377 research outputs found
Navigation mechanisms of herring during feeding migration: the role of ecological gradients on an oceanic scale
The feeding migration of Norwegian spring-spawning herring was studied in relation to prey abundance and environmental factors that may affect their feeding migration. Temperature, salinity, chlorophyll a, nitrate concentration, abundance of Calanus finmarchicus, zooplankton biomass, acoustic data on herring and trawl samples were collected during four basin-scale surveys in the Norwegian Sea from April to August 1995. Herring abundance was positively associated with the overwintering population of C. finmarchicus. We suggest that spatial gradients and temporal dynamics of the seasonal ascent of the C. finmarchicus overwintering generation provide stimuli for and affect the feeding migration of herring. The clockwise migration pattern of herring, observed during the 1990s, can be explained by delayed ascent and development of C. finmarchicus toward the west and north in the Norwegian Sea. We further suggest that herring leave a specific area before their zooplankton prey is depleted. The first generation of C. finmarchicus likely has a minor influence in directing the herring feeding migration due to the low abundance of older stages available as prey. The feeding migration was constantly directed toward colder water, and temperature probably has a secondary effect on herring distribution
Fish vertical distribution and marine mammal co-occurrence off Cape Hatteras, NC
Mesopelagic (mid-water) fish are important components of toothed whale (Odontocete) diets. Few studies have simultaneous measurements of predator occurrence and potential prey density distributions over long durations. Echoshounder and hydrophone measurements were used to characterize vertical distributions of potential prey and relative abundance of 7 marine mammal groups in the water column off Cape Hatteras, NC. Co-occurrence of the two groups was used as an index of predator-prey interaction. There were fewer than expected (2/7 daily resolution; 1/7 6-hourly resolution) significant correlations between the number of marine mammal occurrences and the potential prey field density. There were no significant distributional correlations when there were significant density correlations. At both resolutions, Cuvier’s and Gervais’ beaked whales and Sperm whales were correlated with salinity and/or water temperature. Further research is necessary to determine whether metrics of prey field density influence the occurrence and potential foraging of Odontocete marine mammals
Fish and Zooplankton Distributions in a Seasonally Hypoxic Fjord
Hypoxia has been identified as a major threat to marine ecosystem health in the world’s coastal waters including Puget Sound. This study is evaluating the potential effects of hypoxia on fish and zooplankton distributions in Hood Canal, WA, using multifrequency acoustics and net sampling. Field surveys were conducted monthly from June to October in 2012 and 2013 to characterize pre-, during, and post-hypoxia nekton distributions at four sites along the Canal. Using the repeated samplings and high-resolution survey data, we are examining how seasonal and inter-annual difference in the timing and intensity of hypoxia affects distributions of predators (primarily Pacific herring and Pacific hake) and prey (primarily copepods and euphausiids). Depth of the zooplankton backscatter layer changed seasonally with hypoxia intensity. Toward late-summer, the daytime zooplankton layer was closer to the surface, increasing the vertical separation between zooplankton and fish. In spite of low oxygen levels in late-summer, fish remained in low-oxygen regions of Hood Canal. This suggests a decrease in energy flow toward higher trophic level during hypoxia
Probing the deep: Acoustic characterization of the Mid-Atlantic Ridge ecosystem
Abstract only. Journal home page: http://scitation.aip.org/jasa
Seismic Response to Injection Well Stimulation in a High-Temperature, High-Permeability Reservoir
Fluid injection into the Earth's crust can induce seismic events that cause damage to local infrastructure but also offer valuable insight into seismogenesis. The factors that influence the magnitude, location, and number of induced events remain poorly understood but include injection flow rate and pressure as well as reservoir temperature and permeability. The relationship between injection parameters and injection-induced seismicity in high-temperature, high-permeability reservoirs has not been extensively studied. Here we focus on the Ngatamariki geothermal field in the central Taupō Volcanic Zone, New Zealand, where three stimulation/injection tests have occurred since 2012. We present a catalog of seismicity from 2012 to 2015 created using a matched-filter detection technique. We analyze the stress state in the reservoir during the injection tests from first motion-derived focal mechanisms, yielding an average direction of maximum horizontal compressive stress (SHmax) consistent with the regional NE-SW trend. However, there is significant variation in the direction of maximum compressive stress (σ1), which may reflect geological differences between wells. We use the ratio of injection flow rate to overpressure, referred to as injectivity index, as a proxy for near-well permeability and compare changes in injectivity index to spatiotemporal characteristics of seismicity accompanying each test. Observed increases in injectivity index are generally poorly correlated with seismicity, suggesting that the locations of microearthquakes are not coincident with the zone of stimulation (i.e., increased permeability). Our findings augment a growing body of work suggesting that aseismic opening or slip, rather than seismic shear, is the active process driving well stimulation in many environments
Parallax and Distance Estimates for Fourteen Cataclysmic Variable Stars
I used the 2.4 m Hiltner telescope at MDM Observatory in an attempt to
measure trigonometric parallaxes for 14 cataclysmic variable stars. Techniques
are described in detail. In the best cases the parallax uncertainties are below
1 mas, and significant parallaxes are found for most of the program stars. A
Bayesian method which combines the parallaxes together with proper motions and
absolute magnitude constraints is developed and used to derive distance
estimates and confidence intervals. The most precise distance derived here is
for WZ Sge, for which I find 43.3 (+1.6, -1.5) pc. Six Luyten Half-Second stars
with previous precise parallax measurements were re-measured to test the
techniques, and good agreement is found.Comment: 33 pages, 3 figures. Astronomical Journal, accepte
Spectroscopy and Component Masses of the Eclipsing Dwarf Nova HS0907+1902
HS0907+1902 was recently discovered to be one of a handful of deeply
eclipsing dwarf novae with periods longward of the 2 -- 3 hr `gap'. This paper
presents orbit-resolved spectra and time series photometry of an eclipse. The
apparent velocity amplitude of the M-dwarf secondary is K_2 = 297 +- 15 km/s.
The phase of the radial velocities of the H-alpha emission line wings agrees
accurately (for once) with the phase of the white-dwarf motion deduced from the
eclipse, and an estimate of the emission-line velocity amplitude yields K1 =
115 +- 7 km/s. The eclipse width is delta-phi = 0.060 +- 0.005. At face value,
these measurements yield mass estimates of M1 = 0.99 +- 0.12 solar masses for
the white dwarf and M2 = 0.38 +- 0.06 solar masses for the secondary. The
eclipse width and nominal mass ratio constrain the binary inclination to be
77.3 +- 0.9 degree. The influence of systematic uncertainties on these values
is discussed; the conclusion that the white dwarf is somewhat more massive than
typical field white dwarfs appears to be robust.
The H-alpha emission line profile out of eclipse is only slightly
double-peaked, but the line shows a strong rotational disturbance in eclipse.
Models of the line profile through eclipse using a flat, Keplerian disk do not
give a good quantitative match to the observations.Comment: One tex file, and 7 figures Replaced because of typo in abstract
(should be M2=0.38+-0.06
Shotgun Proteomics Identifies Serum Fibronectin as a Candidate Diagnostic Biomarker for Inclusion in Future Multiplex Tests for Ectopic Pregnancy
Ectopic pregnancy (EP) is difficult to diagnose early and accurately. Women often present at emergency departments in early pregnancy with a 'pregnancy of unknown location' (PUL), and diagnosis and exclusion of EP is challenging due to a lack of reliable biomarkers. The objective of this study was to identify novel diagnostic biomarkers for EP. Shotgun proteomics, incorporating combinatorial-ligand library pre-fractionation, was used to interrogate pooled sera (n = 40) from women undergoing surgery for EP, termination of viable intrauterine pregnancy and management of non-viable intrauterine pregnancy. Western blot was used to validate results in individual sera. ELISAs were developed to interrogate sera from women with PUL (n = 120). Sera were collected at time of first symptomatic presentation and categorized according to pregnancy outcome. The main outcome measures were differences between groups and area under the receiver operating curve (ROC). Proteomics identified six biomarker candidates. Western blot detected significant differences in levels of two of these candidates. ELISA of sera from second cohort revealed that these differences were only significant for one of these candidates, fibronectin. ROC analysis of ability of fibronectin to discriminate EP from other pregnancy outcomes suggested that fibronectin has diagnostic potential (ROC 0.6439; 95% CI 0.5090 to 0.7788; P>0.05), becoming significant when 'ambiguous' medically managed PUL excluded from analysis (ROC 0.6538; 95% CI 0.5158 to 0.7918; P<0.05). Fibronectin may make a useful adjunct to future multiplex EP diagnostic tests
An International Ultraviolet Explorer Archival Study of Dwarf Novae in Outburst
We present a synthetic spectral analysis of nearly the entire far ultraviolet
International Ultraviolet Explorer (IUE) archive of spectra of dwarf novae in
or near outburst. The study includes 46 systems of all dwarf nova subtypes both
above and below the period gap. The spectra were uniformly analyzed using
synthetic spectral codes for optically thick accretion disks and stellar
photospheres along with the best-available distance measurements or estimates.
We present newly estimated accretion rates and discuss the implications of our
study for disk accretion physics and CV evolution.Comment: Accepted for publication in the ApJ, Part
FUSE Observations of a Full Orbit of Hercules X-1: Signatures of Disk, Star, and Wind
We observed an entire 1.7 day orbit of the X-ray binary Hercules X-1 with the
Far Ultraviolet Spectroscopic Explorer (FUSE). Changes in the O VI 1032,1037
line profiles through eclipse ingress and egress indicate a Keplerian accretion
disk spinning prograde with the orbit. These observations may show the first
double-peaked accretion disk line profile to be seen in the Hercules X-1
system. Doppler tomograms of the emission lines show a bright spot offset from
the Roche lobe of the companion star HZ Her, but no obvious signs of the
accretion disk. Simulations show that the bright spot is too far offset from
the Roche lobe to result from uneven X-ray heating of its surface. The absence
of disk signatures in the tomogram can be reproduced in simulations which
include absorption from a stellar wind. We attempt to diagnose the state of the
emitting gas from the C III 977, C III 1175, and N III 991 emission lines. The
latter may be enhanced through Bowen fluorescence.Comment: Accepted for publication in The Astrophysical Journa
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