A tertiary lamprophyre dike with high pressure xenoliths and megacrysts from Wiedemanns Fjord,East Greenland

Lamprophyric dikes, mainly of camptonite/monchiquite affinities occur in the Wiedemanns Fjord area. One example contains a complex assemblage of olivine-orthopyroxene-chrome spinel nodules, megacrysts of kaersutite, diopside, strongly reverse-zoned green salite and various spinel phases. Microprobe analyses are presented for all these phases and for the lilac-coloured titansalites and strongly-coloured kaersutites of the groundmass. It is concluded that these minerals record evolution under various P, T and oxidation regimes during the formation of a lamprophyric parent magma. The nodules provide evidence for deep fractures in this area supposedly associated with early rifting in the North Atlantic.     

Mapping of benthic enrichment patterns in Narragansett Bay,Rhode Island

A synoptic reconnaissance survey was performed over a five-day period in August 1988 to assess benthic habitat quality throughout Narragansett Bay, Rhode Island, using REMOTS^® sediment-profile photography and analysis in combination with measurements of the levels ofClostridium perfringens spores (a fecal indicator) in sediments. Three main areas of degraded benthic habitat quality related to either excessive organic enrichment or physical disturbance were identified based solely on the REMOTS^® analysis: the Providence River Reach, Greenwich Bay and its associated coves and harbors, and an area located along the southwest side of Prudence Island. Sediments at many stations in these areas exhibited shallow apparent redox-potential discontinuity (RPD) depths, high apparent oxygen demand, and low-order benthic successional stages. ElevatedClostridium perfringens spore counts in surface sediments were attributed to inputs from wastewater treatment facilities. The highest spore counts occurred at the head of the bay, where wastewater treatment discharges and associated combined sewer overflows are numerous. Using data from the REMOTS^® analysis and the sediment inventory ofC. perfringens spores, a distinction was made between organic enrichment of the bottom from sewage, versus nonsewage enrichment or physical disturbance. The combination of techniques employed in this investigation could be used to design more efficient monitoring programs to assess eutrophication effects in estuaries and determine the effectiveness of regulatory or management initiatives to reduce organic overenrichment of benthic habitats.     

Anoxic carbon degradation in Arctic sediments: Microbial transformations of complex substrates

Complex substrates are degraded in anoxic sediments by the concerted activities of diverse microbial communities. To explore the effects of substrate complexity on carbon transformations in permanently cold anoxic sediments, four substrates—Spirulina cells, Isochrysis cells, and soluble high molecular weight carbohydrate-rich extracts of these cells (Spir-Ex and Iso-Ex)—were added to sediments collected from Svalbard. The sediments were homogenized, incubated anaerobically in gas-tight bags at 0°C, and enzyme activities, fermentation, and terminal respiration were monitored over a 1134 h time course. All substrate additions yielded a fraction (8%-13%) of carbon that was metabolized to CO₂ over the first 384 h of incubation. The timecourse of VFA (volatile fatty acid) production and consumption, as well as the suite of VFAs produced, was similar for all substrates. After this phase, pathways of carbon degradation diverged, with an additional 43%, 32%, 33%, and 8% of Isochrysis, Iso-Ex, Spirulina, and Spir-Ex carbon respired to CO₂ over the next 750 h of incubation. Somewhat surprisingly, the soluble, carbohydrate-rich extracts did not prove to be more labile substrates than the whole cells from which they were derived. Although Spirulina and Iso-Ex differed in physical and chemical characteristics (solid/soluble, C/N ratio, lipid and carbohydrate content), nearly identical quantities of carbon were respired to CO₂. In contrast, only 15% of Spir-Ex carbon was respired, despite the initial burst of activity that it fueled, its soluble nature, and its relatively high (50%) carbohydrate content. The microbial community in these cold anoxic sediments clearly has the capacity to react rapidly to carbon input; extent and timecourse of remineralization of added carbon is similar to observations made at much higher temperatures in temperate sediments. The extent of carbon remineralization from these specific substrates, however, would not likely have been predicted on the basis of general substrate characteristics.