Back to the future: reflections and directions of South African marine bioinvasion research

Biological invasions continue to increase around the world, with impacts on many coastal marine systems. Here we review the South African marine invasion literature which, despite the field being relatively new, has grown to have significant presence in both the local and international arenas. Of the 79 papers reviewed, 70% focused on the establishment and spread of alien species, with modes of transport and introduction largely overlooked. An emphasis was also apparent towards field studies, in particular survey work, with few experimental studies. The overwhelming majority of papers focused on a single species, the Mediterranean mussel Mytilus galloprovincialis, reflecting the scale of this invasion and the tractable nature of rocky shores as study systems. With the exception of this one species, the impacts of marine alien species have rarely been quantified. We suggest that future research extends the taxonomic coverage of present work and develops a better understanding of the mechanisms of introduction, establishment and spread of marine alien species. Through an experimental approach, the drivers of altered ecological patterns and processes resulting from invasions should be addressed, providing insight into associated impacts. This approach will maintain the local applicability and international relevance of South African marine invasion research.     

Defining the Potential of Nanoscale Re‐Os Isotope Systematics Using Atom Probe Microscopy

Atom probe microscopy (APM) is a relatively new in situ tool for measuring isotope fractions from nanoscale volumes (< 0.01 μm³). We calculate the theoretical detectable difference of an isotope ratio measurement result from APM using counting statistics of a hypothetical data set to be ± 4δ or 0.4% (2s). However, challenges associated with APM measurements (e.g., peak ranging, hydride formation and isobaric interferences), result in larger uncertainties if not properly accounted for. We evaluate these factors for Re‐Os isotope ratio measurements by comparing APM and negative thermal ionisation mass spectrometry (N‐TIMS) measurement results of pure Os, pure Re, and two synthetic Re‐Os‐bearing alloys from Schwander et al. (2015, Meteoritics and Planetary Science, 50, 893) [the original metal alloy (HSE) and alloys produced by heating HSE within silicate liquid (SYN)]. From this, we propose a current best practice for APM Re‐Os isotope ratio measurements. Using this refined approach, mean APM and N‐TIMS ¹⁸⁷Os/¹⁸⁹Os measurement results agree within 0.05% and 2s (pure Os), 0.6–2% and 2s (SYN) and 5–10% (HSE). The good agreement of N‐TIMS and APM ¹⁸⁷Os/¹⁸⁹Os measurements confirms that APM can extract robust isotope ratios. Therefore, this approach permits nanoscale isotope measurements of Os‐bearing alloys using the Re‐Os geochronometer that could not be measured by conventional measurement principles.     

Textural and micro-analytical insights into mafic–felsic interactions during the Oruanui eruption,Taupo

Quenched juvenile mafic inclusions (enclaves) are an occasional but informative component in the deposits of large felsic eruptions. Typically, the groundmasses of these inclusions rapidly crystallize as the mafic magma is chilled against a more voluminous, cooler felsic host, providing a physical and chemical record of the nature and timing of mafic–felsic interactions. We examine mafic inclusions of two compositional lineages (tholeiitic and calc-alkaline) from deposits of the 25.4 ka Oruanui eruption (Taupo, New Zealand). 2-D quantitative textural data from analysis of back-scattered electron images reveal a marked diversity in the groundmass textures of the inclusions, including median crystal sizes (amphibole: 14–45 µm; plagioclase: 21–75 µm) and aspect ratios (amphibole: 1.7–4.2; plagioclase: 2.1–4.0), area number densities (amphibole: 122–2660 mm^?2; plagioclase: 117–2990 mm^?2), area fractions (?) of minerals (?_plag?=?23–45%, ?_amph?=?0–28%, ?_cpx?=?0–6%, ?_oxides?=?0.6–5.5%), and the relative abundance of plagioclase and amphibole (?_plag/?_amph?=?1.0–4.6). Textural parameters vary more significantly within, rather than between, the two compositional lineages, and in some cases show marked variations across individual clasts, implying that each inclusion’s cooling history, rather than bulk composition, was the dominant control on textural development. Groundmass mineral compositions are also diverse both within and between inclusions (e.g. plagioclase from An_34–92, with typical intra-clast variability of ~?20 mol%), and do not correlate with bulk chemistry. Diverse groundmass textures and mineral and glass chemistries are inferred to reflect complex interplay of a range of factors including the degree and rate of undercooling, bulk composition, water content and, possibly, intensive variables. Our data are inconsistent with breakup of a crystallizing ponded mafic layer at the base of the Oruanui melt-dominant body, instead implying that each inclusion partially crystallized as a discrete body with a unique cooling history. Extensive ingestion of mush-derived macro-crystals suggests that mechanical breakup of mafic feeder dikes occurred within a transition zone between the mush and melt-dominant magma body. In this zone, the mush lacked yield strength, as has been inferred from field studies of narrow (meters to few tens of meters) mush-melt transition zones preserved in composite intrusions. Evidence for plastic deformation of inclusions during eruption and the abundance of fresh residual glass in inclusions from all eruptive phases suggest that the inclusions formed syn-eruptively, and must have been formed recurrently at multiple stages throughout the eruption.     

Analysis of stratigraphical sequences at Cocina Cave (Spain) using rare earth elements geochemistry

This study investigates the stratigraphical sequence of Cocina Cave (Spain) employing and testing for the first time the capability of rare earth elements as markers of human activities in caves. Located in Dos Aguas (Valencian Community, Spain), Cocina Cave is characterized by the presence of several Holocene archaeological deposits from the final Mesolithic to the present day and is a pivotal site for understanding the socio-ecological dynamics of the last hunter-gatherer inhabitants of the Iberian Peninsula and the transition to pastoral and agricultural economies in the Western Mediterranean. However, the identification of strata from particular time-periods in the cave is often difficult due to the homogeneity of layers, the poor archaeological record in some strata and the presence of severe disturbance phenomena. The methodological approach of this study consisted of cross-referencing rare earth elements and other chemical markers with the archaeological stratigraphical interpretation, in an attempt to not only support the identification of the anthropic contribution to the formation of Cocina Cave strata, but also to characterize and confirm different natural and occupational episodes, particularly those associated with hunter-gatherer, early agriculturalist, and shepherd activities. Sediments were collected from different excavation areas and analysed for major elements, trace elements, rare earth elements (REE), soil organic matter (SOM) amounts and pH. Multivariate statistics were employed to group samples according to their elemental profile, and these were then compared to the archaeological temporal interpretation. The obtained results showed that REE amount and fractionation geochemical processes were regulated by carbonates, phosphates and pH. The use of REE as markers was particularly useful as their concentrations and their calculated ratios and anomaly distributions were demonstrated to be highly consistent with the archaeological stratigraphical interpretation.     

Recharge response and kinematics of an unusual earthflow in Liechtenstein

Landslides - Understanding landslide behavior over medium and long timescales is crucial for predicting landslide hazard and constructing accurate landscape evolution models. The behavior of...     

Can marine fisheries and aquaculture meet fish demand from a growing human population in a changing climate?

Expansion in the world's human population and economic development will increase future demand for fish products. As global fisheries yield is constrained by ecosystems productivity and management effectiveness, per capita fish consumption can only be maintained or increased if aquaculture makes an increasing contribution to the volume and stability of global fish supplies. Here, we use predictions of changes in global and regional climate (according to IPCC emissions scenario A1B), marine ecosystem and fisheries production estimates from high resolution regional models, human population size estimates from United Nations prospects, fishmeal and oil price estimations, and projections of the technological development in aquaculture feed technology, to investigate the feasibility of sustaining current and increased per capita fish consumption rates in 2050. We conclude that meeting current and larger consumption rates is feasible, despite a growing population and the impacts of climate change on potential fisheries production, but only if fish resources are managed sustainably and the animal feeds industry reduces its reliance on wild fish. Ineffective fisheries management and rising fishmeal prices driven by greater demand could, however, compromise future aquaculture production and the availability of fish products.