OS53A-0965
Multibeam Bathymetry Mapping for U.S. UNCLOS Concerns: A Gold Mine for Marine Geology
Since 2003, the University of New Hampshire's Center for Coastal and Ocean Mapping–Joint Hydrographic Center has conducted mapping of several U.S. continental margins in areas where a potential exists for an extended continental shelf as defined under Article 76 of the United Nations Convention on the Law of the Sea. UNH was directed by Congress, through funding to NOAA, to map the bathymetry in areas in the Arctic Ocean, Bering Sea, Gulf of Alaska, Atlantic, Gulf of Mexico, Philippine Sea, and slopes of Kingman Reef and Palmyra Atoll. These new data can be used to accurately locate the 2500-m isobath and to determine the location of the maximum change in gradient at the base of the continental slopes. To achieve these objectives, the area between ~1000 m and ~5000 m isobaths are mapped. The program has mapped >900,000 km2 as of September 2007. The bathymetry data are collected with multibeam echosounders navigated with inertial-aided DGPS and are fully motion compensated. An integral part of the data collection is measurements of the sound-speed profile in the water column to correct for refraction. The data are fully processed at sea. Most cruises also collect 3.5-kHz high-resolution profiles and some have included gravity measurements. All processed bathymetry and associated acoustic backscatter data are immediately available one the web and the raw multibeam datagrams and processed gravity data are archived at NOAA/NGDC. The new data provide a wealth of new information on the geomorphology of the continental margins. The mapping discovered many new features on the U.S. margins, as well as better defined features known to exist but either poorly mapped or mapped with obsolete mapping technology. New features discovered during the surveys include an undiscovered seamount, christened Healy Seamount and a series of huge sediment ridges striking normal to the Barrow margin in the Arctic Ocean; a series of plateaus and ridges north of Bowers Ridge in the Bering Sea; deep-sea channels incising two submarine fans and a meandering channel on a channel levee in the Gulf of Alaska and an almost completely buried seamount of the Bowie-Kodiak Seamount chain; dendritic channel systems trending west from the summit of the West Mariana Ridge, as well as 10 seamount summits <500-m deep also on ridge. Other surprises include what appear to be plunge pools and cascades at the end of steep canyons in water depths of several thousand meter found in the Gulf of Alaska, Bering Sea, Atlantic margin, Gulf of Mexico and the eastern Philippine Sea. Other common features seen in the new bathymetry are intricate channel systems resembling subaerial drainage systems but that have never been subaerial. These have been mapped in the Gulf of Alaska and Atlantic margins and the eastern Philippine Sea. Better-definition of known features include the offshore trace of the Transition Fault and details of Surveyor and Baranoff Fans and Channels in the Gulf of Alaska, a 1200-m high seamount SW of New Jersey on the Atlantic continental rise that was named Knauss Knoll in 1967 but has remained uncharted, 6 bends in Hudson Canyon channel that approach 90 degrees, and a 150-km wide collapsed section of the lower continental slope off New Jersey, and a 20 km wide zone of furrows that run for 200 km roughly parallel to the isobaths of the northern Sigsbee Abyssal Plain adjacent to the Sigsbee Escarpment. http://ccom.unh.edu/law_of_the_sea.html
OS53A-0966
A spatial correlation of the flow distribution on the outer continental shelf of Louisiana during the major hurricanes in the Gulf of Mexico during the 2005 season
The 2005 hurricane season was unusually active, producing 31 named storms in the Atlantic, Caribbean, and Gulf of Mexico. Of these 31 storms, 11 entered the Gulf of Mexico, the most notable of which were Hurricanes Cindy, Dennis, Katrina, and Rita. Data were collected during these storms by acoustic Doppler current profilers (ADCPs) based on 58 oil and gas platforms scattered across the outer continental shelf (OCS) region of the northern Gulf of Mexico. Nine to 31 ADCPs were active and recording data during each major storm passage through the Gulf of Mexico. Data were recorded from depths of 60 to 70m down to 1100 to 1200m, with a few extending to depths around 2000m. From these data, the flow distribution of the OCS region was studied with the use of time series and spectrum analysis. Preliminary analysis has shown temporal variations in the vertical structure, increased diurnal oscillation current velocities (by a factor of approximately two), near-inertial oscillations, and variations in the overall direction of the flow before, during, and after the passage of the hurricanes. Methods of harmonic analysis and rotary spectra were implemented in this study. These data and results provide an estimate of the spatial extent to which a hurricane influences subsurface currents. http://www.ndbc.noaa.gov/maps/ADCP_WestGulf.shtml
OS53A-0967
Influence of margin segmentation and anomalous volcanism upon the break-up of the Hatton Bank rifted margin, west of the UK
The Hatton Bank margin, flanking the Iceland Basin is a widely cited example of a volcanic rifted margin. Prior to this study insights into the break-up history of the margin have been limited to profiles in the north and south, yet whilst valuable, the along margin tectono-magmatic variability has not been revealed. Over 5660 line km of high quality reflection seismic profiles with supplementary multibeam bathymetry were collected to support the UK's claim to Hatton region under the United Nations Convention on Law of the Sea (UNCLOS). Integration of this new data with existing profiles, allowed the margin to be divided into three segments, each of which are flanked by oceanic crust with a smooth upper surface and internal dipping reflectors. The southernmost segment is characterised by a series of inner and outer seaward dipping reflector (SDR) packages, which are separated by an outer high feature. The outer SDR are truncated by Endymion Spur, a chain of steep sided, late stage volcanic cones linked with necks. The central sector has no inner SDR package and is characterised by the presence of a highly intruded continental block, the Hatton Bank Block (HBB). The northern sector is adjacent to Lousy Bank, with a wider region of SDR recognised than to the south and a high amount of volcanic cones imaged. The variations in the distribution of the SDR's along the margin, the presence of the HBB and Endymion Spur all suggest that the break-up process was not uniform alongstrike. The division of the margin into three sectors reveals that structural segmentation played an important role in producing the variations along the margin. Break- up initiated in the south and progressed north producing the SDR packages witnessed, when the HBB was encountered the focus of break-up moved seaward of the block. The northern sector was closer to the Iceland Hotspot and hence a greater amount of volcanism is encountered. The smooth oceanic basement also indicates a high thermal flux leading to high melt production and subsidence rates forming the dipping reflectors. Shortly after break-up the eruption of Endymion Spur occurred. The nature of the magma erupted is unknown but from the steepness of the cones, it is inferred to be viscous and considering the setting, mostly likely a tholeiitic cumulate. A possible trigger for the Endymion Spur is the passage of a pulse of hotter than normal asthenospheric material along the margin, which interacted with lower crustal material to produce melt to feed the volcanic centres. Enhanced asthenospheric heat flow has been invoked to explain the V-shaped ridges along the present day Reykjanes Ridge and it is probable that the Endymion Spur represents previous such pulses along the margin/spreading axis. The location of the enhanced volcanism is itself controlled by crustal segmentation, with the Endymion Spur limited to the southern sector. The crustal thickness in this sector is approx. 2 to 3 km thinner than that found in the central segment, in which Endymion Spur is absent. The role of the segmentation along the margin has influenced the break-up style (presence or absence of SDR) and also the location and nature of post break-up volcanism.
OS53A-0968
Investigations of the bottom current sculpted margin of Hatton Bank, NE Atlantic
The NW Hatton Bank in the NE Atlantic represents a unique opportunity to examine the interaction of bottom currents with complex seabed topography and to analyse the affects on the morphology and distribution of sediments along the margin. The NW Hatton Bank margin is a slope located remote from any major terrigenous sediment supply and at present is over 200 NM from the closest sediment source onshore. The data presented in this study were collected on the research vessel R.R.S. Charles Darwin in 1999, for the purpose of determining the outer limit of the legal continental shelf according to the United Nations Convention on the Law of the Sea. Swath bathymetry and high resolution acoustic data allow us to evaluate both local and regional controls on slope sedimentation and the possible mechanisms for bottom current velocity variability across a slope setting within the NW European continental margin. The slope is characterised by an intense bottom current flow related to the Deep Northern Boundary Current. Along the slope, bottom-current sedimentation is dominant, leading to the development of the Hatton drift and sediment wave fields. Non-depositional and erosional features related to bottom current activity were also identified and include moats encircling the volcanic cones and deep erosional scours. The interaction between bottom current circulation and complex margin morphology controls the distribution, geometry and scale of the sediment wave fields.
OS53A-0969
A margin transformed: Pure extension to pure translation along the North Falklands Escarpment. Results of Article 76 surveying in the South Atlantic.
The Falklands Plateau comprises an elongate continental block extending eastwards from the Falkland Islands to the Maurice Ewing Bank, 900 kilometres away. While complicated by the transpressive convergence of the Scotia Sea Plate in the South, its margin in the north is characterised by the extreme rectilinearity resulting from its transform separation from the South African craton along the Agulhas Plateau/Ridge system. The translational regime is flanked in the west by the well documented seaward dipping reflector sequences dominating the south Argentine margin, but new and extensive swath bathymetric surveying along the escarpment reveals a transition between the two opening modes characterised by a complex of sheared crustal segments, offset zones, and transform discontinuities. Within this 60 km wide margin parallel zone, en echelon arrays of crustal ‘tears’, many defining a crude tension gash geometry, host submarine elevations, which show varying degrees of rotation in response to the increasing development of shear moment toward the east. We examine the tectonic origin of the ridges in the context of the geological evolution of the margin, their connectivity to the margin, and the comparison with the latest data from the conjugate Agulhas margin off South Africa.
OS53A-0970
Massive Data Collection: Scientists' Nuggets and Basis for the Future
Particularly after the advent of the multi-beam echosounders (aka, swath mapping system), accumulation of high- resolution bathymetric data invoked tremendous impact on marine sciences worldwide. In the last two decades with rapid improvements of the swath-mapping technologies, our knowledge and view of the seafloor made great advancement. Japan as a coastal state has also been conducting quite extensive and intensive "Continental Shelf Survey" for many years now and has benefited from the swath mapping technology as well. Japanese EEZ covers wide area of the northwestern Pacific and shares borders with tectonically complex and scientifically challenged neighboring regions. The "Continental Shelf Survey" of Japan is a multi-institutional effort by private, academic and governmental sectors, administered by the government. Huge amounts of marine geological, geophysical and bathymetric data are still being collected, compiled and analyzed at each sector who has its responsibility and priority, so the full access to the compiled scientific data or the disclosure of the data to science community would take some more time in future. But the parts of scientific results and data have been presented and published as they come out, at the meetings and in journals, which is also the policy of the administering government. Eyes only preview of the ongoing compiled data is not prohibited, so the international scientific cooperation discussion, for example, could be started earlier and the session like this is a best opportunity for marine scientists to be aware of what we have and what we should have for regional/global sciences to the next step, which are generally costly pursued separately. I will present and discuss on the compiled bathymetric map of the northwestern Pacific together with geophysical data or meta-data in the same region, e.g. gravity, magnetic and seismic data compiled.
OS53A-0971
The East China Sea continental shelf data and it's scientific merits
About 40 years ago (1968), when the US Naval research vessel Hunt surveyed in the East China Sea and Taiwan Strait, 3 leaders of the cruise (Emory, Wageman and Hilde, co-author of this paper) first discovered several thick sedimentary deposits forming the sub-basins. Some of these sedimentary sub-basins can be up to 9 kms thick. This was quickly translated to be a possible for the petroleum resource. The marine surveys of both the geological and geophysical fields in the East China Sea continental shelf have been increased significantly, even up to date. Our collections of the seismic, magnetic, gravity, and bathymetry data include the sources from Taiwan, USA, France, and Japan as well as from the commercial oil companies. The total seismic profiles alone can be up to 20,000 kms. This big data base has been gathered as a focus to better understand the tectonic structure, geological evolution, marine slope stability, and also be treated as an early tsunami warning system for the East Asia region. Some of the data can also be used to evaluate the local hydrocarbon potentials.
OS53A-0972
Tectonics of the northwestern corner of the West Philippine Basin: results from new bathymetry and magnetic data
In order to meet the requirement of the Law of the Sea, we have conducted a survey of multi-beam bathymetry and magnetic data during a continental shelf survey in northwestern corner of the West Philippine Basin. The bathymetric images show obvious fracture zones trending NE-SW. Post-spreading volcanism is found in this region; some sea-mounts are across a fracture zone but some are truncated by a fracture zone. It suggests in fact the different stages of volcanism. In addition to obvious spreading fabrics, overlapping spreading features are also found in the northern part of the study area. The bathymetric depressions close to the Gagua Ridge in the west and Ryukyu Trench in the north are filled by deep-sea sediments. We have compiled the newly collected magnetic data and reduced the data by IGRF model. The magnetic data are then inverted to get the equivalent magnetization distribution of the study region. We have also conducted an age model simulation to infer the probable age of the oceanic crust of the northwestern corner of the West Philippine Basin.
OS53A-0973
The possible fault system in northern Taiwan
In this study, we have compiled several year studies of the refraction and reflection seismic (Ocean Bottom Seismometer, Multi-Channel Seismic and Chirp Sonar) collected by Taiwan R/V Ocean Research No.2 at northern offshore area of Taiwan. We have analyzed the fault structure system between the land and sea areas to realize the fault and linear structure systems in Big Taipei areas. Moreover, we also compare with the previous study of onshore fault system to adjust the fault location of digital landforms model. Using these integrated new data to understand the relation between the fault and tectonic structure especially in northern offshore Taiwan. It is hope the results of this study may be set as an early warning system for geological hazards. The Chinsan fault is major fault structure of early Miocene in this area. The Kanchiau / Keelung/ Taipei/ Wunzaikeng faults parallel to it, along the NE-SW direction. Because the collision and compression of the Luzon arc, a series of thrust fault system happened in the east of Taiwan , and the deformation were followed. This occurred probably at an early orogeny in Taiwan at the age of Miocene. Late Miocene, the arc-land collision zone migrated southward, the subduction zone under the Ryukyu arc extended to the west, it changed the mountain of northeast Taiwan turning over the subduction direction, and created a series of avalanches in the Okinawa Trough. If this model is acceptable, the fault of north Taiwan is from the compress stress to the extension stress and from the thrust fault to the normal fault. There is no large river system northward to the sea in north Taiwan, the sediment is too less to overlaps the trace of fault activity, and the depth of continental shelf is only about 100 meters, it is easy to be effected by the sea water rise/drop, and created the seabed canyons. The collision continued, the rotation and transverse stress caused the strike slip fault and flower structure. The last fault activity is probably involved with the extension. The Datun Mountains and the Keelung volcano are produced by the extension, as well as the submarine igneous bodies and three of north igneous islands and the Diaoyu islands.
OS53A-0974
Insights from new bathymetric, gravimetric and magnetic data of the continental margin of the northern South China Sea
The opening of the South China Sea Basin is suggested to be started from Late Eocene (ca. 37 Ma). The sea floor spreading began from the northern South China Sea. After the spreading, the oceanic crust was in fact intruded by post-spreading volcanism. The obvious evidence is that sea mounts are distributed in the northern South China Sea. To better understand the transition from continental crust to oceanic crust, we have conducted a marine geophysical survey in the continental margin of the northern South China Sea by using R/V Marion Dufresnes. New bathymetric data show that the margin in the southwest is relatively steeper than in the northeast. Several canyons have cut through the continental slope. In contrast, the slope is quite diffusive in the northern portion. However, the sea mounts are concentrated near the Tung-Sha (Pratas) island. The presence of the sea mounts in this area suggests that the post-spreading volcanism had occurred in the continental-ocean transition zone. Is the continental margin of the northern South China Sea an active margin or a passive margin? It is still controversial. The mechanism and distribution of the volcanism in the northern South China Sea need to be further explored. That will improve our understanding about the formation or break-up of the South China Sea continental margin.
OS53A-0975
The crustal structure of South China Sea continental slope
The sea-floor spreading of the South China Sea (SCS) was stopped since Miocene; this probably means that the plate tectonics in the SCS is in a stable situation. According to the magnetic anomaly, the sea-floor spreading of SCS was started in Oligocene and stopped in Miocene, and the continental rifting probably happened around Mesozoic. There are many differences between the northern and the southern sides of SCS. As we can see in the SCS regional map; the northern side is the continental shelf covered by thick sediments; and the southern side are numerous coral reef islands, the Spratly islands, covered up to 2-3 km thick of carbonates. Based on the seismic profiles, it shows a serial of normal faults in the northern side, and in the southern side are normal faults and thrust faults with different slip directions. The southern side has also a long history related to the formation of the reef islands. It probably means that the early continental rifting of the SCS is the passive Atlantic type shear processes. During 8/20 ¡V 9/11, 2007, we have conducted a two-ship MCS/OBS study in the northern continental slope of the SCS. Previously, the area had been surveyed by a China-Japan OBS study in 1983, the US Columbia University for an ESP study in 1985, a China-German OBH study in 1996, and a Taiwan-China MCS/OBS study in 2001. All are aiming to better understand the crustal structure of the SCS continental shelf.
OS53A-0976
The MicrOBS study around Taiwan
Since 2005, we have managed 16 MicrOBS, designed by the French IFREMER, to study the earthquake and crustal structute around Taiwan. The instrument itself is very light (20 kgs) and easy to operate. This OBS has a measuring period up to 2 weeks in the seafloor. We have conducted the works, aiming to get a better understanding of the ¡§marine¡¨ earthquakes, from the in situ small event to the big earthquake. For example, a study of the seismic gaps in the offshore region becomes workable as compare with the time when we only have the land seismological instruments. We have also used this instrument to obtain a detail study of the gas hydrate and free gas zone. Whenever a large seismic source is available, we then conduct the local and regional crustal studies, such as in the Philippine Sea and South China Sea. In the last 3 years, we have directed 285 deployments of MicrOBS around Taiwan. More than 80 per cent of the natural earthquakes in Taiwan (in an average of about 15,000 events of Mm greater than 2 events per year) were occurred in offshore area. Big earthquakes (i.e. Mm greater than 6) are more often happen in the offshore area than that in the onshore region. Therefore, the tools (MicrOBS and OBS) to measure these ¡§marine¡¨ earthquakes become essential to understand the character and origin of crustal dynamics, particularly in the seismogenic zone.
OS53A-0977
Mudflows in the Southwest Pass Region of the Mississippi River Delta: Results From Multibeam, Sidescan Sonar, and Subbottom Profiler Data
The offshore portion of the active Mississippi delta is characterized by frequent submarine mudflows, which have caused extensive damage to offshore infrastructure in the area. The slopes in this area are very gentle (typically < 1.5°) and the mudflows are thought to be triggered by deep waves during storms. The 2005 hurricane season in particular caused unprecedented levels of damage in the Gulf of Mexico. Post-hurricane surveys carried out by the industry determined that much of the damage was caused by mudflows that originated on the upper portions of the Mississippi birdsfoot delta, just outboard of Southwest Pass. Mudflows generally consist of a source area, a chute (or gully), and a downslope depositional lobe. Large erratic blocks are characteristic of the mudflow gully floor, and recently emplaced mudflow lobes show a more irregular and blocky surface topography. Gullies often form natural levees, which can give the gully a perched topographic expression. A June 2007 survey aboard the UNOLS vessel R/V Pelican focused on the upslope portion of the mudflow area with the goal of imaging the source of the mudflows. Multibeam echosounder, sidescan sonar, and subbottom profiler data were acquired over an 8 km by 2 km grid at a 100 m line spacing in order to study the possible sources of the mudflows. Multibeam and sidescan sonar data imaged the upslope portions of eight separate mudflows, including the origin of one of the flows. The five westernmost flows originate at a known dredge dump site and appear significantly wider than the three flows to the east. The eastern flows are more clearly delineated on the seafloor data and follow more tortuous downslope paths. This suggests a possible anthropogenic component to mudflow sourcing in this area. The subbottom profiler data show large blocks of material containing intact stratigraphy located within the mudflow gullies. High dips were observed in numerous blocks in both the strike and dip directions. The base of these blocks was imaged in places, suggesting that the blocks move downslope by sliding on top of more rigid material. No high relief mudflows were observed in these data.
OS53A-0978
Geophysical and Geotechnical Determination of Sand Resources on the Florida Atlantic Continental Shelf: Preliminary Results
The State of Florida is committed to maintaining beaches to sustain beach width and protect coastal infrastructure. Nearshore sand resources must be identified and cataloged for potential beach nourishment projects in response to sea-level rise and increased tropical storm activity. Given the vast length of Florida coastline, application of a variety of remote sensing techniques are required for measuring large areas in a short amount of time. The study area encompasses a shelf area of about 2,053,220 ha (20,532 km2) from Miami to the Georgia State line (about 653 km shoreline length) and extends up to 27 km offshore to about the 45 m isobath offshore Jacksonville. The continental shelf along the east coast of the Florida peninsula contains a wide range of seafloor environments that lie above the Florida-Hatteras Slope on the shoreface and inner, middle, and outer shelf floors. This study used Airborne Laser Bathymetry (ALB), 3D digital terrain models based on reformatted NOAA bathymetric data, sidescan sonar, and seismic reflection profiling to map seafloor geomorphological conditions that range from coralline-algal reef systems to drowned karst, submerged paleo shorelines (drowned beach ridge plains), and buried paleo channels. Seatruthing of morphosedimentary features is achieved via jetprobe and vibracore surveys in the study of inter-reefal sand troughs, ebb-tidal deltas, transverse bars, shoals, sand waves, ridges, and banks. Preliminary results, which visualize seafloor topography as color-ramped morphoforms, indicate the presence of sedimentary deposits that may constitute viable sand resources for shore protection in the form of beach renourishment. Use of ALB and reformatted NOAA bathymetric data in the form of 3D terrain models permits classification of submarine landform topologies that was heretofore not possible using isobaths. The combination of multiple remote sensing methods showed the spatial distribution of morphosedimentary features and provided the ability to assess sand resource potential on the shelf. Sand resources on the Florida Atlantic continental shelf amount to something on the order of about 85 x 109 m3. These potential sand volumes, based on average 3 m depth assumptions, break down to about 1 x 109 m3 for the southeast (Miami, Broward, Palm Beach counties), 4.3 x 109 m3 for the central (Martin, St. Lucie, Indian River, Brevard counties), and 78.5 x 109 m3 for the northeast (Volusia, Flagler, St. Johns, Duval, Nassau counties) Florida shelf areas. It is effective to use multiple remote sensing methods to locate large sand bodies, but more detailed geotechnical surveys are required to better estimate these sand resource potentials.
OS53A-0979
Latest Pleistocene Deposition and Erosion on the New Jersey Shelf
The New Jersey margin is an ideal location for the study of sedimentary response to glacioeustatic forcing because this passive continental edge is both wide and stable. Although the region has been intensively imaged and mapped geophysically, it is still far from being understood stratigraphically because of a lack of samples to constrain timing and paleo-depositional environment. This study examines the timing and nature of latest Pleistocene erosion and deposition on the shelf, using grab samples and core recovered using the AHC-800 (Active Heave Compensation – 800 m) drilling system. The latest Pleistocene shelf is characterized by (1) downcutting and erosion by rivers associated with subaerial exposure during glacial retreat of sea level; (2) deposition at the shelf edge during sea level fall associated with formation of an outer shelf wedge; and (3) deposition in estuarine environments as sea level rose. Foraminiferal and sediment textural analyses of cores samples ground truth previous seismic reflection-based interpretations of incision and paleochannel formation. Grab samples analyzed for foraminiferal content and grain size identify environment of deposition within three main bathymetric features: sand ridges, sand ribbons, and glacial scours. Radiometric dating (14C) further constrains the timing of intervals of erosion and deposition. We relate our results to other studies and suggest a complex, spatially variable shelf response to glacial advance and retreat. K-Ar analyses of hornblende crystals provide constraints on sediment sources. Two assemblages exist: one consistent with ages of Proterozoic age plutons in the New Jersey area, and another, younger, indicating mixing. K-Ar dates show a clear difference between and Holocene (930- 970 +/- 20 Ma) sedimentary assemblages and sediments older than 30 k.y, (850-880 Ma +/- 20-30 Ma). Holocene hornblend crystal ages are consistent with Grenvillian aged plutons common to the source region (e.g., northwestern New Jersey) and were likely delivered to the depositional region by glacial erosion during the last glacial stage. The 40 – 30 Ka aged hornblende crystals are likely a mixture of Grenville and Paleozoic source rocks such as the Cortland complex (55 km north of NYC on the Hudson River), and implies a different source for sediment delivery during stages 4 and 3.
OS53A-0980
The Study of Geotechnical Properties of Sediment in C-C Zone in the Northeastern Pacific for Deep-sea Mining
Recently the market price of valuable metals are rapidly increased due to the high demand and limited resources. Therefore, manganese (Mn)-nodules (Polymetallic nodules) in the Clarion-Clipperton fracture zone have stimulated economic interest. Nickel, copper, cobalt and manganese are the economically most interesting metals of Mn-nodules. In order to mine Mn-nodules from sea floor, understanding the geotechnical properties of surface sediment are very important for two major reasons. First, geotechnical data are required to design and build the stable and environmentally acceptable mining vehicles. Second, deep-sea mining activity could significantly effect on the surface layer of deep sea floor. For example, surface sediments will be redistributed through the resuspension and redeposition. Reliable sedimentological and soil mechanical baseline data of the undisturbed benthic environment are essential to assess and evaluate these environmental impacts by mining activity using physical and numerical modeling. The 225 times deployments of the multiple corer guaranteed undisturbed sediment samples in which geotechnical parameters were measured including sediment grain size, density, water content, shear strength. The sea floor sediments in this study area are generally characterized into three different types as follow. The seabed of the middle part (8-12° N) of this study area is mainly covered with biogenic siliceous sediment compared with pelagic red clays in the northern part (16-17° N). However, the southern part (5-6° N) is dominant with calcareous sediments because its water depth is shallower than the carbonate compensation depth (CCD). This result suggests that middle area, covered with siliceous sediment, is more feasible for commercial mining than northern area, covered with pelagic red clay, with the consideration of the nodule miner maneuverability and the environmental impact. Especially, middle part with the highest nodule abundance and valuable metal contents is mainly (more than 90% of area) covered with consolidated sediments, which are expected to be appropriate for effective miner movement. Furthermore, middle part with coarse siliceous sediments could be less environmentally disturbed by the mining activity. It makes middle part more plausible site than other sites in this study area for the commercial mining.
OS53A-0981
Developing GIS Model for Suitable Sites Selection of Manganese Nodule Development in Clarion-Clipperton Fracture Zone, northeastern Pacific
Manganese nodules are found on the seabed in many areas and have been comparatively well studied for their distribution because of their potential economic importance. The study area is located in the southern central part of the C-C zone, about 2,500 km from the East Pacific Rise (EPR). It consists of three blocks, A2, B2, and C1 between 9°N - 12°N and 128°W - 136°W. The aims of this study are to suggest priority manganese nodule development sites by quantifying the rating values for development potential using probability and statistical methods, and to verify the selection results using three statistical approaches. The collected data were converted into a 100 x 100 m grid using the raster module of the ArcGIS package, and then converted into Data Base File (DBF) data. The each factor considered in this study was then further divided into a few meaningful classes, in order to investigate the dependence of nodule abundance on each class of each factor. As a next step, rating value, average nodule abundance explained by each class, was calculated using the following equation R = ¡Æ w ∙ Np ¨M Nt where R is rating of each class and w is weight of sampling abundance and Np is number of sampling point and Nt is total number of sampling point. Finally, development potential index (DPI) was calculated for each 100 x 100 grid by summing the rating values of all the classes considered. A high DPI indicates a high potential for development and vice versa. The calculated DPIs were verified by comparing them with actual sampling data to understand the most suitable models and the factors that predict the development potential of the study area. Verification was conducted in three ways : success and prediction rates, linear regression analysis, and testing independence. The success rate provides the best model in terms of both area and cumulative frequency diagram for all blocks. The success rate of block A2 provides the best model among the success rates, while the A2toC1 prediction rate provides the best model among prediction rates. The A2 success rate gives the best model out of nine models. The verification for linear regression analysis was conducted to identify the most suitable models. The success rate provides the best model for block A2. The difference in fit between the success and prediction rates is small and both ratings show a general increase irrespective of any anomalies in the data. The B2 success rate model is most suitable for block B2, particularly as its slope is greater than that of the prediction rate and the difference in the R2 value is small. The success rate model was most suitable for block C1. The test of independence was conducted to identify the factors that predict the development potential of an area, by using 21 combinations of the seven factors (copper and nickel grades, slope, aspect, water depth, topography, and transparent layer thickness) for each of blocks A2 and C1 and using 15 combinations of six factors (all but the transparent layer thickness) for block B2. There are no correlations between the factors for blocks A2 and C1, while there are correlations between copper and nickel grade and between topography and water depth in block B2. Verification of the success and prediction rates was conducted for four factors of copper, slope, aspect, and topography in block B2. The results are the same as those using six factors, but the area becomes smaller than when all factors are used.
OS53A-0982
Iceberg scours offshore of South Carolina
High resolution swath bathymetry data collected offshore of South Carolina as part of the NOAA Ocean Explorations program in 2006 and 2007 show evidence of extensive iceberg scouring along the upper slope (170-220 m water depth). Numerous furrows, 10-100 m wide and <10 m deep, are oriented WSW along regional bathymetric contours. Lateral berms along the length of the furrows record the plowing of iceberg keels along the seafloor. Video observations along these berms show evidence of large upturned blocks and boulders. Many of the furrows terminate in semicircular pits ringed by several meters high ridges. These are interpreted as terminal grounding pits, indicating icebergs have come to rest on the seafloor. The location and orientation of the keel marks suggests icebergs were entrained a southwestward flowing coastal current. Presently, warm waters of the rapid, northeastward flowing Gulf Stream bathe the upper slope across the region. An offshore shift in the Gulf Stream axis during sea level lowstand may have allowed glacially fed coastal currents to penetrate farther south, transporting icebergs to this portion of the margin. Subsequent reintroduction of the Gulf Stream appears to have enhanced the scour topography through bottom current erosion and reworking. This is the first evidence of iceberg transport to subtropical latitudes along the U.S. Atlantic margin. Additional high resolution surveys along the upper slope of the eastern United States will likely reveal further evidence of iceberg scouring along the margin.
OS53A-0983
CHIRP seismic reflection study of falling-stage (forced regressive) sediment wedges on the New Jersey outer continental shelf
High-resolution (1-12 kHz), deep-towed and hull-mounted CHIRP seismic data were collected on the New Jersey outer shelf in 2001, 2002 and 2006 as part of Office of Naval Research-funded projects. These data have imaged two well-developed, offlapping sedimentary wedges (named outer-shelf wedge and deep-shelf wedge) that are now postulated to have developed on the falling-stage limb of the last glacial cycle, during some time prior to the Last Glacial Maximum (20-22 kyrs BP). These wedges formed atop the high-amplitude, regional R horizon, a complex erosional unconformity that formed about 40,000 years ago. The outer shelf wedge is also characterized in part by an enigmatic, erose boundary separating layered horizons below from a mostly transparent section above. New Jersey shelf wedges appear analogous to forced-regressive units imaged on the Rhone shelf edge, as well as Eocene sections documented from seismic-scale outcrops on Spitsbergen Island. These examples can reach thicknesses up to 100 m on the shelf edge and uppermost slope, but usually thin rapidly downslope. Such wedges represent one of two documented mechanisms involving sand transport across a shelf margin into deeper water settings, the other being a canyonized shelf-edge. Our study will includes analysis of the CHIRP data and, if available, additional ground truth provided by short cores collected in summer 2007 at numerous intra-wedge stratigraphic horizons. Our goals are to understand the external and internal geometry of the wedges and sediment pathways across the paleo-shelf. These data should allow us to characterize margin segments that build during sea-level fall by slope-apron accretion rather than by the formation of channel-levee complexes. The literature is heavily weighted by the latter and their associated canyon systems, but information on shelf-edge attached slope aprons and how they contribute to deep-water sedimentation, and in particular the delivery of clean sands to slope settings, remains sparse.
OS53A-0984
Transgressive shoreline deposits seaward of coastal ponds along northeastern South Carolina coastline.
The arcuate Long Bay coastline of northeastern South Carolina is dominated by the 75 km long Grand Strand, which is the result of landward retreat of the shoreline intersecting the paleo Myrtle Beach barrier system. As the shoreline transgresses, three stages of development have been recognized in this large coastal embayment: (1) coastal barrier island landforms north and south of the central Grand Strand that are migrating across an irregular Pleistocene paleolandscape and have not intersected emergent Quaternary paralic terraces; (2) an intermediate stage where the transgressing shoreline has created shore parallel coastal lakes and vegetated wetlands between the transgressive sediment mass and the emergent terraces; and (3) coastal segments where the transgressive shoreline is actively eroding into the emergent Pleistocene core. This study uses ground penetrating radar (GPR) and vibracore data to study the intermediate stage lake coastline. The GPR data reveals landward dipping reflectors infilling uneven topography and channels formed in the low between the irregular paleo barrier high and retreating shoreline. Study of the transgressive architecture and intersection with paleo- shoreface is important for understanding future shoreline retreat and for understanding potential storm records preserved in the infill.
OS53A-0985
Sediment Transport Pathways in a High-Energy Source-to-Sink System: Results From the Submarine Topsets of the Ganges-Brahmaputra Delta, Bangladesh
The transition between river and marine environments is the most complex and least understood component of coastal source-to-sink systems. The Ganges-Brahmaputra Delta, Bangladesh, represents an end-member in the continuum of estuarine environments, discharging the largest sediment load into a high energy canyon incised shelf. Toward the goal of understanding how fluvial, oceanographic and climactic processes interact to control sediment dispersal in this zone, a shallow high-resolution seismic survey was conducted on the inner shelf of the Bay of Bengal during the 2007 low-discharge winter monsoon. The data show that subsurface architecture within the river mouth estuary and adjacent to modern active distributaries includes extensive cut- and-fill features, "stair-step" reflective surfaces, and patches of acoustically transparent layers. Seismic facies bordering abandoned tidal channels in the westernmost part of the delta show comparatively little stratigraphic structure, implying limited penetration in sand. However, cross-shelf sections south of the abandoned distributaries and nearest the canyon head contain more complex cut-and-fill stratigraphy than along-shelf sections in the same area. Correlation of canyon feeder gullies with these infilled shelf features, which may be contiguous from the abandoned delta to areas of active sedimentation, may lead to a more precise understanding of transport mechanisms linking the river mouth and offshore depocenters.
OS53A-0986
Distribution and characteristics of deep-sea sediment waves in the northern South China Sea
In the northern South China Sea (SCS), the deep-sea sediment waves are distributed in two zones; one is between the lower reach of the Formosa Canyon and Penghu Canyon, the other is between the lower reach of the Formosa Canon and LRTPB (Luzon-Ryukyu Transform Plate Boundary). The distribution of these deep-sea sediment waves are found below 3000 m deep and the wave front is rather parallel to the bathymetric contour lines. Base on high resolution seismic data, we suggest that these sediment waves are caused by turbidity currents. The sediment waves have shown asymmetrical internal structures which may be induced by high gravity flow activity. Most of these sediment waves are less than 85 m high, and most of wavelengthes are less than 6 km long. Most of slopes are less 0.8 degree. We suggest that the Formosa Canyon and Penghu Canyon are two major sediment transportation channels. The turbidity flows downward and may overflow directly from the turning points of these two canyons. The sediment deposits in the stoss side and erodes in the lee side. It proceedes downslope continuously because of gravity effect. Due to the bathymetric offset across the LRTPB, the turbidity current can not overflow to the south of this tectonic structure, which makes LRTPB a natural sediment wave dam.