OS51A-1216
Tectono-climatic signals in linear, confined, point-sourced, deep-marine siliciclastic systems as analog for submarine-canyon fills, Eocene, Spanish Pyrenees
The linear, confined geometry, and point-sourced nature, of the deep-marine siliciclastic systems in the Eocene Ainsa-Jaca basin, Spanish Pyrenees, provides a useful ancient spatial-temporal comparison and partial analog for the architecture and controls on the sedimentary infill of large submarine canyons / multiple canyons at continental margins with active tectonics, including salt and shale diapirism. The cumulative ~4 km of stratigraphy contains 8 sandy systems with a total of ~25 discrete channelized sandbodies that accumulated over ~10 Myr in water depths of ~400 to 800 m, that were controlled by the ~400-kyr Milkankovitch frequency with modes, at ~100 kyr and ~41 kyr (possibly stacked ~23-kyr) influencing bottom- water conditions, causing periodic stratification in the water column across a submarine sill within the western part of the more proximal depositional systems. Local tectonics defined and controlled the position and stacking patterns of the 8 sandy systems and their constituent channelized sandbodies, in a process of "seesaw tectonics" by: (i) Westward lateral offset-stacking of channelized sandbodies due to growth of the eastern side of the basin, and (ii) Eastward (orogenwards) "back-stepping" of the depositional axis of each sandy system, due to phases of relative uplift of the opposing lateral margin. Thus, the first-order control on accommodation for deep-marine sedimentation was tectonic, with the pacing of the supply of coarse siliciclastics being driven by global climatic processes, particularly Milankovitch-type frequencies. The dominance of eccentricity and obliquity is similar to results from the continental lacustrine, Eocene Green River Formation. The age model for the Ainsa basin yields an average sediment accumulation rate of ~40 cm kyr-1, that is consistent with that inferred from the spectral analysis on bioturbation intensity for fine-grained sedimentation (~30 cm kyr-1). This paper compares and contrasts depositional patterns and controls for submarine canyons with this ancient linear, confined, point-sourced deep-marine system.
OS51A-1217
Shelf and Slope Sedimentation in the Arctic Ocean: Comparison of the Alaskan Margin with Deep-Sea Sediments; Drift Deposits and the Role of Sea Ice
A study of several cores from the outer shelf and continental slope north of Alaska indicate that localized drift deposits occur here with sedimentation rates of more than 1.5m/kyr during the Holocene. Currents in this area average about 5-20 cm/s but can reach 100 cm/s and these are certainly capable of entraining even cohesive sediment on the inner and mid-shelf or from the slope and depositing it where eddies or bottom topography causes separation of flow such as in canyons. Unlike most textural investigations of Arctic sediment that focus on the coarser ice-rafted detritus (IRD), this paper focuses on the greater than 95% of the sediment finer than 45 microns. The mean size of this fraction varies between 6 and 15 microns in several Holocene core sections with the higher values closer to shore. Analysis of detailed size distributions of these Holocene deposits are compared to 34 sea ice samples collected across the Arctic Ocean and to Holocene sediment from central Arctic cores and indicate that similar textural parameters occur in all of these sediments with the finest sediments on the central Arctic ridges. Principal components of these size distributions indicate that sea ice is an important link between the shelves and the central Arctic. Factor scores provide new insights into the processes of transport and deposition in the Arctic.
OS51A-1218
Onset of submarine debris flow deposition far away from original giant landslide
Submarine landslides can generate sediment-laden flows whose scale is impressive. Individual flow deposits have been mapped that extend for 1,500 km offshore from northwest Africa. These are the longest run-out sediment density flow deposits yet documented on Earth. This contribution analyses one of these deposits, which contains ten times the mass of sediment transported annually by all of the World's rivers. This flow originated near the upper part of the Agadir Canyon offshore Morocco. Previous work has shown how progressive disintegration of landslide blocks can generate debris flow, whose deposit extends down slope from the original landslide. Here we provide new evidence that submarine flows can produce giant debris flow deposits that start several hundred kilometres from the original landslide, encased within deposits of a turbidity current. Very little sediment was deposited across the intervening large expanse of sea floor (including the distal part of the Agadir Canyon), where the flow was locally very erosive. Sediment cores show that the flow eroded several metres of sediment, in locations hundreds of metres above the canyon floor. Sediment deposition was finally triggered by a remarkably small but abrupt decrease in sea-floor gradient from 0.05 to 0.01 degrees beyond the canyon mouth. Debris flow was most likely generated by flow transformation from the decelerating turbidity current. The alternative is that non-channelised debris flow left almost no trace of its passage (bypassed) across one hundred kilometres of flat (0.2 to 0.05 degrees) sea floor.
OS51A-1219
Sedimentary Filling of the Submarine Canyon „Swatch of No Ground", Bengal Shelf
The submarine canyon "Swatch of No Ground" (SoNG), deeply incised into the Bengal Shelf, plays an important role in the source to sink system Himalaya-Bengal Fan by connecting the Ganges and Brahmaputra rivers, which drain the Himalayas, with the largest submarine fan on Earth. It is believed that around one third of the delivered sediments of at least 1 billion ton per year are transported through this canyon to the deep sea fan. In general the SoNG acts as a temporary trap and releases the sediments episodically by turbidity currents to the fan. Transportation of the sediments to the head of the canyon under quite weather conditions is done by tidal currents during high discharge periods. More effective, passages of cyclones remobilize shelf sediments and transport them to the canyon, and trigger also failures in the canyon flanks with consequent mass wasting downward. Finally all processes lead to high sedimentation rates of 50 cm per year in the head of the canyon. To understand the filling architecture and depositional processes, high-resolution multichannel seismic data were collected in summer 2006 in the upper canyon with the German research vessel "Sonne". Additionally, multibeam and sediment echosounder data were gathered, together with gravity cores. Hydroacoustic data and cores were also already collected on cruises in 1994 and 1997 and consequently, some lines and stations were revisited to study the deposition within the last years. The seismic data, shot on a dense grid of lines along and across the axis including flanks and shoulders, reveal a thick (1.5 sec TWT) sedimentary fill. Well stratified layer alternate with transparent to chaotic units intercalated by filled channels. Two main unconformities could be identified in the seismic data. Faulting is also found in the study area, probably caused by sediment compaction. The data set should be used to develop an IODP proposal to drill into this unique high resolution archive.
OS51A-1220
Deep Canyon and Slope Suspended Sediment Transport in the Western Gulf of Lions During the 2006 Intense Cascading Period
Recent studies have demonstrated that most of the off-shelf suspended sediment transport in the Gulf of Lions occurs in its westernmost sector, preferentially through the Cap de Creus submarine canyon. Based on this previous knowledge, a focussed monitoring strategy was designed within the HERMES project, to better constrain the contemporary sediment transport processes in this region. A network of mooring lines equipped with current meters and turbidity sensors at 5 m above bottom were deployed between 300 m and 1900 m depth along the axes of the two Lacaze-Duthiers and Cap de Creus neighbor canyons, as well as across the southern open slope from October 2005 to October 2006. Dense shelf water cascading was the main shelf-to-slope sediment transport process in the area, acting from January to April-May 2006. The dense water and sediment transport was not only through submarine canyons, but also along the southern open slope. The most important suspended sediment transport event was due to the intense cascading pulse occurring in January 2006, which produced a strong sediment flux increase along the Cap de Creus Canyon down to 1900 m depth and also along the open slope at 1000 m depth. A significant sediment flux increase also occurred in March-April 2006 due to another intense cascading pulse. In this transport event, suspended sediment concentration only increased at 1000 m depth in the Cap de Creus Canyon and on the open slope, but not at the canyon head, suggesting a redistribution of sediments previously deposited at mid-canyon depths. Deeper than 1000 m, net fluxes show that most of the suspended sediment left the canyon and flowed along the southern open slope towards the Catalan margin, whereas a small part flowed downcanyon and was exported basinward through the canyon mouth. Additionally, the increase of the deep-sea near-bottom currents induced by open-sea convection processes, combined with the arrival of deep cascading pulses, also generated moderate but continuous suspended sediment transport at deeper slope regions.
OS51A-1221
Export of terrigenous organic carbon along submarine canyons driven by dense shelf water cascading
At current highstand in sea level, shelves are considered major sites of terrigenous organic carbon (OCterr) accumulation with relatively little connectivity to the ocean interior. In recent years, the process of dense water cascading from the continental shelf, which occurs in numerous places around the world, has been suggested as carrier for OCterr to the deep ocean. The land-locked Mediterranean Sea is characterized by intense and recurrent cascades of dense shelf water. In winter, cold and dry winds cause the formation of dense water over the shelf that may overflow it and travel down to the outer margin and basin. Moored instruments were deployed in the canyons of the Gulf of Lion (France-Spain) and the Adriatic Sea (Italy) to intercept particulate material escaping the shelf and to investigate hydrodynamic and physical properties of the water column. Surface sediments along the shelves were also sampled to evaluate their contribution to the particle fluxes. The relative fractions of autochthonous and advected OC in sediment trap samples were investigated using biogeochemical proxies including alkaline CuO oxidation products (lignin phenols, dicarboxylic acids, and fatty acids), radiocarbon measurements (Ä14C), and elemental and carbon stable isotope (ä13C) compositions. Lignin-derived CuO products were a powerful biogeochemical tool that allowed us to identify the provenance of the material from the continental margin and to assess the amount of OCterr transferred across the slope in both Mediterranean regions. The results indicate that the composition of OC escaping the shelf through submarine canyons depends on the geomorphological setting. At the present sea level stage, cascading on a broad shelf limits the transport of OCterr, promoting instead the down-slope export of material accumulated in the mid- and outer-shelf. In contrast, cascade events on narrow shelves lead to the efficient export of OCterr from shallower regions of the margin along with the dense water formed on the inner-shelf.
OS51A-1222
Sediment Flux in Hueneme and Mugu Submarine Canyons
Subsurface moorings were deployed at ~190 m water depth for 6 months (9/07 - 3/08) inside Hueneme and Mugu submarine canyons in southern California. Data collected from the sediment traps, located at 30 and 60 meters above canyon floor, showed marked temporal and spatial variations of sediment flux. Not surprisingly, high sediment flux correlated well with high river discharge, which occurs mostly during episodic winter storms and precipitation, from Santa Clara River, ~12 km upcoast of Hueneme Canyon, and Calleguas Creek, which empties directly into Mugu Canyon. But the observation that both of the Hueneme traps had much higher sediment flux than the Mugu traps was unexpected, because the Mugu canyon head is right next to the mouth of Calleagus Creek whereas the Hueneme canyon is more than 12 km from either Calleguas Creek or Santa Clara River. In this presentation we attempt to characterize the relationships between sediment flux and turbidity current pulses, whose down-canyon speed exceeded 250 cm/s. These pulses seem closely correlated with high waves in the region. We will also describe and discuss the grain size, isotope, and mineral properties of the sediment during high sediment flux events and relate these fluxes to different sediment sources.
OS51A-1223
Source Area of Earthquake- and Storm-Induced Turbidite Events in Submarine Canyons Along the Central California Coast Identified by Entrained Microfauna
Earthquakes, storm wave disturbances, and internal waves may cause localized sediment displacement and if intense enough, these disturbance events may result in full submarine canyon and fan channel flushing events. In submarine canyons along the central California coast, it is often assumed that these turbidity currents originate in the upper canyons below about 110 m water depth. However, the source area of these flows may actually range from the inner shelf to the slope, as identified by benthic foraminiferal assemblages entrained within the displaced sediments. Off central California, benthic foraminiferal faunas are assignable to six biofacies that can be used to identify the source area of displaced sediments: inner shelf (0-50 m), outer shelf (50-150 m), upper bathyal (150-500 m), upper middle bathyal (500-1,500 m), lower middle bathyal (1,500-2,000 m), and lower bathyal (>2,000 m). Sediment cores may yield information on turbidite deposition over millennial or longer time scales. Core S3- 15G from the western levee of Monterey fan valley (3,491 m depth) contains a 19,000-year record of hemipelagic and submarine fan overbank deposits. The sediments were deposited in 45 turbiditic sequences of sand and silt separated by hemipelagic mud. A minimum of 19 displaced species from a total count of 140 species identified were recovered from 65 turbiditic samples investigated. The relative abundance of allochthonous foraminifers was found to correlate positively with grain size. Sands of one of the two cross- bedded turbiditic (Tc) units recovered originated on the inner shelf and included faunal elements from all of the shelf and slope biofacies; the source of the other was the upper slope and included only the bathyal foraminifers. In both of these sands, 75% of the fauna was displaced. Of the 29 laminated turbiditic sand (Td) units, ten had faunal elements from all six biofacies, seven had only those from the slope, and the remaining had faunal elements from non-adjacent biofacies. On average, 9% of the fauna was displaced. Most of the 35 turbiditic mud (Tet) units included constituents of only three biofacies with 15% displaced specimens, whereas the 18 hemipelagic muds (Tep) had only rare (3%) allochthonous foraminifers.
OS51A-1224
Quantitative differential geomorphology of the Monterey Canyon from time-separated multibeam surveys
Changes of bathymetry derived from multibeam sonars are useful for quantifying the effects of many sedimentary and tectonic processes. The assessment of resolution limits is an essential component of the analysis This research compares submarine morphology as they manifest tectonics in a rapidly transform continental margin (Monterey Bay – California). We study modern submarine processes from a geomorphic change using high-resolution multibeam bathymetry. We first used different techniques that quantify uncertainties and reveals the spatial variations of errors. An sub-area of immobile seafloor in the study area, mapped by the high-resolution multibeam record of the seafloor of the MBR collected by MBARI in each survey in a four years period (spring 2003 to winter 2006), provides a common 'benchmark'. Each survey dataset over the benchmark is filtered with a simple moving-averaging window and depth differences between the two surveys are collated to derive a difference histogram. The procedure is repeated using different length-scales of filtering. By plotting the variability of the differences versus the length-scale of the filter, the different effects of spatially uncorrelated and correlated noise can be deduced. Beside that, a variography analysis is conducted on the dataset build by differencing the benchmark surveys to highlight spatial structures and anisotropies of the measure errors. Data analysis of the Monterey Bay area indicates that the canyon floor contains an axial channel laterally bounded by elevated complex terrace surfaces. Asymmetrical megaripples dominate the active part of the canyon floor, indicating sediment transport. Terraces represent the evidence of recent degradation of the canyon floor. Slump scars and gullies, having a variety of size, shape the canyon walls. Significant changes over the analyzed period include: (a) complete reorganization of the megaripples on the channel floor, (b) local slump scar on the head of the canyon and on the channel flanks, (c) local channel widening that laterally eroded older channel, (d) extension of gully head on canyon walls, (e) erosion and sedimentation cycles all over the canyon. The analyses carried out shows how the results are based on a map of uncertainties, which can be used to remove insignificant data from the bathymetric change map.
OS51A-1225
Sedimentary erosive processes and sediment dispersal in the Gaoping Submarine Canyon in the southwestern Taiwan margin
The Gaoping submarine canyon, connected to the Gaoping River in the coastal plain in SW Taiwan, continues the dispersal path of Gaoping River sediments from an active, small mountainous drainage basin to the receiving South China Sea basin. Using seismic reflection sections, Chirp sonar profiles and bathymetric mapping, this study reveals the characteristic erosive processes responsible for multiple cut-and- fill features, deeply entrenched thalweg and sediment dispersal in the canyon, closely related to turbidity currents in the canyon. The river-canyon connection setting of the Gaoping Canyon with its extreme climatic conditions and active tectonic activity is favorable for the generation of turbidity currents at the canyon head. The upper reach of the Gaoping Canyon is distinguished by three distinct morpho/sedimentary features. The canyon head is characterized by V-shaped axial thalweg erosion. The proximal segment of the upper reach is dominated by a deeply incised canyon pathway with trough-like morphology. Cut-and-fill features are common along the canyon floor, resulting in a flat-floored pathway. Sliding and slumping are dominant features on the steep canyon walls, producing and transporting sediments to the canyon floor and partially filling up the canyon thalweg. The distal segment is characterized by erosive features where deeply down- cutting erosion occurs mainly in the outer bend of the major sea valley, forming the V-shaped entrenched thalweg. The recurrences of turbidity currents have caused continuous incision of the canyon head and have kept the connection between the canyon head and the river mouth during the Holocene highstand of sea level. The upper reach of the Gaoping Canyon is linked to the drainage area, and remains active as a conduit and/or sink for terrigenous and shallow marine material. Oceanic flood sedimentation operates in the Gaoping River- Canyon system; inferred turbidity currents flush river sediments into the canyon head where the canyon thalweg is the most erosive. Presently, the upper reach of the Gaoping Canyon can be considered as a temporal sediment sink rather than a major sink.
OS51A-1226
The Contribution of Polycyclic Aromatic Hydrocarbons From Gaoping (Kaoping) River to Coastal Ocean Including Gaoping Submarine Canyon, Taiwan.
Polycyclic aromatic hydrocarbon, as a particle tracer, provides valuable information in land-to-sea particulate transport. Nevertheless, information of its riverine flux to coastal ocean is sparse. Therefore, in this study, a monthly sampling campaign in Gao-ping River was executed from NOV 2006 to NOV 2007. Concentrations of 50 polycyclic aromatic hydrocarbons in both dissolved and particulate phases were analyzed for water samples collected. The total PAH concentrations ranged from 13.0 to 565ng/L and 11.8 to 502ng/L in the dissolved and particulate phase, respectively. The particulate PAH concentrations were correlated significantly with the total suspended particles (R2=0.90, p<0.0001). It is observed that after the Krosa typhoon, the dissolved PAH concentrations reached the lowest because of heavy rainwater dilution, while both of the total suspended particle and particulate PAH concentrations reached the highest. According to the PAH isomer ratios, IP/IP+BghiP and BaA/228, petrogenic origin dominates at wet season (except a sample collected with a nearby straw burning activity) while pyrogenic origin dominates at dry season. The PAH compositional pattern also indicates the same result. At last, during this period, the annual dissolved and particulate PAH fluxes from river to the coastal ocean were 0.37 and 2.46 metric tons, respectively. Compared with dry season, wet season (May to October) contributes much more in total annual fluxes (about 89.2% and 99.6%, respectively).
OS51A-1227
Biogenic Particle Transport in the Gaoping Submarine Canyon off Southwestern Taiwan
Foraminifera shells have shown to be useful tracers of delivery and transport of biogenic particles in the Gaoping Submarine Canyon (KPSC). Foraminifera collected from sediment trap and sediment cores were analyzed to provide information on biogenic particle transport in the Gaoping River and Gaoping Submarine Canyon system off southwestern Taiwan. A non-sequential sediment trap mooring configured with an acoustic current meter was deployed in the head region of the KPSC, resulting in a 82-cm long ¡§suspended core¡¨ in the water column after 70 days of deployment. There exists a positive relationship between the concentration of planktonic foraminiferal shells (tests/g) from the sediment trap samples and wave height recorded on the nearby shelf, albeit with a slight time-lag by 1~2 cm interval. On the other hand, benthic foraminiferal shells do not have any significant correlation with hydrographic parameters, including water temperature, along-canyon component of the current velocity, and the wave height. Furthermore, historical hydrographic conditions off southwestern Taiwan could be reconstructed based on downcore planktonic foraminiferal isotopic records retrieved from continental slope with chronology constrained by Pb-210 and Cs-137 for the last century. Variation of temperature and/or salinity reflected by the del O18 generated from Globigerinoides sacculifer (without sac) could be correlated with the temperature record provided by the Hengchun Weather Station nearby. Nevertheless, some distinctive foraminiferal del O18 signals may be related to the Multivariate ENSO Index (MEI), providing a short but high resolution paleoceanographic record. A common progressive depletion of planktonic foraminiferal del C13 towards present (coretop) found in many cores suggests the influence of anthropogenic activities since the late 1970s. Results of this study indicate that foraminifera provide useful information on the transport and settling of biogenic particle of marine origin in the KPSC. Foraminifera on the slope off southwestern Taiwan also reflect the atmospheric temperature change in the last century.
OS51A-1228
Polycyclic Aromatic Hydrocarbons in the Coastal Sediments of Southwestern Taiwan: an Appraisal of Diagnostic Ratios in Source Recognition
Fifty seven surface sediment samples along the coast of southwestern Taiwan were collected and analyzed for polycyclic aromatic hydrocarbons (PAHs). Concentrations of total PAH (sum of 28 PAH compounds) ranged from15 to 907 ng/g dry weight (dw). Diagnostic ratios revealed petroleum origin PAHs was a significant source to the sediments at Gao-ping estuary stations. However, sediments of Kaohsiung coast might be a combustion-derived PAHs of petroleum, coal, and vehicles. The result of perylene/penta-aromatic PAHs ratio was higher in Tainan coast, Hsinda harbour coast, and some off-shore stations of Kaohsiung coast, suggesting a diagenetic PAH source. A comprehensive appraisal suggested that certain diagnostic ratios are much useful in tracing the distribution of PAHs from specific sources in southwestern Taiwan. P/A (phenanthrene/anthracene) ratio is a better indicator than MP/P (methylphenanthrenes/phenanthrene) ratio in tracing petrogenic PAHs. Moreover, BaA/Chr (benzo(a)anthracene/chrysene) and IP/BghiP (indeno(1,2,3- c,d)pyrene/benzo(g,h,i)perylene) ratios can provide more appropriate assignments than BaP/BeP (benzo(a)pyrene/benzo(e)pyrene) and BbF/BkF (benzo(b)fluoranthcene/benzo(k)fluoranthcene) in distinguishing PAHs from various pyrogenic sources in this study. More specifically, automobile and coal sources were found dominant in stations of pyrogenic group delineated by principal component analysis (PCA).
OS51A-1229
Turbidity currents, submarine landslides and 2006 Pingtung earthquake off SW Taiwan
Submarine landslides or slumps may generate turbidity currents consisting of dilute mixture of sediment and water. Large and fast-moving turbidity currents can incise and erode continental margins and cause damage to artificial structures such as telecommunication cables on the seafloor. In this study, we show submarine landslides and turbidity currents associated with the 2006 Pingtung earthquake off SW Taiwan. Furthermore, eleven submarine cables across the Kaoping canyon and Manila trench were broken in sequence from 1500 m to 4000 m deep. We have established a full-scale calculation of the turbidity current velocities along the Kaoping canyon channel from the middle continental slope to the adjacent deep ocean. Our results show that turbidity current velocities vary downstream at steps of 20 m/s, 3.7 m/s and 5.7 m/s which demonstrates a positive relationship between turbidity current velocities and bathymetric slopes. As evidenced by the violent cable faults happened in the 2006 Pingtung earthquakes, the destructive power of turbidity current to underwater facilities is largely underestimated.
OS51A-1230
Correlations Between Remotely-Sensed Particle Backscattering Coefficients and Terrestrial Sediment Discharge at the Kaoping River Shelf and Canyon System
Because of high concentrated rainstorms, unsettled geology, and frequent earthquakes, high fluctuated terrestrial sediment load was delivered to the Kaoping River shelf and canyon (KPRSC), affecting the biogeochemical systems of both coastal waters and the deep-ocean. The image taken by Sea-viewing Wide Field-of-view Sensor (SeaWiFS) was used to obtain the particle backscattering coefficient (bbp) map as a multi-temporal and multi-spatial tracer to quantify the effect of the terrestrial sediment discharge. The SeaWiFS mission period included the Chi-Chi earthquake (September 21, 1999) and the extremely high and low flow conditions of Kaoping River (KPR). During the study period of October 1997 to November 2006, the pattern and intensity of the monthly bbp maps are significantly correlated to the sediment load in the aerial range of KPRSC; this became much clear when the contribution of phytoplankton was removed from the bbp maps. The relationship between bbp and sediment load analyzed before and after the Chi-Chi earthquake exhibits different patterns that are related to possible triggers of terrestrial sediment. Based on 111 bbp maps of KPRSC, regression models are developed to estimate the monthly sediment load discharged from KPR.
OS51A-1231
Investigate the relationship between the precipitation and the dispersion of terrestrial substances using shipborne hyper-spectral reflectance ¡V the case of Gaoping River, Shelf and Canyon System
Recent work on categorizing the dispersal patterns of river-borne substances in the Gaoping River, Shelf and Canyon System (GRSCS) using satellite observations of ocean color reveals the close relationship between the precipitation and the dispersion of terrestrial substances. Limited by the satellite observation of ocean color in time (one clear image per month) and space (1-km resolution of MODIS image), however, it is still not clear how the dispersion of terrestrial substances response to the precipitation in the short scale of time and space, for example, the short-term and regional blooming event triggered by the extra nutrients carried by the dispersion of terrestrial substances after a large rainfall. In this research, we used Hyper Surface Acquisition System (HyperSAS) and High Resolution Spectral Absorption and Attenuation Meter (ac-s) to measure the hyperspectral values of water surface reflectance, absorption coefficient, and beam attenuation coefficient. In addition, both the salinity and temperature were obtained using onboard CTD (conductivity, temperature, depth) facility. The water samples were taken and brought into the laboratory to analyze the inherent optical properties (IOP) and various parameters of water quality, following the standard procedure of operation. These results were used as the ground truth for validating the retrievals from HyperSAS later on. We employed our latest progress in hyperspectral data analysis, namely GA-SA approach, to process the HyperSAS data. The retrievals of IOPs and water quality parameters were then compared to the earlier results obtained form the laboratory analysis. We plan to acquire the transactions of chlorophyll-a, colored dissolved organic matter, suspended solids, salinity and temperature near the Gaoping River mouth at a higher frequency after a major rain fall event. These transactions would assist us to gain a better understanding of the relationship between the precipitation and the dispersion of terrestrial substances using shipborne hyper-spectral reflectance.
OS51A-1232
Continental Margin as A Small River Organic Carbon Sink
Burial of organic carbon in marine sediments is an important sink of the global carbon cycle. Hedges and Kiel (1995) and Berner (1982) showed that major river delta and continental shelf are the most important burial environments for the modern organic carbon. Even though small rivers are exporting tremendously high amount of particles to the ocean and probably carrying, at the same time, high amount of terrigenous organic carbon as well, there is little information available in evaluating organic carbon burial in areas subjecting to small rivers particles and fate of these small river derived organic carbon. We have investigated organic carbon burial in the continental margin offshore southwestern Taiwan where a combined small river particle flux reaching 104 MT/yr, about half of what from the Mississippi River. Samples from continental margin (shelf and slope) offshore three small rivers (the Kaoping, Erjeng, and Tsengwen) in the region were sampled. Organic carbon and del C13, organic nitrogen content, grain sizes, and carbonate content were analyzed. Burials of organic carbon in the region were calculated and evaluated. Although small rivers carrying high amount of organic carbon and nutrients to the adjacent sea, organic carbon concentrations in the study region are relatively low, in the range of 0.1-1.0%, probably a result of dilution effect by the high amounts of inorganic siliceous materials carrying out by the river. Higher concentrations of organic carbon, 0.8-1.0%, were found either near river mouth, in the KP canyon, or adjacent to the sewage outlet. High carbonate sediments were found only in regions with limited terrigenous material input or influenced by the Kuroshio Current away from shore. Del C13 values in region with high carbonate content were mostly near -20 per mil while in regions near river mouth and in the canyon were mostly near -26 per mil. A fraction of organic carbon was found burying in the shelf and slope region near small rivers offshore southwestern Taiwan, however, a greater majority of the organic carbon exported from small rivers in southwestern Taiwan was not found in the study continental margin.
OS51A-1233
Comparison of Sedimentary Processes on Adjacent Passive and Active Continental Margins Offshore of Southwest Taiwan Based on Echo Character Studies
Echo character recorded on Chirp sub-bottom sonar data from offshore area of southwest Taiwan were analyzed to examine and compare the sedimentary processes of adjacent passive and active continental margin settings. Seafloor echoes in the study area are classified into four types: (1) distinct echoes, (2) indistinct echoes, (3) hyperbolic echoes, and (4) irregular echoes. Based on the mapped distribution of the echo types, the sedimentary processes offshore of southwest Taiwan are different in the two tectonic settings. On the passive South China Sea margin, slope failure is the main process on the upper continental slope, whereas turbidite deposits accumulate in the lower continental slope. In contrast, the submarine Taiwan orogenic wedge is characterized by fill-and-spill processes in the intraslope basins of the upper slope, and mass-transport deposits are observed in the canyons and on the lower Kaoping slope. This difference is largely caused by the huge influx of terrigenous sediments into the submarine Taiwan orogenic wedge province compared to the passive South China Sea continental margin. In the passive South China Sea margin, loading and movement of the Taiwan orogenic wedge has had significant effect on the seafloor morphology, and triggered retrogressive failures. Gas hydrate dissociation may have enhanced the slope failure processes at some locations.
OS51A-1234
Submarine mass movements on the northern margin of the southern Okinawa Trough, offshore NE Taiwan
The southern Okinawa Trough back-arc basin has extended in the East China Sea continental margin where large volume of sediments on the seafloor is accumulated. The northern continental slope of the southern Okinawa Trough offshore Taiwan has been cut across by three major NW-SE trending submarine canyons. In order to understand the morphologic seafloor patterns of submarine mass movements on both sides of the Mienha Canyon, we have collected multi-channel seismic (MCS) reflection, subbottom profiler and multi-beam swath data during OR1-1387 and OR2-1573 cruises. In the west side of the Mienha Canyon, numerous small gullies are developed in the upslope areas where water depths are shallower than about 300 m. It is generally reflects an active erosion environment. Steep scarps and parallel channel systems are well developed in the slope of water depths between 300 to 800 m. In the downslope area where water depths are greater than about 800 m, submarine mass landslide with chaotic facie was found. In contrast, gentle bathymetric features and well-developed canyons are observed in the east side of the Mienha Canyon. Sub- bottom profiler shows that submarine mass transport and deposit in water depths greater than about 350 m. Several disturbed unconformities and seamounts were found in MCS profiles. Therefore, the features in the east side of the Mienha Canyon may suggest that submarine mass movements had well developed through several times. In contrast, the tectonic context in the west side of the Mienha Canyon could be unstable and may generate large mass movements in the future.
OS51A-1235
Clay Minerals And Sr-Nd Isotopes Constraint On Sediments Provenance And Transport Pathways In The Eastern South China Sea
Mineralogy and Sr-Nd isotopic composition of the <2μm fraction of 178 surface sediment samples collected by grab sampler in the eastern South China Sea(116°45'-121°14'E,12°- 22°N) were used to identify the sediment provenance and delineate its transport pathways. The clay mineral assemblages mainly consist of illite, chlorite, smectite and kaolinite with an average content of 62.33%, 17.43%, 11.63%, 8.53% respectively. From NE to SW of the survey area, the contents of illite and chlorite are gradually decreased, while the contents of smectite and kaolinite show a trend of gradually increase. A high illite zone extends intermittently along NNE to the north of 16.5°N, while the high smectite content zone occurs in the east of the study area, i.e., in the open sea to the west coast of the Philippines, and smectite shows a trend of gradual decrease from east toward west to the south of 16.5°N. 87Sr/86Sr and 143Nd/144Nd isotopic compositions of the aluminum silicate phase in the clay fractions (<2μm) range from 0.71058 to 0.73050 and from 0.512040 to 0.512468 respectively. The 87Sr/86Sr ratios in the northern continental shelf and slope to the north of 16.5°N are relatively high, majority of 87Sr/86Sr ratios are little higher than the average ratio of the crust (0.720), and turn out to be gradually decreased toward the abyssal area in the south, while the 143Nd/144Nd ratios simply show the opposite variation trend with 87Sr/86Sr. The 87Sr/86Sr ratio for sediments in the south of 16.5°N shows a trend of gradual increase from east toward west, and the minimum value along the coast of Luzon Island, while the 143Nd/144Nd ratio also show the opposite variation trend. Locally in areas around the Luzon Straits the 143Nd/144Nd ratio shows a trend of gradual decrease while the 87Sr/86Sr ratio shows a trend of gradual increase from SE toward NW. Through a coupling approach based on clay minerals and Sr-Nd isotopes, it can be concluded that the terrigenous materials occurring approximately to the north of 16.5°N in the eastern South China Sea mainly originate from the Taiwan Islands and the Taiwan Straits. Continued supply of sediment fed from the Taiwan orogen are transported southward via the Penghu Canyon into the Manila Trench due to the influence of the gravity flow of sediments. However, this gravity flow of sediments was blocked by the seamount on the seabed around 16.5°N, and got settled down in the central sea basin. While the volcanic materials occurring to the south of 16.5°N mainly result from volcanic ashes from the volcanoes on Luzon Island, and were transported into South China Sea mainly via both wind and ocean currents.
OS51A-1236
Physiographical and sedimentological characteristics of submarine canyons developed upon an active forearc slope: The Kushiro Submarine Canyon, northern Japan
Submarine canyons on active forearc margins are major conduits for huge amounts of detritus from uplifting land areas to subduction zones. Comprehensive geological surveys have revealed the physiographical and sedimentological characteristics of the Kushiro Submarine Canyon, one of the largest submarine canyons around Japan. The canyon indents the outer shelf along a generally straight, deeply excavated course of more than 230~km in length upon the active forearc slope of the Kuril Trench in the Northwest Pacific. The forearc slope has a convex-upward geometry that can be divided into upper and lower parts separated by an outer-arc high (3200--3500~m water depth). The upper slope consists of gently folded forearc sediments, and the lower slope is underlain by sedimentary rocks deformed by subduction-related processes. The upper reaches of the canyon (~3250~m of thalweg water-depth) are developed on the upper slope, showing a weakly concave-upward longitudinal profile with a gradual down-canyon increase in relief between the thalweg and the canyon rim. Although an infill of hemipelagic mud and the absence of turbidite deposits indicates that the upper part of the upper reaches of the canyon (~900~m thalweg water-depth) is inactive, the lower part of the upper reaches (900--3250~m thalweg water-depth) is considered to be an active conduit to the lower reaches, as determined from voluminous turbidites recovered in sediment cores (ca.~76-year intervals) and rockfalls observed in the canyon bottom by deep-sea camera. A number of gullies developed upon the northern slope of the lower part of the upper reaches might well provide a frequent supply of turbidity currents, giving rise to a down-canyon increase in the frequency of flow events. The down-canyon increase in flow occurrence is related to a gradual decrease in gradient, demonstrating an inverse power-law relationship between slope and drainage area. In contrast, the lower reaches of the canyon (3250--7000~m thalweg water-depth) are characterized by a gradual decrease in relief, a high gradient, and extremely low sinuosity. The limited increase in drainage area down-canyon indicates that the erosional force of turbidity currents decreases down-canyon. The gradient of the lower reaches largely reflects the morphology of the forearc slope along the canyon, which has been deformed by subduction- related tectonics. The lack of an inverse power-law relationship between gradient and drainage area in the lower canyon supports the hypothesis that the topography of the lower reaches is dominated by subduction- related tectonic deformation of the substrate rather than canyon erosion. Interrelationships between canyon erosion by currents and that by tectonic processes along the forearc slope are important in the development of the physiography of submarine canyons along active forearc margins.
OS51A-1237
Distribution Pattern Of Carbonate Sediments Near Dok Island, East Sea, Republic Of Korea
Dok Island in the East Sea of Korea is located 37 degrees N in latitude. Sediments near the Dok Island are mostly composed of biogenic carbonate constituents and volcanic rock fragments. Thus, carbonate sediments near the Dok Island are probably the northernmost limit in Pacific Ocean. The sedimentary are typical temperate carbonates. Sedimentary distribution pattern is clearly divided into four facies with depth. At less than 100 m in water depth, shallow marine sediments are mostly composed of mollusks, calcareous red algae, and volcanic rocks fragments. Between 100 and 200 m in water depth, carbonate sediments of shallow marine origin decrease, and the sediments are composed of sponge spicules and planktonic foraminifers. This interval is a transitional zone from shallow to deep water. Between 200 and 700 m in water depth, the sediments are characterized by planktonic foraminifers. The sediments are only composed of pelagic clays of terrigenous origin. This sedimentary distribution pattern is clearly reflected by ecologic habits of carbonate producers and physical energy of seawater.
OS51A-1238
Hudson Submarine Canyon Head Offshore New York and New Jersey: a Dynamic Interface II
Hudson Canyon is the largest submarine canyon on the US Atlantic continental margin. Our multidisciplinary study focuses on the canyon head from where it begins as an indentation in the outer continental shelf (water depth 100 m) to 75 km seaward along the canyon axis (water depth 2000 m). A shallow trough, the Hudson Shelf Valley extends about 185 km across the continental shelf and connects the mouth of the Hudson River where the river discharges into New York Bay to the head of the canyon. Our study comprises high-resolution bathymetry using Autonomous Underwater Vehicle (AUV) Eagle Ray (100 square km area),and delineation of interacting shelf and slope water masses using shipboard and AUV hydrocasts including water samples for methane analysis. The initial 10 km of the canyon head (axial depth 100 m to 300 m) bifurcates where it indents the outer shelf, with one branch aligned NW-SE with the Hudson Shelf Valley and a second branch aligned N-S along the shelf. The walls and floor of the NW-SE branch are smoothed by sediment accumulation and appear inactive in terms of sediment transport. The N-S branch is rough and appears active. Ravines orthogonal to the axis progressively increase in frequency and relief seaward through successive 10 km-long N-S and NW-SE trending sections of the canyon attaining a 1 km spacing. Two circular depressions (diameters 100 m and 300 m; relief c.15 m; depths 345 m and 390 m) occur at the base of the W wall of the N-S segment. The depressions may be collapse features related to gas discharge evidenced by a high methane anomaly (50 nM) detected in the adjacent canyon axis (water depth 421 m). Multiple layers of inter-leaved shelf (fresh) and slope (warm, salty) water masses were observed in the canyon head in summer 2007 and 2008. The dynamic interaction of these water masses is being studied in context of shelf-slope exchange and potential influence on canyon topography and ecosystems. We thank NOAA for support.
OS51A-1239
Inferring Depositional Processes and Tempos in Fine-Grained Deep-Water Sediments by X-ray Fluorescence Mapping
Fine-grained sediments are deposited in deep-water settings by hemipelagic and pelagic settling, contour currents, turbidity currents, and debris flows. These processes can be difficult to distinguish by their deposits in mud-dominated sequences. Since different modes of transport and deposition sort on grain "equivalence classes" based on various combinations of grain size, density, shape, and bed roughness, they are potentially distinguishable by characteristic patterns of grading imparted on silt-sized rutile and zircon grains. Moreover, suspension-load windblown sediment is characteristically enriched in zircons relative to other minerals, making Zr/Al or Zr/Ti ratios useful tracers for concentrations of windblown dust. We show that it is possible to map the distributions of fine rutile and zircon grains on centimeter-scale surfaces of slabs and cores using an x-ray fluorescence microprobe. Preliminary mapping of core and slab from a number of locations has identified both massive and graded mud and silt layers as well as distinct laminations with elevated Zr/Ti and Zr/Al. Continuing work in turbidite sequences focuses on correlating observed rutile and zircon distribution patterns with depositional processes.
OS51A-1240
A 250-Year Sediment Record of Anthropogenic Contaminants in the Lisbon Canyon, Portuguese Margin
The Lisbon Canyon on the continental margin of Portugal is located in the immediate vicinity of a densely populated and industrialized metropolitan area, and receives terrigenous sediments from the Tagus River draining a large part of the Iberian Peninsula. Radionuclide records (210Pb, 137Cs) for piston cores retrieved from the canyon indicate rapid and almost continuous accumulation over the last 250 years, with sedimentation rates of up to 1 cm per year. The devastating 1755AD Lisbon Earthquake is represented in some cores by a sandy turbidite layer with erosive base, but subsequently disturbance of the sedimentary record by mass sedimentation events has been very limited. In one core at 1710 m water depth, Pb concentrations increased gradually over the last 250 years, and more abruptly after ~1960AD. Subsequently, anthropogenic lead contributed more than half of total lead deposition. Stable Pb isotope ratios indicate concurrent shifts in sources of Pb and increasing influence of anthropogenic pollutants. A slight reversal in both long-term trends after ~1990AD presumably reflects the phase-out of leaded gasoline. Organic contaminant analyses of a core collected from 1112 m water depth demonstrate enrichment of the canyon sediments with a variety of polychlorinated biphenyls (PCBs) and polyaromatic hydrocarbons (PAHs) over the last century. PCBs increased abruptly during the second half of the 20th century but show a slight decrease over the most recent decade. PAHs appear to have had their maximum in the late 19th century, possibly reflecting fallout of coal dust from one of the busiest shipping routes of the eastern Atlantic. The present study illustrates the potential of submarine canyon sediments as high-resolution archives of human impacts on the continental margin.