Significance of some geotechnical properties of continental slope and rise sediments off northeast Newfoundland

1982 ◽  
Vol 19 (1) ◽  
pp. 153-161 ◽  
Author(s):  
Charles T. Schafer ◽  
Kenneth W. Asprey
Keyword(s):  
Shear Strength ◽  
Continental Slope ◽  
Bottom Current ◽  
Western Boundary ◽  
Sediment Texture ◽  
Surficial Sediments ◽  
Mean Values ◽  
Sediment Reworking ◽  
Middle Slope ◽  
Upper Slope

Shear strength measurements carried out on the 0–20 cm interval of continental slope and continental rise surficial sediments yielded mean values per station that ranged from 3.7 to 8.9 kPa. The factors controlling the bathymetric variation of sediment shear strength appear to be sediment texture (which is controlled locally by sediment spillover) on the upper slope, increased deposition of fines (silt- and clay-sized particles) from suspension and greater bioturbation activity on the middle slope, and bottom current sediment reworking on the base-of-slope and upper rise.Sediments deposited on the downslope side of the present presumed location of the Western Boundary Undercurrent (WBU) axis have comparatively high shear strength gradients that appear to denote the increased proportion of fine sediment deposition during early to middle Holocene time when the WBU axis may have been located further upslope than at present.

Observations on depositional environments and benthos of the continental slope and rise, east of Newfoundland

1979 ◽  
Vol 16 (4) ◽  
pp. 831-846 ◽  
Author(s):  
Lionel Carter ◽  
Charles T. Schafer ◽  
M. A. Rashid
Keyword(s):  
Continental Slope ◽  
High Speed ◽  
Planktonic Foraminifera ◽  
Depositional Environments ◽  
Depth Interval ◽  
Western Boundary ◽  
Muddy Sand ◽  
Foraminiferal Assemblage ◽  
Labrador Current ◽  
Upper Slope

Sedimentologic, biologic, and morphologic criteria permit recognition of four depositional environments on the continental slope and rise, east of Newfoundland. The 'upper slope' (300–700 m) has a hummocky substrate with a mantle of terrigenous, gravelly muddy sand which is a mixture of ice-rafted detritus and sediment reworked from underlying glacial drift deposits. Reworking presumably took place during the last major lowering of sea level and it is continuing today under the influence of the Labrador Current and other oceanographic and biologically-related forces. The featureless bottom of the 'middle slope' (700–2000 m) is the principal depositional site of Recent mud. Fines, reworked from shelf and upper slope sediments, settle out together with fines transported to the area by the southeast-flowing Western Boundary Under-current (WBU). Compared to the upper slope this deeper environment receives less ice-rafted clasts, supports a richer macrofauna, and has a higher total species diversity of foraminifera. The 'lower slope' (2000–2500 m) is characterized by higher amounts of gravel and sand mixed with the mud, increasing numbers of current bedforms, and a more diverse foraminiferal assemblage, all of which correlate with the increasing power of the WBU with depth. The gravel was ice rafted probably at the end of the late Wisconsin to early Holocene and its presence on the seabed reflects the power of the WBU to inhibit deposition of Recent mud. The 'rise' (2500 to > 3000 m) is heralded by a subtle break in slope at about 2500 m. A high speed core of the undercurrent is situated in this area as indicated by the coarseness of the sediments (gravelly muddy sand) and the observed current bedforms. A marked increase in the numbers of benthonic and planktonic foraminifera is related primarily to the winnowing capacity of WBU. Numerous arenaceous deep sea forms first occur between 2500 and 3000 m and appear to reflect the reduced salinity, low temperature, high dissolved oxygen characteristics of the watermass that is associated with this depth interval.

Late Cenozoic evolution of Sackville Spur: a sediment drift on the Newfoundland continental slope

1990 ◽  
Vol 27 (6) ◽  
pp. 863-878 ◽  
Author(s):  
L. Kennard ◽  
C. Schafer ◽  
L. Carter
Keyword(s):  
Continental Slope ◽  
Large Scale ◽  
Lower Percentage ◽  
Western Boundary ◽  
Sediment Reworking ◽  
Grand Banks ◽  
The North ◽  
Sediment Drift ◽  
Labrador Current ◽  
Erosional Event

The Sackville Spur is a sediment drift feature that forms a northeastward extension of the Grand Banks continental slope between the 900 and 2500 m isobaths near latitude 48°N. At present, the Labrador Current (LC) and the Western Boundary Undercurrent (WBUC) appear to be the two major hydrodynamic forces controlling sedimentation patterns on the flanks of the spur. Near the upper part of the spur's north flank, a deep offshore component of the LC appears to be selectively winnowing silt and clay-size particles, leaving a lag deposit composed of about 43% sand-size material. The base of the north flank (≈2500 m) is in a zone in which sediments can be reworked by the fast-flowing core of the WUBC. Here surficial sediments are characterized by a relatively high percentage of fine (2–3[Formula: see text]) sand and by a lower percentage of silt compared with sediments observed near the spur crest.Reflection seismic data suggest that current-influenced deposition, associated predominantly with bottom-sediment reworking by the deeper offshore component of the LC, has been active over the uppermost part of the spur since Late Miocene to Early Pliocene time. The initiation of deep LC flow at this time is marked by a distinctive angular unconformity near the base of the spur drift deposit. Following this erosional event, deposition caused rapid progradation of the spur to the northeast. The latest phase of the spur's evolution is characterized by (i) intermittent erosion with concomitant large-scale submarine sliding; (ii) smaller scale mass-flow deposition; and (iii) a distinctive southeastward shift of its depocentre toward the Flemish Pass.

scholarly journals Living Benthic Foraminifera from the Surface and Subsurface Sediment Layers Applied to the Environmental Characterization of the Brazilian Continental Slope (SW Atlantic)

Water ◽  
2021 ◽  
Vol 13 (13) ◽  
pp. 1863
Author(s):  
Luciana Cristina de Carvalho Santa-Rosa ◽  
Sibelle Trevisan Disaró ◽  
Violeta Totah ◽  
Silvia Watanabe ◽  
Ana Tereza Bittencourt Guimarães
Keyword(s):  
Continental Slope ◽  
Benthic Foraminifera ◽  
Subsurface Layer ◽  
Environmental Characterization ◽  
Potiguar Basin ◽  
Middle Slope ◽  
Sw Atlantic ◽  
Sediment Layers ◽  
Lower Slope

Living benthic foraminifera (>63 µm) were studied to characterize the continental slope of the Potiguar Basin (SW Atlantic). Foraminifers from the surface (0–2 cm), subsurface (2–5 cm), and integrated (0–5 cm) sediment layers were analyzed to verify their contribution to environmental characterization. It was also estimated if and which changes occur when the subsurface is added. Sampling stations were distributed in five transects in four isobaths (150, 400, 1000, and 2000 m). Sediment samples were fixed with 4% buffered formaldehyde and stained with Bengal rose. Were recorded 396 species in the surface layer, 228 in the subsurface, and 449 in integrating both layers. This study did not include tubular agglutinated species. The assemblages from 150 m isobath indicated the upper slope, from 400 m indicated the middle slope and the ones from the 2000 m indicated the lower slope. The surface layer’s assemblage at 1000 m isobath was more similar to the middle slope; in contrast, its subsurface layer´s assemblage had more similarity with the lower slope. Rarefaction curves, Permanova, and NMDS routines indicated a high resemblance between surface and integrated layers. Therefore, the first two centimeters were sufficient to characterize this region based on living benthic foraminifera.

Reducing shear strength uncertainties in clays by multivariate correlations

2010 ◽  
Vol 47 (1) ◽  
pp. 16-33 ◽  
Author(s):  
Jianye Ching ◽  
Kok-Kwang Phoon ◽  
Yi-Chu Chen
Keyword(s):  
Shear Strength ◽  
Site Investigation ◽  
Mean Values ◽  
Reliability Based Design ◽  
Economical Design ◽  
Coefficients Of Variation ◽  
Final Design ◽  
Available Information ◽  
Undrained Shear ◽  
Multivariate Correlations

Quantifications of uncertainties in soil shear strengths, including undrained shear strength of clay, are essential for geotechnical reliability-based design. In particular, how to reduce the uncertainties in undrained shear strengths based on all available information by correlation is a practical research subject, given the considerable cost of a typical site investigation. Although it is simple to reduce the uncertainties by correlation when the information is one dimensional (or univariate), it is quite challenging to reduce the uncertainties by using multivariate information through multiple correlations. This study proposes a systematic way of achieving multivariate correlations on undrained shear strengths. A set of simplified equations are obtained through Bayesian analysis for the purpose of reducing uncertainties: the inputs to the equations are the results of in situ or laboratory tests and the outputs are the updated mean values and coefficients of variation (c.o.v.s) of the undrained shear strengths. Two case studies are used to demonstrate the consistency of the proposed simplified equations. Results show that uncertainties in undrained shear strengths can be effectively reduced by incorporating multivariate information. Given that reliability-based design can justify more economical design with reduced uncertainties, the proposed equations essentially link the value of more and better tests directly to final design savings.

Mid-to-late Holocene upper slope contourite deposits off Capo Vaticano (Mediterranean Sea): High-resolution record of contourite cyclicity, bottom current variability and sandy facies

2021 ◽  
Vol 431 ◽  
pp. 106372
Author(s):  
Eleonora Martorelli ◽  
Alessandro Bosman ◽  
Daniele Casalbore ◽  
Francesco Chiocci ◽  
Aida Maria Conte ◽  
...  
Keyword(s):  
High Resolution ◽  
Mediterranean Sea ◽  
Late Holocene ◽  
Bottom Current ◽  
Upper Slope

scholarly journals Demersal Assemblages on the Soft Bottoms off the Catalan-Levante Coast of the Spanish Mediterranean

2011 ◽  
Vol 2011 ◽  
pp. 1-16 ◽  
Author(s):  
Mariano García-Rodríguez ◽  
Pere Abelló ◽  
Angel Fernández ◽  
Antonio Esteban
Keyword(s):  
Fisheries Management ◽  
Depth Distribution ◽  
Ecosystem Approach ◽  
Western Mediterranean ◽  
Multispecies Fisheries ◽  
Middle Slope ◽  
Soft Bottoms ◽  
High Species Richness ◽  
Total Species ◽  
Upper Slope

The analysis of 255 bottom trawl samples obtained in annual experimental surveys (2007–2010) along the western Mediterranean shows the existence of five well-defined demersal assemblages that follow a depth distribution: (a) upper shelf assemblages, including two assemblages differentiated by the type of substrate (sand-muddy and terrigenous muddy bottoms); (b) a middle shelf assemblage; (c) an upper slope assemblage; (d) a middle slope assemblage. Faunally, they are dominated by fish (37% of 452 total species), followed by crustaceans (22%), molluscs (17%), echinoderms (9%), and other invertebrates (15%). The assemblages identified showed major alterations on the shelf and shelf edge and less pronounced ones on the upper and middle slope. The average diversity values were more or less high, evidencing the high species richness in the western Mediterranean. The identified assemblages may facilitate future multispecies fisheries management based on an ecosystem approach.

Upper slope processes and seafloor ecosystems on the Sabrina continental slope, East Antarctica

2020 ◽  
Vol 422 ◽  
pp. 106091 ◽  
Author(s):  
A.L. Post ◽  
P.E. O'Brien ◽  
S. Edwards ◽  
A.G. Carroll ◽  
K. Malakoff ◽  
...  
Keyword(s):  
Continental Slope ◽  
East Antarctica ◽  
Upper Slope

scholarly journals Coherence of Western Boundary Pressure at the RAPID WAVE Array: Boundary Wave Adjustments or Deep Western Boundary Current Advection?

2013 ◽  
Vol 43 (4) ◽  
pp. 744-765 ◽  
Author(s):  
Shane Elipot ◽  
Chris Hughes ◽  
Sofia Olhede ◽  
John Toole
Keyword(s):  
Continental Slope ◽  
Time Scales ◽  
Propagation Speed ◽  
Large Error ◽  
Western Boundary ◽  
Ocean Bottom ◽  
Boundary Current ◽  
Coherent Signals ◽  
Woods Hole Oceanographic Institution ◽  
Meridional Transport

Abstract This study investigates the coherence between ocean bottom pressure signals at the Rapid Climate Change programme (RAPID) West Atlantic Variability Experiment (WAVE) array on the western North Atlantic continental slope, including the Woods Hole Oceanographic Institution Line W. Highly coherent pressure signals propagate southwestward along the slope, at speeds in excess of 128 m s−1, consistent with expectations of barotropic Kelvin-like waves. Coherent signals are also evidenced in the smaller pressure differences relative to 1000-m depth, which are expected to be associated with depth-dependent basinwide meridional transport variations or an overturning circulation. These signals are coherent and almost in phase for all time scales from 3.6 years down to 3 months. Coherence is still seen at shorter time scales for which group delay estimates are consistent with a propagation speed of about 1 m s−1 over 990 km of continental slope but with large error bounds on the speed. This is roughly consistent with expectations for propagation of coastally trapped waves, though somewhat slower than expected. A comparison with both Eulerian currents and Lagrangian float measurements shows that the coherence is inconsistent with a propagation of signals by advection, except possibly on time scales longer than 6 months.

The effects of organic matter concentration on sediment reworking of Perinereis aibuhitensis : a mesocosm study

2020 ◽  
Author(s):  
Jaehwan Seo ◽  
Bon Joo Koo
Keyword(s):  
Organic Matter ◽  
Feeding Activity ◽  
Transport Rate ◽  
Benthic Organism ◽  
Mean Values ◽  
Sediment Reworking ◽  
Pellet Production ◽  
Organic Matter Concentration ◽  
Perinereis Aibuhitensis ◽  
The Mean

<p>The organic matter (OM) concentration is one of the most important factors influencing benthic organism sediment reworking during bioturbation. This study was designed to evaluate differences in sediment reworking rate of Perinereis aibuhitensis based on quantification of its pellet production (PP) and OM transport rate from ambient sediment to the surface due to its feeding. The mesocosm experiment was conducted in acrylic container (15×1×20 cm) with two treatments (high OM treatment and low OM treatment) and each treatment had ten replicates. The pellets in each container were removed 2h before the beginning of the pellet collection, and then newly produced pellets were collected every 2 h during 24 h at each treatment. The mean grain size of pellets (5.1 ∅) was smaller than that of ambient sediment particles (5.9 ∅), and the mean OM concentration was much higher in pellet (0.69% for C and 0.06% for N) than in ambient sediment (0.46% for C and 0.05% for N). Since an organism cannot produce more organic matter than it ingests, production of organically enriched pellets by this species indicates selective ingestion. The overall OM transport rate was 0.7 g C m<sup>-2</sup> day<sup>-1</sup> in carbon and 0.06 g N m<sup>-2</sup> day<sup>-1 </sup>in nitrogen, respectively. The daily PP was much higher in high OM treatment than that of low OM treatment with mean values of 0.007 and 0.002 g ind.<sup>-1</sup> h<sup>-1</sup>, respectively. It is expected that Perinereis feeding activity strongly depended on OM concentrations. The overall sediment reworking rate based on the pellet production was much higher in high OM concentration (0.005 mm day<sup>-1</sup>) than in low OM (0.001 mm day<sup>-1</sup>) concentration.</p>

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