[1] This paper describes a new instrument that uses a combination of thermal dissociation and laserinduced fluorescence detection of NO 2 for in situ detection of the sum total peroxy nitrates, the sum total of alkyl nitrates and hydroxyalkyl nitrates, and HNO 3 . The instrument is capable of routine, continuous in situ measurements of these three classes of compounds that are accurate (15%) with a low detection limit (90 parts per trillion (ppt) 10 s À1 , S/N ratio = 2 on a background of 1 ppb NO 2 and 30 ppt 10 s À1 on a background of 100 ppt NO 2 ). Theoretical analysis of potential interferences combined with laboratory experiments that test for interferences show that rapidly cooling the gas and dropping the pressure after the thermal dissociation reduces interferences to the order of 1 -5%. Observations in ambient air at the University of California Blodgett Forest Research Station demonstrate the capabilities of this instrument under field conditions. These field observations are compared with independent total NO y observations.

Measurements of anthropogenic hydrocarbons, ozone, and meteorological variables were obtained during the summer of 1997 near the University of California Blodgett Forest Research Station on the western slope of the Sierra Nevada Mountains. These measurements and related observations obtained upwind in Sacramento and Folsom, California, by the California Air Resources Board and the National Weather Service demonstrate that the transport of the Sacramento plume is controlled by extremely consistent, terrain‐driven winds that draw polluted air into the Sierra Nevada by day and flush the mountains at night with clean, continental background air. In effect the plume serves as a mesoscale (100 km) daytime flow reactor where the daily evolution of the Sacramento urban plume can be characterized as a Lagrangian air parcel transported from the urban core into the sparsely populated Sierra Nevada mountains. Using observations of slowly reacting anthropogenic hydrocarbons, we demonstrate that at the peak impact of the Sacramento plume the air at Blodgett Forest can be characterized as a mixture of 32% air from the urban core and 68% from the relatively clean background. From measurements of more reactive hydrocarbons we infer an average daytime OH concentration of 1.1 × 107 molecules cm−3 during the transit of the urban plume.

S U M M A R YMany of the natural materials studied in rock and environmental magnetism contain a mixed assemblage of mineral grains with a variety of different origins. Mathematical decomposition of the bulk magnetic mineral assemblage into populations with different properties can therefore be a source of useful environmental information. Previous investigations have shown that such unmixing into component parts can provide insights concerning source materials, transport processes, diagenetic alteration, authigenic mineral growth and a number of other processes.A new approach will be presented that performs a linear unmixing of remanence data into coercivity based end-members using only a minimal number of assumptions. A non-negative matrix factorization (NMF) algorithm for unmixing remanence data into constituent endmembers is described with case studies to demonstrate the utility of the approach. The shape of the end-members and their abundances obtained by NMF is based solely on the variation in the measured data set and there is no requirement for mathematical functions or type curves to represent individual components. Therefore, in contrast to previous approaches that aimed to unmix curves into components corresponding to individual minerals and domain states, NMF produces a genetically more meaningful decomposition showing how a data set can be represented as a linear sum of invariant parts. It has been found that the NMF algorithm performs well for both absolute and normalized remanence curves, with the capacity to process thousands of measured data points rapidly.

[1] Diagenesis has extensively affected the magnetic mineral inventory of organic-rich late Quaternary sediments in the Niger deep-sea fan. Changes in concentration, grain size, and coercivity document modifications of the primary magnetic mineral assemblages at two horizons. The first front, the modern iron redox boundary, is characterized by a drastic decline in magnetic mineral content, coarsening of the grain size spectrum, and reduction in coercivity. Beneath a second front, the transition from the suboxic to the sulfidic anoxic domain, a further but less pronounced decrease in concentration and bulk grain size occurs. Finer grains and higher coercive magnetic constituents substantially increase in the anoxic environment. Low-and high-temperature experiments were performed on bulk sediments and on extracts which have also been examined by X-ray diffraction. Thermomagnetic analyses proved ferrimagnetic titanomagnetites of terrigenous provenance as the principal primary magnetic mineral components. Their broad range of titanium contents reflects the volcanogenic traits of the Niger River drainage areas. Diagenetic alteration is not only a grain size selective process but also critically depends on titanomagnetite composition. Low-titanium compounds are less resistant to diagenetic dissolution. Intermediate titanium content titanomagnetite thus persists as the predominant magnetic mineral fraction in the sulfidic anoxic sediments. At the Fe redox boundary, precipitation of authigenic, possibly bacterial, magnetite is documented. The presence of hydrogen sulfide in the pore water suggests a formation of secondary magnetic iron sulfides in the anoxic domain. Grain size-specific data argue for a gradual development of a superparamagnetic and single-domain iron sulfide phase in this milieu, most likely greigite.Citation: Dillon, M., and U. Bleil (2006), Rock magnetic signatures in diagenetically altered sediments from the Niger deep-sea fan,