Paleoclimatic changes in southern Africa during the intensification of Northern Hemisphere glaciation: evidence from ODP Leg 175 Site 1085

Pliocene age sediments from Ocean Drilling Program Leg 175, Site 1085-A and B in the Cape Basin were analyzed to investigate the impact of the intensification of Northern Hemisphere glaciation (INHG) on the South Atlantic Benguela Current system from 4 to 2 Ma. Proxies for productivity (concentrations and mass accumulation rates of total organic carbon, carbon to nitrogen ratios, percent calcium carbonate, and percent biogenic silica) as well as weight percent sand (a proxy for preservation or winnowing) peak at 3.2, 3.0, 2.4, and 2.25 Ma. Normative calculations of allied trace and major elemental determinations indicate synchronous increases in productivity peaks, as well as high concentrations and accumulations of terrigenous sediments. Coeval increases in hemipelagic sedimentation and productivity indicators could be the result of enhanced eolian sedimentation resulting from strengthened winds, leading to elevated rates of upwelling and enhanced productivity. However, rapid burial, as indicated by high sedimentation rates, could also enhance preservation. The very high concentrations (>30%) and accumulations (up to 60 g/cm²/kyr) limit the likelihood that eolian sedimentation was the only transport mechanism, invoking an additional fluvial source. Rapid burial by either eolian or fluvial transport links these intervals of enhanced preservation and productivity with continental climate changes resulting from (1) increased winds and/or dust availability due to higher aridity in the Namibia/northern South Africa region; (2) lowered sea-level related to increased ice volume; (3) increased sediment load due to wetter conditions in the continental interior; or (4) some combination. Peaks at 3.2, 2.4 and 2.25 Ma are coincident with maximum precession, suggesting a link between hemipelagic sedimentation and enhanced monsoonal circulation over southern Africa. The Site 1085 sedimentary record during the INHG seems to be controlled by low-latitude processes linked to precession rather than hig-latitude processes.     

The cosmic ray energy spectrum between 10 and 10 eV

The energy spectrum of cosmic rays with primary energies between 10¹⁴ eV and 10¹⁶ eV has been studied with the CASA-MIA air shower array. The measured differential energy spectrum is a power law (dj/dE ∝ E^−y) with spectral indices γ of 2.66±0.02 below approximately 10¹⁵ eV and 3.00±0.05 above. A new method is used for measuring primary energy derived from ground-based data in a compositionally insensitive way. In contrast with some previous reports, the “knee” of the energy spectrum does not appear sharp, but rather a smooth transition over energies from 10¹⁵ eV to 3.0 × 10¹⁵ eV.     

Graphical estimation of extreme value prediction functions

Graphical application of the Type 1 (Gumbel) extreme value distribution is very simple since the distribution inverse gives a linear x-y plot. In contrast, the Type 2 and Type 3 extreme value distributions have nonlinear functions with respect to the same axes. A simple three-point graphical estimation procedure is described for these two distributions. This approach allows the nonlinear flood magnitude prediction functions to be located in any desirable position relative to the plotted annual maxima, subject to the constraint of having an extreme value form. The computation is very simple and requires only the location of a unique zero of a one-parameter function within a defined interval.     

Chemically Distinct Mafic Dike/Sill Sequences of Contrasting Age Ranges, Sawyers Bar Area, Central Klamath Mountains, Northern California

Mafic hypabyssal rocks in the western Triassic and Paleozoicbelt provide important clues to the nature of accretion andarc evolution along this sector of the North American margin.In the east-central part of the belt, near Sawyers Bar, somediabases have been metamorphosed before and accompanying emplacementof the mid-Jurassic English Peak and Russian Peak granitoidswithin the North Fork/Salmon River + Stuart Fork amalgamatedterrane. Certain other dikes/sills, chiefly mafic microdiorites,cut the calc-alkaline plutons but are themselves deutericallyaltered; at least two of these mafic microdiorites near theEnglish Peak body possess hornfelsic textures. Thus, althoughmost mafic microdioritic hypabyssals seem to have been injectedafter granitoid emplacement, a few must have preceded plutonicintrusion. Macroscopic appearances, phase assemblages, mineralcompositions, and textures of the mafic microdioritic and metadiabasicdikes/sills are sufficiently alike to preclude the ready fieldand petrographic distinction of the different magma series.Bulk-rock chemistries fall into two groups, however, with slightlymore porphyritic, altered, synplutonic mafic microdiorite samplesbeing distinctly richer in Si, K, P, Rb, Sr, Zr, and light rareearth elements (LREE) relative to the Mg + Cr + Ni-rich, preplutonicmetadiabases. Analyzed mafic microdiorites have bulk-rock chemicaland isotopic compositions similar to the more ferromagnesianportions of the mid-Jurassic English Peak and Russian Peak plutoniccomplexes, whereas the metadiabases are comparable with theearly Mesozoic Salmon River metabasalts. Although the two groupsof dikes/sills probably overlap in age of emplacement, the maficmicrodiorite group is predominantly younger and uniform in oxygenisotopic composition (bulk-rock ¹⁸O 11•37, 11•4 and11•46) compared with the older, more intensely metamorphosed,and variably metasomatized Salmon River metadiabases (bulk-rock5¹⁸ 9•4, 11•0, and 15•3). Both types of maficdike/sill locally intrude the more easterly Stuart Fork terrane.Therefore, suturing and regional metamorphism of the outboardNorth Fork/Salmon River oceanic-island arc and inboard StuartFork subduction complex must have occurred during terminal stagesof injection of the pregranitoid diabases into the North Fork(oceanic-island basalts)/Salmon River (island-arc tholeiites)arc + Stuart Fork terrane, but before invasion of the amalgamatedterrane assembly by the calc-alkaline plutons and most compositionallyrelated synplutonic mafic microdiorite dikes/sills. Becauseof their lateral continuation both north and south of the SawyersBar area, the North Fork/Salmon River igneous suite documentsthe construction of an oceanic arc of considerable lateral extentin the central Klamaths before terrane accretion. Suturing wasimmediately followed by the mid-Jurassic intrusion of calc-alkalineplutons + syngranitoid mafic microdioritic hypabyssals.     

The Venus ionosphere at grazing incidence of solar radiation: Transport of plasma to the night ionosphere

Using a quasi-two-dimensional model of the Venus ionosphere, we calculated the ion number densities and horizontal ion bulk velocities expected for a range of solar zenith angles near the terminator (80 to 100°), and compared them with data obtained from the Pioneer Venus Orbiter retarding potential analyzer. The calculated ion bulk velocity arises entirely from the solar EUV-induced plasma pressure gradient and has a magnitude consistent with observations; ionization by suprathermal electrons is neglected in those computations. We find that while photoionization is the dominant source of ionospheric plasma for solar zenith angles less than 92°, plasma transport from the dayside is the dominant plasma source for solar zenith angles greater than 95°. We also show that the main nightside plasma peak at approximately 140 km altitude is of the F₂ type (i.e., is diffusion controlled). Its altitude and shape are thus quite insensitive to the altitude of the ion source.     

Results of the solar constant experiment onboard Spacelab 1

A cavity type absolute radiometer was flown on Spacelab 1 in December 1983. We obtain a value of the solar constant of 1361.5 W m^–2 with an estimated accuracy of ±2.3 W m^–2 or 0.17%. When comparing this with other recent determinations, we find discrepancies which we consider indicative of metrological problems in present day absolute radiometry.     

Contemporary ocean and coastal management issues in Australia and New Zealand: an overview

The past decade has witnessed an unprecedented increase in the number of international treaties, conventions and agreements dealing with maritime issues and oceans governance. Most nations are attempting to cope with this expanding agenda at a time of fiscal constraint, competing environmental demands and the emergence of a new global strategic, political and economic order. However, similar issues do not always lead to similar outcomes. Australia and New Zealand share some common oceanic and coastal management problems, but variations in response arise from geographical differences, constitutional provisions, political style and administrative arrangements. This paper provides a brief overview of contemporary maritime issues and attempted solutions in both nations.     

Late Pleistocene to Holocene sedimentation and hydrocarbon seeps on the continental shelf of a steep,tectonically active margin,southern California,USA

Small, steep, uplifting coastal watersheds are prolific sediment producers that contribute significantly to the global marine sediment budget. This study illustrates how sedimentation evolves in one such system where the continental shelf is largely sediment-starved, with most terrestrial sediment bypassing the shelf in favor of deposition in deeper basins. The Santa Barbara–Ventura coast of southern California, USA, is considered a classic area for the study of active tectonics and of Tertiary and Quaternary climatic evolution, interpretations of which depend upon an understanding of sedimentation patterns. High-resolution seismic-reflection data over >570 km² of this shelf show that sediment production is concentrated in a few drainage basins, with the Ventura and Santa Clara River deltas containing most of the upper Pleistocene to Holocene sediment on the shelf. Away from those deltas, the major factor controlling shelf sedimentation is the interaction of wave energy with coastline geometry. Depocenters containing sediment 5–20 m thick exist opposite broad coastal embayments, whereas relict material (bedrock below a regional unconformity) is exposed at the sea floor in areas of the shelf opposite coastal headlands. Locally, natural hydrocarbon seeps interact with sediment deposition either to produce elevated tar-and-sediment mounds or as gas plumes that hinder sediment settling. As much as 80% of fluvial sediment delivered by the Ventura and Santa Clara Rivers is transported off the shelf (some into the Santa Barbara Basin and some into the Santa Monica Basin via Hueneme Canyon), leaving a shelf with relatively little recent sediment accumulation. Understanding factors that control large-scale sediment dispersal along a rapidly uplifting coast that produces substantial quantities of sediment has implications for interpreting the ancient stratigraphic record of active and transform continental margins, and for inferring the distribution of hydrocarbon resources in relict shelf deposits.     

Observations of Coronal Mass Ejections with the Coronal Multichannel Polarimeter

The Coronal Multichannel Polarimeter (CoMP) measures not only the polarization of coronal emission, but also the full radiance profiles of coronal emission lines. For the first time, CoMP observations provide high-cadence image sequences of the coronal line intensity, Doppler shift, and line width simultaneously over a large field of view. By studying the Doppler shift and line width we may explore more of the physical processes of the initiation and propagation of coronal mass ejections (CMEs). Here we identify a list of CMEs observed by CoMP and present the first results of these observations. Our preliminary analysis shows that CMEs are usually associated with greatly increased Doppler shift and enhanced line width. These new observations provide not only valuable information to constrain CME models and probe various processes during the initial propagation of CMEs in the low corona, but also offer a possible cost-effective and low-risk means of space-weather monitoring.