Electrical properties of seafloor massive sulfides

Seafloor massive sulfide (SMS) deposits are increasingly seen as important marine metal resources for the future. A growing number of industrialized nations are involved in the surveying and sampling of such deposits by drilling. Drill ships are expensive and their availability can be limited; seabed drill rigs are a cost-effective alternative and more suitable for obtaining cores for resource evaluation. In order to achieve the objectives of resource evaluations, details are required of the geological, mineralogical, and physical properties of the polymetallic deposits and their host rocks. Electrical properties of the deposits and their ore minerals are distinct from their unmineralized host rocks. Therefore, the use of electrical methods to detect SMS while drilling and recovering drill cores could decrease the costs and accelerate offshore operations by limiting the amount of drilling in unmineralized material. This paper presents new data regarding the electrical properties of SMS cores that can be used in that assessment. Frequency-dependent complex electrical resistivity in the frequency range between 0.002 and 100 Hz was examined in order to potentially discriminate between different types of fresh rocks, alteration and mineralization. Forty mini-cores of SMS and unmineralized host rocks were tested in the laboratory, originating from different tectonic settings such as the intermediate-spreading ridges of the Galapagos and Axial Seamount, and the Pacmanus back-arc basin. The results indicate that there is a clear potential to distinguish between mineralized and non-mineralized samples, with some evidence that even different types of mineralization can be discriminated. This could be achieved using resistivity magnitude alone with appropriate rig-mounted electrical sensors. Exploiting the frequency-dependent behavior of resistivity might amplify the differences and further improve the rock characterization.     

A meteorological study of Dry-fallout of radioactive debris

Summary A general expression is derived for the intensity of dryfallout based on time variations of beta-activity in surface air, due to worldwide tropospheric distribution of debris from nuclear testings. Model assumptions are outlined for the consideration of large-scale effects of horizontal divergence of air flow, and small-scale effects of eddy diffusion. The parameterization is based on the concept of geostrophic drag coefficients and atmospheric boundary layer theory. The model is completed by a two-parameter representation of tropospheric profiles of beta activity. Case studies of dry-fallout in 1962 and 1963 at three stations of the United States Public Health Service (USPHS) network are discussed. Dry-fallout rates per day are found to be approximately 10% of average wet-fallout rates of the same period. The average residence time of debris in the troposphere is estimated to be about 65 days if dry-fallout would be the only cleansing process.

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Zusammenfassung Für die Intensität von radioaktivem Ausfall wird eine allgemeine Formel abgeleitet. Sie beruht auf der beobachteten zeitlichen Veränderung der bodennahen Konzentration radioaktiver Beta-Teilchen, die als Abfallprodukte der Kernwaffenversuche weltweite Verteilung erfuhren. Das theoretische Modell zur Berechnung von Trockenausfall erfordert gewisse Annahmen zur Berücksichtigung von 1. großräumigen Effekten der horizontalen Divergenz der Luftströmung und 2. kleinräumigen Turbulenzeinflüssen. Diese Effekte werden durch Parameter der horizontalen Luftdruckverteilung berücksichtigt, die auf dem Konzept des geostrophischen Widerstandsbeiwertes und der atmosphärischen Grenzschichttheorie beruhen. Das Modell ist durch zwei weitere Parameter vervollständigt, welche das troposphärische Profil der Beta-Aktivität repräsentieren. Beispiele von Trockenausfall in den Jahren 1962 und 1963 werden für drei Stationen des Beobachtungsnetzes des United States Public Health Service diskutiert. Es ergab sich, daß Trockenausfall pro Tag etwa 10% des Ausfalles durch Niederschlag (pro Regentag) für den gleichen Zeitabschnitt ausmacht. Ferner wird abgeschätzt, daß die Verweilzeit der radioaktiven Teilchen in der Troposphäre im Durchschnitt 65 Tage beträgt, wenn Trockenausfall der alleinige Reinigungsprozeß ist.

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Résumé On développe ici une formule générale permettant le calcul de l'intensité des retombées radio-actives. Cette formule est fondée sur la variation de la concentration au voisinage du sol des particules radio-actives béta, disséminées dans l'atmosphère entière à la suite d'essais d'armes nucléaires. Le modèle théorique permettant de représenter la sédimentation en atmosphère sèche nécessite certaines suppositions afin de tenir compte d'une part des effets à grandes dimensions de la divergence horizontale des courants aériens et d'autre part des effets de la turbulence à petites dimensions. On tient compte de ces effets au moyen de paramètres de la répartition horizontale de la pression, paramètres basés sur le coefficient de la résistance géostrophique et sur la théorie des couches limites atmosphériques. Ce modèle est complété par deux paramètres supplémentaires qui représentent le profil troposphérique de l'activité béta. Comme exemple, on discute les quantités de retombées recueillies à trois stations du «United States Public Health Service» durant les années 1962 et 1963. Le résultat en est que la sédimentation à sec par jour représente environ le 10% des retombées entraînées par les précipitations durant la même période. On estime en outre que les particules se maintiennent en moyenne durant 65 jours dans la troposphère si la sédimentation se fait uniquement sans le concours de précipitations.

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The research reported was supported, in part, by the National Science Foundation, Grant No. GP-444.     

River discharge reduces reef coral diversity in Palau

Coral community structure is often governed by a suite of processes that are becoming increasingly influenced by land-use changes and related terrestrial discharges. We studied sites along a watershed gradient to examine both the physical environment and the associated biological communities. Transplanted corals showed no differences in growth rates and mortality along the watershed gradient. However, coral cover, coral richness, and coral colony density increased with increasing distance from the mouth of the bay. There was a negative relationship between coral cover and mean suspended solids concentration. Negative relationships were also found between terrigenous sedimentation rates and the richness of adult and juvenile corals. These results have major implications not only for Pacific islands but for all countries with reef systems downstream of rivers. Land development very often leads to increases in river runoff and suspended solids concentrations that reduce coral cover and coral diversity on adjacent reefs.     

Close correlation between Sr/Ca ratios in bulk sediments from the southern Cape Basin and the SPECMAP record

High-resolution records of Ca and Sr were obtained from shipboard XRF analyses of bulk sediments in five gravity cores from the southern Cape Basin, South Atlantic Ocean. Sr/Ca ratios display regular glacial/interglacial variations of 14–40% and reveal a close correlation with the SPECMAP record, minimum Sr/Ca ratios appearing during glacial (¹⁸ O) maxima, distinct increases during periods of deglaciation, and highest ratios in interstadials. Shifts in carbonate-producing phytoplankton and/or zooplankton assemblages over glacial/interglacial cycles are suggested to be the main cause for the observed variations in Sr/Ca patterns. Quick assessment of the relationship between Sr/Ca ratios and the SPECMAP record made it possible to easily transfer an age model to the newly collected cores already during the cruise.     

Ant mounds as a source of sediment in a tropical rainforest?

In Lutzito catchment on Barro Colorado Island, Panama, extraordinarily high suspended‐sediment yields of 1–2 Mg ha^?1 year^?1 were generated despite the dense forest cover coinciding with erosion‐resistant soils. We hypothesized that ant mounding activity is an important zoogeomorphological mechanism in this area, providing relevant quantities of easily transportable material at the soil surface. To test this hypothesis, all ant mound material was collected collected for dry mass determination from thirty 4 m² plots installed in the study area every 1–3 days during the 39‐day sampling period. Additionally, three ground‐nesting ant species responsible for mounds in the study area, Ectatomma ruidum, Trachymyrmex cornetzi and Strumigenys marginiventris, were identified. On the basis of the total of 1.38 kg of material collected in the wet season of 2011, the estimate for the whole 8 months wet season amounts to 725 kg ha^?1. As this value is in the same order of magnitude as sediment output, it shows that ants may act as important ecosystem engineers and contribute to sediment production here by providing large quantities of fine‐grained, readily erodible material at the soil surface for subsequent transport to the streambed. Copyright © 2014 John Wiley & Sons, Ltd.     

Pigmentation of massive corals as a simple bioindicator for marine water quality

Photo-acclimatisation by the algal endosymbionts of scleractinian corals to changes in environmental conditions may influence their density and/or the concentration of photosynthetic pigments, and hence coral brightness, on short time-scales. To examine coral pigmentation as a bioindicator of water quality, the brightness of massive corals was quantified using colour charts, concentrations of the pigment chlorophyll a and reflectance spectrometry in the field and with manipulative experiments. Along a water quality gradient, massive Porites became progressively lighter as nutrients decreased and irradiance increased. A laboratory experiment showed that Porites nubbins darkened within 25 days following exposure to reduced water quality. The results of a transplantation experiment of Porites nubbins in a manipulation incorporating multiple depths and zones of water quality confirmed colony brightness as a simple tool to monitor changes in marine water quality, provided effects due to other influences on pigmentation, e.g. seawater temperatures, are taken into consideration.     

Validation of official erosion modelling based on high‐resolution radar rain data by aerial photo erosion classification

The universal soil loss equation (USLE) is the most frequently applied erosion prediction model and it is also implemented as an official decision‐making instrument for agricultural regulations. The USLE itself has been already validated using different approaches. Additional errors, however, arise from input data and interpolation procedures that become necessary for field‐specific predictions on a national scale for administrative purposes. In this study, predicted event soil loss using the official prediction system in Bavaria (Germany) was validated by comparison with aerial photo erosion classifications of 8100 fields. Values for the USLE factors were mainly taken from the official Bavarian high‐resolution (5 × 5 m²) erosion cadastre. As series of erosion events were examined, the cover and management factor was replaced by the soil loss ratio. The event erosivity factor was calculated from high‐resolution (1 × 1 km², 5 min), rain gauge‐adjusted radar rain data (RADOLAN). Aerial photo erosion interpretation worked sufficiently well and average erosion predictions and visual classifications correlated closely. This was also true for data broken down to individual factors and different crops. There was no reason to assume a general invalidity of the USLE and the official parametrization procedures. Event predictions mainly suffered from errors in the assumed crop stage period and tillage practices, which do not reflect interannual and farm‐specific variation. In addition, the resolution of radar data (1 km²) did not seem to be sufficient to predict short‐term erosion on individual fields given the strong spatial gradients within individual rains. The quality of the input data clearly determined prediction quality. Differences between USLE predictions and observations are most likely caused by parametrization weaknesses but not by a failure of the model itself. Copyright © 2017 John Wiley & Sons, Ltd.     

Grid point surface air temperature calculations with a fast turnaround: Combining the results of IMAGE and a GCM

This paper describes a methodology that combines the outputs of (1) the Integrated Model to Assess the Greenhouse Effect (IMAGE Version 1.0) of the Netherlands National Institute of Public Health and Environmental Protection (RIVM) (given a greenhouse gas emission policy, this model can estimate the effects such as global mean surface air temperature change for a wide variety of policies) and (2) ECHAM-1/LSG, the Global Circulation Model (GCM) of the Max-Planck Institute for Meteorology in Hamburg, Germany. The combination enables one to calculate grid point surface air temperature changes for different scenarios with a turnaround time that is much quicker than that for a GCM. The methodology is based upon a geographical pattern of the ratio of grid point temperature change to global mean values during a certain period of the simulation, as calculated by ECHAM-1/LSG for the 1990 Scenarios A and D of the Intergovernmental Panel on Climate Change (IPCC). A procedure, based upon signal-to noise ratios in the outputs, enabled us to estimate where we have confidence in the methodology; this is at about 23% to 83% of the total of 2,048 grid points, depending upon the scenario and the decade in the simulation. It was found that the methodology enabled IMAGE to provide useful estimates of the GCM-predicted grid point temperature changes. These estimates were within 0.5K (0.25K) throughout the 100 years of a given simulation for at least 79% (74%) of the grid points where we are confident in applying the methodology. The temperature ratio pattern from Scenario A enabled IMAGE to provide useful estimates of temperature change within 0.5K (0.25K) in Scenario D for at least 88% (68%) of the grid points where we have confidence; indicating that the methodology is transferable to other scenarios. Tests with the Geophysical Fluid Dynamics Laboratory GCM indicated, however, that a temperature ratio pattern may have to be developed for each GCM. The methodology, using a temperature ratio pattern from the 1990 IPCC Scenario A and involving IMAGE, gave gridded surface air temperature patterns for the 1992 IPCC radiative-forcing Scenarios C and E and the RIVM emission Scenario B; none of these scenarios has been simulated by ECHAM-1/LSG. The simulations reflect the uncertainty range of a future warming.The work reported by the authors was carried out during their stay at the project Forestry and Climate Change of the International Institute for Applied Systems Analysis, Laxenburg, Austria.