A kinetic approach to describe trace-element distribution between particles and solution in natural aquatic systems

The partitioning of radioactive trace elements between seawater and particulate matter from surface sediments and sediment traps was investigated in laboratory experiments. For the elements Na, Zn, Se, Sr, Cd, Sn, Sb, Cs, Ba, Hg, Th and Pa (group I) constant distribution coefficients (K_d) were found after a few days of equilibration, whereas the elements Be, Mn, Co and Fe (group II) showed an increasing K_d over the whole time of observation of 108 days. The time dependence of K_d is described by an adsorption-desorption equilibrium (group I elements), followed by a lattice transport reaction step (group II elements). The reaction rate constants are compared to Mn oxidation rates and to adsorption rate constants derived from in situ measurements of the $\text{U}\text{Th}$ disequilibrium as available from literature.     

Lake Floor Morphology and Sediment Architecture of Lake Torneträsk,Northern Sweden

Here we present datasets from a hydroacoustic survey in July 2011 at Lake Torneträsk, northern Sweden. Our hydroacoustic data exhibit lake floor morphologies formed by glacial erosion and accumulation processes, insights into lacustrine sediment accumulation since the beginning of deglaciation, and information on seismic activity along the Pärvie Fault. Features of glacial scouring with a high‐energy relief, steep slopes, and relative reliefs of more than 50 m are observed in the large W‐basin. The remainder of the lacustrine subsurface appears to host a broad variety of well preserved formations from glacial accumulation related to the last retreat of the Fennoscandian ice sheet. Deposition of glaciolacustrine and lacustrine sediments is focused in areas situated in proximity to major inlets. Sediment accumulation in distal areas of the lake seldom exceeds 2 m or is not observable. We assume that lack of sediment deposition in the lake is a result of different factors, including low rates of erosion in the catchment, a previously high lake level leading to deposition of sediments in higher elevated paleodeltas, tributaries carrying low suspension loads as a result of sedimentation in upstream lakes, and an overall low productivity in the lake. A clear off‐shore trace of the Pärvie Fault could not be detected from our hydroacoustic data. However, an absence of sediment disturbance in close proximity to the presumed fault trace implies minimal seismic activity since deposition of the glaciolacustrine and lacustrine sediments.     

Lithospheric thickness beneath the southern Kenya Rift: implications from basalt geochemistry

Geochemical data are reported for samples from the flanks and floor of the southern Kenya Rift Valley in the Lake Magadi area, and from two central volcanoes located within the rift valley. Rift lavas include samples of Singaraini and Ol Tepesi basalts on the eastern flank, Kirikiti basalts from the western flank, and plateau trachytes from the rift valley floor. Central volcano samples are from Ol Esayeiti and Lenderut located on the eastern flank. The rift basalts are mildly ne-normative, moderately evolved (Mg#=0.39-0.62) alkali basalts and show an overall range in differentiation. Incompatible trace element abundances are moderately elevated (Nb=17-51; Zr=93-274; La=17-55 ppm) and show strongly coherent variations and constant inter-element ratios (e.g. Zr/Nb=4.2-5.5; Nb/Ta=17.5ǂ.4; (La/Sm)_n=7.3ǃ.1); isotope ratios are restricted in range (⁸⁷Sr/⁸⁶Sr=0.70393-0.70436; ¹⁴³Nd/¹⁴⁴Nd=0.51272-0.51280; ²⁰⁶Pb/²⁰⁴Pb=19.87-19.92; ²⁰⁷Pb/²⁰⁴Pb=15.68-15.70; ²⁰⁸Pb/²⁰⁴Pb=39.56-39.71). Central volcano lavas are more alkaline in character and include basanite (Ol Esayeiti; Mg# >60) and hawaiite to benmoreite (Lenderut; Mg#=0.48-0.38). Incompatible element ratio are similar to those of the rift basalts, although the chondrite normalised REE patterns are steeper (La/Sm)_n=17.4ǃ.2). ⁸⁷Sr/⁸⁶Sr (0.70358, 0.70391), ¹⁴³Nd/¹⁴⁴Nd (0.51280, 0.51267), ²⁰⁶Pb/²⁰⁴Pb (19.96,20.17), ²⁰⁷Pb/²⁰⁴Pb (15.66,15.76) and ²⁰⁸Pb/²⁰⁴Pb (39.80,40.00) ratios of Ol Esayeiti basanites are similar to the rift basalts, whereas the Lenderut lavas have unusually low¹⁴³Nd/¹⁴⁴Nd (0.512388-0.512453) ratios for their ⁸⁷Sr/⁸⁶Sr (0.70370-0.70481) ratios, and distinctly less radiogenic and variable Pb isotope compositions (²⁰⁶Pb/²⁰⁴Pb=17.93-19.01; ²⁰⁷Pb/²⁰⁴Pb=15.43-15.58; ²⁰⁸Pb/²⁰⁴Pb=37.91-39.14). An integrated model is developed in which the geochemical signature of the lavas is attributed to variable degrees of melting to depths within the garnet stability field, and in the presence of residual amphibole. The stability fields of these phases in P-T space indicates that the lavas must have formed within the sub-continental lithosphere rather than within the underlying ambient asthenosphere or a rising mantle plume. The subcontinental lithospheric mantle must therefore extend to a depth of at least 75 km beneath the Lake Magadi area, which contrasts with recent gravity models for the area, which infer that lithospheric mantle is absent beneath this section of the southern Kenya Rift.     

Winners, losers and curate's eggs: Urban and regional outcomes of Australian economic restructuring 1971–1991

Since the early 1970s the Australian economy has undergone major transformations common to other western industrialised countries. Jobs in manufacturing declined precipitately whilst the service economy grew, most significantly in producer services but also in lower skilled jobs. Tourism and services exports began to rival traditional agricultural and mining staples. Social outcomes, also typical of international trends, included rising unemployment and polarisation of incomes. Australia's changing global context, especially the nation's increasing orientation towards Asian growth economies, have underpinned restructuring. A political climate of economic rationalism has facilitated and accentuated restructuring. The economic shifts of the past quarter century have meant that everywhere the basis for economic growth has changed. Overlaying and reinforcing the re-definition of competitive advantage has been a shift in the pattern of agglomeration economies and diseconomies. New growth regions have emerged, others have had their prospects reinforced, and still others have had their outlook diminished in absolute or, more commonly, relative terms. The paper traces the regional outcomes of national economic restructuring and shifts in the balance of agglomeration economies and diseconomies over the period from 1971 to 1991. The focus is on the top end of the urban hierarchy, on specialised industrial cities where job loss from manufacturing has hit hard, amenity regions where international and domestic tourism have been major factors in growth, and non-metropolitan balances where growth has been uneven but generally low. Demographic, economic sectoral and welfare indicators are woven into a tableau of change expressed at national, intra-state and intrametropolitan scales.     

Quantifying the suspended sediment discharge to the ocean from the Markham River,Papua New Guinea

The Markham River is a small river draining a tropical mountain range with altitudes between 1000 and 3000 m and discharges directly into a submarine canyon, the head of which is at 30 m depth and reaches depths of 500 m only 4 km from the shore. As such, the Markham discharge system serves as a possible analogue for rivers discharging onto margins during low stands of sea-level. Located in a tectonically active area and with high rainfall, sediment supply is high and episodic and is sometimes related to catastrophic mountain landslides. The river has an estimated sediment load of 12 Mt yr⁻¹. Occasionally, high energy flows are generated at the river mouth which is evident from the channel morphology and sediment distribution. Profiles of salinity and suspended sediment concentrations (SSC) show that sediment is dispersed via a plume with components at both the surface, intermediate depth along isopycnal surfaces and near the sea bed. The dispersal pattern of the surface freshwater plume is largely determined by the buoyancy force. The surface plume is very thin with salinity gradients 15 ppt m⁻¹ while a Richardson number greater than unity suggested that the mixing zone is highly stratified. Estimates of the horizontal sediment flux gradient of the surface plume along the estuary axis suggest that about 80% of the sediment discharged is lost from the plume within a distance of 2 km from the river mouth. Particle fall velocities estimated from the vertical flux indicate values less than those of flocculated material. Layers of sediment with SSCs between 500 and 1000 mg l⁻¹ were observed at intermediate depths and near the seabed during periods of both high and intermediate discharge. The mass of sediment in a SSC layer at intermediate depths between 150 and 250 m within the canyon channel was estimated to be equivalent to an average of 2 to 3 days of Markham sediment discharge. SSCs near the seabed of between 250 and 750 mg l⁻¹ suggest that layers of significantly elevated density exist near the seabed, moving under the influence of gravity down steep seabed slopes of the Markham canyon.     

Spatial variability in specific discharge and streamwater chemistry during low flows: Results from snapshot sampling campaigns in eleven Swiss catchments

Catchments consist of distinct landforms that affect the storage and release of subsurface water. Certain landforms may be the main contributors to streamflow during extended dry periods, and these may vary for different catchments in a given region. We present a unique dataset from snapshot field campaigns during low‐flow conditions in 11 catchments across Switzerland to illustrate this. The catchments differed in size (10 to 110 km²), varied from predominantly agricultural lowlands to Alpine areas, and covered a range of physical characteristics. During each snapshot campaign, we jointly measured streamflow and collected water samples for the analysis of major ions and stable water isotopes. For every sampling location (basin), we determined several landscape characteristics from national geo‐datasets, including drainage area, elevation, slope, flowpath length, dominant land use, and geological and geomorphological characteristics, such as the lithology and fraction of quaternary deposits. The results demonstrate very large spatial variability in specific low‐flow discharge and water chemistry: Neighboring sampling locations could differ significantly in their specific discharge, isotopic composition, and ion concentrations, indicating that different sources contribute to streamflow during extended dry periods. However, none of the landscape characteristics that we analysed could explain the spatial variability in specific discharge or streamwater chemistry in multiple catchments. This suggests that local features determine the spatial differences in discharge and water chemistry during low‐flow conditions and that this variability cannot be assessed a priori from available geodata and statistical relations to landscape characteristics. The results furthermore suggest that measurements at the catchment outlet during low‐flow conditions do not reflect the heterogeneity of the different source areas in the catchment that contribute to streamflow.     

A community-wide intercomparison exercise for the determination of dissolved iron in seawater

The first large-scale international intercomparison of analytical methods for the determination of dissolved iron in seawater was carried out between October 2000 and December 2002. The exercise was conducted as a rigorously “blind” comparison of 7 analytical techniques by 24 international laboratories. The comparison was based on a large volume (700 L), filtered surface seawater sample collected from the South Atlantic Ocean (the “IRONAGES” sample), which was acidified, mixed and bottled at sea. Two 1-L sample bottles were sent to each participant. Integrity and blindness were achieved by having the experiment designed and carried out by a small team, and overseen by an independent data manager. Storage, homogeneity and time-series stability experiments conducted over 2.5 years showed that inter-bottle variability of the IRONAGES sample was good (< 7%), although there was a decrease in iron concentration in the bottles over time (0.8–0.5 nM) before a stable value was observed. This raises questions over the suitability of sample acidification and storage.