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Pere Puig - One of the best experts on this subject based on the ideXlab platform.
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trawling induced daily sediment resuspension in the flank of a mediterranean submarine canyon
Deep-sea Research Part Ii-topical Studies in Oceanography, 2014Co-Authors: Jacobo Martin, Albert Palanques, Pere Puig, Marta RiboAbstract:Abstract Commercial bottom trawling is one of the anthropogenic activities causing the biggest impact on the seafloor due to its recurrence and global distribution. In particular, trawling has been proposed as a major driver of sediment dynamics at depths below the reach of storm waves, but the issue is at present poorly documented with direct observations. This paper analyses changes in water turbidity in a tributary valley of the La Fonera (=Palamos) submarine canyon, whose flanks are routinely exploited by a local trawling fleet down to depths of 800 m. A string of turbidimeters was deployed at 980 m water depth inside the tributary for two consecutive years, 2010–2011. The second year, an ADCP profiled the currents 80 m above the seafloor. The results illustrate that near-bottom water turbidity at the study site is heavily dominated, both in its magnitude and temporal patterns, by trawling-induced sediment resuspension at the fishing ground. Resuspended sediments are channelised along the tributary in the form of sediment gravity flows, being recorded only during working days and working hours of the trawling fleet. These sediment gravity flows generate turbid plumes that extend to at least 100 m above the bottom, reaching suspended sediment concentrations up to 236 mg l−1 close to the seafloor (5 m above bottom). A few hours after the end of daily trawling activities, water turbidity progressively decreases but resuspended particles remain in suspension for several hours, developing bottom and intermediate Nepheloid Layers that reach background levels ∼2 mg l−1 before trawling activities resume. The presence of these Nepheloid Layers was recorded in a CTD+turbidimeter transect conducted across the fishing ground a few hours after the end of a working day. These results highlight that deep bottom trawling can effectively replace natural processes as the main driving force of sediment resuspension on continental slope regions and generate increased near-bottom water turbidity that propagates from fishing grounds to wider and deeper areas via sediment gravity flows and Nepheloid Layer development.
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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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formation of a basin wide bottom Nepheloid Layer in the western mediterranean after the winter 2005 dense shelf water cascading event
Geotemas ( Madrid ), 2010Co-Authors: Pere Puig, Jordi Salat, Albert Palanques, Xavier Durrieu De Madron, Katrin Schroeder, Jose Luis Lopezjurado, G P Gasparini, Mikhail EmelianovAbstract:The analysis of a compilation of deep CTD casts conducted in the western Mediterranean after winter 2005 have documented the role that dense shelf water cascading (DSWC) plays in transporting suspended particulate matter from the coastal regions down to the basin. Deep CTD casts revealed the formation of thick and persistent bottom Nepheloid Layer (BNL) associated with the winter 2005 DSWC event, which was not present in 2004. This BNL spread throughout the western Mediterranean basin and scaled in thickness with a thermo-haline anomaly generated by the mixture of dense waters formed by deep convection in the open sea and by cascading, being up to 1450 m thick at some locations. Excess of concentrations within the BNL in the central part of the basin were around 0.2 mg/l, but reached concentrations >2 mg/l close to the continental rise. This BNL could be observed to progress from the Gulf of Lions and Catalan margin towards the central part of the basin, reaching south of the Balearic Islands and west of Sardinia in May 2005, and covered the entire western Mediterranean basin in June 2006. BNL thickness and concentration diminished with distance away from its source and also with time, although its turbidity signal can still be detected at present (2010).
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responses of deep water shrimp populations to intermediate Nepheloid Layer detachments on the northwestern mediterranean continental margin
Deep Sea Research Part I: Oceanographic Research Papers, 2001Co-Authors: Pere Puig, Francisco Sarda, Albert PalanquesAbstract:A clear link between the distribution of intermediate Nepheloid Layer detachments on the Northwestern Mediterranean continental margin and the population structure of five congeneric megafaunal species of deep-water benthic shrimps inhabiting different depth ranges between 100 and 1100 m was found. The results of the multidisciplinary approach presented in this study provide evidence for the ecological conditions that affect the spatial distribution of juveniles and females of a deep-water fishery resource. The significantly higher occurrence of juveniles and females in regions where intermediate Nepheloid Layers detach from the seabed allows us to define these areas as potential deep-water nursery habitats. The spatial recognition of these habitats could contribute to the management of the stocks concerned and afford a basis for protecting these vulnerable habitats from fishing pressure. Overall, our findings furnish support for the hypothesis that deep-water benthic biological processes are linked to pelagic processes, suggesting that the detachments of intermediate Nepheloid Layers serve as one of the physical links between these two environments.
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near bottom suspended sediment variability caused by storms and near inertial internal waves on the ebro mid continental shelf nw mediterranean
Marine Geology, 2001Co-Authors: Pere Puig, A Palanques, Jorge GuillenAbstract:Abstract Near-bottom currents and suspended sediment concentrations (SSC) recorded on the Ebro continental shelf at 60 m depth during the transition between fair and stormy weather have revealed some of the major processes controlling the sediment re-suspension and transport at mid shelf depths in this NW Mediterranean area. Storm waves were the main contributor to the transport of sediment, although they only resuspended surface sediments during extreme wave conditions ( H s >4.5 m and T s >11 s ). During the recording period, the net suspended sediment flux along the shelf was one order of magnitude higher than the net suspended sediment flux across the shelf, and the resultant transport was towards the SW and seaward. Fluctuations of the near-bottom SSC during fair weather showed a periodicity around 17 h, and were related to the occurrence of near-inertial internal waves caused by wind pulses during storm events. The energy propagation of these internal waves reached critical angles at the mid and outer shelf, which could favor the development and maintenance of the bottom Nepheloid Layer on the Ebro continental shelf, as well as, on other Mediterranean continental shelves.
Peter H Santschi - One of the best experts on this subject based on the ideXlab platform.
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sedimentary sources of old high molecular weight dissolved organic carbon from the ocean margin benthic Nepheloid Layer
Geochimica et Cosmochimica Acta, 2000Co-Authors: Laodong Guo, Peter H SantschiAbstract:Average 14 C ages of dissolved organic carbon (DOC) in the ocean are 3- 6,000 years, and are influenced by old DOC from continental margins. However, sources of DOC from terrestrial, autochthonous, and sedimentary organic carbon seem to be too young to be responsible for the old DOC observed in the ocean. Since colloidal organic carbon (COC, i.e., high molecular weight DOC), which is chemically very similar to that of bulk DOC, can be effectively isolated from seawater using cross-flow ultrafiltration, it can hold clues to sources and pathways of DOC turnover in the ocean. Radiocarbon measurements on COC in the water column and benthic Nepheloid Layer (BNL) from two continental margin areas (the Middle Atlantic Bight and the Gulf of Mexico) and controlled laboratory experiments were carried out to study sources of old DOC in the ocean margin areas. Vertical distributions of suspended particulate matter (SPM), particulate organic carbon (POC), nitrogen (PON), and DOC in the water column and bottom waters near the sediment-water interface all demonstrate a well developed benthic Nepheloid Layer in both ocean margin areas. D 14 C values of COC isolated from the BNL (ranging from 2362 6 4‰ to 2456 6 3‰) were distinctly lower than their counterparts in surface waters (with a range of .0‰ to 2210 6 5‰). In other words, COC from the BNL was much older than COC from the overlying water column. These results, together with strong concentration gradients of SPM, POC, PON, and DOC, suggest a sedimentary source for organic carbon species and possibly for old COC as well in BNL waters. This is confirmed by the results from controlled laboratory experiments which showed that COC isolated from sediment resuspension had D 14 C values between 2260‰ and 2352‰, which are significantly lower than those of bulk sediment (287 6 6‰) or resuspended particles ( 2138 6 8‰). The heterogeneity of D 14 C signatures in bulk SOC thus points to a preferential release of old organic components from sediment resuspension, which can be the transport mechanism of the old benthic COC observed in ocean margin areas. Old COC from continental margin Nepheloid Layers may thus be a potential source of old DOC to the deep ocean. Copyright © 1999 Elsevier Science Ltd
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cycling of high molecular weight dissolved organic matter in the middle atlantic bight as revealed by carbon isotopic 13c and 14c signatures
Limnology and Oceanography, 1996Co-Authors: Laodong Guo, Peter H Santschi, Luis A Cifuentes, Susan E Trumbore, J R SouthonAbstract:Carbon isotopes (13C and 14C) and elemental composition (C and N) in two fractions of colloidal organic matter (COM) were measured to study the origin and cycling of dissolved organic matter (DOM) in the Middle Atlantic Bight (MAB). COM, (1 kDa-O.2 pm) was 59% of the bulk DOM in surface Chesapeake Bay waters and decreased to 30-35% in waters of the MAB. COMlo (10 kDa-0.2 pm), which was the highmolecular-weight (HMW) component of COM,, comprised 3-l 2% of’ the bulk DOM, with highest concentrations in Chesapeake Bay waters and the lowest in deep waters in the MAB. AL4C values of COM, decreased from nearshore (-2 1 to + 12Yb0) to offshore and from surface (- 166 to -SS%&$ to bottom waters (-400 to -304’?&). Although A14C values of surface-water HMW COM,, were generally high (-2 to -7%0), values for bottom-water COM,, were much lower (- 129 to -709o/oo). The high A14C values in the surface water suggest a particulate origin of pelagic COM, consistent with the contemporary A14C values of particulate organic matter (POM). The very low A14C values of bottom-water COM,, imply that in addition to the pelagic origin, sedimentary organic C may serve as an important source for the benthic colloids in the bottom Nepheloid Layer. The general flow direction of organic carbon is from POM to HMW and to LMW DOM. Three colloidal end-members were identified in the MAB as well as in the Gulf of Mexico: estuarine colloids with high A14C values, high C : N ratios, and lower 613C values; offshore surface water colloids with intermediate A14C values, lower C : N ratios, and higher a13C values; and offshore deep-water colloids with low A14C values, intermediate C : N ratios, and variable 613C values.
Laodong Guo - One of the best experts on this subject based on the ideXlab platform.
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sedimentary sources of old high molecular weight dissolved organic carbon from the ocean margin benthic Nepheloid Layer
Geochimica et Cosmochimica Acta, 2000Co-Authors: Laodong Guo, Peter H SantschiAbstract:Average 14 C ages of dissolved organic carbon (DOC) in the ocean are 3- 6,000 years, and are influenced by old DOC from continental margins. However, sources of DOC from terrestrial, autochthonous, and sedimentary organic carbon seem to be too young to be responsible for the old DOC observed in the ocean. Since colloidal organic carbon (COC, i.e., high molecular weight DOC), which is chemically very similar to that of bulk DOC, can be effectively isolated from seawater using cross-flow ultrafiltration, it can hold clues to sources and pathways of DOC turnover in the ocean. Radiocarbon measurements on COC in the water column and benthic Nepheloid Layer (BNL) from two continental margin areas (the Middle Atlantic Bight and the Gulf of Mexico) and controlled laboratory experiments were carried out to study sources of old DOC in the ocean margin areas. Vertical distributions of suspended particulate matter (SPM), particulate organic carbon (POC), nitrogen (PON), and DOC in the water column and bottom waters near the sediment-water interface all demonstrate a well developed benthic Nepheloid Layer in both ocean margin areas. D 14 C values of COC isolated from the BNL (ranging from 2362 6 4‰ to 2456 6 3‰) were distinctly lower than their counterparts in surface waters (with a range of .0‰ to 2210 6 5‰). In other words, COC from the BNL was much older than COC from the overlying water column. These results, together with strong concentration gradients of SPM, POC, PON, and DOC, suggest a sedimentary source for organic carbon species and possibly for old COC as well in BNL waters. This is confirmed by the results from controlled laboratory experiments which showed that COC isolated from sediment resuspension had D 14 C values between 2260‰ and 2352‰, which are significantly lower than those of bulk sediment (287 6 6‰) or resuspended particles ( 2138 6 8‰). The heterogeneity of D 14 C signatures in bulk SOC thus points to a preferential release of old organic components from sediment resuspension, which can be the transport mechanism of the old benthic COC observed in ocean margin areas. Old COC from continental margin Nepheloid Layers may thus be a potential source of old DOC to the deep ocean. Copyright © 1999 Elsevier Science Ltd
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cycling of high molecular weight dissolved organic matter in the middle atlantic bight as revealed by carbon isotopic 13c and 14c signatures
Limnology and Oceanography, 1996Co-Authors: Laodong Guo, Peter H Santschi, Luis A Cifuentes, Susan E Trumbore, J R SouthonAbstract:Carbon isotopes (13C and 14C) and elemental composition (C and N) in two fractions of colloidal organic matter (COM) were measured to study the origin and cycling of dissolved organic matter (DOM) in the Middle Atlantic Bight (MAB). COM, (1 kDa-O.2 pm) was 59% of the bulk DOM in surface Chesapeake Bay waters and decreased to 30-35% in waters of the MAB. COMlo (10 kDa-0.2 pm), which was the highmolecular-weight (HMW) component of COM,, comprised 3-l 2% of’ the bulk DOM, with highest concentrations in Chesapeake Bay waters and the lowest in deep waters in the MAB. AL4C values of COM, decreased from nearshore (-2 1 to + 12Yb0) to offshore and from surface (- 166 to -SS%&$ to bottom waters (-400 to -304’?&). Although A14C values of surface-water HMW COM,, were generally high (-2 to -7%0), values for bottom-water COM,, were much lower (- 129 to -709o/oo). The high A14C values in the surface water suggest a particulate origin of pelagic COM, consistent with the contemporary A14C values of particulate organic matter (POM). The very low A14C values of bottom-water COM,, imply that in addition to the pelagic origin, sedimentary organic C may serve as an important source for the benthic colloids in the bottom Nepheloid Layer. The general flow direction of organic carbon is from POM to HMW and to LMW DOM. Three colloidal end-members were identified in the MAB as well as in the Gulf of Mexico: estuarine colloids with high A14C values, high C : N ratios, and lower 613C values; offshore surface water colloids with intermediate A14C values, lower C : N ratios, and higher a13C values; and offshore deep-water colloids with low A14C values, intermediate C : N ratios, and variable 613C values.
Nathan Hawley - One of the best experts on this subject based on the ideXlab platform.
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response of the benthic Nepheloid Layer to near inertial internal waves in southern lake michigan
Journal of Geophysical Research, 2004Co-Authors: Nathan HawleyAbstract:[1] Time series measurements of water transparency, water temperature, and current velocity were made at a station located in 58 m of water in southern Lake Michigan during the summer of 1995. Currents generated by near-inertial internal waves are correlated with variations in the thickness and in the vertical distribution of suspended sediment in the benthic Nepheloid Layer. Although a direct causal link between internal wave action and changes in the Nepheloid Layer could not be established, the data suggest that local resuspension by shoaling internal waves maintains the Layer during the stratified period. The origin and maintenance of the benthic Nepheloid Layer is most likely the result of local resuspension due to a combination of internal wave action and longer-term processes.
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suspended sediment transport in the benthic Nepheloid Layer in southeastern lake michigan
Other Information: PBD: [1995], 1995Co-Authors: Nathan Hawley, Barry M LeshtAbstract:Time series observations of water temperature, water transparency, and current velocity were made at four stations located on the lake slope of southeastern Lake Michigan. The observations show that during stratified conditions the benthic Nepheloid Layer is probably not maintained by the local resuspension of bottom sediment. A more likely source is sediment resuspended further inshore and then transported across the shelf and slope during downwelling events. Internal wave action may be an important source of energy for this transport. Although sediment trap studies suggest that resuspension does occur, it is more likely that increased fluxes observed near the bottom are due to the vertical redistribution of material already in suspension. A benthic Nepheloid Layer also exists at times during the unstratified period, when occassionally enough energy reaches the bottom to directly resuspend bottom material at the sites.
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does local resuspension maintain the benthic Nepheloid Layer in southeastern lake michigan
Journal of Sedimentary Research, 1995Co-Authors: Nathan Hawley, Barry M LeshtAbstract:Time-series observations of water temperature, water transparency, and current velocity at four stations in southeastern Lake Michigan show that the benthic Nepheloid Layer is probably not maintained by the local resuspension of bottom sediment. Local resuspension may occasionally occur in the deep parts of the lake, but it seems likely that vertical mixing and offshore advection of sediment-laden water maintain the benthic Nepheloid Layer during most of the year. Although sediment trap data have been interpreted as indicating that local resuspension does occur, it is more likely that the increased sediment fluxes observed near the bottom are due to vertical redistribution of material already in suspension.
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the response of the benthic Nepheloid Layer to a downwelling event
Journal of Great Lakes Research, 1995Co-Authors: Nathan Hawley, C R MurthyAbstract:Abstract Time series observations of water temperature, current velocity, and water transparency were made at three elevations at a mooring in southwestern Lake Ontario over a 14-day period. Although a strong downwelling event occurred during the deployment, there was no indication of either local sediment resuspension or of downslope transport of suspended material. Our observations, when combined with those of Hawley and Lesht (1995), indicate that material is not supplied to the benthic Nepheloid Layer by either local resuspension or offshore transport during the stratified period. Although several authors have suggested that the maintenance of the benthic Nepheloid Layer during the stratified period requires the periodic supply of additional material after it is formed, the sources of this material are not well known. Some material is most likely supplied by the settling of material from the epilimnion, but an additional—as yet unidentified—source seems to be needed to explain the observed changes in both the thickness and the concentration of material suspended in the benthic Nepheloid Layer.
Albert Palanques - One of the best experts on this subject based on the ideXlab platform.
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trawling induced daily sediment resuspension in the flank of a mediterranean submarine canyon
Deep-sea Research Part Ii-topical Studies in Oceanography, 2014Co-Authors: Jacobo Martin, Albert Palanques, Pere Puig, Marta RiboAbstract:Abstract Commercial bottom trawling is one of the anthropogenic activities causing the biggest impact on the seafloor due to its recurrence and global distribution. In particular, trawling has been proposed as a major driver of sediment dynamics at depths below the reach of storm waves, but the issue is at present poorly documented with direct observations. This paper analyses changes in water turbidity in a tributary valley of the La Fonera (=Palamos) submarine canyon, whose flanks are routinely exploited by a local trawling fleet down to depths of 800 m. A string of turbidimeters was deployed at 980 m water depth inside the tributary for two consecutive years, 2010–2011. The second year, an ADCP profiled the currents 80 m above the seafloor. The results illustrate that near-bottom water turbidity at the study site is heavily dominated, both in its magnitude and temporal patterns, by trawling-induced sediment resuspension at the fishing ground. Resuspended sediments are channelised along the tributary in the form of sediment gravity flows, being recorded only during working days and working hours of the trawling fleet. These sediment gravity flows generate turbid plumes that extend to at least 100 m above the bottom, reaching suspended sediment concentrations up to 236 mg l−1 close to the seafloor (5 m above bottom). A few hours after the end of daily trawling activities, water turbidity progressively decreases but resuspended particles remain in suspension for several hours, developing bottom and intermediate Nepheloid Layers that reach background levels ∼2 mg l−1 before trawling activities resume. The presence of these Nepheloid Layers was recorded in a CTD+turbidimeter transect conducted across the fishing ground a few hours after the end of a working day. These results highlight that deep bottom trawling can effectively replace natural processes as the main driving force of sediment resuspension on continental slope regions and generate increased near-bottom water turbidity that propagates from fishing grounds to wider and deeper areas via sediment gravity flows and Nepheloid Layer development.
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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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formation of a basin wide bottom Nepheloid Layer in the western mediterranean after the winter 2005 dense shelf water cascading event
Geotemas ( Madrid ), 2010Co-Authors: Pere Puig, Jordi Salat, Albert Palanques, Xavier Durrieu De Madron, Katrin Schroeder, Jose Luis Lopezjurado, G P Gasparini, Mikhail EmelianovAbstract:The analysis of a compilation of deep CTD casts conducted in the western Mediterranean after winter 2005 have documented the role that dense shelf water cascading (DSWC) plays in transporting suspended particulate matter from the coastal regions down to the basin. Deep CTD casts revealed the formation of thick and persistent bottom Nepheloid Layer (BNL) associated with the winter 2005 DSWC event, which was not present in 2004. This BNL spread throughout the western Mediterranean basin and scaled in thickness with a thermo-haline anomaly generated by the mixture of dense waters formed by deep convection in the open sea and by cascading, being up to 1450 m thick at some locations. Excess of concentrations within the BNL in the central part of the basin were around 0.2 mg/l, but reached concentrations >2 mg/l close to the continental rise. This BNL could be observed to progress from the Gulf of Lions and Catalan margin towards the central part of the basin, reaching south of the Balearic Islands and west of Sardinia in May 2005, and covered the entire western Mediterranean basin in June 2006. BNL thickness and concentration diminished with distance away from its source and also with time, although its turbidity signal can still be detected at present (2010).
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responses of deep water shrimp populations to intermediate Nepheloid Layer detachments on the northwestern mediterranean continental margin
Deep Sea Research Part I: Oceanographic Research Papers, 2001Co-Authors: Pere Puig, Francisco Sarda, Albert PalanquesAbstract:A clear link between the distribution of intermediate Nepheloid Layer detachments on the Northwestern Mediterranean continental margin and the population structure of five congeneric megafaunal species of deep-water benthic shrimps inhabiting different depth ranges between 100 and 1100 m was found. The results of the multidisciplinary approach presented in this study provide evidence for the ecological conditions that affect the spatial distribution of juveniles and females of a deep-water fishery resource. The significantly higher occurrence of juveniles and females in regions where intermediate Nepheloid Layers detach from the seabed allows us to define these areas as potential deep-water nursery habitats. The spatial recognition of these habitats could contribute to the management of the stocks concerned and afford a basis for protecting these vulnerable habitats from fishing pressure. Overall, our findings furnish support for the hypothesis that deep-water benthic biological processes are linked to pelagic processes, suggesting that the detachments of intermediate Nepheloid Layers serve as one of the physical links between these two environments.