Margin Off Research Articles

A benthic source of isotopically heavy Ni from continental margins and implications for global ocean Ni isotope mass balance

Nickel (Ni) is a bio-essential element for phytoplankton in the modern oceans, and yet, the global ocean mass balance of Ni has puzzled scientists for decades. Many estimates of total Ni output flux are larger than the total Ni input flux to the ocean. The measurement of Ni stable isotopes (δ60Ni) in earth materials may inform our understanding of ocean biogeochemistry and redox conditions in both the modern ocean and the geological past. An ocean Ni stable isotope imbalance has also concerned scientists, with a global ocean δ60Ni of +1.4 ‰ which is notably heavier than the major source of Ni to the oceans from rivers. Recent efforts to resolve Ni and δ60Ni imbalances have focused on the role which manganese (Mn) oxides play in marine Ni cycling, both in the water column and in marine sediments. Manganese oxide rich marine sediments can supply isotopically heavy dissolved Ni to porewater fluids and seawater, but the source of the isotopically heavy porewater Ni remains unclear. Here we present porewater trace metal concentrations and δ60Ni from two sites from the continental margin off southern California. Porewater Ni concentrations are up to roughly 100-fold higher than deep seawater concentrations (∼1 μM compared to 10 nM, respectively). Porewater δ60Ni is near 0 ‰ in the subsurface region where Ni concentrations are highest, suggesting dissolution of lithogenic material from sediments. Porewater δ60Ni increases dramatically towards the sediment-water interface with values of up to +2.66 ‰, which to our knowledge are the heaviest Ni isotope compositions ever reported for natural materials. Measurements of porewater and sediment Ni and Mn concentrations suggest that Ni is released to porewaters in the Mn-reducing zone, and then removed by newly precipitated Mn oxides as Mn and Ni move towards the oxygenated zone of sediments. A simple Rayleigh model suggests a Ni isotope fractionation of factor of -0.61 ‰ for Ni sorption onto Mn oxides, while a diffusion-reaction model suggests a Ni isotope fractionation of -1.80 to -0.96 ‰, always with preferential adsorption of lighter Ni isotopes. This flux of Ni toward the sediment-water interface, coupled with preferential removal of lighter Ni isotopes in marine sediments, provides evidence supporting an isotopically heavy benthic source of new Ni to the oceans, which we estimate has a magnitude of 0.65 × 108 to 1.66 × 108 moles/year. We find that a benthic flux such as measured here over just 0.27-2.70 % of the ocean seafloor could mix with the river δ60Ni of +0.8 ‰ to achieve the observed deep ocean δ60Ni of +1.4 ‰. This study reveals the similarities in how rivers and continental margin sediments supply heavy Ni isotopes to the ocean. In both continental rivers and margin sediments, terrigenous Ni is released with an δ60Ni near 0.1 ‰, but lighter isotopes are captured by precipitation onto oxides so that the dissolved flux to the ocean is isotopically heavier than the terrigenous material from which Ni was released, and in the case of margin sediments may be heavier than even bulk seawater δ60Ni. We thus recognize continental margin sediments with active Mn cycling as a ‘new’ source of isotopically heavy dissolved Ni to the ocean.

CAGE14-5 Cruise Report: Fram Strait – NW Svalbard

CAGE 14-5 cruise allowed to study the gas release from gas hydrated sub-seabed environments at the continental margin off NW and N-Svalbard and the transport and distribution of methane within the water column. We carried out acoustic profiling (18, 38 and 120 kHz) in the water column, CTD water sampling for gas analyses, seismic profiling (mini GI guns), bathymetry mapping (EM300), and sediment gravity coring (3m corer). Though water above gas flares may be enriched in methane, methanotrophic microbescan reduce the methane concentrations and thus the amount of methane that may escape from the seabed to the ocean, one of the topics investigated during this cruise The cruise may be known as: CAGE14_5_JM

CAGE13-7 Cruise Report: Gas Release Activity & Underwater Landslide Research Cruise

The overall aim of the CAGE 13-7 cruise was to study the gas release activity from gas hydrated sub-seabed environments at the continental margin off Svalbard towards the Norwegian-Greenland Sea and Arctic Ocean. Acoustic measurements in the water column, water sampling for gas analyses, seismic profiling, bathymetry mapping, and sediment coring allowed to reach this aim. Generally, the water column above gas flares may be rich in methane but methanotrophic microorganisms might hinder an escape of methane from the water to the atmosphere. At the Molloy transform and the Vestnesa ridge we collected seismic data and sediment cores for sampling gas hydrates. We also took sediment cores from a submarine slide complex at the continental margin of NW Svalbard. The age of this slide is of interest because it sits on gas hydrated sediments as indicated by a BSR. The timing of the slope failure is unknown. At the massive Hinlopen slide area we surveyed the eastern sidewall, the toe of the slope and a block within the major slide debris flow area to understand better a potential coupling between slide processes and gas hydrates. Seismic profiles show bottom simulating reflectors that are indicative for gas hydrate underneath the southeastern headwall of this slide complex.
 The cruise may be known as: CAGE13_JM

Sedimentary cycling of zinc and nickel and their isotopes on an upwelling margin: Implications for oceanic budgets and paleoenvironment proxies

Zinc and Ni are essential micronutrients whose stable isotope systematics in marine sediments represent promising, but still developing, tracers of past ocean chemistry and biology. Sediments from upwelling continental margins have been identified as important sinks for Zn and Ni, driven by high productivity, incorporation of the metals into cells and organic carbon burial. At present, however, our understanding of how Zn and Ni isotope composition of upwelling sediments reflects specific processes in the water column is incomplete. Here, we present coupled Zn and Ni abundance and isotope data for both solid phase and porewater in a series of sediment cores collected on a shelf-to-slope transect across an oxygen minimum zone (OMZ) from the southwest African margin off Namibia.Zinc/Al and Ni/Al ratios in Namibian margin sediments are elevated relative to the lithogenic background, by factors of 1.4–2.4 and 1.7–5.7, respectively. Systematic relationships between solid phase Zn and Ni concentrations and organic carbon accumulation corroborate the view that authigenic Zn and Ni are mainly delivered to these sediments via export production from the photic zone. Corrections for detrital Ni are sometimes substantial, but authigenic δ60Ni values are within uncertainty of the modern deep ocean, at 1.38 ± 0.18 ‰ (mean and 1SD, n = 42). Authigenic δ66Zn is more variable, at −0.09 to 0.50 ‰, at or below the value for the deep ocean average. This latter observation can be attributed to Zn isotope fractionation during sequestration into authigenic ZnS phases in the sediments, either quantitatively, or partially.Porewater systematics are more complex and the profiles do not necessarily reflect the redox state of the sediment-porewater system at the time of sampling, but rather characteristics inherited from more reducing conditions in a temporally heterogeneous system. Porewater zinc concentrations (30–369 nM) are much higher than the deep ocean and increase with depth beneath the sediment–water interface. Despite this prominent increase in Zn concentrations, δ66Zn is rather constant and lighter than the deep ocean average, at 0.18 ± 0.06 ‰ (mean and 1SD, n = 33). These observations are most consistent with the buffering of the small porewater pool by the dissolution of a previously formed sulfide phase. Porewater Ni concentrations are closer to the deep ocean, mostly at 5–15 nM. The lightest porewater isotope compositions (δ60Ni as low as 0.15 ‰) are consistent with a Mn-oxide source of Ni, whereas the heaviest isotope compositions (up to 1.76 ‰) clearly reflect uptake of light Ni into sulfide at depth within the sediment.Our data, for the largest upwelling site in the modern ocean, add to sparse data from the eastern Pacific, and confirm that upwelling margin sediments bury Ni that is close to the deep ocean in isotope composition, but Zn that is generally lighter. The data thus confirm the importance of such margins in setting the heavy isotope composition of oceanic Zn. Sediments from this kind of setting hold significant potential for the construction of records of past oceanic Ni isotopes.

A submarine morphotectonic analysis combining GIS-based methods and virtual reality: Case study of the low-rate active thrust faulting off Boumerdès (Algeria)

The Algerian margin is located at the slow-rate convergent boundary between African and Eurasian plates and experienced several strong earthquakes in the last centuries. Among them, the 2003 Mw 6.8 Boumerdès event has triggered large turbidity currents in the slightly concave canyons of the slope and numerous cable breaks in the abyssal plain. In this study, we explore where, how and when the tectonic inversion of the margin off Boumerdès has left witnesses in the seafloor morphology and whether the observed deformation correlates with the 2003 coseismic rupture zone and with the Plio-Quaternary sedimentation. We have performed a careful analysis of the seafloor morphology and subsurface seismic reflectors at the landscape scale and along/between canyons by combining classical GIS-based methods and Virtual Reality techniques. From the mid-slope to the deep basin off the ∼60 km long Boumerdès-Dellys coast, we evidence large knickpoints corresponding to the development of four main cumulative fault scarps and two perched basins which are deeply incised by steep canyons and gullies. We interpret these structures to result from frontal propagation of two main south-dipping thrusts by upper crustal décollement ramping, evidencing an incipient sub-thrust imbrication in a stage of initiation of an accretionary wedge. The flat-ramp thrust geometry and their along-strike segmentation explain the development and shape of the perched basins in the backlimb of fault-related folds. The onset of growth strata is dated at 1.5 ± .5 Ma on the slope and .9 ± .3 Ma in the deep basin. The length, position, strike and segmentation of the older, southern thrust ramp are consistent with the coseismic characteristics of the Mw 6.8 2003 earthquake. The cumulative vertical scarp throw exceeds 1 km, supporting Quaternary shortening rates of 1.6 ± .7 mm/yr, in agreement with geodetic strain rates across the western Mediterranean basin. Virtual Reality offers powerful and promising means to correlate seismic imagery and seafloor morphology and is of great help to improve the robustness of tectonostratigraphic interpretation.

Climatic control on detrital sedimentation in the continental margin off Chennai, western Bay of Bengal – A 42 kyr record

While the peninsular Indian rivers deliver considerable loads of detrital sediments to the Bay of Bengal, changes in their depositional patterns with time are relatively less constrained compared to those deposited by Himalayan Rivers. Here, we present a 42 kyr record of detrital sedimentation, studied using whole-core logging, environmental magnetism, and major element geochemistry from the continental margin near Chennai, in the western Bay of Bengal. The variations of magnetic mineral properties and elemental concentrations of detrital sediments combined with the published oxygen isotope record, suggest monsoonal control on detrital input to the margin. Four major periods of changes in sedimentation are identified 1) the lower section of the core representing marine isotope stage (MIS) 3 (42–24 ka) shows varying detrital input, while magnetic minerals are affected by early diagenesis, 2) the period between 24 and 15 ka exhibits increased detrital input as a result of subaerial erosion in southern India during the last glacial sea-level lowstand, 3) the deglacial period from 15 to 10 ka is marked by decreased detrital input and increased productivity, and 4) the Holocene (10–2 ka) period experienced increased detrital input and chemical weathering in the source areas. Although the post-depositional alteration of magnetic minerals in MIS 3 limits the use of environmental magnetism, major elements and δ18O record the variations in paleomonsoon and detrital input during this period. The increased detrital input during 24–15 ka, despite the glacial conditions and intensified NE winter monsoon, indicates the increased subaerial erosion of exposed continental shelf during the sea-level lowstand owing to the proximity of the sampling site to the coast. The high magnetic susceptibility (χlf), chemical index of alteration (CIA), Al and Ti content beginning at ∼10 ka marks the intensification of SW summer monsoon through the Holocene.

E&P Notes (November 2022)

E&P Notes (November 2022)

Late Pleistocene- Holocene architecture and sedimentary processes on the glacially influenced SW Grand Banks Slope off Newfoundland

Complex inter-relationships between alongslope and downslope sediment dispersion exist on glaciated continental margins and vary widely along continental margins depending on sediment supply and bottom current strength. In eastern Canada, proglacial sedimentation rates are relatively high on the SW Grand Banks Slope compared to the sediment starved SE Grand Banks margin, but relatively low compared to the glacially dominated Scotian margin off eastern Canada. As on other parts of the Canadian margin, its late Quaternary sediment architecture has been constructed by interacting alongslope and downslope processes. These include sediment transported by downslope glacial meltwater discharge, alongslope bottom currents and ice-rafting. Based on the analysis of sediment cores going back to 24 ka (Heinrich event 2), this study investigates fine-grained sedimentary facies and the development of variable depositional patterns on the glacially influenced SW Grand Banks Slope off Newfoundland (eastern Canada). Both turbidites and contourites show stratification, but differ in internal structure, the presence of IRD, and the nature of their upper and lower boundaries. Sandy contourites are mostly massive, occurring either as lenses or as part of the ideal bi-gradational vertical sequence with mottled silt-mud. Glacial silty contourites have distinct rhythmic laminae with the long axis of IRD parallel to bedding. Regional scale thickness variations allow discrimination between hemipelagites and muddy contourites. Depositional architecture is built through temporal and spatial coupling of the diverse sedimentary processes. During the last glacial maximum and early deglaciation, turbidity currents fed either by meltwater or oceanographic processes flowed in canyons, and a contourite depositional system developed between the canyons. The two systems interacted on inter-canyon ridges, where contourite sedimentation was not completely overwhelmed by energetic turbidity currents. In the Holocene, alongslope processes became dominant, building a drift with clearly variable thickness, in part related to seabed morphology. A conceptual model is proposed to present the key elements of depositional processes in this depositional system, and a similar evolutionary history can be expected on other distal glacial margins.

“Improvement in Power Quality of Grid Connected PV & Wind Power Generation System”

Abstract: Power structure is really extraordinary and future one system. In this structure, there is wind system with neighboring planetary gathering and diesel generator system, which is limit in one spot that is reserves (Batteries) and yield, gives age sources, little turbines system used in hybrid, infers relationship with battery, diesel-generator and photovoltaic system. The breeze is a wellspring of free-energy, which has been used since bygone era. It is used of wind stream through wind turbine to provide the mechanical ability to change into electrical power this structure for used by a wide margin off and off-network system in like manner, that marvel called hybrid power system. Now and again, this blend power system in any case called Green Energy. Mix of something like two economical power sources is more convincing than single. This is called as blend system. 'Hybrid' connotes unite harmless to the ecosystem power sources headways. This advancements yield gives electric deftly gets at home, on-network and so forth Numerous combination system sources, which worked off-grid structure, not related with an appropriated structure from this system, we set aside the energy power stream in batteries. A mix of somewhere around two supportable power sources is more effective than a singular is brought with respect to cost, capability and reliability. Energy is the main element for both present day and agribusiness progression of any country. Keywords: Charging station, DC grid, Electric vehicle, MATLAB Simulink

Characterization of the organic matter in pockmark areas of the Southwestern Atlantic upper slope

Pockmarks are circular or elliptical structures formed at the seabed by the expulsion of gas from the subsurface. They are widely distributed along the continental margin off southeastern Brazil and can be over a kilometer wide and 100 meters deep. However, studies concerning the organic characteristics of these pockmark areas are scarce. This study sought to evaluate the organic composition of the sedimentary matter in pockmark areas located in the continental slope region of the southern Brazilian coast. Hydrocarbons, sterols, long-chain alcohols, stable isotopes of C and N, total organic carbon, and total nitrogen were assessed to provide an organic molecular characterization of the pockmarks located in the Southwestern Atlantic Ocean. These compounds did not reflect the organic characteristics of the scape of fluids that generate pockmark structures.

Biogeochemical responses to internal-wave impacts in the continental margin off Dongsha Atoll in the Northern South China Sea

This study aimed to understand the effects of nonlinear internal waves (NLIWs) on nutrient-involved biogeochemical processes and the consequences in the continental margin off Dongsha Atoll (DA) in the northern South China Sea (NSCS). Shipboard and mooring observations were conducted to determine hydrological and biogeochemical conditions mainly from two transects covering the DA-associated upper slope, shelf break, and shelf zones. A dense array of thermistor moorings and a temperature-fluorescence-sediment trap array were deployed on the same transect to determine the short-period variability of transport and shoaling of NLIWs across the shelf and to link physical variability to biogeochemical consequences induced by NLIW events. The shoaling of NLIWs appeared to uplift cooler and nutrient-rich subsurface water into the nutrient-deplete surface in shelf and nearshore environments as well as increase nutrient concentrations and biological production. We observed shoaling events that induced a notable range of upward fluxes in nitrate and nitrite (0.42–2.92 mmol N m−2 d−1) onto the euphotic zone to enhance and sustain new production, depending on the strength of shoaling activity in various observations. The shoaling-derived new production may fully elucidate the amount of sinking fluxes of particulate organic carbon measured from the shoaling field. According to short-time sequential observations during the passage of a single NLIW, the depressed waves may play a crucial role in enhancing the vertical transfers of surface-replete dissolved gases, carbon, or suspended constituents through the surface layers of stratified waters. This NLIW forcing appears to be effective in supplying cooler and nutrient-rich water to the DA-associated coral community, and this may be vital for improving the future development and conservation of the coral ecosystem.

The occurrence of the parasitic amphipod Trischizostoma crosnieri Lowry & Stoddart, 1993 (Amphipoda: Amphilochidea: Lysianassida) in a methane seep site in the southeastern Pacific

The genus Trischizostoma Boeck, 1861 is a cosmopolitan group of parasitic and symbiotic aristoidean amphipods whose distribution is poorly known, with scarce specimens reported principally from pelagic environments until 3655 m depth. In this note, Trischizostoma crosnieri Lowry & Stoddart,1993, a species described for the southwest Pacific, is recorded for the first time in the southeast Pacific. The species was known previously only from a female specimen, described from the Philippines, with two additional unpublished records from the east coast of Australia and Tasmania. The specimens studied herein were obtained at 874 m depth, 36 nm to the northwest of Concepción, Biobío Region, in a methane seep site. However, the relationship between this species with this particular habitat is still uncertain. The genus Trischizostoma has been cited for the Nazca and Salas y Gómez ridges; nevertheless, our finding constitutes the first record of a species at the continental margin off Chile, raising to four the known species of the genus for Chilean waters.

Distribution of Methane Plumes on Cascadia Margin and Implications for the Landward Limit of Methane Hydrate Stability

Nearly 3,500 methane bubble streams, clustered into more than 1,300 methane emission sites, have been identified along the US Cascadia margin, derived both from archived published data and 2011, 2016–2018 dedicated multibeam surveys using co-registered seafloor and water column data. In this study, new multibeam sonar surveys systematically mapped nearly 40% of the US Cascadia margin, extending from the Strait of Juan de Fuca in the north to the Mendocino fracture zone in the south, and bounded East–West by the coast and the base of the accretionary prism. The frequency-depth histogram of the bubble emission sites has a dominant peak at the 500 m isobar, which extends laterally along much of the Cascadia margin off Oregon and Washington. Comparisons with published seismic data on the distribution of bottom simulating reflectors (BSR), which is the acoustic impedance boundary between methane hydrate (solid phase) and free gas phase below, correlates the bottom simulating reflectors upward termination of the feather edge of methane hydrate stability (FEMHS) zone and the newly identified bubble emission sites off Oregon and Washington. The Cascadia margin off northern California, where the BSR ends seaward of the FEMHS, has fewer sites centered on the 500 m isobaths, although data are more limited there. We propose that the peak in bubble emission sites observed near the 500 m isobath results from migration of free gas from beneath the solid phase of the BSR upslope to the FEMHS termination zone, and suggest that this boundary will be useful to monitor for a change in methane release rate potentially related to a warming ocean.

Detrimental conditions affecting Xestospongia muta across shallow and mesophotic coral reefs off the southwest coast of Puerto Rico.

Sponges are fundamental components of coral reef communities and, unfortunately, like other major benthic members, they too have been impacted by epizootic and panzootic events. We report on the prevalence of disease-like conditions affecting populations of the giant barrel sponge Xestospongia muta across shallow and mesophotic coral reefs off La Parguera Natural Reserve (LPNR) and Mona Island Marine Reserve (MIMR) in Puerto Rico. Four different conditions affecting X. muta were observed during our surveys, of which 3 have been previously reported: cyclic spotted bleaching (CSB; apparently non-lethal), Xestospongia-tissue wasting disease (X-TWD; apparently lethal), and sponge orange band disease (SOB; sparsely associated with X-TWD infected individuals). Additionally, we describe a fourth condition, Xestospongia-tissue hardening condition (X-THC), a previously unreported disease recently observed along the insular shelf margin off LPNR and MIMR. Within LPNR, a total of 764 specimens of X. muta were inspected and measured. Of these, 590 sponges (72.2%) had CSB, 25 (3.27%) had signs of X-TWD, 7 (0.92%) had SOB, and the remaining 142 (18.6%) were apparently healthy. Three colonies inhabiting upper mesophotic depths on the LPNR insular shelf showed signs of CSB and X-TWD. At MIMR, video-transect surveys revealed a total of 514 colonies, of which 40 (7.78%) had signs of CSB and/or XTWD, 14 (2.72%) were affected by X-THC, while the remaining 460 (89.5%) showed no external signs of disease and appeared healthy. The presence of 4 concomitant disease-like conditions in barrel sponges of Puerto Rico is alarming, and indicative of the deteriorating status of Caribbean coral reefs.

Deep-Sea Habitats and Megafauna on the Slopes of the São Paulo Ridge, SW Atlantic

The Sao Paulo Ridge (SPR) is a 350 km-long linear geological feature located in the Continental Margin off Brazil (Latitude 28 - 29°S, Longitude 40 - 45°W). In 2013, the region was mapped during the SW Atlantic ‘Iata-Piuna’ expedition and explored by a series of deep-sea dives of the manned submersible Shinkai 6500. A digital bathymetric model analyzed for seafloor morphology, delimited four major bathymetric sectors namely plateau, ridge crest, ridge escarpment and ridge foot. These sectors further enclosed 12 morphological features at smaller spatial scales (structural classes) including plains, valleys, peaks, terraces and troughs. Video profiles across the depth gradient (4219 to 2644 m depths) revealed that the slopes of the SPR southern flank were gentle and terraced, mostly covered by biogenic sediments and interrupted by rocky cliffs/crests, dispersed outcrops and loose particles. The North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW) overlaid at the escarpment along which they established colder (0.4 - 1.0°C; 4200 – 3400 m) and warmer (2.0-3.0°C; 3400 – 2600 m) habitats, respectively. Physical components were used to define seven seascape units in the ridge foot (2), escarpment (3), and plateau-ridge crest (2), where a total of 914 organisms of the epibenthic and benthopelagic megafauna were recorded. Over 70% of these records were sessile suspension feeders, including sponges (61.5%) and anthozoans (11.4%). Most taxonomic groups concentrated above 3800 m, under the influence of NADW, where densities reached maximum values (mean 0.26 organisms.m-2; 0.024 – 0.027 organisms.m2 95% CI). Also, nearly half of megafauna records concentrated in patches delimited by the 3800 – 3300 m and 2900 – 2700 m isobaths. The deepest patch (3800 - 3300 m) coincided with the interface zone between AABW and NADW, where mixing processes create a density gradient. Evidences suggested that topography-related deep-water flow dynamics, and not substrate availability, drives benthic megafauna distribution at meso-habitat scale.

Cenozoic increase in subduction erosion during plate convergence variability along the convergent margin off Trujillo, Peru

Subduction erosion is a long-term, large-scale geological process that dominates the structural inventory of a large number of convergent margins. Along the Peruvian convergent margin, this process has controlled the structural deformation of the forearc as a consequence of spatio-temporal variations during the Cenozoic. However, the pace at which tectonic erosion occurred has not been linked to regional, subduction-related events. The aim of this study is to show that subduction erosion along the Central Peruvian convergent margin off Trujillo (7∘S–9∘S) was influenced by plate convergence variability since the Late Cretaceous. Drilling data, multi-channel seismic (MCS) data and subsidence analyses are used to investigate the long-term effect of subduction erosion on the tectonic evolution of the Peru margin. Our study shows that subduction erosion (1) did not occur between the Cretaceous and Early Eocene (110–56 Ma), (2) increased and fluctuated between the Eocene and Pliocene (56–5 Ma) with a maximum average trench retreat of 3 km.Myr−1 between the Middle Miocene and Late Miocene (20–5 Ma), and (3) has decreased since the Pliocene (5 Ma) (1 km.Myr−1 of average trench retreat). A remarkable finding is that shorter periods of faster subduction erosion coincide with or follow major plate reorganization events that were marked by changes in the velocity and direction of relative plate convergence as well as with well-known phases of Andean orogeny. Based on our analyses, we therefore conclude that convergence variability off Peru is a primary mechanism controlling the pace at which tectonic erosion occurred along the Trujillo Basin during the Cenozoic.

Three types of modern submarine canyons on the tectonically active continental margin offshore southwestern Taiwan

Six submarine canyons are distributed along the active margin off SW Taiwan. Using multi-beam bathymetric data and reflection seismic profiles to determine canyon head locations with respect to shelf edge, five of these canyons were classified into the following three types: 1. river-connected; 2. shelf-indenting; and 3. slope-confined. The remaining canyon was re-interpreted as a sea valley. Type 1 canyon, the Kaoping Canyon, is directly connected to the Kaoping River and supplied with terrestrial sediment. The canyon head segment tends to generate hyperpycnal flows during flooding, causing intense erosion of seafloor across the shelf and slope and forming a major sediment conduit. The Penghu, Kaohsiung and Fangliao canyons are of type 2 and incise into the shelf, forming a V-shaped head segment with abundant slumping features. Without continuous sediment supply from rivers, the canyon head receives sediments mainly from local slope failures on canyon walls and is unable to generate intense erosive sediment flows, resulting in an indentation into the shelf over a short distance. Oceanographic/hydrodynamic measurements close to the canyons are still not available for the region, despite they could shed light on the on-going sediment dynamics in the area. The Shoushan Canyon is a type 3 canyon characterized by limited sediment input from the Kaoping Shelf and weak canyon erosion, especially during sea-level highstands, resulting in a relatively straight canyon course confined to the upper slope. These submarine canyons share common regional tectonics, sea-level changes and climatic conditions. However, they evolved via local processes mainly controlled by sediment input directly related to head location, resulting in distinct morphologies and sizes. These canyons have remained active during the present-day sea-level highstand. Frequent earthquake and flooding events are the major triggering factors for sediment failures and generation of subsequent turbidity currents, resulting in substantial incision into the canyon. The results of the present study indicate that the SW Taiwan margin is characterized by canyons of type 1 and type 2 (n = 4) with only one type 3 canyon. This represents large percentages of type 1 and type 2 canyons compared to other regions of the world. Narrow shelf and abundant sediment supply are the two main controls for the presence of river-connecting and shelf-incising canyons on the active Taiwan margin.

Late Cretaceous to recent ocean-bottom currents in the SW Pacific Gateway, southeastern Chatham Rise, New Zealand

Sedimentary drifts archive the history of the ocean-bottom current dynamics. Bottom currents associated with the Pacific Deep Western Boundary Current (DWBC) along the submarine continental margin off southern and eastern New Zealand are of particular interest because of their potential to contain records of changes in the SW Pacific circulation. Analysis of multi-channel seismic reflection data from the RV Sonne expedition SO246 together with earlier seismic data enabled us to reconstruct bottom currents and map sediment deposits along the southeastern Chatham Rise margin for the past 80 million years. The seismic records are supplemented by sub-bottom profiler and bathymetric data, which provide detailed information on the youngest stratigraphy, sedimentary structures and bathymetry. This approach allows time-dependent mapping of sedimentary deposits and reconstruction of current regimes. The opening of the Tasmanian Gateway in the early Oligocene led to the development of the DWBC, which influenced regional sedimentary processes. However, the occurrence of bottom current activity prior to opening the Tasmanian Gateway suggests the existence of a proto-DWBC. Increased bottom current activity in the Miocene indicates a change to a more dynamic circulation regime in the SW Pacific, consistent with intensification of Antarctic glaciation and increased Antarctic Bottom Water formation. Plio/Pleistocene records indicate a weakening of the bottom-water energy along the Chatham Rise margin. Overall, sediment deposition was widespread before gateway opening, almost non-existent in the Oligocene and sparse in the Neogene.

Giant protists (xenophyophores) function as fish nurseries.

During a recent research cruise on the continental margin off Costa Rica, we observed many giant agglutinating Xenophyophoroidea (Foraminifera) on both hard and soft substrates. These fist-sized protists, which occur only below 400 m, are one of the few groups of organisms limited to the deep ocean (Tendal 1972). Xenophyophores are known to be abundant on sloped topography where there is high particle flux, as many have a morphology designed to trap settling particles which they can feed on or use to form tests (Levin 1991, Levin and Gooday 1992).

A new record of Lamellibrachia columna (Siboglinidae, Annelida) from cold seeps off New Zealand, and an assessment of its presence in the western Pacific Ocean

Lamellibrachia columna Southward was originally described from hydrothermal vents of the Lau Basin, between Fiji and Tonga. This study utilizes phylogenetic and morphological analyses to confirm the collection of Lamellibrachia columna from cold seeps on the Hikurangi Margin off New Zealand, thereby extending its geographic range southward by approximately 1900 km. We also propose, based on molecular evidence, that specimens previously reported from vents in the Nankai Trough, Japan and seeps off southern and eastern Japan are L. columna. Furthermore, we suggest that Lamellibrachia sagami Kobayashi et al. described from cold seeps off southern and eastern Japan is a junior synonym of Lamellibrachia columna. Our work confirms that L. columna is found at two types of chemosynthetic habitat over a wide geographic range in the western Pacific Ocean.