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At least 1,729 records · Page 96Linked to original sources
USGS1993

The global carbon dioxide budget

The increase in atmospheric CO 2 levels during the last deglaciation was comparable in magnitude to the recent historical increase. However, global CO 2 budgets for these changes reflect fundamental differences in rates and in sources and sinks. The modern oceans are a rapid net CO 2 sink, whereas the oceans were a gradual source during the deglaciation. Unidentified terrestrial CO 2 sinks are important uncertainties in both the deglacial and recent CO 2 budgets. The deglacial CO 2 budget represents a complexity of long-term dynamic behavior that is not adequately addressed by current models used to forecast future atmospheric CO 2 levels.

Science↗
USGS1986

Formation of methane and carbon dioxide from dimethylselenide in anoxic sediments and by a methanogenic bacterium

Anaerobic San Francisco Bay salt marsh sediments rapidly metabolized [ 14 C]dimethylselenide (DMSe) to 14 CH 4 and 14 CO 2 . Addition of selective inhibitors (2-bromoethanesulfonic acid or molybdate) to these sediments indicated that both methanogenic and sulfate-respiring bacteria could degrade DMSe to gaseous products. However, sediments taken from the selenium-contaminated Kesterson Wildlife Refuge produced only 14 CO 2 from [ 14 C]DMSe, implying that methanogens were not important in the Kesterson samples. A pure culture of a dimethylsulfide (DMS)-grown methylotrophic methanogen converted [ 14 C]DMSe to 14 CH 4 and 14 CO 2 . However, the organism could not grow on DMSe. Addition of DMS to either sediments or the pure culture retarded the metabolism of DMSe. This effect appeared to be caused by competitive inhibition, thereby indicating a common enzyme system for DMS and DMSe metabolism. DMSe appears to be degraded as part of the DMS pool present in anoxic environments. These results suggest that methylotrophic methanogens may demethylate methylated forms of other metals and metalloids found in nature.

California↗
USGS1993

Carbonate-periplatform sedimentation by density flows: A mechanism for rapid off-bank and vertical transport of shallow-water fines

Existing theories of off-bank sediment transport cannot account for rapid rates of sedimentation observed in Bahama bank and Florida shelf periplatform environments. Analysis of the physical processes operating during winter cold fronts suggests that accelerated off-bank transport of shallow-water mud may be achieved by sinking off-bank flows of sediment-charged hyperpycnal (super-dense) platform waters.

Geology↗
USGS2007

The Pennsylvanian-early permian bird spring carbonate shelf, Southeastern California: Fusulinid biostratigraphy, paleogeographic evolution, and tectonic implications

The Bird Spring Shelf in southeastern California, along with coeval turbidite basins to the west, records a complex history of late Paleozoic sedimentation, sea-level changes, and deformation along the western North American continental margin. We herein establish detailed correlations between deposits of the shelf and the flanking basins, which we then use to reconstruct the depositional history, paleogeography, and deformational history, including Early Permian emplacement of the regionally significant Last Chance allochthon. These correlations are based on fusulinid faunas, which are numerous both on the shelf and in the adjoining basins.

Special Paper of the Geological Society of America↗
USGS2011

Oxygen-isotope trends and seawater temperature changes across the Late Cambrian Steptoean positive carbon-isotope excursion (SPICE event)

The globally recognized Late Cambrian Steptoean positive C-isotope excursion (SPICE) is characterized by a 3‰–5‰ positive δ 13 C shift spanning <4 m.y. Existing hypotheses suggest that the SPICE represents a widespread ocean anoxic event leading to enhanced burial/preservation of organic matter (C org ) and pyrite. We analyzed δ 18 O values of apatitic inarticulate brachiopods from three Upper Cambrian successions across Laurentia to evaluate paleotemperatures during the SPICE. δ 18 O values range from ∼12.5‰ to 16.5‰. Estimated seawater temperatures associated with the SPICE are unreasonably warm, suggesting that the brachiopod δ 18 O values were altered during early diagenesis. Despite this, all three localities show similar trends with respect to the SPICE δ 13 C curve, suggesting that the brachiopod apatite preserves a record of relative δ 18 O and temperature changes. The trends include relatively high δ 18 O values at the onset of the SPICE, decreasing and lowest values during the main event, and an increase in values at the end of the event. The higher δ 18 O values during the global extinction at the onset of the SPICE suggests seawater cooling and supports earlier hypotheses of upwelling of cool waters onto the shallow shelf. Decreasing and low δ 18 O values coincident with the rising limb of the SPICE support the hypothesis that seawater warming and associated reduced thermohaline circulation rates contributed to decreased dissolved O 2 concentrations, which enhanced the preservation/burial of C org causing the positive δ 13 C shift.

Geology↗
USGS2016

Response comment: Carbon sequestration on Mars

Martian atmospheric pressure has important implications for the past and present habitability of the planet, including the timing and causes of environmental change. The ancient Martian surface is strewn with evidence for early water bound in minerals (e.g., Ehlmann and Edwards, 2014) and recorded in surface features such as large catastrophically created outflow channels (e.g., Carr, 1979), valley networks (Hynek et al., 2010; Irwin et al., 2005), and crater lakes (e.g., Fassett and Head, 2008). Using orbital spectral data sets coupled with geologic maps and a set of numerical spectral analysis models, Edwards and Ehlmann (2015) constrained the amount of atmospheric sequestration in early Martian rocks and found that the majority of this sequestration occurred prior to the formation of the early Hesperian/late Noachian valley networks (Fassett and Head, 2011; Hynek et al., 2010), thus implying the atmosphere was already thin by the time these surface-water-related features were formed.

Geology↗
USGS2007

Effect of lipid extraction on analyses of stable carbon and stable nitrogen isotopes in coastal organisms of the Aleutian archipelago

We tested whether extracting lipids reduced confounding variation in ??13C and ??15N values by analyzing paired lipid-extracted (LE) and non-lipid-extracted (NLE) samples of bald eagle (Haliaeetus leucocephalus (L., 1766)) whole eggs, muscle tissue from nine seabird and one terrestrial bird species, muscle tissue from four marine fish species, and blue mussels (Mytilus edulis L., 1758) collected from the Aleutian archipelago, Alaska. Lipid extraction significantly increased ??13C by an average of 2.0??? in whole eggs, 0.8??? in avian muscle, 0.2??? in fish muscle, and 0.6??? in blue mussels. Lower ??13C values in NLE samples covaried positively with lipid content across all sample types. Lower ??13C values in NLE samples were not correlated with lipid content within bald eagle eggs and blue mussels, but covaried positively with percent lipid in avian and fish muscles. Neither lipid extraction nor percent lipid significantly changed ??15N values for any sample type. Lower ??13C values in most NLE avian and fish muscle tissues should not confound interpretation of pelagic versus nearshore sources of primary production, but lipid extraction may be necessary when highly precise estimates of ??13C are needed. Lipid extraction may not be necessary when only ??15N is of interest. ?? 2007 NRC.

Canadian Journal of Zoology↗
USGS2008

Discrimination of carbon and nitrogen isotopes from milk to serum and vibrissae in Alaska Steller sea lions (Eumetopias jubatus)

Knowledge of diet-tissue stable isotope discrimination is required to properly interpret stable isotope values and to identify possible diet shifts, such as might be expected from nursing through weaning. This study compared ??13C and ??15N of paired serum and vibrissal roots with those of ingested milk (n = 52) from free-ranging Steller sea lion (Eumetopias jubatus (Schreber, 1776)) pups (1-11 months) and juveniles (14-27 months) to estimate diet-tissue discrimination. Mean 15N enrichment from ingested milk to serum was 2.1??? ?? 0.6%??? and ??15N at the root of the vibrissae (representing current growth) were not significantly different from serum values. Milk was enriched for mean 13C by 5.0??? ?? 1.0%??? and 7.3??? ?? 1.2??? relative to serum and vibrissal roots, respectively, which was due to the presence of 13C-depleted lipids in milk. This was confirmed by lipid extraction from a subset of milk and serum samples, resulting in a 5.8??? ?? 1.0??? change only in milk. This study established that vibrissal roots and serum are reflective of a milk diet with approximately 2.0??? 15N enrichment, and vibrissal roots reflect serum and lipid-extracted milk values with approximately 2.0??? 13C enrichment. These discrimination factors are important to establish for stable isotope studies assessing diet shifts. ?? 2008 NRC.

Canadian Journal of Zoology↗
USGS2019

Integrating structure from motion, numerical modelling and field measurements to understand carbonate sediment transport in coral reef canopies

Reef canopies are complex and extremely variable across a range of spatial scales. This variability affects the velocity above as well as within the canopy, and directly impacts the transport of sediment along the bed as well as suspended in the water column. How a canopy affects the transport of sediment is important to understand and predict changes in the position of the adjacent shoreline, particularly as reefs change. In this study, high-resolution seabed complexity models derived from photogrammetry for low roughness and high roughness canopy sites at Moloka’i (Hawai’i) are combined with direct field measurements and three-dimensional numerical modelling to investigate these canopy and sub-canopy impacts on velocity and sediment transport.

Hawaii↗
USGS2013

Fate of process solution cyanide and nitrate at three Nevada gold mines inferred from stable carbon and nitrogen isotope measurements

Stable isotope methods have been used to identify the mechanisms responsible for cyanide consumption at three heap-leach operations that process Carlin-type gold ores in Nevada, U.S.A. The reagent cyanide had δ 15 N values ranging from -5 to -2‰ and δ 13C values from -60 to -35‰. The wide δ 13 C range reflects the use by different suppliers of isotopically distinct natural-gas feedstocks and indicates that isotopes may be useful in environmental studies where there is a need to trace cyanide sources. In heap-leach circuits displaying from 5 to 98% consumption of cyanide, barren-solution and pregnant-solution cyanide were isotopically indistinguishable. The similarity is inconsistent with cyanide loss predominantly by HCN offgassing (a process that in laboratory experiments caused substantial isotopic changes), but it is consistent with cyanide retention within the heaps as solids, a process that caused minimal isotopic changes in laboratory simulations, or with cyanide oxidation, which also appears to cause minimal changes. In many pregnant solutions cyanide was carried entirely as metal complexes, which is consistent with ferrocyanides having precipitated or cyano-complexes having been adsorbed within the heaps. It is inferred that gaseous cyanide emissions from operations of this type are less important than has generally been thought and that the dissolution or desorption kinetics of solid species is an important control on cyanide elution when the spent heaps undergo rinsing. Nitrate, nitrite and ammonium had δ 15 N values of 1-16‰. The data reflect isotopic fractionation during ammonia offgassing or denitrification of nitrate–particularly in reclaim ponds–but do not indicate the extent to which nitrate is derived from cyanide or from explosive residues.

Nevada↗
USGS2007

Improving resolution and understanding controls on GPR response in carbonate strata: Implications for attribute analysis

For more than a decade, environmental, engineering, groundwater, and shallow stratigraphic studies have demonstrated and advanced the usefulness of ground-penetrating radar (GPR) in lithified and unconsolidated sedimentary deposits (e.g., see Neal, 2004 and references therein). Despite the advances, important questions still remain on factors that control the actual appearance and characteristics of GPR reflections and diffractions in any given setting. ?? 2007 Society of Exploration Geophysicists.

Leading Edge (Tulsa, OK)↗
USGS1996

Authigenic feldspar as an indicator of paleo-rock/water interactions in Permian carbonates of the Northern Calcareous Alps, Austria

Dolostones interbedded with Upper Permian evaporites at the base of the Northern Calcareous Alps contain abundant authigenic K-feldspar. Two petrographically, structurally, and isotopically distinct generations of K-feldspar can be distinguished: crystals composed of an inclusion. rich core and a clear rim, and optically unzoned, transparent crystals. Both feldspar types have essentially identical K-feldspar end-member compositions with >= 99.5 mole % Or component. Low oxygen isotope ratios (+16.1 per thousand to +18.1 per thousand SMOW) suggest precipitation from 18 O-enriched, saline fluids at temperatures in excess of nearly equal 140 degrees C. 40 Ar/ 39 Ar plateau-age spectra of five samples range from 145 + or - 1 to 144 + or -1 Ma (Early Berriasian) and suggest that both types of feldspar were formed within an interval that did not exceed nearly equal 2 m.y. Rb/Sr model ages range from 152 to 140 Ma, assuming that the burial diagenetic regime was buffered with respect to strontium by the associated marine Permian evaporites. Authigenic K-feldspar records two distinct events of hot brine flow, most likely triggered by tectonic movements (detachment) and by an increase in the subsurface temperature in response to thrust loading.

Journal of Sedimentary Research↗
USGS2024

Interlamellar adsorption of carbon dioxide by smectites

The adsorption of CO 2 at low temperature (∼ −70°C) on thin films of homoionic smectites was studied by X-ray diffraction and by i.r. absorption. An increase in the d 001 spacings of these clay films upon adsorption of CO 2 was observed. In addition, a dichroic effect was readily discernible by comparing the i.r. spectra at two different orientations of the smectite films; i.e. with the film normal and tilted 35° with respect to the i.r. beam. The CO 2 stretching vibration at 2350 cm −1 was used for the i.r. study. These observations conclusively show that CO 2 intercalates the smectite structure rather than being adsorbed only in pores between clay tactoids—the limiting process proposed by other investigators. Adsorption isotherm data from earlier surface area studies are re-examined here through application of the Dubinin equation. Again, intercalation is demonstrated by convergence of the plotted experimental data for smectites containing large monovalent interlayer cations toward a pore volume that is near the calculated theoretical value for a monolayer of intercalated CO 2 . Scanning electron photomicrographs of Li- and Cs- smectites provide additional evidence that aggregation differences are not responsible for the large observed difference in BET surface areas obtained for these smectites with CO 2 as the adsorbate. At low magnification, visual differences in macro-aggregates are apparent, but at high magnification no significant differences are observed in the micro-structure of individual aggregates where the major amount of gas adsorption really occurs.

Clays and Clay Minerals↗
USGS2021

Computational methodology to analyze the effect of mass transfer rate on attenuation of leaked carbon dioxide in shallow aquifers

Exsolution and re-dissolution of CO 2 gas within heterogeneous porous media are investigated using experimental data and mathematical modeling. In a set of bench-scale experiments, water saturated with CO 2 under a given pressure is injected into a 2-D water-saturated porous media system, causing CO 2 gas to exsolve and migrate upwards. A layer of fine sand mimicking a heterogeneity within a shallow aquifer is present in the tank to study accumulation and trapping of exsolved CO 2 . Then, clean water is injected into the system and the accumulated CO 2 dissolves back into the flowing water. Simulated exsolution and dissolution mass transfer processes are studied using both nearequilibrium and kinetic approaches and compared to experimental data under conditions that do and do not include lateral background water flow. The mathematical model is based on the mixed hybrid finite element method that allows for accurate simulation of both advection- and diffusion- dominated processes.

Acta Polytechnica↗