No description available.

Carbonaceous materials found in Archean rocks have been the source of study and controversy for the last two decades due to questions of the biogenecity of these particles. One of the key locations for these studies is the Barberton Greenstone Belt (BGB), in South Africa which contains some of the oldest known rocks on Earth, ranging in age from 3.5 to 3.2 billion years old. Preserved within the Onverwacht and Fig Tree Groups of the BGB are spherules that formed by the condensation of an impact-produced global vapor plume. The spherules are distal deposits that would have been deposited globally, but are only preserved at this location and in western parts of Australia. Like several other sediments in the BGB, there is evidence of minor amounts of carbonaceous particles contained within the spherule beds. Four individual impact events are preserved in distinct beds designated as S1, S2, S3, and S4. Due to the wide distribution of this bed in a variety of depositional settings, including both protected shallow and deep water depositional settings where there is little evidence of reworking, the S3 bed is an ideal choice for mineralogical, geochemical, and petrographic studies of impact spherules. This research examines samples from four different locations of the S3 spherule bed layer, the Barite Syncline, Maid-of-the-Mist, Sheba Mine, and Loop Road locations, in order to determine the origin of carbonaceous particles contained within the bed. Several geologic processes could account for the presence of the carbonaceous materials within the S3 spherule bed layer. These processes include: (1) Diagenetic processes, (2) Fisher-Tropsch Synthesis, (3) Microbial activity, and (4) Primary condensates from the impact plume. In order to distinguish between these processes, the spatial distribution of the carbonaceous matter was mapped, noting the mineral associations with these grains. Petrographic and electron microanalytical studies of the S3 samples reveal the presence of carbonaceous material in the sections with highly concentrated spherules, Barite Syncline, Loop Road, and Sheba Mine locations, but not in the samples from the Maid-of-the-Mist location, where there is a low concentration of spherules and abundant admixed volcanic detritus. Only Fischer-Tropsch Synthesis can be excluded as a process responsible for the origin of carbonaceous materials in the S3 beds. Though there is no direct evidence of the biogenecity of the observed carbonaceous materials, other textual observations within the S3 spherule bed are consistent with microbial activity, including Ambient Inclusion Trails and an unusual feature with a cyanobacteria-like morphology. While microbial activity cannot be ruled out as a process responsible for the origins of the carbonaceous materials, the findings of this study indicate that the carbon was mobilized from within the spherules during diagenesis. The location of carbon along spherule rims and microfractures within the spherules can also be attributed to diagenetic processes, such as fracture flow, dissolution, and replacement. A plausible explanation is that the carbon was a primary condensate from the impact plume, but has been diagenetically remobilized locally into microfractures and along the rims of the spherules. / Geology

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No description available.

The Arctic is a region undergoing unprecedented and unequivocal climate change. The seas of this extreme region form a major component of the oceanic thermohaline conveyor and natural carbon cycle. Using a combination of recent and historical datasets this study examines the distribution, diversity, photophysiology and primary productivity of phytoplankton in the Atlantic sector of the Arctic Ocean. CHEMTAX analysis reveals a diverse phytoplankton community structure in the Greenland Sea comprising six main phytoplankton groups. The influence of sea-ice and water column stratification are key factors in the presence or absence of groups such as haptophytes and prasinophytes. Group-specific differences are observed in spectral absorption and photophysiological parameters. However, the influence of environmental factors has a stronger influence than taxonomic composition on photophysiology. A clear division between the photoacclimatory response of algal communities beneath sea-ice and those of open-ocean stations is predominantly due to ‘E_k independent’ photoacclimation beneath sea-ice. This occurs due to the combined effect of sea-ice decreasing irradiance entering the water column and a positive correlation between P_m ^B and temperature. This variation in photophysiology is important for primary production models as a sensitivity analysis shows that errors in these parameters propagate to give the largest final errors in primary production values. The importance of other model parameters varies with the level of biomass in the water column and the presence or absence of sea ice. Accelerated ice-melt and an increase in open water due to climate change are likely to increase primary production in the Atlantic Arctic alongside an altered distribution of phytoplankton groups, with an increase in the importance of prasinophytes or haptophytes.

The global marine distributions of Cd and phosphate are closely correlated, which has led to Cd being considered as a marine micronutrient. Recent developments in Cd stable isotope mass spectrometry have revealed that Cd uptake by phytoplankton causes isotopic fractionation in the open ocean and in culture. The explanation for this nutrient-like behaviour is unknown as there is only one identified biochemical function for Cd, an unusual Cd/Zn carbonic anhydrase (CdCA1). This thesis investigates why Cd appears to act as an algal nutrient by performing subcellular analyses of microorganisms genetically-modified to express the CdCA1 gene. It was found that CdCA1 was not a significant contributor to whole-cell Cd isotope compositions. Instead, a large proportion of the internalized Cd is sequestered into cell membranes with a similar direction and magnitude of Cd isotopic fractionation as seen in surface seawater. This observation is explained if Cd is mistakenly imported with other divalent metals and subsequently managed by binding within the cell to avoid toxicity. This result implies that surface seawater Cd isotope compositions, if captured by an appropriate archive, may be invaluable for reconstructions of past marine productivity. The role of environmental factors in modulating the inorganic partitioning of Cd isotopes into calcite was investigated through a series of laboratory analogue experiments. In seawater, the light isotopes of Cd are always preferred in calcite. The magnitude of fractionation showed no response to temperature, ambient [Mg], or precipitation rate. To further identify suitable palaeaoceanographic archives, the Cd isotopic composition of a suite of modern deep-sea corals were investigated. It was found that the Cd/Ca and Cd isotope composition of coralline calcium carbonate followed the predicted trend for closed-system Rayleigh fractionation in the calcifying space. The lack of isotopic offsets between some corals and seawater will simplify the application of Cd isotopes in deep-sea corals -- and potentially other marine calcifying organisms that vacuolize seawater prior to calcium carbonate precipitation -- to palaeoceanography.

abstract: Utilizing both 16S and 18S rRNA sequencing alongside energetic calculations from geochemical measurements offers a bridged perspective of prokaryotic and eukaryotic community diversities and their relationships to geochemical diversity. Yellowstone National Park hot spring outflows from varied geochemical compositions, ranging in pH from < 2 to > 9 and in temperature from < 30°C to > 90°C, were sampled across the photosynthetic fringe, a transition in these outflows from exclusively chemosynthetic microbial communities to those that include photosynthesis. Illumina sequencing was performed to document the diversity of both prokaryotes and eukaryotes above, at, and below the photosynthetic fringe of twelve hot spring systems. Additionally, field measurements of dissolved oxygen, ferrous iron, and total sulfide were combined with laboratory analyses of sulfate, nitrate, total ammonium, dissolved inorganic carbon, dissolved methane, dissolved hydrogen, and dissolved carbon monoxide were used to calculate the available energy from 58 potential metabolisms. Results were ranked to identify those that yield the most energy according to the geochemical conditions of each system. Of the 46 samples taken across twelve systems, all showed the greatest energy yields using oxygen as the main electron acceptor, followed by nitrate. On the other hand, ammonium or ammonia, depending on pH, showed the greatest energy yields as an electron donor, followed by H2S or HS-. While some sequenced taxa reflect potential biotic participants in the sulfur cycle of these hot spring systems, many sample locations that yield the most energy from ammonium/ammonia oxidation have low relative abundances of known ammonium/ammonia oxidizers, indicating potentially untapped sources of chemotrophic energy or perhaps poorly understood metabolic capabilities of cultured chemotrophs. / Dissertation/Thesis / Masters Thesis Geological Sciences 2018

Within this dissertation, I document how—and hypothesize why—the quirks and qualities of the Cambrian Period demarcate this interval as fundamentally different from the preceding Proterozoic Eon and succeeding periods of the Phanerozoic Eon. To begin, I focus on the anomalous marine deposition of the mineral apatite. Sedimentary sequestration of phosphorus modulates the capacity for marine primary productivity and, thus, the redox state of the Earth system. Moreover, sedimentary apatite minerals may entomb and replicate skeletal and soft-tissue organisms, creating key aspects of the fossil record from which paleontologists deduce the trajectory of animal evolution. I ask what geochemical redox regime promoted the delivery of phosphorus to Cambrian seafloors and conclude that, for the case of the Thorntonia Limestone, apatite nucleation occurred under anoxic, ferruginous subsurface water masses. Moreover, I infer that phosphorus bound to iron minerals precipitated from the water column and organic-bound phosphorus were both important sources of phosphorus to the seafloor. Petrographic observations allow me to reconstruct the early diagenetic pathways that decoupled phosphorus from these delivery shuttles and promoted the precipitation of apatite within the skeletons of small animals. Together, mechanistic understandings of phosphorus delivery to, and retention within, seafloor sediment allow us to constrain hypotheses for the fleeting occurrence of widespread apatite deposition and exquisite fossil preservation within Cambrian sedimentary successions. Next, I describe and quantify the nature of carbonate production on a marine platform deposited at the hypothesized peak of Cambrian skeletal carbonate production. I find that fossils represent conspicuous, but volumetrically subordinate components of early Cambrian carbonate reef ecosystems and that despite the evolution of mineralized skeletons, Cambrian carbonate platforms appear similar to their Neoproterozoic counterparts, primarily reflecting abiotic and microbial deposition. Finally, I investigate the geodynamic mechanism responsible for rapid, oscillatory true polar wander (TPW) events proposed for the Neoproterozoic and Phanerozoic Earth on the basis of paleomagnetic data. Using geodynamic models, I demonstrate that elastic strength in the lithosphere and stable excess ellipticity of Earth’s figure provided sufficient stabilization to return the pole to its original state subsequent to convectively-driven TPW. / Earth and Planetary Sciences

No description available.

abstract: Biological soil crusts (BSCs) are critical components of arid and semiarid environments and provide the primary sources of bioavailable macronutrients and increase micronutrient availability to their surrounding ecosystems. BSCs are composed of a variety of microorganisms that perform a wide range of physiological processes requiring a multitude of bioessential micronutrients, such as iron, copper, and molybdenum. This work investigated the effects of BSC activity on soil solution concentrations of bioessential elements and examined the microbial production of organic chelators, called siderophores. I found that aluminum, vanadium, copper, zinc, and molybdenum were solubilized in the action of crusts, while nickel, zinc, arsenic, and zirconium were immobilized by crust activity. Potassium and manganese displayed behavior consistent with biological removal and mobilization, whereas phosphorus and iron solubility were dominated by abiotic processes. The addition of bioavailable nitrogen altered the effects of BSCs on soil element mobilization. In addition, I found that the biogeochemical activites of BSCs were limited by molybdenum, a fact that likely contributes to co-limitation by nitrogen. I confirmed the presence of siderophore producing microbes in BSCs. Siderophores are low-molecular weight organic compounds that are released by bacteria to increase element solubility and facilitate element uptake; siderophore production is likely the mechanism by which BSCs affect the patterns I observed in soil solution element concentrations. Siderophore producers were distributed across a range of bacterial groups and ecological niches within crusts, suggesting that siderophore production influences the availability of a variety of elements for use in many physiological processes. Four putative siderophore compounds were identified using electrospray ionization mass spectrometry; further attempts to characterize the compounds confirmed two true siderophores. Taken together, the results of my work provide information about micronutrient cycling within crusts that can be applied to BSC conservation and management. Fertilization with certain elements, particularly molybdenum, may prove to be a useful technique to promote BSC growth and development which would help prevent arid land degradation. Furthermore, understanding the effects of BSCs on soil element mobility could be used to develop useful biomarkers for the study of the existence and distribution of crust-like communities on ancient Earth, and perhaps other places, like Mars. / Dissertation/Thesis / Ph.D. Geological Sciences 2012