In situ tests for ice strength measurements

Ice effects have caused extensive damage. Enormous forces have been recorded. On the other hand, ice has been used as a structural material under various situations. To use ice beneficially and to assess the danger of ice forces, it is necessary to know the mechanical properties of ice.Results from the large number of ice tests carried out in laboratories show the difficulties of sampling and testing procedures. Most of the tests have not reproduced faithfully enough the conditions existing in nature. To obtain adequate results, laborious and slow samplings and preparations of test specimens have been necessary. Recently, extensive use has been made of in situ tests in order to reduce the number of factors whixh can induce errors in measurements. Large scale tests have simulated actual structures. General ice properties have become available from small-scale in situ tests. Since these tests give rapid results, a large number are already available with a good coverage of field conditions.A theoretical basis has been devised for these in situ tests which measure essentially the unconfined and confined compressive strengths of ice, and practical devices have been developed to execute these tests. A correlation of measurements from laboratory tests and in situ tests has established a link between natural and artificial environments. Brittle elastic and clastic theories have been applied, to find the best correlations for ice tests. Test results have been related to the mechanical properties as used in engineering practice.A very summary conclusion of results is that cold sea ice and cold fresh water ice are both very strong. However, depending on the load rate, ice can be quite brittle, which mitigates dangerous effects from ice action against massive structures.     

Remote determination of momentum-flux profiles in the lower atmospheric boundary layer

An acoustic locator—a sodar—is a unique instrument for getting the objective characteristics of the current state of the atmospheric boundary layer (ABL) owing to a combination of such properties as remoteness, mobility, resolution, and information content. This study demonstrates the capabilities of a sodar to obtain data on the second moments of the field of wind-velocity fluctuations, in particular, the profiles of momentum flux in the lower ABL, which are very important in practical applications. A corresponding method is described, and the results of its experimental verification and some examples of its application under the conditions of different ABL stratification are presented.     

Nitrate assimilation by zooxanthellae maintained in laboratory culture

The ability of cultured zooxanthellae to use ammonium and nitrate was tested. The zooxanthellae were initially isolated from the anemone Aiptasia pulchella. The zooxanthellae were able to grow on media supplemented with either form of dissolved inorganic nitrogen (DIN) although ammonium was inhibitory above 300 μM. In accord with the intact symbiosis and freshly isolated algae, the cultured zooxanthellae took up ammonium. In contrast, the cultured algae demonstrated nitrate uptake and utilization. This was enhanced with DIN deprivation. Nitrate reductase was found in the algae and appeared to be inducible. Within the animal host, excretory ammonium may repress this induction.     

Secondary flow caused by differential roughness,Langmuir circulations,and their effect on the development of sand ribbons

The process of Differential Roughness Secondary Flow (DRSF), hitherto little recognized, recently was demonstrated in a wind tunnel and in a flume. It is suggested here the DRSF may, in the natural environment, play an important part in the persistence and sharp definition of sand ribbons, previously initiated by other processes. In 1980 Karl described a series of sand ribbons, alternating with exposed substrate, which he attributed to the effect of Langmuir circulations. Although Langmuir Circulation Secondary Flow (LCSF) may indeed, in some cases, initiate sand ribbons, the sharply-defined edges typical of these features are explained better by DRSF.     

Palaeo-carbonate seep structures above an oil reservoir, Gryphon Field, Tertiary, North Sea

Petrographic and geochemical analyses performed on a North Sea core from the Gryphon Field reveal the presence of palaeo-degassing features surrounded by injected sandstones in the Eocene interval. The injected sandstones are oil-stained and poorly cemented by carbonate and quartz. ¹⁸O isotope analyses indicate that carbonate cementation occurred during shallow burial (likely less than about 300 m). Depleted ¹³C (around –30 V-PDB) carbonate cement suggests that bicarbonate was derived from the microbial oxidation of oil and gas. Late quartz overgrowths enclose oil present in the injected units. The tubular degassing conduits are composed of zoned cements and have ¹⁸O and ¹³C isotope values similar to the injected sandstones, indicating that oil and gas seepage induced the precipitation of authigenic carbonate in the shallow subsurface. Oil inclusions in inter- and intra-crystal cement sites in both injected sandstones and degassing conduits indicate that oil seepage was an ongoing feature at shallow burial. A proposed model involves oil and gas seepage and the formation of the degassing conduits, followed by a sand injection phase. It seems likely that oil and gas continued to leak towards the seabed by exploiting the network of permeable injected sandstones and the horizons of porous degassing features.     

New seismic data in the Mozambique Channel

This paper presents seismic reflection and refraction data from the Mozambique Channel, collected between 1971 and 1973. A deep sedimentary basin (up to 5 km of sediments) opens southwards to the Mozambique Basin, and is bounded to the east by the Davie Ridge and beyond by the marginal plateau of Malagasy. A continuous reflector (C), possibly of Cretaceous age, is identified between layers having seismic interval velocities of 2.4–2.8 km/s and 3.1–3.4 km/s. The deepest sediments have velocities of 4.5–4.9 km/s and overlie a layer with velocity 5.5 km/s, which may be volcanic in the north-east of the Channel.The crust occupying most of the Channel is probably pre-Cretaceous in age, and may be largely continental in nature. This is supported by subdued magnetic anomalies and the possibility of a continuous Karroo sedimentary section across the northern Channel. The oceanic crust of the Mozambique Basin may extend as far north as 24°S, into the western Channel only. The problem of the origin of the Mozambique Channel remains unresolved, although a long sedimentary history indicates that Malagasy may have separated from Mainland Africa prior to Karroo times. The Davie Ridge may possibly represent a relict strike-slip fault, which permitted movement along a north-south line.     

Vertical and lateral transport of organic carbon and the carbon budget in Santa Monica Basin, California

The flux and compositions of solvent-extractable lipid fractions were measured in particulate matter collected periodically by moored sediment traps in the Santa Monica Basin from 1985–1988. The purpose was to assess the compositional changes during settling, the carbon dynamics in the basin and to estimate the impacts of energy-related by-products on the surface sediments. Sediment traps recorded consistently high lipid fluxes in the eastern slope relative to the central basin, reflecting elevated terrigenous carbon inputs possibly from land-based human activities. Generally, lipid fluxes decrease offshore but increase vertically with water depth below 500m, implying lateral transport of particles. The steep decline of flux in the top 500m of the water is related to the rapid decomposition and mineralization of the marine-derived cellular carbon compounds. Less than 5% of the marine lipid components reach the seabed. In contrast, preferential preservation of terrigenous lipid is clearly evident from the chemistry of deeper traps and surface sediments.The lateral transport of particles is reflected in the presence of higher plant-derived lignin phenols and sewage-derived coprostanol and epicoprostanol in the deep trap material as well as in surface sediment throughout the basin. Petroleum triterpanes characteristic of natural seepage also permeates through the entire basin. Based on the data collected from both the trap particulte matter and surface sediments, a carbon budget for the Santa Monica Basin has been constructed.     

Comparison of cytochrome P450 in three butterflyfish species: Ecological implications of elevated CYP2B and CYP3A in Chaetodon capistratus

The relationship between cytochrome P450 and feeding on terpenoid-rich gorgonian corals was investigated in a species of tropical butterflyfish and compared with two other sympatric congeners that do not feed on gorgonians. Fish were collected from non-polluted waters in Belize and the levels of two cytochrome P450 isozymes (CYP2B and CYP3A) were immunoquantitated in addition to quantification of total P450. Chaetodon capistratus regularly feeds on gorgonian corals and has higher levels of total hepatic microsomal cytochrome P450 than C. ocellatus or C. striatus. The content of hepatic P450 (0.588–0.794 nmol mg⁻¹) in C. capistratus is among the highest ever reported in teleosts from non-polluted waters and is significantly greater than detected in C. ocellatus or C. striatus. Chaetodon capistratus also had a larger hepatic index (g liver per g fish) and more microsomal protein (mg protein per g liver), factors that translate into 3.3- to 8-fold more total P450 per g fish. Sexual differences in total P450 were observed between male and female C. capistratus, but not among the other species. The contents of proteins detected by immunoassay with polyclonal anti-scup P450B (CYP2B) and anti-human P4503A (CYP3A) were 2- to 10-fold and 2- to 20-fold greater, respectively, in C. capistratus than in the congeneric species. CYP2 and CYP3 gene families in mammals are thought to have evolved partially in response to dietary allelochemicals. These results suggest that these P450 isozymes may also be important in marine teleosts that feed on terpenoid-rich prey.     

Surface heat fluxes and subsurface heat content at a site over the southeastern Bering Sea shelf, May–July 1996

Observations from a surface mooring, in a weak-flow regime over the southeastern Bering Sea shelf, were used to derive surface heat fluxes for the period May–July 1996. Changes in heat content of the water column also were determined from subsurface temperature measurements. Agreement of net surface heat flux and change in heat content was within 2%. This result provides additional evidence that heat advection and diffusion are small in this region.