Equilibrium exchange constants were calculated for exchange of sulphite with other sulphur compounds. The equilibrium constant for sulphur Isotope exchange between sulphate in solution and solid calcium sulphate was calcu­lated and measured experimentally. In the chemical reduc­tion of sulphate to sulphide S^32O-4 reacted 2.5% faster than S340-4 , in agreement with the calculated kinetic isotope effect for the step sulphate to sulphite. The isotope effect in the reduction of sulphate by Desulphovibrio desulphuricans was found to vary from 0.0 to 2.5% The results were inter­preted on the basis of a mechanism involving two consecutive steps, pick-up of sulphate and reduction of sulphate to sul-phite, competing for control of the rate. The isotope effect in bacterial reduction of sulphite was studied briefly. / Thesis / Doctor of Philosophy (PhD)

Isotopic investigations of speleothem CR1 from Cristal Cave in southeastern Brazil have established a high-resolution record of climate change extending 4,100 years prior to sample collection in 2007. A total of 14 subsamples were collected from CR1 for U/Th age determination. ICP-MS analysis yielded very precise ages with analytical errors (2σ) averaging ± 13 years. An initial growth rate of .062 mm y-1 for the first 2860 years is followed by a rate of .08 mm y-1 for the remaining growth period allowing for sampling of δ18O at sub-decadal resolution. Stable isotope analyses show a large range of δ18O values between -7.5 ‰ to -4 ‰. The data show a trend of steadily decreasing values over the past 4,000 y BP. The exception to this trend is the last 150 years BP when some of the least negative and most variable values for the record are observed. Variations in speleothem δ18O in southern Brazil have been shown to reflect changes in rainfall δ18O, which in turn indicate changes in rainfall source or rainfall amount (Cruz et al., 2006). In Southeastern Brazil, δ18O is controlled mainly by moisture source location, in particular South American monsoonal versus extratropical sources (Cruz et al., 2005). The relative contribution of monsoonal and extratropical moisture help to define the δ18O of regional precipitation via the mean location and southward extent of Hadley cell convective activity associated with the South American summer monsoon (Cruz et al., 2005). For example, decreases in precipitation δ18O are often interpreted as a decreased contribution of winter versus summer precipitation (Cruz et al., 2005). Assuming that the modern (observed) relationship between the seasonality and moisture source location effect occurring in southeastern Brazil have functioned for the past ~ 4,100 years, trends of more negative values towards modern day are likely due to increased summer precipitation and/or an overall increase in total yearly precipitation. The more enriched values of the past 100 years suggest a recent decrease in summer and/or total rainfall.

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No description available.

Since the discoveries of vertebrate bioapatite’s ability to record oxygen isotopecomposition of ambient seawater were made (Kolodny, 1983), oxygen isotopes have beenwidely used as a climatic and oceanographic proxy. The δ18OP aquatic vertebrate apatite isa function of the δ18Ow value of the ambient water, yet “vital effects” on the δ18OP compositionhave been reported previously (Venneman et al., 2013). I have analysed δ18O compositionin the teeth of six extant shark and ray (chondrichthyan) species from the tropical ocean tankof the Blackpool Sea Life Center, UK. The teeth were naturally shed and collected from thetank substrate.Preparation of samples was performed in the Laboratory of Isotope Geology at the NaturalHistory Museum of Stockholm (Sweden), and the δ18O was measured at the NordSIM facility,using secondary ionization mass spectrometry (SIMS) by a high precision and high spatialresolutionCAMECA IMS 1280 ion microprobe.Data treatment was followed by statistical analysis. Results show significant δ18O differencesat inter-tissue level. I could also illustrate the impact of organics-pretreatment on the finalδ18O values, with the outcome of one more favourable pretreatment for SIMS analysis. Intertaxonvariability was observed, without much statistical confidence, but I hypothesize that itmay be due to the difference in tissue crystallization and organic quantity between species.

Several thousand coastal perennially ice-covered oligotrophic lakes and ponds have been identified on the Antarctic continent. To date, most hydrochemical studies on Antarctica’s ice-covered lakes have been undertaken in the McMurdo Dry Valleys (more than 20 lakes/ponds studied since 1957) because of their proximity to the McMurdo research station and the New Zealand station Scott Base. Yet, little attention has been given to coastal ice-covered lakes situated in Antarctica’s central Queen Maud Land region, and more specifically in the Untersee Oasis: a polar Oasis that encompasses two large perennially ice-covered lakes (Lake Untersee & Lake Obersee), and numerous small ice-covered morainic ponds. Consequently, this PhD research project aims to describe and understand the distribution, ice cover phenology, and contemporary hydrochemistry of perennially ice-covered lakes and ponds located in the Untersee Oasis and their effect on the activity of the benthic microbial ecosystem. Lake Untersee, the largest freshwater coastal lake in central Queen Maud Land, was the main focus of this study. Its energy and water mass balance was initially investigated to understand its current equilibrium and how this perennially well-sealed ice-covered lake may evolve under changing climate conditions. Results suggest that Lake Untersee’s mass balance was in equilibrium between the late 1990s and 2018, and the lake is mainly fed by subglacial meltwater (55-60%) and by subaqueous melting of glacier ice (40-45%). A recursive stable water isotope (δD-δ18O) evolution model for well-sealed perennial ice-covered lakes that takes into account the effect of changing chemistry in residual waters on δD-δ18O values was then developed and determined that Lake Untersee is in isotopic steady-state. Modeling results also showed that Untersee most likely did not receive additional inputs from surface streams during the last 300–500 years at the time of sampling, in November-December 2017. However, in mid-January 2019, Untersee experienced a glacial lake outburst flood (GLOF) that increased the water level by 2 m (contributing 1.75×107 m3 of water), modifying its water chemistry and inorganic carbon load. High-resolution grain size and carbon isotope analyses of the benthic microbial mats suggest that GLOFs occurred periodically over the Holocene and that those events sporadically increased the primary productivity of its benthic microbial ecosystem. Finally, ice-covered ponds in the Oasis were identified and sampled to compare their morphometric properties, hydrochemical properties, and microbial mat activity with Lake Untersee. It was discovered that the Untersee Oasis ponds offer the full spectrum of ice cover types (i.e., perennial well-sealed, perennial and moat forming, and seasonally ice-covered) and that their hydrochemical properties depend on ice cover type. Empirical pond data was used to determine how Lake Untersee and the ponds themselves will evolve as they transition under a warming climate from well-sealed to moat forming and from moat forming to seasonally ice-covered.

No description available.

<p>  </p> <p>Reconstructing past glacier and ice-sheet extents is important to better understand how glacial systems have responded to past climate changes in hope of constraining predictions of their responses to ongoing anthropogenic climate warming. As such, the most recent period of climatic variations, from the Last Glacial Maximum (LGM, ca. 21 ka) through today, is of great interest as a prominent example of how ice has reacted to past climatic warming events. Surface exposure dating utilizing cosmogenic nuclides can directly constrain when past ice deglaciated in current and former glacial landscapes. Numerous studies have utilized long-lived cosmogenic radionuclides (i.e., 10Be, 26Al) in polar regions to reconstruct glacial systems. However, due to prevalent non-erosive cold-based ice, prior nuclides from pre-LGM can be preserved. </p> <p>The research described in this dissertation applies <em>in situ </em>cosmogenic 14C (<em>in situ</em> 14C), an emerging geochronometer, to polar glacial landscapes in Sweden and Antarctica to constrain the timing and rate of glacial ice retreat. <em>In situ </em>14C more closely reflects the post-LGM deglacial signal in polar regions because it is less likely to preserve prior nuclides (inheritance) under minimally erosive ice. Our cosmogenic 10Be–26Al–14C concentrations near the Riukojietna ice cap, the last remaining ice cap in Sweden, combined with a sedimentary record from a proximal proglacial lake, indicate the ice cap likely survived during a warm period in the Holocene, but was less extensive than today. The <em>in situ</em> 14C exposure data from nunataks in western Dronning Maud Land (DML), East Antarctica indicate significant coastal thickening (up to 850 m) not predicted by models to date. In addition, this work dates the timing of post-LGM ice surface lowering in two drainage basins in western DML. These results demonstrate the significant contribution of <em>in situ</em> 14C in polar regions.</p> <p>In addition to applications of <em>in situ</em> 14C in polar regions, this work also describes the development of a compositionally dependent <em>in situ</em> 14C production rate calculator. The ability to extract <em>in situ</em> 14C from samples which quartz cannot be separated (either quartz-poor or fine-grained) would allow new avenues of research. The computational framework will be a useful tool in efforts to broaden the utility of <em>in situ</em> 14C to quartz-poor and fine-grained rock types. </p>

A mass grave containing the remains of at least 3269 Napoleonic soldiers from 1812 was discovered in Vilnius, Lithuania in 2001. Stable carbon and nitrogen isotopic analyses were performed on collagen from 78 femoral samples to explore dietary variation within the sample. Starvation and nutritional distress were also evaluated through the examination of nitrogen enrichment in bone collagen. Clinical studies have demonstrated that enriched nitrogen isotope values can indicate periods of nutritional stress and starvation; however, this is the first study to examine its use as a diagnostic indicator of starvation in a historical population using bone tissue. According to the carbon isotope data, a vast majority of the soldiers in this sample consumed predominantly C3 plants with only five individuals consuming more than 50% of their plant dietary protein in the form of C4 plants, with δ13C ratios for this sample ranging from -19.22‰ to -11.76‰ and a mean of -17.18‰. This conforms to expectations given that a majority of human plant consumption in Europe is C3 pathway plants. Twenty-nine individuals exhibit enriched δ15N values, with δ15N values for this sample ranging from 7.14‰ to 13.63‰ and a mean of 10.49‰. The combination of historical and isotopic evidence suggests prolonged nutritional stress may be the cause of enrichment in this sample. The results of this study demonstrate the applicability of this method on archaeological samples as a line of evidence in the investigation of starvation and famine.

Successful translocation of a listed species into an area of previous occupation requires knowledge of the habitat needs. The presence of the necessary food items is critical to the successful establishment of a new population; this information is unknown for Peromyscus polionotus niveiventris, the southeastern beach mouse, a threatened subspecies on the east coast of Florida. I used fecal and stable isotope analysis to determine the diet of this subspecies at Cape Canaveral Air Force Station, Brevard County, Florida, between the autumn of 2003 and the spring of 2005. Six trapping grids were established, three in the dune/swale and three in the coastal scrub communities. Fecal and hair samples were collected and analyzed. The diet varied in the amount of 13C consumed between habitats and in the amount of both 15N and 13C consumed among grids within a habitat. There was no significant interaction between habitat and sex in the amount of either 15N or 13C consumed, and sexes also did not differ significantly. Fecal analysis uncovered the dominance in the diet of C3 plants. My data refuted the current belief, that the southeastern beach mouse prefers beach grass seeds of C4 plants, which were consumed but not in the frequency or quantity expected. I also analyzed the diet of Peromyscus gossypinus, the cotton mouse, and Sigmodon hispidus, the hispid cotton rat, using the two techniques. Both species consumed a combination of plant and arthropod material. Their diets varied between dune/swale and coastal scrub habitats. All three species' diets were significantly different, with Peromyscus polionotus niveiventris and Peromyscus gossypinus being the most similar. Both consume a greater proportion of arthropod material compared to the hispid cotton rat. Interspecific competition between the southeastern beach mouse and the cotton mouse may occur in times of limited resources.