Interaction between prices of nickel, copper and cobalt, the latter a by-product of nickel and copper in laterites and sulphite deposits, are analysed in relation to the price of oil, the US real interest rate and the real effective exchange rate of dollar using an autoregressive distributed lag model, to draw considerations on the profitability in the exploitation of polymetallic manganese nodules and cobalt crust in a mutually exclusive scenario. The results show co-movements between these variables through the presence of three long-run relationships. Focusing mainly on the cobalt/nickel relationship, it is shown that price of cobalt anticipates and exerts a negative effect on nickel while, as expected, the price of oil has a positive impact and the exchange rate a negative one. Conversely, the impact of the real interest rate is not significant. A Monte Carlo simulation is employed to forecast a robust average price of nickel in the long run, finding that under the actual stagnant economic conditions and an average price of cobalt of $40/kg (at 2000 price equivalence), the price of nickel will remain close to the actual, around $18/kg (at 2000 price equivalence). This result, coupled with the literature findings that in a mutually exclusive scenario, the prevalence of cobalt crust over manganese nodules can be shown only if the price of nickel is below $9/kg (at 2000 price equivalence), justifies why increased attention has been redirected towards polymetallic nodules.

The past 20 years have been characterised by limited interest in the economic viability of deep seabed mining with the exception of those mineral ores rich in precious metals such as polymetallic sulphides. This paper goes against the tide. After reviewing the most significant literature, it compares the economic feasibility of mining polymetallic manganese nodules and cobalt-rich ferromanganese crusts in a scenario of mutual exclusivity. It uses a new indicator, the cobalt–nickel price ratio, whose aim is to verify at what metal prices the net present value of the two mining projects equalises. Previous research has shown that the turning margin between manganese nodules and cobalt crusts is a cobalt price of $50/kg. The present paper revises this by showing that the choice between mining crust and nodules depends on fluctuations in the price of nickel. A Monte Carlo simulation proves that cobalt crust mining could be reasonably preferred to manganese nodules at cobalt prices of $40–60/kg if the price of nickel fell below $11/kg. Within this condition, investors would receive the minimum acceptable internal rate of return of 15%, which is at a level of risk closer to the land-based mining. However, when the price of nickel passes the $11/kg threshold, the equilibrium between the two ventures can be reached only at a cobalt price greater than $100/kg, causing cobalt crust to become uncompetitive. Finally, the paper, recognising that prices are not unique drivers, introduces legal, political, technological and environmental concerns to show that the final choice between the two mining ventures cannot be merely driven by economic issues.

This paper compares the economic feasibility of two deep seabed mining deposits, manganese nodules and cobalt crust using a new quantitative indicator, the cobalt/nickel price ratio, that verifies the equality between the net present value (NPV) of the two resources. NPV is based on two different models, a multi-period and a singleperiod time cash-flow. In both cases results are similar and show that the current price of nickel could produce equality between NPV of manganese nodules and cobalt crust only if the cobalt price were several hundreds dollars per kg. Results are based on cost of mining estimated by Yamazaki for Japanese licensed deposits, and can be used as a guide in the absence of more recent commercially-derived cost models.

The Sargasso Sea is a fundamentally important part of the world’s ocean, located within the North Atlantic sub-tropical gyre with its boundaries defined by the surrounding currents. It is the only sea without land boundaries with water depths ranging from the surface coral reefs of Bermuda to abyssal plains at 4500 m. The Sargasso Sea’s importance derives from the interdependent mix of its physical structure and properties, its ecosystems, its role in global scale ocean and earth system processes, its socio-economic and cultural values, and its role in global scientific research. Despite this, the Sargasso Sea is threatened by a range of human activities that either directly adversely impact it or have the potential to do so. Being open ocean, the Sargasso Sea is part of the High Seas, the area of ocean that covers nearly 50% of the earth’s surface but which is beyond the jurisdiction and responsibility of any national government, and as such it enjoys little protection. To promote the importance of the Sargasso Sea, the Sargasso Sea Alliance was created under the leadership of the Government of Bermuda in 2010. This report provides a summary of the scientific and other supporting evidence for the importance of the Sargasso Sea and is intended to develop international recognition of this; to start the process of establishing appropriate management and precautionary regimes within existing agreements; and to stimulate a wider debate on appropriate management and protection for the High Seas. Nine reasons why the Sargasso Sea is important are described and discussed. It is a place of legend with a rich history of great importance to Bermuda; it has an iconic ecosystem based upon floating Sargassum, the world’s only holopelagic seaweed, hosting a rich and diverse community including ten endemic species; it provides essential habitat for nurturing a wide diversity of species many of which are endangered or threatened; it is the only breeding location for the threatened European and American eels; it lies within a large ocean gyre which concentrates pollutants and which has a variety of oceanographic processes that impact its productivity and species diversity; it plays a disproportionately large role in global ocean processes of carbon sequestration; it is of major importance for global scientific research and monitoring and is home to the world’s longest ocean time series of measurements; it has significant values to local and world-wide economies; and it is threatened by activities including over-fishing, pollution, shipping, and Sargassum harvesting. Apart from over-fishing many of the threats are potential, with few direct causal relationships between specific activities and adverse impacts. But there is accumulative evidence that the Sargasso Sea is being adversely impacted by human activities, and with the possibility of new uses for Sargassum in the future, the lack of direct scientific evidence does not preclude international action through the established precautionary approach. The opportunity to recognise the importance of the Sargasso Sea and to develop and implement procedures to protect this iconic region and the wider High Seas should be taken before it is too late.

Geochemistry of volcanic rocks of the Davis and Aurora Banks, North Scotia Ridge, is presented with the aim to infer their petrogenesis and implications in regional tectonics. The analyses show consistent major and trace element patterns which are conformable with calc-alkaline series volcanics with typical signatures of subduction zone magma. The source melt of the studied volcanics is deciphered to be subduction zone mantle wedge metasomatised by sediments. Geochemical analyses of the volcanics from the Davis and Aurora Banks are compared with geochemical data of volcanics of the South Sandwich island arc and Jurassic, Cretaceous and Paleogene arc volcanics of Patagonia, South America. This comparative study shows that the Davis and Aurora Banks' volcanics are akin to Cretaceous arc volcanics of the Hardy Formation, South America. Rocks of Hardy Formation are also reported from South Georgia. Further, based on established trace element ratio diagrams, it is deciphered that source magma characteristics of arc volcanics from South Georgia, Hardy Formation and Davis and Aurora Banks are the same. Integration of our findings with previous studies, we propose a geodynamic model for the Davis and Aurora Banks in conformity with accepted model for the evolution of the West Scotia Sea.

The continental margin of SW Africa is typical of a volcanic rifted margin associated with a hotspot trail characterized by a large volcanic ridge, the Walvis Ridge, defining the hotspot migration, and extensive extrusive volcanism that produced seaward-dipping reflectors (SDR). Previously unpublished seismic data show two significant anomalies of the SW African Margin when compared to other typical volcanic rifted margins: (1) Hyaloclastitic outer highs are rare, and (2) the SDR in the North dip towards the Walvis Ridge. We explain these anomalies by a major transform segment close to the centre of volcanism combined with pulsed volcanism. The Walvis Ridge represents an east-west striking extrusive centre which produced a SDR sequence. Following break-up the northern boundary of the Walvis Ridge became a left lateral transform fault. Our data support the idea that a transform fault system interacting with a ridge jump were responsible for the accretion of the São Paulo Plateau to the American plate.

The Maury Channel is a deep-sea sediment transport system located in the Iceland Basin and extends from the Icelandic plateau southwards towards the Charlie-Gibbs Fracture Zone (CGFZ). This study has utilised multibeam bathymetry and multi-channel seismic reflection survey data along 480km of its 1200km pathway. In the northern reach of the channel it is predominantly broad (>20km) and shallow (∼10m). Further to the south the channel narrows (5–10km) and locally deepens to 150m prior to finally discharging onto the Eriador Plain to the north of the CGFZ. DSDP Site 115 in the Iceland Basin can provide insight into the evolution of the system as it sampled a suite of volcaniclastic turbidites of unequivocal Icelandic provenance. This sequence produces distinct amplitude anomalies on seismic reflection profiles allowing it to be mapped over an area of at least 26,000km2. The southern edge of the high velocity unit is delimited by onlap onto the flanks of the Miocene (and younger) Gardar Drift. The drift appears to have initially acted as a barrier to southerly flows and promoted ponding of flows in the Maury Fan. Continued sediment supply from Iceland eventually filled the Maury Fan leading to the overspilling of the Gardar Drift dam. A result was the initiation of the Maury Channel. To the south of the drift, where the seabed is steep, flows are confined to the channel, whereas to the north of the drift, where the gradient is less, unconfined flow pathways dominate. The Maury Channel system highlights the interaction between turbidity currents and bottom currents on abyssal plains. The growth of sediment drifts not only mould the seafloor through their bathymetric development but also, through the building of seafloor topography, influence the passage and behaviour of gravity-driven sediment-laden flows along the seafloor.

The northwest Hatton Bank margin is an ideal locality to demonstrate the interaction between bottom currents and slope configuration in controlling the distribution and morphology of bottom current deposits. The slope area investigated is isolated from any major terrigenous sediment supply and at present is influenced by the Deep Northern Boundary Current (DNBC). 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 exhibits sculpting by bottom currents that flow in a predominantly southwest to northeast direction, and is only locally modified by slope failures. Positive relief features such as the Endymion Spur play an important role in constraining and accelerating bottom-current flow and, consequently, in redistributing sediment along the margin. We demonstrate that the size, morphology and distribution of bottom-current deposits along the slope vary as a function of the interaction between bottom currents, regional slope orientation and local seafloor topography.

The Hatton Bank margin, flanking the Iceland Basin, is an example of a volcanic rifted margin and has been studied to examine the along margin tectono-magmatic variability. Integration of 5660 km of new seismic reflection profiles with >60.000 km(2) of new multibeam bathymetry has allowed the margin to be divided into three segments, each of which are flanked by oceanic crust. 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 SDRs are truncated by Endymion Spur, a chain of steep sided, volcanic cones connected by narrow septa or necks. The central segment has no Inner SDR package and is characterised by the presence of a continental block, the Hatton Bank Block (HBB). The northern segment is adjacent to Lousy Bank, with a wider region of SDRs recognised than to the south, and characterised by many volcanic cones. The variations in the distribution of the SDRs along the margin, the presence of the HBB and Endymion Spur all suggest that the break-up process was not a uniform smooth process along-strike. Structural segmentation controlled the variations along the margin with break-up initiated in the south, producing the SDR packages. The HBB prompted the focus of break-up to relocate outboard of the block. The northern segment was closest to the Iceland "hot-spot", and regular seafloor spreading did not become established until Chron 21. Shortly after break-up, the eruption of Endymion Spur occurred and may have been triggered by the passage of a pulse of hot asthenospheric material along the margin. The margin segmentation pattern we describe controlled the location of the enhanced volcanism along the Endymion Spur to the southern sector. In addition the segmentation has influenced the break-up style (presence or absence of SDR) and also the location and nature of post break-up volcanism. Crown Copyright (C) 2008 Published by Elsevier B.V. All rights reserved.

We report results from an investigation of the geologic processes controlling hydrothermal activity along the previously-unstudied southern Mid-Atlantic Ridge (3-7 degrees S). Our study employed the NOC (UK) deep-tow sidescan sonar instrument, TOBI, in concert with the WHOI (USA) autonomous underwater vehicle, ABE, to collect information concerning hydrothermal plume distributions in the water column co-registered with geologic investigations of the underlying seafloor. Two areas of high-temperature hydrothermal venting were identified. The first was situated in a non-transform discontinuity (NTD) between two adjacent second-order ridge-segments near 4 degrees 02'S, distant from any neovolcanic activity. This geologic setting is very similar to that of the ultramafic-hosted and tectonically-controlled Rainbow vent-site on the northern Mid-Atlantic Ridge. The second site was located at 4 degrees 48'S at the axial-summit centre of a second-order ridge-segment. There, high-temperature venting is hosted in an similar to 18 km(2) area of young lava flows which in some cases are observed to have flowed over and engulfed pre-existing chemosynthetic vent-fauna. In both appearance and extent, these lava flows are directly reminiscent of those emplaced in Winter 2005-06 at the East Pacific Rise, 9 degrees 50'N and reference to global seismic catalogues reveals that a swarm of large (M 4.6-5.6) seismic events was centred on the 5 degrees S segment over a similar to 24 h period in late June 2002, perhaps indicating the precise timing of this volcanic eruptive episode. Temperature measurements at one of the vents found directly adjacent to the fresh lava flows at 5 degrees S MAR (Turtle Pits) have subsequently revealed vent-fluids that are actively phase separating under conditions very close to the Critical Point for seawater, at similar to 3000 m depth and 407 degrees C: the hottest vent-fluids yet reported from anywhere along the global ridge crest. (C) 2008 Elsevier B.V. All rights reserved.

Leg 135 of the Ocean Drilling Program drilled and cored eight sites across the Lau Basin and adjacent Tonga Ridge to study the geological evolution of a backarc basin and adjacent oceanic arc and forearc. Six sites (Sites 834, 835, 836, 837, 838, and 839) were drilled within the Lau Basin, each within smaller and narrower (<10 km) north-south fault basins and collectively representing a broad east-west transect. Two other sites were drilled on the Tonga Ridge, in the forearc of the Tofua Arc. Site 840 lies on the crest of the Tonga Ridge, a shallow, uplifted carbonate platform overlying older volcanic basement, while Site 841 lies on the arc-trench slope in 4800 m of water. Results from this cruise will provide crucial data toward determining the geological history of the Lau Basin-Tofua/ Tonga Arc oceanic-arc system as well as provide a heretofore uncollected observational base for the understanding of oceanic-arc and backarc spreading systems in general. The principal results of Leg 135 were quite different than anticipated, with two results being of particular significance. First, the Lau Basin is much older than expected (>5.6 Ma instead of 2.5-3 Ma), with seafloor-type spreading having occurred in the backarc only in the last 1 to 2 Ma or so. Prior to this, extension occurred by a combination of repeated extensional rifting ("basin and range") with associated local volcanism, with new crust created, if at all, only within the north-trending fault basins. No consistent variations in the chemistry of the Lau Basin volcanic products were noted either within time or space; the igneous basement rocks collected represent basalts, basaltic andesites, and andesites with affinities to both oceanic-arc and mid-ocean-ridge lavas, and indicate complex heterogeneity of the mantle source. Volcaniclastic sediments collected in the cores also show that volcanism of arc affinity may have occurred throughout much of the Lau Basin during extension, rather than being confined to a narrowly defined arc. The second principal result was the coring of dacitic tuffs, welded tuffs, and lavas of upper Eocene or older age at the base of Hole 84IB. These are in fault contact with overlying upper Eocene to lower Oligocene carbonates and a thick sequence of Miocene proximal and distal volcaniclastic sediments. These subaerially erupted dacitic igneous rocks have subsided more than 6 km since their formation, representing profound tectonic foundering. Similar rhyolites of Late Cretaceous age were cored at DSDP Site 207 on the Lord Howe Rise to the west of the Lau Basin; reconstruction of pre-Eocene plate geometry allows speculation for a common source of the silicic volcanic rocks at both sites.

Ocean ridge discontinuities partition and offset spreading centres at a range of scales. Large scale discontinuities (10's-100's km) are synonymous with first-order transform faults, which have well defined linear fault zone valleys. In contrast, Non-Transform Discontinuities (NTDs) are diffuse, smaller scale offsets (0 to < 20 km), characterised by central basins or topographic highs. The geometry of NTD offsets can be categorised by the sense of offset, either right-stepping or left-stepping, and by the relative positions of the segment tips. The segment tip configurations include under-lapping, over-lapping or simple across-axis jumps or stepping in the ridge axis. In this study finite difference software is used to model segment geometry at a slow-spreading ridge under a normal tensile-stress within a homogeneous and isotropic medium. Along- and across-axis segment separations were varied incrementally for left- and right-stepping senses. The results show that the ratio of along-axis to across-axis segment tip separation is a dominant control of stress field rotation within an NTD. Features which most clearly show rotation within an NTD include basins and tectonically controlled constructional ridges. The obliquity of these features along with measurements of the surrounding fault fabrics are used as a way of observing and determining stress rotations within NTDs along the Central Indian Ridge (CIR). These rotations were used to obtain segment geometries from models where the central tensor showed an equivalent rotation. The results show that geometry has a profound effect on stress field rotation under which large- and small-scale volcano-tectonic fabrics form. In addition, a shortfall of the predicted model tip relative to interpreted positions, along with morphology and observation of the ridge fabrics at the terminations to some segments, suggests the existence of a zone, broadly analogous to the process zone observed in fracture mechanics, which we call a damage zone. Given the criteria for the promotion of hydrothermal circulation, this damage zone would have a greater potential for hosting hydrothermal activity. (c) 2007 Elsevier B.V. All rights reserved.