Currently our understanding of both system and phytoplankton metabolism in large rivers is somewhat limited. Knowledge of the metabolic balance in such systems is necessary not only for proper management of the river itself, but also for the lakes into which they discharge. The River Continuum Concept proposes that the deep, turbid waters of large rivers have a poor light climate which leads to heterotrophic conditions (respiration > photosynthesis) yet this idea has been challenged. Similarly, it has been predicted that phytoplankton growth in large rivers is limited to areas of unusually favourable light climate and water retention (e.g. margins, backwaters), but the evidence is limited. Through longitudinal and diel measurements of Chl a, nutrient concentrations, dissolved oxygen and stable oxygen isotopes it was shown in this study that the lower Grand River was autotrophic during the two successive summers but either balanced or heterotrophic in other seasons. This implies that large rivers such as the Grand can be a transition zone for nutrients and a phytoplankton source, depending on season. Experimental incubations to measure oxygen production under varying irradiance demonstrated that phytoplankton could indeed grow (i.e., achieve positive net production) in the main river channel. Comparison of system and plankton metabolic rates further indicated that the phytoplankton were responsible for the major portion of the system production, but much less of the respiration. Sediment oxygen demand probably accounted for much of the additional respiration, but interactions with marginal and upstream habitats was probably an additional influence on both consumption and production of oxygen. The results further showed that stable oxygen isotope dynamics did not conform to the steady state model commonly used to infer metabolic patterns from environmental isotope data. A non-steady model was more successful and largely supported independent assessments of metabolism.

Currently our understanding of both system and phytoplankton metabolism in large rivers is somewhat limited. Knowledge of the metabolic balance in such systems is necessary not only for proper management of the river itself, but also for the lakes into which they discharge. The River Continuum Concept proposes that the deep, turbid waters of large rivers have a poor light climate which leads to heterotrophic conditions (respiration > photosynthesis) yet this idea has been challenged. Similarly, it has been predicted that phytoplankton growth in large rivers is limited to areas of unusually favourable light climate and water retention (e.g. margins, backwaters), but the evidence is limited. Through longitudinal and diel measurements of Chl a, nutrient concentrations, dissolved oxygen and stable oxygen isotopes it was shown in this study that the lower Grand River was autotrophic during the two successive summers but either balanced or heterotrophic in other seasons. This implies that large rivers such as the Grand can be a transition zone for nutrients and a phytoplankton source, depending on season. Experimental incubations to measure oxygen production under varying irradiance demonstrated that phytoplankton could indeed grow (i.e., achieve positive net production) in the main river channel. Comparison of system and plankton metabolic rates further indicated that the phytoplankton were responsible for the major portion of the system production, but much less of the respiration. Sediment oxygen demand probably accounted for much of the additional respiration, but interactions with marginal and upstream habitats was probably an additional influence on both consumption and production of oxygen. The results further showed that stable oxygen isotope dynamics did not conform to the steady state model commonly used to infer metabolic patterns from environmental isotope data. A non-steady model was more successful and largely supported independent assessments of metabolism.

Authigenic carbonate rock (ACR) is derived from microbial oxidation of methane, biodegradation of crude oil, and oxidation of sedimentary organic matter. The precipitation of ACR was characterized petrographically, mineralogically, and geochemically. ACR collected from the seafloor in the Gulf of Mexico (GOM) and ACR recovered from drilled cores in the Krishna-Godawari (KG) basin offshore India were used. All study sites are associated with hydrocarbon gas venting, seepage, free gas, or gas hydrate. ACR from the GOM is densely cemented and extremely irregular in shape, whereas ACR from offshore India is generally an oval-shaped smooth nodule and also densely cemented. The dominant mineral in ACR is authigenic calcite. ACR contains carbon derived from sedimentary organic carbon oxidation that geologically sequesters much fossil carbon. Bulk carbon and oxygen isotopes of ACR were measured. ACR from the GOM is strongly depleted in 13C with ?13C of ?42.5? and enriched in 18O with ?18O of 4.67?. The ?13C of hydrocarbon is typically more depleted in 13C than in the associated ACR. The reason is that authigenic carbonate cements from hydrocarbon oxidation generally enclose skeletal material characterized by normal marine carbonate. Three groups that represent different hydrocarbon sources to ACR were classified in this study: primary carbon sources to ACR from (1) methane plus biodegraded oil, (2) methane, or (3) biodegraded oil. Wide ranges in ?13C (?49.12 to 14.06?) and ?18O ( 1.27 to 14.06?) were observed in ACR from offshore India. In sediments, the ?13C may be affected by differences in the rate of organic carbon oxidation, which generate varying ?13C with depth during methanogenesis. Based on the wide range in ?13C, ACR from offshore India was classified: (1) ?13C may reflect high rates of organic carbon oxidation, (2) ACR may be derived primarily from methane oxidation, and (3) ?13C may reflect low rates of organic carbon oxidation. ?18O values are heavier than those of normal marine carbonates. The ?18O may be caused by reaction with deep-sourced water that was isotopically heavier than ambient seawater. Some samples may reflect heavy ?18O from gas hydrate decomposition, but it would not cause significant heavy oxygen isotopes.

We test the fidelity of shallow-water gastropod skeletons as multi-proxy archives of seasonal paleo-environmental change by performing isotopic and trace-metal analyses on specimens of Conus ermineus from the Gulf of Mexico. Four adult specimens were collected from Stetson Bank in the Flower Garden Banks National Marine Sanctuary during the summer of 2002. Shell samples were milled along axes of growth to produce time-series profiles spanning up to eight years. We corrected the profiles for growth rate effects and compared the tuned results with in situ temperature and salinity records at the reef surface and temperature profiles from nearby surface buoys. Examination of sample densities in δ18O cycles shows that shell growth is faster during summers and slower during winters. Tuning the profiles versus time yields δ18O values that co-vary closely with seasonal temperatures to a high degree of coherency (R2 = 0.84). The δ13C profiles show cyclic variation modified by ontogenetic decreases in δ13C. These ontogenetic trends are attributable to decreasing metabolic efficiency, while seasonal cycles reflect hydrographic changes in the gastropods’ habitat. Salinity and δ13C of dissolved inorganic carbon show a strong correlation at Stetson Bank (R2 = 0.80), and early summer shell δ13C minima coincide with local salinity minima during times of peak river discharge. The terminations of these δ13C minima occur during annual upcoast reversals of shelf currents in this area. These effects are augmented by summer stratification and productivity minima that further decrease seawater δ13C. Sr/Ca ratios increase through ontogeny, most likely due to decreasing metabolic efficiency. However, seasonal variations in Sr/Ca profiles show strong similarity with δ18O profiles, confirming the temperature dependence of Sr/Ca and minimal influence of salinity on shell δ18O at Stetson Bank. The results of this study show that tuned δ18O and Sr/Ca profiles can be used to reconstruct seasonal paleotemperatures. Carbon isotope profiles and environmental data also demonstrate the utility of Conus δ13C as a proxy for freshwater flux and shelf circulation.

Title from PDF of title page. / Document formatted into pages; contains 93 pages / Thesis (M.S.)--University of South Florida, 2003. / Includes bibliographical references. / Text (Electronic thesis) in PDF format. / ABSTRACT: Coral-based climate studies commonly use elemental ratios and stable isotopes of coral skeletons to address seawater temperature and hydrologic balance issues in the tropical surface oceans. Replication, or cross-checking, a standard technique used to assess the fidelity of proxy records in paleoclimatology has not been widely applied in coral-based climate studies, primarily because of the time and cost associated with generating multiple records from a single reef site. Modern and paleoclimate reconstructions based on a single proxy-coral record from a site may contain errors if individual corals from the same reef record different geochemical signals. In this study we perform a replication test using elemental ratios and stable isotopes in three Porites corals from New Caledonia. / ABSTRACT: The reef complex offshore Amédée Island, New Caledonia is an ideal site to perform a coral replication test because instrumental sea surface temperatures (SST) and sea surface salinity measurements (SSS) have been made there for over 25 years. In this study, we compare sub-monthly resolved, geochemical variations (Sr/Ca, d18O and d13C) in three Porites lutea coral heads, located 500 m apart, with the instrumental SST and SSS records over the interval 1992-1967. The monthly coral Sr/Ca and d18O time series are well correlated to each other (r=0.86, p[.0001) and to the monthly instrumental SST record (r= -0.86, p[.0001, coral Sr/Ca to SST; r= -0.77, p[.0001, coral d18O to SST). The three, sub-monthly resolved, 30-year coral Sr/Ca-SST time series have mean SST values that agree within 0.2oC with the instrumental mean SST value. A similar comparison for the coral d18O-SST records indicate a maximum difference between predicted and observed mean SST of 0.5°C. / ABSTRACT: Analysis of the monthly climatological means also indicates that Sr/Ca-SST records closely match the instrumental SST record ±0.4°C; a similar comparison using the d18O-SST record yields an average offset of ±0.6°C between observed and predicted monthly SST. Stacking the three records to form composite Sr/Ca-SST and d18O-SST records does not appreciably improve the goodness of fit between the proxy and instrumental SST records; hence a coral-based proxy climate record from a single coral accurately reflects the observed record of climate variability at this locality. These results support the concept that high fidelity climate records can be generated using a single coral core. / System requirements: World Wide Web browser and PDF reader. / Mode of access: World Wide Web.

Core samples were collected in September 1995 from live coral heads of Montastraea annularis at Bird Key reef in the Dry Tortugas, Florida (24 degrees 55 minutes N, 82 degrees 92 minutes W). Four 4 mm-thick coral slabs from two cores were continuously sampled at 12 samples per year (0.025 cm per sample for Core 31, 0.023 cm per sample for Core 35). Visual inspection of X-radiographs indicates an average skeletal extension rate of about 3 mm per year in Bird Key corals. The goal of this study was to perform a replication test in Montastraea annularis by using elemental and stable isotopes from four coral slabs from two different coral heads to address the following questions: 1) how well do geochemical signals replicate within a single coral head, 2) how well do geochemical signals replicate from two different cores from the same coral head, 3) how well do geochemical signals replicate from two coral heads from the same general area, and 4) do growth effects influence the geochemistry of slow-growing corals at the Dry Tortugas? Geochemical variations versus depth and time of all coral records show strong seasonal cyclicity. Variations in d18O in the suite of Bird Key coral records replicate the best; d13C and Sr/Ca variations replicate less well. For example, differences in the mean Sr/Ca record from two different coral heads are large (0.179 mmol/mol for BK31B-BK35CC; 0.196 mmol/mol for BK31C-BK35CC; ~4 degrees C) and nearly 4 times greater than analytical precision. Therefore, caution must be exercised in interpreting Sr/Ca-SST records in Montastraea annularis. Mean differences in coral d18O for all records, on the other hand, are within analytical precision and translate to temperature differences of less than 0.5 degrees C. Robust d18O values among cores that co-vary with a significant level of agreement further point to this proxy being more reliable than Sr/Ca. Because of its skeletal complexity, drilling difficulty, and large bio-geological error for Sr/Ca, Montastraea annularis seems poorly suited for coral-based Sr/Ca-SST studies. However, the species must be studied to understand tropical Atlantic interannual-decadal scale variability, so further assessment is warranted.

Tufa and lacustrine deposits are useful paleoclimate archives in reconstructing the early to middle Holocene climate and paleohydrology of southern Yemen's Wadi Idim and Wadi Sana, which are north-flowing tributaries to Wadi Hadramawt. Numerical age estimates and oxygen-isotopes are used to assess the onset and cessation of tufa formation and reconstruct the environment of lacustrine sediment deposition in the region in order to understand the broader early to middle Holocene hydrologic system.Numerical age estimates from the studied wadis show a correspondence between early to mid-Holocene humid-phase sediment deposition and the northward shift of the ITCZ, as documented in paleoclimate records from other East Africa -- Arabia -- India continental and marine sediments. The interval between ca. 10-5 ka B.P. corresponds to a period of greater availability of moisture from the Arabian Sea region. Increases in precipitation allowed for a lake and wetland systems to develop, and increased spring discharge contributed to the formation of the tufa. Within the lacustrine sediments are ostracodes, mollusks, and flora casts that are found in a much wetter climate compared to today's hyper-arid environment. This early to mid-Holocene humid phase corresponds with a more northerly positioned ITCZ, which shifted south to its present day position around 5,000 yr B.P.Oxygen isotope measurements from ostracods show a range of isotope values from ~ -4.0%â?? at approximately 10 ka B.P. to ~ -6.0%â?? at approximately 5 ka B.P. Theses values represent the early to middle Holocene pluvial phase. Changes in the oxygen isotopic signature represent a change in evaporation or a possible change in source.The early to middle Hol ocene humid phase also corresponds with periods of agricultural activity, which are being investigated by the archaeological team of the Roots of Agriculture in Southern Arabia Project (RASA). Research into the effects of climate change on human activities, specifically agricultural processes, is the focus of RASA. Southern Arabia offers not only a convergence of three major agricultural regions, but also preserves a sedimentary record of the climate shift that affected the region during the period of study.

The Sierra Mojada district consists of multiple types of mineral concentrations ranging from polymetallic sulfide deposits, "non-sulfide Zn" (NSZ) deposits, and a Pb carbonate deposit hosted by Upper Jurassic to Lower Cretaceous carbonates. This study focuses on the two non-sulfide Zn deposits, the Smithsonite Manto and the Iron Oxide Manto, that occur south of the San Marcos fault. The Smithsonite Manto shows karst features, including internal sediments interbanded with smithsonite (ZnCO₃). The Iron Oxide Manto consists of strata-bound zones dominantly of hemimorphite (Zn₄Si₂O₇ (OH)₂·H₂O) that fills pores in Fe-oxides. The mineralogy of the NSZ mineralization consists of smithsonite, hemimorphite and Zn clays (sauconite) associated mainly with calcite and Mn-Fe-oxides. Zn clays are abundant in the Smithsonite Manto, but no Zn clays have been found in the Iron Oxide Manto. This project attempts to constrain the origin of the NSZ concentrations through petrographic and mineralogical study of major Zn-bearing minerals, and their carbon and oxygen stable isotopes and Pb isotope geochemistry. Smithsonite in the Smithsonite Manto occurs as botryoidal aggregates consisting of scalenohedral or rhombohedral microcrystals and banded colloform or massive smithsonite in open spaces, whereas smithsonite in the Iron Oxide Manto occurs as rhombic microcrystals grown in pore spaces or finely intergrown with Fe-oxides. Both Fe-poor and Fe-rich smithsonite are found in the Iron Oxide Manto. Under optical-CL, smithsonite displays complex growth zoning that can be related to variable trace element content. Trace elements semiquantitatively analyzed using LA-ICP-MS show that most blue luminescent smithsonite has lower Mn contents than pink to bright red luminescent zones in smithsonite. Preliminary fluid inclusion petrography in hemimorphite and calcite suggests that fluid composition can be related to precipitation of NSZ minerals from freshwater to slightly saline waters. Calculated salinities for two phase (liquid +vapor) and single phase (liquid) inclusions in hemimorphite range between 0.0 and 1.6 wt. % NaCl equivalent, and salinities of inclusions in calcite were between 0.0 and 1.1 wt. % NaCl equivalent. The oxygen isotope values for smithsonite are relatively constant (avg. [delta]¹⁸O[subscriptVSMOW] = 21.9 ± 0.5[per mille]), whereas [delta]¹³C[subscriptVPDB] values range from -8.4 to -1.1 [per mille]. The oxygen isotope values in late calcite are within the same range of smithsonite, whereas the average values of the carbon isotope are lower by 5 [per mille]. Formational temperature of smithsonite is calculated to be between 26 ~ 40 °C using the modern groundwater composition at Cuatro Ciénegas. Similar Pb isotopic compositions of smithsonite and cerussite to galena suggest the source of metals in the NSZ deposits presumably originate from the sulfide deposits. / text

In the summer of 2010, fieldwork was conducted in the Robertson Valley, Canadian Rocky Mountains, Alberta to assess the magnitude and controls of microbial nitrification in proglacial till and in supraglacial, subglacial, and proglacial streams. Seasonal precipitation and glacial and proglacial runoff was sampled for hydrochemical and stable isotope analyses (δ18O and δ15N of nitrate [NO3-]). Lower Ca:Mg ratios, higher mean Σmajor ions, and an increased importance of reactions with slower dissolution kinetics in subglacial streams and proglacial seeps indicated waters here experienced longer rock-water contact time than in dilute supraglacial streams. Additionally, waters emanating from longer residence time flowpaths acquired substantial NO3- from nitrification reactions. Using δ18O-NO3- in a simple end-member mixing model, the fraction of NO3- derived from microbial nitrification was estimated to be 44 to 56% in the two subglacial streams, and greater than 80% in proglacial seeps. These results show that atmospherically-derived nitrogen (N) in this glacial valley undergoes substantial biological cycling prior to export in surface runoff. Water flowing from the east subglacial stream (RE) received a larger portion of its melt from a sediment-rich, slow drainage system and had a higher proportion of nitrified NO3- compared to the west subglacial stream (RW), where runoff was similar in composition to supraglacial runoff, indicating that the nature of subglacial flowpaths is an important factor in determining the amount of microbially-cycled nutrients that are exported from a glacier. Sixteen 34-day in situ soil incubations revealed that net mineralization and net nitrification occurred at all four sampling sites in the glacier forefield along a 1.6 km chronosequence; however, there was no significant difference among these rates with time since deglaciation or temperature. Instead, net mineralization and net nitrification rates were significantly correlated (p < 0.05, n = 16) with measured physical and chemical soil variables, including total organic carbon, total N, bulk density, pH, and clay content, suggesting that substrate availability is a larger control on N-cycling processes than time since deglaciation. High variability in inorganic soil N pools and N-cycling rates indicates that there are likely hot spots of biogeochemical activity within glacial till. / Thesis (Master, Geography) -- Queen's University, 2012-04-26 14:47:17.29

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