Upwelling and river runoff as sources of dissolved nitrous oxide to the Alsea estuary,Oregon

Surface waters of Alsea Bay, an unpolluted estuary on the Oregon coast, were analysed for nitrous oxide, nitrate and nitrite on a weekly or biweekly basis during the summer of 1979. The estuary was found to be a variable source of N₂O to the atmosphere. Large and rapid increases in the concentrations of N₂O, NO₃^?, and NO₂^? occurred at the beginning of the sampling period and are attributed to the influx of nutrient-rich upwelling water into the estuary with the tide. The subsequent decline in concentrations of nitrate, nitrite and nitrous oxide over the remainder of the summer is attributed to a decrease in upwelling intensity, a decline in nitrification rates and to assimilatory nitrate reduction. Measurements of nitrous oxide at six stations along the Alsea River were also made in September and October before and after the onset of the rainy season. Samples taken after flood conditions were established were systematically 50% higher than pre-flood samples. The data suggest that soil runoff results in elevated concentrations of N₂O in rivers.     

Chronology and evolution of the northern Iceland Plateau

New aeromagnetic data, K-Ar age determinations of dredged marine igneous rocks, as well as other geophysical evidence have shed light on the chronology, nature and evolution of the northern Iceland Plateau. Correspondence between seismic refraction profiles taken on the Jan Mayen Ridge and westward through Jan Mayen Island, suppressed aeromagnetic anomalies, earthquake surface wave studies, and ages of dredged igneous rocks suggest these strata may form an extended region of thickened crust, possibly of Caledonian age, extending westward toward the Kolbeinsey Ridge and northwest to the south wall of the Jan Mayen Fracture Zone.     

About Darcy's law in non-Galilean frame

This paper is aimed towards investigating the filtration law of an incompressible viscous Newtonian fluid through a rigid non-inertial porous medium (e.g. a porous medium placed in a centrifuge basket). The filtration law is obtained by upscaling the flow equations at the pore scale. The upscaling technique is the homogenization method of multiple scale expansions which rigorously gives the macroscopic behaviour and the effective properties without any prerequisite on the form of the macroscopic equations. The derived filtration law is similar to Darcy's law, but the tensor of permeability presents the following remarkable properties: it depends upon the angular velocity of the porous matrix, it verifies Hall–Onsager's relationship and it is a non-symmetric tensor. We thus deduce that, under rotation, an isotropic porous medium leads to a non-isotropic effective permeability. In this paper, we present the results of numerical simulations of the flow through rotating porous media. This allows us to highlight the deviations of the flow due to Coriolis effects at both the microscopic scale (i.e. the pore scale), and the macroscopic scale (i.e. the sample scale). The above results confirm that for an isotropic medium, phenomenological laws already proposed in the literature fails at reproducing three-dimensional Coriolis effects in all types of pores geometry. We show that Coriolis effects may lead to significant variations of the permeability measured during centrifuge tests when the inverse Ekman number Ek⁻¹ is 𝒪(1). These variations are estimated to be less than 5% if Ek⁻¹<0.2, which is the case of classical geotechnical centrifuge tests. We finally conclude by showing that available experimental data from tests carried out in centrifuges are not sufficient to determining the effective tensor of permeability of rotating porous media. Copyright © 2004 John Wiley & Sons, Ltd.     

Simultaneous operation of the Sea Beam multibeam echo-sounder andthe SeaMARC II bathymetric sidescan sonar system

An experiment aboard the Scripps Institution of Oceanography's RV Thomas Washington has demonstrated the seafloor mapping advantages to be derived from combining the high-resolution bathymetry of a multibeam echo-sounder with the sidescan acoustic imaging plus wide-swath bathymetry of a shallow-towed bathymetric sidescan sonar. To a void acoustic interference between the ship's 12-kHz Sea Beam multibeam echo-sounder and the 11-12-kHz SeaMARC II bathymetric sidescan sonar system during simultaneous operations, Sea Beam transmit cycles were scheduled around SeaMARC II timing events with a sound source synchronization unit originally developed for concurrent single-channel seismic, Sea Beam, and 3.5-kHz profile operations. The scheduling algorithm implemented for Sea Beam plus SeaMARC II operations is discussed, and the initial results showing their combined seafloor mapping capabilities are presented     

Deep-ocean vertical noise directionality

The structure of beam noise measured at the output of a vertical array in a range dependent ocean basin was investigated using the modified wide-angle parabolic equation (PE). Noise sources were distributed throughout the basin, and the field due to each noise source at an array located in the midbasin was calculated. The response of the array to the superposition of the noise sources was found by beamforming. An efficient and direct approach that superimposes the noise sources on the PE field as the field is marched toward the array was developed. Downslope calculations of the midbasin vertical directionality were made between 50 and 400 Hz with this technique. Use of a geoacoustic model shows that the bottom behaves as a low-pass filter     

Low-cost volcano surveillance from space: case studies from Etna, Krafla, Cerro Negro, Fogo, Lascar and Erebus

 Satellite data offer a means of supplementing ground-based monitoring during volcanic eruptions, especially at times or locations where ground-based monitoring is difficult. Being directly and freely available several times a day, data from the advanced very high resolution radiometer (AVHRR) offers great potential for near real-time monitoring of all volcanoes across large (3000×3000 km) areas. Herein we describe techniques to detect and locate activity; estimate lava area, thermal flux, effusion rates and cumulative volume; and distinguish types of activity. Application is demonstrated using data for active lavas at Krafla, Etna, Fogo, Cerro Negro and Erebus; a pyroclastic flow at Lascar; and open vent systems at Etna and Stromboli. Automated near real-time analysis of AVHRR data could be achieved at existing, or cheap to install, receiving stations, offering a supplement to conventional monitoring methods. Received: 21 January 1997 / Accepted: 3 April 1997