No description available.

No description available.

Thesis (Ph. D.)--Oregon Graduate Center, 1979.

Depth and temporal variability of organic carbon (POC) and total nitrogen (TN) and their isotopic compositions (£_13C and £_15N) in sinking particulate organic matter (POM) collected at the SEATS time-series station (18¢X15¡¦ N; 115¢X50¡¦ E), northern South China Sea, respond closely to the strong seasonality (changes in sea surface temperatures and mixed layer depths) in the surface layer, but are modified considerably by subsequent microbial degradation/remineralization and probably by re-suspension of sediments from the surrounding shelf region in the deep water. Lower C/N and £_15N in summer than the other seasons reflects the change of nutrient supply from NO3-rich, 15N-enriched subsurface waters to N2-fixation-dominated nitrogen source in the surface waters. Below the euphotic zone (>100m), both POC and TN decrease, whereas C/N increases progressively with depth owing to the biodegradation and the preferential removal of more degradable nitrogen-containing compounds through the water column. The C/N increase rate is estimated to be 0.4 unit per 1 km water depth, which is significantly higher than the world average (0.2/km) as a result of the input of higher C/N organic matter from sediments deposited nearby the SEATS site. POC and TN and total particulate mass fluxes decrease sharply within the euphotic zone and continue to decrease all way through the water column to seafloor. For site comparison and global synthesis, an average fraction (e-ratio) of 0.22 of POC exported from the euphotic zone and a POC attenuation rate (b value) of 0.97 are derived. Since the results of this study were obtained from a marginal sea characteristic of strong monsoonal modulation, they should contribute to a better understanding of the fate and pathway of POC in the world ocean.

A variety of lunar soils (bulk soils, grain size fractions and mineral separates) and regolith breccias are studied for nitrogen abundance and isotopic composition. in order to investigate the isotopic variation in the lunar regolith and to constrain the origin of the nitrogen. The lunar soils and breccias are analysed using a high sensitivity static-vacuum mass spectrometer. capable of measuring nanogram quantities of nitrogen with a δ¹⁵N precision of ±0.5‰. In addition to nitrogen abundance measurements, conjoint carbon and argon abundances (allthough the latter are semi-quantitative) are also measured. Lunar soils and breccias are analysed by stepped combustion and pyrolysis extraction. Typically employing temperature resolution of 25-50°C. However, some soils and breccias are analysed by high-resolution extraction using temperature increments of 10°C. constituting the highest resolution studies performed to date. The high-resolution extractions of lunar soils and breccias has confirmed the existence of the heavy-light-heavy-light-heavy (W-shaped) isotopic profile observed by previous workers for pyrolysis extractions of lunar breccias. The current study has confirmed that the W-shaped profile is restricted to pyrolysis extractions, but is present in both soils and breccias. The well documented heavy-light-heavy (V-shaped) isotopic profile is observed in stepped combustion extractions. The nitrogen in the lunar regolith has been shown to be of both solar and non-solar origin. The former is confirmed from the solar-like C/N ratios in lunar soils. and the latter is confirmed from the excess N/³⁶Ar ratio. between 5 and 39 times the solar value. Although neither nitrogen source is believed to be a minor component, the solar wind is believed to contribute -30% of the total nitrogen, although the relative proportions of solar and non-solar nitrogen are not well constrained. The surface-correlation of the low temperature nitrogen release (LTN), from the <10μm fraction from soil A12023. has enabled calculation of the isotopic composition of this component with δ¹⁵N = +35.3 ±3.6‰. It is believed that this value is representative of the isotopic composition of the recent solar wind. Furthermore, the absence of isotopically light nitrogen in agglutinates separated from A12073. and the increasing contribution of high temperature nitrogen (HTN) with increasing grain size from the same soil. has suggested that the volume-correlated nitrogen is released at temperatures ≥1050°C. This is believed to be representative of the ancient solar wind, and has a mean δ^l5N = +77.0 ± 6.0‰. This work has shown that the maximum secular variation of ¹⁵N/¹⁴N in the lunar regolith is -2.8%. significantly lower than previous estimates. The low temperature. isotopically heavy nitrogen component. NLT. and the isotopically light nitrogen components. NMT and NHT (although the latter is only observed during stepped pyrolysis extractions). display a ^l5N/^l4N variation of 38%. This cannot be accounted for by a secular variation of ¹⁵N/^l4N in this work. The origin of NLT is not well constrained. but may be due to re-implantation of atmospheric nitrogen. or fractionation of solar wind gases during the formation of amorphous rims around soils grains. A proportion 1-3% I of NHT has been observed in soil A12023. with δ¹⁵N = -186‰, the lightest observed in a lunar soil. The similarity of this value with that obtained for lunar breccia A79035. has suggested the possibility of a relict component. implanted prior to breccia consolidation. No evidence of presolar grains could be identified in A79035, although there is some evidence for amorphous carbon. This may also be associated with the presence of fine-grained metallic iron as a significant proportion of this in lunar soils is believed to originate from meteorite contamination.

<p> The Proterozoic' Coldwell Alkaline Complex is the southernmost intrusion of a number of N -S trending igneous bodies occurring in the Midcontinental Rift system exposed in the Lake Superior area. The Coldwell complex is host to several Ni-Cu-PGEbearing intrusions two of which; the Two-Duck Lake intrusion (Marathon deposit) and the Geordie Lake gabbro (MacRae occurrence) have been investigated in some detail with respect to PGE mineralisation. Both of these have been suggested to have experienced crustal contamination in conjunction with mineralisation. As a test of this possibility, a detailed Sm-Nd, oxygen isotope, and whole-rock geochemical study of these mineralised occurrences as well as of the Dunlop occurrence and the Middleton occurrence, together with unmineralised rocks of the complex was undertaken. The primary objectives are to determine whether crustal contamination is indicated in mineralised rocks and to try and ascertain the nature of the magma which formed the complex. </p> <p> The Coldwell complex is thought to have been formed by emplacement of magma at three intrusive centres. Sm-Nd data for rocks from these three centres reveal similar isotopic values, with slight variations; samples taken from the western gabbros exhibit eNd values averaging -0.9 ranging from -2.9 to 0.9, whereas rocks from the eastern margin and centre of the complex have eNd values of about an average of 0.5 ranging from -0.5 to 1.2 suggesting that the magma that formed these rocks has undergone a lesser degree of crustal contamination. This data, supported by oxygen isotope and wholerock geochemical information indicates that crustal contamination seems to play a small, and varied role in the genesis of the Coldwell magmas. The Nd isotope data all clusters at values for CHUR, which indicates that it has been enriched relative to the depleted mantle. It has been postulated that an enriched mantle plume resided under the rift and promoted rift-related magmatism. The data from this study would seem to support this supposition. </p> <p> Geochemical parameters utilised to define fields to geochemically delineate possible end member contributors to this primarily plume-derived magma indicate, that in addition to small, variable amounts of assimilation of upper and lower crust, the plume magmas also interacted with the lithospheric upper mantle to a small degree. </p> / Thesis / Master of Science (MSc)

An investigation was undertaken to check the difference in isotopic content between two boron samples measured earlier in this laboratory by using different methods of sample preparation from those used in the previous investigation. Yields of preparation were measured throughout. Measurements using methyl borate and boron trifluoride indicated a difference of slightly over 2% in the isotopic content of the samples, whereas the difference found in the previous investigation was 3.5%. / Thesis / Master of Science (MS)

No description available.

No description available.

No description available.