Hafnium and neodymium isotopes in surface waters of the eastern Atlantic Ocean: Implications for sources and inputs of trace metals to the ocean

We present hafnium (Hf) and neodymium (Nd) isotopic compositions and concentrations in surface waters of the eastern Atlantic Ocean between the coast of Spain and South-Africa. These data are complemented by Hf and Nd isotopic and concentration data, as well as rare earth element (REE) concentrations, in Saharan dust.Hafnium concentrations range between a maximum of 0.52 pmol/kg in the area of the Canary Islands and a minimum value of 0.08 pmol/kg in the southern Angola Basin. Neodymium concentrations also show a local maximum in the area of the Canary Islands (26 pmol/kg) but are even higher between ∼20°N and ∼4°N reaching maximum concentrations of 35 pmol/kg. These elevated concentrations provide evidence of inputs from weathering of the Canary Islands and from the partial dissolution of dust from the Sahara/Sahel region. The inputs from ocean island weathering are also reflected in radiogenic Hf and Nd isotopes.The Hf isotopic compositions of dust samples themselves are highly variable, ranging between ε_Hf = −20 and −0.6. The combined Hf and Nd isotopic compositions of dust plot close to the “terrestrial array” during periods of appreciable dust load in the atmosphere. During low atmospheric dust loading combined Hf and Nd isotopic compositions similar to seawater are observed. Most of the variability can be explained in terms of variable degrees of zircon loss from the dust samples, which in turn is linked to sorting during atmospheric transport to the eastern Atlantic Ocean and possibly presorting by sedimentary redistribution on the continent. In addition, increasing relative proportions of radiogenic clay minerals with decreasing grain size may contribute to the radiogenic Hf isotopic compositions observed.While the Nd isotopic composition in the surface ocean reflects the Nd isotopic composition of the Saharan dust adjacent to the Sahara/Sahel region, the release of Hf from that dust appears to be incongruent and results in surface ocean Hf isotopic compositions which are ∼10 ε_Hf more radiogenic than the bulk dust. Radiogenic Hf appears to be released from clays and possibly from trace apatite. Rare earth element patterns of dust samples indicate the presence of apatite but provide no evidence for ferromanganese grain coatings, suggesting that such coatings are insignificant in the release of Hf and Nd from Saharan dust to the surface ocean.The Nd isotopic composition of the surface waters becomes less radiogenic south of the equator, most likely reflecting the release of Nd from Congo river sediments. The release of Hf from Saharan dust and the Congo river sediments, however, does not produce distinct Hf isotopic signatures in the surface ocean, implying that the mobile fraction of Hf integrated over large continental areas is isotopically uniform. The Hf isotopic uniformity in the surface ocean means that the limited variability in deep water isotopic compositions is consistent with a short deep water residence time and reflects homogenous continental inputs rather than efficient deep water homogenization.     

High‐Resolution Photography for Soil Micromorphology Slide Documentation

It is common practice today in soil micromorphology to scan slides with a flatbed scanner for slide documentation as well as for mesoscopic scale observation. However, the imagery produced by flatbed scanners often results in boundaries becoming diffuse when zooming in, a side effect of the continuously changing refraction of light caused by the moving scan head. This can be restricting or even unsatisfactory to specialists who rely on such imagery and while alternatives exist, their availability or suitability is not always guaranteed. This paper describes two variations on a static high‐resolution image acquisition method using a professional camera and common attributes of a standard photography studio. Minor postphotography processing too can be done with commonly used software packages. The presented method results in pictures with a resolution of 36 million pixels per image, providing high enough quality and resolution (approximately 4200 dpi) to allow the soil micromorphology practitioner to navigate the entire mesoscopic spectrum and as such offers a continuum of observation from the macroscopic scale to the optical microscopic observation at low (40×) magnification.     

The dissolved Beryllium isotope composition of the Arctic Ocean

We present the first comprehensive set of dissolved ¹⁰Be and ⁹Be concentrations in surface waters and vertical profiles of all major sub-basins of the Arctic Ocean, which are complemented by data from the major Arctic rivers Mackenzie, Lena, Yenisey and Ob. The results show that ¹⁰Be and ⁹Be concentrations in waters below 150 m depth are low and only vary within a factor of 2 throughout the Arctic Basin (350-750 atoms/g and 9-15 pmol/kg, respectively). In marked contrast, Be isotope compositions in the upper 150 m are highly variable and show systematic variations. Cosmogenic ¹⁰Be concentrations range from 150 to 1000 atoms/g and concentrations of terrigenous ⁹Be range from 7 to 65 pmol/kg, resulting in ¹⁰Be/⁹Be ratios (atom/atom) between 0.5 and 14 × 10⁻⁸. Inflowing Atlantic water masses in the Eurasian Basin are characterized by a ¹⁰Be/⁹Be signature of 7 × 10⁻⁸. The inflow of Pacific water masses across the Bering Strait is characterized by lower ratios of 2-3 × 10⁻⁸, which can be traced into the central Arctic Ocean, possibly as far as the Fram Strait. A comparison of the high dissolved surface ¹⁰Be and ⁹Be concentrations (corresponding to low ¹⁰Be/⁹Be signatures of ∼2 × 10⁻⁸) in the Eurasian Basin with hydrographic parameters and river data documents efficient and rapid transport of Be with Siberian river waters across the Siberian Arctic shelves into the central Arctic Basin, although significant loss and exchange of Be on the shelves occurs. In contrast, fresh surface waters from the Canada Basin also show high cosmogenic ¹⁰Be contents, but are not enriched in terrigenous ⁹Be (resulting in high ¹⁰Be/⁹Be signatures of up to 14 × 10⁻⁸). This is explained by a combination of efficient scavenging of Be in the Mackenzie River estuary and the shelves and additional supply of cosmogenic ¹⁰Be via atmospheric fallout and melting of old sea ice. The residence time of Be in the deep Arctic Ocean estimated from our data is 800 years and thus similar to the average Be residence time in the global ocean.     

Surface features on glass spherules from the Luna 16 sample

Two ellipsoidal spherules approximately 0.5 mm in diameter were studied in detail using a scanning electron microscope. A variety of surface features were observed: vesicles, mounds, dimples, streaks, ridges, grooves, accretion phenomena, and high-speed impact craters. The diameters of 27 glass-lined pits formed by impact on one spherule range from less than 1m to approximately 50m. Intermediate-sized glass-lined pits surrounded by concentric fractures demonstrate the transition between larger craters that have both a pit and a spall zone and generally smaller craters that have only a pit. Assuming all craters showing evidence of impact-related melting or flow are the result of primary impacts, the differential mass spectrum of impacting meteoroids in the range 10^–11 to 10^–10 g is in good agreement with a spectrum based on satellite-borne particle-detecting experiments.     

A comparison between compton-synchrotron and Compton black-body emission in radio sources

A simple relation between observational parameters of radiosources that allows to state the predominance in the X-ray emission of either the Compton-synchrotron or the Compton black-body effect is derived.The obtained results suggest that the Compton-synchrotron contribution is dominant in compact radiosources.Operated by the CNICT with the participation of the University of Buenos Aires and the Comisión Nacional de Estudios Geoheliofísicos.     

Uncertainty and asymmetric information: An overview

This paper provides an overview of the literature on fisheries economics related to uncertainty and asymmetric information. It is argued that uncertainty is relevant in connection with present and future stock sizes and prices, while asymmetric information is important for cost functions, catches, catch per unit of effort, and effort. The literature on uncertainty and asymmetric information can be seen as providing the basis of an argument for using taxes in fisheries management. It is, therefore, surprising that over 55 countries regulate their fisheries with individual quotas, while taxes are not used at all.     

Suspended barite as a tracer of biological activity in the Southern Ocean

During two cruises in the Southern Ocean (INDIGO 3, Indian sector and EPOS 2, Scotia-Weddell Confluence) suspended matter samples were collected for analysis of several biogenic elements including Ba, Si and particulate organic carbon (POC).The good agreement between particulate barium in subsurface water with oxygen minimum concentrations as well as with nitrate depletions suggests that it reflects the intensity of new production over the past season. As a consequence of new production in the Southern Ocean being performed mainly by diatoms, the occurrences of barite and diatoms are related in the water column. In areas characterized by diatom-poor phytoplankton, barite does occur, but in lower concentrations.