@mastersthesis {476,
	title = {Deciphering arctic climate in a past greenhouse world: Multiproxy reconstructions of pliocene climate},
	volume = {PhD},
	year = {2011},
	school = {University of Arizona},
	abstract = {<p>The high sensitivity of high latitudes to global climate changes is the stimulus for the study of ancient Arctic ecosystems under greenhouse conditions. With an increasing number of studies, including the most recent Intergovernmental Panel on Climate Change (IPCC) report highlighting Pliocene climate as key example for the study of Earth system sensitivity to higher levels of atmospheric CO$_{2}$ , the need for accurate proxy records for this period is crucial. In order to investigate Pliocene climate, I used stable isotopic studies of fossil molluscs, moss and wood from two fossil forest deposits in the Canadian High Arctic. Temperatures were determined for an Early Pliocene (4-5 Ma) fossil forest site located on Ellesmere Island using \&lsquo;clumped\&rsquo; and stable isotopic analysis of mollusc shells and stable isotope values of fossil wood. Mollusc inferred growing season (May-Sept) temperatures derived using two independent techniques were estimated to be 11-16\&deg;C warmer than present (1950-1990) Ellesmere Island temperatures. Tree ring inferred growing season (June-July) temperatures (JJ) were 10-16\&deg;C and mean annual temperatures (MAT) were 18-20\&deg;C warmer than present (1950-1990). Mean annual and growing season (JJ) temperatures were also determined using fossil wood from a younger (2.4-2.8 Ma) late Pliocene-early Pleistocene site on Bylot Island. This deposit represents the remains of a flora that grew during an interglacial warm period during the transition to large-scale Northern Hemisphere glaciation that occurred between 2.5 to 3 million years ago. Mean annual temperatures were \&sim;12\&deg; C and growing season temperatures were \&sim;13\&deg;C warmer than present (1923-2010). The interglacial setting of the Bylot Island site and the warm temperatures suggests that prior to using such sites as true analogues of future conditions we may need to consider how close the feedbacks operating then were to the feedbacks we might expect in the future. However, that temperatures so much warmer than present existed in the high Arctic during a period when levels of atmospheric CO$_{2}$ were at nearpresent levels indicates that we may be moving beyond our ability to use the Pliocene as an example of the future.</p>},
	keywords = {Paleoclimate Science},
	author = {Csank, Adam Zoltan}
}
@mastersthesis {464,
	title = {Elevated atmospheric carbon dioxide impacts carbon dynamics in a C(4)-sorghum-soil agroecosystem: An application of stable carbon isotopes (delta carbon-13) in tracing the fate of carbon in the atmosphere-plant-soil ecosystem},
	volume = {PhD},
	year = {2005},
	school = {University of Arizona},
	abstract = {Although a strong inter-dependence exists between atmospheric carbon dioxide (CO$_{2}$) and the terrestrial carbon (C) cycle, the response of plant-soil ecosystems to the rapid increase in atmospheric CO$_{2}$ is not well understood. My dissertation research focused on the impacts of elevated CO$_{2}$ on the carbon dynamics of plant-soil ecosystems, which were a major part of the overall C$_{4}$-sorghum Free-Air CO$_{2}$ Enrichment (FACE) experiment conducted by the University of Arizona and USDA at the Maricopa Agriculture Center, Arizona, USA, in 1998 and 1999. In the experiment, sorghum (Sorghum bicolor (L) Moench) crop was exposed to elevated CO$_{2}$ ({\textquotedblleft}FACE{\textquotedblright}: ca. 560 {\textmu}mol mol$^{-}${\textonesuperior}) and ambient CO$_{2}$ ({\textquotedblleft}Control{\textquotedblright}: ca. 360 {\textmu}mol mol$^{-}${\textonesuperior}) interacting with well-watered and water-stressed treatments. The results from my study showed that the seasonal mean soil respiration rate measured in elevated CO$_{2}$ plots over two growing seasons was 3.3 {\textmu}mol m$^{-}${\texttwosuperior}s$^{-}${\textonesuperior}, i.e., 12.7\% higher than the 2.9 {\textmu}mol m$^{-}${\texttwosuperior}s$^{-}${\textonesuperior}in ambient CO$_{2}$ plots. The increased respiration mainly resulted from the stimulated root respiration under elevated CO$_{2}$, which increased 36.1\% compared to that under ambient CO$_{2}$. Measured changes in sorghum residue biochemistry caused by CO$_{2}$ were detected, with decrease of amino acids and hemicellulose carbohydrates by 7\% and 8\%, respectively, and increase of cellulose carbohydrates and lignin by 49\% and 5\%, respectively. Phenolics were only significantly higher in FACE roots. The C:N ratio of sorghum tissues was not affected by elevated CO$_{2}$, but was substantially lower under water stress. The laboratory incubation showed that an average of 7.3\% significantly less respired CO$_{2}$ was released from the FACE-tissue-amended soil than the Control-tissues-amended soil over the full 79-d incubation period. Non-lignin phenolics (r{\texttwosuperior} = 0.93, p = 0.002), and lignin (r{\texttwosuperior} = 0.89, p = 0.004) were found to be the most important factors related to the sorghum tissue decomposition. Highly stable residues of FACE sorghum input to the soil resulted in the increase of the recalcitrant C pool and the decrease of the labile C pool. As a result, mean residence time of SOC in FACE field plot increased compared to that in Control plot, suggesting that the SOC under elevated CO$_{2}$ was more stable against decomposition.},
	url = {http://ezproxy.library.arizona.edu/login?url=http://proquest.umi.com/pqdweb?did=885700691\&sid=10\&Fmt=2\&clientId=43922\&RQT=309\&VName=PQD},
	author = {Cheng, Li}
}
@mastersthesis {591,
	title = {Delta-deuterium and delta-oxygen-18 in mixed conifer systems in the United States southwest: The potential of delta-oxygen-18 in Pinus ponderosa tree rings as a natural environmental recorder},
	volume = {PhD},
	year = {2001},
	school = {University of Arizona},
	abstract = {The North American Monsoon provides half of the annual precipitation in Tucson, Arizona. The other half occurs dominantly during the winter and early spring. Late spring is the transitional period to the monsoon and is characterized by high temperatures and low humidity. The reliability of this hyperarid period, the consistency of the timing of monsoon onset, and the recognition that certain high-elevation trees produce annual false latewood bands in response to this transitional period, were critical to the design of this dissertation research. I hypothesized that subannual environmental signals might be fixed in stable oxygen isotopes in cellulose from such trees. Existence of a long-term dataset of δD and δ 18 O from Tucson precipitation provided impetus for the collection of a companion dataset at a high-elevation site in the Santa Catalina Mountains north of Tucson. Trees were sampled near the precipitation collection site. The relations between the stable isotope ratios in the precipitation and in the tree cellulose were identified through extraction of water from bimonthly samples of nearby soil, tree stems and needles. Spatial consistency of the cellulose stable isotope signals was measured using tree samples from seven additional sites across the U.S. desert Southwest. Correlations between Tucson summer precipitation δ 18 O and both local and extra-regional environmental parameters resulted in the identification of the dominant monsoonal moisture source for the Tucson area. Similar correlations with the cellulose δ 18 O timeseries from the post-false latewood cellulose, supported the previous interpretations, and suggest long-term reconstructions may be possible. Correlations between the earliest cellulose δ 18 O division and extra-regional environmental parameters suggest environmental measures may be reconstructable for the cool season. Comparison of the high and low elevation precipitation δD and δ 18 O datasets yielded many baseline measures of precipitation stable-isotope dynamics in the U.S. desert Southwest. Comparison of the high-elevation precipitation stable isotope record with soil and stem water δD and δ 18 O from nearby confirmed that local trees were using dominantly deeper soil water. I noted correlations between measured needle-water stable isotope values and values calculated using a leaf-water model, but systematic departures suggest an additional unmodeled process may operate in this system.},
	keywords = {Geochemistry},
	url = {http://ezproxy.library.arizona.edu/login?url=http://proquest.umi.com/pqdweb?did=728996441\&sid=11\&Fmt=2\&clientId=43922\&RQT=309\&VName=PQD},
	author = {Wright, William Edward}
}
@mastersthesis {549,
	title = {Precipitation seasonality recorded in D/H ratios of pinyon pine cellulose in the southwestern United States},
	volume = {PhD},
	year = {1997},
	school = {University of Arizona},
	abstract = {I assessed the paleoclimatic significance of $\delta$D values of pinon pine (Pinus edulis and P. monoyhylla) cellulose nitrate (cn) by developing, testing and applying deterministic and empirical models, in the context of the soil-plant-atmosphere continuum. Stable isotope values of precipitation, soil water, xylem sap, leaf water, atmospheric vapor, annual and sub-annual samples of tree-ring and needle cellulose, and climatic parameters, were measured along, a gradient of decreasing summer rain in the southwestern U.S. Stable isotope composition of sap indicated depth of moisture extraction. Over the growing season in New Mexico and Arizona, where monsoon rains are important, trees shifted their water use to shallower depths. In Nevada, where summer rain is scarce, trees shifted to deeper moisture late in the growing season. Evaporation altered $\delta$D and $\delta\sp{18}$O values of precipitation inputs to soil. Only after heavy monsoons did soil water and sap isotopically resemble recent precipitation. Average precipitation $\delta$D values set the baseline for $\rm\delta D\sb{cn}$ values at each site, but interannual variations in relative humidity and precipitation amount altered wood and leaf $\rm\delta D\sb{cn}$ values, via leaf water effects. Leaf water (lw) was evaporatively enriched by seasonal moisture stress. $\rm\delta D\sb{lw}$ and $\rm\delta\sp{18}O\sb{lw}$ values were strongly correlated with relative humidity on a seasonal basis, but not on a diurnal basis. Measured $\rm\delta\sp{18}O\sb{lw}$ values fit a steady-state model, with an offset attributable to relative humidity. Measured $\rm\delta D\sb{lw}$ values were more depleted than predicted by the model, suggesting leaf water-organic matter isotopic exchange. Biochemical fractionation $\rm(\epsilon\sb{B})$ of hydrogen isotopes between leaf water and cellulose was inversely correlated with relative humidity. Empirical models based on linear regressions demonstrated significant correlations between $\rm\delta D\sb{cn}$ values and precipitation seasonality. An El Nino-Southern Oscillation signal (wood $\rm\delta D\sb{cn}$ values inversely related to winter precipitation amount) was found in New Mexico and Arizona. A summer rain signal (leaf $\rm\delta D\sb{cn}$ values inversely related to summer humidity) was found at all sites. $\rm\delta D\sb{cn}$ values of pinon needles in packrat middens from Sevilleta LTER, New Mexico, suggest that late Pleistocene summers were as wet as today{\textquoteright}s, and/or that storm tracks could have shifted, bringing in more tropical moisture than currently.},
	url = {http://ezproxy.library.arizona.edu/login?url=http://proquest.umi.com/pqdweb?did=736806701\&sid=12\&Fmt=2\&clientId=43922\&RQT=309\&VName=PQD},
	author = {Pendall, Elise Gislaine}
}
@mastersthesis {707,
	title = {Inference of past atmospheric delta carbon-13 and atmospheric carbon-dioxide from carbon-13/carbon-12 measurements in tree rings},
	volume = {PhD},
	year = {1982},
	school = {University of Arizona},
	abstract = {<p>Carbon dioxide release from fossil-fuel burning is significant enough that we may soon experience perceptible changes in climate with important human consequences. Man\&$\#$39;s activities involving deforestation and agriculture have undoubtedly also affected atmospheric CO(,2), although quantitative, and even qualitative, net effects of these processes are incompletely understood relative to fossil-fuel production. An accurate reconstruction of past (\&$\#$39;13)C/(\&$\#$39;12)C ratios of atmospheric CO(,2) may provide key constraints on the historical activity of the biosphere as CO(,2) source or sink. Tree rings appear to be a repository of this information but there is much noise in the collection of previous reconstructions, presumably associated with site selection, radial variability, choice of representative wood chemical constituent, and subtle effects of climate on fractionation. This study attempts to avoid these pitfalls and develop a 50-yr (delta)(\&$\#$39;13)C(,ATM) record from juniper trees (genus Juniperus), in fact, by taking advantage of the influence of climate on fractionation. Trees were harvested from suitable sites in close proximity to weather stations with monthly records of temperature and precipitation. Ring material was then separated from each of the sections in 5-yr intervals from 1930 to 1979 around their full circumference, and cellulose was extracted from the wood. After measuring (delta)(\&$\#$39;13)C of the cellulose by standard mass-spectrometric techniques, a variety of (delta)(\&$\#$39;13)C vs. climate functions were examined for each interval. The most useful relationships for at most 7 of the 10 sites were (delta)(\&$\#$39;13)C with December temperature or precipitation, because the coefficients were nearly constant from one interval to the next (averaging -0.27(\&$\#$39;o)/oo(DEGREES)C(\&$\#$39;-1) for temperature and -0.04(\&$\#$39;o)/oo mm(\&$\#$39;-1) for precipitation) and the intercepts differed. Local pollution effects are believed responsible for the three anomalous sites. The separation of these regression lines of different intervals is interpreted as the response of the trees to the changing (delta)(\&$\#$39;13)C of atmospheric CO(,2) so that (delta)(\&$\#$39;13)C(,ATM) curves are constructed from this spacing. The shape of the best-fit reconstruction suggests the biosphere has acted as CO(,2) source to about 1965 and may now be a net sink. Although these conclusions are limited by certain assumptions and statistical restrictions, evidence from the recent scientific literature tends to support the increasing role of the biosphere as an important carbon sink.</p>},
	url = {http://ezproxy.library.arizona.edu/login?url=http://proquest.umi.com/pqdweb?did=752855841\&sid=22\&Fmt=2\&clientId=43922\&RQT=309\&VName=PQD},
	author = {Leavitt, S.}
}
