Volcanism in the Sumisu Rift, I. Major element, volatile, and stable isotope geochemistry

A bimodal volcanic suite with KAr ages of 0.05–1.40 Ma was collected from the Sumisu Rift using alvin. These rocks are contemporaneous with island arc tholeiite lavas of the Izu-Ogasawara arc 20 km to the east, and provide a present day example of volcanism associated with arc rifting and back-arc basin initiation. Major element geochemistry of the basalts is most similar to that of basalts found in other, more mature back-arc basins, which indicates that back-arc basins need not begin their magmatic evolution with lavas bearing strong arc signatures.Volatile concentrations distinguish Sumisu Rift basalts from island arc basalts and MORB. H₂O contents, which are at least four times greater than in MORB, suppress plagioclase crystallization. This suppression results in a more mafic fractionating assemblage, which prevents Al₂O₃ depletion and delays the initiation of Fe₂O_3^(tot) and TiO₂ enrichment. However, unlike arc basalts,Fe^3+/ΣFe ratios are only slightly higher than in MORB and are insufficient to cause magnetite saturation early enough to suppress Fe₂O_3^(tot) and TiO₂ enrichment. Thus, major element trends are more similar to those of MORB than arcs.H₂O, CO₂ and S are undersaturated relative to pure phase solubility curves, indicating exsolution of an H₂O-rich mixed gas phase. HighH₂O/S, highδD, and low (MORB-like)δ³⁴S ratios are considered primary and distinctive of the back-arc basin setting.     

The Tamayo transform fault in the mouth of the Gulf of California

The Tamayo transform fault is located at the north end of the East Pacific Rise where it enters the Gulf of California. This paper presents bathymetric, seismic reflection, magnetic, and gravity data from a detailed survey of the transform fault. The dominant feature of the offset region is a bathymetric ridge trending 120°, parallel to the predicted transform plate boundary. This transform ridge is associated with a large (600 ) positive magnetic anomaly, and a very small positive free-air gravity anomaly. Magnetic and gravity models indicate either a basalt or serpentinite composition for the ridge, but cannot distinguish between these possibilities. At its eastern end, the modern zone of strike-slip motion is in a narrow valley south of the transform ridge. The transform plate margin appears to pass through a saddle in the transform ridge and meet the western spreading center segment in the trough north of the transform ridge. On the basis of this survey and previous work, the history of the Tamayo from continental breakup to the present has been reconstructed. Initial rifting occurred along a trend of 130° at approximately 3.5 m.y.b.p. Once the transform fault was free of the constraints imposed by continent-continent and continent-oceanic lithospheric interaction, the trend of the transform fault rotated counter-clockwise. This rotation resulted in a leaky transform fault and intrusion of a large continuous transform ridge. Further adjustments in the spreading center/transform fault plate boundary configuration have given rise to an incipient zone of rifting cutting across the transform ridge and emplacement of diapiric structures.Contribution of the Scripps Institution of Oceanography, new series.     

A nested numerical tidal model of the southern New England Bight

A nested, barotropic numerical tidal model has been applied to the southern New England Bight to include Long Island Sound (LIS), Block Island Sound (BIS), Rhode Island Sound (RIS), Buzzards Bay (BB) and a portion of the southern New England shelf. An explicit finite difference representation of the two-dimensional vertically averaged equations of motion and continuity, employing forward time and centered spatial differences with the bottom friction term being evaluated at both time levels, is applied to the study area to predict tidal circulation dynamics. Horizontal friction and advective terms have been neglected. Tidal height data along the open boundaries is specified from available data. Model predictions of corange and high and low cophase lines agree with available data and show the strongly co-oscillatory behavior of LIS. Tidal current ellipses agree reasonably well with available data showing rectilinear motion in LIS, BIS and BB and rotary motion in RIS.     

Ecosystem management bioindicators: the ECOMAN project--a multi-biomarker approach to ecosystem management

The ECOMAN project was initiated from an awareness of the complexity of the functioning of coastal marine systems and the clear need for more pragmatic environmental assessment techniques linking environmental degradation with its causes. The aim of the project is to develop a suite of easy to use, cost effective and environmentally valid biological responses (biomarkers) to assess the general health of coastal systems, including estuaries. To achieve this aim, various sublethal endpoints are being measured and evaluated from a range of common coastal organisms showing different feeding types (filter feeding, grazing and predation) and habitat requirements (estuary and rocky shore) and at different levels of biological response (cellular, physiological and behavioural). This holistic integrated approach is essential to identify the full impact of chemical contamination on organisms, and enables the sensitivity of organisms to be ranked and key sentinel species for specific habitats to be identified.     

Dispersion and stability analyses of the linearized two-dimensional shallow water equations in Cartesian coordinates

In the present study, a Fourier analysis is used to develop expressions for phase and group speeds for both continuous and discretized, linearized two-dimensional shallow water equations, in Cartesian coordinates. The phase and group speeds of the discrete equations, discretized using a three-point scheme of second order, five-point scheme of fourth order and a three-point compact scheme of fourth order in an Arakawa C grid, are calculated and compared with the corresponding values obtained for the continuous system. The three-point second-order scheme is found to be non-dispersive with grid resolutions greater than 30 grids per wavelength, while both the fourth-order schemes are non-dispersive with grid resolutions greater than six grids per wavelength. A von Neumann stability analysis of the two- and three-time-level temporal schemes showed that both schemes are stable. A wave deformation analysis of the two-time-level Crank–Nicolson scheme for one-dimensional and two-dimensional systems of shallow water equations shows that the scheme is non- dispersive, independent of the Courant number and grid resolution used. The phase error or the dispersion of the scheme decreases with a decrease in the time step or an increase in grid resolution.     

Hindcast of the Argo merchant spill using the uri oil spill fates model

A comprehensive oilspill fates model, developed by Cornillon and Spaulding at the University of Rhode Island, has been employed to hindcast the well-studied Argo Merchant spill. Using data collected during the spill to define the environmental conditions and the oil composition, properties and release rates, the oil spill fates model was used to predict the spatial and temporal distribution of spilled oil from December 16 to 31, 1976. Comparison of model predictions to observations for spilled oil mass balance, surface trajectories and oiled surface area was in general quite good. Improved predictions require a better definition of the wind and tidally-forced circulation in the vicinity of the wreck site, a more soundly based theory for oil entrainment or dispersion into the water column and an oil spreading theory which more accurately addresses the complex behaviour of a weathering multicomponent petroleum hydrocarbon.