Systematic variations of sialic and volcanic detritus in piston cores from the Red Sea

The ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios and Sr concentrations of the non-carbonate fractions of sediment from two cores taken in the median valley of the Red Sea indicate that the detrital fractions are mixtures of two components originating from old sialic and young volcanic rocks of the surrounding land areas. The mixing equations were derived from the data and were used to estimate the Sr concentrations of the two components. The volcanogenic detritus has a Sr content between 770 and 800 ppm while the component derived from old sialic rocks contains from 50 to 70 ppm. The volcanic component consists primarily of unweathered particles of alkali basalt and volcanic glass while the sialic component is represented by clay minerals and X-ray amorphous material. Systematic variations of the concentration of volcanogenic detritus were used to define layers of sediment which correlate over a distance of about 200 km separating the two cores. The concentrations of quartz, feldspar, amphibole, illite, kaolinite and chlorite were found to vary systematically with the content of volcanogenic detritus as calculated from the Sr data. The carbonate concentrations of the sediment range from 33 to 87% and appear to increase in a southerly direction. The rate of carbonate deposition increased at times of more efficient input of sediment derived from old sialic rocks. This relationship is explained by the hypothesis that both were influenced indirectly by brief warming trends during the Würm glaciation. The occurrence of sediment layers enriched in sediment derived from old sialic rocks correlates approximately with interstadials of the Würm glaciation in northern Europe. Increased input of volcanogenic detritus occurred around 37,000 and 26,000yr ago and during the past 5000 yr. A plot of ${}^{87}\text{Sr}{}^{86}\text{Sr}$ and ${}^{87}\text{Rb}{}^{86}\text{Sr}$ ratios defines a line on the Rb-Sr isochron diagram yielding a fictitious date of about 230 million yr.     

Cation partitioning versus temperature in spinel: optimization of site occupants

 Pavese et al. (1999) examined cation partitioning vs. temperature in a synthetic spinel of composition (Mg_0.70 Fe_0.23 ³⁺) Al_1.97 O₄ using structure data obtained from in situ neutron powder diffraction. After imposing assumptions on the site assignment of vacancies and Fe³⁺, they assigned the remaining cations by applying least-squares minimization to chemical constraints on site-occupancy sums, site-scattering, chemical composition, and thermal expansion of the octahedral site. Their proposed site assignments exhibit a sharp discontinuity in occupancy fractions versus temperature, a necessary consequence of their assumptions on vacancy assignments. In this paper we reexamine the cation partitioning of the same spinel using the constrained least-squares formulation of OccQP (Wright et al. 2000), which optimizes site occupancies without ad hoc assumptions. We obtain strikingly different results, supporting the general view that spinel undergoes a lambda transition at ∼1000 K. For all observed parameters, the residuals obtained with the OccQP assignments are lower than those obtained with the Pavese et al. assignments, in some cases by more than 1 order of magnitude. Received: 05 April 2000 / Accepted: 19 October 2000     

Spatial variation in delaware bay (U.S.A.) marsh creek fish assemblages

Delaware Bay is one of the largest estuaries on the U.S. eastern seaboard and is flanked by some of the most extensive salt marshes found in the northeastern U.S. While physicochemical and biotic gradients are known to occur along the long axis of the bay, no studies to date have investigated how the fish assemblage found in salt marsh creeks vary along this axis. The marshes of the lower portion of the bay, with higher salinity, are dominated bySpartina spp., while the marshes of the upper portion, with lower salinity, are currently composed primarily of common reed,Phragmites australis, S. alterniflora, or combinations of both. Extensive daytime sampling (n=815 tows) during May–November 1996 was conducted with otter trawls (4.9 m, 6 mm mesh) in six intertidal and subtidal marsh creek systems (upper and lower portions of each creek) where creek channel depths ranged from 1.4–2.8 m at high tide. The fish taxa of the marsh creeks was composed of 40 species that were dominated by demersal and pelagic forms including sciaenids (5 species), percichthyids (2), and clupeids (7), many of which are transients that spawn outside the bay but the early life history stages are abundant within the bay. The most abundant species wereMorone americana (24.3% of the total catch),Cynoscion regalis (15.4%),Micropogonias undulatus (15.3%),Anchoa mitchilli (12.0%), andTrinectes maculatus (10.8%). Non-metric Multi-Dimensional Scaling ordination of catch per unit effort (CPUE) data indicated two fish assemblages that were largely independent of the two major vegetation types, but generally corresponded with spatial variation in salinity. This relationship was more complex because some of the species for which we could discriminate different age classes by size had different patterns of distribution along the salinity gradient.     

Last glacial ice‐rafted debris off southwestern Europe: the role of the British–Irish Ice Sheet

Ice‐rafted debris (IRD) seeded into the ocean from Northern Hemisphere ice sheets is found in ocean cores along the southwestern European margin through the last glacial period. It is known that the origin of this IRD, especially off Iberia, can vary between North America and western Europe during short‐lived episodes of greatly enhanced iceberg flux, known as Heinrich events, although in most Heinrich events the IRD has a North American source. During the longer times of much lower IRD fluxes between Heinrich events, use of an intermediate complexity climate model, coupled to an iceberg dynamic and thermodynamic model, shows that background levels of IRD most likely originate from western Europe, particularly the British–Irish Ice Sheet. Combining modelling with palaeoceanographic evidence supports reconstructions of a short‐lived, but substantial, Celtic and Irish Sea Ice Stream around 23 ka. Copyright © 2010 John Wiley & Sons, Ltd.     

Arm hooks of coleoid cephalopods from the Jurassic succession of the Wessex Basin,Southern England

The Jurassic succession of the Wessex Basin – especially that cropping out within the Dorset and East Devon Coast World Heritage Site – contains important lagerstätten for coleoid cephalopods. The Blue Lias and Charmouth Mudstone formations of West Dorset, the Oxford Clay Formation of North Wiltshire and the Kimmeridge Clay Formation of Purbeck have provided large numbers of important body fossils that inform our knowledge of coleoid palaeobiology, including the hooks present in the arms. Isolated hooks are also found in the processed residues studied by micropalaeontologists and these occurrences can be used – in some cases – to record the presence of key taxa in the absence of well-preserved body fossils. While some hook morphotypes can be attributed to known species, there are many forms of hook described where the parent animal remains unknown. The present state of our knowledge of the Jurassic assemblages in the Wessex Basin is presented and remaining issues identified.     

The emerging role of genetic diversity for ecosystem functioning: Estuarine macrophytes as models

Recent experiments in macrophyte dominated communities on the relationship between biological diversity and ecosystem functioning suggest that effects and mechanisms of genetic-genotypic and species diversity are analogous. As previously shown for species diversity, genotypic diversity enhances ecosystem productivity and recovery from disturbance. These findings generalize ecological theory, and provide an empirical basis for explicitly considering the maintenance of genetic or genotypic diversity for conservation strategies. Macrophyte systems such as seagrasses or salt-marshes may be excellent systems to test the interaction between diversity across several (genetic versus species) levels of biological organization because they are relatively species poor while simultaneously allowing the manipulation of genotypic diversity by taking advantage of clonal propagation in many species.     

An organic geochemical investigation of the practice of manuring at a Minoan site on Pseira Island,Crete

Lipid components in a soil profile developed in an agricultural terrace at a Minoan site on Pseira Island, Crete, were analyzed to determine whether the practice of manuring in antiquity, as inferred by distributional and temporal sherd scatter, could be confirmed through the use of biomarker compounds as proxies for manuring. Analysis of total organic carbon and the abundance of n‐alkyl lipids (n‐alkanols and fatty acids) demonstrated that while the upper part of the soil profile had received more recent inputs of vegetation‐derived organic matter, the deeper archaeological strata remained essentially undisturbed. Further analysis of 5β‐stanols, sterol components which may be utilized as fecal biomarkers, revealed a signal indicative of manuring, with human or porcine‐derived fecal material, in the lower 15 cm of the profile. Additional appraisal of epicoprostanol abundance inferred the possible practice of composting in later periods. This study represents a detection of manuring, in the oldest samples to date, using organic geochemical methods. © 2001 John Wiley & Sons, Inc.