Abstract Amorphous Calcium Carbonate (ACC) is a naturally occurring amorphous form of the widely distributed mineral calcium carbonate (CaCO3). ACC has been found increasingly as a precursor phase, calcium storage site, or strengthening structural phase in a wide array of different biomineralizing organisms. An accurate understanding of the widely used classic carbonate-water paleothermometry relies on formation of CaCO3 minerals and associated oxygen isotope effects. Moreover, ACC has oft been pointed to as a possible reason for non-equilibrium isotope effects, also called vital effects, in biogenic carbonates. It is, therefore, vital to understand whether ACC can reach equilibrium with its surrounding solution, as well as the role of ACC precursors in the isotopic composition and evolution of the final crystalline phase they transform into. This study is designed to answer these questions through the precipitation of stable ACC by two methods, the alkaline method (AM) which utilizes high pH to precipitate ACC, and the silica method (SM) which envelopes precipitating ACC particles in silica vesicles to prevent crystallization. These differently precipitated ACCs are then subjected to several different experimental treatments. This is achieved by monitoring the crystallization by X-ray Diffraction (XRD), and isotopic evolution of the ACC precipitates by Isotope Ratio Mass Spectrometry (IRMS) as they age and concurrently crystallize in parent solution, or in 18O enriched re-equilibration solution. This research indicated a marked difference in the crystallization behaviour, isotopic composition, and isotopic evolution of ACC produced by these two precipitation methods. With the AM method, ACC precipitates (AM-ACC) crystallized more predictably to calcite and maintained δ18O signatures that were slightly lower than the equilibrium CO32- and resisted further isotopic exchange with surrounding solution. We propose that the former is mostly due to an incomplete DIC-water oxygen isotope equilibrium prior to the AM-ACC precipitation and the latter is a result of the high pH of the precipitating solution decreasing the solubility of the precipitated ACC phase, disallowing isotope exchange, and favouring crystallization by solid-state transformation. Conversely, while ACC precipitated using the SM (SM-ACC) yielded much more variable results, both in terms of mineralogical identity upon crystallization, and δ18O values. Isotopic results were much closer to the expected equilibrium δ18O value for calcite, hinting at an expedited oxygen isotope exchange between SM-ACC and parent solution. Furthermore, SM-ACC was capable of isotopic exchange with the 18O enriched re-equilibration solution, a feat corresponding AM-ACC was incapable of. Overall, our experimental results gleaned here that precipitation method or precipitation environment play a critical role in the isotopic evolution of precursor ACC to crystalline CaCO3, suggesting ACC as an important source of the vital effect. / Thesis / Master of Science (MSc)

The peopling of the Americas, including the possibility that maritime peoples followed a coastal route from Northeast Asia into the New World, is a topic of major interest in archaeology. Paleocoastal sites on California`s Northern Channel Islands (NCI), dating between ~13,000 and 8000 years ago, may support this coastal migration theory. Until recently, however, we knew little about Paleocoastal technologies, settlement, and lifeways on the islands. Combining traditional archaeological approaches with experimental and archaeometric techniques, I examine Paleocoastal settlement and resource use on San Miguel and Santa Rosa islands. Recently discovered Paleocoastal sites have produced sophisticated chipped stone technologies, with bifacially-flaked points and crescents of extraordinary craftsmanship. Exploring lithic raw material procurement strategies, I demonstrate a Paleocoastal preference for island cherts from sources centered on western Santarosae. Using experimental and archaeometric techniques, I show that Paleocoastal peoples systematically employed heat-treatment to manufacture finely crafted bifaces from island cherts. Using stable oxygen isotope (δ18O) analyses of marine shells from Paleocoastal sites, I examine paleo-sea surface temperatures, seasonality of shellfish collecting, and human sedentism. Evaluating whether such occupations were seasonal or year-round, I tested different sampling strategies for California mussel shells, showing that a method used by many California archaeologists provides erroneous seasonality interpretations for ~35 percent of sampled shells. Using a more intensive sampling strategy, I demonstrate that some Paleocoastal sites were used seasonally, but three substantial middens dating to 8200, 9000, and 10,000 cal BP produced evidence for shell harvesting during all four seasons. This suggests that the NCI were occupied more or less permanently and year-round by at least 10,000 years ago. My research suggests that Paleocoastal peoples had a strong commitment to maritime and island lifeways starting at least 12,000 years ago. From that time until ~8000 years ago, Paleocoastal peoples relied primarily on island resources despite their close proximity to the mainland. The presence of a relatively large, permanent, and distinctive Paleocoastal population on the NCI may also support the coastal migration theory and an even deeper antiquity of human settlement and sedentism on the NCI. This dissertation includes previously published and unpublished co-authored material.

The work presented in this dissertation explores the nature of agro-pastoral strategies developed by Neolithic farmers as a way to understand how early food production was inter-twined with environmental and socio-economic opportunities and constraints. Towards this end, a multi-isotope approach is used to address questions of scale and intensity of crop cultivation and animal management at the archaeological sites of Kouphovouno, southern Greece, Makriyalos, northern Greece, and Çatalhöyük, south-central Turkey. Measurements of stable carbon, nitrogen, oxygen and strontium isotope values of carbonized plant remains, human and animal bone collagen and animal tooth enamel are used to examine the similarities and differences in the types of treatments that individual species of plants and animals received during the agricultural cycle at the distinct locations. The results show that farmers at the three sites developed variable methods for exploiting the arable and pastoral landscape and catering to their economic and culinary needs. The discussion considers the implications of these findings to our understanding of the complexity and adaptability of early farming systems.

La vitesse de surrection du l’Himalaya et du plateau tibétain tout au long du Cénozoïque reste encore aujourd’hui largement débattue. L’analyse des isotopes stables de l’oxygène pour reconstruire les paléo-altitudes est considérée comme une technique très efficace et a été largement utilisée. Néanmoins, cette méthode a deux limites principales: 1) les relations entre δ18O et climat ne sont pas bien établies et 2) le climat Cénozoïque en Asie est mal contraint. Dans le cadre de cette thèse, nous avons étudié le lien entre la surrection des montagnes, les changements climatiques associés et le δ18O dans la paléo-précipitation. Nous utilisons le modèle de circulation générale atmosphérique isotopique LMDZ-iso. Nos simulations climatiques montrent que le retrait de la Paratéthys, le déplacement latitudinal de l’Inde et l’altitude du plateau tibétain contrôlent les précipitations et la variabilité de la mousson en Asie. Afin de comprendre où et comment ces changements climatiques liés à la surrection des montagnes affectent le δ18O, nous avons proposé une expression théorique de la composition isotopique des précipitations fondée sur la distillation de Rayleigh. Nous avons montré que seulement 40 % des sites échantillonnés de l’Himalaya et du plateau tibétain contiennent une signature isotopique représentant la topographie. Les résultats obtenus dans cette étude montrent que l’Himalaya pourrait avoir atteint son altitude actuelle plus tardivement que précédemment proposé. Des conditions aux limites réalistes nous permettent de reconstruire le δ18O des paléo-précipitations pour quatre époques du Cénozoïque (55, 42, 30 et 15 Ma). Dans la mesure où les reconstructions des paléo-altitudes sont particulièrement controversées pour les premières étapes de l’évolution du plateau tibétain, nous avons ensuite approfondi notre étude en nous focalisant sur l’Eocène (en utilisant une paléogéographie qui correspond à 42 Ma). Pour ce cas, nous montrons que le δ18O des précipitations est insensible à l’altitude en Asie, tandis que le δ18O dans les archives naturelles (carbonates) enregistre le signal de la paléo-élévation puisque le fractionnement entre la calcite et l’eau est sensible à la température, qui elle-même dépend en partie de l’altitude. La comparaison du δ18O simulé pour l’Eocène avec les données du δ18O mesuré dans les carbonates suggère que, pendant l’Eocène, l’Himalaya et le plateau tibétain n’avaient pas encore atteint leur élévation actuelle (> 3000 m). / The timing and rate of surface elevations of the Himalayas and the Tibetan Plateau remain controversial and their impact on Asian climate and the onset of monsoon systems in this area is highly debated. Stable oxygen paleoaltimetry is considered to be a very efficient and widely applied technique, but has limitations from two sides: 1) the link between stable oxygen composition of precipitation and climate is not well established, 2) Cenozoic climate over Asia is poorly reconstructed. With a purpose of filling the gap in our knowledge of climate variability over Asia during the Cenozoic, we use the isotope-enabled atmospheric general circulation model LMDZ-iso to understand the links between the growth of mountains, associated climate changes and δ18O in paleo-precipitation. Our results show a significant influence of the Paratethys retreat, the latitudinal displacement of India and the height of the Tibetan Plateau on Asian hydrological cycle. For the purpose of understanding where and how the climatic changes linked with the growth of mountains affect δ18O in precipitation, we develop a theoretical expression for the precipitation composition based on the Rayleigh distillation and show that only 40% of sampled sites for paleoaltimetry depict signal attributed to topography changes. We conclude that the Himalayas may have attained their current elevation later than expected. Realistic Cenozoic boundary conditions allow us reconstructing δ18O in paleoprecipitation for several periods during the Cenozoic (for 55 Ma, 42 Ma, 30 Ma and 15 Ma). The focus has been put on the Eocene (42 Ma), since paleoelevation reconstructions are particularly controversial for this time. We show that Eocene precipitation δ18O is rather insensitive to topographic height in Asia. However, carbonate δ18O still records paleo-elevation because the fractionation between calcite and water is sensitive to temperature, which partly depends on altitude. Comparison of simulated Eocene δ18O patterns with data from the carbonate archives suggest that the Himalayas and the Tibetan Plateau did not reach present-day (> 3000 m) elevations during the Eocene.

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The Late Cretaceous–early Paleogene is the most recent period of Earth history with a dynamic carbon cycle that experienced sustained global greenhouse warmth and can offer a valuable insight into our anthropogenically-warmer future world. Yet, knowledge of ambient climate conditions and evolution of the carbon cycle at this time, along with their relation to forcing mechanisms, are still poorly constrained. In this thesis, I examine marine sediments recovered from the South Atlantic Walvis Ridge (ODP Site 1262) and Indian Ocean Ninetyeast Ridge (IODP Site U1443 and ODP Site 758), to shed new light on the evolution of the climate and carbon cycle from the Late Maastrichtian through to the Early Eocene (~67.10–52.35 Ma). The overarching aims of this thesis are: 1) to identify the long-term trends and principle forcing mechanisms driving the climate and carbon cycle during this time period, through construction of 14.75 million-year-long, orbital-resolution (~1.5–4 kyr), stratigraphically complete, benthic stable carbon (δ13Cbenthic) and oxygen (δ18Obenthic) isotope records; 2) to investigate in more detail the climatic and carbon-cycle perturbations of the Early–Middle Paleocene (e.g., the Dan-C2 event, Latest Danian Event and the Danian/Selandian Transition Event) and place these in their proper (orbital) temporal context; 3) to investigate the Late Maastrichtian warming event and its relationship to the eruption of the Deccan Traps Large Igneous Province, as well as its role (if any) in the subsequent Cretaceous/Paleogene (K/Pg) mass extinction; 4) to provide the first orbital-resolution estimates of temperature and carbonate chemistry variability from the low latitude Indian Ocean spanning the Late Paleocene–Early Eocene, through analysis of trace element and stable isotope data from multiple foraminiferal species. Taken together, the results presented in this thesis provide a critical new insight into the dynamic evolution of the climate and carbon cycle during the greenhouse world of the early Paleogene, and shed light on the potential forcing mechanisms driving the climate and carbon cycle during this time.