Determination of sulfide ligands and association with natural organic matter

Group B metals, such as Hg, Cu, Ag, Pb and Cd bind strongly to reduced inorganic and organic S(II−) ligands. These S(II−) ligands, stable in oxic waters for significant periods of time, occur at the <1–100 s nM concentrations. It is hypothesized that S(II−) ligands are stabilized as Cu–S molecules associated with organic matter by multi-ligand binding or in nano-pore encapsulations in organic matter. S(II−) ligands are estimated by two methods: purge/trap analysis as Cr-reducible sulfide (CRS), and strong ligand (SL_T) from a competitive ligand titration with Ag(I). The CRS/SL_T ratio is nearly one for selected samples. CRS correlates reasonably well (r² ∼ 0.5) with organic C with a slope of 14.6 nM per mg C. The conditional binding constant of Ag–SL is 11.3 for effluent associated with waste-water and decreases for river waters from about 12–8.8 as the strong sites are occupied with Ag(I).     

Iron isotope compositions of carbonatites record melt generation, crystallization, and late-stage volatile-transport processes

Carbonatites define the largest range in Fe isotope compositions yet measured for igneous rocks, recording significant isotopic fractionations between carbonate, oxide, and silicate minerals during generation in the mantle and subsequent differentiation. In contrast to the relatively restricted range in δ⁵⁶Fe values for mantle-derived basaltic magmas (δ⁵⁶Fe?=?0.0?±?0.1‰), calcite from carbonatites have δ⁵⁶Fe values between ?1.0 and +0.8‰, similar to the range defined by whole-rock samples of carbonatites. Based on expected carbonate-silicate fractionation factors at igneous or mantle temperatures, carbonatite magmas that have modestly negative δ⁵⁶Fe values of ~ ?0.3‰ or lower can be explained by equilibrium with a silicate mantle. More negative δ⁵⁶Fe values were probably produced by differentiation processes, including crystal fractionation and liquid immiscibility. Positive δ⁵⁶Fe values for carbonatites are, however, unexpected, and such values seem to likely reflect interaction between low-Fe carbonates and Fe³⁺-rich fluids at igneous or near-igneous temperatures; the expected δ⁵⁶Fe values for Fe²⁺-bearing fluids are too low to produced the observed positive δ⁵⁶Fe values of some carbonatites, indicating that Fe isotopes may be a valuable tracer of redox conditions in carbonatite complexes. Further evidence for fluid-rock or fluid-magma interactions comes from the common occurrence of Fe isotope disequilibrium among carbonate, oxide, silicate, and sulfide minerals in the majority of the carbonatites studied. The common occurrence of Fe isotope disequilibrium among minerals in carbonatites may also indicate mixing of phenocyrsts from distinct magmas. Expulsion of Fe³⁺-rich brines into metasomatic aureols that surround carbonatite complexes are expected to produce high-δ⁵⁶Fe fenites, but this has yet to be tested.     

In bed with the state: political geography and sexual politics

Part of the task of reconfiguring Political Geography must be to consider forms of political activism and participation other than those which have traditionally been the mainstay of the discipline. The rise of new democratic struggles and new social movements, including those around sexual politics, must be integrated into the agenda of a reformulated Political Geography. This paper considers some of the most pressing concerns of contemporary sexual politics—queer politics, sexual citizenship, and AIDS activism—as a way of opening up Political Geography to ‘sex’.     

Isotopic composition of lead and strontium in lavas and coarse-grained blocks from Ascension Island,South Atlantic—an addendum

Natural marokite (CaMn₂O₄) has been studied at high pressures and temperatures using a diamond-anvil press coupled with laser heating in the pressure range 100–250 kbar. A mixture of marokite, CaMnO₃ (perovskite) and MnO (rocksalt) has been observed in all runs in the above pressure range by X-ray diffraction study of the quenched samples. It was interpreted that marokite disproportionates into the mixture CaMnO₃ (perovskite) + MnO (rocksalt) at pressures below 100 kbar. A general comparison of the molar volume for all known compounds having the marokite-related structures (including CaFe₂O₄ and CaTi₂O₄) with those for a mixture of perovskite plus rocksalt structures suggested that the mixture is more stable than the marokite-related structures at high pressures, as confirmed by the present experimental result. The CaFe₂O₄-modification of common nepheline (NaAlSiO₄) is also suggested to be unstable relative to the component oxides of α-NaAlO₂ + SiO₂ (stishovite) at high pressures.     

Transforming management of tropical coastal seas to cope with challenges of the 21st century

Over 1.3 billion people live on tropical coasts, primarily in developing countries. Many depend on adjacent coastal seas for food, and livelihoods. We show how trends in demography and in several local and global anthropogenic stressors are progressively degrading capacity of coastal waters to sustain these people. Far more effective approaches to environmental management are needed if the loss in provision of ecosystem goods and services is to be stemmed. We propose expanded use of marine spatial planning as a framework for more effective, pragmatic management based on ocean zones to accommodate conflicting uses. This would force the holistic, regional-scale reconciliation of food security, livelihoods, and conservation that is needed. Transforming how countries manage coastal resources will require major change in policy and politics, implemented with sufficient flexibility to accommodate societal variations. Achieving this change is a major challenge – one that affects the lives of one fifth of humanity.     

Morphology and star formation in nearby low surface brightness galaxies

We present observations ( B, R, K , Hα and H  i ) of six nearby low surface brightness galaxies (LSBGs). They show an astonishing amount of variety; while some systems appear smooth and featureless, others resolve into loose assemblies of gas clouds. We have derived rotation curves, gas surface density profiles and star formation thresholds for three of the galaxies.
The results have been used to test two ideas describing their star formation: one in which star formation depends solely on the H  i gas surface density, and one that depends on differential rotation. We find that a critical H  i surface density criterion in the range  2.6–12.6 × 10²⁰ cm⁻² (2.1–10.1 M_⊙ pc⁻²)  best describes the star-forming ability of these galaxies on local and global scales. A critical gas surface density based on the rotation of the gas is also able to describe the results on a global scale for two of the three galaxies for which we were able to derive rotation curves.