Geochemical variation in ferromanganese nodules and associated sediments from the Pacific Ocean

The major and minor element compositions of a suite of abyssal sea-floor ferromanganese nodules and associated sediments from the eastern central Pacific have been used to examine inter-element relationships and the mineralogy of the nodules, the relationship between the composition of nodules and their associated sediments and regional variations in composition with respect to likely modes of formation of such deposits. Apart from Mn and Fe, significant proportions of the total Ti, Ca, Mg, K, Ba, Sr, Th and Y and almost all the P, As, Ce, Co, Cu, Mo, Ni, Pb, Zn and Zr are present in the oxide fractions of the nodules. The Mg, Ba, Cu, Mo, Ni and Zn contents are significantly correlated with the Mn content, while Ti, P, As, Pb, Sr, Y and Zr are similarly correlated with the total Fe content.Nodules from the northeastern tropical Pacific have Mn/Fe ratios higher than those in the oxide fractions of their associated sediments, todorokite as the principal Mn phase and relatively high concentrations of minor elements associated with Mn. Nodules from the south central Pacific have Mn/Fe ratios similar to those in the oxide fractions of the associated sediments, δ-MnO₂ as the only Mn-phase, and relatively high concentrations of minor elements associated with Fe. There appears to be a smooth gradation in composition in the tropical Pacific between these two end members.The regional compositional variation is interpreted as a reflection of different sources of metals for, and different growth mechanisms of, sea-floor nodules. The oxide precipitate from sea water consists of δ-MnO₂, has a relatively low Mn/Fe ratio and minor element contents related to the total Fe and Mn(δ-MnO₂) content. The oxide precipitate forming in areas of very low sedimentation as a result of diagenetic remobilisation in the surface sediment consists of todorokite, and has a high Mn/Fe ratio and enhanced metal content in the Mn-(todorokite)phase. Available information on the morphology and compositional variation of individual nodules from the tropical Pacific corroborates these contrasting metal sources and suggests that they can be resolved on the scale of an individual oxide concretion.     

Spectral Simulation and Conditioning to Local Continuity Trends in Geologic Modeling

Spectral simulation has gained application in building geologic models due to the advantage of better honoring the spatial continuity of petrophysical properties, such as reservoir porosity and shale volume. Distinct from sequential simulation methods, spectral simulation is a global algorithm in the sense that a global density spectrum is calculated once and the inverse Fourier transform is performed on the Fourier coefficient also only once to generate a simulation realization. The generated realizations honor the spatial continuity structure globally over the whole field instead of only within a search neighborhood, as with sequential simulation algorithms. However, the disadvantage of global spectral simulation is that it traditionally cannot account for the local information such as the local continuity trends, which are often observed in reservoirs and hence are important to be accounted for in geologic models. This disadvantage has limited wider application of spectral simulation in building geologic models. In this paper, we present ways of conditioning geologic models to the relevant local information. To account for the local continuity trends, we first scale different frequency components of the original model with local-amplitude spectrum ratios that are specific to the local trend. The sum of these scaled frequency components renders a new model that displays the desired local continuity trend. The implementation details of this new method are discussed and examples are provided to illustrate the algorithm.     

Phylogeography of the pelagic fish Seriola lalandi at different scales: confirmation of inter-ocean population structure and evaluation of southern African genetic diversity

The study investigated the global and regional phylogeography of the yellowtail kingfish Seriola lalandi by examining genetic diversity and population genetic structure of this species at inter-and intra-ocean level and on a regional scale. DNA fragments of two mitochondrial genes, cytochrome b (Cytb) and cytochrome c oxidase subunit I (COI) and one nuclear gene, recombination activating gene 1 (RAG1), were sequenced to investigate the global-scale phylogeography of this species. The population genetic structure within the South Pacific, as well as along the South African coastline, was examined further using six microsatellite markers. Three distinct clades were identified for S. lalandi, which correspond with previously described subspecies of the North-East Pacific, North-West Pacific and the Southern Hemisphere. Within the latter, additional divergence was observed between the South Pacific and the South-East Atlantic regions. Divergence estimates were indicative of a Pacific origin for S. lalandi populations, because of Pleistocene vicariant events. Microsatellite analyses revealed overall significant genetic differentiation between South African and South Pacific samples. This corroborates recent findings on the global phylogeography of the species. No population differentiation was observed within South Africa, indicating high levels of gene flow.     

Age of the Pomeranian ice‐marginal position in northeastern Germany determined by Optically Stimulated Luminescence (OSL) dating of glaciofluvial sediments

Lüthgens, C., Böse, M. & Preusser, F. 2011: Age of the Pomeranian ice‐marginal position in northeastern Germany determined by Optically Stimulated Luminescence (OSL) dating of glaciofluvial sediments. Boreas, 10.1111/j.1502‐3885.2011.00211.x. ISSN 0300‐9843 The Pomeranian ice margin is one of the most prominent ice‐marginal features of the Weichselian glaciation in northern Europe. Previous results of surface‐exposure dating (SED) of this ice margin disagree with established chronologies and ice retreat patterns, i.e. are much younger than previously expected. We crosscheck the age of the Pomeranian ice‐marginal position in northeastern Germany using single‐grain quartz Optically Stimulated Luminescence (OSL) dating of glaciofluvial sediments. OSL dating indicates an active ice margin between 20.1±1.6 ka and 19.4±2.4 ka forming outwash plains attributed to the Pomeranian ice‐marginal position. On the basis of these results, we suggest a critical reassessment of previous SED data available for the Pomeranian ice‐marginal position within their respective regional geomorphological contexts. From a process‐based point of view, SED ages derived from glacigenic boulders document the stabilization of the landscape after melting of dead ice and landscape transformation under periglacial conditions rather than the presence of an ice margin. SED indicates a first phase of boulder stabilization at around 16.4±0.7 ka, followed by landscape stabilization within the area attributed to the recessional Gerswalder subphase around 15.2±0.5 ka. A final phase of accumulation of glaciolacustrine and glaciofluvial sediments at around 14.7±1.0 ka documents the melting of buried dead ice at that time.     

Analysis of bycatch in the South African midwater trawl fishery for horse mackerel Trachurus capensis based on observer data

The South African midwater trawl fishery targets adult horse mackerel Trachurus capensis. The bulk of the catch is taken by a single freezer-trawler, the biggest fishing vessel operating in South African waters. As fishing takes place off the south coast in ecologically sensitive areas, there are concerns about the potential impacts of this fishing operation on non-target species. Fishing behaviour and bycatch of this fishery from 2004 to 2014 were investigated by analysing observer records with regard to catch composition, volume and temporal and spatial patterns. The midwater trawl fishery was estimated to have caught 25 415 tonnes annually, with a bycatch of 6.9% of the total catch, by weight. There are species overlaps with various fisheries, namely the demersal trawl, small-pelagic, line, shark longline and squid fisheries, yet the total bycatch estimates from this fishery are generally small relative to catches taken in the target fisheries. Bycatch species with the highest average annual catches were chub mackerel Scomber japonicus, redeye roundherring Etrumeus whiteheadi, ribbonfish Lepidopus caudatus and hake Merluccius spp. Large-fauna bycatch species included sunfish Mola mola as well as a number of CITES II- and IUCN-listed species, such as Cape fur seal Arctocephalus pusillus, dusky shark Carcharhinus obscurus, smooth hammerhead shark Sphyrna zygaena and thresher sharks Alopias spp. The 97.9% observer coverage is high and the 6.9% bycatch rate low compared to other South African fisheries; however, due to the large size of the individual hauls (average of 46.3 t), the average sampling rate of 1.56% is low. Our analyses suggest that bycatch in the South African midwater trawl fishery has been lower than in other South African fisheries and similar fisheries elsewhere, but due to the combination of high catch volumes and low sampling rates, estimation errors for rare species are high and there is a substantial risk of incidental unmonitored bycatch of rare large fauna and aggregations of small fauna. This could be mitigated by spatio-temporal management of this fishery, to avoid fishing in high-risk areas, and the introduction of an electronic monitoring programme.     

<Superscript>40</Superscript>Ar/<Superscript>39</Superscript>Ar dating of tuff vents in the Campi Flegrei caldera (southern Italy): toward a new chronostratigraphic reconstruction of the Holocene volcanic activity

The Campi Flegrei hosts numerous monogenetic vents inferred to be younger than the 15 ka Neapolitan Yellow Tuff. Sanidine crystals from the three young Campi Flegrei vents of Fondi di Baia, Bacoli and Nisida were dated using ⁴⁰Ar/³⁹Ar geochronology. These vents, together with several other young edifices, occur roughly along the inner border of the Campi Flegrei caldera, suggesting that the volcanic conduits are controlled by caldera-bounding faults. Plateau ages of ∼9.6 ka (Fondi di Baia), ∼8.6 ka (Bacoli) and ∼3.9 ka (Nisida) indicate eruptive activity during intervals previously interpreted as quiescent. A critical revision, involving calendar age correction of literature ¹⁴C data and available ⁴⁰Ar/³⁹Ar age data, is presented. A new reference chronostratigraphic framework for Holocene Phlegrean activity, which significantly differs from the previously adopted ones, is proposed. This has important implications for understanding the Campi Flegrei eruptive history and, ultimately, for the evaluation of related volcanic risk and hazard, for which the inferred history of its recent activity is generally taken into account.     

Postshield stage transitional volcanism on Mahukona Volcano, Hawaii

Age spectra from ⁴⁰Ar/³⁹Ar incremental heating experiments yield ages of 298 ± 25 ka and 310 ± 31 ka for transitional composition lavas from two cones on submarine Mahukona Volcano, Hawaii. These ages are younger than the inferred end of the tholeiitic shield stage and indicate that the volcano had entered the postshield alkalic stage before going extinct. Previously reported elevated helium isotopic ratios of lavas from one of these cones were incorrectly interpreted to indicate eruption during a preshield alkalic stage. Consequently, high helium isotopic ratios are a poor indicator of eruptive stage, as they occur in preshield, shield, and postshield stage lavas. Loihi Seamount and Kilauea are the only known Hawaiian volcanoes where the volume of preshield alkalic stage lavas can be estimated. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Fishing and Farming at Lake Chad: Responses to Lake-level Fluctuations

Lake Chad lies at the southern extreme of the Sahara Desert and is well known for large fluctuations in its surface area this century. Seasonal fluctuations, however, have received much less attention. This paper presents the results of two complimentary research efforts on the south-west shore of the lake. These illustrate how important both inter and intra-annual fluctuations in the level of the lake are, both in terms of their impact on the environment and in the response of the communities living on the lake shore. The paper compares a time series of the fluctuations in the level of Lake Chad as monitored by the TOPEX/POSEIDON satellite with findings from participatory research with the communities of the south-west lake shore. It shows how the communities of the lake have responded to lake-level fluctuations with their livelihood choices. These results are used to show that although vastly different in scope, a high degree of complimentarity exists between remotely-sensed information and community-based research and that they are of potentially great value to development initiatives on the shores of Lake Chad.