Extending the generality of ecological models to artificial floating habitats

Marine assemblages on natural hard substrata are generally different from those on artificial habitats. There is, however, the potential for certain ecological processes to operate on both types of structures. On the sides of floating pontoons in Sydney Harbour, there were strong patterns of vertical distribution of sessile epibiotic organisms and molluscan grazers across relatively small spatial scales (in three defined zones, namely splash, shallow and deep). Patterns of vertical distribution of the tubeworms Hydroides spp. were reversed depending on the cover of mussels. A manipulative experiment was done to test if patterns of vertical distribution of Hydroides spp. were due to (1) the functioning of mussels or (2) the structure provided by mussels. Neither the functioning nor structure of mussels accounted for the patterns of distribution of Hydroides spp. Mussels increased recruitment of Hydroides spp., in the shallow and deep zones, and this was not due to increased surface area of the mussel shells. Manipulation of numbers of grazers and covers of sessile epibiota showed that the observed negative relationship between grazers and epibiota was due to grazers reducing recruitment of epibiota and epibiota decreasing survival of grazers. Most importantly, processes that accounted for patterns of distribution of mobile and sessile organisms on artificial floating structures were similar to those repeatedly shown to create such patterns on natural rocky shores.     

Germanotype Tektonik und die Plattentektonik-Hypothese

Zusammenfassung Durch eine Zusammenstellung sämtlicher bisher vorliegender paläomagnetischer Me\ergebnisse aus dem Präkambrium von Nordamerika, Afrika und Europa lä\t sich der Nachweis erbringen, da\ diese Kontinente weder unter Zugrundelegung ihrer heutigen geographischen Position noch jener vor Einsetzen der mesozoisch-känozoischen Plattendrift übereinstimmende Wanderbewegungen durchführten. Die paläomagnetischen Befunde von Nordamerika sind durch einige kleinrangige Verschiebungen gekennzeichnet, die jedoch in den Me\werten des afrikanischen Präkambriums nicht wiedergefunden werden konnten. Daraus ergibt sich als vorläufige Schlu\folgerung, da\ während des Präkambriums zwischen den beiden Kontinenten horizontale Relativbewegungen stattfanden, wenn auch die Ausbildung vieler präkambrischer Orogengürtel nicht unbedingt als Konsequenz der Plattendrift angesehen werden mu\. Vielmehr scheint es so, da\ diese Orogene weitgehend das Resultat von Vertikalbewegungen sind, die von intensiven krustalen Aufheizungen begleitet waren. Dieser Mechanismus ist jenem ähnlich, der die Plattenbewegung in Gang setzt, nur da\ dadurch kein kontinentales Aufrei\en mit einhergeht. Die Problematik, die solch einem, den driftenden Platten mitgegebenen Mechanismus anhaftet, wird aufgezeigt (aber nicht gelöst).

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A survey of the Precambrian paleomagnetic data at present available for North America, Africa and Europe shows that it is inconsistent with these continents either in their present geographic positions or their positions prior to Mesozoic rifting. The data within North America show few signs of smaller scale displacement, and none is apparent in the present African data. The tentative conclusions are that relative motion did occur during Precambrian times but that many of the Precambrian orogenic belts do not require plate motion as a causative mechanism. It is suggested that these belts may be the result of largely vertical movements accompanied by strong heating. The mechanism is suggested to be similar to that driving plate motions, differing in that it did not lead to rupture. The problem of accounting for such a mechanism given moving plates is indicated (but not solved).

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Résumé La compilation des résultats de mesures paléomagnétiques recueillies dans le Précambrien d'Amérique du Nord, de l'Afrique et de l'Europe, montre que ces continents n'ont pas accompli de mouvements de dérive concordants en ce qui concerne soit leur position géographique actuelle soit leur position avant la dérive méso-cénozoÏque. Les résultats paléomagnétiques se rapportant à l'Amerique du Nord ne montrent que des déplacements insignificants qui ne peuvent Être retrouvés dans les mesures relatives au Précambrien africain. On en tire comme première conclusion qu'il y eut, au cours du Précambrien, des mouvements relatifs entre les deux continents, bien que la formations de nombreuses ceintures orogéniques précambriennes ne doive pas Être absolument envisagée comme la conséquence de la migration de plaques. Il semble bien plus que ces zones orogéniques soient le résultat de mouvements verticaux qui furent accompagnés par des réchauffements intensifs de la croûte. Ce méchanisme est analogue à celui qui déclanche le mouvement des plaques, mais sans toutefois entrainer de déchirure continentale. L'auteur soulève, sans vouloir la résoudre, la problématique qui s'attache à un tel mécanisme affectant des plaques dérivantes.

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Für die übersetzung des Manuskripts sowie für Diskussionen danke ich Herrn Prof. Dr. K.Schäfer, Karlsruhe.     

Late quaternary hydrothermal explosion breccias at Kawerau Geothermal Field,New Zealand

Two large (10⁶–10⁷ m³ erupted volume) hydrothermal explosions occurred from craters on the eastern margin of Kawerau Geothermal Field at c. 14,500 and 9,000 yrs B.P. Explosion products are interbedded within C14 dated pyroclastic fall deposits and contain clasts of hydrothermally altered ignimbrite, rhyolite and tuff, in a silty hydrothermal clay matrix. No magmatic ejecta are found. Some ejected blocks record earlier pre-eruption episodes of shallow hydraulic fracturing and silica cementation. Drillhole stratigraphy indicates that explosion extended to about 190 m below present ground level. The explosion is analysed as a rock/water interaction with eruptive energy provided by flashing of about half the available water. Although surface heat flow and shallow temperatures are now low at eastern Kawerau, the hydrothermal explosions demonstrate the previous existence of a high temperature shallow geothermal system, probably related to a major fault feeding water up through the basement.     

Surface magnetic survey of the Souss Basin, southwestern Morocco: Evaluation of the tectonic role postulated for the Agadir and Tarfaya fault zones and the South Atlas flexure

The results of a surface magnetic survey over the Souss Basin, the High Atlas and Anti-Atlas margins, combined with the gravity data of Van den Bosch (1971) and a review of the regional geology permits us to trace structures from the High Atlas into the Souss Basin. The South Atlas flexure is an east—west trending structure imposed during the Cenozoic upon an area with a northeast—southwest, Anti-Atlas structural grain.The major structure is the Tarfaya fault zone, whose location, projected by Choubert and Faure-Muret (1970), lies within a corridor of low residual magnetic anomalies. The continuation of this structure in the High Atlas is the Tizi n'Test fault zone. The Hercynian activity of the Tizi n' Test fault zone (Mattauer et al., 1972) was just one period of reactivation of an older, Precambrian, structure for we believe the Tarfaya fault zone was also active in post-late Triassic time.The Agadir earthquake occurred along a minor fault parallel to the Tarfaya-Tizi n' Test zone and is not related to the South Atlas flexure. Neither does it represent the entry into the African continent of a major ocean linked structure. The Tarfaya-Tizi n' Test fault zone is a much more likely candidate, for its offshore trend appears to match that of the Canary Fracture Zone.     

Temporal analysis of groundwater nitrate concentrations from wells in Prince Edward Island,Canada: application of a linear mixed effects model

Changes in nitrate concentration in groundwater from wells in Prince Edward Island, Canada were investigated over time using two datasets. Temporal trends in groundwater nitrate concentrations were assessed annually during 1981–1996 (1,299 observations), and both seasonally and monthly during 1988–1991 (1,868 observations). Data were analysed using linear mixed models with random effects and correlation structures. The average nitrate concentration in the monthly dataset was 3.99 mg/L as NO₃–N, with January, May, and November concentrations being higher (p?=?0.018). A seasonal effect was present when season was combined with land use type in an interaction term (p?=?0.004). Wells located in agricultural areas had greater nitrate concentrations than urban areas, which in turn, had greater values than low human-impact areas. Row-cropped areas had higher groundwater nitrate concentrations in the summer, whereas manure storage areas were higher in the spring and autumn. Nitrate in groundwater in areas with low human impact and with centralized sewage disposal infrastructure remained relatively low and stable throughout the seasons. There was no significant annual trend (p?=?0.954), but for individual sites, 9.6% significantly increased in nitrate concentration over time, and 6.6% significantly decreased over time.     

High Plains groundwater isotopic composition in northeastern New Mexico (USA): relationship to recharge and hydrogeologic setting

Hydrogeology Journal - In the High Plains (HP) region of northeastern New Mexico (NE NM), USA, underlying bedrock aquifers are utilized where the High Plains Aquifer is thin, absent, or...     

Current status of coral takeover by an encrusting excavating sponge in a Caribbean reef

On Caribbean reefs, the excavating sponge Cliona tenuis opportunistically colonized dead skeletons of the elkhorn coral Acropora palmata after its massive die‐off in the 1980s. Further C. tenuis population increase occurred by colonization of other coral species, causing coral tissue death through undermining of live tissue and lateral growth. To follow up on a previous (2001) characterization of the abundance and size structure of C. tenuis at Islas del Rosario (Colombia), these factors were again estimated in 2014, along with its substratum utilization. The fate of sponge individuals colonizing massive coral colonies marked in 2001–2004 was also followed. By 2014 C. tenuis was still disproportionally occupying dead A. palmata branches, but its abundance and density, and the cover of other benthic elements, had not significantly changed over the 13‐year period, suggesting that a stasis has been reached. Cliona tenuis was thus initially favored in the 1980s, but substratum monopolization did not occur. From 2001 to 2014, small individuals increased in number and very large ones decreased, suggesting not only that new recruitment is occurring, but also that larger sponges are shrinking or fragmenting. Marked sponges continued killing corals over the first few years, but over longer times they retreated or died, allowing corals to resume upward growth. However, it could not be ascertained whether the sponge retreat was age‐related or the result of some environmental effect. The apparent preference for recently dead clean coral by larvae of C. tenuis and its current dynamics of recruitment, growth, fragmentation and mortality have stabilized its space occupation at Islas del Rosario.     

Archaeogeophysical-Based Approach for Inca Archaeology: Overview and one operational application

Even if, in recent decades, the use of remote sensing technologies (from satellite, aerial and ground) for archaeology is stepping into its golden age, in Southern America geophysics for preventive archaeology is more recent and less used than in Europe, Central America and Middle East. In this paper, we provide a brief overview and show the preliminary results obtained from the investigations conducted in Chachabamba (Peru). The archaeological area is located on a strategic terrace overlooking three Inca roads, which served the most important ceremonial centres (including Machu Picchu) of the Urubamba Valley also known as the Sacred Valley. In particular, Chachabamba investigations were conducted with two principal aims: (1) to give new impetus to archaeological research with targeted investigations aimed at improving and completing the site’s knowledge framework; (2) to experiment and validate an archaeogeophysical approach to be reapplied in other sites of the Urubamba valley, including Machu Picchu, having similar characteristics as those found in Chachabamba.