Oceanographic and climatologic controls on the compositions and fluxes of biogenic materials in the water column and sediments of the Cariaco Basin over the Late Holocene

Materials collected by sediment traps over a 3-y period and sedimentary horizons from a gravity core covering the last 6000 y were used to investigate the effects of climate-related processes such as wind-driven upwelling and regional rainfall on the production, export and burial of particulate organic matter in the Cariaco Basin. A variety of chemical analyses, including organic carbon and nitrogen, biogenic opal, calcite, lithogenic contents, stable carbon isotopic ratios of organic matter and the yields of CuO reaction products derived from distinct biochemicals such as amino acids, fatty acids and lignins, were carried out for this purpose. Principal component analyses were used to investigate the trends in this multivariate data set. These analyses reveal marked temporal differences in the composition of the materials sinking through the water column, which were related to distinct oceanographic and climatic forcings. For example, autochthonous fluxes, characterized by elevated contents of organic carbon and opal as well as high yields of amino acid and fatty acid reaction products, displayed peaks during periods of intense wind-driven upwelling. In contrast, allochthonous materials, characterized by elevated lithogenic contents and elevated yields of lignin-derived products, were more important during periods of high rainfall, low wind and enhanced stratification. In addition to the strong seasonal contrasts, there was significant temporal variability at both shorter (monthly) and longer (inter-annual) time scales. Hence, other factors, such as zooplankton grazing and El Niño effects on local climatology, may also be important. Examination of the gravity core record yielded several significant trends. For example, there was a marked increase in sediment accumulation rates from 5000 to ca. 700 y before present with concomitant increases in the concentrations of organic carbon, opal and most biomarkers. These results suggest that the Cariaco Basin experienced a marked increase in primary productivity and particle flux to the underlying sediments since the Holocene Thermal Maximum. Also within the sedimentary record, we observed distinct variations in the relative contributions of autochthonous and allochthonous organic matter. The frequency of these variations is roughly 1500 y and appears to match ice-rafted debris records from the North Atlantic. Such coincidence indicates cold periods within the Holocene, which are related to minima in insolation, may have led to the southern migration of the inter-tropical convergence zone and the enhancement of wind-driven upwelling, primary productivity and autochthonous organic matter flux to the seabed in the Cariaco Basin. Alternatively, during warm periods, the opposite climatic conditions would have increased both the thermal stratification of the water column and average rainfall in the Cariaco Basin, leading to elevated inputs of allochthonous materials.     

Imaging X-ray Polarimeter for Solar Flares (IXPS)

We describe the design of a balloon-borne Imaging X-ray Polarimeter for Solar flares (IXPS). This novel instrument, a Time Projection Chamber (TPC) for photoelectric polarimetry, will be capable of measuring polarization at the few percent level in the 20?C50 keV energy range during an M- or X-class flare, and will provide imaging information at the ??10 arcsec level. The primary objective of such observations is to determine the directivity of nonthermal high-energy electrons producing solar hard X-rays, and hence to learn about the particle acceleration and energy release processes in solar flares. Secondary objectives include the separation of the thermal and nonthermal components of the flare X-ray emissions and the separation of photospheric albedo fluxes from direct emissions.     

Mapping sub‐pixel fluvial grain sizes with hyperspatial imagery

This study presents an investigation of image texture approaches for mapping sub‐pixel fluvial grain‐size features from airborne imagery, allowing for the rapid acquisition of surface sand and coarse fraction (>1·41 mm) grain‐size information. Imagery at 30 mm resolution was acquired over four gravel bars from the Fraser River (British Columbia, Canada). Combined first‐order and second‐order image texture approaches (windowed standard deviation filter and the grey level co‐occurrence matrix) were used. First‐order image texture, through the application of a standard deviation filter and subsequent thresholding was used to detect the presence of surface sand, with optimal accuracy achieved at 91 ± 1·9%. A wide‐ranging parameter space investigation was used to derive optimum parameters for the grey‐level co‐occurrence matrix. Subsequently first‐order and second‐order image textures were used in multiple linear regression to achieve good calibrations with several sub‐pixel grain‐size percentiles; relative error at 1·44%, 3·18%, 6·80% and 10·6% for D₅, D₁₆, D₃₅ and D₅₀, respectively. The larger percentiles of D₈₄ and D₉₅ had relative errors of 24·7% and 29·7%, respectively. The breakdown of calibration precision for larger percentiles is attributed to a ‘pixel averaging effect’. It is concluded that multispectral imagery is not required, because sufficient image texture information can be derived from standard colour imagery. Recommendations are suggested for the application of this method to other localities and data sets, thus reducing exhaustive parameter searches in future studies.     

Use of chemical tracers in assessing the diet and foraging regions of eastern North Pacific killer whales

Top predators in the marine environment integrate chemical signals acquired from their prey that reflect both the species consumed and the regions from which the prey were taken. These chemical tracers-stable isotope ratios of carbon and nitrogen; persistent organic pollutant (POP) concentrations, patterns and ratios; and fatty acid profiles-were measured in blubber biopsy samples from North Pacific killer whales (Orcinus orca) (n=84) and were used to provide further insight into their diet, particularly for the offshore group, about which little dietary information is available. The offshore killer whales were shown to consume prey species that were distinctly different from those of sympatric resident and transient killer whales. In addition, it was confirmed that the offshores forage as far south as California. Thus, these results provide evidence that the offshores belong to a third killer whale ecotype. Resident killer whale populations showed a gradient in stable isotope profiles from west (central Aleutians) to east (Gulf of Alaska) that, in part, can be attributed to a shift from off-shelf to continental shelf-based prey. Finally, stable isotope ratio results, supported by field observations, showed that the diet in spring and summer of eastern Aleutian Island transient killer whales is apparently not composed exclusively of Steller sea lions.     

Surgeon island granite SHRIMP zircon ages: a clue for the Cambrian tectonic setting and evolution of the Palaeopacific margin of Gondwana (northern Victoria Land, Antarctica)

In northern Victoria Land (NVL), Antarctica, the palaeopacific margin of Gondwana is made up of the inboard Wilson (WT) and the two outboard Bowers (BT) and Robertson Bay (RBT) terranes. The occurrence of a Cambro-Ordovician magmatic arc in the WT argues for a southwestward subduction leading to the final configuration of this margin during the Ross–Delamerian Orogeny. A U-Pb SHRIMP crystallization age (511.7 ± 2.9 Ma) obtained on the Surgeon Island Granite (SIG), located at the eastern end of the RBT, indicates that the SIG also belongs to the Ross cycle, and provides evidence for multiple subduction zones during the Ross Orogeny. Structural observations show that the SIG and its country rocks are basement to the RBT turbidites. SIG inherited zircon ages indicate the occurrence of Proterozoic crust east of the RBT and constrains the location of the Proterozoic–Palaeozoic boundary in Cambrian Gondwana.     

Arecibo radar observations of Rhea, Dione, Tethys, and Enceladus

We have measured the bulk radar reflectance properties of the mid-size saturnian satellites Rhea, Dione, Tethys, and Enceladus with the Arecibo Observatory's 13 cm wavelength radar system during the 2004 through 2007 oppositions of the Saturn system. Comparing to the better studied icy Galilean satellites, we find that the total reflectivities of Rhea and Tethys are most similar to Ganymede while Dione is most similar to Callisto. Enceladus' reflectivity falls between those of Ganymede and Europa. The mean circular polarization ratios of the saturnian satellites range from ∼0.8 to 1.2, and are on average lower than those of the icy Galilean satellites at this wavelength although still larger than expected for single reflections off the surface. The ratio for the trailing hemisphere of Enceladus may be the exception with a value ?0.56. The 13 cm wavelength radar albedos and polarization ratios may be systematically lower than similar results from the Cassini orbiter's RADAR instrument at 2.2 cm wavelength [Ostro, S.J., and 19 colleagues, 2006. Icarus 183, 479-490]. Overall, these reflectivities and polarization properties, together with the shapes of the echo spectra, suggest subsurface multiple scattering to be the dominant reflection mechanism although operating less efficiently than on the large icy moons of Jupiter. All these saturnian moons and icy jovian moons are atmosphere-less, low temperature water ice surfaces, and any differences in radar properties may be indicative of differences in composition or the effects of various processes that modify the regolith structure. The degree of variation in radar properties with wavelength on each satellite may constrain the thickness and efficiency of the scattering layer.     

Teleconnections between Ethiopian summer rainfall and sea surface temperature: part II. Seasonal forecasting

A seasonal forecasting system that is capable of skilfully predicting rainfall totals on a regional scale would be of great value to Ethiopia. Here, we describe how a statistical model can exploit the teleconnections described in part 1 of this pair of papers to develop such a system. We show that, in most cases, the predictors selected objectively by the statistical model can be interpreted in the light of physical teleconnections with Ethiopian rainfall, and discuss why, in some cases, unexpected regions are chosen as predictors. We show that the forecast has skill in all parts of Ethiopia, and argue that this method could provide the basis of an operational seasonal forecasting system for Ethiopia.     

Teleconnections between Ethiopian summer rainfall and sea surface temperature: part I��observation and modelling

In this study, the oceanic regions that are associated with anomalous Ethiopian summer rains were identified and the teleconnection mechanisms that give rise to these associations have been investigated. Because of the complexities of rainfall climate in the horn of Africa, Ethiopia has been subdivided into six homogeneous rainfall zones and the influence of SST anomalies was analysed separately for each zone. The investigation made use of composite analysis and modelling experiments. Two sets of composites of atmospheric fields were generated, one based on excess/deficit rainfall anomalies and the other based on warm/cold SST anomalies in specific oceanic regions. The aim of the composite analysis was to determine the link between SST and rainfall in terms of large scale features. The modelling experiments were intended to explore the causality of these linkage. The results show that the equatorial Pacific, the midlatitude northwest Pacific and the Gulf of Guinea all exert an influence on the summer rainfall in various part of the country. The results demonstrate that different mechanisms linked to sea surface temperature control variations in rainfall in different parts of Ethiopia. This has important consequences for seasonal forecasting models which are based on statistical correlations between SST and seasonal rainfall totals. It is clear that such statistical models should take account of the local variations in teleconnections.     

Rock lead isotopes in northeast Queensland

U‐Pb and Th‐Pb studies of rocks from an extensive Palaeozoic volcano‐plutonic province in northeast Queensland support conclusions derived from a previous Rb‐Sr study. The data oppose an earlier hypothesis, that two widespread and fundamentally different magma types are present. Interpretation of the lead data, however, must be treated with some caution since uranium movement apparently begins at a very early stage of weathering; X‐ray fluorescence data are displayed in a manner which suggests a simple rejection criterion.     

Rb‐Sr systematics of the Coolgarra Batholith,North Queensland

The Coolgarra Batholith in north‐east Queensland is composed of the Go Sam and Nettle granite suites which were emplaced approximately 314 Ma ago. Initial ⁸⁷Sr/⁸⁶Sr ratios of the Nettle Suite appear to be marginally above 0.710, a value characteristic of a wide range of Late Palaeozoic felsic igneous rocks in the region. This suite appears to have been derived from an extensive isotopically homogeneous crustal source distinct from rocks which crop out in the Palaeozoic Hodgkinson Basin or Precambrian Georgetown Inlier. Higher and more variable initial ⁸⁷Sr/⁸⁶Sr ratios (0.727–0.744) of the Go Sam Suite are attributed to a combination of magmatic and hydrothermal processes. Isotopic data, thus, cannot be used to constrain the nature of the Go Sam source rocks. Tungsten (with or without tin) mineralization is associated with the Nettle Suite plutons, with which it shares a common age, whereas the Go Sam Suite is characterized by prominent tin mineralization. One tin occurrence is the same age as, or only slightly younger than, the Nettle Suite tungsten (with or without tin) mineralization. Another tin deposit yields an age of 301 Ma, suggesting the presence of a significantly younger granite at depth.