Carbonate escarpments are submarine limestone and dolomite cliffs that have been documented in nu... more Carbonate escarpments are submarine limestone and dolomite cliffs that have been documented in numerous sites around the world. Their geomorphic evolution is poorly understood due to difficulties in assessing escarpment outcrops and the limited resolution achieved by geophysical techniques across their steep topographies. The geomorphic evolution of carbonate escarpments in the Mediterranean Sea has been influenced by the Messinian salinity crisis (MSC). During the MSC (5.97-5.33 Ma), the Mediterranean Sea became a saline basin due to a temporary restriction of the Atlantic-Mediterranean seaway, resulting in the deposition of more than one million cubic kilometres of salt. The extent and relative chronology of the evaporative drawdown phases associated to the MSC remain poorly constrained. In this paper we combine geophysical and sedimentological data from the central Mediterranean Sea to reconstruct the geomorphic evolution of the Malta Escarpment and infer the extent and timing of evaporative drawdown in the eastern Mediterranean Sea during the MSC. We propose that, during a MSC base-level fall, fluvial erosion formed a dense network of canyons across the Malta Escarpment whilst coastal erosion developed extensive palaeoshorelines and shore platforms. The drivers of geomorphic evolution of the Malta Escarpment after the MSC include: (i) canyon erosion by submarine gravity flows, with the most recent activity taking place <2600 cal. years BP; (ii) deposition by bottom currents across the entire depth range of the Malta Escarpment; (iii) tectonic deformation in the southern Malta Escarpment in association with a wrench zone; (iv) widespread, small-scale sedimentary slope failures preconditioned by oversteepening and loss of support due to canyon erosion, and triggered by earthquakes. 3 We carry out an isostatic restoration of the palaeoshorelines and shore platforms on the northern Malta Escarpment to infer an evaporative drawdown of 1800-2000 m in the eastern Mediterranean Sea during the MSC. We interpret the occurrence of pre-evaporite sedimentary lobes in the western Ionian Basin as suggesting that either evaporative drawdown and canyon formation predominantly occurred before salt deposition, or that only the latest salt deposition at the basin margin occurred after the formation of the sedimentary lobes.
In this paper we present the seabed maps of the shallow-water areas of Lampedusa and Linosa, belo... more In this paper we present the seabed maps of the shallow-water areas of Lampedusa and Linosa, belonging to the Pelagie Islands Marine Protected Area. Two surveys were carried out ("Lampedusa2015" and "Linosa2016") to collect bathymetric and acoustic backscatter data through the use of a Reson SeaBat 7125 high-resolution multibeam system. Ground-truth data, in the form of grab samples and diver video-observations, were also collected during both surveys. Sediment samples were analyzed for grain size, while video images were analyzed and described revealing the acoustic seabed and other bio-physical characteristics. A map of seabed classification, including sediment types and seagrass distribution, was produced using the tool Remote Sensing Object Based Image Analysis (RSOBIA) by integrating information derived from backscatter data and bathy-morphological features, validated by ground-truth data. This allows to create a first seabed maps (i.e. benthoscape classification), of Lampedusa and Linosa, at scale 1:20 000 and 1: 32 000, respectively, that will be checked and implemented through further surveys. The results point out a very rich and largely variable marine ecosystem on the seabed surrounding the two islands, with
ABSTRACT We present bathymetric and sidescan sonar results from the Mid-Atlantic Ridge between 45... more ABSTRACT We present bathymetric and sidescan sonar results from the Mid-Atlantic Ridge between 45°20&amp;#39;N and 45°44&amp;#39;N, where the axial valley is host to a ~4km wide and ~500m high axial volcanic ridge (AVR). The AVR and surrounding seafloor was surveyed concurrently using: a) the ship-mounted Simrad EM-120 echosounder, yielding bathymetry gridded at a resolution of 50m per pixel, and b) TOBI (Towed Ocean Bottom Instrument), which collected both sidescan sonar data (resolution 3m/pixel) and phase data, which were processed to provide bathymetry with a resolution of 10m/pixel. The TOBI survey entailed two ~45km-long north-south tracks and twenty-two ~15km-long east-west tracks; thus, much of the area was surveyed from up to four orthogonal and reciprocal directions, eliminating most regions of shadow and poor image quality. Phase bathymetry was used to generate a synthetic sidescan image, which can be compared to the original sidescan image to subtract angle-of-incidence effects from the image brightness, yielding an image of seafloor reflectivity, a proxy for age. Two areas on the AVR (~4km2 and ~6km2, respectively) were surveyed using the MS2000 sonar mounted on the ROV Isis. These microbathymetry data have a resolution of ~0.5m and provide an independent check of the TOBI phase bathymetry processing techniques. Preliminary study of sidescan and bathymetry from the region suggests that the AVR consists of over 8000 individual monogenetic volcanic cones, and our seafloor reflectivity data allow us to investigate temporal variations in volcanic eruptions during the development of the AVR. The combination of comprehensive data coverage and hierarchy of resolutions of these datasets allow for an unprecedented study of the development of this AVR, which in turn allows for the development of new insights into the timing and distribution of the construction of the volcanic seafloor.
The 20th May 2006 lava dome collapse of the Soufrière Hills Volcano, Montserrat, had a total non-... more The 20th May 2006 lava dome collapse of the Soufrière Hills Volcano, Montserrat, had a total non-dense rock equivalent (non-DRE) collapse volume of approximately 115×10 6 m 3. The majority of this volume was deposited into the ocean. The collapse was rapid, 85% of the mobilized volume being removed in just 35 min, giving peak pyroclastic flow flux of 66×10 3 m 3 s −1. Channel and levee facies on the submarine flanks of the volcano and formation of a thick, steep-sided ridge, suggest that the largest and most dense blocks were transported proximally as a high concentration granular flow. Of the submerged volume, 30% was deposited from the base of this granular flow, forming a linear, high-relief ridge that extends 7 km from shore. The remaining 70% of the submerged volume comprises the finer grain sizes, which were transported at least 40 km by turbidity currents on gradients of <2°. At several localities, the May 2006 distal turbidity currents ran up 200 m of topography and eroded up to 20 cm of underlying substrate. Multiple turbidites are preserved, representing current reflection from the graben margins and deflection around topography. The high energy of the May 2006 collapse resulted in longer submarine run out than the larger (210×10 6 m 3) Soufrière Hills dome collapse in July 2003.
Cold-water corals are azooxanthellate species found throughout the ocean at water depths down to ... more Cold-water corals are azooxanthellate species found throughout the ocean at water depths down to 5000 m. They occur in patches, reefs or large mound structures up to 380 m high, and as ecosystem engineers create important habitats for a diverse fauna. However, the majority of these habitats are now within reach of deep-sea bottom trawling. Many have been
severely damaged or are under threat, despite recent protection initiatives. Here we present a cold-water coral habitat type that so far has been overlooked – quite literally – and that has received minimal impact from human activities. Vertical and overhanging cliffs in deep-sea canyons, revealed using an innovative approach to marine habitat mapping, are shown to provide the perfect substratum for extensive cold-water coral-based communities. Typical canyon-related processes, including locally enhanced internal tides and focussed downslope organic carbon transport, provide favourable environmental conditions (current regime, food input) to sustain the communities, even outside the optimal depth and density envelopes reported elsewhere in the NE Atlantic. Our findings show that deep-sea canyons can form natural refuges for faunal communities sensitive to anthropogenic disturbance, and have the potential to fulfil the crucial role of larval sources for the recolonisation of damaged sites elsewhere on the margin.
Submarine Mass Movements and Their Consequences, 2007
The flanks of the Cape Verde Islands Fogo, Brava and Santiago show extensive evidence of past and... more The flanks of the Cape Verde Islands Fogo, Brava and Santiago show extensive evidence of past and potential slope failure. Analyses of bathymetric and subaerial datasets show debris avalanches, turbidite pathways and debris flows, with the transportation of large volumes of rock and sediment. Similarities are seen with many of the processes operating on the flanks of the Canary Islands.
ABSTRACT We present bathymetric and sidescan sonar results from the Mid-Atlantic Ridge between 45... more ABSTRACT We present bathymetric and sidescan sonar results from the Mid-Atlantic Ridge between 45°20&amp;#39;N and 45°44&amp;#39;N, where the axial valley is host to a ~4km wide and ~500m high axial volcanic ridge (AVR). The AVR and surrounding seafloor was surveyed concurrently using: a) the ship-mounted Simrad EM-120 echosounder, yielding bathymetry gridded at a resolution of 50m per pixel, and b) TOBI (Towed Ocean Bottom Instrument), which collected both sidescan sonar data (resolution 3m/pixel) and phase data, which were processed to provide bathymetry with a resolution of 10m/pixel. The TOBI survey entailed two ~45km-long north-south tracks and twenty-two ~15km-long east-west tracks; thus, much of the area was surveyed from up to four orthogonal and reciprocal directions, eliminating most regions of shadow and poor image quality. Phase bathymetry was used to generate a synthetic sidescan image, which can be compared to the original sidescan image to subtract angle-of-incidence effects from the image brightness, yielding an image of seafloor reflectivity, a proxy for age. Two areas on the AVR (~4km2 and ~6km2, respectively) were surveyed using the MS2000 sonar mounted on the ROV Isis. These microbathymetry data have a resolution of ~0.5m and provide an independent check of the TOBI phase bathymetry processing techniques. Preliminary study of sidescan and bathymetry from the region suggests that the AVR consists of over 8000 individual monogenetic volcanic cones, and our seafloor reflectivity data allow us to investigate temporal variations in volcanic eruptions during the development of the AVR. The combination of comprehensive data coverage and hierarchy of resolutions of these datasets allow for an unprecedented study of the development of this AVR, which in turn allows for the development of new insights into the timing and distribution of the construction of the volcanic seafloor.
ABSTRACT A recent survey obtained TOBI sidescan and acoustic phase data at ~ 10 m resolution over... more ABSTRACT A recent survey obtained TOBI sidescan and acoustic phase data at ~ 10 m resolution over a complete axial volcanic ridge (AVR) on the Mid-Atlantic Ridge at 45 degrees N. We have updated earlier software to process the phase data to high resolution bathymetry, including renavigating the data by superposition of common features seen on overlapping swaths. We obtained high quality phase bathymetry over approximately 50% [?} of the AVR. Since we now have precisely co-registered sidescan and bathymetry, we calculated angles of incidence for the sidescan. Comparing this with the recorded backscatter provides a backscatter- versus angle of incidence law. This approximates, but does not exactly fit, a cosine squared relation. By correcting for the varying angle of incidence we obtain an approximation of absolute backscatter levels independent of seafloor slope, and use these to estimate average sediment cover. Since the AVR lies entirely within the Brunhes normal chron, we use the sediment distribution to infer an approximation for crustal age. The sidescan data reveal ~3000 small, probably monogenetic volcanic hummocks within the AVR. With average diameters of ~150 m and heights ~50 m these are barely resolved by ship-based multibeam bathymetry. By combining the sidescan and phase bathymetry data we carry out a statistical study of the hummock shapes, dimensions and distribution.
ABSTRACT Deep towed side-scan sonar vehicles acquire high quality imagery of the seafloor morphol... more ABSTRACT Deep towed side-scan sonar vehicles acquire high quality imagery of the seafloor morphology with very high spatial resolution but poor overall locational accuracy. Correlation and comparison of the side-scan sonar data (TOBI) with bathymetry data is highly desirable to enhance seafloor modelling, and to derive further geological interpretations which were previously hidden or confused. It also improves data confidence and aid the data processing in areas such as slant-range correction and texture analysis. However the main obstacle is positional registration of the two datasets. Hydrosweep bathymetry has relatively accurate satellite positioning (via GPS) though its spatial resolution is significantly less than TOBI imagery. The usual method for satellite registration requires picking of ground controls points, on features such as road junctions, large buildings and held corners. These features are not present on the seafloor and thus a different method is required. A two stage process is suggested firstly taking an edge detector over both datasets and secondly using Chamfer matching to find the best fit of the edges. The method is fully automatic and quick. Once registration is complete, comparison of the data is possible and processing improved. For example slant-range correction can now be improved, and normalisation (removal of topographic bias) on the side-scan imagery has been attempted
An extensive dataset of shallow sediment cores is used here to describe one of the World's mo... more An extensive dataset of shallow sediment cores is used here to describe one of the World's most voluminous and extensive submarine gravity flows. The Bed 5 event, dated at ~60 ka, originated on the upper slope offshore Atlantic Morocco, in the vicinity of Agadir Canyon. The volume of initial failure was ~130 km3 of sediment, and the failure appeared to
Advances in Natural and Technological Hazards Research, 2013
14 15 The Malta-Sicily Escarpment (MSE) is a steep carbonate escarpment that appears 16 to have l... more 14 15 The Malta-Sicily Escarpment (MSE) is a steep carbonate escarpment that appears 16 to have largely remained isolated from inputs of fluvial and littoral sediments 17 since the Messinian Salinity Crisis. Mass movement activity has so far only been 18 inferred from sediment cores at the base of the MSE. In this study we use geo-19 physical and sedimentological data acquired from the upper MSE and outer Malta 20 Plateau to: (i) map and characterise the dominant forms of mass movements, and 2
Deep towed side-scan sonar vehicles such as TOBI acquire high quality imagery of the seafloor wit... more Deep towed side-scan sonar vehicles such as TOBI acquire high quality imagery of the seafloor with very high spatial resolution but poor locational accuracy. Fusion of the side-scan sonar data with bathymetry data from an independent source is often desirable to reduce ambiguity in geological interpretations, to aid in slant-range correction and to enhance seafloor representation. The main obstacle to
Background: Environmental impacts of human activities on the deep seafloor are of increasing conc... more Background: Environmental impacts of human activities on the deep seafloor are of increasing concern. While activities within waters shallower than 200 m have been the focus of previous assessments of anthropogenic impacts, no study has quantified the extent of individual activities or determined the relative severity of each type of impact in the deep sea.
Cold-water corals are azooxanthellate species found throughout the ocean at water depths down to ... more Cold-water corals are azooxanthellate species found throughout the ocean at water depths down to 5000 m. They occur in patches, reefs or large mound structures up to 380 m high, and as ecosystem engineers create important habitats for a diverse fauna. However, the majority of these habitats are now within reach of deep-sea bottom trawling. Many have been severely damaged or are under threat, despite recent protection initiatives. Here we present a cold-water coral habitat type that so far has been overlooked -quite literally -and that has received minimal impact from human activities. Vertical and overhanging cliffs in deep-sea canyons, revealed using an innovative approach to marine habitat mapping, are shown to provide the perfect substratum for extensive cold-water coral-based communities. Typical canyon-related processes, including locally enhanced internal tides and focussed downslope organic carbon transport, provide favourable environmental conditions (current regime, food input) to sustain the communities, even outside the optimal depth and density envelopes reported elsewhere in the NE Atlantic. Our findings show that deep-sea canyons can form natural refuges for faunal communities sensitive to anthropogenic disturbance, and have the potential to fulfil the crucial role of larval sources for the recolonisation of damaged sites elsewhere on the margin. Citation: Huvenne VAI, Tyler PA, Masson DG, Fisher EH, Hauton C, et al. (2011) A Picture on the Wall: Innovative Mapping Reveals Cold-Water Coral Refuge in Submarine Canyon. PLoS ONE 6(12): e28755.
Carbonate escarpments are submarine limestone and dolomite cliffs that have been documented in nu... more Carbonate escarpments are submarine limestone and dolomite cliffs that have been documented in numerous sites around the world. Their geomorphic evolution is poorly understood due to difficulties in assessing escarpment outcrops and the limited resolution achieved by geophysical techniques across their steep topographies. The geomorphic evolution of carbonate escarpments in the Mediterranean Sea has been influenced by the Messinian salinity crisis (MSC). During the MSC (5.97-5.33 Ma), the Mediterranean Sea became a saline basin due to a temporary restriction of the Atlantic-Mediterranean seaway, resulting in the deposition of more than one million cubic kilometres of salt. The extent and relative chronology of the evaporative drawdown phases associated to the MSC remain poorly constrained. In this paper we combine geophysical and sedimentological data from the central Mediterranean Sea to reconstruct the geomorphic evolution of the Malta Escarpment and infer the extent and timing of evaporative drawdown in the eastern Mediterranean Sea during the MSC. We propose that, during a MSC base-level fall, fluvial erosion formed a dense network of canyons across the Malta Escarpment whilst coastal erosion developed extensive palaeoshorelines and shore platforms. The drivers of geomorphic evolution of the Malta Escarpment after the MSC include: (i) canyon erosion by submarine gravity flows, with the most recent activity taking place <2600 cal. years BP; (ii) deposition by bottom currents across the entire depth range of the Malta Escarpment; (iii) tectonic deformation in the southern Malta Escarpment in association with a wrench zone; (iv) widespread, small-scale sedimentary slope failures preconditioned by oversteepening and loss of support due to canyon erosion, and triggered by earthquakes. 3 We carry out an isostatic restoration of the palaeoshorelines and shore platforms on the northern Malta Escarpment to infer an evaporative drawdown of 1800-2000 m in the eastern Mediterranean Sea during the MSC. We interpret the occurrence of pre-evaporite sedimentary lobes in the western Ionian Basin as suggesting that either evaporative drawdown and canyon formation predominantly occurred before salt deposition, or that only the latest salt deposition at the basin margin occurred after the formation of the sedimentary lobes.
In this paper we present the seabed maps of the shallow-water areas of Lampedusa and Linosa, belo... more In this paper we present the seabed maps of the shallow-water areas of Lampedusa and Linosa, belonging to the Pelagie Islands Marine Protected Area. Two surveys were carried out ("Lampedusa2015" and "Linosa2016") to collect bathymetric and acoustic backscatter data through the use of a Reson SeaBat 7125 high-resolution multibeam system. Ground-truth data, in the form of grab samples and diver video-observations, were also collected during both surveys. Sediment samples were analyzed for grain size, while video images were analyzed and described revealing the acoustic seabed and other bio-physical characteristics. A map of seabed classification, including sediment types and seagrass distribution, was produced using the tool Remote Sensing Object Based Image Analysis (RSOBIA) by integrating information derived from backscatter data and bathy-morphological features, validated by ground-truth data. This allows to create a first seabed maps (i.e. benthoscape classification), of Lampedusa and Linosa, at scale 1:20 000 and 1: 32 000, respectively, that will be checked and implemented through further surveys. The results point out a very rich and largely variable marine ecosystem on the seabed surrounding the two islands, with
ABSTRACT We present bathymetric and sidescan sonar results from the Mid-Atlantic Ridge between 45... more ABSTRACT We present bathymetric and sidescan sonar results from the Mid-Atlantic Ridge between 45°20&amp;#39;N and 45°44&amp;#39;N, where the axial valley is host to a ~4km wide and ~500m high axial volcanic ridge (AVR). The AVR and surrounding seafloor was surveyed concurrently using: a) the ship-mounted Simrad EM-120 echosounder, yielding bathymetry gridded at a resolution of 50m per pixel, and b) TOBI (Towed Ocean Bottom Instrument), which collected both sidescan sonar data (resolution 3m/pixel) and phase data, which were processed to provide bathymetry with a resolution of 10m/pixel. The TOBI survey entailed two ~45km-long north-south tracks and twenty-two ~15km-long east-west tracks; thus, much of the area was surveyed from up to four orthogonal and reciprocal directions, eliminating most regions of shadow and poor image quality. Phase bathymetry was used to generate a synthetic sidescan image, which can be compared to the original sidescan image to subtract angle-of-incidence effects from the image brightness, yielding an image of seafloor reflectivity, a proxy for age. Two areas on the AVR (~4km2 and ~6km2, respectively) were surveyed using the MS2000 sonar mounted on the ROV Isis. These microbathymetry data have a resolution of ~0.5m and provide an independent check of the TOBI phase bathymetry processing techniques. Preliminary study of sidescan and bathymetry from the region suggests that the AVR consists of over 8000 individual monogenetic volcanic cones, and our seafloor reflectivity data allow us to investigate temporal variations in volcanic eruptions during the development of the AVR. The combination of comprehensive data coverage and hierarchy of resolutions of these datasets allow for an unprecedented study of the development of this AVR, which in turn allows for the development of new insights into the timing and distribution of the construction of the volcanic seafloor.
The 20th May 2006 lava dome collapse of the Soufrière Hills Volcano, Montserrat, had a total non-... more The 20th May 2006 lava dome collapse of the Soufrière Hills Volcano, Montserrat, had a total non-dense rock equivalent (non-DRE) collapse volume of approximately 115×10 6 m 3. The majority of this volume was deposited into the ocean. The collapse was rapid, 85% of the mobilized volume being removed in just 35 min, giving peak pyroclastic flow flux of 66×10 3 m 3 s −1. Channel and levee facies on the submarine flanks of the volcano and formation of a thick, steep-sided ridge, suggest that the largest and most dense blocks were transported proximally as a high concentration granular flow. Of the submerged volume, 30% was deposited from the base of this granular flow, forming a linear, high-relief ridge that extends 7 km from shore. The remaining 70% of the submerged volume comprises the finer grain sizes, which were transported at least 40 km by turbidity currents on gradients of <2°. At several localities, the May 2006 distal turbidity currents ran up 200 m of topography and eroded up to 20 cm of underlying substrate. Multiple turbidites are preserved, representing current reflection from the graben margins and deflection around topography. The high energy of the May 2006 collapse resulted in longer submarine run out than the larger (210×10 6 m 3) Soufrière Hills dome collapse in July 2003.
Cold-water corals are azooxanthellate species found throughout the ocean at water depths down to ... more Cold-water corals are azooxanthellate species found throughout the ocean at water depths down to 5000 m. They occur in patches, reefs or large mound structures up to 380 m high, and as ecosystem engineers create important habitats for a diverse fauna. However, the majority of these habitats are now within reach of deep-sea bottom trawling. Many have been
severely damaged or are under threat, despite recent protection initiatives. Here we present a cold-water coral habitat type that so far has been overlooked – quite literally – and that has received minimal impact from human activities. Vertical and overhanging cliffs in deep-sea canyons, revealed using an innovative approach to marine habitat mapping, are shown to provide the perfect substratum for extensive cold-water coral-based communities. Typical canyon-related processes, including locally enhanced internal tides and focussed downslope organic carbon transport, provide favourable environmental conditions (current regime, food input) to sustain the communities, even outside the optimal depth and density envelopes reported elsewhere in the NE Atlantic. Our findings show that deep-sea canyons can form natural refuges for faunal communities sensitive to anthropogenic disturbance, and have the potential to fulfil the crucial role of larval sources for the recolonisation of damaged sites elsewhere on the margin.
Submarine Mass Movements and Their Consequences, 2007
The flanks of the Cape Verde Islands Fogo, Brava and Santiago show extensive evidence of past and... more The flanks of the Cape Verde Islands Fogo, Brava and Santiago show extensive evidence of past and potential slope failure. Analyses of bathymetric and subaerial datasets show debris avalanches, turbidite pathways and debris flows, with the transportation of large volumes of rock and sediment. Similarities are seen with many of the processes operating on the flanks of the Canary Islands.
ABSTRACT We present bathymetric and sidescan sonar results from the Mid-Atlantic Ridge between 45... more ABSTRACT We present bathymetric and sidescan sonar results from the Mid-Atlantic Ridge between 45°20&amp;#39;N and 45°44&amp;#39;N, where the axial valley is host to a ~4km wide and ~500m high axial volcanic ridge (AVR). The AVR and surrounding seafloor was surveyed concurrently using: a) the ship-mounted Simrad EM-120 echosounder, yielding bathymetry gridded at a resolution of 50m per pixel, and b) TOBI (Towed Ocean Bottom Instrument), which collected both sidescan sonar data (resolution 3m/pixel) and phase data, which were processed to provide bathymetry with a resolution of 10m/pixel. The TOBI survey entailed two ~45km-long north-south tracks and twenty-two ~15km-long east-west tracks; thus, much of the area was surveyed from up to four orthogonal and reciprocal directions, eliminating most regions of shadow and poor image quality. Phase bathymetry was used to generate a synthetic sidescan image, which can be compared to the original sidescan image to subtract angle-of-incidence effects from the image brightness, yielding an image of seafloor reflectivity, a proxy for age. Two areas on the AVR (~4km2 and ~6km2, respectively) were surveyed using the MS2000 sonar mounted on the ROV Isis. These microbathymetry data have a resolution of ~0.5m and provide an independent check of the TOBI phase bathymetry processing techniques. Preliminary study of sidescan and bathymetry from the region suggests that the AVR consists of over 8000 individual monogenetic volcanic cones, and our seafloor reflectivity data allow us to investigate temporal variations in volcanic eruptions during the development of the AVR. The combination of comprehensive data coverage and hierarchy of resolutions of these datasets allow for an unprecedented study of the development of this AVR, which in turn allows for the development of new insights into the timing and distribution of the construction of the volcanic seafloor.
ABSTRACT A recent survey obtained TOBI sidescan and acoustic phase data at ~ 10 m resolution over... more ABSTRACT A recent survey obtained TOBI sidescan and acoustic phase data at ~ 10 m resolution over a complete axial volcanic ridge (AVR) on the Mid-Atlantic Ridge at 45 degrees N. We have updated earlier software to process the phase data to high resolution bathymetry, including renavigating the data by superposition of common features seen on overlapping swaths. We obtained high quality phase bathymetry over approximately 50% [?} of the AVR. Since we now have precisely co-registered sidescan and bathymetry, we calculated angles of incidence for the sidescan. Comparing this with the recorded backscatter provides a backscatter- versus angle of incidence law. This approximates, but does not exactly fit, a cosine squared relation. By correcting for the varying angle of incidence we obtain an approximation of absolute backscatter levels independent of seafloor slope, and use these to estimate average sediment cover. Since the AVR lies entirely within the Brunhes normal chron, we use the sediment distribution to infer an approximation for crustal age. The sidescan data reveal ~3000 small, probably monogenetic volcanic hummocks within the AVR. With average diameters of ~150 m and heights ~50 m these are barely resolved by ship-based multibeam bathymetry. By combining the sidescan and phase bathymetry data we carry out a statistical study of the hummock shapes, dimensions and distribution.
ABSTRACT Deep towed side-scan sonar vehicles acquire high quality imagery of the seafloor morphol... more ABSTRACT Deep towed side-scan sonar vehicles acquire high quality imagery of the seafloor morphology with very high spatial resolution but poor overall locational accuracy. Correlation and comparison of the side-scan sonar data (TOBI) with bathymetry data is highly desirable to enhance seafloor modelling, and to derive further geological interpretations which were previously hidden or confused. It also improves data confidence and aid the data processing in areas such as slant-range correction and texture analysis. However the main obstacle is positional registration of the two datasets. Hydrosweep bathymetry has relatively accurate satellite positioning (via GPS) though its spatial resolution is significantly less than TOBI imagery. The usual method for satellite registration requires picking of ground controls points, on features such as road junctions, large buildings and held corners. These features are not present on the seafloor and thus a different method is required. A two stage process is suggested firstly taking an edge detector over both datasets and secondly using Chamfer matching to find the best fit of the edges. The method is fully automatic and quick. Once registration is complete, comparison of the data is possible and processing improved. For example slant-range correction can now be improved, and normalisation (removal of topographic bias) on the side-scan imagery has been attempted
An extensive dataset of shallow sediment cores is used here to describe one of the World's mo... more An extensive dataset of shallow sediment cores is used here to describe one of the World's most voluminous and extensive submarine gravity flows. The Bed 5 event, dated at ~60 ka, originated on the upper slope offshore Atlantic Morocco, in the vicinity of Agadir Canyon. The volume of initial failure was ~130 km3 of sediment, and the failure appeared to
Advances in Natural and Technological Hazards Research, 2013
14 15 The Malta-Sicily Escarpment (MSE) is a steep carbonate escarpment that appears 16 to have l... more 14 15 The Malta-Sicily Escarpment (MSE) is a steep carbonate escarpment that appears 16 to have largely remained isolated from inputs of fluvial and littoral sediments 17 since the Messinian Salinity Crisis. Mass movement activity has so far only been 18 inferred from sediment cores at the base of the MSE. In this study we use geo-19 physical and sedimentological data acquired from the upper MSE and outer Malta 20 Plateau to: (i) map and characterise the dominant forms of mass movements, and 2
Deep towed side-scan sonar vehicles such as TOBI acquire high quality imagery of the seafloor wit... more Deep towed side-scan sonar vehicles such as TOBI acquire high quality imagery of the seafloor with very high spatial resolution but poor locational accuracy. Fusion of the side-scan sonar data with bathymetry data from an independent source is often desirable to reduce ambiguity in geological interpretations, to aid in slant-range correction and to enhance seafloor representation. The main obstacle to
Background: Environmental impacts of human activities on the deep seafloor are of increasing conc... more Background: Environmental impacts of human activities on the deep seafloor are of increasing concern. While activities within waters shallower than 200 m have been the focus of previous assessments of anthropogenic impacts, no study has quantified the extent of individual activities or determined the relative severity of each type of impact in the deep sea.
Cold-water corals are azooxanthellate species found throughout the ocean at water depths down to ... more Cold-water corals are azooxanthellate species found throughout the ocean at water depths down to 5000 m. They occur in patches, reefs or large mound structures up to 380 m high, and as ecosystem engineers create important habitats for a diverse fauna. However, the majority of these habitats are now within reach of deep-sea bottom trawling. Many have been severely damaged or are under threat, despite recent protection initiatives. Here we present a cold-water coral habitat type that so far has been overlooked -quite literally -and that has received minimal impact from human activities. Vertical and overhanging cliffs in deep-sea canyons, revealed using an innovative approach to marine habitat mapping, are shown to provide the perfect substratum for extensive cold-water coral-based communities. Typical canyon-related processes, including locally enhanced internal tides and focussed downslope organic carbon transport, provide favourable environmental conditions (current regime, food input) to sustain the communities, even outside the optimal depth and density envelopes reported elsewhere in the NE Atlantic. Our findings show that deep-sea canyons can form natural refuges for faunal communities sensitive to anthropogenic disturbance, and have the potential to fulfil the crucial role of larval sources for the recolonisation of damaged sites elsewhere on the margin. Citation: Huvenne VAI, Tyler PA, Masson DG, Fisher EH, Hauton C, et al. (2011) A Picture on the Wall: Innovative Mapping Reveals Cold-Water Coral Refuge in Submarine Canyon. PLoS ONE 6(12): e28755.
Uploads
Papers by Tim Le Bas
severely damaged or are under threat, despite recent protection initiatives. Here we present a cold-water coral habitat type that so far has been overlooked – quite literally – and that has received minimal impact from human activities. Vertical and overhanging cliffs in deep-sea canyons, revealed using an innovative approach to marine habitat mapping, are shown to provide the perfect substratum for extensive cold-water coral-based communities. Typical canyon-related processes, including locally enhanced internal tides and focussed downslope organic carbon transport, provide favourable environmental conditions (current regime, food input) to sustain the communities, even outside the optimal depth and density envelopes reported elsewhere in the NE Atlantic. Our findings show that deep-sea canyons can form natural refuges for faunal communities sensitive to anthropogenic disturbance, and have the potential to fulfil the crucial role of larval sources for the recolonisation of damaged sites elsewhere on the margin.
severely damaged or are under threat, despite recent protection initiatives. Here we present a cold-water coral habitat type that so far has been overlooked – quite literally – and that has received minimal impact from human activities. Vertical and overhanging cliffs in deep-sea canyons, revealed using an innovative approach to marine habitat mapping, are shown to provide the perfect substratum for extensive cold-water coral-based communities. Typical canyon-related processes, including locally enhanced internal tides and focussed downslope organic carbon transport, provide favourable environmental conditions (current regime, food input) to sustain the communities, even outside the optimal depth and density envelopes reported elsewhere in the NE Atlantic. Our findings show that deep-sea canyons can form natural refuges for faunal communities sensitive to anthropogenic disturbance, and have the potential to fulfil the crucial role of larval sources for the recolonisation of damaged sites elsewhere on the margin.