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R W Sternberg - One of the best experts on this subject based on the ideXlab platform.
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Sediment transport event analysis on the western adriatic continental Shelf
Continental Shelf Research, 2007Co-Authors: A M V Fain, Andrea S Ogston, R W SternbergAbstract:The Sediment-transport mechanisms that contribute to and redistribute the modern Sediment deposits on the western Adriatic continental Shelf were evaluated utilizing data collected from two instrumented benthic tripods deployed at 12-m water depth, one in the northern Adriatic basin on the Po River subaqueous delta, and the other in the central Adriatic basin on the Pescara River Shelf. Sediment-resuspension events driven by cold, northeasterly Bora winds dominate the along-Shelf transport climatology at both tripod locations, but at the Po delta site, the southwesterly Scirocco wind events also play a significant role. At the Pescara Shelf site, interaction between Bora wind-driven currents and the Western Adriatic Coastal Current strongly contributes to the resuspension and advection of suspended Sediment. Interannual variability of the forcing mechanisms (including strength, frequency, and relative mix of Bora and Scirocco wind events) is evident in the three winters of data collected on the Po River subaqueous delta. In both types of wind events, and throughout all years of data collection, the net along-Shelf Sediment transport is significantly larger than the net across-Shelf transport at the 12-m sites. This may be characteristic of low-energy environments, where Sediment resuspension and transport occurs in such shallow water that it is not subjected to strong downwelling features characteristic of higher-energy environments.
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Shelf to canyon Sediment transport processes on the eel continental margin northern california
Marine Geology, 2003Co-Authors: Pere Puig, Charles A Nittrouer, Andrea S Ogston, B L Mullenbach, R W SternbergAbstract:Abstract To investigate the processes by which Sediment is supplied to the head of a submarine canyon, an instrumented tripod and a mooring were deployed in the northern thalweg of the Eel Canyon during autumn and winter 1999–2000. This was done as part of the STRATAFORM program, and in combination with a long time-series benthic-tripod data collection on the Eel continental Shelf. Sediment-resuspension events on the Shelf were forced by waves, and near-bottom suspended-Sediment concentrations (SSC) were enhanced during the Eel River flood season. Periodic SSC fluctuations in intermediate waters (corresponding to water depths equal to the Shelf-break depth) were predominantly recorded at semidiurnal tidal frequencies, associated with decreases of water salinity and increases of temperature. Within the Eel Canyon, increases of water turbidity were not directly related to the Eel River discharge, but they were linked to the occurrence of storms. This relationship was evident in the bottom-boundary-layer measurements at 120 m depth in the canyon head, although farther down-thalweg (280 m depth), significant increases of near-bottom SSC associated with storm events were recorded also. The highest SSC measured within the canyon coincided with a highly energetic storm on 28 October 1999, in the absence of any river flood event, but associated with a down-canyon density-driven flow. On the Shelf at 60 m depth, near-bottom SSC during this storm event reached extremely high concentrations (>10 g l−1), characteristic of fluid-mud suspensions. The across-Shelf Sediment transport near the bottom showed a persistent off-Shelf direction through the entire recording period, while the along-Shelf transport fluctuated in direction, but resulted in net transport toward the Eel Canyon head. Within the canyon, near-bottom Sediment fluxes were continuously directed down-canyon, while the across-canyon flux was negligible. Sediment fluxes through intermediate slope waters (above the canyon rims) were directed toward the north, following the orientation of the adjacent Shelf-break. Results from this field study have identified some of the major processes controlling the off-Shelf Sediment export in the Eel continental margin, and corroborate previous findings that a substantial portion of the Eel River Sediment discharged on the Shelf can be exported into the Eel submarine canyon.
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Sediment transport events on the northern california continental Shelf
Marine Geology, 1999Co-Authors: Andrea S Ogston, R W SternbergAbstract:Abstract A long-term monitoring tripod has been maintained in 60-m water depth at the northern end of the STRATAFORM study site on the northern California continental Shelf. As part of this ongoing study, tripod data for 1 year beginning 24 September 1995 are used to provide a Sediment-transport analysis on an event-by-event basis. The objective of this paper is to highlight the energetic nature of this Shelf region in terms of the frequency, duration, and magnitude of Sediment-suspension events and the associated particle flux. Analyses are based on measurements from two current meters and two optical backscatterance sensors located at 30 and 100 cm above the bed. Data from these instruments and a pressure sensor were averaged over 7.5 min every hour. During the year of record, 41 distinct Sediment-suspension events occurred (i.e., sustained suspended-Sediment concentrations greater than 20 mg/l above background level at 100 cm above bed). Suspended-Sediment events were associated with significant wave activity, tidal currents, and river discharge. The average duration of a Sediment-suspension event was 3.1 days and varied from 0.7 to 8 days. During events, mean suspended-Sediment concentrations of 110 mg/l were observed with peak hourly observations exceeding 1000 mg/l. Concentrations between events averaged 35 mg/l. The overall Sediment flux for the period of record was directed seaward and southward. The distribution and magnitude of Sediment-suspension events and particle flux showed a strong seasonality. For example, of the Sediment transport during events, 98% of the net along-Shelf, and 73% of the net across-Shelf Sediment transport occurred in the winter. Three major winter storms could account for 72% of the total along-Shelf transport but only 10% of the across-Shelf transport. The across-Shelf flux was more evenly distributed over the year and occurred as a result of mean currents and very low-frequency seaward flows associated with mesoscale circulation patterns.
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fluid mud processes on the amazon continental Shelf
Computer Science Symposium in Russia, 1996Co-Authors: G C Kineke, R W Sternberg, John H Trowbridge, W. R. GeyerAbstract:Abstract A Sediment transport study conducted on the Amazon continental Shelf as part of AmasSeds (A Multi-disciplinary Amazon Shelf Sediment Study) revealed extensive regions of dense nearbed suspensions of Sediment, known as fluid mud (suspended-Sediment concentration > 10 g1−1 ). Fluid mud was found near the river mouth on the inner- and middle-Shelf, in the region of the bottom salinity front, and was most extensive during periods of rising and high river discharge. Fluid mud, up to 7.25 m thick, but generally 1–2 m thick, appears to form by processes similar to those occurring at an estuarine turbidity maximum, i.e. enhanced settling and lateral convergence of near-bottom flows. A modeling study showed that vertical mixing was controlled by the suppression of turbulence, due to the stratification induced by suspended Sediment, and established an upper bound for the total amount of suspended Sediment that may be carried in suspension. Sediment leaving the Amazon River appears to go through cycles of trapping and resuspension at the river mouth, before being partially advected seaward and alongShelf, where it is largely incorporated into fluid mud along the bottom salinity front. The fluid muds have far-reaching effects on the Amazon Shelf system by reducing boundary shear stresses, affecting water-column seabed exchange, and serving as the agent of outward growth of the subaqueous delta through episodic offshore transport.
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an introduction to the geological significance of Sediment transport and accumulation on the amazon continental Shelf
Marine Geology, 1995Co-Authors: Charles A Nittrouer, R W Sternberg, Steven A Kuehl, Alberto G Figueiredo, Luis E C FariaAbstract:In order to understand the formative processes and resulting stratigraphy on the Amazon Shelf and adjacent shoreline of Amapa, geological investigations were undertaken as part of A Multidisciplinary Amazon Shelf Sediment Study (AmasSeds). The design of the study provided results of a multifaceted nature: integrated with observations in other disciplines; focused on Sedimentary processes; representative of fluctuating conditions on several time scales; and broadly distributed on the Shelf, including regions not investigated in the past. On short time scales, most muddy Sediment is transported northwest of the river mouth. From there, it moves seaward as fluid mud to cause rapid accumulation of foreset beds, and moves northwestward to prograde the northernmost Amapa shoreline and to supply Sediment to the Guianas. Fluid muds cover the Shelf as far northward as ~3.5 °N and allow strong tides to propagate to shore, where tidal currents cause most of the Amapa shoreline to undergo erosion today. Averaged over decades and centuries, about half of the Amazon Sediment discharge accumulates on the adjacent Shelf, and another significant fraction (~one-sixth) leads to accretion of the northernmost Amapa shoreline and northwestward bypassing of Sediment. The remaining Sediment is hypothesized to be trapped in deltaplain deposits of the lower Amazon River system. The foreset region and shoreline represent the two common loci of Sediment accumulation that alternate their predominance on time scales of millennia, and lead to a two-stage progradation of coastal-plain and subaqueous-deltaic deposits. This muddy regressive Sedimentation during high sea level is replaced by formation of erosional sand layers during low sea level and transgressive conditions. Future research in the study area should address important considerations that were delineated by the present study, including: mechanisms of shoreline accretion; the Holocene history recorded in topset and coastal-plain strata; the role in local Sedimentation played by the large shoal extending from Cabo Norte; and the entrapment of Amazon Sediment by the delta plain.
Charles A Nittrouer - One of the best experts on this subject based on the ideXlab platform.
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Sediment accumulation in the western gulf of lions france the role of cap de creus canyon in linking Shelf and slope Sediment dispersal systems
Continental Shelf Research, 2008Co-Authors: A L Degeest, Pere Puig, Charles A Nittrouer, B L Mullenbach, Durrieu X De Madron, Tina M Drexler, Daniel L OrangeAbstract:Previous work in the Gulf of Lions (western Mediterranean Sea) has suggested that significant amounts of Sediment escape through the western part of this tectonically passive margin, despite it being far removed from the primary Sediment source (the Rhone River, � 160 km to the NE). The primary mechanism behind this export is hypothesized to be the interaction of a regional, southwestward Sediment-transport path with a canyon deeply incising the southwestern part of the Shelf, Cap de Creus Canyon. To understand the pattern of off-Shelf Sediment export from the western Gulf of Lions, and more specifically, the role of Cap de Creus Canyon in this transport, box cores were collected within the canyon and on the adjacent Shelf during five cruises from November 2003 to April 2005. Geochronology ( 210 Pb-derived accumulation rates), grain-size distributions, and Sedimentary structures (X-radiography) were analyzed to assess temporal and spatial Sedimentation patterns. Results indicate two mid-Shelf depocenters (30–90 m water depth) in the northern and southern portions of the study area, separated by a zone of bypassing due to current acceleration around a headland (Cap Bear). Estimates of a Sediment budget indicate that � 6–8% of the Sediment input to the Gulf is sequestered on the Shelf region. Within the Cap de Creus Canyon, there is a significant spatial asymmetry in both grain size and accumulation rates. The northern flank is a modern depocenter of fine-grained Sediments, while the southern flank is primarily non-depositional for mud and includes locations of apparent erosion. This suggests the influence of multiple oceanographic processes supplying Sediment to the canyon: advection of nepheloid layers from the northern rim that provide a relatively continuous Sediment supply (over decadal timescales), and episodic strong currents affecting the southern rim, which can scour Sediment from the southern flank. The mid-depth thalweg has an ephemeral mud layer, overlying sand and consolidated mud. The mud layer appears to be flushed down canyon periodically. The canyon head contains coarse material, suggesting reworked sands may be entering. The 100-year Sediment budget, based on accumulation rates for the fine-grained fraction in the upper canyon, indicates that � 1% of the total Sediment input to the Gulf is accumulating in upper Cap de Creus Canyon. However, this number may significantly underestimate the total Sediment entering the canyon because water-column measurements show that Sediment is likely moving through the upper canyon during major dense-water cascading events from the Shelf and being deposited deeper in the canyon system. The ephemeral mud layer also indicates rapid deposition and frequent flushing of Sediment through the upper canyon. Overall, this study
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contrasting styles of off Shelf Sediment accumulation in new guinea
Marine Geology, 2003Co-Authors: J P Walsh, Charles A NittrouerAbstract:Abstract The accumulation of river Sediment (and associated materials) off the continental Shelf is widely acknowledged to have been significant during the last glacial maximum, when Shelf accommodation space was reduced in many areas. However, the importance of off-Shelf sinks during modern sea-level conditions is largely unknown. This study examined off-Shelf Sediment accumulation for two dispersal systems, the Gulf of Papua and the Sepik margin, using radionuclide (210Pb, 234Th), Sediment texture and structure data. These study areas were selected because they have a similar source of Sediment (the Papuan Fold Belt) with dramatically different margin morphologies. The Gulf of Papua is part of a foreland basin that lies in the northern Coral Sea, and receives over 3×108 tons of Sediment annually from numerous rivers. The majority of this load accumulates on the Shelf, and a small fraction (
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Shelf to canyon Sediment transport processes on the eel continental margin northern california
Marine Geology, 2003Co-Authors: Pere Puig, Charles A Nittrouer, Andrea S Ogston, B L Mullenbach, R W SternbergAbstract:Abstract To investigate the processes by which Sediment is supplied to the head of a submarine canyon, an instrumented tripod and a mooring were deployed in the northern thalweg of the Eel Canyon during autumn and winter 1999–2000. This was done as part of the STRATAFORM program, and in combination with a long time-series benthic-tripod data collection on the Eel continental Shelf. Sediment-resuspension events on the Shelf were forced by waves, and near-bottom suspended-Sediment concentrations (SSC) were enhanced during the Eel River flood season. Periodic SSC fluctuations in intermediate waters (corresponding to water depths equal to the Shelf-break depth) were predominantly recorded at semidiurnal tidal frequencies, associated with decreases of water salinity and increases of temperature. Within the Eel Canyon, increases of water turbidity were not directly related to the Eel River discharge, but they were linked to the occurrence of storms. This relationship was evident in the bottom-boundary-layer measurements at 120 m depth in the canyon head, although farther down-thalweg (280 m depth), significant increases of near-bottom SSC associated with storm events were recorded also. The highest SSC measured within the canyon coincided with a highly energetic storm on 28 October 1999, in the absence of any river flood event, but associated with a down-canyon density-driven flow. On the Shelf at 60 m depth, near-bottom SSC during this storm event reached extremely high concentrations (>10 g l−1), characteristic of fluid-mud suspensions. The across-Shelf Sediment transport near the bottom showed a persistent off-Shelf direction through the entire recording period, while the along-Shelf transport fluctuated in direction, but resulted in net transport toward the Eel Canyon head. Within the canyon, near-bottom Sediment fluxes were continuously directed down-canyon, while the across-canyon flux was negligible. Sediment fluxes through intermediate slope waters (above the canyon rims) were directed toward the north, following the orientation of the adjacent Shelf-break. Results from this field study have identified some of the major processes controlling the off-Shelf Sediment export in the Eel continental margin, and corroborate previous findings that a substantial portion of the Eel River Sediment discharged on the Shelf can be exported into the Eel submarine canyon.
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Sediment deposition accumulation and seabed dynamics in an energetic fine grained coastal environment
Computer Science Symposium in Russia, 1996Co-Authors: Charles A Nittrouer, Steven A Kuehl, Mead A Allison, Ercilio L C Faria, David A Dukat, John M Jaeger, Thomas D Pacioni, Alberto G Figueiredo, Ellen C UnderkofflerAbstract:Abstract Sedimentary processes on the continental Shelf and shoreline northwest of the Amazon River mouth were investigated as part of A Multidisciplinary Amazon Shelf Sediment Study (AmasSeds) during four field expeditions between 1989 and 1991. Periodic deposition and resuspension of seabed layers as much as a meter thick dominate Sedimentary processes for most of the inner Shelf and for the shoreface and foreshore north of Cabo Cassipore. Strata forming as a result of this process consist of decimeter-thick mud beds separated by hiatal (scour) surfaces. The volume of Sediment resuspended seasonally from the inner Shelf surface layer (SL) is of the same order of magnitude as the annual input from the river, indicating that resuspension is an important control on suspended-Sediment distributions in Shelf waters. Most resuspension from the SL occurs during February–May (the period of maximum wind stress), which is also the time of rapid deposition on the mudflats, suggesting that Sediment resuspended from the SL could contribute to shoreface and foreshore accretion for the northern portion of the study area. In addition, some of the Sediment resuspended from the SL is transported seaward periodically in the form of near-bottom fluid-mud flows. This results in non-steady-state input of certain particle-reactive trace metals, which is reflected in the occurrence of quasi-cyclic210Ph profiles in the foreset region of the subaqueous delta. As determined using228Ra/226Ra geochronology, Sediment accumulation rates in this region are 10–60 cm y−1. Farther seaward, in the bottomset region, accumulation rates decrease and there is increased evidence of biological activity preserved in Sedimentary structures. However, episodic (but reduced) Sediment input from fluid-mud flows also extends to this region, affecting the fauna and fine-scale stratigraphy.
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an introduction to the geological significance of Sediment transport and accumulation on the amazon continental Shelf
Marine Geology, 1995Co-Authors: Charles A Nittrouer, R W Sternberg, Steven A Kuehl, Alberto G Figueiredo, Luis E C FariaAbstract:In order to understand the formative processes and resulting stratigraphy on the Amazon Shelf and adjacent shoreline of Amapa, geological investigations were undertaken as part of A Multidisciplinary Amazon Shelf Sediment Study (AmasSeds). The design of the study provided results of a multifaceted nature: integrated with observations in other disciplines; focused on Sedimentary processes; representative of fluctuating conditions on several time scales; and broadly distributed on the Shelf, including regions not investigated in the past. On short time scales, most muddy Sediment is transported northwest of the river mouth. From there, it moves seaward as fluid mud to cause rapid accumulation of foreset beds, and moves northwestward to prograde the northernmost Amapa shoreline and to supply Sediment to the Guianas. Fluid muds cover the Shelf as far northward as ~3.5 °N and allow strong tides to propagate to shore, where tidal currents cause most of the Amapa shoreline to undergo erosion today. Averaged over decades and centuries, about half of the Amazon Sediment discharge accumulates on the adjacent Shelf, and another significant fraction (~one-sixth) leads to accretion of the northernmost Amapa shoreline and northwestward bypassing of Sediment. The remaining Sediment is hypothesized to be trapped in deltaplain deposits of the lower Amazon River system. The foreset region and shoreline represent the two common loci of Sediment accumulation that alternate their predominance on time scales of millennia, and lead to a two-stage progradation of coastal-plain and subaqueous-deltaic deposits. This muddy regressive Sedimentation during high sea level is replaced by formation of erosional sand layers during low sea level and transgressive conditions. Future research in the study area should address important considerations that were delineated by the present study, including: mechanisms of shoreline accretion; the Holocene history recorded in topset and coastal-plain strata; the role in local Sedimentation played by the large shoal extending from Cabo Norte; and the entrapment of Amazon Sediment by the delta plain.
Pere Puig - One of the best experts on this subject based on the ideXlab platform.
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nepheloid layer distribution in the gulf of valencia northwestern mediterranean
Journal of Marine Systems, 2013Co-Authors: Marta Ribo, Pere Puig, Jordi Salat, Albert PalanquesAbstract:According to previous studies, the surface circulation of the Gulf of Valencia (GoV) is characterized by a convergence between the southwestward Northern Current carrying old Atlantic Waters (oAW) and the northward intrusions of recent Atlantic Waters (rAW) imported through the Ibiza Channel. This paper focuses on the distribution of the suspended Sediment concentration in the GoV obtained from a dense grid of CTD observations in June 1995 during the oceanographic cruise MESO'95 (MESOscale processes). We evaluate the relation between currents, water masses and the nepheloid structure at the time of the survey. Results showed higher suspended Sediment concentration (SSC) in the oAW than in the rAW. At the Shelf-break depth, an important detachment of particulate matter was observed off Cap La Nao, extending seawards all across the Ibiza Channel. The presence of this intermediate nepheloid layer detachment indicates a preferential off-Shelf Sediment export at the southern end of the GoV, where the orientation of the continental margin changes, and oAW and rAW merge. On the continental slope, several nepheloid layers detachments were observed between 400 and 600 m, where the Levantine Intermediate Water (LIW) interacts with the seafloor, suggesting the possible presence of internal waves causing Sediment resuspension and/or maintaining particles in suspension in the mid-slope region. A bottom nepheloid layer was also observed at deeper locations along the central and southern part of the GoV continental slope, but not at the Ibiza Sill.
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storm driven Shelf to canyon suspended Sediment transport at the southwestern gulf of lions
Continental Shelf Research, 2008Co-Authors: Albert Palanques, Pere Puig, Jorge Guillen, Durrieu X De MadronAbstract:Abstract Shelf-to-canyon suspended Sediment transport during major storms was studied at the southwestern end of the Gulf of Lions. Waves, near-bottom currents, temperature and water turbidity were measured on the inner Shelf at 28-m water depth and in the Cap de Creus submarine canyon head at 300 m depth from November 2003 to March 2004. Two major storm events producing waves H s >6 m coming from the E–SE sector took place, the first on 3–4 December 2003 (max H s : 8.4 m) and the second on 20–22 February 2004 (max H s : 7 m). During these events, Shelf water flowed downcanyon producing strong near-bottom currents on the canyon head due to storm-induced downwelling, which was enhanced by dense Shelf water cascading in February 2004. These processes generated different pulses of downcanyon suspended Sediment transport. During the peak of both storms, the highest waves and the increasing near-bottom currents resuspended Sediment on the canyon head and the adjacent outer Shelf causing the first downcanyon Sediment transport pulses. The December event ended just after these first pulses, when the induced downwelling finished suddenly due to restoration of Shelf water stratification. This event was too short to allow the Sediment resuspended on the shallow Shelf to reach the canyon head. In contrast, the February event, reinforced by dense Shelf water cascading, was long enough to transfer resuspended Sediment from shallow Shelf areas to the canyon head in two different pulses at the end of the event. The downcanyon transport during these last two pulses was one order of magnitude higher than those during the December event and during the first pulses of the February event and accounted for more than half of the total downcanyon Sediment transport during the fall 2003 and winter 2004 period. Major storm events, especially during winter vertical mixing periods, produce major episodes of Shelf-to-canyon Sediment transport at the southwestern end of the Gulf of Lions. Hydrographic structure and storm duration are important factors controlling off-Shelf Sediment transport during these events.
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Sediment accumulation in the western gulf of lions france the role of cap de creus canyon in linking Shelf and slope Sediment dispersal systems
Continental Shelf Research, 2008Co-Authors: A L Degeest, Pere Puig, Charles A Nittrouer, B L Mullenbach, Durrieu X De Madron, Tina M Drexler, Daniel L OrangeAbstract:Previous work in the Gulf of Lions (western Mediterranean Sea) has suggested that significant amounts of Sediment escape through the western part of this tectonically passive margin, despite it being far removed from the primary Sediment source (the Rhone River, � 160 km to the NE). The primary mechanism behind this export is hypothesized to be the interaction of a regional, southwestward Sediment-transport path with a canyon deeply incising the southwestern part of the Shelf, Cap de Creus Canyon. To understand the pattern of off-Shelf Sediment export from the western Gulf of Lions, and more specifically, the role of Cap de Creus Canyon in this transport, box cores were collected within the canyon and on the adjacent Shelf during five cruises from November 2003 to April 2005. Geochronology ( 210 Pb-derived accumulation rates), grain-size distributions, and Sedimentary structures (X-radiography) were analyzed to assess temporal and spatial Sedimentation patterns. Results indicate two mid-Shelf depocenters (30–90 m water depth) in the northern and southern portions of the study area, separated by a zone of bypassing due to current acceleration around a headland (Cap Bear). Estimates of a Sediment budget indicate that � 6–8% of the Sediment input to the Gulf is sequestered on the Shelf region. Within the Cap de Creus Canyon, there is a significant spatial asymmetry in both grain size and accumulation rates. The northern flank is a modern depocenter of fine-grained Sediments, while the southern flank is primarily non-depositional for mud and includes locations of apparent erosion. This suggests the influence of multiple oceanographic processes supplying Sediment to the canyon: advection of nepheloid layers from the northern rim that provide a relatively continuous Sediment supply (over decadal timescales), and episodic strong currents affecting the southern rim, which can scour Sediment from the southern flank. The mid-depth thalweg has an ephemeral mud layer, overlying sand and consolidated mud. The mud layer appears to be flushed down canyon periodically. The canyon head contains coarse material, suggesting reworked sands may be entering. The 100-year Sediment budget, based on accumulation rates for the fine-grained fraction in the upper canyon, indicates that � 1% of the total Sediment input to the Gulf is accumulating in upper Cap de Creus Canyon. However, this number may significantly underestimate the total Sediment entering the canyon because water-column measurements show that Sediment is likely moving through the upper canyon during major dense-water cascading events from the Shelf and being deposited deeper in the canyon system. The ephemeral mud layer also indicates rapid deposition and frequent flushing of Sediment through the upper canyon. Overall, this study
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Sediment dynamics during wet and dry storm events on the tet inner Shelf sw gulf of lions
Marine Geology, 2006Co-Authors: Jorge Guillen, Pere Puig, Albert Palanques, Durrieu X De Madron, Francois Bourrin, Roselyne BuscailAbstract:Abstract The importance of short-term processes, such as floods and storms, on Sediment delivery and reworking on the Tet inner Shelf was investigated. The Tet inner Shelf is a small, event-dominated system located in the south-western part of the Gulf of Lions. The expected Sedimentary scenario in this environment is that fluvial Sediment should be deposited on the prodelta and later dispersed around the Shelf and slope by wave and current reworking during storms. This paper investigates differences in inner Shelf Sediment dynamics between storm events occurring during usual river discharges and those occurring during river floods. Waves, current velocities, near-bottom water turbidity, bottom Sediment grain-size and sea-floor erosion/accretion were concurrently measured at 28-m water depth on the Tet inner Shelf from November 2003 to March 2004. Two major storms took place on 4 December 2003 and 21 February 2004, and two moderate storms occurred on 8 December 2003 and 14 March 2004. The two major storms displayed similar wave characteristics: maximum significant wave height ( H s ) > 7 m, peak period ( T p ) > 12 s and wave direction around 90°. The main environmental differences during the two major storm events correspond to the amount of Sediment discharged from the Tet River. About 2 × 10 4 t of Sediment was delivered by the river during the 4 December flood (wet storm) and less than 5 × 10 2 t during the 21 February storm (dry storm). Sediment dynamics were quite similar during the storm events: resuspension caused by waves and Sediment advection towards the southeast due to near-bottom Shelf currents were the dominant Sedimentary processes. The result was a bottom Sediment erosion of several centimetres at the study site during both the wet and dry events. The main differences between the wet and dry events arose after the storm. Immediately after the peak of the wet storm, Sediment supplied by the Tet River (and probably from other rivers) was deposited around the river mouth. A few days later, during a moderate storm, this unconsolidated Sediment was resuspended, transported offshore and deposited on the inner Shelf. In contrast, a moderate storm which occurred some days after the dry February storm caused bottom erosion on the inner Shelf, because no fresh Sediment was available on the shallower area. The results from this study indicate that the Tet inner Shelf at 28-m water depth is mainly a bypass zone for Sediment that is transported S–SE towards the middle–outer Shelf and slope, although ephemeral Sediment deposits may be favoured by the Sediment supplied from flood events. Sediment transport across the Shelf, from the river to the slope, follows a complex, multi-step pattern that needs to be addressed using a multi-event approach.
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composition and variability of downward particulate matter fluxes in the palamos submarine canyon nw mediterranean
Journal of Marine Systems, 2006Co-Authors: Jacobo Martin, Albert Palanques, Pere PuigAbstract:Abstract To study the temporal and spatial variability of downward particle fluxes in the Palamos submarine canyon, seven Sediment traps were moored inside and in the vicinity of the canyon from March to November 2001. Total mass fluxes, major constituent (organic carbon, opal, calcium carbonate and lithogenics) contents and fluxes, and 210 Pb activity of particulate matter were obtained from two consecutive deployments at intervals of 10 and 12 days, respectively. Downward particle fluxes measured at the Palamos canyon head were 2 to 9 times higher than those measured in other northwestern Mediterranean canyons, and this relation increased drastically at 1200 m depth, where observed particle fluxes were 1 to 2 orders of magnitude higher than those reported in other surrounding canyons at similar depths. The highest near-bottom downward particle fluxes were not recorded in the canyon head but in the mid-canyon axis during late spring/summer, as a result of Sediment gravity flows triggered by trawling activities at the canyon rims. In comparison to the adjacent open slope, Palamos Canyon is a prime site for the focusing and across-margin transference of total and organic matter. Off-Shelf Sediment transport was enhanced during a severe storm in November 2001, when a sharp increase in downward particulate fluxes was observed in the whole canyon both near the bottom and at intermediate waters. Despite the dominance of lithogenic particles all year round, a siliceous bloom affected the whole study area in March–April. An asymmetrical pattern was observed between the north and south canyon walls, with higher mean downward fluxes in the latter case, a fact related to the flow regime inside the canyon. The spatial–temporal distribution of total mass fluxes and major constituents defined two domains in the Palamos Canyon: an “inner” domain (up to 1200 m depth) constricted by the canyon topography and mainly influenced by a lateral transport of particles resuspended from the adjoining Shelf and upper slope, and an “outer” domain, where slope dynamics and seasonal trends are more important in determining the composition and amount of downward particulate fluxes.
Peter Traykovski - One of the best experts on this subject based on the ideXlab platform.
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constraining denitrification in permeable wave influenced marine Sediment using linked hydrodynamic and biogeochemical modeling
Earth and Planetary Science Letters, 2008Co-Authors: Bayani M Cardenas, Perran L M Cook, Houshuo Jiang, Peter TraykovskiAbstract:Abstract Permeable marine Sediments are ubiquitous complex environments, the biogeochemistry of which are strongly coupled to hydrodynamic process above and within the Sediment. The biogeochemical processes in these settings have global scale implications but are poorly understood and challenging to quantify. We present the first simulation of linked turbulent-oscillatory flow of the water column, porous media flow, and solute transport in the Sediment with oxygen consumption, nitrification, denitrification, and ammonification, informed by field- and/or experimentally-derived parameters. Nitrification and denitrification were significantly impacted by advective pore water exchange between the Sediment and the water column. Denitrification rates showed a maximum at intermediate permeabilities, and were negligible at high permeabilities. Denitrification rates were low, with only ∼ 15% of total N mineralized being denitrified, although this may be increased temporarily following Sediment resuspension events. Our model-estimated denitrification rates are about half of previous estimates which do not consider solute advection through the Sediment. Given the critical role of Sediment permeability, topography, and bottom currents in controlling denitrification rates, an improved knowledge of these factors is vital for obtaining better estimates of denitrification taking place on Shelf Sediment. Broad application of our approach to myriad conditions will lead to improved predictive capacity, better informed experimental and sampling design, and more holistic understanding of the biogeochemistry of permeable Sediment.
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The role of wave-induced density-driven fluid mud flows for cross-Shelf transport on the Eel River continental Shelf
Continental Shelf Research, 2000Co-Authors: Peter Traykovski, W. R. Geyer, James D. Irish, James F LynchAbstract:Abstract Observations of cross-Shelf Sediment transport conducted in the winter of 1997–1998 as part of the STRATAFORM program reveal that gravitationally forced density flows of fluid mud trapped within the thin wave bottom boundary layer provide a mechanism for forming flood deposits on the Eel river continental Shelf. The data from two moored tripods located on the 20 and 60 m isobaths combined with “rapid response” hydrographic surveys, indicate a process whereby the Eel River delivers Sediment on to the inner Shelf faster than dispersal and transport processes are able to move it offshore. The river does not deliver Sediment beyond the inner Shelf because the plume is trapped along the coast due to onshore surface flow associated with downwelling favorable winds. However, the final flood deposition region is located seaward of the 50-m isobath. Acoustic backscattering data taken on the 60-m isobath (in the historic flood deposit region) show two depositional events of 6 and 13 cm during a period of high river discharge and high waves in January of 1998. These depositional events are associated with fluid mud layers that scale in thickness with the wave boundary layer. Velocity profiles from a vertical array of current meters spanning the bottom 2 m of the water column show that the current meter closest to the seafloor has the largest offshore velocity during the depositional events, indicating an offshore flow of the fluid mud from the inner Shelf to the flood deposit region. During periods of low concentration suspended Sediment transport without fluid mud layers present, either no deposition or erosion was found indicating that the offshore flow of the fluid mud is the dominant depositional mechanism.
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the structure of the eel river plume during floods
Computer Science Symposium in Russia, 2000Co-Authors: Rockwell W Geyer, Paul S Hill, T G Milligan, Peter TraykovskiAbstract:Abstract Several large floods of the Eel River in northern California occurred during 1997 and 1998, with peak discharge ranging from 4000 to 12,000 m 3 s −1 . The flood conditions persisted for 1–3 days and were usually accompanied by strong winds from the southern quadrant. The structure of the river plume was strongly influenced by the wind-forcing conditions. During periods of strong southerly (downwelling favorable) winds, the plume was confined inside the 50-m isobath, within about 7 km of shore, with northward velocities of 0.5–1 m s −1 . Occasional northerly (upwelling favorable) winds arrested the northward motion of the plume and caused it to spread across the Shelf. Sediment transport by the plume was confined to the inner Shelf (water depths less than 50 m), during both southerly and northerly wind conditions. During southerly wind periods, fine, unaggregated Sediment was rapidly transported northward to at least 30 km from the river mouth, but flocculated Sediment was deposited within 1–10 km of the river mouth. During northerly (upwelling-favorable) winds, most of the Sediment fell out within 5 km of the mouth, and negligible Sediment was carried offshore, even though the low-salinity plume extended beyond the 60-m isobath. Although Sediment deposition from the plume is confined to the inner Shelf, the stratigraphy indicates that the principal flood deposits on the adjacent continental Shelf occur in a patch between the 60- and 90-m isobath. Thus, the deposition on the inner Shelf is ephemeral, and some mechanism other than plume transport delivers the Sediment from the inner Shelf to the mid-Shelf.
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estimates of suspended Sediment flux and bedform activity on the inner portion of the eel continental Shelf
Marine Geology, 1999Co-Authors: David A Cacchione, James D. Irish, James F Lynch, Patricia Wiberg, Peter TraykovskiAbstract:Energetic waves, strong bottom currents, and relatively high rates of Sediment discharge from the Eel River combined to produce large amounts of suspended-Sediment transport on the inner continental Shelf near the Eel River during the winter of 1995–1996. Bottom-boundary-layer (BBL) measurements at a depth of ∼50 m using the GEOPROBE tripod showed that the strongest near-bottom flows (combined wave and current speeds of over 1 m/s) and highest Sediment concentrations (exceeding 2 g/l at ∼1.2 m above the bed) occurred during two storms, one in December 1995 and the other in February 1996. Discharge from the Eel River during these storms was estimated at between 2 and 4×103 m3/s. Suspended-Sediment flux (SSF) was measured 1.2 m above the bed and calculated throughout the BBL, by applying the tripod data to a Shelf Sediment-transport model. These results showed initially northward along-Shelf SSF during the storms, followed by abrupt and persistent southward reversals. Along-Shelf flux was more pronounced during and after the December storm than in February. Across-Shelf SSF over the entire measurement period was decidedly seaward. This seaward transport could be responsible for surficial deposits of recent Sediment on the outer Shelf and upper continental slope in this region. Sediment ripples and larger bedforms were observed in the very fine to fine sand at 50-m depth using a sector-scanning sonar mounted on the tripod. Ripple wavelengths estimated from the sonar images were about 9 cm, which compared favorably with photographs of the bottom taken with a camera mounted on the tripod. The ripple patterns were stable during periods of low combined wave–current bottom stresses, but changed significantly during high-stress events, such as the February storm. Two different sonic altimeters recorded changes in bed elevation of 10 to 20 cm during the periods of measurement. These changes are thought to have been caused principally by the migration of low-amplitude, long-wavelength sand waves into the measurement area.
Andrea S Ogston - One of the best experts on this subject based on the ideXlab platform.
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in situ observations of wave supported fluid mud generation and deposition on an active continental margin
Journal of Geophysical Research, 2015Co-Authors: R P Hale, Andrea S OgstonAbstract:Wave-supported fluid muds (WSFM) are a type of gravity flow that can rapidly transport Sediment across continental margins. They occur when wave-induced bed stress maintains suspended-Sediment concentrations (SSC) >10 g l−1, and Sediment-induced stratification near the top of the wave boundary layer limits upward diffusion of Sediment. Observations from near-bed instrumentation are used to evaluate the conditions under which WSFMs form on the continental Shelf offshore of the Waipaoa River, NZ. An event in July 2010 featured >130 hours river of energetic ocean conditions, and water discharge >1900 m3 s−1. A calibrated acoustic backscatter sensor at the mid-Shelf measured near-bed SSC >50 g l−1, with a strong lutocline occurring >15 cm above the predicted wave-current boundary layer, resulting in ~5-cm deposition. A velocity anomaly occurred during this time, with offshore-directed currents faster at 1 meter above bed (mab) than at 3.5 mab. Using these observations, we empirically solve a simple buoyancy-drag force balance to estimate the gravity-driven velocity of the WSFM, which is always <0.03 m s−1. Extending the force balance across a Shelf transect suggests that WSFM-carried Sediment can reach the Shelf edge in 50–240 hours. Spatial and temporal patterns of deposition predicted by the gradient of modeled Sediment flux correlate well with seabed observations on the Waipaoa Shelf reported in Walsh et al. (2014). This study highlights the importance of WSFMs for cross-Shelf Sediment transport, despite relatively slow gravity-driven velocities and the infrequency with which they occur.
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Sediment transport and event deposition on the waipaoa river Shelf new zealand
Computer Science Symposium in Russia, 2014Co-Authors: R P Hale, J P Walsh, Andrea S Ogston, Alan R OrpinAbstract:Abstract A one-year study examining water-column and near-bed time-series observations from benthic-boundary-layer tripods was undertaken in the Waipaoa Sedimentary System (WSS) on the Poverty Bay continental Shelf, offshore of the Raukumara Ranges, New Zealand. Here, the nature of the adjacent post-glacial Shelf deposits, fed by the Waipaoa River, and century-scale Sediment accumulation is well established, but event-scale Sediment dispersal and hydrodynamics had not been measured. Data from two tripods outfitted with acoustic and optical instrumentation, and x-radiograph images of seabed cores collected at 4-month intervals, were analyzed to quantify progressive Sedimentological changes, and to document processes responsible for seabed strata formation, destruction, and preservation. At the Northern Tripod (NT) mid-Shelf location 15 km southeast of the river mouth, we observed increases in near-bed suspended Sediment concentration when shear velocities exceeded 0.03 m s−1 on 33 occasions over an 11.5-month period. Of these events, 9 were depositional, 10 were erosional, and 14 had no bed-elevation change at the 1-cm resolution of our instrumentation. Relatively high (2–5 m) and short-period ( 0.15 m s−1) typically induced erosion. Despite the short reach of this mountainous riverine dispersal system, we observed a consistent delay between river discharge and apparent deposition on the mid-Shelf at the NT location. Following the three largest floods, ~120 h of strong, wave-driven bed shear stress preceded measurable deposition on the mid-Shelf, suggesting that event duration and intensity are key for transporting material offshore from Poverty Bay. The largest flux event recorded over the study year was a 130-hour-long storm and associated river flood that resulted in near contemporaneous deposition at the NT site. Suspended-Sediment concentration data suggest transport by a wave-supported fluid mud. X-radiographs from the NT location corroborate the instrumental record of 5 cm deposition, but only the two largest depositional events were preserved in the strata. On the southern Shelf we observed no evidence of deposition in either the instrumental data or in the x-radiographs of cores. This study suggests that event duration, and spatial and inter-annual variability are critical considerations when evaluating along- and across-Shelf Sediment transport and seabed stratigraphic evolution associated with discharge from small mountainous rivers.
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Sediment transport event analysis on the western adriatic continental Shelf
Continental Shelf Research, 2007Co-Authors: A M V Fain, Andrea S Ogston, R W SternbergAbstract:The Sediment-transport mechanisms that contribute to and redistribute the modern Sediment deposits on the western Adriatic continental Shelf were evaluated utilizing data collected from two instrumented benthic tripods deployed at 12-m water depth, one in the northern Adriatic basin on the Po River subaqueous delta, and the other in the central Adriatic basin on the Pescara River Shelf. Sediment-resuspension events driven by cold, northeasterly Bora winds dominate the along-Shelf transport climatology at both tripod locations, but at the Po delta site, the southwesterly Scirocco wind events also play a significant role. At the Pescara Shelf site, interaction between Bora wind-driven currents and the Western Adriatic Coastal Current strongly contributes to the resuspension and advection of suspended Sediment. Interannual variability of the forcing mechanisms (including strength, frequency, and relative mix of Bora and Scirocco wind events) is evident in the three winters of data collected on the Po River subaqueous delta. In both types of wind events, and throughout all years of data collection, the net along-Shelf Sediment transport is significantly larger than the net across-Shelf transport at the 12-m sites. This may be characteristic of low-energy environments, where Sediment resuspension and transport occurs in such shallow water that it is not subjected to strong downwelling features characteristic of higher-energy environments.
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Shelf to canyon Sediment transport processes on the eel continental margin northern california
Marine Geology, 2003Co-Authors: Pere Puig, Charles A Nittrouer, Andrea S Ogston, B L Mullenbach, R W SternbergAbstract:Abstract To investigate the processes by which Sediment is supplied to the head of a submarine canyon, an instrumented tripod and a mooring were deployed in the northern thalweg of the Eel Canyon during autumn and winter 1999–2000. This was done as part of the STRATAFORM program, and in combination with a long time-series benthic-tripod data collection on the Eel continental Shelf. Sediment-resuspension events on the Shelf were forced by waves, and near-bottom suspended-Sediment concentrations (SSC) were enhanced during the Eel River flood season. Periodic SSC fluctuations in intermediate waters (corresponding to water depths equal to the Shelf-break depth) were predominantly recorded at semidiurnal tidal frequencies, associated with decreases of water salinity and increases of temperature. Within the Eel Canyon, increases of water turbidity were not directly related to the Eel River discharge, but they were linked to the occurrence of storms. This relationship was evident in the bottom-boundary-layer measurements at 120 m depth in the canyon head, although farther down-thalweg (280 m depth), significant increases of near-bottom SSC associated with storm events were recorded also. The highest SSC measured within the canyon coincided with a highly energetic storm on 28 October 1999, in the absence of any river flood event, but associated with a down-canyon density-driven flow. On the Shelf at 60 m depth, near-bottom SSC during this storm event reached extremely high concentrations (>10 g l−1), characteristic of fluid-mud suspensions. The across-Shelf Sediment transport near the bottom showed a persistent off-Shelf direction through the entire recording period, while the along-Shelf transport fluctuated in direction, but resulted in net transport toward the Eel Canyon head. Within the canyon, near-bottom Sediment fluxes were continuously directed down-canyon, while the across-canyon flux was negligible. Sediment fluxes through intermediate slope waters (above the canyon rims) were directed toward the north, following the orientation of the adjacent Shelf-break. Results from this field study have identified some of the major processes controlling the off-Shelf Sediment export in the Eel continental margin, and corroborate previous findings that a substantial portion of the Eel River Sediment discharged on the Shelf can be exported into the Eel submarine canyon.
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Sediment transport events on the northern california continental Shelf
Marine Geology, 1999Co-Authors: Andrea S Ogston, R W SternbergAbstract:Abstract A long-term monitoring tripod has been maintained in 60-m water depth at the northern end of the STRATAFORM study site on the northern California continental Shelf. As part of this ongoing study, tripod data for 1 year beginning 24 September 1995 are used to provide a Sediment-transport analysis on an event-by-event basis. The objective of this paper is to highlight the energetic nature of this Shelf region in terms of the frequency, duration, and magnitude of Sediment-suspension events and the associated particle flux. Analyses are based on measurements from two current meters and two optical backscatterance sensors located at 30 and 100 cm above the bed. Data from these instruments and a pressure sensor were averaged over 7.5 min every hour. During the year of record, 41 distinct Sediment-suspension events occurred (i.e., sustained suspended-Sediment concentrations greater than 20 mg/l above background level at 100 cm above bed). Suspended-Sediment events were associated with significant wave activity, tidal currents, and river discharge. The average duration of a Sediment-suspension event was 3.1 days and varied from 0.7 to 8 days. During events, mean suspended-Sediment concentrations of 110 mg/l were observed with peak hourly observations exceeding 1000 mg/l. Concentrations between events averaged 35 mg/l. The overall Sediment flux for the period of record was directed seaward and southward. The distribution and magnitude of Sediment-suspension events and particle flux showed a strong seasonality. For example, of the Sediment transport during events, 98% of the net along-Shelf, and 73% of the net across-Shelf Sediment transport occurred in the winter. Three major winter storms could account for 72% of the total along-Shelf transport but only 10% of the across-Shelf transport. The across-Shelf flux was more evenly distributed over the year and occurred as a result of mean currents and very low-frequency seaward flows associated with mesoscale circulation patterns.
