Ocean cable measurements of the tsunami signal from the 1992 Cape Mendocino earthquake

The movement of the seawater across the earth's magnetic field produces a large-scale motional electric field. Using the Point Arena, California, to Hanauma Bay, Hawaii, unpowered HAW-1 cable, we have studied the geopotential across this distance to look for possible tsunami-induced fields that might have been produced following the April 1992 Cape Mendocino earthquake. We have used a ten-day interval prior to and including the earthquake as a reference for geopotential signals and for geomagnetic activity. We have also used geomagnetic data from Point Arena, Honolulu and Boulder as reference data. The results of the analyses show that there are tsunami-related effects in the cable geopotential data. These are (a) larger voltage prediction errors (residuals) for the interval following the main shock; (b) enhanced (compared to the 10d reference interval) geopotential spectral power following the main shock: two enhancements are larger than geomagnetically-induced spectral power enhancements in the same time interval; and (c) strong evidence for an 30 min echo in the cable geopotential signal following the main shock.     

Responses of the mussel Mytilus edulis to copper and phenanthrene: Interactive effects

Most investigations of the responses of marine organisms to xenobiotics have concentrated on single contaminants and little is known of possible interactive effects of different classes of xenobiotics. As these latter seldom occur in environmental isolation, it is important to understand any interactions (synergistic or antagonistic) which may occur. This problem has been approached in the mussel Mytilus edulis by exposing estuarine mussels to copper (20 μg litre⁻¹) and phenanthrene (100 μg litre⁻¹) both individually and in combination, and measuring cytochemical subcellular and physiological responses after 3 days exposure and 3 days and 12 days recovery period. Results showed that mussels accumulated both xenobiotics during 3 days exposure. Depuration of copper was complete in 3 days recovery period, while loss of phenanthrene ranged from 30% to 70% of the concentration reached after 3 days exposure. There were no interactive effects on depuration.Both copper and phenanthrene reduced lysosomal hydrolase latency in digestive cells, and copper appeared to have a synergistic effect in preventing recovery of latency of lysosomal N-acetyl-β-hexosaminidase during the recovery period. There was evidence, in the digestive cells, of an antagonistic effect of copper on stimulation of activity of the microsomal respiratory chain (measured as NADPH-neotetrazolium reductase) by phenanthrene. Stimulation of this system by phenanthrene persisted after 12 days recovery period. There was a synergistic interaction of copper and phenanthrene on elevation of oxygen consumption and ammonium excretion. Clearance rates and scope for growth (physiological condition) were depressed by copper but not by phenanthrene after 3 days exposure.These findings are discussed in terms of known effects of copper and phenanthrene and the interactions are considered in terms of environmental effects measurements.     

Oceanic Odyssey of a satellite-tracked drifter: North Pacific variability delineated by a single drifter trajectory

A near-surface satellite-tracked drifter launched off the east coast of the Kuril Islands on September 4,1993 began a 2.5-year Odyssey across the North Pacific Ocean. During its travels, the drifter encountered numerous energetic oceanographic regimes as it moved from the region of the Kuril-Kamchatka Trench to the continental margin of the Kuril Islands, through Friza Strait into the Sea of Okhotsk, seaward again through Bussol’ Strait, and then eastward across the North Pacific. Oceanic features detected along the basin-wide trajectory include a quasi-permanent anticyclonic eddy over the Kuril-Kamchatka Trench, open-ocean wind-driven inertial oscillations, coastal-trapped diurnal shelf waves, semidiurnal tidal currents, transient cyclonic and anticyclonic eddies, through-strait flows, and wave-like mesoscale meanders. The single drifter track delineates the dynamically-rich variability of upper ocean currents, emphasizes the marked difference in flow dynamics between boundary and open ocean regions, and provides a time-scale for the movement of surface waters across the entire North Pacific.     

An Experimental Evaluation of Dock Shading Impacts on Salt Marsh Vegetation in a New England Estuary

Docks constructed over salt marsh can reduce vegetation production and associated ecosystem services. In Massachusetts, there is a 1:1 height-to-width ratio (H:W) dock design guideline to reduce such impacts, but this guideline’s efficacy is largely untested. To evaluate dock height effects on underlying marsh vegetation and light availability, we deployed 1.2-m-wide experimental docks set at three different heights (low (0.5:1 H:W), intermediate (1:1 H:W), and high (1.5:1 H:W)) in the high and low marsh zones in an estuary in Massachusetts, USA. We measured temperature, light, vegetation community composition, and stem characteristics under the docks and in unshaded control plots over three consecutive growing seasons. Temperature and light were lower under all docks compared with controls; both increased with dock height. Maximum stem height and nitrogen content decreased with available light. In the Spartina patens-dominated high marsh, stem density and biomass were significantly lower than controls under low and intermediate but not high docks. Spartina alterniflora, the dominant low marsh vegetation, expanded into the high marsh zone under docks. S. alterniflora aboveground biomass significantly differed among all treatments in the low marsh, while stem density was significantly reduced for low and intermediate docks relative to controls. Permit conditions and guidelines based on dock height can reduce dock impacts, but under the current guideline of 1:1 H:W, docks will still cause significant adverse impacts to vegetation. Such impacts may interfere with self-maintenance processes (by decreasing sediment capture) and make these marshes less resilient to other stressors (e.g., climate change).     

Relative current effect on short wave growth

Ocean Dynamics - Short waves growth is characterized by nonlinear and dynamic processes that couple ocean and atmosphere. Ocean surface currents can have a strong impact on short wave steepness and...     

Eruptive conditions and depositional processes of Narbona Pass Maar volcano,Navajo volcanic field,Navajo Nation,New Mexico (USA)

Phreatomagmatic deposits at Narbona Pass, a mid-Tertiary maar in the Navajo volcanic field (NVF), New Mexico (USA), were characterized in order to reconstruct the evolution and dynamic conditions of the eruption. Our findings shed light on the temporal evolution of the eruption, dominant depositional mechanisms, influence of liquid water on deposit characteristics, geometry and evolution of the vent, efficiency of fragmentation, and the relative importance of magmatic and external volatiles. The basal deposits form a thick (5–20 m), massive lapilli tuff to tuff-breccia deposit. This is overlain by alternating bedded sequences of symmetrical to antidune cross-stratified tuff and lapilli tuff; and diffusely-stratified, clast-supported, reversely-graded lapilli tuffs that pinch and swell laterally. This sequence is interpreted to reflect an initial vent-clearing phase that produced concentrated pyroclastic density currents, followed by a pulsating eruption that produced multiple density currents with varying particle concentrations and flow conditions to yield the well-stratified deposits. Only minor localized soft-sediment deformation was observed, no accretionary lapilli were found, and grain accretion occurs on the lee side of dunes. This suggests that little to no liquid water existed in the density currents during deposition. Juvenile material is dominantly present as blocky fine ash and finely vesiculated fine to coarse lapilli pumice. This indicates that phreatomagmatic fragmentation was predominant, but also that the magma was volatile-rich and vesiculating at the time of eruption. This is the first study to document a significant magmatic volatile component in an NVF maar-diatreme eruption. The top of the phreatomagmatic sequence abruptly contacts the overlying minette lava flows, indicating no gradual drying-out period between the explosive and effusive phases. The lithology of the accidental clasts is consistent throughout the vertical pyroclastic stratigraphy, suggesting that the diatreme eruption did not penetrate below the base of the uppermost country rock unit, a sandstone aquifer ∼360 m thick. By comparison, other NVF diatremes several tens of kilometers away were excavated to depths of ∼1,000 m beneath the paleosurface (e.g., Delaney PT. Ship Rock, New Mexico: the vent of a violent volcanic eruption. In: Beus SS (ed) Geological society of America Centennial Field Guide, Rocky Mountain Section 2:411–415 (1987)). This can be accounted for by structurally controlled variations in aquifer thickness beneath different regions of the volcanic field. Variations in accidental clast composition and bedding style around the edifice are indicative of a laterally migrating or widening vent that encountered lateral variations in subsurface geology. We offer reasonable evidence that this subsurface lithology controlled the availability of external water to the magma, which in turn controlled characteristics of deposits and their distribution around the vent. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.