scholarly journals Scavenging amphipods from the Wallaby-Zenith Fracture Zone: Extending the hadal paradigm beyond subduction trenches

2020 ◽  
Vol 168 (1) ◽  
Author(s):  
Johanna N. J. Weston ◽  
Rachael A. Peart ◽  
Heather A. Stewart ◽  
Heather Ritchie ◽  
Stuart B. Piertney ◽  
...  
Keyword(s):  
Fracture Zone ◽  
Evolutionary Dynamics ◽  
Large Population ◽  
Free Fall ◽  
Phylogeographic Structure ◽  
Fracture Zones ◽  
Flat Bottom ◽  
Community Assemblage ◽  
Mtdna Phylogeny ◽  
Hadal Zone

AbstractOur understanding of the ecology of the hadal zone (> 6000 m depth) is based solely on subduction trenches, leaving other geomorphological features, such as fracture zones, troughs, and basins, understudied. To address this knowledge gap, the Wallaby-Zenith Fracture Zone, Indian Ocean (WZFZ; ~ 22°S, 102°E; maximum depth 6625 m measured during Expedition SO258) was studied using free-fall baited landers. We assessed the amphipod distribution and community assemblage of this non-subduction hadal feature and compared it to subduction hadal features. Eleven species were identified across the abyssal-hadal transition zone using a paired morphological and DNA barcoding approach. The community composition was found to change gradually from abyssal to hadal depths, which contrasts with the ecotone shift characteristic of subduction trenches. A large population of Bathycallisoma schellenbergi (Birstein & Vinogradov, 1958), a quintessential hadal amphipod, was present at the flat bottom of the WZFZ. Further, an mtDNA phylogeny resolved a degree of phylogeographic structure between the B. schellenbergi WZFZ population and four previously sampled Pacific Ocean subduction trench populations, indicating these features are not interconnected through ongoing gene flow. Combined, these data indicate that some amphipods have far broader distributions than previously understood, with some species present in both hadal subduction trenches and non-subduction fracture zones and basins interspersed across the abyssal plains. This initial exploration highlights that whilst non-subduction features are an overlooked minor fraction of the total hadal area, they are essential to our understanding of the ecological and evolutionary dynamics across the hadal zone.

Imaging of fracture zones in the Finnsjön area, central Sweden, using the seismic reflection method

Geophysics ◽  
1995 ◽  
Vol 60 (1) ◽  
pp. 66-75 ◽  
Author(s):  
Christopher Juhlin
Keyword(s):  
Fracture Zone ◽  
Seismic Profile ◽  
Decay Rates ◽  
Damping Factor ◽  
Fracture Zones ◽  
Borehole Data ◽  
Seismic Reflection Method ◽  
Adequate Quality ◽  
Initial Processing ◽  
Geophone Spacing

In 1987 the Swedish Nuclear Fuel and Waste Management Co. (SKB) funded the shooting of a 1.7-km long, high‐resolution seismic profile over the Finnsjön study site using a 60‐channel acquisition system with a shotpoint and geophone spacing of 10 m. The site is located about 140 km north of Stockholm and the host rocks are mainly granodioritic. The main objective of the profile was to image a known fracture zone with high hydraulic conductivity dipping gently to the west at depths of 100 to 400 m. The initial processing of the data failed to image this fracture zone. However, a steeply dipping reflector was imaged indicating the field data were of adequate quality and that the problem lay in the processing. These data have now been reprocessed and a clear image of the gently dipping zone has been obtained. In addition, several other reflectors were imaged in the reprocessed section, both gently and steeply dipping ones. Correlations with borehole data indicate that the origin of these reflections are also fracture zones. The improvement over the previous processing is caused mainly by (1) refraction statics, (2) choice of frequency band, (3) F-K filtering, and (4) velocity analyses. In addition to reprocessing the data, some further analyses were done including simulation of acquisition using only the near‐offset channels (channels 1–30) and the far‐offset channels (channels 31–60), and determining the damping factor Q in the upper few hundred meters based upon the amplitude decay of the first arrivals. The data acquisition simulation shows the far‐offset contribution to be significant even for shallow reflectors in this area, contrary to what may be expected. A Q value of 10, determined from observed amplitude decay rates, agrees well with theoretical ones assuming plane wave propagation in an attenuating medium.

Influence of Impact Angle and Real Target Properties on Drop Test Results of Cubic Containers

2017 ◽  
Author(s):  
Uwe Zencker ◽  
Linan Qiao ◽  
Holger Völzke
Keyword(s):  
Free Fall ◽  
Impact Angle ◽  
Drop Test ◽  
Storage Site ◽  
Flat Bottom ◽  
Energy Agency ◽  
Accident Scenarios ◽  
Interim Storage ◽  
The Impact ◽  
Real Target

Drop test scenarios with cubic containers without impact limiters at interim storage sites or in a final repository have been investigated by numerical simulations. An ideally flat drop is impossible to conduct as a free fall of a container even under laboratory conditions. Dynamic stresses and strains inside the container structure are sensitive to the impact angle. Even very small impact angles cause remarkable changes in the experimental or numerical results when a flat bottom or wall of a container hits a flat target. For drop tests with transport packages the International Atomic Energy Agency (IAEA) regulations define an essentially unyielding target. In contrast, potential accident scenarios for storage containers are derived from site-specific safety analyses or acceptance criteria in Germany. Each interim storage site or repository has a yielding or so-called real target with individual structural and material properties. The real target acts as a kind of impact limiter. A more conservative container design is required if the impact limiting effect of the target is not considered.

scholarly journals Long-term experimental evolution of HIV-1 reveals effects of environment and mutational history

PLoS Biology ◽  
2020 ◽  
Vol 18 (12) ◽  
pp. e3001010
Author(s):  
Eva Bons ◽  
Christine Leemann ◽  
Karin J. Metzner ◽  
Roland R. Regoes
Keyword(s):  
Evolutionary Dynamics ◽  
Fitness Landscape ◽  
Large Population ◽  
Parallel Evolution ◽  
Cell Types ◽  
Drug Pressure ◽  
Evolutionary Paths ◽  
The Impact ◽  
Hiv 1

An often-returning question for not only HIV-1, but also other organisms, is how predictable evolutionary paths are. The environment, mutational history, and random processes can all impact the exact evolutionary paths, but to which extent these factors contribute to the evolutionary dynamics of a particular system is an open question. Especially in a virus like HIV-1, with a large mutation rate and large population sizes, evolution is expected to be highly predictable if the impact of environment and history is low, and evolution is not neutral. We investigated the effect of environment and mutational history by analyzing sequences from a long-term evolution experiment, in which HIV-1 was passaged on 2 different cell types in 8 independent evolutionary lines and 8 derived lines, 4 of which involved a switch of the environment. The experiments lasted for 240–300 passages, corresponding to approximately 400–600 generations or almost 3 years. The sequences show signs of extensive parallel evolution—the majority of mutations that are shared between independent lines appear in both cell types, but we also find that both environment and mutational history significantly impact the evolutionary paths. We conclude that HIV-1 evolution is robust to small changes in the environment, similar to a transmission event in the absence of an immune response or drug pressure. We also find that the fitness landscape of HIV-1 is largely smooth, although we find some evidence for both positive and negative epistatic interactions between mutations.

Numerical Analysis of Impact Loads on Subsea Structures During Water Entry in Presence of Waves

2020 ◽  
Author(s):  
Gustavo Garcia Momm ◽  
Ivan Fábio Mota de Menezes
Keyword(s):  
Constant Velocity ◽  
Oil And Gas ◽  
Free Fall ◽  
Water Entry ◽  
Gas Production ◽  
Rigid Bodies ◽  
Bottom Surface ◽  
Impact Loads ◽  
Flat Bottom ◽  
The Impact

Abstract Subsea structures employed on offshore oil and gas production systems are likely to be subject to severe loads during deployment. Lowering these structures through the wave zone is a critical operation and the prediction of the loads associated is complex as it involves accelerations of these bodies induced by the vessel motion and the sea surface displacements. This work presents a numerical approach to assessment of the effect of waves on the impact loads that subsea structures are subject to during water entry. A 2D one degree of freedom model using the SPH method was developed to estimate slamming loads on rigid bodies during water entry considering both calm and wavy surfaces. Initially the model was employed to simulate the water entry of wedge considering both free fall and constant velocity cases, obtaining loads profile similar to experiments and numerical simulations from the literature. Later, the constant velocity model was configured to a flat bottom surface rigid body in order to represent a subsea manifold. A regular waves generator provided different wavelength, height and phase enabling slamming load assessment in various situations.

scholarly journals Transformation and Upwelling of Bottom Water in Fracture Zone Valleys

2020 ◽  
Vol 50 (3) ◽  
pp. 715-726 ◽  
Author(s):  
A. M. Thurnherr ◽  
L. Clément ◽  
L. St. Laurent ◽  
R. Ferrari ◽  
T. Ijichi
Keyword(s):  
Fracture Zone ◽  
Bottom Water ◽  
Vertical Structure ◽  
Buoyancy Flux ◽  
Global Ocean ◽  
Fracture Zones ◽  
Flux Divergence ◽  
Flux Boundary Condition ◽  
Midocean Ridges ◽  
Slow Spreading

AbstractClosing the overturning circulation of bottom water requires abyssal transformation to lighter densities and upwelling. Where and how buoyancy is gained and water is transported upward remain topics of debate, not least because the available observations generally show downward-increasing turbulence levels in the abyss, apparently implying mean vertical turbulent buoyancy-flux divergence (densification). Here, we synthesize available observations indicating that bottom water is made less dense and upwelled in fracture zone valleys on the flanks of slow-spreading midocean ridges, which cover more than one-half of the seafloor area in some regions. The fracture zones are filled almost completely with water flowing up-valley and gaining buoyancy. Locally, valley water is transformed to lighter densities both in thin boundary layers that are in contact with the seafloor, where the buoyancy flux must vanish to match the no-flux boundary condition, and in thicker layers associated with downward-decreasing turbulence levels below interior maxima associated with hydraulic overflows and critical-layer interactions. Integrated across the valley, the turbulent buoyancy fluxes show maxima near the sidewall crests, consistent with net convergence below, with little sensitivity of this pattern to the vertical structure of the turbulence profiles, which implies that buoyancy flux convergence in the layers with downward-decreasing turbulence levels dominates over the divergence elsewhere, accounting for the net transformation to lighter densities in fracture zone valleys. We conclude that fracture zone topography likely exerts a controlling influence on the transformation and upwelling of bottom water in many areas of the global ocean.

Amplitudes of oceanic magnetic anomalies and the chemistry of oceanic crust: Synthesis and review of 'magnetic telechemistry'

1979 ◽  
Vol 16 (12) ◽  
pp. 2236-2262 ◽  
Author(s):  
P. R. Vogt
Keyword(s):  
Oceanic Crust ◽  
Fracture Zone ◽  
Hot Spots ◽  
Hot Spot ◽  
Magnetic Anomalies ◽  
High Amplitude ◽  
Fracture Zones ◽  
Juan De Fuca ◽  
Sea Floor Spreading ◽  
Ocean Ridge

A growing body of evidence suggests that certain areas of high-amplitude (H) sea-floor spreading-type magnetic anomalies reflect FeTi-enriched basalts of high remanent magnetization. A worldwide tabulation of these 'H-zones' is presented, together with a review of pertinent geochemical, rock magnetic, and deep-tow data relevant to the hypothesis of magnetic telechemistry.' H-zones are found in two tectonic settings: (1) along 102–103 km long sections of spreading axis close to hot spots; and (2) in narrow bands extending a few hundred kilometres along the edges of some fracture zones. Amplitudes in both provinces are 1.5 to 5, typically 2 to 3 times normal, and the hot spot H-zones are known from spreading half-rates of 0.6 to 3.7 cm yr−1 The highest amplitudes, magnetizations, and FeTi enrichment (up to 15–18% FeOT and 2–3% TiO2) seem to occur where both provinces overlap, i.e., where fracture zones occur near hot spots, for example along the Blanco Fracture Zone south of the Juan de Fuca hot spot and along the Inca Fracture Zone east of the Galapagos hot spot. The FeTi enrichment appears to reflect shallow-depth crystal fractionation (plagioclase, augite, and olivine), which is more extensive near hot spots, and more generally for fast-spreading ridges. H-zones presently affect at least 2.6 × 103 km, or 6.5% of the Mid-Ocean Ridge axis. However, the total known H-area of 8.5 × 105 km2 represents only 0.3% of oceanic crust. This suggests that older H-zones remain to be discovered, or/and that conditions favoring the formation of FeTi basalt and H-anomalies are more prevalent now than they have been on the average for the last 108 years. Evidence for the latter is provided by the known expansion of the magnetically well surveyed Juan de Fuca, Galapagos, and Yermak (Arctic) H-zones in the last 5 million years.

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