Simon R. Poulson

Sulphur isotope evidence for an oxic Archaean atmosphere

The presence of mass-independently fractionated sulphur isotopes (MIF-S) in many sedimentary rocks older than ∼2.4 billion years (Gyr), and the absence of MIF-S in younger rocks, has been considered the best evidence for a dramatic change from an anoxic to oxic atmosphere around 2.4 Gyr ago. This is because the only mechanism known to produce MIF-S has been ultraviolet photolysis of volcanic sulphur dioxide gas in an oxygen-poor atmosphere. Here we report the absence of MIF-S throughout ∼100-m sections of 2.76-Gyr-old lake sediments and 2.92-Gyr-old marine shales in the Pilbara Craton, Western Australia. We propose three possible interpretations of the MIF-S geologic record: (1) the level of atmospheric oxygen fluctuated greatly during the Archaean era; (2) the atmosphere has remained oxic since ∼3.8 Gyr ago, and MIF-S in sedimentary rocks represents times and regions of violent volcanic eruptions that ejected large volumes of sulphur dioxide into the stratosphere; or (3) MIF-S in rocks was mostly created by non-photochemical reactions during sediment diagenesis, and thus is not linked to atmospheric chemistry.

Stable isotope and trace element geochemistry of the basal Bouse Formation carbonate, southwestern United States: Implications for the Pliocene uplift history of the Colorado Plateau

The upper Miocene to Pliocene Bouse Formation, exposed in the lower Colorado River trough (Arizona, California, Nevada), has variously been interpreted as a marine, estuarine, or freshwater deposit. The Bouse Formation is now commonly found at elevations of >300 m and up to 550 m above sea level. Deposition of the Bouse in a transgressive marine (or estuarine) environment requires rapid drowning of the lower Colorado River trough during Pliocene time and subsequent uplift of the nearby Colorado Plateau. Basal Bouse Formation carbonate samples were analyzed for stable isotope composition, minor and trace element concentrations, and mineralogy, in order to investigate the depositional environment. Most of the data presented here are consistent with deposition of the basal Bouse Formation carbonate in a lacustrine environment, although some data are consistent with a possible estuarine origin, with additional evidence for diagenesis affecting individual samples. Our preferred interpretation is that deposition took place in a chain of freshwater lakes fed by the proto–Colorado River, which may have built a delta out into an estuarine environment now exposed as the southernmost part of the formation. This interpretation is in accord with that proposed by J.E. Spencer and P.J. Patchett and implies that the present-day elevations of basal Bouse Formation carbonate in the Colorado River trough place no constraints upon the rate and timing of uplift of the Colorado Plateau.

The lundgreni Extinction Event: Integration of paleontological and geochemical data from Arctic Canada

Abstract The lundgreni Extinction Event (LEE) in Arctic Canada, as in other regions globally, exhibited an apparently abrupt and catastrophic reduction of graptolite and radiolarian taxa, followed by a short period of extremely low diversity, the dubius-nassa Biozone, followed in the subsequent praedeubeli-deubeli Biochron by the rapid evolutionary diversification of new taxa. The extinction event was very close to, or coincided with, a regression, as well as with a moderately strong positive δ13Corganic excursion. The excursion is bifurcated with the lower fork occurring at or near the LEE and the upper fork occurring in about the lower part of the praedeubeli-deubeli Biozone, possibly coinciding with a modest transgression. Radiolarians are diverse and abundant throughout the lundgreni Biozone, sparse to absent directly following the LEE (i.e., in the dubius-nassa Biozone), and found only sporadically within the praedeubeli-deubeli Biozone. Acritarch frequency throughout the entire investigated interval is extremely low, and only in one level in the lundgreni Biozone so-called “giant acritarchs” were observed. Sphaeromorph acritarchs and amorphous organic matter are moderately common in the lundgreni Biozone, extremely abundant in the brief time interval of the dubius-nassa Biozone at Rookery Creek, and only moderately common in higher strata. The presence of dark yellow and light brown-colored organic matter indicates that the absence of acritarchs is not due to reworking or thermal degradation but is, instead, suggestive of paleoecological control. Proximity to a shallower water shelf may have strongly influenced palynomorph/organic content.

Isotope Geochemistry and Plankton Response to the Ireviken (Earliest Wenlock) and Cyrtograptus lundgreni Extinction Events, Cape Phillips Formation, Arctic Canada

Several Canadian Arctic Silurian stratigraphic sections from the basinal facies of Cape Phillips Formation have been sampled across the Llandovery–Wenlock and early–late Homerian (late Wenlock) boundary intervals for integration of biotal (graptolite, radiolarian, palynomorph) and geochemical (13C) data for two well-known extinction events, the Ireviken and lundgreni Extinction (LEE) events. Graptolites, abundant and well preserved, provide a refined biostratigraphic base for other paleontologic and geochemical data. They were globally affected by both extinction events: about 64% reduction for the Ireviken and 90–95% for the LEE. Recovery from the LEE event was slow and diversity low through the late Homerian. Radiolarians—diverse (28 species), abundant, and beautifully preserved through the early Homerian―are sharply reduced slightly below the LEE boundary. Data for the late Homerian are more scattered, but it appears that diversity was low; few early Homerian taxa crossed the extinction boundary and new taxa appeared. Palynological studies around the LEE interval are at a preliminary level, but it appears that chitinozoans and microflora (acanthomorph acritarchs, prasinophytes, sphaeromorphs) were impacted by the extinction event. Chitinozoans, though seldom abundant, appear to disappear briefly across the LEE boundary, as do palynomorphs. Amorphous organic matter is abundant in the upper part of the lundgreni Zone; it is much less common in the early and middle–late Homerian and common in the latest part. Stable isotope geochemistry shows well-marked, positive excursions in the δ13Corganic fraction associated with the Ireviken event and LEE. The Ireviken excursion (C1) curve has a sharp base, reaches a peak in the early Wenlock, and then tapers more slowly. The LEE excursion (C4) peaks at, or slightly below, the early–late Homerian boundary. Both are positive excursions. Considering the limits of biostratigraphic placement of the boundaries, they were close to or coincident with regressions, particularly across the LEE interval. The δ13Corganic excursions are greater for inshore sections compared with the offshore section. The most parsimonious explanation for increased carbon content is accelerated weathering of carbonates exposed during a lowstand.

Effects of Partial Replacement of Corn with Glycerin on Ruminal Fermentation in a Dual-Flow Continuous Culture System

The objective of this study was to evaluate the effects of partially replacing dry ground corn with glycerin on ruminal fermentation using a dual-flow continuous culture system. Six fermenters (1,223 ± 21 ml) were used in a replicated 3x3 Latin square arrangement with three periods of 10 d each, with 7 d for diet adaptation and 3 d for sample collections. All diets contained 75% concentrate and three dietary glycerin levels (0, 15, and 30% on dry matter basis), totaling six replicates per treatment. Fermenters were fed 72 g of dry matter/d equally divided in two meals/d, at 0800 and 2000 h. Solid and liquid dilution rates were adjusted daily to 5.5 and 11%/h, respectively. On d 8, 9, and 10, samples of 500 ml of solid and liquid digesta effluent were mixed, homogenized, and stored at -20°C. Subsamples of 10 ml were collected and preserved with 0.2 mL of a 50% H2SO4 solution for later determination of NH3-N and volatile fatty acids. Microbial biomass was isolated from fermenters for chemical analysis at the end of each experimental period. Data were analyzed using the MIXED procedure in SAS with α = 0.05. Glycerin levels did not affect apparent digestibility of DM (P Lin. = 0.13; P Quad. = 0.40), OM (P Lin. = 0.72; P Quad. = 0.15), NDF (P Lin. = 0.38; P Quad. = 0.50) and ADF (P Lin. = 0.91; P Quad. = 0.18). Also, glycerin inclusion did not affect true digestibility of DM (P Lin. = 0.35; P Quad. = 0.48), and OM (P Lin. = 0.08; P Quad. = 0.19). Concentrations of propionate (P < 0.01) and total volatile fatty acids (P < 0.01) increased linearly and concentrations of acetate (P < 0.01), butyrate (P = 0.01), iso-valerate (P < 0.01), and total branched-chain volatile fatty acids, as well as the acetate: propionate ratio (P < 0.01) decreased with glycerin inclusion. Linear increases on NH3-N concentration in digesta effluent (P < 0.01) and on NH3-N flow (P < 0.01) were observed due to glycerin inclusion in the diets. Crude protein digestibility (P = 0.04) and microbial N flow (P = 0.04) were greater in the control treatment compared with the other treatments and responded quadratically with glycerin inclusion. Furthermore, the inclusion of glycerin linearly decreased (P = 0.02) non-ammonia N flow. Glycerin levels did not affect the flows of total N (P Lin. = 0.79; P Quad. = 0.35), and dietary N (P Lin. = 0.99; P Quad. = 0.07), as well as microbial efficiency (P Lin. = 0.09; P Quad. = 0.07). These results suggest that partially replacing dry ground corn with glycerin may change ruminal fermentation, by increasing total volatile fatty acids, and propionate concentration without affecting microbial efficiency, which may improve glucogenic potential of beef cattle diets.

Stable Isotope Characterization of the Ecohydrological Cycle at a Tropical Treeline Site

ABSTRACT We investigated the seasonal variation in pools of water available to mature trees growing at high elevation in a tropical environment. The study focused on the dominant tree species (Pinus hartwegii) at about 3800 m a.s.l. on Nevado de Colima, Mexico, where climate is typical of the North American Monsoon System. Stable isotope ratios of hydrogen and oxygen in water extracted from soil, xylem, and leaves were measured through a cycle of two dry and two wet seasons in 2003–2004. Isotopic ratios were also measured in accumulated precipitation, a few single precipitation events, and in spring water over the two-year period. Based on evidence from water, stable isotopes in soil, and xylem samples, trees utilized water from relatively shallow soil depths, which are representative of current conditions, rather than tapping groundwater, which is more representative of long-term trends. While the stable isotope signature in environmental waters showed a slightly different pattern before and during the monsoon, the more pronounced differences in leaf water isotopes between the two seasons, due to drought stress, will lead to a clear seasonal isotopic signal in tree ring cellulose. This study represents a unique snapshot of water cycling in a tropical treeline ecosystem, where our understanding of eco-hydrological pathways is limited. This type of analysis is also useful for proper calibration of stable isotopic signals in tree ring records.

Diurnal variations of needle water isotopic ratios in two pine species

Diurnal fluctuations of leaf water isotope ratios (δ18O and δD) were measured for Jeffrey (Pinus jeffreyi Balf.) and lodgepole (Pinus contorta Douglas ex Louden) pine. Two trees per species were sampled every few hours on 15–16 October 2005 and 19–20 June 2006. Diurnal gas exchange was measured during the summer sampling. In fall 2005, leaf water δ18O ranged from 0.7 to 9.0‰, and leaf water δD ranged from −70 to −50‰. In summer 2006, leaf water δ18O ranged from 7.7 to 20.7‰, and leaf water δD ranged from −61 to −24‰. Diurnal variation of leaf water isotope values typically reached a maximum in early afternoon, began decreasing around midnight, and reached a minimum in mid-morning. Both periods showed a high degree of enrichment relative to source water, with leaf water–source water enrichments ranging up to 37.8‰ for δ18O, and up to 95‰ for δD. Leaf water enrichment varied by season with summer enrichment being greater than fall enrichment. A steady-state model (i.e., modified Craig–Gordon modeling) for leaf water isotope compositions did not provide a good fit to measured values of leaf water. In summer, a non-steady state model provided a better fit to the measured data than the steady-state model. Our findings demonstrate substantial leaf water enrichment above source water and diurnal variations in the isotopic composition of leaf water, which has application to understanding short-term variability of atmospheric gases (water vapor, CO2, O2), climate studies based on the isotopic composition of tree rings, and ecosystem water fluxes.

Microbial Transformation of Multiwalled Carbon Nanotubes by Mycobacterium vanbaalenii PYR-1

Carbonaceous nanomaterials are widely used in industry and consumer products, but concerns have been raised regarding their release into the environment and subsequent impacts on ecosystems and human health. Although many efforts have been devoted to understanding the environmental fate of carbonaceous nanomaterials, information about their microbial transformation is still rare. In this study, we found that within 1 month a polycyclic aromatic hydrocarbon-degrading bacterium, Mycobacterium vanbaalenii PYR-1, was able to degrade both pristine and carboxyl-functionalized multiwalled carbon nanotubes (p-MWCNT and c-MWCNT), as demonstrated by consistent results from high resolution transmission electron microscopy, Raman spectroscopy, and confocal Raman microspectroscopy. Statistical analysis of Raman spectra identified a significant increase in the density of disordered or amorphous carbon in p-MWCNT and c-MWCNT after biodegradation. Microbial respiration further suggested potential mineralization of MWCNTs within about 1 month. All of our analyses consistently showed higher degradation or mineralization of c-MWCNT compared to p-MWCNT. These results highlight the potential of using bacteria in engineered systems to remove residual carbonaceous nanomaterials and reduce risk of human exposure and environmental impact. Meanwhile, our finding suggests possible transformation of carbonaceous nanomaterials by polycyclic aromatic hydrocarbon-degrading bacteria in the natural environment, which should be accounted for in predicting the environmental fate of these emerging contaminants and in nanotechnology risk regulation.

Paleohydrographic influences on Permian radiolarians in the Lamar Limestone, Guadalupe Mountains, west Texas, elucidated by organic biomarker and stable isotope geochemistry

Abstract The late Guadalupian Lamar Limestone Member of the Bell Canyon Formation, Delaware Basin, west Texas, records dramatic fluctuations in radiolarian faunal composition that are interpreted to record basin-scale changes in hydrography. Samples taken across one of these intervals of fluctuation show a change from a sparse, nearly monospecific fauna dominated by Follicucullus ventricosus to a more radiolarian-rich interval dominated by spongy spumellarians of the Copicyntrinae and Spongodiscidae. Carbonate stable isotope and organic biomarker geochemical data from this same interval support a strong terrestrial-freshwater influence on the spumellarian-dominated beds. Specifically, biomarker data show lower C22/C27 ratios and n-alkane distributions indicative of terrestrial organic matter sources in the spumellarian-dominated beds. In the whole-rock carbonate fraction, δ18O and δ13C show a shift to more negative values, consistent with increased meteoric water influence in the spumellarian-dominated interval. Lithologically, the spumellarian-dominated beds are siltier; however, they lack any increase in shallow water allochems, such as sponge spicules, that might indicate the spumellarians and associated terrestrial signature are a function of transporting a shallower radiolarian fauna into the basin via turbidity flows. Faunal changes more likely represent a stimulatory response to increased runoff by in situ spumellarians in the surface waters of the basin.

Rate of oxygen isotope exchange between selenate and water.

The rate of oxygen isotope exchange between selenate and water was investigated at conditions of 10 to 80 °C and pH -0.6 to 4.4. Oxygen isotope exchange proceeds as a first-order reaction, and the exchange rate is strongly affected by reaction temperature and pH, with increased rates of isotope exchange at higher temperature and lower pH. Selenate speciation (HSeO(4)(-) vs SeO(4)(2-)) also has a significant effect on the rate of isotope exchange. The half-life for isotope exchange at example natural conditions (25 °C and pH 7) is estimated to be significantly in excess of 10(6) years. The very slow rate of oxygen isotope exchange between selenate and water under most environmental conditions demonstrates that selenate-δ(18)O signatures produced by biogeochemical processes will be preserved and hence that it will be possible to use the value of selenate-δ(18)O to investigate the biogeochemical behavior of selenate, in an analogous fashion to the use of sulfate-δ(18)O to study the biogeochemical behavior of sulfate.