During the Deepwater Horizon oil spill in 2010 we used vessel mounted single beam echo sounders t... more During the Deepwater Horizon oil spill in 2010 we used vessel mounted single beam echo sounders to acoustically map gas seeps (both natural and from the capped Macondo wellhead) and, in one instance, leaking oil as it rose through the water column. In 2011, we returned to the area surrounding the Macondo wellhead with a 30 kHz multibeam echo sounder in order to test our ability to systematically map gas seeps in the water column. In both of these cases the acoustic systems offered an efficient means of gaining a synoptic view of the environment resulting, for example, in 100\u27s of multibeam echo sounder observations of natural gas seeps collected over the course of only a few days. Estimates of flow rate have been made based on assumptions about droplet/bubble size and composition; measurements of these parameters are required in order to unambiguously determine quantities of interest such as flux rate
Quantitative analyses of multibeam sonar backscatter data have become increasingly important for ... more Quantitative analyses of multibeam sonar backscatter data have become increasingly important for a range of applications. A critical requirement for these applications is the ability to analyze the spatial and temporal variations of the backscatter data within a single survey or among several different surveys. In this paper, two backscatter surveys in Portsmouth Harbor, NH are used to evaluate different comparison techniques and infer the data requirements for comparison. The backscatter surveys were conducted in June 2007 by University of New Hampshire (UNH) and in September 2007 by Kongsberg in support of this conference. Both data sets were collected using an EM 3002D (300 kHz) installed on UNH’s R/V Coastal Surveyor. A video survey and bottom grab samples collected in December, 2007 indicated that the study area is comprised of rocky outcrops, flat sandy regions, gravel bottoms, and some gravel and sand ripples.
The crash of SwissAir Flight 111, off Nova Scotia in September 1998, triggered one of the largest... more The crash of SwissAir Flight 111, off Nova Scotia in September 1998, triggered one of the largest seabed search surveys in Canadian history. The primary search tools used were sidescan sonars (both conventional and focussed types) and multibeam sonars. The processed search data needed to be distributed on a daily basis to other elements of the fleet for precise location of divers and other optical seabed search instruments (including laser linescan and ROV video). As a result of the glacial history of the region, many natural targets, similar in gross nature to aircraft debris were present. These included widespread linear bedrock outcrop patterns together with near ubiquitous glacial erratic boulders. Because of the severely broken-up nature of the remaining aircraft debris, sidescan imaging alone was often insufficient to unambiguously identify targets. The complementary attributes of higher resolution, but poorly located, sidescan imagery together with slightly lower resolution, ...
Between 2008-2012, as part of the U.S. Extended Continental Shelf project in the Amerasia Basin, ... more Between 2008-2012, as part of the U.S. Extended Continental Shelf project in the Amerasia Basin, Arctic Ocean, 17 dredges were successfully collected sampling the first rock outcrops in the Chukchi Borderland and surrounding regions for the purpose of describing the geologic nature of the bathymetric features in this area. Multiple lines of evidence indicate that the specimens were collected from submarine rock exposures and were not samples of ice rafted debris, common in the ice covered waters of the Arctic Ocean. Using the USCGC Healy, each dredge was collected along very steep slopes (\u3e35 degrees) measured with high resolution multibeam swath bathymety data. Each haul yielded samples of similar lithologies and identical metamorphic grade with manganese crusts on the surfaces exposed to seawater and fresh surfaces where the rocks were broken from outcrop. High tension pulls on the dredge line also indicated sampling of bedrock exposures. Dredged samples from a normal fault scarp in the central Chukchi Borderland consisted of Silurian (c. 430 Ma) orthogneisses that intruded older (c. 487-500 Ma) gabbros and luecogranties that were all metamorphosed to amphibolite grade (Brumley et al., 2011). Samples from the northern Northwind Ridge consisted of metasediments (greenschist facies) interpreted to have been deposited in a proximal arc setting with detrital zircon U-Pb age peaks at 434, 980 Ma with lesser peaks between 500-600, 1100-2000 Ma, and rare 2800 Ma grains (Brumley et al, 2010). Other dredges in the region of the Northwind Ridge yielded deformed and metamorphosed calcareous sandstones and low-grade phyllites (O\u27Brien et al., 2013). Taken together these rocks indicate a relationship to the Pearya Terrane of northern Ellesmere Island and S.W. Svalbard that were thought to represent a Cambro-Ordovician volcanic arc terrane that was involved in Caledonian orogenesis (Brumley et al., 2011). These findings constrain plate tectonic reconstruction models and bring into question long held ideas that the Chukchi Borderland was made up of an undeformed platformal sequence that was part of the Laurentian passive margin from Proterozoic through Jurassic time (e.g. Grantz et al., 1998). Dredges collected along fault scarps that border the edges of the Nautilus Basin yielded undeformed but highly altered volcaniclastic rocks that were deposited in a shallow water setting and contain primary potassium feldspar phenocrysts that are not associated with mafic magmas. Also in this region, several dredges contained undeformed Late Cretaceous (112, 88-80 Ma) basalts (Andronikov et al., 2008; Mukasa et al., 2009) interpreted to have been derived from a continental lithospheric source similar to continental flood basalts from other regions (Mukasa et al., 2009). These dredged rock samples not only have implications for the Extended Continental Shelf projects of Arctic nations, but add greatly to the body of geologic information about the history of the Arctic Ocean and provide the first ground truth as to the nature of the bathymetric features within the Amerasia Basin
The Chukchi Borderland (CB) is a bathymetric high in the Arctic Ocean that is extended by N-S and... more The Chukchi Borderland (CB) is a bathymetric high in the Arctic Ocean that is extended by N-S and E-W striking faults. Based on sediment cores of talus slope fragments at the base of the Northwind Ridge (NWR), basement of the CB was previously interpreted as a Paleozoic platform sequence comparable to passive margin strata of western Laurentia (Grantz et al., 1998). The discovery of Silurian (~430 Ma) orthogneiss dredged from a fault scarp in the central CB suggests instead that the CB is a displaced fragment of the Caledonian orogen (Brumley et al., 2008). U-Pb geochronology of zircon suites from rocks dredged from the NWR and central CB fault scarps help resolve the make-up of the CB basement. Samples from the central CB are believed to represent the country rocks of the previously dated Silurian orthogneiss. They consist mostly of paragneiss and lesser orthogneiss intruded by leucosomal segregations, all deformed and metamorphosed to amphibolite facies with assemblages Qtz Kfs Plag Bt Grt ± Ms ± Chl (retrograde) with accessory zircon, sphene and apatite. The abundance of Kfs Plag Bt in paragneiss samples suggest a volcanogenic sediment protolith. Dynamic recrystallization of quartz by grain-boundary migration and recrystallization/myrmekite development along the edges of feldspar crystals suggest final deformation at temperatures of ~450 C. U-Pb geochronology of zircon from an orthogneiss sample from the central CB yields an age of 499.2 ± 0.9 Ma with late Neoproterozoic (600 Ma) and Mesoproterozoic - early Paleoproterozoic (1100-1700 Ma) grains. Detrital zircon geochronology from four paragneiss samples show a broad range of ages between 480-650 Ma with a dominant age peak ~500 Ma. Lesser, mostly discordant, Mesoproterozoic and Paleoproterozoic zircons are also present. The paragneiss sampled represent an arc-proximal sediment intruded by Silurian granitoids. Dredge samples from the NWR consist of deformed and metamorphosed calcareous sandstones, low-grade phyllites and highly altered but undeformed basalts. Low-grade (sub to greenschist facies) deformation is indicated by pressure solution cleavage in phyllites and minor recrystallization of quartz in sandstones. Detrital zircons from a silty phyllite from the NWR display age peaks of 1070-1170, 1600-2000 and 2300-3000 Ma. These peaks are known to be characteristic of sediments deposited along the northern passive margin of Laurentia, developed as the result of the breakup of Rodinia in the Late Precambrian and existing as a passive margin until the onset of the Caledonian orogeny. The contrasting rock types and geochronology from this study of dredged bedrock from the CB suggest the juxtaposition of a Cambro-Ordovician volcanic arc terrane intruded by Silurian granitoids with sedimentary rocks representing the northern margin of Laurentia, thus providing a more accurate geologic tie point of the Chukchi Borderland back to the region of Pearya, Lomonosov Ridge and Svalbard. This new data argues against previous interpretations of the CB as part of the Proterozoic to Jurassic passive margin of western Laurentia (Grantz et al. 1998) as well as the restoration of CB to the Chukotka margin of Russia (Lawver et al. 2011)
Coastal settings are complicated by seabed sediment and bedform variability that often exist at s... more Coastal settings are complicated by seabed sediment and bedform variability that often exist at spatial scales on the order of 1-10s m, well below either numerical model grid size or satellite-based observational scales. This pronounced spatiotemporal heterogeneity is a critical first-order factor in determining sediment transport and seabed geoacoustic properties. Being able to map this heterogeneity using remote acoustic methods is a critical component of predictive sea floor modeling efforts. We present recent results of a small autonomous underwater vehicle (AUV) equipped with an advanced phase measuring bathymetric sonar system (PMBS) for shallow seafloor mapping. The development of multibeam echo-sounders to look at the angular dependence of the acoustic response of the seafloor has opened up new possibilities with respect to seafloor characterization. The angular response of the echo holds important information about seafloor roughness and volume reverberation, as well as acoustic impedance. In this work, we employ a physics-based model known as ARA (Angular Response Analysis) that uses the angular dependence of backscatter for the remote prediction of seafloor properties. The ARA technique corrects sonar backscatter for radiometric and geometric factors, parameterizes the corrected angular response curve, and applies a constrained inversion to solve for seafloor properties such as roughness and grain size. The AUV configuration in this study has been designed specifically with coastal seafloor mapping studies in mind. To this end the AUV is configured with a 500 kHz phase measuring bathymetric sonar (PMBS) for collocated micro-bathymetry and backscatter intensity. One of the key features of the PMBS is that it collects simultaneous digital side-scan data with the bathymetry, which is used in mapping and classifying the seafloor bottom type via implementation of ARA. We present examples of efforts to implement automated classification systems to the AUV gathered bathymetric sonar data. Field data collection was conducted in July 2009 in Nantucket Sound and in the vicinity of the Martha’s Vineyard Coastal Observatory (MVCO). The AUV was operated at depths between 8-20 m deep, flying survey patterns at a constant 6 m altitude and accumulating a total of \u3e50 km of trackline survey over 3 days of missions. The surveys were run with parallel lines up to 1.9 km long spaced at 10 to 30 m. The MVCO location possesses a very broad range of sediment textural composition ranging from well-sorted fine sand to poorly sorted gravelly sand. Having collected data in the same area as part of the ONR Mine Burial Program allows us to leverage the previous data sets of backscatter, bathymetry, and ground-truthing sediment samples for use in comparing our approach using Angular Response Analysis for sediment inversion. The July surveys off of Martha’s Vineyard demonstrated the ability of the AUV to conduct high-resolution detailed seabed mapping in a shallow energetic coast
In the seismic reflection method, it is well known that seismic amplitude varies with the offset ... more In the seismic reflection method, it is well known that seismic amplitude varies with the offset between the seismic source and detector and that this variation is a key to the direct determination of lithology and pore fluid content of subsurface strata. Based on this fundamental property, amplitude-versus-offset (AVO) analysis has been used successfully in the oil industry for the exploration and characterization of subsurface reservoirs. Multibeam sonars acquire acoustic backscatter over a wide range of incidence angles and the variation of the backscatter with the angle of incidence is an intrinsic property of the seafloor. Building on this analogy, we have adapted an AVO-like approach for the analysis of acoustic backscatter from multibeam sonar data. The analysis starts with the beam-by-beam time-series of acoustic backscatter provided by the multibeam sonar and then corrects the backscatter for seafloor slope (i.e. true incidence angle), time varying and angle varying gains, ...
Journal of Geophysical Research: Solid Earth, 2020
Submarine volcanism in the western Arctic Ocean, known as Amerasia Basin, is attributed to a mant... more Submarine volcanism in the western Arctic Ocean, known as Amerasia Basin, is attributed to a mantle plume based on geophysics and meager geochemical evidence. Basaltic samples dredged from Chukchi Borderland within the basin have produced minimum 40Ar/39Ar ages for eruption at circa 118–112, circa 105–100, and circa 90–70 Ma, which we use to constrain tectonic models for basin opening. Major oxide and trace element concentrations and Sr, Nd, and Hf isotopic ratios of the lavas show that the circa 118–112 Ma samples from Northwind Ridge are tholeiites (low‐Ti tholeiite I) with low degrees of rare‐earth element (REE) fractionation, high overall heavy rare‐earth element (HREE), and Mg# (Mg‐number), which suggests magma derivation from a garnet‐free source followed by minor crystal fractionation. Strontium, Nd, and Hf isotope systematics for these lavas and ratios of highly incompatible trace elements point toward a lithospheric source. Eruptions at circa 105–100 and circa 90–70 Ma, bot...
Ice sheets extending over parts of the East Siberian continental shelf have been proposed during ... more Ice sheets extending over parts of the East Siberian continental shelf have been proposed during the last glacial period, and during the larger Pleistocene glaciations. The sparse data available over this sector of the Arctic Ocean has left the timing, extent and even existence of these ice sheets largely unresolved. Here we present new geophysical mapping and sediment coring data from the East Siberian shelf and slope collected during the 2014 SWERUS-C3 expedition (SWERUS-C3: Swedish – Russian – US Arctic Ocean Investigation of Climate-Cryosphere-Carbon Interactions). The multibeam bathymetry and chirp sub-bottom profiles reveal a set of glacial landforms that include grounding zone formations along the outer continental shelf, seaward of which lies a >65 m thick sequence of glaciogenic debris flows. The glacial landforms are interpreted to lie at the seaward end of a glacial trough – the first to be reported on the East Siberian margin, here referred to as the...
During the Deepwater Horizon oil spill in 2010 we used vessel mounted single beam echo sounders t... more During the Deepwater Horizon oil spill in 2010 we used vessel mounted single beam echo sounders to acoustically map gas seeps (both natural and from the capped Macondo wellhead) and, in one instance, leaking oil as it rose through the water column. In 2011, we returned to the area surrounding the Macondo wellhead with a 30 kHz multibeam echo sounder in order to test our ability to systematically map gas seeps in the water column. In both of these cases the acoustic systems offered an efficient means of gaining a synoptic view of the environment resulting, for example, in 100\u27s of multibeam echo sounder observations of natural gas seeps collected over the course of only a few days. Estimates of flow rate have been made based on assumptions about droplet/bubble size and composition; measurements of these parameters are required in order to unambiguously determine quantities of interest such as flux rate
Quantitative analyses of multibeam sonar backscatter data have become increasingly important for ... more Quantitative analyses of multibeam sonar backscatter data have become increasingly important for a range of applications. A critical requirement for these applications is the ability to analyze the spatial and temporal variations of the backscatter data within a single survey or among several different surveys. In this paper, two backscatter surveys in Portsmouth Harbor, NH are used to evaluate different comparison techniques and infer the data requirements for comparison. The backscatter surveys were conducted in June 2007 by University of New Hampshire (UNH) and in September 2007 by Kongsberg in support of this conference. Both data sets were collected using an EM 3002D (300 kHz) installed on UNH’s R/V Coastal Surveyor. A video survey and bottom grab samples collected in December, 2007 indicated that the study area is comprised of rocky outcrops, flat sandy regions, gravel bottoms, and some gravel and sand ripples.
The crash of SwissAir Flight 111, off Nova Scotia in September 1998, triggered one of the largest... more The crash of SwissAir Flight 111, off Nova Scotia in September 1998, triggered one of the largest seabed search surveys in Canadian history. The primary search tools used were sidescan sonars (both conventional and focussed types) and multibeam sonars. The processed search data needed to be distributed on a daily basis to other elements of the fleet for precise location of divers and other optical seabed search instruments (including laser linescan and ROV video). As a result of the glacial history of the region, many natural targets, similar in gross nature to aircraft debris were present. These included widespread linear bedrock outcrop patterns together with near ubiquitous glacial erratic boulders. Because of the severely broken-up nature of the remaining aircraft debris, sidescan imaging alone was often insufficient to unambiguously identify targets. The complementary attributes of higher resolution, but poorly located, sidescan imagery together with slightly lower resolution, ...
Between 2008-2012, as part of the U.S. Extended Continental Shelf project in the Amerasia Basin, ... more Between 2008-2012, as part of the U.S. Extended Continental Shelf project in the Amerasia Basin, Arctic Ocean, 17 dredges were successfully collected sampling the first rock outcrops in the Chukchi Borderland and surrounding regions for the purpose of describing the geologic nature of the bathymetric features in this area. Multiple lines of evidence indicate that the specimens were collected from submarine rock exposures and were not samples of ice rafted debris, common in the ice covered waters of the Arctic Ocean. Using the USCGC Healy, each dredge was collected along very steep slopes (\u3e35 degrees) measured with high resolution multibeam swath bathymety data. Each haul yielded samples of similar lithologies and identical metamorphic grade with manganese crusts on the surfaces exposed to seawater and fresh surfaces where the rocks were broken from outcrop. High tension pulls on the dredge line also indicated sampling of bedrock exposures. Dredged samples from a normal fault scarp in the central Chukchi Borderland consisted of Silurian (c. 430 Ma) orthogneisses that intruded older (c. 487-500 Ma) gabbros and luecogranties that were all metamorphosed to amphibolite grade (Brumley et al., 2011). Samples from the northern Northwind Ridge consisted of metasediments (greenschist facies) interpreted to have been deposited in a proximal arc setting with detrital zircon U-Pb age peaks at 434, 980 Ma with lesser peaks between 500-600, 1100-2000 Ma, and rare 2800 Ma grains (Brumley et al, 2010). Other dredges in the region of the Northwind Ridge yielded deformed and metamorphosed calcareous sandstones and low-grade phyllites (O\u27Brien et al., 2013). Taken together these rocks indicate a relationship to the Pearya Terrane of northern Ellesmere Island and S.W. Svalbard that were thought to represent a Cambro-Ordovician volcanic arc terrane that was involved in Caledonian orogenesis (Brumley et al., 2011). These findings constrain plate tectonic reconstruction models and bring into question long held ideas that the Chukchi Borderland was made up of an undeformed platformal sequence that was part of the Laurentian passive margin from Proterozoic through Jurassic time (e.g. Grantz et al., 1998). Dredges collected along fault scarps that border the edges of the Nautilus Basin yielded undeformed but highly altered volcaniclastic rocks that were deposited in a shallow water setting and contain primary potassium feldspar phenocrysts that are not associated with mafic magmas. Also in this region, several dredges contained undeformed Late Cretaceous (112, 88-80 Ma) basalts (Andronikov et al., 2008; Mukasa et al., 2009) interpreted to have been derived from a continental lithospheric source similar to continental flood basalts from other regions (Mukasa et al., 2009). These dredged rock samples not only have implications for the Extended Continental Shelf projects of Arctic nations, but add greatly to the body of geologic information about the history of the Arctic Ocean and provide the first ground truth as to the nature of the bathymetric features within the Amerasia Basin
The Chukchi Borderland (CB) is a bathymetric high in the Arctic Ocean that is extended by N-S and... more The Chukchi Borderland (CB) is a bathymetric high in the Arctic Ocean that is extended by N-S and E-W striking faults. Based on sediment cores of talus slope fragments at the base of the Northwind Ridge (NWR), basement of the CB was previously interpreted as a Paleozoic platform sequence comparable to passive margin strata of western Laurentia (Grantz et al., 1998). The discovery of Silurian (~430 Ma) orthogneiss dredged from a fault scarp in the central CB suggests instead that the CB is a displaced fragment of the Caledonian orogen (Brumley et al., 2008). U-Pb geochronology of zircon suites from rocks dredged from the NWR and central CB fault scarps help resolve the make-up of the CB basement. Samples from the central CB are believed to represent the country rocks of the previously dated Silurian orthogneiss. They consist mostly of paragneiss and lesser orthogneiss intruded by leucosomal segregations, all deformed and metamorphosed to amphibolite facies with assemblages Qtz Kfs Plag Bt Grt ± Ms ± Chl (retrograde) with accessory zircon, sphene and apatite. The abundance of Kfs Plag Bt in paragneiss samples suggest a volcanogenic sediment protolith. Dynamic recrystallization of quartz by grain-boundary migration and recrystallization/myrmekite development along the edges of feldspar crystals suggest final deformation at temperatures of ~450 C. U-Pb geochronology of zircon from an orthogneiss sample from the central CB yields an age of 499.2 ± 0.9 Ma with late Neoproterozoic (600 Ma) and Mesoproterozoic - early Paleoproterozoic (1100-1700 Ma) grains. Detrital zircon geochronology from four paragneiss samples show a broad range of ages between 480-650 Ma with a dominant age peak ~500 Ma. Lesser, mostly discordant, Mesoproterozoic and Paleoproterozoic zircons are also present. The paragneiss sampled represent an arc-proximal sediment intruded by Silurian granitoids. Dredge samples from the NWR consist of deformed and metamorphosed calcareous sandstones, low-grade phyllites and highly altered but undeformed basalts. Low-grade (sub to greenschist facies) deformation is indicated by pressure solution cleavage in phyllites and minor recrystallization of quartz in sandstones. Detrital zircons from a silty phyllite from the NWR display age peaks of 1070-1170, 1600-2000 and 2300-3000 Ma. These peaks are known to be characteristic of sediments deposited along the northern passive margin of Laurentia, developed as the result of the breakup of Rodinia in the Late Precambrian and existing as a passive margin until the onset of the Caledonian orogeny. The contrasting rock types and geochronology from this study of dredged bedrock from the CB suggest the juxtaposition of a Cambro-Ordovician volcanic arc terrane intruded by Silurian granitoids with sedimentary rocks representing the northern margin of Laurentia, thus providing a more accurate geologic tie point of the Chukchi Borderland back to the region of Pearya, Lomonosov Ridge and Svalbard. This new data argues against previous interpretations of the CB as part of the Proterozoic to Jurassic passive margin of western Laurentia (Grantz et al. 1998) as well as the restoration of CB to the Chukotka margin of Russia (Lawver et al. 2011)
Coastal settings are complicated by seabed sediment and bedform variability that often exist at s... more Coastal settings are complicated by seabed sediment and bedform variability that often exist at spatial scales on the order of 1-10s m, well below either numerical model grid size or satellite-based observational scales. This pronounced spatiotemporal heterogeneity is a critical first-order factor in determining sediment transport and seabed geoacoustic properties. Being able to map this heterogeneity using remote acoustic methods is a critical component of predictive sea floor modeling efforts. We present recent results of a small autonomous underwater vehicle (AUV) equipped with an advanced phase measuring bathymetric sonar system (PMBS) for shallow seafloor mapping. The development of multibeam echo-sounders to look at the angular dependence of the acoustic response of the seafloor has opened up new possibilities with respect to seafloor characterization. The angular response of the echo holds important information about seafloor roughness and volume reverberation, as well as acoustic impedance. In this work, we employ a physics-based model known as ARA (Angular Response Analysis) that uses the angular dependence of backscatter for the remote prediction of seafloor properties. The ARA technique corrects sonar backscatter for radiometric and geometric factors, parameterizes the corrected angular response curve, and applies a constrained inversion to solve for seafloor properties such as roughness and grain size. The AUV configuration in this study has been designed specifically with coastal seafloor mapping studies in mind. To this end the AUV is configured with a 500 kHz phase measuring bathymetric sonar (PMBS) for collocated micro-bathymetry and backscatter intensity. One of the key features of the PMBS is that it collects simultaneous digital side-scan data with the bathymetry, which is used in mapping and classifying the seafloor bottom type via implementation of ARA. We present examples of efforts to implement automated classification systems to the AUV gathered bathymetric sonar data. Field data collection was conducted in July 2009 in Nantucket Sound and in the vicinity of the Martha’s Vineyard Coastal Observatory (MVCO). The AUV was operated at depths between 8-20 m deep, flying survey patterns at a constant 6 m altitude and accumulating a total of \u3e50 km of trackline survey over 3 days of missions. The surveys were run with parallel lines up to 1.9 km long spaced at 10 to 30 m. The MVCO location possesses a very broad range of sediment textural composition ranging from well-sorted fine sand to poorly sorted gravelly sand. Having collected data in the same area as part of the ONR Mine Burial Program allows us to leverage the previous data sets of backscatter, bathymetry, and ground-truthing sediment samples for use in comparing our approach using Angular Response Analysis for sediment inversion. The July surveys off of Martha’s Vineyard demonstrated the ability of the AUV to conduct high-resolution detailed seabed mapping in a shallow energetic coast
In the seismic reflection method, it is well known that seismic amplitude varies with the offset ... more In the seismic reflection method, it is well known that seismic amplitude varies with the offset between the seismic source and detector and that this variation is a key to the direct determination of lithology and pore fluid content of subsurface strata. Based on this fundamental property, amplitude-versus-offset (AVO) analysis has been used successfully in the oil industry for the exploration and characterization of subsurface reservoirs. Multibeam sonars acquire acoustic backscatter over a wide range of incidence angles and the variation of the backscatter with the angle of incidence is an intrinsic property of the seafloor. Building on this analogy, we have adapted an AVO-like approach for the analysis of acoustic backscatter from multibeam sonar data. The analysis starts with the beam-by-beam time-series of acoustic backscatter provided by the multibeam sonar and then corrects the backscatter for seafloor slope (i.e. true incidence angle), time varying and angle varying gains, ...
Journal of Geophysical Research: Solid Earth, 2020
Submarine volcanism in the western Arctic Ocean, known as Amerasia Basin, is attributed to a mant... more Submarine volcanism in the western Arctic Ocean, known as Amerasia Basin, is attributed to a mantle plume based on geophysics and meager geochemical evidence. Basaltic samples dredged from Chukchi Borderland within the basin have produced minimum 40Ar/39Ar ages for eruption at circa 118–112, circa 105–100, and circa 90–70 Ma, which we use to constrain tectonic models for basin opening. Major oxide and trace element concentrations and Sr, Nd, and Hf isotopic ratios of the lavas show that the circa 118–112 Ma samples from Northwind Ridge are tholeiites (low‐Ti tholeiite I) with low degrees of rare‐earth element (REE) fractionation, high overall heavy rare‐earth element (HREE), and Mg# (Mg‐number), which suggests magma derivation from a garnet‐free source followed by minor crystal fractionation. Strontium, Nd, and Hf isotope systematics for these lavas and ratios of highly incompatible trace elements point toward a lithospheric source. Eruptions at circa 105–100 and circa 90–70 Ma, bot...
Ice sheets extending over parts of the East Siberian continental shelf have been proposed during ... more Ice sheets extending over parts of the East Siberian continental shelf have been proposed during the last glacial period, and during the larger Pleistocene glaciations. The sparse data available over this sector of the Arctic Ocean has left the timing, extent and even existence of these ice sheets largely unresolved. Here we present new geophysical mapping and sediment coring data from the East Siberian shelf and slope collected during the 2014 SWERUS-C3 expedition (SWERUS-C3: Swedish – Russian – US Arctic Ocean Investigation of Climate-Cryosphere-Carbon Interactions). The multibeam bathymetry and chirp sub-bottom profiles reveal a set of glacial landforms that include grounding zone formations along the outer continental shelf, seaward of which lies a >65 m thick sequence of glaciogenic debris flows. The glacial landforms are interpreted to lie at the seaward end of a glacial trough – the first to be reported on the East Siberian margin, here referred to as the...
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