Exchange of water in a stratified estuary with an application to Krka (Adriatic Sea)

A method of computing the exchange time of freshwater and marine water in a stratified estuary is presented. The method is based on the inflow of the river and its tributaries, the depth of the halocline and salinity in the upper brackish water layer. Exchange time of freshwater and seawater in the Krka Estuary is shorter during winter than during summer. During winter the exchange time of freshwater is between 6 and 20 days, whereas during summer it is up to 80 days. The exchange time of marine water during winter is from 50 to 100 days, whereas during summer it lengthens to 250 days. The renewal time of water in the Krka Estuary as a whole may be approximated by the exchange time.     

Basalt from Louisiana continental shelf

A basalt outcrop was discovered on Alderdice Bank on the outer Louisiana continental shelf. The basalt shows an age of 76.8 ± 3.3 × 10⁶ years. Textural, mineralogical, and chemical characteristics indicate that it is an alkali basalt of shallow intrusive origin. It was probably brought to the seafloor by salt tectonics and exposed due to salt dissolution.An accurate account of the Mesozoic geologic history of the Gulf of Mexico must consider the apparent consanguinity of all magmatic rocks of the region, including the Alderdice Bank basalt, and the apparent basinward decrease in age of magmatic activities.     

Measuring run-up on a natural beach

Field experiments have been performed to evaluate and intercompare two techniques for measuring run-up on natural beaches, resistance wires and films. Simultaneous deployment of wire sensors shows a low error (< 5%) in electronics gain, but a strong sensitivity to the elevation of the wires above the beach face. On a low slope (β ～ 0.02) beach, with incident wind waves of moderate height (H ～ 1 m), differences of only a few cm in the wire elevation cause variance differences as large as 25%, in otherwise identical sensors. Replicate digitizations of the same run-up film show variance differences as large as 20%, with an average deviation from the mean variance of 8%.Use of the film and resistance wire sensors on the same run-up field showed small differences in the mean swash elevation (i.e., set-up), but an 83% difference in swash variance. Much further work is needed to determine the dependence of sensor differences on beach slope, porosity, camera elevation and other factors.     

A NEW MODEL FOR PEBBLE BEACH TRACER DISPERSAL

A series of eight tracer experiments were carried out over one year (1983) on a low energy, macro-tidal beach in South Wales, UK. Tracer movement was monitored and 30 pebbles adjacent to coloured tracer pebbles were measured. Measurements were of the A, B, and C axes, roundness, Maximum Projection Sphericity and Oblate-Prolate indices. Analysis shows that through time, the percentage rejection of these properties increased. It is theorised that the surface tracers are 'misfits' or 'rejects' which have not found their equilibrium position in the pebble facies.     

Hypothesis for a submarine landslide and cohesionless sediment flows resulting from a 17th century earthquake-triggered landslide in Quebec,Canada

Textural isotopic and microfossil data from two gravity cores obtained in Saguenay Fjord, Quebec, suggest that a distinctive sandy clay bed was deposited as the result of a major landslide in the Saguenay River basin. Pb-210 dating of the cores indicate that the bed is of similar age to the magnitude 7 earthquake of February 5, 1663. The slide involved sensitive marine clays and may have occurred in two stages. Slide sediments carried into the Saguenay River channel were probably reworked and subsequently transported down the Fjord basin as two distinct cohesionless mass flows. Fine clay laminae that overlie the older mass flow bed record the modulation of depositional processes by tidal currents for several weeks after this event.     

Influence of structural flexibility and wave interference on dynamic behavior of idealized offshore platform

An approximate method is presented to estimate the hydrodynamic loading and structural response of an idealized offshore platform subjected to a regular train of linear surface waves. The platform is taken to consist of four bottom-mounted, flexible, circular cylinders supporting a rigid deck and is assumed to be aligned parallel to the incident wave direction. The response of each column is assumed to be one-dimensional and to be governed by linear beam theory. The solution technique for the fluid velocity potential involves replacing scattered waves by equivalent plane waves together with non-planar, first-correction terms, and can be shown to be a large spacing approximation.Numerical results are presented which show the effect of hydrodynamic interference and structural flexibility on the platform response.     

Contaminant concentrations and toxicity of sea-surface microlayer near Los Angeles, California

Sea-surface microlayer samples were collected from six nearshore areas receiving different amounts of anthropogenic inputs. The samples were analyzed for selected trace metals, chlorinated hydrocarbons, and polycyclic aromatic hydrocarbons. The relative toxicities of the samples were determined with fish embryo bioassays.Contaminant concentrations generally increased from offshore to the inshore stations. Contaminant concentrations were several orders of magnitude higher in microlayer samples from the highly industrialized Los Angeles and Long Beach harbors compared to samples from a site 15km offshore. Microlayer samples from the inshore stations were significantly more toxic, and induced significantly more developmental abnormalities and chromosome aberrations, than samples from the offshore stations.     

Effect of oil and dispersants on the growth of Mussels

Mussels (Mytilus edulis L.) were exposed to North Sea crude oil, microencapsulated oil and dispersants, singly and in combination, and growth rates measured at 24–48 h intervals.Exposure to microencapsulated pure oil (2·0–2·1 mg litre⁻¹) and to microencapsulated mixtures of oil (2·2−2·5 mg litre^-1+5 % of the different dispersants (FINASOL OSR 5, COREXIT 9527, DISPOLENE 36 S) gave approximately the same reduction in growth rate (80–90%) within 170h.Oil chemically dispersed with DISPOLENE 36 S and a pure oil mechanically dispersed in water were significantly less toxic. In high concentrations (2 mg litre⁻¹) all disperants are toxic, DISPOLENE 36 S ssignificantly more than the others.Mussels exposed for 170 h to microencapsulated oil and to microencapsulated oil dispersant mixtures recovered to control growth within 300 h in clean seawater, while in those given pure oil-in-water suspension, the recovery was slower.It is concluded that the toxicity of oil is mainly related to size and concentration of oil particles, while the effect of 5% dispersants added is negligible.     

Submersible observations of an iceberg pit and scour on the Grand Banks of Newfoundland

An elongated sea bed depression (pit), 80 by 125 m and 10 m deep located on the Grand Banks of Newfoundland was identified on high resolution surficial geophysical survey lines and investigated using a manned submersible. The pit occurs at the termination of a long (greater than 3 km) iceberg scour, 1.5 m deep, and 80 m wide in 91 m of water. It is similar to other depressions in the region that indent the sea bed up to seven times deeper than the surrounding deepest iceberg furrows. The pit is interpreted to be the sea bed response to impact and loading by a rolling and grounding iceberg. The iceberg scour and pit appear to be of recent origin.