Multi-AUV Control and Adaptive Sampling in Monterey Bay

Operations with multiple autonomous underwater vehicles (AUVs) have a variety of underwater applications. For example, a coordinated group of vehicles with environmental sensors can perform adaptive ocean sampling at the appropriate spatial and temporal scales. We describe a methodology for cooperative control of multiple vehicles based on virtual bodies and artificial potentials (VBAP). This methodology allows for adaptable formation control and can be used for missions such as gradient climbing and feature tracking in an uncertain environment. We discuss our implementation on a fleet of autonomous underwater gliders and present results from sea trials in Monterey Bay in August, 2003. These at-sea demonstrations were performed as part of the Autonomous Ocean Sampling Network (AOSN) II project     

Spatial Variation in the Structure of Kelp Forest Communities Along a Wave Exposure Gradient

Abstract. Four sites were sampled in kelp (Macrocysiis pyrifera) forests occupying rocky bottom habitats along a wave exposure gradient in central California. Consistent betwecn-site differences were found in the three major structural elements - the surface canopy, the undcrstory assemblage, and the ground cover/turf assemblage - of kelp forest communities. Macrocysiis pyrifera was found at all four sites. Nereucyslis tuelkeana only at the most exposed site. The understory kelps Laminaria setchellii and Pterygopltora californica were also characteristic of exposed sites. Articulated coralline algae were more abundant at exposed sites than protected, while fleshy red algae showed the opposite pattern. All four study sites were located along 8.5 km of coastline, and thus were assumed to have available to them the same species pool for colonization. The substrate composition was the same and the amount of unconsolidated substrate was similar at all four sites. We suggest that exposure to wave-generated water motion, through its influence on the surface canopy and therefore on the amount of light reaching the bottom, is responsible for these between-site differences.     

Heat influx and exhumation of the Shimanto accretionary complex: Miocene fission track ages from the Kii Peninsula, southwest Japan

Abstract   To determine how local geological events contributed to the evolution of accretionary complexes and eventual exposure of rocks with different structural levels, geochronological mapping was carried out using fission track (FT) analysis at the Kii Peninsula, southwest Japan. At this site, the original zonal structure of Cretaceous accretionary complexes parallel to the subduction zone is disturbed by the northward projection of the Shimanto accretionary complex. Twenty-six zircon FT ages were obtained from an area of ∼12 km in an east–west direction and ∼15 km in a north–south direction, and classified into three groups: (i) ages ∼15 Ma (range ∼10–20 Ma), which are distributed along the northwest–southeast valley; (ii) ages of ∼50 Ma in the northwest of the study area; and (iii) ages older than those in Groups 1 and 2. Based on results from eight zircon FT length distributions, the Miocene ages appear to be the result of spatial variations in heat influx and cooling after the regional exhumation of the area, as recorded by FT ages of ∼50 Ma.     

K-Ar Ages of Granitic Magmatism and Related Pegmatite Formation at the Umanotani-Shiroyama Mine, Shimane Prefecture, SW Japan and Their Bearings on Cooling History

Abstract. The Umanotani-Shiroyama pegmatite deposits, the largest producer of K-feldspar and quartz in Japan, are of typical granitic pegmatite. Ilmenite-series biotite granite and granite porphyry, hosting the ore deposits, and biotites separated from these rocks yielded K-Ar ages ranging from 89.0 to 81.4 Ma and 95.2 to 93.7 Ma, respectively. Muscovite and K-feldspar separated from the ore zone yielded K-Ar ages with the range of 96.2 to 93.1 Ma and 87.3 to 80.7 Ma, respectively. Muscovites from quartz-muscovite veins in the ore zone and in the granite porphyry yielded K-Ar ages of 90.4 and 76.3 Ma, respectively. K-feldspar is much younger in age than coexisting muscovite. It is noted that the K-Ar ages of biotite separates and the whole-rock ages are identical to those of muscovite and K-feldspar in the ore zone, respectively. These time relations, as well as field occurrence, indicate that the formation of the pegmatite deposits at the Umanotani-Shiroyama mine is closely related in space and time to a series of granitic magmatism of ilmenite-series nature. Using closure temperatures of the K-Ar system for biotite and K-feldspar (microcline), cooling rate of the pegmatite deposits is estimated to be about 82C/m.y. at the beginning, but slowed down to about 15C/m.y. in the later period.     

Methane in the East China Sea water

Methane in the East China Sea water was determined four times at a fixed vertical section along PN line consisting of 11–14 stations, in February 1993, October 1993, June 1994 and August 1994. The mean concentration of methane in the surface water was not significantly higher than that in the open ocean. The methane concentration below the pycnocline increased during the stratified period in summer to autumn and reached to 15 nmoles/l at most in October. The concentration of methane was fairly well correlated with AOU in the layer below the pycnocline in the stratified season. This means that methane in the bottom water has only a single source, which is expected to be anoxic sediments near the coast, and that the oxidation rate of methane in the water is extremely slow in the oxic water. The high methane observed in October completely disappeared in February, indicating that the methane was escaped to the atmosphere or transported to the pelagic ocean by the Kuroshio current. The East China Sea, therefore, is not a large direct and stationary source for the atmospheric methane, but may have some role as a source by supplying it sporadically to the atmosphere in early winter or indirectly from the surface of the pelagic ocean.     

Correlation between petrography,NAA, and ICP analyses: Application to early bronze Egyptian pottery from Canaan

Under favorable circumstances petrographic studies supported by chemical analysis using inductively coupled plasma (ICP) suffice to establish the provenience of pottery. A case in point is Egyptian-style pottery of Early Bronze Age found in Canaan. The pottery was divided into three groups according to four criteria determined by thin section analysis supplemented by X-ray diffraction: sorting and volume of silt-sized quartz, heavy minerals, the amount of carbonates in the matrix, and the firing temperature. Chemical analyses confirmed the classification. The source materials inferred for the three groups are Nile muds, Egyptian marly sediments, and local loess. Although the chemical analyses obtained by ICP and neutron activation analysis (NAA) were compatible, the existing database for NAA cannot be used indiscriminately. However, for provenience studies based on mineralogical and petrographic data, knowledge of the geology of the potential source areas can replace an extensive database.     

“Extreme boiling” model for variable salinity of the Hokko low-sulfidation epithermal Au prospect, southwestern Hokkaido, Japan

The Hokko prospect is located in the Minamikayabe area southwestern Hokkaido, Japan, where gold-bearing quartz veins of Pliocene age are exposed at the surface. The alteration mineral assemblage is typical of low-sulfidation epithermal systems, with the quartz veins associated with adularia alteration overprinted on Late Miocene propylitic alteration. Fluid inclusion studies of the vein quartz reveal mean homogenization temperatures of approximately 220 °C, and the co-existence of low-salinity (<2 wt.% NaCl equivalent) and moderate salinity (2 to 12 wt.% NaCl equivalent) fluid inclusions within the same veins. The moderate salinity fluid inclusions (2–12 wt.% NaCl equivalent) typically have relatively low homogenization temperatures between 150° to 200 °C. The results obtained from stable isotope analysis of  δ¹⁸O in quartz vein material showed a gradual decrease in  δ¹⁸O signatures with increasing depth. The majority of the samples have calculated fluid source signatures (δ¹⁸O_H2O) between −8.0 and −10.0‰, but there is a significant change in the composition above 185 m drill depth. The shallower samples in particular show a wide range of oxygen isotope signatures that are associated with the moderate salinity fluid inclusions. We interpret that low-salinity inclusions within the Hokko system represent the composition of the liquid phase of the fluid, before boiling, and that the moderate-salinity inclusions are representative of the residual liquid phase, after extensive non-adiabatic boiling and vapor loss in an open system. This mechanism resulted in the entrapment of fluids with variable salinities at the same time, and in close proximity to each other. This is also reflected in the  δ¹⁸O_H2O values which become more variable and heavier where the moderate-salinity inclusions occur. Deposition of ore minerals within the Hokko vein system also occurred at this time as a result of boiling and gas loss. Received: 30 May 1997 / Accepted: 6 January 1998     

NEUTRON ACTIVATION ANALYSIS OF FIFTEEN GSJ IGNEOUS ROCK REFERENCE SAMPLES

Fifteen rock reference samples "Igneous rock series" issued by the Geological Survey of Japan were analysed for up to 31 elements by neutron activation analysis (NAA); 14 MeV-NAA for Si and Al, fission track method for U, radiochemical and instrumental NAA for rare-earth elements, and instrumental NAA for the remaining elements, with reactor neutrons for the latter three. The present results are compared with published values.     

On the inclusion of ground-based gravity measurements to the calibration process of a global rainfall-discharge reservoir model: case of the Durzon karst system (Larzac, southern France)

This work examines the relevance of the inclusion of ground-based gravity data in the calibration process of a global rainfall-discharge reservoir model. The analysis is performed for the Durzon karst system (Larzac, France). The first part of the study focuses on the hydrological interpretation of the ground-based gravity measurements. The second part of the study investigates further the information content of the gravity data with respect to water storage dynamics modelling. The gravity-derived information is found unable to either reduce equifinality of the single-objective, discharge-based model calibration process or enhance model performance through assimilation.