Degree Type

Thesis

Date of Award

2019

Degree Name

Master of Science

Department

Geological and Atmospheric Sciences

Major

Geology

First Advisor

Alan D. Wanamaler

Abstract

The negative impacts of climate change are exacerbated for some tropical countries,

which face water shortages due to technological limitations and lack of appropriate

environmental mitigation. Water accessibility in these regions depends heavily on rainfall caused

by the seasonal migrations of the intertropical convergence zone (ITCZ). Thus, the ability to

adequately forecast the future behavior of this tropical rain belt under the current and projected

path of global CO 2 emissions and warming is of tremendous interest. Many problems related to

forecasting tropical rainfall are due to the complexity of modeling several scales of cloud

dynamics and their interaction with the climate system. In the last decade, improved computing

power has facilitated more robust climate simulations and therefore reduced some uncertainties

regarding precipitation forecasts, however, there are still persistent issues related to the efficacy

of these models in replicating the real structure of the ITCZ. For these reasons, paleoarchives

including speleothems, ice cores, sediment records, tree rings, corals, mollusks and others are

useful to test the effectiveness and accuracy of climatic models in reconstructing aspects of

regional climate. In particular, long and continuous proxy archive records spanning centuries to

millennia can reveal needed information about the behavior of the climate system during

different boundary conditions (for example, glacial versus interglacial periods). For example,

understanding the extent of latitudinal movements of the ITCZ during millennial climatic

oscillations (Dansgaard-Oeschger; DO and Heinrich events; HE) is essential to improve climate

model output. Specifically, the study of the tropical rainfall response to DO and Heinrich events

could provide important insights about how the climate system balances, through both

atmospheric and oceanic circulation, asymmetrical temperature increases over intervals

considerably shorter than orbital time scales where changes in the thermal balance of the planet

are more evident. Although there is compelling evidence about the behavior of tropical rainfall

variations in response to DO and Heinrich events, the extent and magnitude of these changes is

poorly constrained. Furthermore, the potential importance of the ocean in forcing or modulating

tropical climate over these time scales is of wide interest. Despite this, however, few continuous,

long-term, hydroclimate records exist from locations sensitive to ITCZ dynamics.

In this study, we provide a stable oxygen isotope record constrained by 23 uranium-

thorium dates from four partially overlapping stalagmites collected in the eastern Colombian

Andes spanning the last 50 kyr. Both cave sites, Hipocampo and Finca Caracol (hereafter HFC)

caves, are located at ~6 °N where the mean annual climatological cycle presents a bimodal

rainfall pattern controlled by the seasonal migrations of the ITCZ. When compared with other

South American records, this precipitation-sensitive composite record indicates that the

continental ITCZ over South America experienced orbital-scale drifts and millennial-scale

oscillations (dry/wet) during the last 50 kyr in concert with well-recognized climatic phenomena

such as DO and HE. Our results suggest a poleward migration of the ITCZ towards the southern

hemisphere from part of the early Holocene to the middle Holocene following changes in the

boreal summer insolation, and from 50 kyr towards the last glacial maximum accompanying

changes in global ice volume. On millennial time scales, the HFC record shows variable

response to DO and Heinrich events sometimes displaying coherent responses with records north

and south of the equator. During the largest DO events, the HFC record reveals reduced rainfall

in phase with other regional southern hemisphere records, while weaker DO events are

coincident with wet conditions in Colombia and in phase with other northern South American

records. These results suggest a possible relationship between the magnitude of the temperature

anomalies in the North Atlantic and the degree of displacement of the ITCZ. During glacial

Heinrich events the HFC record is wet and coherent with records from the southern hemisphere

indicating that latitudinal movements of the ITCZ were relatively small. Moreover, precipitation

increases in Colombia and Peru during HE suggest that the ITCZ was also wider. Paleo-

productivity and wind speed proxy records sensitive to northwest trade wind strength indicate

stronger northern hemisphere Hadley cell circulation and provide support for a wider ITCZ,

which is necessary to balance mass and energy by these stronger trades.

Copyright Owner

Juan Carlos Romero Romero Gelvez

Language

en

File Format

application/pdf

File Size

96 pages

Included in

Geology Commons

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