The state‐of‐the‐art in marine navigation

Tide gauges distributed all over the world provide valuable information for monitoring mean sea level changes. The statistical models used in estimating sea level change from the tide gauge data assume implicitly that the random model components are stationary in variance. We show that for a large number of global tide gauge data this is not the case for the seasonal part using a variate-differencing algorithm. This finding is important for assessing the reliability of the present estimates of mean sea level changes because nonstationarity of the data may have marked impact on the sea level rate estimates, especially, for the data from short records.     

Ferromanganese Nodules and Crusts from the Christmas Island Region,Indian Ocean

A sampling expedition has shown that largely hydrogenetic marine ferromanganese deposits occur in the Christmas Island region south of Java (~10°S), as small nodules on seamount slopes and abyssal plains (red clay), and as thick crusts on volcanic ridges and seamounts. Vernadite is dominant, with birnessite, jacobsite and todorokite common. Nodules were recovered in 25% of free-fall grab stations in water 4600-5900 m deep, and are not abundant where present. The nodules average 9.6% Fe, 19.7% Mn, 0.51% Ni, 0.49% Cu, and 0.12% Co. Crusts are common in water 1450-3700 m deep, with average deposition rates of 1-1.5 mm / m.y. The crusts average 13.9% Fe, 16.2% Mn, 0.35% Ni, 0.11% Cu, and 0.44% Co. Cobalt grades are higher (~0.8%) in shallower water ( < 2500 m), so future exploration should concentrate on depths of 500-1500 m near the oxygen minimum zone.     

Evaluation of Bearing Capacity for Multi-Layered Clay Deposits with Geosynthetic Reinforcement using Discrete Element Method

A stability analysis of reinforced foundation soil is presented in this paper. A method based on the discrete element method (DEM) is suggested for calculating the bearing capacity on strip footings over multilayer soils reinforced with a horizontal layer of geosynthetics. The proposed method can estimate the ultimate bearing capacity and the distribution of tensile force developed in the geosynthetics of the footing system by Winkler springs to account for the compatibility between soil blocks and tensile elements to consider the tensile behavior between soil and geosynthetics. For footings on various multilayer soils with or without reinforcement of geosynthetics, the results of the method were compared to the field test results as well as to those obtained by various methods proposed by other researchers.     

Pore‐water pressure measurements: Mississippi delta submarine sediments

Abstract

A pore‐water pressure probe (piezometer) was implanted in Mississippi delta sediments at a preselected site (Block 28, South Pass area, 29°00´N, 89°15´W) 145 m from an offshore production platform (water depth approx. 19 m) in September 1975. Total pore‐water pressures (u_w ) were monitored for extended periods of time at depths of approximately 15 and 8 m below the mudline concurrently with hydrostatic pressures (u₈ ) measured at depths of 15 m and approximately 1 m below the mudline. Relatively high excess pore‐water pressures, u_e = (u_w ‐u₈ ), were recorded at the time of probe insertion measuring 99 kPa (14.4 psi) at 15 m and 50 kPa (7.3 psi) at 8 m. Six hours after the probe was implanted, excess pore pressures were still high at 81 kPa (11.8 psi, 15 m) and 37 kPa (5.4 psi, 8 m). Pore pressures appeared to become relatively constant at the 8‐m depth after 7 h had elapsed, and at the 15 m depth after 10–12 h. Excess pore‐water pressures averaged 72 kPa (10.4 psi, 15 m) and 32 kPa (4.6 psi, 8 m) prior to the initial effects of Hurricane Eloise, which passed in close proximity to the probe site. Significant variations in pressures were recorded during storm activity. As the effects of the storm subsided, excess pore‐water pressures began to decline slightly at the 15‐m depth; however, concurrently at the 8‐m depth, pore pressures began to increase gradually. During the period of 21–25 days after the probe was implanted, excess pore pressures appeared to become more constant, averaging 24 kPa (3.5 psi) at 15 m and 43 kPa (6.2 psi) at the 8‐m depth. The presence of methane, a common occurrence in these delta muds, may have influenced, or contributed to, the total pore‐water pressures measured during this experiment.     

Wave‐induced pore pressure in relation to ocean floor stability of cohesionless soils

One of the important geotechnical considerations for many engineering installations, such as pipelines and anchors, in an oceanic environment involving sand deposits is that of potential ocean floor instability due to the development of high pore pressures caused by the direct action of waves. This article presents a procedure for evaluating the magnitude and distribution of wave‐induced pore pressures in ocean floor deposits. The method takes into account the distribution of wave‐induced pore pressures in ocean floor deposits. The method takes into account the distribution of cyclic shear stresses in the soil profile as well as the important factor of pore‐pressure dissipation. The variation of properties within the soil profile can also be easily incorporated into the analytical procedure. The analysis provides the complete time history of pore‐pressure response and shows clearly that failure to include the pore‐pressure dissipation effects would lead to radically conservative design. The results also provide a basis for designing remedial measures, if required, to avert the development of high pore pressures and their deleterious effects.     

Assessment of Dynamic Characteristics for Compaction Piles with Geophysical Logging in Soft Ground

In this paper, a case study was performed on a sand compaction pile (SCP) and a gravel compaction pile (GCP) to estimate the dynamic characteristics and the improvement effect of soft ground. The dynamic elastic modulus, shear modulus, bulk modulus, and Poisson's ratio were estimated and the dynamic characteristics were analyzed using the compression and shear wave velocity of the improved ground based on the results of suspension P- and S-wave (PS) logging. The results revealed that the dynamic properties were increased in the order of unimproved subsoil and improved subsoil using SCP and GCP. The increase in the effects of dynamic properties with each replacement ratio of SCP was not large, whereas a good increase in the effects was observed in the case of the improved subsoil with GCP. Consequently, it was presented that the resistance characteristics against the seismic loading of GCP are excellent. As a result of analyzing the density distribution of the improved subsoil through density field logging, the overall density distribution gradually exhibits increasing trends in the order of unimproved subsoil and improved subsoil with SCP and GCP. Thus, the improvement effect of GCP was relatively high in comparison with the same replacement ratio of SCP.     

Accurate GPS measurement of the location and orientation of a floating platform

Abstract

This article describes the design and initial tests of the GPS portion of a system for making seafloor geodesy measurements. In the planned system, GPS antennas on a floating platform will be used to measure the location of an acoustic transducer, attached below the platform, which interrogates an array of transponders on the seafloor. Since the GPS antennas are necessarily some distance above the transducer, a short‐baseline GPS interferometer consisting of three antennas is used to measure the platform's orientation.

A preliminary test of several crucial elements of the system was performed at the Scripps Institution of Oceanography (SIO) in December 1989. The test involved a fixed antenna on the pier and a second antenna floating on a buoy about 80 m away. GPS measurements of the vertical component of this baseline, analyzed independently by two groups using different software, agree with each other and with an independent measurement within a centimeter.

The first test of an integrated GPS/acoustic system took place in the Santa Cruz Basin off the coast of southern California in May 1990. In this test a much larger buoy, designed and built at SIO, was equipped with three GPS antennas and an acoustic transducer that interrogated a transponder on the ocean floor. Preliminary analysis indicates that the horizontal position of the transponder can be determined with a precision of about a centimeter. Further analysis will be required to investigate the magnitude of systematic errors.     

Late Devonian rifting in the central North Sea: Evidence from altered felsic volcanic rocks in the Embla oil field

In the Embla oil field on the northern flank of the Mid North Sea High, the central North Sea, multiple quartz porphyric volcanic beds at ca. 4600 m depth form part of a volcano-sedimentary interval above the Caledonian basement as interpreted from seismic data. Zircon U–Pb laser ablation ICPMS date one bed to 374 ± 3 Ma, indicating that the volcanic rocks and interbedded sediments are early Famennian and correlate to the Buchan Formation. The volcanic rocks have been extensively clay and carbonate altered in a near-surface environment, but high field strength element data show that the protoliths were alkali rhyolites, yielding intra-plate signatures in tectonic discrimination diagrams. Famennian quartz porphyric volcanic rocks have also been reported from well A17-1 on the southern flank of the Mid North Sea High. The Famennian volcanism on the northern and southern flanks testify to an active magmatic environment in the central North Sea in the early Famennian, supporting the existence of a late Devonian proto-Central Graben rift extending northwards into the central North Sea. The rift is likely an early example of strain localisation to a zone of reduced crustal strength along the Caledonian suture between Avalonia and Baltica.     

Lagrangian analysis of mixing and transport of water masses in the marine bays

The Lagrangian approach to studying the mixing and transport of a passive admixture in marine bays and gulfs based on the methods of a theory of dynamic systems is developed. This approach is employed to investigate the lateral mixing and transport of waters in the Peter the Great Bay, Japan Sea, using a velocity field of the predictive numerical hydrodynamic circulation model of a synoptic scale. It is shown that the Lagrangian characteristics, such as the maximum accumulated Lyapunov exponent, the time of particle stay in the bay, particle relative displacements, and the number of cyclonic and anticyclonic rotations, allow us to describe the movement of water masses, the character of mixing, and chaos in the Bay. In integrating the advection equations forward and backward in time, maps showing a number of particle arrivals to different regions of the Bay make it possible to establish corridors through which particles leave and enter the Bay.     

Genetic variation and population structure in the New Zealand snapper

Fifteen proteins encoded by 23 gene loci were electrophoretically surveyed in two samples of snapper Chrysophrys auratus (Forster) from Wellington Harbour and the Hauraki Gulf. Between 17% and 26% of the loci examined were found to be polymorphic and the proportion of heterozygous loci per individual was 7.9% to 8.4%. Using Rogers’ genetic distance coefficient an overall similarity of 0.98 was calculated between the two samples.

Three polymorphic loci Est‐4, Gpi‐1, and Idh were examined in an additional 10 samples from around New Zealand. Two genetically distinct stocks were apparent: one along the west coast, the other along the east coast of the North Island. There was an indication of stock mixing at Ninety Mile Beach and in the Bay of Plenty and East Cape. The distribution of alleles at the Est‐4 locus revealed a third stock in Hawke Bay that is genetically more similar to the west coast than the east coast stock. Hydrological conditions in Hawke Bay are more similar to those of the west coast than to those of the north east coast of the North Island. Thus it is possible that Est‐4 alleles are selectively maintained in response to an environmental factor.