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Date of Award

2-2012

Document Type

Campus Access

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Geosciences

First Advisor

Stephen J. Burns

Second Advisor

Bethany A. Bradley

Third Advisor

Robert M. DeConto

Subject Categories

Climate | Geochemistry | Geology

Abstract

The overarching goal of this study is to investigate the nature of precipitation variability in tropical South America over interannual to orbital timescales during the last 50,000 years. In order to address high-resolution climate changes over modern and ancient timescales, this research integrates instrumental records with model simulations and proxy reconstructions from geologic archives. The specific region of focus is the central Peruvian Andes (12°S, 76°W), where recent temperature and precipitation changes are magnified and glacial retreat has accelerated.

Monthly output of modern simulations from isotope-enabled global circulation models are validated using precipitation and temperature observations from the Peruvian Meteorological Service (SENAMHI). Interpretation of model results is focused on analysis of the oxygen isotopic composition of precipitation, which also can be readily measured in geologic archives. Interannual variability for the last 133 years (1870-2003) demonstrate that precipitation in central Peruvian Andes is largely influenced by upstream variability, primarily related to the intensity of the South American Summer Monsoon. Over decadal timescales, the sea surface temperatures in the tropical Pacific Ocean and the North Atlantic Ocean also affect the strength of regional summer precipitation.

Speleothems (cave samples) were recently collected in the central Peruvian Andes and are used extend the climate record through Holocene and Last Glacial periods. Two stalagmite samples from Huagapo Cave demonstrate that an intensification of regional precipitation is associated with an increase in austral summer insolation over the Holocene. A significant deviation from mean-state changes is observed in the Late Holocene when monsoon intensity decreases, tropical sea surface temperatures increase, and paleoclimatic records indicate a shift to El Niño-like conditions. A stalagmite collected from Pacupahuain Cave grew over a 35,000-year interval (16,000-50,000 years ago) during the Last Glacial period. Abrupt millennial-scale events demonstrate that the SASM is sensitive to high latitude temperature changes in both hemispheres. The dating-precision of speleothem samples provides constraints on the timing of abrupt events in the high North and South Atlantic. Future work includes development of additional stalagmite samples that span distinct intervals of time over the last 275,000 years.

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