On the Structure of Small-Scale Motion in the Core of the Earth

In 1996, St Pierre (1996) reported numerical simulations of a buoyant blob migrating across the earth's outer core and subject to the combined effects of rotation and an azimuthal magnetic field. He noted that the blob rapidly fragments into a series of plate-like structures. Quite independently, Davidson (1995, 1997) discovered a similar behaviour in the context of low- R m turbulence (without a Coriolis force) and showed that this phenomenon has its roots in the destruction of angular momentum by the Lorentz force. The purpose of this paper is to pull together these earlier studies and, in particular, to determine whether or not St. Pierre's platelets are also a consequence of the destruction of angular momentum. We confirm that this is indeed the case.     

The role of palaeolimnology in assessing eutrophication and its impact on lakes

Eutrophication is perhaps the most pervasive form of pollution. Here we first review its effects on lake ecosystems based largely on modern ecological investigation. The longer time scale afforded by palaeolimnological investigation has seen an increase in the number of the publications since 1990 with a disproportionate increase in citations demonstrating the increasing use and usefulness of palaeolimnology to help understand lakes ecosystems and their response to eutrophication. We summarise briefly the history and origins of palaeolimnological investigation into eutrophication and its impacts in lakes. Then we review quantitative and qualitative palaeolimnological methods for tracking change in nutrient concentrations, algal community and abundance, macrophyte community composition and abundance and zooplanktivorous fish density. The usefulness of stable isotope analysis on sediment organic matter to track eutrophication is assessed and alternative methods discussed. A current challenge is to determine the effects of recent climate change on lake ecosystems. The impacts of climate change and eutrophication on the ecology of lakes have many similarities making it difficult to disentangle the impact of one from the other, in particular where the eutrophication impacts are greatest. We review a number of recent palaeolimnological studies, in particular those integrating long term monitoring data, which have gone some way to identifying when nutrients or climate may be having the greatest impact. Finally, we discuss possible future directions for the discipline, such as the greater integration of studies of evolutionary change using molecular techniques.     

Palaeolimnological records of shallow lake biodiversity change: exploring the merits of single versus multi-proxy approaches

Shallow lakes are among the most threatened ecosystems in the world and many contemporary studies have demonstrated declines in biodiversity due to anthropogenic forcing. Mostly, however, these studies have not covered the full period of human-induced diversity change in lakes which is typically over decades-centuries. Here we provide two examples of palaeoecological studies focussed on reconstructing biodiversity changes in contrasting shallow lake environments that demonstrate the efficacy of the approach—a shallow UK lake and a suite of floodplain lakes (called billabongs) in the Murray-Darling basin, Australia. In the Murray-Darling billabongs, complex sedimentary processes operate, sediment chronologies are less certain and replication of sites is needed to confirm patterns. The combination of sediment records from 10 billabongs showed that diatom diversity changes pre- and post-European (>1850) disturbance were inconsistent; however, reductions in diversity were more common and appear to reflect reductions in macrophyte abundance. At Felbrigg Lake, a multi-proxy study with strong chronological control demonstrated divergent responses of macrophyte, diatom, cladoceran and chironomid richness and diversity to a century of eutrophication. Eutrophication of the site was qualitatively inferred from changes in the macrophyte community in turn reconstructed from plant macrofossils. Benthic cladocerans showed a consistent decline in richness through the record, reflecting the gradual reduction in their macrophyte associated habitat over the past century. Diatom richness and diversity responses were complex, with increases in diversity and richness linked to both increases and decreases in macrophyte species richness and abundance. Chironomid richness and diversity patterns were less consistently linked to eutrophication. The loss of the dominant zooplanktivore (perch) in the 1970s was reflected in the richness and diversity profiles for all groups. Our study reveals clear potential for using sediment cores to infer biodiversity change in shallow lakes and shallow lake regions. However, given the contrasting patterns of diversity change for the different biological groups both in Felbrigg Lake and between Felbrigg and the billabongs, caution is required when interpreting whole-ecosystem biodiversity changes (or the absence of change) based on single as opposed to multi-proxy studies.     

Bi-level optimization for risk-based regional hurricane evacuation planning

Almost all engineering evacuation models define the objective as minimizing the time required to clear the region or total travel time, thus making an implicit assumption that who will or should evacuate is known. Conservatively evacuating everyone who may be affected may be the best strategy for a given storm, but there is a growing recognition that in some places that strategy is no longer viable and in any case, may not be the best alternative by itself. Here, we introduce a new bi-level optimization that reframes the decision more broadly. The upper level develops an evacuation plan that describes, as a hurricane approaches, who should stay and who should leave and when, so as to minimize both risk and travel time. The lower level is a dynamic user equilibrium (DUE) traffic assignment model. The model includes four novel features: (1) it refocuses the decision on the objectives of minimizing both risk and travel time; (2) it allows direct comparison of more alternatives, including for the first time, sheltering-in-place; (3) it uses a hurricane-scenario-based analysis that explicitly represents the critically important uncertainty in hurricane track, intensity, and speed; and (4) it includes a new DUE algorithm that is efficient enough for full-scale hurricane evacuation applications. The model can be used both to provide an evacuation plan and to evaluate a plan’s performance in terms of risk and travel time, assuming the plan is implemented and a specified hurricane scenario then actually occurs. We demonstrate the model with a full-scale case study for Eastern North Carolina.     

The competing models for the origin and internal evolution of granitic pegmatites in the light of melt and fluid inclusion research

In this paper we discuss the main petrogenetic models for granitic pegmatites and how these models have evolved over time. We suggest that the present state of knowledge requires that some aspects of these models to be modified, or absorbed into newer ones. Pegmatite formation and internal evolution have long supposed the need for highly water- and flux-enriched magmas to explain the differences between pegmatites and other intrusives of similar major element composition. Compositions and textural characteristics of fluid and melt inclusions in pegmatite minerals provide strong evidence for such magmas. Furthermore, we show that melt inclusion research has increased the number of potential flux components, which may include H₂O, OH^?, CO₂, HCO ₃ ^? , CO ₃ ^2? , SO ₄ ^2? , PO ₄ ^3? , H₃BO₃, F , and Cl, as well as the elements Li, Na, K, Rb, Cs, and Be, herein described as melt structure modifiers. In this paper we emphasize that the combined effect which these components have on the properties of pegmatite melts is difficult to deduce from experimental studies using only a limited number of these components. The combination and the amount of the different magmatic species, together with differences in the source region, and variations in pressure and temperature cause the great diversity of the pegmatites observed. Some volatile species, such as CO ₃ ^2? and alkalis, have the capacity to increase the solubility of H₂O in silicate melt to an extraordinary degree, to the extent that melt-melt-fluid immiscibility becomes inevitable. It is our view that the formation of pegmatites is connected with the complex interplay of many factors.     

Assessing the ‘wicked problems’ associated with the quality of groundwater used in irrigation: a case study from the North China Plain

Studies on the quality of groundwater have moved beyond the physical realm of contamination and purification, towards the economic concerns of choice and the management of the problem. With these approaches the complex biophysical processes are assessed from the users’ perspective and the policy outcomes that could be used to resolve the problems of groundwater contamination are evaluated. However, in a set of unrelated studies, it has been found that attempts by governments to resolve the problems of groundwater contamination in agriculture have a poor record of success. This could be because the problem is too extensive and diverse to handle or it could be a case of poor policy selection. Taking an example from the North China Plain to illustrate some of the major issues raised in this study, it is concluded that the problem itself is unresolvable on a large scale. In other words, groundwater contamination can be defined as a ‘wicked problem’, i.e. unresolvable by applying pure science, closely linked with social issues, and for which there are no optimal solutions. In this situation, the best solution is possibly to encourage farmers to live with and handle the problem as they best see fit.     

Be-daughter minerals in fluid and melt inclusions: implications for the enrichment of Be in granite–pegmatite systems

The study of re-homogenized melt inclusions in the same growth planes of quartz of pegmatites genetically linked to the Variscan granite of the Ehrenfriedersdorf complex, Erzgebirge, Germany, by ion microprobe analyses has determined high concentrations of Be, up to 10,000 ppm, in one type of melt inclusion, as well as moderate concentrations in the 100 ppm range in a second type of melt inclusion. Generally, the high Be concentrations are associated with the H₂O- and other volatile-rich type-B melt inclusions, and the lower Be concentration levels are connected to H₂O-poor type-A melt inclusions. Both inclusion types, representing conjugate melt pairs, are formed by a liquid–liquid immiscibility separation process. This extremely strong and very systematic scattering in Be provides insights into the origin of Be concentration and transport mechanisms in pegmatite-forming melts. In this contribution, we present more than 250 new analytical data and show with ion microprobe and fs-LA-ICPMS studies on quenched glasses, as well as with confocal Raman spectroscopy of daughter minerals in unheated melt inclusions, that the concentrations of Be may achieve such extreme levels during melt–melt immiscibility of H₂O-, B-, F-, P-, ± Li-enriched pegmatite-forming magmas. Starting from host granite with about 10 ppm Be, melt inclusions with 10,000 ppm Be correspond to enrichment by a factor of over 1,000. This strong enrichment of Be is the result of processes of fractional crystallization and further enrichment in melt patches of pegmatite bodies due to melt–melt immiscibility at fluid saturation. We also draw additional conclusions regarding the speciation of Be in pegmatite-forming melt systems from investigation of the Be-bearing daughter mineral phases in the most H₂O-rich melt inclusions. In the case of evolved volatile and H₂O-rich pegmatite systems, B, P, and carbonates are important for the enrichment and formation of stable Be complexes.     

Clues from Current High CO2 Environments on the Effects of Ocean Acidification on CaCO3 Preservation

Acidification of surface seawater owing to anthropogenic activities has raised serious concerns on its consequences for marine calcifying organisms and ecosystems. To acquire knowledge concerning the future consequences of ocean acidification (OA), researchers have relied on incubation experiments with organisms exposed to future seawater conditions, numerical models, evidence from the geological record, and recently, observations from aquatic environments exposed to naturally high CO₂ and low pH, e.g., owing to volcanic CO₂ vents, upwelling, and groundwater input. In the present study, we briefly evaluate the distribution of dissolved CO₂–carbonic acid parameters at (1) two locations in the Pacific and the Atlantic Ocean as a function of depth, (2) a mangrove environment in Bermuda, (3) a seasonally stratified body of water in a semi-enclosed sound in Bermuda, and (4) in temporarily isolated tide pools in Southern California. We demonstrate that current in situ conditions of seawater pCO₂, pH, and CaCO₃ saturation state (Ω) in these environments are similar or even exceed the anticipated changes to these parameters in the open ocean over the next century as a result of OA. The observed differences between the Pacific and Atlantic Oceans with respect to seawater CO₂–carbonic acid chemistry, preservation of CaCO₃ minerals, and the occurrence and distribution of deep-sea marine calcifiers, support the hypothesized negative effects of OA on the production and preservation of CaCO₃ in surface seawater. Clues provided from shallow near-shore environments in Bermuda and Southern California support these predictions, but also highlight that many marine calcifiers already experience relatively high seawater pCO₂ and low pH conditions.     

Scaling Ecological Dynamics: Self-Organization, Hierarchical Structure, and Ecological Resilience

Assessing impacts of global change is complicated by the problems associated with translating models and data across spatial and temporal scales. One of the major problems of ecological scaling is the dynamic, self-organized nature of ecosystems. Ecological organization emerges from the interaction of structures and processes operating at different scales. The resilience of ecological organization to changes in key cross-scale processes can be used to assess the contexts within which scaling methods function well, need adjustment, and break down.