The formation of the Oort cloud in open cluster environments

We study the influence of an open cluster environment on the formation and current structure of the Oort cloud. To do this, we have run 19 different simulations of the formation of the Oort cloud for 4.5 Gyrs. In each simulation, the Solar System spends its first 100 Myrs in a different open cluster environment before transitioning to its current field environment. We find that, compared to forming in the field environment, the inner Oort cloud is preferentially loaded with comets while the Sun resides in the open cluster and that most of this material remains locked in the interior of the cloud for the next 4.4 Gyrs. In addition, the outer Oort cloud trapping efficiencies we observe in our simulations are lower than previous formation models by about a factor of 2, possibly implying an even more massive early planetesimal disk. Furthermore, some of our simulations reproduce the orbits of observed extended scattered disk objects, which may serve as an observational constraint on the Sun's early environment. Depending on the particular open cluster environment, the properties of the inner Oort cloud and extended scattered disk can vary widely. On the other hand, the outer portions of the Oort cloud in each of our simulations are all similar.     

Fishers' perceptions as indicators of the performance of Marine Protected Areas (MPAs)

How users perceive the performance of Marine Protected Areas (MPAs) is fundamental for the social acceptance of these zones. Moreover, their perceptions may be relevant for monitoring the effects of MPAs on extractive activities. This study analyzes artisanal fishers' perceptions of the performance of a north-western Mediterranean coastal MPA, which encompasses two no-take zones (NTZs). Three viewpoints have been considered: the effect on the personal activity of fishers, the effect on the local fishery and the effect on the ecosystem. In order to test the hypothesis that biomass export (spillover) - which had previously been evidenced from the two NTZs - may influence fishers' perceptions of NTZ effects, fishers' perceptions were compared with both declared and observed fishing activity over an one-year period.The results show that negative perceptions of NTZs are either nil or are negligible. Most fishers are aware of the beneficial effects of NTZs on ecosystems and fisheries. However, they remain to be convinced of the beneficial effects of the NTZs on their own activity. For instance, the proximity of a NTZ appears never to be involved in the choice of a fishing spot. This partial lack of correspondence between scientific expectation and fishers' perceptions is discussed in the light of fishing habits in the zone adjacent to NTZs, and takes into account fishing grounds, targeted species and seniority (defined as the number of years the fisher has been fishing within the MPA). All three factors appear to influence fishers' perceptions. For example, having a positive perception about a NTZ and spending more time fishing in the adjacent zone are habits that can be associated with fishers with less seniority. Fishers' perceptions obviously indicate the social acceptance of the MPA and are an essential monitoring tool for MPA managers. However, perceptions cannot be seen as a substitute for scientific monitoring, as both approaches are clearly complementary.     

Abrupt axial variations along the slow to ultra-slow spreading centers of the northern North Fiji Basin (SW Pacific): Evidence for short wave heterogeneities in a back-arc mantle

This study presents results of surveys conducted along the slow to ultra-slow spreading axis of the Northern North Fiji Basin (NNFB), including the Hazel Holmes, Tripartite and South Pandora Ridges, and the newly discovered Futuna and North Cikobia spreading centers. Spreading segments along these axes display highly contrasted axial morphologies, ranging from a rift valley to a prominent axial high. In some places, abrupt inversions of topography are observed between neighboring segments. Detailed analyses of bathymetry and backscatter maps reveal that axial highs are spotted with numerous coalescent volcanoes forming features ranging from irregular terrains to well-organized ridges. The volcanic edifices are distributed over a wide neovolcanic zone, which corresponds to the axial relief, suggesting on important contribution of volcanism to the relief construction. Comparisons between various ridge-shaped segments reveal that axial volcano-tectonic patterns are directly related to the local magma production and delivery, in a context of tectonic extension related to plate divergence, and suggest that coalescent volcanoes are fed from multiples short-lived and unconnected magma lenses. In the competition between horizontal and vertical accretion of oceanic crust, the spreading centers of the NNFB represent a special case where lava production is locally high enough and spreading rate is low enough to allow prominent axial highs to develop. The along axis morphologic variability is related to intermittent volcanic activity that may result from rapid temporal and spatial variations in the distribution of upper mantle convection cells below accretion centers, superimposed on the regional thermal anomaly located under the whole basin.     

Sediment velocity estimation using iterative 3-D migrations of short offset seismic reflection data in deep water

In deep ocean settings where water depth greatly exceeds the source-to-receiver length, the geometry is insufficient for accurate determinations of velocity from reflection-moveout. However, velocities are crucial for estimates of physical properties and image processing. Focusing analyses with conventional post-stack two-dimensional migration improves images, but does not produce geologically meaningful velocities except in the special case of a two-dimensional earth. For the more general case of the three-dimensional earth there is no a priori method to determine the degree of geometrical complexity. We present a technique using a short-offset three-dimensional (3-D) data set over the 5 km deep trench west of the Lesser Antilles. These data illustrate highly sensitive post-stack 3-D focusing analyses (± 20 m s^–1 interval velocities), and the relationship of these seismically derived velocities to rock velocities. In our Barbados example we were able to establish the presence of a widespread 80-160 m thick low-velocity zone at and above the main low-angle fault. This observation suggests the water-rich décollement leaks water into the overlying sections. Also evident is a low-velocity section associated with turbidite sands. These results are confirmed with sparse logging data and well samples. Deep-water short offset 3-D experiments provide a potentially effective approach for velocity estimation, replacing the operational complexity of long-offsets with simpler short-offset techniques. In areas of structural complications and abundant diffracted energy, it is a surprisingly accurate method, utilizing the high fidelity 3-D wavefield and the information carried in zero-offset diffraction ellipsoids. The velocity used to properly collapse a diffraction ellipsoid is explicitly the velocity of propagation in the media since the travel path is known exactly. Thus, the derived velocities should closely represent rock velocities, unlike the 2-D case where the propagation geometry is not known.     

Distribution of Winter Flounder, Pseudopleuronectes americanus, in the Hampton–Seabrook Estuary, New Hampshire: Observations from a Field Study

From July to October 2004, five sites in the Hampton–Seabrook Estuary in New Hampshire were sampled with beam and otter trawls. The goals were to describe winter flounder (1) abundance in the estuary, (2) size class distributions, (3) spatial distribution by different size classes, and (4) distribution patterns. Of the 19 species caught, winter flounder was the most abundant and was dominated by young-of-the-year (YOY) fish. The five sites were fairly homogenous in depth, bottom type, salinity, and temperature. However, YOY abundance ranged from 2.1 to 32.1 fish 1,000 m^?2 depending on the site. Benthic community was the best indicator of juvenile winter flounder abundance. Catch data of other organisms fluctuated, but no one species was a strong predictor of winter flounder abundance and distribution. During late summer and early fall, the estuary is used primarily by YOY winter flounder, indicating that this estuary functions as a nursery ground.     

Ecological Risk Assessment for seabird interactions in Western and Central Pacific longline fisheries

The risk of seabird–fishery interactions in the Western and Central Pacific Ocean (WCPO) was examined by analysing the overlap of seabird distributions with tuna and swordfish pelagic longline fisheries managed by the Western and Central Pacific Fisheries Commission (WCPFC) and its constituent members. The study used spatially-explicit Productivity–Susceptibility Analysis (PSA). Key data inputs were species productivity, fishing effort, likelihood of capture and species density by region. The outputs tailored results to the needs of fisheries- and wildlife-managers, indicating areas of greatest risk of species interactions, species of greatest concern for population impacts, and the flags or fisheries most likely to contribute to the risk. Large albatross species were found to be most likely to suffer population effects when exposed to longline fishing activity, followed by the larger petrels from the genuses Procellaria, Macronectes and Pterodroma. A mixture of coastal states with nesting seabird populations in their Exclusive Economic Zones (New Zealand, Australia and United States of America), distant water fishing nations (Japan, Taiwan) and flags of convenience (Vanuatu) contributed 90% of the risk to seabird populations. Recommendations include enhancing the level of fisheries observer monitoring in areas indicated as high to medium risk for seabird interactions, and consideration of spatial management tools, such as more intensive or more stringent seabird bycatch mitigation requirements in high- to medium-risk areas. The methods used, and similar studies conducted in the Atlantic Ocean could lead to improved targeting of monitoring resources, and greater specificity in the needs for seabird-mitigation measures. This will assist in reducing seabird mortality in longline fishing operations and with more effective use of resources for fishery managers in both domestic fisheries and RFMOs.