Fouling community of the Loxahatchee River estuary,Florida, 1980–81

Monthly growth of the fouling community at eight test panel sites in the Loxahatchee River Estuary was related to salinity and temperature. Growth was lowest in January 1981 (averaging 23 g per m², dry weight), and increased during spring and early summer with increasing water temperature. Maximum growth occurred during early or midsummer at upstream locations, before river or canal discharge substantially reduced salinity, and in late summer at downstream locations. Growth was greatest at salinities slightly less than that of seawater and decreased at salinities less than about 10‰. Growth was suppressed throughout the estuary in August 1981, probably because of the sudden decrease in temperature and salinity, and perhaps the increase in physical scouring, caused by runoff from Tropical Storm Dennis. Large loads of nutrients transported to the estuary from storm runoff, however, may have subsequently stimulated growth, which increased in September 1981 to the maximum for the year (averaging 683 g per m², dry weight).     

Analysis of some aromatic hydrocarbons in a benzene-soluble bitumen from Green River shale

The hydrocarbon content of an aromatic fraction, isolated from the bitumen of Green River shale, was studied by mass spectrometry, infra-red spectrometry, gas chromatography and a dehydrogenation technique. The hydrocarbon types and their distribution in this aromatic fraction, as determined by mass spectrometry, include the following: C_nH_2n?6(10%), C_nH_{2n?8 (31 %)}, C_nH_2n?10(18%), C_nH_2n?12(12%), C_nH_2n?14(8%) and a series of alkenylbenzenes (20%). The carbon-number range, empirical formulae and quantity of each compound in the major types are reported. Mass spectra of several compounds and homologous mixtures of compounds isolated from the aromatic fraction are also given.     

The Catoca kimberlite pipe, Republic of Angola: A paleovolcanological model

The Catoca kimberlite pipe is among the world’s largest primary diamond deposits. The Catoca volcanic edifice is only slightly eroded. Kimberlitic rocks of various facies compose a crater of about 1 km in diameter and a diatreme. The structure of the pipe and mining conditions of the deposit are complicated by intense intrapipe tectonic processes related to large-amplitude subsidence. Based on geological data, we propose a structural model of the deposit and a paleovolcanological model of the Catoca pipe formed during a full cycle beginning with a stage of active volcanism and completed by stages of gradually waning volcanic activity and sedimentation. It is suggested that the banded tuffisitic kimberlite of the crater zone was deposited at the stage of active volcanic eruption from specific pyroclastic suspension as a low-viscosity mixture of crystals and aqueous sol rich in serpentine.     

Observations of polar patches generated by solar wind Alfvén wave coupling to the dayside magnetosphere

A long series of polar patches was observed by ionosondes and an all-sky imager during a disturbed period (K_p = 7- and IMF B_z <0). The ionosondes measured electron densities of up to 9 × 10¹¹ m⁻³ in the patch center, an increase above the density minimum between patches by a factor of ≈4.5. Bands of F-region irregularities generated at the equatorward edge of the patches were tracked by HF radars. The backscatter bands were swept northward and eastward across the polar cap in a fan-like formation as the afternoon convection cell expanded due to the IMF B_y > 0. Near the north magnetic pole, an all-sky imager observed the 630-nm emission patches of a distinctly band-like shape drifting northeastward to eastward. The 630-nm emission patches were associated with the density patches and backscatter bands. The patches originated in, or near, the cusp footprint where they were formed by convection bursts (flow channel events, FCEs) structuring the solar EUV-produced photoionization and the particle-produced auroral/cusp ionization by segmenting it into elongated patches. Just equatorward of the cusp footprint Pc5 field line resonances (FLRs) were observed by magnetometers, riometers and VHF/HF radars. The AC electric field associated with the FLRs resulted in a poleward-progressing zonal flow pattern and backscatter bands. The VHF radar Doppler spectra indicated the presence of steep electron density gradients which, through the gradient drift instability, can lead to the generation of the ionospheric irregularities found in patches. The FLRs and FCEs were associated with poleward-progressing DPY currents (Hall currents modulated by the IMF B_y) and riometer absorption enhancements. The temporal and spatial characteristics of the VHF backscatter and associated riometer absorptions closely resembled those of poleward moving auroral forms (PMAFs). In the solar wind, IMP 8 observed large amplitude Alfvén waves that were correlated with Pc5 pulsations observed by the ground magnetometers, riometers and radars. It is concluded that the FLRs and FCEs that produced patches were driven by solar wind Alfvén waves coupling to the dayside magnetosphere. During a period of southward IMF the dawn-dusk electric field associated with the Alfvén waves modulated the subsolar magnetic reconnection into pulses that resulted in convection flow bursts mapping to the ionospheric footprint of the cusp.     

Biogeochemical Modelling of a Seasonally Anoxic Lake: Calibration of Successive and Competitive Pathways and Processes in Lake Aydat,France

A reactive transport model was developed to describe seasonal variations of biogeochemical and physical processes in Lake Aydat. The model includes physical processes such as vertical mixing, sedimentation and advection related to inflows into the lake and biogeochemical conversion processes in the water column and in the sediment surface layer. The reactions described in the model include primary redox reactions such as primary production, aerobic and anaerobic respiration, methanogenesis and secondary reactions established between oxidants and reducers produced by the primary reactions. After adjusting various kinetic constants, the model reasonably reproduced the main features of seasonal variations of dissolved oxygen and nitrate depth profiles and pH. The reactive transport model was also used to quantify the relative importance of different biogeochemical pathways. For instance, ferrous denitrification seems to play an important role when stratification is increasing.     

Tectonics and sedimentation around Kashinosaki Knoll: A subducting basement high in the eastern Nankai Trough

Abstract   When seamounts and other topographic highs on an oceanic plate are subducted, they cause significant deformation of the overriding plate and may act as asperities deeper in the seismogenic zone. Kashinosaki Knoll (KK) is an isolated basement high of volcanic origin on the subducting Philippine Sea Plate that will soon be subducted at the eastern Nankai Trough. Seismic reflection imaging reveals a thick accumulation of sediments (∼1200 m) over and around the knoll. The lower portion of the sedimentary section has a package of high-amplitude, continuous reflections, interpreted as turbidites, that lap onto steep basement slopes but are parallel to the gentler basement slopes. Total sediment thickness on the western and northern slopes is approximately 40–50% more than on the summit and southeastern slopes of KK. These characteristics imply that the basal sedimentary section northwest of KK was deposited by infrequent high-energy turbidity currents, whereas the area southeast of KK was dominated by hemipelagic sedimentation over asymmetric basement relief. From the sediment structure and magnetic anomalies, we estimate that the knoll likely formed near the spreading center of the Shikoku Basin in the early Miocene. Its origin differs from that of nearby Zenisu Ridge, which is a piece of the Shikoku Basin crust uplifted along a thrust fault related to the collision of the Izu–Bonin arc and Honshu. KK has been carried into the margin of the Nankai Trough, and its high topography is deflecting Quaternary trench turbidites to the south. When KK collides with the accretionary prism in about 1 My, the associated variations in sediment type and thickness around the knoll will likely result in complex local variations in prism deformation.