Thesis (Ph.D.) - University of Queensland, 2005. / Includes bibliography.

The isotopic and elemental composition of speleothem calcite precipitated from dripwaters in caves have been used to elucidate changes in karst groundwater flow paths and changes in climate such as shifts in vegetation and rainfall patterns. Given that recent studies have shown seasonal isotopic and elemental changes in cave dripwater chemistry, then these changes are most likely reflected in the precipitated calcite. This affirms the need to study the environmental controls on the dripwater isotopic and elemental chemistry on seasonal time scales, since ultimately these are environmental controls on the precipitated speleothem calcite. In this study, physical, chemical, and meteorological variations at 13 drip-water and pool sites in two cave systems in the Edwards aquifer of central Texas are used to delineate the controls on the evolution of cave waters. The chemical evolution of these cave waters can be accounted for by variations in calcite precipitation, soil geochemistry, flow paths, and degassing of CO₂ driven by seasonal overturn of the cave atmosphere.Calcite precipitated on glass substrates placed under three of the thirteen dripwaters in this study was analyzed for its C and O isotopic composition in order to assess 1) seasonal variations in the isotopic composition and 2) the extent to which precipitation occurs in isotopic equilibrium with its host dripwater. Each winter season, calcite growth rates increase, which corresponds to changes in the C and O isotopic composition of the calcite: higher ơ13C and ơ18O values during winter and lower ơ13C and ơ18O values during summer. Some calcite samples were found to precipitate out of C and O isotopic equilibrium, with maximum departures of 1.3% with respect to carbon and 1.4% with respect to oxygen. The results show that ơ13C and ơ18O in the modern speleothem calcite:1) can vary sub-annually without change in vegetation or climate, and 2) reflect in the majority of cases precipitation out of isotopic equilibrium with the host dripwater that precipitates the calcites. / text

Στην παρούσα εργασία πραγματοποιήθηκε πετρογραφική μελέτη των σπηλαιοθεμάτων του σπηλαίου της Αλιστράτης, με σκοπό την άντληση πληροφοριών από τα σπηλαιοθέματα για τις παλαιοκλιματολογικές συνθήκες. / In this present paper we study Alistratis' cave speleothems petrographicly, with the purpose of obtaining information from these speleothems for paleoclimatic conditions.

Thesis (M.S.)--University of Missouri-Columbia, 2004. / Typescript. Includes bibliographical references (leaves 42-45). Also available on the Internet.

Thesis (M.S.)--University of Missouri-Columbia, 2004. / Typescript. Includes bibliographical references (leaves 42-45). Also available on the Internet.

My research focuses on reconstructing past climate in southern Arizona using cave deposits called speleothems. However, this necessitates a broader perspective than simply a geochemical time series, and therefore, I also investigate modern cave systems using a combination of modeling and observational datasets. Finally, cave deposits are fundamentally non-renewable resources, and sampling for past climate reconstruction can be destructive, unlike other cave uses. My last investigation is focused on developing possible best practice recommendations for paleoclimate scientists and other cave stakeholders moving forward. We developed two new stalagmite records of past climate variability in southern Arizona over the past 7000 years. Past climate reconstruction from two caves (Cave of the Bells and Fort Huachuca Cave) highlights insolation control of southern Arizona hydroclimate from 7000-2000 years before present. Additionally, comparison between two stalagmites with different seasonal sensitivities uncovers a few eras of multi-decade long droughts in southern Arizona, which align with other regional reconstructions of past climates and elucidate forcings on Southwest paleoclimate as emergent from both external (insolation) and internal climate variability in the Pacific and Atlantic Ocean basins. Although the oxygen isotopic signal of cave calcite in speleothems is complex, agreement with these other records indicates that the speleothem records from these caves primarily record a climate signal.Modeling and monitoring of modern caves both helps us interpret paleoclimate records and enhances our understanding of cave systems in their own right. Modeling of Cave of the Bells dripwaters demonstrates the effect of storage and mixing on the dripwater oxygen isotope signal; non-climate processes can imprint on dripwater variability on multidecadal timescales. Monitoring shows that on very small spatial scales, every cave is different, and even sites within the same cave respond uniquely to surface climate. Most notably, calcite oxygen isotopic composition, used to reconstruct past climate, shows seasonal variability unrelated to dripwater and surface rainfall oxygen isotope variability. Substantial oxygen isotope disequilibrium is identified at numerous caves sites in southern Arizona, and this understanding aligns with a growing number of cave studies that demonstrate the long-held assumption of isotopic equilibrium in cave systems may not always be valid or that the way in which we define isotopic equilibrium insufficiently captures the variety of processes controlling the oxygen isotopic composition of speleothems. Overall, however, monitoring can identify stalagmites that are more sensitive to surface climate and less sensitive to these in-cave processes by identifying sites with dripwater variability responses to surface rainfall variability and sites that precipitate close to oxygen isotopic equilibrium. Finally, a major missing component in speleothem research is the fact that speleothems take thousands and sometimes hundreds of thousands of years to form. They are non-renewable resources on human timescales, and habitat for myriad microbes that have yet to be identified. Removal of speleothems for paleoclimate research is one of the only destructive uses of these deposits. With that in mind, I also analyze current methods of collecting speleothems and develop a framework based on two surveys of scientists and stakeholders to assist scientists and managers when evaluating potential methods of incorporating cave conservation into the speleothem sampling process. Thus, I approach caves from a variety of angles and timescales, from the past through the present to the future, illuminating caves as complex scientific and social systems.

Thesis advisor: Jeremy D. Shakun / Arctic permafrost contains a substantial stock of carbon that could be released to the atmosphere as CH4 and CO2 upon thawing, making it a potentially powerful amplifier of future warming. The sensitivity of permafrost to climate change is uncertain, however, and occurs on time scales longer than those captured by the instrumental record. Speleothems – cave precipitates deposited from flowing or dripping water – in currently frozen regions record past episodes of thaw, which can be used to assess the response of permafrost to long-term warmth. Here, we present 90 uranium-thorium ages on speleothems from across the North American Arctic, sub-Arctic and northern alpine regions to reconstruct a 600-kyr permafrost history. Widespread speleothem growth supports an episode of extensive permafrost thaw during the Marine Isotope Stage 11 interglacial about 400 ka, when global temperature was only slightly warmer than pre-industrial conditions. Additional growth is evident during MIS 13, curiously, a smaller magnitude interglacial. Ice-core records of atmospheric greenhouse gases do not show elevated concentrations at these times, perhaps suggesting that the permafrost carbon pool was smaller than today or released gradually enough to be buffered by other reservoirs. / Thesis (MS) — Boston College, 2017. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

Στην παρούσα εργασία πραγματοποιήθηκε πετρογραφική μελέτη των σπηλαιοθεμάτων του σπηλαίου του Περάματος Ιωαννίνων, με σκοπό την άντληση πληροφοριών από τα σπηλαιοθέματα για τις παλαιοκλιματολογικές συνθήκες. / In the present paper we study Ioannina's cave speleothems petrographicly , with the purpose of obtaining information from speleothems for paleoclimatic conditions.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18804号 / 理博第4062号 / 新制||理||1584(附属図書館) / 31755 / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)教授 田上 高広, 教授 土`山 明, 教授 大沢 信二 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Speleothems (cave carbonate deposits) have been recognized as a multi-proxy paleoclimate archive. Variations in carbon and oxygen isotopes in speleothems can record past climate changes (e.g., temperature, rainfall and vegetation) under isotopic equilibrium conditions. However, non-climatic noises caused by in-cave processes may affect these stable isotope records under non-equilibrium isotopic conditions. The identification of equilibrium and non-equilibrium isotopic conditions in speleothems is still disputed in the speleothem research community; however, this is a prerequisite for the interpretation of carbon and oxygen isotope records in speleothems as paleoclimate proxies. In this Ph.D. thesis, a series of laboratory experiments under cave-analogue conditions were performed to simulate the formation of speleothems in natural caves. The results of these experiments demonstrate that stable isotope equilibrium in speleothems is achieved under slow carbonate precipitation in pool-like settings (pool carbonates). On the basis of these pool carbonates, equilibrium carbon and oxygen isotope fractionation factors between calcite and water (or DIC for carbon) were determined. Our experiments show larger carbon and oxygen isotope non-equilibrium fractionations between calcite and water (or DIC for carbon) in stalagmite-like settings (fast carbonate precipitate) than those determined in pool-like settings. The flow rate of drip water above the surface of stalagmite appears to control the magnitude of these non-equilibrium isotope effects which increase with decreasing the flow rate. Furthermore, a natural speleothem sample was examined as a paleoclimate archive in this thesis. The growth of a double stalagmite (WS-5d) in Wadi Sannur Cave from the Northeastern Sahara was used to infer the greening of the Sahara (intensive rainfall and vegetation). The U/Th dating in the WS-5d stalagmite suggests that greening conditions extended widely in the Sahara during the interglacial Marine Isotope Stages MIS 5.5, MIS 7.3, and the early MIS 9. Based upon oxygen isotope compositions from the WS-5d, we attributed the source of these greening periods to long-traveling rains from the Atlantic Ocean that were delivered via the West African monsoon system. Our study suggests that the two youngest greening periods were concurrent with the arrival of Homo sapiens in the Levant and an earlier possible change in human population at 244 ka, indicating a key role of the Sahara route in early human dispersal out of Africa. Finally, clumped isotope measurements (Δ47) on carbonate-derived CO2 have been shown to reflect the formation temperature of the carbonate minerals. The absolute Δ47 values of these isotopic measurements seem to be sensitive to the standardization methods (heated CO2 gases and water-equilibrated CO2 gases) that are used to normalize the raw Δ47 measurements. Neither the hypothetical base for the heated CO2 gas standardization method nor the theoretical base for the water-equilibrated CO2 gas standardization method has been experimentally tested. A series of CO2 gases were heated in pre-dehumidified quartz tubes to obtain equilibrium Δ47 values of these CO2 gases at temperature range of 50 – 1100 °C. Consequently, the first experimentally derived Δ47 – T calibration in a CO2 gas phase was proposed. This experimental calibration provides a validated base for the standardization of the raw Δ47 data. Moreover, heating CO2 in a pre-humidified quartz tube enables us to easily prepare a CO2 standard gas of a similar Δ47 value to the CO2 sample (i.e., similar Δ47 correction matrix). This will lead to an improvement in the correction scheme of the carbonate clumped isotope thermometry and reliably adjust the absolute Δ47 scale. / Thesis / Doctor of Philosophy (PhD)