Petrological parameters of sands and sandstones from DSDP and ODP holes in arc-related areas

Detrital modes for 524 deep-marine sand and sandstone samples recovered on circum-Pacific, Caribbean, and Mediterranean legs of the Deep Sea Drilling Project and the Ocean Drilling Program form the basis for an actualistic model for arc-related provenance. This model refines the Dickinson and Suczek (1979) and Dickinson and others (1983) models and can be used to interpret the provenance/tectonic history of ancient arc-related sedimentary sequences. Four provenance groups are defined using QFL, QmKP, LmLvLs, and LvfLvmiLvl ternary plots of site means: (1) intraoceanic arc and remnant arc, (2) continental arc, (3) triple junction, and (4) strike-slip-continental arc. Intraoceanic- and remnant-arc sands are poor in quartz (mean QFL%Q < 5) and rich in lithics (QFL%L > 75); they are predominantly composed of plagioclase feldspar and volcanic lithic fragments. Continental-arc sand can be more quartzofeldspathic than the intraoceanic- and remnant-arc sand (mean QFL%Q values as much as 10, mean QFL%F values as much as 65, and mean QmKP%Qm as much as 20) and has more variable lithic populations, with minor metamorphic and sedimentary components. The triple-junction and strike-slip-continental groups compositionally overlap; both are more quartzofeldspathic than the other groups and show highly variable lithic proportions, but the strike-slip-continental group is more quartzose. Modal compositions of the triple junction group roughly correlate with the QFL transitional-arc field of Dickinson and others (1983), whereas the strike-slip-continental group approximately correlates with their dissected-arc field.

Organic petrography and extractable hydrocarbons of sediments at DSDP Leg 58 Holes

The quantity, type, and maturity of organic matter of Quaternary and Tertiary sediments from the Philippine Sea (DSDP Leg 58; Sites 442-446) were determined. Hydrocarbons in lipid extracts were analyzed by capillary-column gas chromatography. Kerogen concentrates were investigated by microscopy for vitrinite reflectance values and maceral composition. In the Shikoku Basin sediments (Sites 442, 443, and 444), organic carbon values range between 0.03 and 0.44 per cent. The higher values in the younger sediments are interpreted as an indication of increasing deposition of eroded organic particles during the past 4 m.y. Microscopic analyses revealed a dominance of reworked organic matter. Primary material could not be distinguished readily; thus, no maturation trend could be established. Extract yields were low. TV-alkane distributions mostly show maxima at n-C29 and n-C31 and high odd-over-even predominances, typical of material which originated in terrigenous higher plants. The organic-carbon values of sediments of the Daito Ridge and Basin region (Sites 444 and 445) range from less than 0.01 to 0.05 per cent. TV-alkanes exhibit varying marine and terrigenous influences. Some carbonate-rich samples show a pronounced even-over-odd predominance. At least the older sediments contained less recycled organic matter than the Shikoku Basin samples. The maturity, where measurable, was low. None of the Philippine Sea samples indicates a significant hydrocarbon-generation potential.

Mineralogy at DSDP Legs 58-60

Sediments recovered by drilling during Legs 58, 59, and 60 in the North and South Philippine Sea have been analyzed by X-ray diffractometry. The CaCO3 content was measured separately. The sites encompass several volcanic ridges and intervening inter-arc basin troughs as well as sites on the Mariana arc fore-arc sediment prism and the Mariana Trench. The sediments at all sites received major volcanogenic input from the various arcs; they tend to be rich in volcanic glass, with associated quartz, feldspar, pyroxenes and amphibole. Carbonate is a major component only at Site 445 at the southern end of the Daito Ridge, and at Site 448 on the Palau-Kyushu Ridge. All other sites were either deep relative to the carbonate compensation depth or had very high non-carbonate sedimentation rates. Clay minerals are mainly smectite and illite with lesser variable proportions of chlorite and kaolinite. Smectite predominates over illite except at sites in the Shikoku Basin and the Daito Ridge, and at one site in the Mariana Trench. At several sites, smectite increases and illite decreases with depth. Principal zeolites are phillipsite and clinoptilolite. Analcime occurs in some samples.

Horizontal profiles of longwave and shortwave radiation components over sea ice near Barrow, Alaska during the 2011 melt

An integrated instrument package for measuring and understanding the surface radiation budget of sea ice is presented, along with results from its first deployment. The setup simultaneously measures broadband fluxes of upwelling and downwelling terrestrial and solar radiation (four components separately), spectral fluxes of incident and reflected solar radiation, and supporting data such as air temperature and humidity, surface temperature, and location (GPS), in addition to photographing the sky and observed surface during each measurement. The instruments are mounted on a small sled, allowing measurements of the radiation budget to be made at many locations in the study area to see the effect of small-scale surface processes on the large-scale radiation budget. Such observations have many applications, from calibration and validation of remote sensing products to improving our understanding of surface processes that affect atmosphere-snow-ice interactions and drive feedbacks, ultimately leading to the potential to improve climate modelling of ice-covered regions of the ocean. The photographs, spectral data, and other observations allow for improved analysis of the broadband data. An example of this is shown by using the observations made during a partly cloudy day, which show erratic variations due to passing clouds, and creating a careful estimate of what the radiation budget along the observed line would have been under uniform sky conditions, clear or overcast. Other data from the setup's first deployment, in June 2011 on fast ice near Point Barrow, Alaska, are also shown; these illustrate the rapid changes of the radiation budget during a cold period that led to refreezing and new snow well into the melt season.

Plutonium and americium concentrations in sea water and in sinking particles

Vertical fluxes of 239+240Pu and 241Am and temporal changes in their inventories in the northwestern Mediterranean Sea have been examined through high-resolution water column sampling coupled with direct measurements of the vertical flux of particle-bound transuranics using time-series sediment traps. Water column profiles of both radionuclides showed well-defined sub-surface maxima (2391240Pu between 100-400 m; 241Am at 100-200 m and 800 m), the depths of which are a result of the different biogeochemical scavenging behavior of the two radionuclides. Comparison of deep water column (0-2,000 m) transuranic inventories with those derived from earlier measurements demonstrate that the total 2391240Pu inventory had not substantially changed between 1976-1990 whereas 241Am had decreased by approximately 24%. Enhanced scavenging of 241Am and a resultant, more rapid removal from the water column relative to 239+240Pu was also supported by the observation of elevated Am/Pu activity ratios in sinking particles collected in sediment traps at depth. Direct measurements of the downward flux of particulate 239+240Pu and 241Am compared with transuranic removal rates derived from observed total water column inventory differences over time, show that particles sinking out of deep waters (1,000-2,000 m) could account for 26-72% of the computed total annual 239+240Pu loss and virtually all of the 241Am removal from the water column. Upper water column (0-200 m) residence times based on direct flux measurements ranged from 20-30 yr for 239+240Pu and 5-10 yr for 241Am. The observation that 241Am/239+240Pu activity ratios in unfiltered Mediterranean seawater are six times lower than those in the north Pacific suggests the existence of a specific mechanism for enhanced scavenging and removal of 241Am from the generally oligotrophic waters of the open Mediterranean. It is proposed that atmospheric inputs of aluminosilicate particles transported by Saharan dust events which frequently occur in the Mediterranean region could enhance the geochemical scavenging and resultant removal of 241Am to the sediments.