This study investigates the runoff process and groundwater behavior in a subarctic watershed called Wolf Creek Research Basin, in Whitehorse, Yukon Territory, Canada. This basin is underlain by discontinuous permafrost that is typical of high latitude watersheds. Goundwater supports the stream flow year round and dominated the hydrology in most of the study period as baseflow. The baseflow was concentrated in dissolved ions. However, the baseflow was diluted during the melt season in May and June of 2012. Multiple chemical and isotopic tracers were used to develop a robust three-component (groundwater, soilwater and precipitation) mixing model for runoff generation. The concentrations of weathering ions decreased with the increased discharge during the melt. Soilwater was responsible for about 60% of the streamwater on the hydrograph in the melt season. The infiltration of the meltwater from the snowpack and the thawed water from the seasonal frost to the baseflow existed. The tritium concentrations indicated that there was fast moving hydrogeological system within the basin. The baseflow was also characterized as relatively enriched in both 13C and 14C, and concentrated in DIC. DIC was the major loss of carbon in Wolf Creek Research Basin.Le pergélisol est grandement sous-jacent dans les bassins-versants à haute latitude. Cette étude examine le processus de ruissellement et le comportement des eaux souterraines dans un bassin-versant subarctique de Wolf Creek, à Whitehorse, territoire du Yukon au Canada. Les eaux souterraines soutenaient l’écoulement fluvial et dominaient l’hydrographe comme débit de base durant la majorité de la période d’étude. Le débit de base était concentré d’ions dissipés. Par contre, le débit de base était dilué durant la saison des fontes au mois de mai et juin 2012. Plusieurs traceurs chimiques et isotopiques étaient utilisé afin de développer un modèle de trois composants (eau souterraine, eau interstitielle de sol et précipitation) de ruissellement. Les concentrations de la déségrégation des ions diminuaient avec l’augmentation du débit durant la fonte. Les eaux interstitielles des sols étaient responsables de 60% de l’eau de ruisseau sur l’hydrographe durant la saison de fontes. L’infiltration de l’eau de fonte du manteau neigeux et l’eau du gel du débit de base existaient. Les concentrations de tritium indiquent qu’il y avait un système hydrogéologique qui se déplaçait à grande vitesse dans les limites du bassin. Le débit de base était aussi caractérisé comme étant enrichi en 13C et 14C, avec des concentrations en carbone inorganique dissous.

The Newmarket Till is a regional aquitard in southern Ontario that overlies the Illinoian to Middle Wisconsinan Lower Sediments and is overlain by the Oak Ridges Moraine (ORM). Geological investigations have mapped the distribution of the till and it is understood that erosional channels, subsequently infilled with fluvial material, breach the till and may create enhanced hydraulic connection between overlying and underlying aquifers. However, little is known about the protective capability of the Newmarket Till where it is intact. This study used natural tracers to assess the extent of transport in the aquitard-aquifer system. Stable isotopes of water (δ18O and δ2H) showed a depletion trend versus depth. In the Newmarket Till most of the samples had isotope ratios similar to meteoric water data from the nearest location (Egbert, ON). The depleted values of δ18O in the Thorncliffe Formation suggest a remnant signature of early-Holocene precipitation (-16‰ at the depth of 60 m). Elevated levels of NO3- and Cl- were detected near the surface and because of the low permeability aquitard (Newmarket Till), they could not migrate to depth. Total extractable ammonium concentrations are ranging from 4.09 ppm from near the surface to 60 ppm in the lowest part of the Newmarket and then gradually increase to 514 ppm in the bottom of the Thorncliffe Formation. The combination of high NH4+ values and organic carbon content in the Thorncliffe Formation suggests a natural source from mineralization of organic N. The fractionation which happened between δ15Nsediment and δ15N-NH4 may have three explanations: (1) lighter isotopes diffuse faster than heavier ones, so the higher rate of diffusion can cause fractionation; (2) heavier isotopes partition to exchange sites, causing fractionation along the transport pathway; (3) dissociation of NH4+ to NH3 under anaerobic condition. Positive values for δ13C in groundwater in the Thorncliffe Formation are likely due to i) a contribution of carbonate mineral dissolution, and ii) methanogenesis - the Archea favor the lighter isotope of C (12C). Methanogenesis, therefore, enriches the δ13C-DIC was enriched; however, the δ13C in dissolved organic carbon (DOC) is depleted. These geochemical characteristics demonstrate a long residence time for the porewater in the system and indicate that the Newmarket till inhibits recharge of recent precipitation, thereby providing protection to the underlying aquifers from surface-derived contaminants.

A recently discovered Bison-bearing fossil locality at Térapa, Sonora, Mexico, had previously been dated to 440 ± 130 ka using whole rock 40Ar/39Ar on a basalt flow that impounds the deposit. This age is considerably older than the accepted age of about 240-160 ka for the migration of Bison into greater North America. The Térapa deposit also contains a mixture of fossils from extralimital or extinct tropical animals and temperate animals. Constraining the age of the deposit is critical to interpret the paleontologic and paleoclimatologic implications of this unique Sonoran fossil locality. Three additional geochronological methods have been applied to this deposit (infrared stimulated luminescence (IRSL), amino acid racemization (AAR), and radiocarbon) and the data from the original 40Ar/39Ar age were revisited. The IRSL data suggest that the impounding basalt flow and the sediments that abut it were emplaced 43 ka ago and that the oldest sediments were deposited shortly after. Two radiocarbon ages suggest the fossiliferous sediments were emplaced by 42 ka. Effective diagenetic temperatures inferred from the AAR results, combined with AAR data from a similar-age deposit in southern Arizona, are in accordance with the 40-43 ka age estimates. For the AAR results to corroborate the 40Ar/39Ar age, the effective diagenetic temperature for the area would need to be approximately 3 °C, which is unrealistically low for northern Mexico. The new geochronological results suggest the Térapa deposit and fossils are 40-43 ka old. The anomalously old 40Ar/39Ar age for the impounding basalt is probably the result of low 40Ar* concentrations and inherited 40Ar.

Willard Libby's development of carbon-14 dating at the University of Chicago immediately following World War II provided an unprecedented opportunity for the collaboration of archaeologists with a physical chemist. Libby's need for archaeological samples to test the dating process (1947-1951) meant that he relied upon the Committee on Radioactive Carbon 14, formed by the American Anthropological Association, for datable materials, as well as for assistance in all other archaeologically related aspects of the testing phase. The committee, under the leadership of archaeologist Frederick Johnson, served the mandated function of providing assistance to Libby, but simultaneously endeavored to utilize the new dating method to promote the development of the authority of anthropological professional organizations and further establish Americanist archaeology in a national and global context. Johnson's and the committee's approach to collaboration was informed by an understanding of opportunities provided by the postwar restructuring of the sciences. The purpose of the present study is to provide a history of the Committee on Radioactive Carbon 14 (1948-1952) as well as a to provide the context necessary to describe the bureaucratic and scientific goals of the committee. Frederick Johnson's career, and the manner in which it reflected general trends in twentieth century American anthropology, is discussed in detail, and utilized to present an explanation of his actions as committee chair. Willard Libby's development of carbon-14 dating is also discussed in detail, particularly in regard to his request for assistance from the archaeological community and subsequent collaborative work. The undeniable influence of carbon-14 dating on archaeological practice worldwide, and Libby's acceptance of the Nobel Prize in Chemistry (1960) for his development of the dating method, has provided reason enough for a plethora of articles and book length studies regarding carbon-14 dating. Yet, little has been written about the Committee on Radioactive Carbon 14 and its place in an analysis of the bureaucratic and collaborative science of the American mid-century. It is for this reason that the present study was undertaken.

No description available.

Thesis (S.M.)--Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and the Woods Hole Oceanographic Institution), 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 49-50). / The focus of this thesis is the design and development of a system for rapid extraction of dissolved inorganic carbon from seawater and groundwater samples for radiocarbon dating. The Rapid Extraction of Dissolved Inorganic Carbon System (REDICS) consists of two subsystems - one for sample introduction, acidification, and carbon dioxide extraction, and one for carbon dioxide quantification and storing. The first subsystem efficiently extracts the dissolved inorganic carbon from the water sample in the form of carbon dioxide by utilizing a gas-permeable polymer membrane contractor. The second subsystem traps, quantifies and stores the extracted gas using cryogenics. The extracted carbon dioxide is further processed for stable and radiocarbon isotope analysis at the National Ocean Sciences Accelerator Mass Spectrometer Facility at the Woods Hole Oceanographic Institution. The REDICS system was tested using seawater standards collected at 470m and 4000m depth in the Atlantic Ocean and analyzing the extracted CO₂. The results were compared to the results for the same standards processed on the current NOSAMS water stripping line. The results demonstrate that the system successfully extracts more than 99% of the dissolved inorganic carbon in less than 20 minutes. Stable isotope and radiocarbon isotope analyses demonstrated system precision of 0.02%c and 3.5% respectively. / by Kalina Doneva Gospodinova. / S.M.

Sclerochronology affirms the well-established fact that banded growth increments in marine molluscs accurately record oscillations in climate and environment for the past millennia or more. This study considers how such records can enhance understanding of environmental shifts across the 18th to 20th centuries. Specifically, it investigates whether sclerochronological data are fundamentally associated with stable carbon and oxygen isotope values and if the climate phenomenon of the Little Ice Age impacts the marine radiocarbon reservoir effect. Furthermore, this study compares the North Sea and the Irish Sea to discover whether observed environmental changes are equivocal or not. Three shells of Arctica islandica were retrieved from the Dutch natural history museum "Naturalis" in Leiden, the Netherlands, to construct a chronology dating back to the 18th century from growth increments. Collection dates for the three shells vary between 1882 and 1954 in the North Sea and the Irish Sea. Shells were prepared, photographed and milled for calcium carbonate material. Digital images allowed counting of increments while the milled material was measured for stable carbon and oxygen isotopes and was radiocarbon dated. The ontogenetic bias was removed from sclerochronological data using MATLAB software to produce a purely environmental growth signal. The results agreed with the proposed hypothesis that there is a link between growth increments and the stable isotope data. However, further analysis is required to validate the presence of the Little Ice Age in the radiocarbon reservoir effect. These results indicate that the stable carbon and oxygen isotopes and growth increments are a good indicator of favourable growth conditions for Arctica islandica. Therefore, this study highlights that Arctica islandica is a suitable proxy for the North Sea and Irish Sea palaeoenvironment reconstructions. On this basis, future climate research can accurately depend on sclerochronological data to aid in understanding the patterns of anthropogenic climate change.

The sequence of timber circle - henge monument - stone circle is widely accepted. This is in spite of the reality that the datable evidence and contextual data upon which this series is based has seldom been subjected to any real form of critical evaluation. The aim of this research was to determine whether this order could still be deemed tenable in light of contemporary research and the continued advances that have been achieved relating to the application of radiocarbon dating. The findings of this study demonstrated that sufficient contextual data exists to enable phases of construction to be identified. However rarely did these data appear to support the currently accepted chronologies. Indeed more commonly they alluded to an alternative series, one that demonstrated how some individual site sequences may have been previously misinterpreted. This study has also proven how methodological and interpretative weaknesses, relating to the use of radiocarbon dating, have created a quantifiable degree of accuracy between individual radiocarbon determinations and their ability to be reliably associated with the event or act that they have been used to date. These findings have not only cast sufficient doubt upon the reliability of the currently accepted chronologies for these three monumental forms but have also alluded to the existence of a far more appropriate sequence that conforms to the overall conclusions of this review far more convincingly. Accordingly a new series of timber circle(s) - stone circle - henge monument is proposed by this study.

No description available.

No description available.