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Description

Title:Archives of climate variability on Kiritimati: lacustrine, aeolian and remote sensing perspectives
Author(s):Higley, Melinda Catherine
Director of Research:Conroy, Jessica L
Doctoral Committee Chair(s):Conroy, Jessica L
Doctoral Committee Member(s):Johnson, Thomas M; Anders, Alison; Curry , Brandon
Department / Program:Geology
Discipline:Geology
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:Ph.D.
Genre:Dissertation
Subject(s):Kiritimati
freshwater
central tropical Pacific
ENSO
hydroclimate
NDVI
paleosol
lake sediment
Abstract:Sedimentary archives from tropical Pacific islands, together with records of modern hydrological processes, can provide information on past changes in tropical hydroclimate and test island landscape sensitivity to changes in the hydrologic cycle. For small tropical islands in particular, insight into past and present hydroclimate variability is important, given the strong influence of the tropical Pacific climate on freshwater resources and hazards like flooding and drought. Reconstructions of hydroclimate from key locations can help test hypotheses regarding mechanisms and drivers of tropical Pacific climate variability. However, such reconstructions are currently temporally and spatially limited, reducing our ability to understand past atmospheric moisture balance over long timescales. A new lake sediment record from Kiritimati Island, in the northern Line Islands of the central tropical Pacific (CTP) Ocean (2°N, 157°W), improves our understanding of the spatial structure of the hydroclimate for the past millennium in the tropical Pacific. Geochemical and sedimentological data indicate drier conditions prevailed during the Medieval Climate Anomaly (MCA) and transitioned to wetter conditions during the Little Ice Age (LIA) on Kiritimati, suggesting a southward shift of the Intertropical Convergence Zone (ITCZ) at the MCA-LIA transition. However, comparing the Kiritimati lake record with hydroclimate proxies around the tropical Pacific does not support a particular pattern of variability for MCA or LIA hydroclimate, thus the results do not point to particular mechanisms to explain tropical Pacific climate variability during the last millennium. Even in the instrumental era, the relationship between climate variability and hydrologic variability for many tropical islands remains uncertain due local hydroclimatic data scarcity and island remoteness. However, utilizing the normalized difference vegetation index (NDVI) to investigate variability in island surface water area, I demonstrate links between climate variability and island freshwater storage. Results indicate that future changes to the frequency and amplitude of interannual hydroclimate variability, as well as seasonal duration, will alter surface water coverage on Kiritimati. This localized assessment of climate stressors to island hydrology helps to inform freshwater stress projections for at-risk tropical islands. However, terrestrial changes associated with Pacific climate variability are not limited to the scope of lacustrine records. Aeolian sedimentary archives are a less common approach to documenting tropical hydroclimate variability but given the profound impact of the ocean-atmosphere system on Kiritimati, aeolian archives provide a unique opportunity to test the role of hydroclimate imprint on the island landscape. To assess a potential aeolian paleoenvironmental record of Pacific climate variability and test island landscape sensitivity in response to climate and anthropogenic disturbance, I utilized sedimentological data and stratigraphic observations associated with paired organic–inorganic radiocarbon dates from coastal aeolian deposits on Kiritimati. Based on this nascent chronology, dune systems on Kiritimati appear sensitive to anthropogenic landscape disturbance. Yet prior to mid 20th century military operations, dune systems may reflect predominantly large-scale shifts in central tropical Pacific atmospheric moisture, and therefore represent a useful terrestrial archive of regional climate.
Issue Date:2018-12-06
Type:Thesis
URI:http://hdl.handle.net/2142/102810
Rights Information:Copyright 2018 Melinda C. Higley
Date Available in IDEALS:2019-02-07
Date Deposited:2018-12


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