In this study, palaeomagnetic methods have been combined with field and volcanological techniques to identify, classify and correlate the pyroclastic deposits found on Ascension Island, South Atlantic, allowing them to be placed into a temporal and geographic framework. Pyroclastic material is abundant on the island and, in general, wellpreserved, making Ascension an ideal site to study the nature and distribution of the pyroclastic products of this type of composite volcano or stratovolcano. A better understanding of the nature and distribution of the products of past pyroclastic eruptions on Ascension should enhance our ability to assess volcanic hazard around stratovolcanoes world-wide. Field mapping and stratigraphic logging have revealed the presence of several major pyroclastic sequences on Ascension. These comprise extensive felsic (pumice) and mafic (scoria) lapilli deposits, two major and several minor exposures of welded material and numerous breccia deposits that exhibit great variation in juvenile/lithic content, matrix type and content and internal structure. Preliminary interpretations of the deposits were made in the field, based on features such as welding, grain shape and internal structures. However many of the deposits - particularly the breccia deposits - display ambiguous field characteristics that could be attributed to pyroclastic or epiclastic processes and their origins could not therefore be determined from field characteristics alone. [See pdf for continuation of abstract].

Graduation date: 1978

The atmospheric response to the oceanic forcing in the eastern Pacific along the northern equatorial sea surface temperature (SST) front is investigated in terms of sensible and latent heat flux during the 6-month period 28 July 1999 through 27 January 2000. Of particular interest is the atmospheric boundary layer (ABL) response to oceanic Tropical Instability Waves (TIWs) that distort the SST front during May through January in normal years. In previous studies, time series of boundary layer properties clearly show the influence of TIWs but the relationship to spatial patterns of SST and wind stress has been inferred only from sparse in situ data. In this study, satellite observations are used to composite in situ data from moorings to compensate for the lack of a spatially dense mooring array. The variability in the position of the SST front caused by propagating TIWs enables fixed mooring locations to measure the atmospheric boundary layer (ABL) response from a large range of locations relative to the front. The satellite data enable determination of the precise location of the mooring relative to the front. The advantage of this strategy is the recurring measurement of the ABL response to the SST front over the six month period considered here. The results indicate that the TIW-induced perturbations of sensible and latent heat flux are spatially shifted in phase towards the east relative to the perturbations of SST. The maximum fluxes are not centered directly over the warmest water, but are shifted towards the portion of the frontal region where a disequilibrium boundary layer is expected due to the advection of colder air from the equatorial region. The changes of sensible and latent heat fluxes across the SST front have magnitudes of about 11 Wm⁻² and 126 Wm⁻², respectively. The sensible and latent heat flux patterns are interpreted in two complementary ways: (1) as an atmospheric response to the change of oceanic forcing as air flows across the SST front; and (2) as the atmospheric response to westward propagating TIWs along the SST front. / Graduation date: 2001

The ecology of patch reef fishes was studied to quantify the main factors that affect the natural variability of the fish community and to determine the effects produced on the community by experimental removal of predators. Initially, a year-long baseline description was completed of the physical, biological and ecological characteristics of 8 pristine patch reefs at Midway lagoon. For over 3 subsequent years, piscivorous predators were spearfished at least monthly, often for days at a time, on 4 of the 8 reefs. Fish populations were visually censused throughout the experiment. In all seasons and years of the project, daily recruitment rate of postlarval fishes to natural patch reefs was compared to that measured on standardized, artificial reefs of various sizes and degrees of inter-reef isolation. Finally, all baseline measurements were replicated and complete collections were made of all fishes, to validate the visual census method. Visual censusing was found to be of adequate precision and accuracy for most resident, non-cryptic species (highest for small patch reefs). Fishes could be assigned to size classes underwater by visual estimate with high accuracy. Rotenone collections were highly effective in quantifying many species commonly missed or underestimated in visual censuses. Only a few species composed the bulk of all recruits, while most species were rare or not seen at all. Variation between species was related to life history strategies or behavioral requirements. High temporal variability was found at the following scales: 1) Annuallywhere variability increased with the magnitude of recruitment, and different species recruited heavily in different years, suggesting that species specific factors in the plankton are more important than general oceanographic conditions; 2) Seasonally- pulsing strongly in summer, and occasionally late fall, when favorable environmental conditions may maximize growth and survival; and 3) Daily- with 1 or 2 strong peaks (each only a few days long) over a period of several weeks of low, variable recruitment. Small-scale spatial variability between replicate attractors (standardized artificial reefs) and between attractor types (coral and wire) were both high for a few species recruiting abundantly, although most recruits are probably substrate generalists. Rigorous visual fish censuses can adequately document moderate- to long-term temporal variation in the abundances of recently recruited juveniles on patch reefs (i.e., based on similar temporal patterns assessed by daily attractors). Daily total recruitment rate increased, although at diminishing densities, with (attractor) reef size, and with degree of inter-reef isolation. Abundances of recently recruited fish censused on neighboring, natural patch reefs (much larger than attractors) increased with reef size. The effect of isolation on these natural reefs was confounded by the stronger effect of reef size. These results suggest that if optimum size and spacing of reefs is provided, either by proper design of artificial reefs or selection of marine reserves, managers may enhance fish recruitment and ultimately improve local fisheries: Of the 135 fishes censused on the patch reefs studied, only 6 species together accounted for 70% of the total number of all fish, mainly due to heavy seasonal recruitment pulses. Strong seasonal and annual variability in recruitment was responsible for most of the temporal variation in fish abundance. The structure of patch reef fish communities at Midway was characterized by high unpredictability (e.g., great seasonal and/or annual variability in recruitment by common species, recruitment limitation for most species, and a high turnover rate detected by frequent sampling). Some predictions of the theory of island biogeography were also met by these fish communities (e.g., species richness correlated strongly with patch reef area, volume and relief). and total fish abundance. Some populations also exhibited a degree of long-term stability. Species diversity [H'] was similar among different size reefs. The experimental fishing on piscivores produced a catch composed mainly of lizardfish, due largely to immigration following the removal of other, competitively superior, highly resident piscivores. Scorpionfish and moray eels were also dominant predators. The expected decreases in catch-per-unit-effort were not realized, except for a quantitatively insignificant family (hawkfish). Conversely, the catch of the highly migratory lizardfish actually increased as fishing progressed. Changes in the catch composition for other piscivores related mainly to major changes in reef size or to patterns of large, inter-year recruitment fluctuations. Census data confirmed the major trends indicted by catch results. Sharks and jacks were attracted to the experimental reefs by spearfishing; the study was unable to determine whether their piscivorous effect was different between reef treatments. Patch reef fish communities at Midway were relatively resilient to long-term, intense fishing pressure on piscivores. However, enhanced survival of a large, annual, summer recruitment pulse of a common cardinalfish, synchronized with a temporary but significant reduction of lizardfish (the most prevalent piscivore) by fishing, suggested that an effect of predation on reef fish populations is experimentally detectable and considerable. However, temporal and spatial variability in recruitment, and reef size differences and changes in size were the primary factors responsible for the observed temporal patterns in fish abundance. COlnmunity analysis involves numerous confounding effects and requires the most careful interpretation for valid conclusions. / xvi, 321 leaves, bound : ill. ; 29 cm.

Three-dimensional gravity analysis is the process of removing the predictable components from the free-air gravity anomalies and has proven to be useful for interpreting the subsurface structures and active processes at mid-ocean ridges. The three-dimensional effects of the seafloor and Moho topography, assuming a constant crustal thickness and constant crust and upper mantle densities, are subtracted from the free-air anomalies, yielding the mantle Bouguer anomalies. Mantle Bouguer anomalies at mid-ocean ridges are believed to be largely due to the three-dimensional thermal structure, which can be predicted using a simple passive flow model. When the gravity contribution from the predicted thermal structure is removed from the mantle Bouguer anomalies, the residual mantle Bouguer anomalies are created, which represent lateral variations in the crustal thickness and/or density variations from the assumed model. Three-dimensional gravity analysis has been carried out over three areas along the Pacific-Antarctic East Pacific Rise (EPR): (1) the eastern intersection of the Menard transform with the EPR, (2) the overlapping spreading center (OSC) at 36.5°S and, (3) the western intersection of the Raitt transform with the EPR. This geophysical analysis provides an essential tool for understanding the subsurface crustal/upper mantle structure of the fast spreading EPR, and more specifically at transform and nontransform offsets along the EPR. Several interesting features were observed at the eastern intersection between the Menard transform and the EPR. The continuous nature of the residual mantle Bouguer anomalies along the ridge axis suggests that the 60 km of ridge axis surveyed here has a fairly uniform crustal/upper mantle structure. Significant features are not observed in the residual mantle Bouguer anomalies at the ridge-transform intersection or along the eastern 75 km of the Menard transform. At the ridge-transform intersection, fresh lavas from the observed overshot ridge have filled in the transform valley and have subsequently thickened the crust, eliminating any crustal thinning that is occurring there. The large OSC at 36.5°S has a left-stepping offset of approximately 34 km. The most significant feature in the gravity data from this study area is the observed low in the mantle Bouguer anomalies which extends from the northern ridge segment, eastward to the "inactive" rift and continued along the southern ridge segment. This gravity low suggests that this region is underlain by thicker crust and/or hotter, less dense material. No significant features are observed in the residual mantle Bouguer anomalies associated with the overlap basin or the two smaller basins that border the "inactive" rift. The western ridge-transform intersection (RTI) between the Raitt transform and the EPR significantly differs from the Menard transform study area. A transform valley is not observed at this RYE and neither is an overshot ridge. Instead, a transformparallel median ridge is observed east of the RTI, and a fossil transform valley is observed north of the RTI. A low in the residual mantle Bouguer anomalies is associated with the fossil transform valley and the median ridge, suggesting that these areas are underlain by thicker crust and/or less dense material. Positive residual mantle Bouguer anomalies observed at the inside corner of the RYE suggest that this area is underlain by thinner crust and/or colder, more dense material; while at the outside corner of the ridge-transform intersection, a residual anomaly low is observed which suggests that the outside corner is underlain with thicker crust and/or hotter, less dense material. / Graduation date: 1995 / Figures in original document are black and white photocopies. Best scan available.

The South Pacific Ocean is an area easily to be disregarded, although it possesses a very significant value of the military strategy.Contemporary,the South Pacific arena has become an important part of Chinese maritime Strategy.The reform and opening up in China bring the growth of economics and trade and the extension of national power for about twenty years, meanwhile, the state suffers from the demands of energy,the dispute of sovereignty,and the problems of the defensive screen of the American Containment Policy in East.Under such circumstances, China formulates a concrete and distinct military strategy in order to strive for the interests of the sea.On this purpose, China chooses the South Pacific area to be a part of Chinese strategic arrangements.According to the strategy, as soon as China invades the defensive screen of the American Containment Policy in east, an American military will be presence. Therefore, China can depend on its base and military power in the South Pacific area to prevent from the presence of an American military and delay it for the strategic purpose of the sea denial.

Thesis (M.S.)--University of Hawaii at Manoa, 2006. / Includes bibliographical references (leaves 44-49). / vii, 50 leaves, bound ill. (some col.) 29 cm

The basement of the Tonga intraoceanic forearc comprises Eocene arc volcanic crust formed during the earliest phases of subduction. Volcanic rocks recovered from the forearc include boninites and arc tholeiites, apparently erupted into and upon older mid-oceanic ridge tholeiites. Rock assemblages suggest that the forearc basement is a likely analog for large supra-subduction zone (SSZ) ophiolites not only in structure and Ethology, but also in the style of hydrothermal alteration. Dredged volcanic samples from the central Tonga forearc (20-24�� S) exhibit the effects of seafloor weathering, low (<200��C, principally <100��C) alteration, and high temperature (>200��C) alteration. Tholeiites and arc tholeiites are significantly more altered than boninites. Seafloor weathering is due to extensive interaction with cold oxidizing seawater, and is characterized by red-brown staining and the presence of Fe-oxyhydroxides. Low temperature alteration is due to circulation of evolving seawater-derived fluids through the volcanic section until fluid pathways were closed by secondary mineral precipitation. Low temperature alteration is characterized by smectites, celadonite, phillipsite, mixed-layer smectite/chlorite, carbonates, and silica. All phases fill veins and cavities; clay minerals and silica also replace the mesostasis and groundmass phases. Low temperature alteration enriches the bulk rock in K, Ba, and Na, and mobilizes other elements to varying extents. The few high temperature samples are characterized by mobilizes other elements to varying extents. The few high temperature samples are characterized by epidote, chlorite, quartz, oxides, and fibrous amphibole, which replace groundmass and phenocrysts, and fill cavities, and are presumed to have originated in zones of concentrated hydrothermal upflow.These three alteration types are similar to those seen in many ophiolites such as Troodos, where low temperatures prevailed in the volcanic section except in localized upflow zones. Alteration mineral chemistries are also broadly similar to those observed for the Troodos Ophiolite. Tonga forearc alteration differs from mid-oceanic ridge alteration in the presence of Al-rich dioctahedral smectites (not common in mid-oceanic ridge crust), the high Al content of saponite, and the predominance of K as an interlayer cation in clays. Hydrothermal alteration of the Tonga forearc is likely the product of extensive interaction with compositionally evolving seawater-derived fluids beginning at the time of emplacement. The distribution and intensity of alteration in these crustal sections depend principally on the porosity and permeability of the crust during alteration, which are influenced by the primary porosity, igneous morphology, and the presence of faults and fractures which could affect fluid flow. / Graduation date: 1999

No description available.

Cadmium in the ocean has a nutrient-like cycling pattern: with biological uptake at the surface, subsequent sinking in particulate form and then regeneration as dissolved species in deeper waters. Many measurements have been made over time of the ratio of the concentrations of dissolved Cd to those of PO₄ (Cd/PO₄) in the world ocean and this has become one of the best relationships documented between a trace metal and a nutrient. Combined with the measurements of the Cd/Ca ratio in foraminifera, the Cd/PO₄ ratio has been used to reconstruct the oceanographic circulation patterns that existed during past glacial periods and hence provides information on past climate changes. In the present study Cd/PO₄ ratios of the Southern Indian Ocean in surface and deep waters were investigated. The slopes of the relationships between Cd and PO₄ concentrations in waters of this region are high compared to the global correlations, and lie between those reported for other parts of the Southern Ocean and the Pacific Ocean. In surface waters of the Southern Indian Ocean, Cd/PO₄ ratios decrease from regions exhibiting high nutrient-low chlorophyll (HNLC) characteristic in the south to oligotrophic waters further north. It is also found that particulate Cd plays an important role in regulating the high Cd/PO₄ ratios reported in waters south of the Polar Front. Very low Cd/PO₄ ratios were measured in waters associated with the Subtropical Front southeast of New Zealand compared to other Southern Ocean and global oceanic waters. Seasonal variations in the Cd/PO₄ ratios measured for these waters strongly suggest they are associated with a significant biological uptake of dissolved Cd particularly during the phytoplankton growth season in summer. Dissolved Fe concentrations in the Southern Indian Ocean and seasonal variations of Fe in waters off the Otago Coast (southeast of New Zealand) suggest that Fe may stimulate phytoplankton growth and this might result in lower Cd/PO₄ ratios in surface waters through enhanced Cd uptake relative to PO₄ by the phytoplankton. However there is no distinct relationship between dissolved Fe concentrations and the dissolved Cd/PO₄ ratios measured in these surface waters. This finding is in disagreement with the recent 2006 hypothesis put forward by J.T. Cullen, which proposed that waters exhibiting low dissolved Cd/PO₄ ratios were associated with the HNLC regions. From a consideration of the potential Zn concentrations calculated from Si concentration measurements reported for these waters, it would appear that Zn may play a more important role than Fe in regulating Cd/PO₄ ratios in these waters. Measurements of dissolved and total Cd concentrations relative to those of PO₄ were also undertaken in the Otago Harbour and immediate surrounding coastal waters. These exhibited higher Cd concentrations and higher Cd/PO₄ ratios than open ocean waters further off the Otago Coast. The particulate Cd concentrations showed a negative correlation with Cd concentrations measured in cockle species (Austrovenus stuchburyi) collected in the harbour, suggesting that particulate Cd is not the source of Cd measured in the tissue of this species. The concentrations of Cd and other trace metals were also measured in samples of green mussel (Perna canaliculus), ribbed mussel (Aulacomya atra maoriana) and oyster (Saccostrea cucullata) collected from Otago Harbour and possible correlations explored between these concentrations and other parameters such as the shellfish condition indices and environmental gradients in the harbour. In summary, measurements of dissolved and particulate Cd concentrations in the water column can provide unique information on a number of processes occurring in the global marine environment.