The role of sea ice formation in cycling of aluminium in northern Marguerite Bay,Antarctica

The use of dissolved Al as a tracer for oceanic water masses and atmospheric dust deposition of biologically important elements, such as iron, requires the quantitative assessment of its sources and sinks in seawater. Here, we address the relative importance of oceanic versus atmospheric inputs of Al, and the relationship with nutrient cycling, in a region of high biological productivity in coastal Antarctica. We investigate the concentrations of dissolved Al in seawater, sea ice, meteoric water and sediments collected from northern Marguerite Bay, off the West Antarctic Peninsula, from 2005 to 2006. Dissolved Al concentrations at 15 m water depth varied between 2 and 27 nM, showing a peak between two phytoplankton blooms. We find that, in this coastal setting, upwelling and incorporation of waters from below the surface mixed layer are responsible for this peak in dissolved Al as well as renewal of nutrients. This means that changes in the intensity and frequency of upwelling events may result in changes in biological production and carbon uptake. The waters below the mixed layer are most likely enriched in Al as a result of sea ice formation, either causing the injection of Al-rich brines or the resuspension of sediments and entrainment of pore fluids by brine cascades. Glacial, snow and sea ice melt contribute secondarily to the supply of Al to surface waters. Total particulate Al ranges from 93 to 2057 mg/g, and increases with meteoric water input towards the end of the summer, indicating glacial runoff is an important source of particulate Al. The (Al/Si)_opal of sediment core top material is considerably higher than water column opal collected by sediment traps, indicative of a diagenetic overprint and incorporation of Al at the sediment–water interface. Opal that remains buried in the sediment could represent a significant sink of Al from seawater.     

Surface trapping and leakage of low-frequency g modes in rotating early-type stars – II. Global analysis

A global analysis of the surface trapping of low-frequency non-radial g modes in rotating early-type stars is undertaken within the Cowling, adiabatic and traditional approximations. The dimensionless pulsation equations governing these modes are reviewed, and the boundary conditions necessary for solution of the equations are considered; in particular, an outer mechanical boundary condition, which does not enforce complete wave trapping at the stellar surface, is derived and discussed in detail. The pulsation equations are solved for a 7-M_⊙ model star over a range of rotation rates, using a numerical approach.
The results of the calculations confirm the findings of the preceding paper in the series: modes with eigenfrequencies below a cut-off cannot be fully trapped within the star, and exhibit leakage in the form of outwardly propagating waves at the surface. The damping rates resulting from leakage are calculated for such 'virtual' modes, and found to be appreciably larger than typical growth rates associated with opacity-driven pulsation. Furthermore, it is demonstrated that the surface perturbations generated by virtual modes are significantly changed from those caused by fully trapped modes; the latter result suggests differences in the line-profile variations exhibited by these two types of mode.
The findings are discussed in the context of the 53 Per, SPB and pulsating Be classes of variable star. Whilst wave leakage will probably not occur for overstable g modes in the 53 Per and slowly rotating SPB stars, the adoption of the new outer mechanical boundary condition may still affect the pulsational stability of these systems. Wave leakage for overstable modes remains a possibility in Be stars and the more rapidly rotating SPB stars.     

Spatial wavelet analysis of line-profile variations

The technique of wavelet analysis is discussed in the context of line-profile variations in rapidly rotating stars undergoing non-radial pulsation. This technique may be used to determine the harmonic degree l of the pulsation using isolated residual spectra; it is able to handle spectra with relatively low signal-to-noise ratio levels, and is well suited to extracting previously unobtainable information from low-quality, patchy data. A demonstration of the technique is presented using data generated from a spectral synthesis code.     

The role of returned migrants in England's poorest region

Work on the growing international phenomenon of return migration requires a base of comparative knowledge on the less conspicuous process of inter-regional return migration. Three questionnaire studies in the North-East of England identified about one-quarter of respondents as ‘returned migrants’ to that region. This group are attracted to work in new factories, but their economic status has not been markedly improved by geographic mobility.     

Comparison of methods for predicting discharge in compound open channels

The relative accuracies of four conventional stage-discharge prediction methods, for flow in compound channels, were compared in a laboratory study. Discharge measurements in a physical model comprising a deep central channel flanked by wide shallow berms (flood plains), as well as similar observations by others, provided the basis for comparison.System discharge was either undertestimated (‘single-channel’ method) or overestimated (various ‘separate channels’ methods) when depth on the flood plain zones was small, i.e. when the velocity differential between the deep and shallow zones was large. These discrepancies can be attributed to questionable assumptions made in the different methods tested regarding the nature of flow in compound channels.A new method is proposed which accounts for momentum transfer between adjacent deep and shallow zones of compound sections. This transfer mechanism and its effect on system conveyance are usually ignored in conventional methods. The new method gives satisfactory results for the conditions examined. Its accuracy can be further improved with the development of more accurate friction factor relationships for compound channels.     

Design principles for individual transferable quotas

Individual transferable quota (ITQ) institutions should be designed to minimize two types of transaction costs. First, to minimize the costs of transferring ITQ rights among rights-holders and users, rights should be separated into three components: a permanent entitlement share, an annual catch allocation, and a license to fish. Second, ITQ rights can reduce the transactions costs for development of self-governance by owners both by specifying a non-unanimous voting rule (preferably one-share/one-vote) and also by delineating clear standards for devolution of responsibility from government. These same two principles for reduction of transactions costs can be applied, with slight variation, to individual transferable input systems.     

The role of frontal currents in larval fish transport on Georges Bank

The hydrography and distributions of cod larvae on Georges Bank were surveyed during two research cruises in April and May 1993 in order to relate larval drift between cruises to the vernal intensification of the frontal component of the residual circulation. We observed the transport of two patches of cod larvae. One patch, which had maximum larval cod densities of 45 larvae 100 m⁻³ in April, appeared to have been advected south about 75 km between surveys, while the other, which had maximum larval cod densities of 20 larvae 100 m⁻³ in April, appeared to have been advected north-northeast about 25 km. Maximum larval densities in each patch sampled during the second cruise in May were 15 and 18 larvae 100 m⁻³, respectively, and mean growth in total length for larvae in the two patches was approximately 5.5 mm and 4.5 mm, respectively, between the two cruises. During the April cruise there was a large volume of anomalous cold, fresh water, of Scotian Shelf origin, which occupied much of the eastern third of Georges Bank. During May, relatively cold, fresh water appeared in a band from the Northeast Peak along the Southern Flank, between Georges Bank water on the top of the Bank, and upper Slope Water offshore. The distribution of cold, fresh water suggests its participation in the general clockwise circulation around the Bank. The transport of cod larvae comprising the first patch appeared to become organized within, and move along, the frontal boundary established by the Scotian Shelf-like water mass, while larvae in the second patch, which we assumed to have moved to the north, may have been transported northward in an on-Bank flow of warmer and saltier upper Slope Water, which may have originated from a Gulf Stream Ring. Based upon observed transport of the first patch of larvae in relation to the frontal boundary, we present a conceptual model of frontal mixing currents on Georges Bank, where current velocities may reach 5 cm s⁻¹ at the depth of the pycnocline. We suggest that this frontal component of the residual circulation, which is in addition to that resulting from tidal rectification, may be important in the transport of fish larvae, and that interannual variability in the degree of intrusion of extrinsic water masses may contribute to variable larval cod drift patterns, to variable larval cod retention on the Bank, and ultimately, to variable larval fish recruitment to the early juvenile stage.