ETD for access worldwide immediately. |
| Institution: |
University of Pittsburgh |
| Schools and Programs: |
Dietrich School of Arts and Sciences > Geology and Planetary Science |
| Degree: |
MS - Master of Science |
| Thesis Type: |
Master's Thesis |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
climate change; northern hemisphere tropics; tropical glacier mass-balance |
| Other ID: |
http://etd.library.pitt.edu/ETD/available/etd-04172005-165343/, etd-04172005-165343 |
| Date Deposited: |
10 Nov 2011 19:37 |
| Last Modified: |
15 Nov 2016 13:40 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/7242 |
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