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At least 1,441 records · Page 80Linked to original sources
USGS2012

Geomagnetic paleointensities by the Thelliers' method from submarine pillow basalts: Effects of seafloor weathering

Measurements of geomagnetic paleointensity using the Thelliers' double‐heating method in vacuum have been made on 10 specimens of submarine pillow basalt obtained from 7 fragments dredged from localities 700,000 years old or younger. In the magnetic minerals, the titanium/iron ratio parameter x and the cation deficiency (oxidation) parameter x were determined by X‐ray diffraction and Curie temperature measurement. Fresh material ( z ≅ 0) provided excellent results: most of the natural remanent magnetization (NRM) could be thermally demagnetized before the magnetic minerals became altered, and the NRM‐TRM lines were straight and well constrained, and geologically reasonable paleointensities were obtained. Somewhat oxidized material ( z ≅ 0.2) also provided apparently valid paleointensities: values were similar to those from fresh specimens cut from the same fragments, although only half or less of the NRM could be thermally demagnetized before alteration of the magnetic minerals. More highly oxidized material ( z ≅ 0.6) gave a result seriously in error: the paleointensity value is much too low, because of continuous disproportionation of titanomaghemite during the heating experiments and because seafloor weathering had decreased the NRM intensity. From limited published data, the extent of oxidation of titanomagnetite to cation deficient titanomaghemite in pillow basalt exposed on the seafloor appears to be approximately z = 0.3 at 0.2–0.5 m.y., z = 0.6 at 1 m.y., and z = 0.8–1.0 at 10–100 m.y. This implies that valid paleointensities can be obtained from exposed submarine basalt, but only if the basalt is younger than a few hundred thousand years. Equally good paleointensities were obtained from strongly magnetized (L‐type) basalt and moderately magnetized (L‐type) basalt. The degree of low‐temperature oxidation of cubic iron‐titanium oxides in submarine basalts correlates very well with the diminution of amplitude of linear magnetic anomalies when both are compared as a function of crustal age. Systematic radial variation of Curie temperature is a primary feature of submarine basalt pillows, so that estimation of the oxidation parameter z from the Curie temperature alone by assuming a value for x can be in error. Reasonably precise and self‐consistent values of both x and z can be obtained if both the cubic cell dimension and the Curie temperature of the cubic oxide are measured.

Journal of Geophysical Research B: Solid Earth↗
USGS2012

Magnetic effects of maghemitization of oceanic crust

Both theoretical considerations and available experimental results indicate that magnetic effects of maghemitization are strongly dependent on the grain size of the originally unoxidized titanomagnetite. Maghemitization of single‐domain titanomagnetite results in a decrease in coercivity, an increase in susceptibility, and a large decrease in Q ratio. Maghemitization of multidomain titanomagnetite results in an increase in coercivity, a decrease in susceptibility, and no large changes in Q ratio. Single‐domain titanomagnetite is probably resistant to the development of a chemical remanent magnetization (CRM), whereas multidomain titanomagnetite can acquire a CRM during maghemitization. The behavior of pseudo‐single‐domain titanomagnetite, which is the main carrier of remanence in submarine extrusive rocks, is investigated by comparing the magnetic properties of the French‐American Mid‐Ocean Undersea Study (FAMOUS) (less than 0.1 m.y. old) and the Leg 37 (3.5 m.y. old) pillow basalts recovered from the Mid‐Atlantic Ridge near 37°N. Combining electron microprobe analyses, Curie temperature measurements, and cell edge determinations, we find that the FAMOUS rocks are already oxidized ( z = 0.38), possibly as a result of some high‐temperature maghemitization during cooling of the magma. Comparison with the more highly oxidized ( z = 0.7) Leg 37 pillow basalts indicates that low‐temperature maghemitization of such rocks does not result in appreciable changes of coercivity and susceptibility, although the Q ratio does decrease and CRM seems to be acquired. Such a CRM could account for the anomalously low magnetic inclinations observed at most of the Leg 37 sites.

Journal of Geophysical Research B: Solid Earth↗
USGS2012

The use of MAGSAT data to determine secular variation

A combined spatial and secular variation model of the geomagnetic field, labeled M061581, is derived from a selection of Magsat data. Secular variation (SV) data computed from linear fits to midnight hourly values from 19 magnetic observatories were also included in the analysis but were seen to have little effect on the model. The SV patterns from this new model are compared with those from the 1980 IGRF and with those for 1970 computed by the DGRF and with the 1960 patterns computed using the GSFC(12/66) model. Most of the features of the M061581 are identical in location and level with those of the 1980 IGRF. Together they confirm that the reversals in sign of field change seen over Asia and North America between 1965 and 1975 are reverting to the pre-1965 states. The M061581 model gives −32 nT/yr for the dipole decay rate, larger than the 70% increase already reported since 1965. This abnormally high value is interpreted as being a defect of the model because it appears to result from a much larger (−100 nT/yr) drop in field over the polar regions not indicated by the 1980 IGRF. This north polar decrease is shown to be of external origin as the result of a combination of the seasonal effect of the north polar ionospheric (counterclockwise) afternoon Sq p cell increasing in intensity from the beginning (November 1979) to the end (June 1980) of the Magsat data collection period, coupled with an enhancement of its effect as the orbit lowered from the 350– 550 km initial altitudes to near 200 km just prior to burnup. This experiment indicates that secular variation can be obtained from satellite data for intervals of less than a full year if corrections can be made for seasonal effects and that ‘annual snapshots’ of the field by a satellite would allow easy and accurate models of secular change without the use of any surface data.

Journal of Geophysical Research Solid Earth↗
USGS2012

The mechanics and three-dimensional internal structure of active magmatic systems: Kilauea volcano, Hawaii

Interpretation of abundant seismic data suggests that Kilauea's primary conduit within the upper mantle is concentrically zoned to about 34-km depth. This zoned structure is inferred to contain a central core region of relatively higher permeability, surrounded by numerous dikes that are in intermittent hydraulic communication with each other and with the central core. During periods of relatively high magma transport, the entire cross section of the conduit is utilized. During periods of relatively low to moderate transport, however, only the central core is active. As the conduit penetrates the oceanic crust and enters the volcanic shield, it simultaneously supplies the deeper sections of the rift zones (6-to 10-km depth) and the roots of the summit reservoir with picritic magma. The rift zones at depth are inferred to be almost wholly molten and to possess a high degree of fluid continuity from Heiheiahulu in the East Rift Zone, 45 km westward through the roots of the summit magma reservoir, and well into the Southwest Rift Zone. Higher in the shield, the subcaldera magma reservoir and the shallow rift zones occupy the 2-to 4-km depth interval. Summit-differentiated olivine tholeiite (ρ ≈ 2.62 g cm −3 ) is periodically injected laterally along a horizon of neutral buoyancy within the rift zones, where the density of the magma is just balanced by the in situ density of the shield (Ryan, 1987 a , b ). Deep rift zone intrusions push seaward the deep tectonic blocks of the volcano's south flank. Shallow rift intrusions build a sheeted dike complex, inferred to be in isostatic equilibrium with the higher-density deep rift cores below. General finite element analyses are presented for the deformation and stress fields surrounding such dikes in the horizontal and vertical planes. The dike tip in two and three dimensions is surrounded by a tubular core of tensile (σ 1 , σ 2 ) and shear stress (τ max ). The displacement field is characterized by counterrotating cells on either side of the dike tip which, in vertical orientation, produce the characteristic subsidence above the dike complex, with uplift on either side, forming a ridge-trough-ridge structure. A finite element model of Kilauea's shield computes the displacement fields and principal stress (σ 1 ) distributions resulting from intrusive activity on each or both of the rift zones. Within the summit region, tensile stress lobes produced by the three-dimensional upward extension of the intrusions superpose constructively to produce calderawide regimes of tensile stress, conducive to caldera development. Parametric studies of (1) intrusion in the East Rift Zone only, (2) intrusion in the Southwest Rift Zone only, and (3) intrusion in both rift zones demonstrate their unique kinematic contributions. For case 1, the caldera undergoes a counterclockwise rotation (torque up state) conducive to the development of rightstepping en echelon eruptive fissures, as exemplified by the August 14, 1971, eruption. For case 2, the caldera undergoes a clockwise rotation (torque down state) conducive to the development of left-stepping eruptive fissures, as occurred during the December 31, 1974, eruption. For case 3, the caldera substructure is driven due southward, producing the southward migration of the upper portions of the summit magma reservoir.

Journal of Geophysical Research Solid Earth↗
USGS2014

Ablation of snow‐fields at high altitudes by radiant solar heat

Snow ‐ fields and the so‐called névés of glaciers on lofty mountains often present a peculiar, honeycombed appearance, the surface being pitted with deep cell‐like hollows a foot or two feet in diameter and from a few inches to several feet in depth. When typically developed these hollows are closely spaced, the divides between them consisting merely of attenuated blades and pinnacles of hard, granular snow (Fig. 1). The hollows are alined roughly in rows and sunk at a uniform, high angle, all in the same direction.

Eos, Transactions, American Geophysical Union↗
USGS2010

On Lagrangian residual currents with applications in south San Francisco Bay, California

The Lagrangian residual circulation has often been introduced as the sum of the Eulerian residual circulation and the Stokes' drift. Unfortunately, this definition of the Lagrangian residual circulation is conceptually incorrect because both the Eulerian residual circulation and the Stokes' drift are Eulerian variables. In this paper a classification of various residual variables are reviewed and properly defined. The Lagrangian residual circulation is then studied by means of a two-stage formulation of a computer model. The tidal circulation is first computed in a conventional Eulerian way, and then the Lagrangian residual circulation is determined by a method patterned after the method of markers and cells. To demonstrate properties of the Lagrangian residual circulation, application of this approach in South San Francisco Bay, California, is considered. With the aid of the model results, properties of the Eulerian and Lagrangian residual circulation are examined. It can be concluded that estimation of the Lagrangian residual circulation from Eulerian data may lead to unacceptable error, particularly in a tidal estuary where the tidal excursion is of the same order of magnitude as the length scale of the basin. A direction calculation of the Lagrangian residual circulation must be made and has been shown to be feasible.

California↗
USGS1991

Microbial reduction of uranium

Reduction of the soluble, oxidized form of uranium, U(VI), to insoluble U(IV) is an important mechanism for the immobilization of uranium in aquatic sediments and for the formation of some uranium ores 1–10 . U(VI) reduction has generally been regarded as an abiological reaction in which sulphide, molecular hydrogen or organic compounds function as the reductant 1,2,5,11 . Microbial involvement in U(VI) reduction has been considered to be limited to indirect effects, such as microbial metabolism providing the reduced compounds for abiological U(VI) reduction and microbial cell walls providing a surface to stimulate abiological U(VI) reduction 1,12,13 . We report here, however, that dissimilatory Fe(III)-reducing microorganisms can obtain energy for growth by electron transport to U(VI). This novel form of microbial metabolism can be much faster than commonly cited abiological mechanisms for U(VI) reduction. Not only do these findings expand the known potential terminal electron acceptors for microbial energy transduction, they offer a likely explanation for the deposition of uranium in aquatic sediments and aquifers, and suggest a method for biological remediation of environments contaminated with uranium.

Nature↗
USGS1995

A new mechanism for calcium loss in forest-floor soils

Calcium is the fifth most abundant element in trees, and is an essential component for wood formation and the maintenance of cell walls. Depletion of Ca from the rooting zone can result in acidification of soil 1 and surface water 2 and possibly growth decline and dieback of red spruce 3,4 . During the past six decades, concentrations of root-available Ca (exchangeable and acid-extractable forms) in forest-floor soils have decreased in the northeastern United States 5,6 . Both net forest growth and acid deposition have been put forth as mechanisms that can account for this Ca depletion 5,6 . Here, however, we present data collected in red spruce forests in the northeastern United States that are inconsistent with either of these mechanisms. We propose that aluminum, mobilized in the mineral soil by acid deposition, is transported into the forest floor in a reactive form that reduces storage of Ca, and thus its availability for root uptake. This results in potential stress to trees and, by increasing the demand for Ca, also decreases neutralization of drainage waters, thereby leading to acidification of lakes and streams.

Maine, New Hampshire, New York, Vermont↗
USGS2014

Respiratory transmission of an avian H3N8 influenza virus isolated from a harbour seal

The ongoing human H7N9 influenza infections highlight the threat of emerging avian influenza viruses. In 2011, an avian H3N8 influenza virus isolated from moribund New England harbour seals was shown to have naturally acquired mutations known to increase the transmissibility of highly pathogenic H5N1 influenza viruses. To elucidate the potential human health threat, here we evaluate a panel of avian H3N8 viruses and find that the harbour seal virus displays increased affinity for mammalian receptors, transmits via respiratory droplets in ferrets and replicates in human lung cells. Analysis of a panel of human sera for H3N8 neutralizing antibodies suggests that there is no population-wide immunity to these viruses. The prevalence of H3N8 viruses in birds and multiple mammalian species including recent isolations from pigs and evidence that it was a past human pandemic virus make the need for surveillance and risk analysis of these viruses of public health importance.

Nature Communications↗
USGS2024

Isotopic evidence against North Pacific Deep Water formation during late Pliocene warmth

Several modelling and observational studies suggest deep water formation in the subpolar North Pacific as a possible alternative mode of thermohaline circulation that occurred in the warm Pliocene, a time when global atmospheric partial pressure of carbon dioxide was like the modern atmosphere (~400 ppm). We test this hypothesis by measuring the δ 13 C of the benthic foraminifer Cibicidoides wuellerstorfi collected from northernmost Pacific mid-Piacenzian Warm Period (3.264–3.025 Myr ago) sediments. The data reveal progressively more isotopically negative dissolved inorganic carbon along a northward Equator-to-pole transect, the opposite of the expected Pliocene Pacific meridional overturning circulation signal. C. wuellerstorfi δ 13 C is also often more positive at the deeper Ocean Drilling Program (ODP) site 887 compared with the shallower ODP site 883, suggesting ‘bottom-up’ ventilation of the deep Pacific Ocean. We then present alkenone sea surface temperature and export-productivity data from ODP site 883, which suggest that late Pliocene subarctic North Pacific carbonate sedimentation was, at least in part, probably due to higher coccolithophore export production, rather than North Pacific Deep Water formation as previously argued. Therefore, we suggest it is unlikely that North Pacific Deep Water formation occurred in the mid-Piacenzian Warm Period, although a shallower overturning cell cannot be ruled out.

Nature Geoscience↗
USGS2019

Virally-vectored vaccine candidates against white-nose syndrome induce anti-fungal immune response in little brown bats (Myotis lucifugus)

White-nose syndrome (WNS) caused by the fungus, Pseudogymnoascus destructans ( Pd ) has killed millions of North American hibernating bats. Currently, methods to prevent the disease are limited. We conducted two trials to assess potential WNS vaccine candidates in wild-caught Myotis lucifugus . In a pilot study, we immunized bats with one of four vaccine treatments or phosphate-buffered saline (PBS) as a control and challenged them with Pd upon transfer into hibernation chambers. Bats in one vaccine-treated group, that received raccoon poxviruses (RCN) expressing Pd calnexin (CAL) and serine protease (SP), developed WNS at a lower rate (1/10) than other treatments combined (14/23), although samples sizes were small. The results of a second similar trial provided additional support for this observation. Bats vaccinated orally or by injection with RCN-CAL and RCN-SP survived Pd challenge at a significantly higher rate (P = 0.01) than controls. Using RT-PCR and flow cytometry, combined with fluorescent in situ hybridization, we determined that expression of IFN-γ transcripts and the number of CD4 + T-helper cells transcribing this gene were elevated (P < 0.10) in stimulated lymphocytes from surviving vaccinees (n = 15) compared to controls (n = 3). We conclude that vaccination with virally-vectored Pd antigens induced antifungal immunity that could potentially protect bats against WNS.

Scientific Reports↗
USGS2022

Fire (plus) flood (equals) beach: Coastal response to an exceptional river sediment discharge event

Wildfire and post-fire rainfall have resounding effects on hillslope processes and sediment yields of mountainous landscapes. Yet, it remains unclear how fire–flood sequences influence downstream coastal littoral systems. It is timely to examine terrestrial–coastal connections because climate change is increasing the frequency, size, and intensity of wildfires, altering precipitation rates, and accelerating sea-level rise; and these factors can be understood as contrasting accretionary and erosive agents for coastal systems. Here we provide new satellite-derived shoreline measurements of Big Sur, California and show how river sediment discharge significantly influenced shoreline positions during the past several decades. A 2016 wildfire followed by record precipitation increased sediment discharge in the Big Sur River and resulted in almost half of the total river sediment load of the past 50 years (~ 2.2 of ~ 4.8 Mt). Roughly 30% of this river sediment was inferred to be littoral-grade sand and was incorporated into the littoral cell, causing the widest beaches in the 37-year satellite record and spreading downcoast over timescales of years. Hence, the impact of fire–flood events on coastal sediment budgets may be substantial, and these impacts may increase with time considering projected intensification of wildfires and extreme rain events under global warming.

California↗
USGS2012

Prevalent flucocorticoid and androgen activity in US water sources

Contamination of the environment with endocrine disrupting chemicals (EDCs) is a major health concern. The presence of estrogenic compounds in water and their deleterious effect are well documented. However, detection and monitoring of other classes of EDCs is limited. Here we utilize a high-throughput live cell assay based on sub-cellular relocalization of GFP-tagged glucocorticoid and androgen receptors (GFP-GR and GFP-AR), in combination with gene transcription analysis, to screen for glucocorticoid and androgen activity in water samples. We report previously unrecognized glucocorticoid activity in 27%, and androgen activity in 35% of tested water sources from 14 states in the US. Steroids of both classes impact body development, metabolism, and interfere with reproductive, endocrine, and immune systems. This prevalent contamination could negatively affect wildlife and human populations.

Scientific Reports↗
USGS2015

Transgenerational effects from early developmental exposures to bisphenol A or 17α-ethinylestradiol in medaka, Oryzias latipes

The transgenerational consequences of environmental contaminant exposures of aquatic vertebrates have the potential for broad ecological impacts, yet are largely uninvestigated. Bisphenol A (BPA) and 17 &alpha; -ethinylestradiol (EE2) are two ubiquitous estrogenic chemicals present in aquatic environments throughout the United States and many other countries. Aquatic organisms, including fish, are exposed to varying concentrations of these chemicals at various stages of their life history. Here, we tested the ability of embryonic exposure to BPA or EE2 to cause adverse health outcomes at later life stages and transgenerational abnormalities in medaka fish. Exposures of F0 medaka to either BPA (100 &mu; g/L) or EE2 (0.05 &mu; g/L) during the first 7 days of embryonic development, when germ cells are differentiating, did not cause any apparent phenotypic abnormalities in F0 or F1 generations, but led to a significant reduction in the fertilization rate in offspring two generations later (F2) as well as a reduction of embryo survival in offspring three generations later (F3). Our present observations suggest that BPA or EE2 exposure during development induces transgenerational phenotypes of reproductive impairment and compromised embryonic survival in fish of subsequent generations. These adverse outcomes may have negative impacts on populations of fish inhabiting contaminated aquatic environments.

Scientific Reports↗
USGS2016

Widespread episodic thiamine deficiency in Northern Hemisphere wildlife

Many wildlife populations are declining at rates higher than can be explained by known threats to biodiversity. Recently, thiamine (vitamin B 1 ) deficiency has emerged as a possible contributing cause. Here, thiamine status was systematically investigated in three animal classes: bivalves, ray-finned fishes, and birds. Thiamine diphosphate is required as a cofactor in at least five life-sustaining enzymes that are required for basic cellular metabolism. Analysis of different phosphorylated forms of thiamine, as well as of activities and amount of holoenzyme and apoenzyme forms of thiamine-dependent enzymes, revealed episodically occurring thiamine deficiency in all three animal classes. These biochemical effects were also linked to secondary effects on growth, condition, liver size, blood chemistry and composition, histopathology, swimming behaviour and endurance, parasite infestation, and reproduction. It is unlikely that the thiamine deficiency is caused by impaired phosphorylation within the cells. Rather, the results point towards insufficient amounts of thiamine in the food. By investigating a large geographic area, by extending the focus from lethal to sublethal thiamine deficiency, and by linking biochemical alterations to secondary effects, we demonstrate that the problem of thiamine deficiency is considerably more widespread and severe than previously reported.

Scientific Reports↗
USGS1975

Crystal structure of the heptamolybdate(VI)(paramolybdate) ion, [Mo7O24]6–, in the ammonium and potassium tetrahydrate salts

The crystal structures of the isomorphous salts M I 6 [Mo 7 O 24 ],4H 2 O (M = NH 4 or K) have been refined by three-dimensional X -ray diffraction methods. Unit cell dimensions of these monoclinic compounds, space group P 2 1 / C with Z = 4, are, ammonium salt: a = 8·3934 ± 0·0008, b = 36·1703 ± 0·0045, c = 10·4715 ± 0·0011 Å, β= 115·958°± 0·008°; and potassium salt: a = 8·15 ± 0·02, b = 35·68 ± 0·1, c = 10·30 ± 0·02 Å, β= 115·2°± 02°. By use of multiple Weissenberg patterns, 8197 intensity data (Mo- K α radiation) for the ammonium compound and 2178 (Cu- K α radiation) for the potassium compound were estimated visually and used to test and refine Lindqvist's proposed structure in the space group P 2 1 / c . Lindqvist's structure was confirmed and the full matrix least-squares isotropic refinement led to R 0·076 (ammonium) 0·120 (potassium), with direct unambiguous location of the cations and water molecules in the potassium compound.

Journal of the Chemical Society, Dalton Transactio↗
USGS2001

Biography of Dr. John L. Fryer

There is probably no one in the fi sh health community who does not recognize the name of Professor John L. Fryer. Active in research for a period of more than 40 years, Dr Fryer has achieved internatio nal acclaim for his wor k on infectious diseases of Pacific salmon . The resea rch from his laboratory at Oregon State University (OSU) has spanned the disciplines of virology, parasitology, bacteriology, cell biology, immuno logy and fi sh physiology, result ing in more than 200 publications, two patents and recognition as one of the world's leading centres for researc h on infec tious diseases of salmon id fi sh.

Journal of Fish Diseases↗
USGS2002

Sea level controls on the textural characteristics and depositional architecture of the Hueneme and associated submarine fan systems, Santa Monica Basin, California

Hueneme and Dume submarine fans in Santa Monica Basin consist of sandy channel and muddy levee facies on the upper fan, lenticular sand sheets on the middle fan, and thinly bedded turbidite and hemipelagic facies elsewhere. Fifteen widely correlatable key seismic reflections in high-resolution airgun and deep-towed boomer profiles subdivide the fan and basin deposits into time-slices that show different thickness and seismic-facies distributions, inferred to result from changes in Quaternary sea level and sediment supply. At times of low sea level, highly efficient turbidity currents generated by hyperpycnal flows or sediment failures at river deltas carry sand well out onto the middle-fan area. Thick, muddy flows formed rapidly prograding high levees mainly on the western (right-hand) side of three valleys that fed Hueneme fan at different times; the most recently active of the lowstand fan valleys, Hueneme fan valley, now heads in Hueneme Canyon. At times of high sea level, fans receive sand from submarine canyons that intercept littoral-drift cells and mixed sediment from earthquake-triggered slumps. Turbidity currents are confined to ‘underfit’ talweg channels in fan valleys and to steep, small, basin-margin fans like Dume fan. Mud is effectively separated from sand at high sea level and moves basinward across the shelf in plumes and in storm-generated lutite flows, contributing to a basin-floor blanket that is locally thicker than contemporary fan deposits and that onlaps older fans at the basin margin. The infilling of Santa Monica Basin has involved both fan and basin-floor aggradation accompanied by landward and basinward facies shifts. Progradation was restricted to the downslope growth of high muddy levees and the periodic basinward advance of the toe of the steeper and sandier Dume fan. Although the region is tectonically active, major sedimentation changes can be related to eustatic sea-level changes. The primary controls on facies shifts and fan growth appear to be an interplay of texture of source sediment, the efficiency with which turbidity currents transport sand, and the effects of delta distributary switching, all of which reflect sea-level changes.

California↗