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)

Two conceptual approaches which offer promise for improved understanding of biological invasions are conceptualizing the invasion process as a series of distinct stages and explicitly incorporating human actions into analyses. This study explores the utility of these approaches for understanding the invasion of Trifolium (true clover) species in New Zealand. From the published literature, I collected a range of Trifolium species attributes, including aspects of global transport and use by humans, opportunistic association with humans in New Zealand, native range attributes, habitat characteristics, and biological traits. I also searched historical records to estimate the extent to which each species had been planted in New Zealand, a search facilitated by the enormous importance of Trifolium in New Zealand’s pastoral agriculture system. Regression analysis and structural equation modelling were then used to relate these variables to success at each invasion stage. Fifty-four of the 228 species in the genus Trifolium were intentionally introduced to New Zealand. Species introduced for commercial agriculture were characterised by a large number of economic uses and presence in Britain, while species introduced for horticulture or experimental agriculture were characterised by a large native range area. Nine of these 54 intentionally introduced species subsequently naturalised in New Zealand. The species that successfully naturalised were those that had been planted extensively by humans and that were well-matched to the New Zealand climate. A further 16 species (from the pool of 174 species that were never intentionally introduced) arrived and naturalised in New Zealand without any recorded intentional aid of humans. Several attributes appeared to assist species in unintentional introduction-naturalisation, including a good match to the New Zealand climate, a large native range area, presence in human-influenced habitats, a widespread distribution in Britain, and self-pollination capability. The 25 total naturalised species varied greatly in their current distributions and in the rates at which they had spread to achieve those distributions. Species that had spread quickly and are currently more widespread had been frequent contaminants in the pasture seed supply and have a long flowering period in New Zealand. Other biological traits and native range attributes played supporting roles in the spread process. Attributes facilitating success clearly varied among invasion stages. Humans played a dominant role at all stages of this invasion, although biological traits had increasing importance as a species moved through the invasion sequence. My findings suggest that incorporation of human actions and the stage-based framework provide valuable insight into the invasion process. I discuss potential avenues by which these approaches might be integrated into predictive invasion models.

Two conceptual approaches which offer promise for improved understanding of biological invasions are conceptualizing the invasion process as a series of distinct stages and explicitly incorporating human actions into analyses. This study explores the utility of these approaches for understanding the invasion of Trifolium (true clover) species in New Zealand. From the published literature, I collected a range of Trifolium species attributes, including aspects of global transport and use by humans, opportunistic association with humans in New Zealand, native range attributes, habitat characteristics, and biological traits. I also searched historical records to estimate the extent to which each species had been planted in New Zealand, a search facilitated by the enormous importance of Trifolium in New Zealand's pastoral agriculture system. Regression analysis and structural equation modelling were then used to relate these variables to success at each invasion stage. Fifty-four of the 228 species in the genus Trifolium were intentionally introduced to New Zealand. Species introduced for commercial agriculture were characterised by a large number of economic uses and presence in Britain, while species introduced for horticulture or experimental agriculture were characterised by a large native range area. Nine of these 54 intentionally introduced species subsequently naturalised in New Zealand. The species that successfully naturalised were those that had been planted extensively by humans and that were well-matched to the New Zealand climate. A further 16 species (from the pool of 174 species that were never intentionally introduced) arrived and naturalised in New Zealand without any recorded intentional aid of humans. Several attributes appeared to assist species in unintentional introduction-naturalisation, including a good match to the New Zealand climate, a large native range area, presence in human-influenced habitats, a widespread distribution in Britain, and self-pollination capability. The 25 total naturalised species varied greatly in their current distributions and in the rates at which they had spread to achieve those distributions. Species that had spread quickly and are currently more widespread had been frequent contaminants in the pasture seed supply and have a long flowering period in New Zealand. Other biological traits and native range attributes played supporting roles in the spread process. Attributes facilitating success clearly varied among invasion stages. Humans played a dominant role at all stages of this invasion, although biological traits had increasing importance as a species moved through the invasion sequence. My findings suggest that incorporation of human actions and the stage-based framework provide valuable insight into the invasion process. I discuss potential avenues by which these approaches might be integrated into predictive invasion models.